NTIA Reply to Comments on the GPS/UWB Measurement Plan

Topics/Subtopics: 
Date: 
October 17, 2000

NATIONAL TELECOMMUNICATIONS AND INFORMATION ADMINISTRATION RESPONSE TO PUBLIC COMMENTS

1.0 INTRODUCTION

On August 14, 2000, a Federal Register Notice (FRN) was published requesting public comment on the National Telecommunications and Information Administration (NTIA) Measurement Plan To Determine The Potential Interference Impact To Global Positioning System Receivers From Ultrawideband Transmission Systems(1) (GPS/UWB Measurement Plan). A fourteen day comment period was established for the public to submit comments on the GPS/UWB Measurement Plan. The FRN also included questions for public comment that are related to the GPS/UWB Measurement Plan. The purpose of this document is to address the public comments submitted in response to the FRN. Section 2 of this document provides NTIA's response to the public comments. Section 3 of this document provides the modifications to be made to the GPS/UWB Measurement Plan in response to the public comments.

2.0 NTIA RESPONSE TO THE PUBLIC COMMENTS

The parties shown below submitted comments in response to the NTIA Federal Register Notice:

- Air Transport Association
- ANRO Engineering, Inc.
- Joint Spectrum Center
- Multispectral Solutions, Inc.
- National Aeronautics and Space Administration Glenn Research Center
- RAND Science and Technology Policy Institute
- Time Domain Corporation
- U.S. GPS Industry Council

A copy of the public comments and NTIA's response will be available on the NTIA homepage at <http://www.ntia.doc.gov/osmhome/uwbtestplan/gpstestfr.htm>.

The following subsections will provide NTIA's response to the comments submitted by each of the parties listed above. Some commenters provided comments that were beyond the scope of this measurement plan. The NTIA responses will be limited to those comments that are applicable to the measurement plan.

2.1 Air Transport Association

Comment: The Air Transport Association indicated that its operational and technical experts have reviewed the GPS/UWB Measurement Plan and agree that its scope and content appear acceptable.(2)

Response: NTIA Office of Spectrum Management (OSM) and Institute of Telecommunication Sciences (ITS) staff members will be available throughout the measurement effort to discuss any issues that require further explanation.

2.2 ANRO Engineering, Inc.

Comment: ARNO Engineering Inc. (ANRO) noted in its comments that in Table 3: UWB Signal Parameters, the planned range of PRFs to be tested spans 0.1 to 20 MHz. ANRO suggested that lower PRF values be included in the test matrix. While adding PRF values will increase the number or permutations to be included in the test, the results may add significantly to the completeness of the test findings. ANRO also suggested that tests that involve PRFs lower than 100 kHz would be useful. ANRO specifically recommended that a PRF of 2.5 kHz be included in the NTIA measurement effort.(3)

Response: NTIA agrees with the commenter that measuring a larger range of UWB signal parameters will provide greater insight into the potential for interference to GPS receivers from UWB transmission systems. However, the continuing development of UWB transmission systems makes it difficult to test all possible parameter combinations. In general, GPS receivers have some immunity to low PRF pulsed interfering signals. For single source interference the pulse repetition frequency of 2.5 kHz is not expected to be a significant problem for GPS receivers. For multiple UWB sources it might cause a slight increase in the GPS receiver noise level.

2.3 Joint Spectrum Center

Comment: The Joint Spectrum Center (JSC) suggested that in Figures 4 and 5, the output of the broadband noise generator should be split off, filtered, and monitored by a power meter as in Figure 3.(4)

Response: For the measurements to be performed using the setups shown in Figure 4 and 5, the broadband noise signal will be set at a constant level throughout the measurement procedure. Prior to beginning the measurement procedure, the level of the broadband noise signal will be measured to ensure that its level has not changed. Since we are not varying the level during the measurement procedures we do not believe that the broadband noise level needs to be monitored continuously.

Comment: JSC also noted that, the previous version of the draft test plan contained measurement procedures to determine UWB radiated signal effects when received by a GPS antenna. In this current version of the test plan, these procedures have been omitted. However, JSC questioned why Figure 1 still has this measurement effort included in the test plan flow diagram.(5)

Response: At the time the GPS/UWB Measurement Plan was released for public comment, funding constraints limited the scope of the measurement effort. The block in Figure 1 entitled "Measurement Procedures (Radiated)" did not correspond to any of the tasks to be performed in the measurement effort and should have been deleted. Additional funding has been made available and limited radiated measurements will now be included as part of this measurement effort. The procedures for the radiated measurements are provided in Appendix A of this document. The GPS/UWB Measurement Plan will be modified to include the radiated measurement task.

2.4 Multispectral Solutions, Inc.

Comment: Multispectral Solutions Inc. (MSSI) also noted that in Figure 1, "Flow Diagram of Measurement Plan", the block entitled "Measurement Procedures (Radiated)" does not appear to correspond to any identified task. Section 3.1. MSSI stated that one objective of the testing for UWB interference to other than GPS was to "4) validate the one-on-one interference analysis procedures with field measurements of selected Federal radio receivers." MSSI suggests that it would seem that field validation of the one-on-one interference potential to GPS is also critical to a thorough assessment of the impact of UWB on GPS.(6)

Response: As noted above, the GPS/UWB Measurement Plan will be modified to include the radiated measurement task.

Comment: MSSI recommends that Table 3, "UWB Signal Parameters" be modified to include a Pulse Repetition Frequency (PRF) of 10.0 MHz; and Continuous Pulse Transmission (i.e., no gating). The former PRF is more representative of multi-user wireless local area network (LAN) operation; while the latter is more representative of streaming audio or video applications.(7)

Response: The signal parameters in Table 3 of the measurement plan were selected in an attempt to bound the range of signal parameters considered to be representative of UWB transmission systems to be used by businesses and consumers. The continuing development of UWB transmission systems makes it difficult to test all possible parameter combinations. Furthermore, time constraints limit the range of UWB signal parameters that can be considered in this measurement effort.

NTIA believes that the effect of the 10 MHz PRF on a GPS receiver will be the same as that of the 20 MHz PRF that is being considered in the measurement effort as long as the PRF is adjusted such that a spectral line is located within 500 kHz of 1575.42 MHz (e.g., 3 dB bandwidth of the C/A code signal).

NTIA also believes that the intent of the Gating entry in Table 3 has been misunderstood by the commenter. It was not intended to use 20, 100 and 1000 pulses per on cycle. The gating duty cycles were to be composed of the following:

  • 1000 pulses during the on cycle followed by the off cycle when 4000 pulses are suppressed (20 % Gating); and
  • continuous pulse transmissions (100 % Gating).

This approach would allow NTIA to consider both a high and low duty cycle with respect to gating in this measurement plan. However, in response to another commenter on the gating issue, the gating duty cycles will be changed to the following:

  • 4 millisecond on-cycle with a 16 millisecond off-cycle (20% gating); and
  • continuous stream of pulse transmissions (100 % Gating).

This modification will be made to the GPS/UWB Measurement Plan.

2.5 National Aeronautics and Space Administration (NASA) Glenn Research Center

Comment: NASA's Glenn Research Center suggests that it might be worthwhile to replace one of the receivers on the candidate list of GPS receivers with one that uses code and carrier tracking to perform position, velocity, time, and attitude determination. Examples of these receivers include the Trimble TANS Vector and the Force 19.(8)

Response: As shown in Table 1, five of the GPS receivers on the candidate list employ code and carrier tracking receiver technology. However, NTIA will review the technical characteristics of the receivers recommended by the commenter for possible inclusion in the list of candidate receivers.

Comment: NASA's Glenn Research Center also states that the final navigation solution should be used as the performance metric not pseudo-range error.(9)

Response: There are two problems associated with using the final navigation solution as the performance metric. The first problem is the final navigation solution is very dependent upon constellation variables such as the dilution of precision, the rising and setting of satellites, and the individual satellite power levels. The problem is exacerbated by the fact that there is no standard constellation (e.g., satellite configuration), it varies continuously and is different depending on the users geographic location. The second problem is that there is no documented application specific performance criteria for the final navigation solution. In the Federal Register Notice, questions 3 through 7 requested information on GPS receiver performance metrics and criteria.

 

As stated in the GPS/UWB Measurement Plan, the pseudo-range error is not being used as the performance metric. The performance metrics used in this measurement effort are break-lock and reacquisition time. NTIA believes that these performance metrics are applicable to all GPS receivers independent of their application. The pseudo-range error will be monitored to ensure that the receiver is operating properly throughout the measurement procedures.

Comment: NASA's Glenn Research Center also suggests that it is important to carry out some limited outdoor "live-sky" testing with at least one receiver in order to assess performance degradation due to UWB interference, and proposes a possible test configuration for a live-sky test.(10)

Response: As stated in the GPS/UWB Measurement Plan, NTIA has concerns regarding live-sky tests. Limited live-sky tests have been performed by the Stanford University in cooperation with Interval Research Corporation and the Time Domain Corporation at NASA's Marshall Space Flight Center. However, the results of these tests provided inconclusive data on the impact of UWB emissions on GPS receivers. NTIA agrees with the commenter that limited radiated measurements are an important element in assessing the potential impact of UWB transmission systems on GPS receivers. The procedures for limited radiated measurements to be performed in this measurement effort are provided in Appendix A of this document. The GPS/UWB Measurement Plan will be modified to include the radiated measurement task.

 

2.6 RAND Science and Technology Policy Institute

Comment: In response to question 1 of the NTIA FRN, RAND notes that the candidate list is a good starting point, but given the multitude of GPS applications, the list is not complete.(11)

Response: As stated in the measurement plan, the list of candidate GPS receivers provided in Table1 were selected to include different receiver technologies as well as receivers from different manufacturers. Due to time constraints, a minimum of three GPS receivers (one from each of the technologies) from the candidate list will be considered in this measurement effort. If time permits, additional GPS receivers from the candidate list will be measured.

NTIA agrees with the commenter that the operational scenarios used in which the GPS receivers are employed must be taken into consideration in determining the maximum permissible output power of a UWB transmission system. The GPS receiver applications provided in Attachment 1 of the commenters submission demonstrates the numerous applications for GPS receivers. The measurements described in this plan will not develop the operational scenarios or the associated link budget analysis. These measurements will define the maximum UWB signal level that can be tolerated at the input of each GPS receiver considered. The maximum tolerable UWB signal level will then be used in a separate link budget analysis for each specific UWB-to-GPS operational scenario identified to calculate the maximum permissible output power of a UWB transmission system, under given parameter combinations, that will ensure compatibility with GPS receivers. The operational scenarios will be dependent upon both existing and projected GPS and UWB applications and will take into consideration circumstances involving both single and multiple UWB transmission systems. For each application, a link budget will be developed under assumptions and/or known conditions that are defined by the particular operational scenario. The list of applications provided in Attachment 1 of the commenters submission will be considered by NTIA in the development of operational scenarios. A series of public meetings are being held to develop the operational scenarios to be considered in the assessment of potential interference to GPS receivers from UWB transmission systems.(12)

Comment: In response to question 2 of the NTIA FRN, RAND states that only UWB signals with pulse widths of 0.5 nanosecond duration are generated. RAND maintains that technical literature suggests UWB signals can have both positive and negative harmonic components and can vary from 0.5-10 nanosecond, and have varying amounts of damping depending on the driving signal and specific transmission antenna.(13)

Response: NTIA agrees with the commenter that the pulse width of the UWB transmission systems can vary. NTIA also agrees that the UWB transmission systems can employ techniques resulting in multiple zero crossings that will effect the bandwidth of the transmission. However, NTIA believes that in assessing the potential interference to GPS receivers from UWB transmission systems, the duration of the pulse from 0.5 to 10 nanosecond will not significantly change the spectrum in the GPS band. From an interference perspective, what is important is that the UWB signal level is constant across the bandwidth of the GPS receiver. The UWB generators used in this measurement effort will produce a constant signal level across the GPS receiver bandwidth. This flat characteristic will be verified through spectrum analyzer measurements. In a limited number of measurement cases, the UWB signal will not be flat (i.e., spectral lines) and steps will be taken to assure that at least one spectral line occurs within the bandwidth of the main lobe of the correlator. However, there will be no attempt made to align the UWB signal spectral line with a dominate spectral line of the C/A code.

Comment: In response to question 2 of the NTIA FRN, RAND also states that it is unclear what is meant by "envisioned for use by the public." RAND suggests that one interpretation is that only UWB devices with characteristics specifically tested by this measurement plan could be considered for public use (licensed or not).(14)

Response: We agree with the commenter that the conclusions drawn from this measurement effort may be limited depending on the outcome of measurements.

Comment: In response to question 5 of the NTIA FRN, RAND notes that there may be a wide variety of associated performance criteria based on specific applications and operational scenarios. RAND suggests, in general, that a conservative assumption should be that harmful interference is that in which intentional emissions lead to the loss of one or more signals from the GPS satellite constellation. RAND proposes then the time to reacquire would indicate whether the loss could be tolerable - that is, lead to no degradation of the GPS application's functionality.(15)

Response: As stated in the GPS/UWB Measurement Plan, the GPS receiver performance metrics to be used are based on the loss of signal reception from a GPS satellite and the time required to reacquire a satellite in the presence of a UWB signal when the GPS signal is lost momentarily due to an obstruction. NTIA agrees with the commenter that these performance metrics constitute harmful interference.

Comment: In response to question 6 of the NTIA FRN, RAND contends that reacquisition time is often related to integrity requirements for applications involving public safety. RAND notes that a one second "time to alarm" requirements for intelligent transportation systems (including automobile, bus, and rail uses) has been reported by NTIA for many years.(16) The criticality of reacquisition time can vary depending on the availability and practicality of additional information sources such as inertial guidance.(17)

Response: In the GPS/UWB Measurement Plan, the manufacturer's specification for reacquisition time is being used to determine whether or not a GPS receiver successfully reacquires in the presence of a UWB signal. If the GPS receiver is capable of reacquiring and reporting reacquisition within 1 second, this threshold will be used in this measurement effort. However, NTIA is still concerned that the latency inherent in the GPS receiver will prohibit measuring a reacquisition time of 1 second. NTIA is also unaware of any documented requirements related to integrity for public safety applications.(18)

The commenter references an NTIA/DOT Report that specifies time to alarm requirements for vehicle navigation, railroad navigation, marine navigation, and air navigation.(19) The performance metric proposed in the GPS/UWB Measurement Plan is reacquisition time. Reacquisition time is used to characterize the ability of a receiver to reacquire a GPS satellite signal that was being tracked but momentarily interrupted and then the signal is restored. The momentary interruption could be caused by shielding of the GPS signal by a building, by passing under a bridge, by going through a tunnel, etc. The reacquisition time is measured from the time of signal restoration until the receiver has again locked onto and is tracking the interrupted GPS satellite signal. The time-to-alarm is a GPS receiver performance metric that was not proposed in this measurement plan. Time-to-alarm is defined as the elapsed time from the onset of a positioning failure until the equipment annunciates an alarm.

Comment: In response to question 7 of the NTIA FRN, RAND asserts that performance metrics are most effectively determined by users and their respective organizations, in conjunction with GPS manufacturers, applications developers, and systems integrators meeting user needs. Thus RAND further contends that those groups should determine criteria for surveying, maritime, and recreational applications in the absence of government or international agreement.(20)

Response: NTIA agrees with the commenter that GPS users in conjunction with equipment manufacturers are in the best position to determine performance metrics for GPS receivers used for different applications. However, with the exception of the RTCA which includes aviation users and manufacturers, NTIA is unaware of any other organization addressing the issue of performance metrics for GPS receivers. If additional information on GPS receiver performance metrics and criteria are made available in a timely manner, they can be considered in this measurement effort.

Comment: RAND provided various comments addressing specific issues with operational scenarios and the link budget analysis that must be performed.(21)

Response: As stated in the GPS/UWB Measurement Plan, the operational scenarios and link budget analysis will be addressed in a separate effort. The measurements described in this measurement plan will not develop the operational scenarios or the associated link budgets. The measurements will define the maximum level of UWB emissions that can be tolerated at the input of each GPS receiver considered. The maximum tolerable UWB emission level will then be used in a separate link budget analysis for each specific UWB-to-GPS operational scenario identified to calculate the maximum permissible output power of a UWB transmission system, under given parameter combinations, that will ensure compatibility with GPS receivers. The operational scenarios will be dependent upon both existing and projected GPS and UWB applications and will take into consideration circumstances involving both single and multiple UWB transmission systems. For each application, a link budget will be developed under assumptions and/or known conditions that are defined by the particular operational scenario. A series of public meetings are being held to develop the operational scenarios to be considered in the assessment of potential interference to GPS receivers from UWB transmission systems. Interested parties have been invited to make presentations describing the GPS/UWB operational scenarios that they recommend for consideration in the NTIA analysis. The operational scenarios will consider single and multiple UWB transmission systems.

Comment: RAND states that in this measurement effort, only one kind of UWB source and three aggregated sources are discussed. RAND asserts that the aim of the measurement plan are not fully supported by the time and resource limitations now imposed on what the measurement plan can actually accomplish.(22)

Response: The commenter correctly states that all of the UWB signal generators are the same. From an interference perspective, what is important is that the UWB signal level is constant across the bandwidth of the GPS receiver. The UWB generators used in this measurement effort will produce a constant signal level across the GPS receiver bandwidth. This flat characteristic will be verified through spectrum analyzer measurements. In a limited number of measurement cases, the UWB signal will not be flat (i.e., spectral lines) and steps will be taken to assure that at least one spectral line occurs within the bandwidth of the main lobe of the correlator. However, there will be no attempt made to align the UWB signal spectral line with a dominate spectral line of the C/A code.

As a result of additional funding NTIA has purchased six additional UWB signal generators for the aggregate measurement task. The key point to remember is that the aggregate measurements are to demonstrate how multiple UWB emissions add within a receiver which can be accomplished with the limited number UWB generators that NTIA has available. There is also a separate NTIA measurement and analysis program that will also be examining the effects of interference from multiple UWB signal emissions on other critical Government radiocommunication systems.(23) To the extent practicable, the aggregate analysis capabilities being developed in this effort will be used in the analysis of GPS receivers.

Therefore, NTIA believes that the goals of this measurement effort can be accomplished using the UWB signal generators currently available.

Comment: RAND states that actual GPS receivers should be compared to minimal International Telecommunication Union (ITU) standards for GPS (space-to-Earth) receivers, citing a recently approved Recommendation that provides technical characteristics for GPS receivers. (24)

Response: NTIA believes that the candidate receivers to be considered in this measurement effort will satisfy the commenters recommendation. The candidate receivers include all of the different receiver technologies currently available. The results of this measurement effort that assess the potential impact from UWB transmission systems should then be applicable to the receivers that are included in the ITU Recommendation.

Comment: RAND also suggests that the measurements are intended to validate a model that assesses the interference to GPS receivers from UWB transmission systems.(25)

Response: The development of a model is an analysis issue and unrelated to the measurement plan. The measurements obtained from this effort will define the maximum level of UWB emissions that can be tolerated at the input of each GPS receiver considered. The maximum tolerable UWB emission level will then be used in a separate link budget analysis for each specific UWB-to-GPS operational scenario identified to calculate the maximum permissible output power of a UWB transmission system, under given parameter combinations, that will ensure compatibility with GPS receivers.

Comment: RAND indicates that UWB signals can have both positive and negative harmonic components and can vary from 0.5 to 10 nanosecond, and can have varying amounts of damping depending on the driving signal and specific transmission antenna.(26)

Response: In general NTIA agrees that UWB signals can be generated with various pulse durations and that the antenna can have an effect on the shape of the UWB signal. However, NTIA believes that in assessing the potential interference to GPS receivers from UWB transmission systems the duration of the pulse from 0.5 to 10 nanosecond will not significantly change the spectrum in the GPS band. From an interference perspective, what is important is that the UWB signal level is constant across the bandwidth of the GPS receiver. The UWB generator used in this measurement effort will produce a constant signal level across the GPS receiver bandwidth. This flat characteristic will be verified through spectrum analyzer measurements. In a limited number of measurement cases, the UWB signal will not be flat (i.e., spectral lines). In this case steps will be taken to assure that at least one spectral line occurs within the bandwidth of the main lobe of the correlator. However, there will be no attempt made to align an interfering signal spectral line with a dominate spectral line of the C/A code.

Comment: RAND states that the pulse duration and shape may have an effect on the measurement if UWB signals exist above or below the GPS band and overlap into the band. The commenter further states that if GPS can be protected by "notch filtering", a more precise characterization of the UWB parameters will be needed.(27)

Response: The measurements performed in this effort will define the maximum level of UWB emissions, in the vicinity of 1575.42 MHz, that can be tolerated at the input of each GPS receiver considered. The maximum tolerable UWB emission level will then be used in a separate link budget analysis for each specific UWB-to-GPS operational scenario identified to calculate the maximum permissible output power of the UWB transmission system. This maximum permissible output power can then be used to specify the filtering necessary for the UWB transmission system to provide adequate protection to GPS receivers used for various applications.

Comment: RAND asserts that the power level may not be the only variable that leads to effects on GPS receivers.(28)

Response: NTIA agrees with the commenter that power level is not the only variable that can impact GPS receivers. Table 3 of the GPS/UWB Measurement Plan lists the UWB parameters and the range of values chosen to assess the interference potential to GPS receivers. Each possible combination will be used to give a total of 32 permutations for each GPS receiver considered in this measurement effort. Time constraints limit the range of UWB signal parameters that can be considered in this measurement effort. However, the parameters to be varied in this measurement will allow NTIA to explore a limited range of the possible UWB signal characteristics. If during the measurement effort, it is determined that certain UWB signal parameters have a greater impact on a GPS receiver, these parameters will be examined in greater detail.

Comment: RAND contends that the sampling rate of present spectrum analyzers is inadequate to provide an accurate measure of the signal amplitude and thus measure power.(29)

Response: As shown in the measurement setup in Figure 4 and described in the measurement procedures, the UWB signal will be measured in a 20 MHz bandwidth filter using a power meter. The 20 MHz bandwidth is consistent with the maximum bandwidth of a GPS receiver. The UWB measurements made in this effort will be compared with the results of the other NTIA measurement effort that is developing measurement procedures to characterize UWB emissions using commercial-off-the-shelf measurement equipment.

Comment: RAND notes that GPS receivers process each channel independently but all satellites that are in view are valuable.(30)

Response: As stated in the GPS/UWB Measurement Plan examining the impact of UWB emissions on a single channel of the GPS receiver simplifies the measurement approach by removing non-pertinent constellation variables such as dilution of precision, the rising and setting of satellites, and the individual satellite powers. The satellite signal power used is the minimum guaranteed level as specified in the GPS Interface Control Document. In establishing the broadband noise level representing sky noise and cross correlation noise, the results of studies conducted for Working Party 8D that were the basis on ITU-R recommendation M.1477 were used.

Comment: RAND requested an explanation of why 2 dB was chosen as the UWB signal level to begin the acquisition measurements.(31)

Response: As described in the measurement procedures, the UWB signal level will be increased until the break-lock point is reached. The UWB signal power will then be decreased by 2 dB and the reacquisition measurement will begin. A value of 2 dB was chosen because a GPS receiver is not expected to be able to reacquire at the break-lock point. As more experience is gained in the measurements, the UWB signal may be decreased further before the reacquisition measurements are initiated.

Comment: RAND also notes that in general, GPS performance criteria have not been identified by the U.S. Government.(32)

Response: NTIA believes that GPS users in conjunction with equipment manufacturers are in a better position than the U.S Government to determine performance criteria for GPS receivers. NTIA is familiar with the aviation process where a Minimum Operational Performance Standard (MOPS) is developed which leads to the development of the International Civil Aviation Organization Standards and Recommended Practices (SARPS). The commenter indicates that GPS performance criteria does exist from GPS manufacturers, but fails to provide any references to support this claim. The Federal Register Notice questions 4 through 7 requested information from GPS manufacturers and users regarding performance metrics and criteria for the different GPS applications. If this information is available and can be provided to NTIA in a timely fashion, it can be included in this measurement effort.

Comment: RAND also questions how multiple UWB emitters may vary among themselves to produce aggregate interference effects.(33)

Response: The GPS/UWB Measurement Plan includes a task to assess the potential of interference to GPS receivers from multiple UWB transmission systems. As shown in Table 4, the measurements will consider the effects from UWB transmission system with similar and different parameters. As a result of additional funding, additional UWB signal generators have been purchased and three of these additional sources will be included in the measurement setup shown in Figure 5. Clarification is also necessary regarding the synchronization of the UWB signal generators in the aggregate interference measurement. There will be no attempt in this measurement plan to synchronize the transmissions of the UWB signal generators used in the aggregate measurements.

Comment: RAND recommends that the UWB peak power observed or filters used should be recorded.(34)

Response: NTIA agrees with the commenter that the frequency response and the group delay characteristics of the 20 MHz filter to be used in the single source and aggregate interference measurements are important. The characteristics of the 20 MHz filter are provided in Appendix B of this document. As can be seen from Figure B-1, the frequency characteristics of this filter are flat across the bandwidth of the GPS C/A code signal. An appendix specifying the characteristics for the 20 MHz filter will be included in the GPS/UWB Measurement Plan.

Comment: RAND also inquires about how spectral lines will be observed and recorded.(35)

Response: The techniques of measuring peak power and the spectral lines of the UWB transmission systems are being developed in the other NTIA measurement effort for non-GPS receivers.

Comment: RAND questions whether the UWB devices used in the NTIA measurement effort produce stable and repeatable signals.(36)

Response: NTIA has verified that the UWB signal generators to be used in this measurement effort provide a stable signal that is repeatable.

 

2.7 Time Domain Corporation

Comment: The Time Domain Corporation (TDC) states that the use of a broadband noise source will likely obscure measurement of the sole impact of UWB. If interference testing is conducted without a broadband noise source, TDC contends that it would be possible to determine the combined impact of both the UWB and white noise sources because the impact of white noise upon GPS receivers is well understood.(37)

 

Response: The purpose of this measurement effort is to determine the maximum UWB emission level that can be tolerated at the input to the GPS receiver. The broadband noise included in the measurement plan represents cross correlation noise (e.g., noise from the other GPS satellites in the constellation) and sky noise (e.g., microwave radiation that is present throughout the universe) which will be present in the environment that a GPS receiver operates in, regardless of it's application. NTIA continues to believe that in order to accurately assess the impact of UWB emissions on a GPS receiver, a broadband noise level representing these noise contributions must be included in the measurements.

Comment: TDC also asserts that if the testing is carried out as currently proposed, it will be impossible to decouple the impact of the two signal sources (e.g., broadband noise and UWB).(38)

Response: The power levels will be measured for each individual signal (i.e., GPS, UWB, and broadband noise), as well as the combined power level. This will permit the analysis of individual interference contributions and the combined effect.

Comment: TDC contends that in order to properly quantify the effect of UWB signals on GPS receivers the UWB signal sources should be fed into the GPS receiver without broadband noise. UWB single source data would permit comparative interference analysis as a function of the existing ambient background interference as it exists at different locations.(39)

Response: NTIA is concerned that the impact to GPS receivers when the UWB signal combines with the existing noise contributions such as cross correlation noise and sky noise could be different than the UWB signal by itself. Since there is no existing data on the impact of the combination of UWB signals with other signals such as broadband noise, NTIA continues to believe that it is imperative that the broadband noise be included in the measurements of the impact of UWB signals on GPS receivers. Furthermore, these measurements will permit a comparative analysis when considered in the different operational scenarios. If the assumptions made by the commenter are correct, one should get the same answer analytically when the UWB signal is combined with a factor that represents the noise contributions.

Comment: TDC asserts that there may be an inconsistency between the ITU-R M.1477 documents cited by NTIA in the NTIA test plan.(40)

 

Response: There appears to be some confusion regarding which portions of ITU-R Recommendation M.1477 that NTIA was referring to in the GPS/UWB measurement plan. ITU-R Recommendation M.1477 contains several different parts. One part contains technical characteristics to be used in sharing studies. These characteristics include an aggregate permissible interference level that is separate from system noise. The other part of the ITU-R Recommendation M.1477 includes the results of a computer simulation that shows the impact of cross correlation noise on a GPS receiver. The results of this simulation support the choice of a C/N0 of 34 dB-Hz which is used in the development of the broadband noise level to be used in the measurements. The section number will be added to Footnote 9 to clarify which portion of ITU-R Recommendation M.1477 is being used in the GPS/UWB Measurement Plan.

Comment: TDC claims that it is not accurate to expect that interfering signals from MSS satellite transmissions will always be present and at the specified levels. TDC also asserts that this needs to be taken into account during the testing in order to collect a more comprehensive set of data and related test points.(41)

Response: NTIA agrees with the commenter that in performing the measurements it should not be assumed that signals from an MSS satellite transmission are always present. The NTIA measurements do not make this assumption. As stated in the GPS/UWB Measurement Plan, the broadband noise level is strictly to represent the contributions from sky noise, cross correlation noise from other satellites within the GPS constellation, GPS augmentation systems, and future radionavigation satellite service systems (e.g., Galileo). The measurements described in the GPS/UWB Measurement Plan do not assume that an MSS signal is present. The presence of an MSS earth station is an issue that should be addressed in the scenario and the associated link budget analysis. In third paragraph of Section 4.4 the reference to MSS earth terminals will be deleted to eliminate any further confusion.

Comment: TDC states that a goal of this test should be to provide a baseline set of measurements to allow for the broadest application of the results.(42)

Response: NTIA agrees with the commenter, and believes that the measurements to be performed in this effort will provide the data that is necessary to be used in the link budget analysis. The set of measurements with only broadband noise as the interference source, will establish a baseline for GPS receiver interference susceptibility measurements. The set of measurements with the combined broadband noise and UWB signal will define the maximum level of UWB emissions that can be tolerated at the input to the GPS receiver. The maximum tolerable UWB emission level, in conjunction with the operational scenario, will be used to calculate the maximum permissible output power of the UWB transmission system. The operational scenarios will define the minimum distance separation, antenna coupling, and other sources of interference that must be taken into consideration depending upon the GPS receiver user application.

Comment: TDC strongly recommends that the testing should also include measurements made with a proper constellation of satellites.(43)

Response: The commenter fails to define what constitutes a proper constellation of GPS satellites. The GPS satellite constellation, which includes number of satellites in view, location of satellites in the sky (e.g., dilution of precision), and the signal power at the surface of the Earth will vary with geographic location and time of day. Defining a single representative GPS constellation that all parties would agree on would be extremely difficult if not impossible.

Comment: TDC proposes that position determination is paramount to both civilian and survey applications, and the impact on position determination requires at least 4 satellites and cannot be determined from a single satellite.(44)

Response: NTIA agrees with the commenter that position determination is an important performance metric that is applicable to most if not all GPS receivers, independent of the application in which it is used. However, the commenter fails to provide a performance threshold for position determination. NTIA believes that the performance metric of loss of satellite is related to position determination. The loss of a single GPS satellite will impact the dilution of precision (DOP). The DOP is the multiplicative factor that modifies ranging error. It is caused solely by the geometry between the user and the available set of satellites. A degradation in the DOP will result in a degradation of the overall accuracy of the position determination obtained by a user of GPS. In order to maintain synchronization between the oscillators in the simulator and the GPS receiver, four satellites signals will be simulated.

Comment: TDC also asserts that it is appropriate to include single channel measurements because a GPS receiver processes each channel independently, and due to spectral features in both the UWB transmission and the GPS code structure, each channel will respond slightly differently to the UWB energy and it is important to measure those differences.(45)

Response: In most cases, the UWB signals considered in this measurement effort will be flat across the bandwidth of the GPS receiver. This flat characteristic will be verified through spectrum analyzer measurements. In a limited number of measurement cases, the UWB signal will not be flat (i.e., spectral lines) and steps are to be taken to assure that at least one spectral line occurs within the bandwidth of the main lobe of the correlator. However, there will be no attempt made to align an interfering signal spectral line with a dominate spectral line of the C/A code. The interference effects of narrowband (i.e., continuous wave (CW)) signals to GPS receivers have been examined and shown to be a function of the particular space vehicle pseudo-random code sequence. These interference effects have been modeled and results are available for consideration and application as appropriate.(46) With the limited time and resources available for this measurement effort, it was decided not to reexamine the interaction of CW signals and the spectral lines of specific C/A codes. Furthermore, theses effects are best examined through measurements using a stable CW signal generator rather than the measurement being developed by NTIA.

Comment: TDC advocates that the test plan include radiated testing to address antenna effects, the impact of multipath interference, and that of ambient noise.(47)

Response: NTIA agrees with the commenter that radiated measurements are needed to determine the effect a GPS antenna will have on an UWB signal. Additional funding has been made available and limited radiated measurements will be included in this measurement effort. The procedures for the radiated measurements are provided in Appendix A of this document.

The effects of multipath are a function of the constellation and the environment in which the GPS receiver is operating. The effects of multipath are very similar to the effects of cross correlation interference and are accounted for in the broadband noise level used in this measurement effort. When considering a harsh multipath environment, an additional factor could be taken into account in the link budget analysis. Furthermore, environment, antenna siting, and antenna characteristics make it virtually impossible to define a "representative" multipath environment.

NTIA believes that radiated measurements will not provide any additional insight regarding the ambient noise environment in which a GPS receiver must operate. The ambient noise environment will vary depending on geographic location (rural versus urban) and time of day (peak verus non-peak). Therefore, radiated measurements made at a single location and at a specific time of day will not provide a basis upon which to establish a representative level of the ambient noise.

Comment: In response to question 1 of the NTIA FRN, TDC states that the receivers proposed by NTIA seem like good candidates to use and overlap in many cases with the receivers being utilized in the ARL/UT GPS Test Program.(48)

 

Response: As stated in the measurement plan, the list of candidate GPS receivers provided in Table 1 of the GPS/UWB measurement plan were selected to include different receiver technologies as well as receivers from different manufacturers. Due to time constraints, a minimum of three GPS receivers (one from each of the technologies) from the candidate list will be considered in this measurement effort. At this point it is difficult to estimate the time required to complete the measurements for a single GPS receiver. If time permits additional GPS receivers from the candidate list will also be measured.

 

Comment: In response to question 2 of the NTIA FRN, TDC asserts that it would be appropriate to have a 10 MHz PRF, but notes that with the time constraints it does not feel it is necessary.(49)

Response: The signal parameters in Table 3 of the measurement plan were selected in an attempt to bound the range of signal parameters considered to be representative of UWB transmission systems to be used by businesses and consumers. The continuing development of UWB transmission systems makes it difficult to test all possible parameter combinations. Furthermore, time constraints limit the range of UWB signal parameters that can be considered in this measurement effort. NTIA believes that the effect of the 10 MHz PRF on a GPS receiver will be the same as that of the 20 MHz PRF that is being considered in the measurement effort as long as the PRF is adjusted such that a spectral line is located within 500 kHz of 1575.42 MHz (i.e., 3 dB bandwidth of the C/A code signal). UWB signal sources operating with a PRF of 10 MHz will be considered in the aggregate measurement task

Comment: In response to question 2 of the NTIA FRN, TDC also recommends that NTIA either set a fixed on/off time regardless of the PRF, or increase the number of pulses per on cycle to at least 10,000.(50)

Response: NTIA agrees with the recommendation made by the commenter. The gated UWB signal will consist of a 4 millisecond on-time and a 16 millisecond off-time (i.e., 20% duty cycle). 100% gating will still consist of a continuous stream of pulses. The GPS/UWB Measurement Plan will be modified to reflect this change.

Comment: In response to question 4 of the NTIA FRN, TDC suggests that an additional metric that may be of value is the impact upon position determination.(51)

Response: NTIA agrees that position determination is an important performance metric that is applicable to most if not all GPS receivers, independent of the application in which it is used. NTIA believes that the performance metric of loss of satellite is related to position determination. The loss of a single GPS satellite will impact the DOP which will result in degradation of the overall accuracy in position determination obtained by a user of GPS. Although not used as the performance metric, position determination will be collected as part of this measurement effort.

Comment: In response to question 5 of the NTIA FRN, TDC asserts that a better approach would be to evaluate the acquisition time (not just the stated manufacturer specification) of the GPS receiver in operation - without UWB generated interference- and determine what additional time, if any, the operational scenario can withstand for reacquisition when such interfering signals are added.(52)

Response: NTIA strongly believes that the ability to reacquire a satellite after it is momentarily lost is important for all users of GPS. As stated in the GPS/UWB Measurement Plan, the reacquisition time will be measured when only the broadband noise signal is present. This will provide a baseline measurement for the reacquisition time that can be compared to the manufacturer specification for time to reacquire. If the GPS receiver cannot reacquire in the time specified by the manufacturer, the manufacturer will be contacted to determine if the receiver is operating properly. The broadband noise baseline measurements for reacquisition can also be compared to reacquisition time when the UWB signal is added.

Comment: In response to question 7 of the NTIA FRN, TDC states they strongly believe that the appropriate performance metric for surveying, maritime, and recreational GPS applications is to examine the impact upon position determination. TDC maintains that the associated criteria would be dependent on the normal error associated with that specific application.(53)

Response: NTIA believes that the performance metric of loss of satellite is related to position determination. The loss of a single GPS satellite will result in degradation of the DOP which will impact the overall accuracy obtained by a user of GPS. The performance metric of loss of a satellite is applicable to all GPS applications. Furthermore, the commenter does not provide a performance criteria for position determination for the different GPS applications.

Comment: TDC asserts that any emissions below 50 µW have little or no potential for interfering with GPS.(54)

Response: The commenter does not provide any references to support the claim that emissions at this level will cause little or no interference to GPS receivers. The 50 µW emission level corresponds to a power level of -43 dBW. This level is 27 dB higher than the limit that has been established to protect GPS receivers from the unwanted emissions from mobile satellite service Earth terminals.

Comment: TDC requests that they have access to the results from [p]reliminary measurements utilizing live GPS satellites that provided inconclusive results as to the potential for interference from UWB signals. TDC specifically asks whether NTIA can make these test results public.(55)

Response: The "live sky" measurements referred to by NTIA in the GPS/UWB measurement plan are the measurements performed by the Stanford University in cooperation with Interval Research Corporation(56) and those performed by the Time Domain Corporation at the National Aeronautics and Space Administration Marshal Space Flight Center.(57) The results of these measurement efforts referred to in the GPS/UWB Measurement Plan are a matter of public record and can be provided to the commenter upon request if they are unable to obtain them.

Comment: TDC asks if NTIA will release a separate document to be published in the Federal Register for comment, on draft operational scenarios. TDC also requests that NTIA provide a schedule for these meetings and include draft scenarios.(58)

Response: On August 31, 2000 a Federal Register Notice was published announcing the first in a series of public meetings to be convened by NTIA to address the development of operational scenarios to be considered in the assessment of potential interference to GPS receivers from UWB transmission systems.(59) Given the time-frame that NTIA is currently working under the number of meetings to be held will depend on the amount of progress that occurs. The Federal Register Notice invites all interested parties to make presentations describing GPS/UWB operational scenarios they recommend for consideration in the NTIA analysis.

Comment: TDC states that it is unclear how the current NTIA GPS testing effort will use the results of the APDs from the ITS UWB Measurement Effort, since NTIA will already possess test data on how UWB energy directly affects GPS receivers.(60)

Response: In the NTIA measurement effort that is considering non-GPS Government radiocommunication systems, one of the tasks involves the characterization of UWB signals with different parameters such as PRF, dithering, and gating. As part of the UWB signal characterization Amplitude Probability Distributions (APDs) will be measured. The APD provides a measure of the statistics of the UWB signal in a specific bandwidth. The APD gives broad insight to the behavior of UWB signals in measurement systems (or victim receivers) of various bandwidths. In the GPS/UWB measurement effort, APDs will be used to gain further insight on how the UWB signal parameters affect GPS receiver performance.

Comment: TDC acknowledges that NTIA is planning on taking the data and results of the DOT/SU effort for MOPS-compliant aviation receivers. TDC contends that this is unsuitable because the stated goal of the DOT/SU data is different from the stated goal of the NTIA effort.(61)

Response: NTIA participated in the development of the DOT/SU measurement plan and supports the approach used for determining the potential interference from UWB transmission systems to GPS receivers. The DOT/SU measurement effort will consider a Minimum Operational Performance Standard (MOPS) compliant GPS receiver and, if resources permit, a land-based GPS receiver. The DOT/SU measurements will define the maximum level of UWB emissions that can be tolerated at the input to the GPS receiver. The maximum tolerable UWB emission level in conjunction with the operational scenario will be used to calculate the maximum permissible output power of the UWB transmission system. NTIA will review the results of the DOT/SU measurement effort to determine if the results are consistent with its own measurement results.

Comment: TDC questions whether the modifications made to the NTIA measurement plan will be recorded for future revisions and whether they will be made publicly available.(62)

Response: The revisions to the GPS/UWB Measurement Plan will be documented in Section 3 of this document which will be made publicly available on the NTIA web page.

Comment: TDC asserts that it is important for NTIA to work closely with GPS equipment manufacturers to ensure that NTIA is able to gain access to all necessary performance parameters.(63)

Response: The GPS Industry Council has provided the candidate GPS receivers for this measurement effort. The GPS Industry Council has also provided a technical point of contact for each of the GPS receivers provided. NTIA ITS staff members are working closely with the identified technical points of contact to ensure that they have access to all of the necessary performance parameters.

Comment: TDC requests an explanation of how NTIA plans to compensate for GPS receivers that use active antenna (i.e., antennas that include an amplifier in the antenna housing). TDC contends that when performing conducted testing, the antenna is not used, so the receiver will not have the usual benefit of the amplifier.(64)

Response: Several of the GPS receivers to be considered in this measurement effort will employ an antenna that includes a preamplifier in the antenna housing. NTIA agrees with the commenter that not including the preamplifier will result in a reduction of the gain and the noise figure of the GPS receiver. For the GPS receivers that employ an active antenna, NTIA ITS staff members will contact the GPS receiver manufacturers requesting the following information: noise figure at the input to the receiver, receiver sensitivity, the minimum signal-to-noise ratio, and the dynamic range of the receiver. Using this information, a matching preamplifier/attenuator configuration can be included in the measurement setup to replicate the front-end of the GPS receiver. Additional text will be added to the GPS/UWB Measurement Plan to clarify how the preamplifier will be included in the measurement setup.

Comment: TDC states that the plan proposes to measure the power from the UWB signal sources and the broadband noise source in a 20 MHz bandwidth using a filter and a power meter. TDC points out that the filter characteristics are not shown and that they will be important in accurately determining the power. TDC also asserts that with regard to measuring the power from the UWB sources over this 20 MHz, they would like to know whether the emissions are flat across the band. If the emissions are not flat across the band, TDC would like NTIA to explain how it plans to handle this situation.(65)

Response: NTIA agrees with the commenter that the frequency response and the phase characteristics of the 20 MHz filter to be used in the single source and aggregate interference measurements are important to accurately measuring the power of the UWB signal. These were factors that NTIA took into consideration in the selection of the filter to be used in this measurement effort. The characteristics of the 20 MHz filter to be used in this measurement effort are provided in Appendix B of this document. As can be seen from Figure B-1, the frequency characteristics of this filter are flat across the bandwidth of the GPS C/A code signal. Figure B-2 shows the phase characteristics of the 20 MHz filter used in this measurement effort. As discussed in the GPS/UWB Measurement Plan, the broadband noise power will also be measured in a 20 MHz bandwidth filter with the frequency and phase characteristics given in Appendix B. An appendix will be added to the GPS/UWB Measurement Plan specifying the characteristics of the 20 MHz filter.

Since there will be some energy that passes through the filter outside of the 20 MHz bandwidth, a power correction factor will be applied to each specific signal measured through the 20 MHz filter. The power correction factor will be determined by taking a trace on a spectrum analyzer for each type of UWB signal as it is passed through the 20 MHz filter. The power is then integrated between the outside edges of the filter skirts. The difference between these two values (in dB) is subtracted from the measured power of each of the signals, giving a spectral power density in the 20 MHz bandwidth. Text clarifying the power correction factor will be added to the GPS/UWB Measurement Plan.

Comment: TDC states that the proposal for reacquisition time as a performance metric was raised in the fourth paragraph. TDC adds that the proposed criterion is to monitor whether the receiver acquires within the manufacturer's stated time. TDC assets that this is not a good criterion. TDC contends that many manufacturer's specifications are either (i) very conservative, or (ii) overly optimistic. TDC maintains that the reacquisition time should be determined without any interfering sources. TDC further states that the receiver should be able to successfully acquire within the stated reacquisition time criterion on numerous occasions, in order to build statistical confidence that the manufacturer specification or other time criterion is correct.(66)

Response: The manufacturer's specification for reacquisition time is only being used as a point of reference. As stated in the GPS/UWB Measurement Plan, the reacquisition time for each GPS receiver will be measured separately with broadband noise and then with a combination of broadband noise and UWB. The broadband noise only measurements, which will include noise levels up to receiver break-lock followed by reacquisition measurements from 2 dB below break-lock to -93 dBm/20 MHz. These measurements will serve as a baseline that can be used to compare the effects of the different UWB signal parameters on GPS receivers. If in the presence of the broadband noise signal, the GPS receiver fails to reacquire within the specification time, the manufacturer will be contacted to determine if the receiver is operating properly. If it is determined that the receiver is operating properly, the reacquisition time measured in the broadband noise baseline measurements will be used as the performance metric.

Comment: TDC states that NTIA introduces the notion of combining the UWB signals with a broadband noise source in the test setup. TDC asserts that this is troublesome and seems counter to the goal of this measurement effort.(67)

Response: As stated earlier, NTIA believes it is imperative that the measurements be performed with a broadband noise representative of operational conditions. There are currently no measurements available that examine how a UWB signal will combine with a broadband noise signal in a GPS receiver. This information is necessary to determine the impact that UWB signals will have on GPS receivers operating in an operational environment and to achieve the stated goal of this measurement effort.

Comment: TDC maintains that based on their review of this test plan, it is not NTIA's goal to measure the difference in impact from a UWB signal to white noise and come up with a correction factor. TDC contends that this is a similar approach to the DOT/SU plan. TDC claims that the DOT/SU plan is using this technique to determine an equivalency factor between UWB and white noise.(68)

Response: The measurements to be performed in this effort will define the maximum tolerable UWB emission level at the GPS receiver input. The broadband noise level used in these measurements will establish the proper baseline for the GPS receiver interference susceptibility measurements. The Department of Transportation/Stanford University (DOT/SU) measurement effort proposes to relate UWB emissions to a broadband noise source for the purpose of determining if there is an equivalence between UWB and a broadband noise source. The DOT/SU does not assume that there is an equivalence between UWB emissions and broadband noise. The fundamental goal of the DOT/SU measurement effort is to quantify the difference between UWB signals and broadband noise. The DOT/SU measurements will also quantify how this difference varies with UWB signal parameters. NTIA participated in the development of the DOT/SU measurement plan and believes that the goals of this measurement effort are consistent with those of the NTIA GPS/UWB Measurement Plan.

Comment: TDC recommends that in order to evaluate the affect of UWB on GPS receivers UWB should be injected into the GPS receiver without broadband noise. TDC maintains that even the ITU-R M.1477 analysis in paragraph 3.2 considers the GPS co-channel self-interference separately from other noise sources.(69)

Response: The broadband noise level to be used in this measurement effort to represent the contributions of cross correlation and sky noise was developed based on the minimum C/N0 threshold of 34 dB-Hz that is required for timely acquisition and reacquisition of the GPS satellite signal. The simulation in ITU-R M.1477 includes the effects of GPS co-channel self-interference (e.g., cross correlation) noise and sky noise.

Comment: TDC states that it is questionable to assume that the interference in the GPS band will have the properties of broadband noise.(70)

Response: Currently, the most likely sources of interference to GPS receivers include out-of-band transmitter signals (e.g., MSS Earth terminals) and possibly spread spectrum signals from other RNSS constellations (e.g., Galileo). In the GPS receiver the correlation process spreads these interfering signals so they are noise-like within the GPS band.

Comment: TDC asserts that by combining UWB with broadband noise other spurious effects can be created that enhance or de-emphasize the affects of UWB. TDC further states that the broadband noise source may cover up some of the effects of the UWB signal when the UWB signal is less than (or equal) the broadband noise source.(71)

Response: There are currently no measurements available that examine how a UWB signal will combine with a broadband noise signal in a GPS receiver. Since the correlation process will spread other interfering signals to make them look noise-like, examining the effects of how UWB signals combine with broadband noise is necessary for GPS receiver interference susceptibility measurements. NTIA agrees with the commenter that when the UWB signal combines with broadband noise other spurious effects can occur. It is exactly these unknown effects that must be quantified and taken into account when determining the potential impact of UWB signals to GPS receivers.

Comment: TDC states that the plan continues to describe the power level chosen for the broadband noise source and the rationale behind that. TDC contends that this rationale seems to be stacking the deck against UWB.(72)

Response: NTIA disagrees with the commeter that the rationale for establishing the broadband noise level stacks the deck against UWB transmission systems. It is an accepted practice in national and international spectrum management to use minimum expected signal and minimum possible carrier-to-noise ratio (C/N) conditions to establish emission limits to protect one radio service from another. The use of minimum signal and C/N conditions is also justified by the proposed unlicensed use of UWB transmission systems, whereby the exact location and density of systems cannot be quantified.

Comment: TDC states that the objective is to use these measurements to determine how much UWB energy is needed to degrade the receiver to a stated level (2 dB below break-lock) and then use these measurements in an operational scenario analysis.(73)

Response: As described in the measurement procedures, the UWB signal level will be increased until the break-lock point is reached. The UWB signal power will then be decreased by 2 dB and the reacquisition measurement will begin. A value of 2 dB was chosen because a GPS receiver cannot reacquire the lost space vehicle at the break-lock point.

Comment: TDC states that in reading through the stated ITU-R document we have seen that the stated threshold for receiver wideband aggregate interference is -146.5 dBW/MHz = -116.5 dBm/MHz = -103.5 dBm/20 MHz. TDC notes that the thermal noise for the receiver is -176.6 dBm/Hz = - 116.6 dBm/MHz = -103.6 dBm/20 MHz. TDC further states that with no other emitter present, thermal noise by itself is at the stated receiver wideband aggregate interference threshold. This means that when any other emitter is added to that environment, the threshold will be exceeded; this includes the broadband noise source that NTIA is proposing to use.(74)

Response: There appears to be some misunderstanding on the part of the commenter regarding ITU-R Recommendation M.1477. As stated earlier, the wideband aggregate interference level of -146.5 dBW/MHz in the ITU-R Recommendation was not used to establish the level of the broadband noise signal. The only portion of this ITU-R recommendation that was used was the simulation results provided in Section 2 of the recommendation. The results of the simulation were used to justify the selection of the C/N0 of 34 dB-Hz that was used in computing the level of the broadband noise signal. For the wideband aggregate interference threshold, the specified noise is already taken into account. That is, the aggregate interference allows the interference to be approximately equal to the noise (i.e., C/N + 3 dB = C/N+I). Therefore, the broadband source used in this measurement effort will not cause the threshold to be exceeded.

Comment: TDC strongly disagrees with the measurement philosophy of judging the impact of UWB signals from a composite of UWB and broadband noise.(75)

Response: Based on the responses to earlier comments NTIA reaffirms that broadband noise provides the proper baseline and must be included for GPS receiver interference susceptibility measurements.

Comment: TDC states that they would like to know the type of 20 MHz bandpass filter that NTIA plans to use in the testing.(76)

Response: The frequency and phase characteristics for the 20 MHz filter used in this test effort are provided in Appendix B of this document. An appendix will be added to the GPS/UWB Measurement Plan specifying the filter characteristics.

Comment: TDC questions how NTIA plans to determine what a significant deviation is ( e.g., 1 dB, 3 dB, 10 dB, 30 dB).(77)

Response: The performance metrics used in this measurement effort are break-lock and time to reacquire a satellite. As stated in the GPS/UWB Measurement Plan, during the break-lock measurements the pseudo-range will be monitored to ensure that prior to break-lock the receiver is operating normally (e.g., no abrupt deviations in the pseudo-range). If the pseudo-range error changes by a factor of 50% over the interval defined by a 3 dB change in interference signal level, this will be considered a significant deviation in the pseudo-range. Text clarifying this will be added to the GPS/UWB Measurement Plan.

Comment: TDC points out a possible discrepancy in Section 4.2 that could be fixed by using "or" rather than "and".(78)

Response: NTIA agrees with the commenter and the proposed modification will be made to the GPS/UWB Measurement Plan.

Comment: TDC states that while a UWB signal has the potential to reduce the C/N0 of a given satellite signal, there will likely be seven other GPS signals to choose from and each channel will be impacted differently depending on its spectral features. TDC strongly recommends that a full (or at a minimum a partial) constellation of satellites be utilized.(79)

Response: There is no guarantee on the number of satellites that a user will be able to see. This is a factor of the users geographic location and the presence of obstacles (e.g., urban canyons). Therefore, assuming that a user will always see seven satellites is not seen as a good approach. NTIA maintains that the loss of a single GPS satellite constitutes a degradation that will impact the DOP, which will degrade the overall accuracy that can be obtained by users of GPS. During the verification of the procedures for the reacquisition measurements it was determined that when the satellite signal was removed to simulate a momentary loss of a satellite, the clock synchronization of the GPS simulator and the GPS receiver was lost. Although some receivers have the ability to externally synchronize the simulator and receiver oscillators, many GPS receivers do not have this capability. Therefore, to resolve the oscillator synchronization problem three additional GPS satellite will be included in the measurement procedures. The characteristics of the GPS satellites are provided in Table 1.

TABLE 1.

Space Vehicle Number Satellite Power
(at the surface of the Earth)
(dBW)
Satellite Elevation Angle
(Degrees)

SV 20

-155 10
SV22 -155 0
SV 25 -160 90
SV 30 -155 15

The GPS Almanac Reference Week is 1075. The duration of the simulation is 1 hour and 15 minutes. Although there are now four GPS satellites being used, the performance metric will still be the loss of a single satellite (SV 25). The GPS/UWB Measurement Plan will be revised to reflect the addition of the three satellites.

Comment: TDC states that a performance metric that is paramount for both civilian and survey uses is the actual impact in the position determination.(80)

Response: NTIA maintains that the performance metric of the loss of a satellite that is being used in this measurement effort is directly related to degradation of position determination. In the Federal Register Notice, NTIA requested information regarding performance metrics and criteria for GPS receivers. The commenter has not provided a performance criterion to be used for position determination.

Comment: TDC states that there is no information about the single channel GPS simulator.(81)

Response: NTIA agrees with the commenter that the GPS/UWB Measurement Plan does not describe the GPS simulator to be used in this measurement effort. At the time the GPS/UWB Measurement Plan was written, the details of the simulator were still in the process of being resolved. To avoid delays in releasing the measurement plan for public comment the simulator information was not included. The GPS simulator to be used in this measurement effort is a Nortel model STR2760. Text will be added to the GPS/UWB Measurement Plan describing the simulator to be used in this measurement effort.

Comment: TDC states that at a minimum NTIA should indicate which channel is being tracked so analysts can consider the code spectral features.(82)

Response: Each GPS space vehicle (SV) will have a unique pseudo-random code sequence with different spectral features. Table 1 of this document provides the SV numbers for the satellites to be used in this measurement effort. As stated earlier, the GPS/UWB Measurement Plan will be revised to include the SV numbers of the satellites to be used in this measurement effort.

Comment: TDC states that the NTIA test plan does not indicate how many minutes of data, sampling interval, and number of samples of pseudo-range will be collected for each attenuation level change. TDC resquests that this be detailed or outlined in the next version of the test plan and the final report. TDC also states that the NTIA plan seems to indicate that the data is only gathered for 1 sigma certainty. TDC also requests clarification on how long the data is to be gathered.(83)

Response: Initially, we plan to set the number of trials for determining the standard deviation of the pseudo-range error to 200. This will result in a 68% confidence that the true standard deviation is within ± 5% of the measured value. Text will be added to the GPS/UWB Measurement Plan to clarify the sampling interval and the data confidence level.

Comment: TDC requests a more detailed explaination as to how the 50 meter step is to be introduced in the reacquisition measurements.(84)

Response: The step in pseudo-range for the reacquisition measurements will be accomplished by simulating GPS receiver motion of 5 meters/second and removing a satellite to cause loss of receiver lock for a period of 10 seconds. Text will be added to the GPS/UWB Measurement Plan to clarify how the 50 meter step is introduced.

Comment: TDC questions why the GPS receivers being tested are required to reacquire with an 80% or greater success rate. TDC contends that if the receiver does not reacquire (without the UWB signal present) 100% of the time to the stated specification then is not either the receiver or the specification invalid for the test.(85)

Response: For the baseline measurement where only broadband noise is used, NTIA agrees with the commenter that the GPS receiver should reacquire 100% of the time within the specification time provided by the manufacturer. If, during the baseline measurements, the GPS receiver does not reacquire within the specified time, the manufacturer will be contacted to ensure that the receiver is operating properly. For the measurements with UWB present a reacquisition success rate of 80% is a reasonable value.

Comment: TDC asserts that it is critically important to have test results that model real-world operational scenarios. TDC asserts that there are three major factors present in the radiated test environment that are not part of the conducted setup - multipath interference, ambient noise, and the impact of transmit and receive antennas.(86)

Response: Outdoor radiated "live sky" measurements, because they cannot be controlled, and cannot be reproduced, are of limited use in producing data to establish a standard. NTIA strongly believes that measurements that are repeatable in a controlled environment are necessary. The ambient noise environment and the contributions from multipath will change for each geographic location and therefore radiated measurements will provide limited additional insight into these factors. NTIA does agree with the commenter that radiated measurements are necessary to determine the effect, if any, that the GPS receive antenna will have on a UWB signal. The GPS/UWB Measurement Plan will be revised to include GPS antenna measurements. The procedures for the GPS antenna measurements are provided in Appendix A of this document.

Comment: TDC requests clarification regarding what is meant by "combined power level range." TDC questions whether the measurement is at the output of the UWB generator combiner or the output of the combiner of the UWB and broadband noise generator.(87)

Response: As in the single source case, the power levels for the aggregate measurements will be recorded for each individual signal (i.e., GPS, UWB, and broadband noise), as well as the combined power level. This will permit any analysis of individual interference contributions and the combined effect.

Comment: TDC states that in Table 4 the level should be set to -94 dBm/20 MHz. TDC contends that this is inconsistent with the step by step measurement procedures, which state that the broadband noise is at -91 dBm/20 MHz and the combined UWB signal will initially be at -97 dBm/20 MHz and then increased up to the break-lock point. TDC requests clarification on this possible discrepancy.(88)

Response: The aggregate measurement task has been expanded to include additional UWB signal generators. As a result Table 4 of the GPS/UWB Measurement Plan has been modified as shown in Section 3.8 of this document. The modifications made to Table 4 addresses the questions raised by the commenter.

Comment: TDC recommends that more combinations in aggregate measurements is needed. TDC specifically recommends a dithered modulation with a gating of 20% (i.e., an amount less than 100%). TDC states that this represents the scenario that they are hoping to deploy if allowed commercial approval.(89)

Response: NTIA agrees with the commenter that measuring a larger range of UWB signal parameters will provide greater insight to the potential for interference to GPS receivers from UWB transmission systems. However, the continuing development of UWB transmission systems and the current time schedule make it difficult if not impossible to test all possible parameter combinations. With the additional UWB signal generators obtained by NTIA, the aggregate measurements task will be expanded. This will also provide for greater flexibility in the UWB signal combinations that can be considered in the aggregate measurement The GPS/UWB Measurement Plan will be revised to reflect the parameters of the additional UWB signal generators to be considered in the expanded aggregate measurements. The purpose of the aggregate measurement task is to determine how UWB signals add in a GPS receiver and not to perform an exhaustive examination of all combinations of UWB signal parameters.

Comment: TDC states that they are not aware of any application that uses simultaneous synchronized UWB transmissions. TDC asserts that to the extent that the test configuration may be used to synchronize the transmissions from multiple UWB sources, such a configuration is unrealistic.(90)

Response: NTIA agrees that clarification is necessary regarding the synchronization of the UWB signal generators in the aggregate interference measurement task. There will be no attempt in this measurement plan to synchronize the transmissions of the UWB signal generators used in the aggregate measurements. The GPS/UWB Measurement Plan will be modified to clarify this.

 

Comment: TDC questions whether in Measurement Case IV, when the multiple sources are on, are they all increased the same amount at the same time, or whether one or two are set to a constant power level and the other source(s) increased.(91)

Response: Section 3.8 of this document describes the expansion of the UWB aggregate measurement task. In Measurement Case I through V, four UWB signal generators will be set at an initial combined signal power level of -96 dBm/20 MHz. The two remaining UWB signal generators will then be introduced separately. In Measurement Case VI, each of the four UWB signal generators will be introduced separately. The intent of the aggregate UWB signal measurements are to examine how UWB signals with different parameters combine in a GPS receiver, and not to model a specific scenario.

 

Comment: TDC states that they have 20 UWB signal generators that were built to support the URL/UT aggregate testing. TDC offers to let NTIA borrow the 20 UWB signal generators for testing, assuming that use of the generators by NTIA can be coordinated with the ARL/UT effort. TDC further states that the use of these devices would allow NTIA to build a better aggregate model with additional data points.(92)

 

 

Response: The key point to remember is that the aggregate measurement task is to examine how multiple UWB emissions add within a GPS receiver. NTIA believes that this can be accomplished with the six and possibly nine(93) UWB signal generators that NTIA now has available. NTIA appreciates the offer made by the commenter but respectfully declines at this time. As stated earlier, the GPS/UWB measurement plan will be revised to reflect how the additional UWB signal generators are to be used in the aggregate measurement task.

Comment: TDC contends that the the radiated section does not include many details about characterizing the GPS receiving antenna, LNA, downstream filters that would occur in an actual receiver, etc. TDC maintains that all of these factors will affect what the GPS receiver front end is presented with from an interference perspective.(94)

Response: Many of the GPS receivers have the antenna, low noise amplifier (LNA), and possibly a preselector filter contained in a single module that cannot be dismantled. One purpose of the radiated measurement is to determine whether or not the GPS receiver front-end (antenna, preselector filter, LNA combined) changes the characteristics of the received UWB signal. By measuring the radiated signal as it is received, and the signal at the output of the LNA, the RF components of the front-end can be characterized.

Comment: TDC states that in addition to the proposed radiated antenna testing, the GPS receivers should be taken outdoors to, as a minimum, validate their performance from the simulator to the real world, with and without a UWB source present.(95)

Response: NTIA is not planning to include "live sky" measurements as part of this effort.

Comment: TDC urges that the NTIA keep the process for revising this plan an open process as we move forward. TDC states that additional briefings should be provided by NTIA to discuss status of this test plan and of the test process.(96)

Response: The document that addresses the public comments submitted in response to the NTIA Federal Register Notice will be available on the NTIA homepage:

<http://www.ntia.doc.gov/osmhome/uwbtestplan/gpstestfr.htm>.

This document will also address the modifications to be made to the measurement plan based on the public comments as well as revisions that are based on internal discussions within NTIA/ITS.

NTIA also provides status briefings of the GPS/UWB measurement effort at each RTCA Working Group 6 (WG ) meeting. The commenter is a member of RTCA WG 6, and will therefore be kept informed of the progress of the NTIA GPS/UWB measurement effort.

Comment: TDC requests that the reporting of data also include the final measurement procedures, including block diagrams of setups, equipment parameters, etc - the info that is required to allow someone to repeat the testing.(97)

Response: In addition to NTIA's submission in response to the Commission's Notice of Proposed Rulemaking, a more detailed report will be prepared that will include all data, final measurement procedures and any other relative documentation of the measurement effort.

Comment: TDC questions whether NTIA plans to record any information from the GPS system simulator, such as the satellite channel number, GPS time and date, etc., in order to determine satellite location for proper analysis.(98)

Response: During the static scenario, the receiver is held at a simulated constant coordinate position of 32 degree 0 minute latitude, -106 degree 0 minute longitude, and 1000 meter elevation. The constellation starts at 21:30:00 on August 16, 2000 and runs for 1 hour and 15 minutes. Only four satellites are simulated (SV 20, SV 22, SV 25, and SV 30). For the simulated movement of the receiver that is required for the reacquisition measurements, the same constellation will be used and the starting latitude, longitude, and elevation are the same as the static scenario. However, the receiver is simulated as moving at a constant rate of 5 meters/second due north. All raw data will be stored in binary format. As stated earlier, NTIA will revise the GPS/UWB Measurement Plan to include information regarding the simulator and SV numbers, and receiver location.

Comment: TDC recommends that the output of the GPS simulator be shown to meet the requirements of an FAA or GPS JPO certified simulator.(99)

Response: The GPS simulator to be used in this measurement effort is a Nortel model STR2760. Calibrations are performed on an annual basis. There is no official certification process that has been established by the GPS Joint Program Office (JPO). However, this simulator was made available from the 746th Test Squadron at Holloman Air Force Base. One of their responsibilities to the Department of Defense is to compare simulated data from GPS simulators against real world data to verify the consistency of the simulator. The STR2760 has proven to meet their requirements. Section A.2 of the GPS/UWB Measurement Plan includes calibration procedures for the GPS simulator to be used in this measurement effort. Additional text will be added to the GPS/UWB Measurement Plan to clarify the GPS simulator certification.

 

Comment: TDC recommends calibrating the receiver to measure the accuracy of the GPS receiver's reported C/N0 relative to a known C/N0.(100)

Response: As stated in the measurement procedures C/N0 as reported by the receiver will be recorded for each receiver with only broadband noise as the interference source. This will establish a baseline for comparison with the C/N0 values that are reported by the receiver when the interference source is the combined broadband noise and the UWB signal.

2.8 U.S. GPS Industry Council

Comment: The U.S. GPS Indusrty Council (U.S. GPS IC) states that by the very nature of the questions asked in the NTIA Notice and from some of the assumptions underlying aspects of the Measurement Plan itself, it is clear that NTIA does not have a complete understanding either of the nature of emissions from UWB transmission systems or what measurement criteria it should use in making its assessments of such emissions.(101)

Response: NTIA agrees with the commenter that a better understanding of UWB emissions in both the time-domain and the frequency-domain is necessary before interference to other radiocommunication systems can accurately be determined. In order to gain a more in-depth understanding of UWB transmission systems, a separate measurement and analysis effort has been undertaken by NTIA.(102)

The purpose of this separate NTIA measurement and analysis effort is to develop accurate, repeatable, and practical methods for characterizing the very narrow pulses and pulse trains of UWB transmission systems. The purpose of this characterization is to provide the information that is necessary to estimate or measure the potential for UWB transmission systems to interfere with existing radiocommunication systems.

Most interference analyses are based on frequency-domain calculations or measurements to determine the interfering power or power density levels. At times, the frequency- domain analyses are followed by time-domain analyses to determine additional, more subtle effects. This measurement and analysis effort will allow NTIA to determine how to use the knowledge of the time-domain characteristics in the analyses of interference in the frequency-domain.

The RF Technology Division of the National Institute of Standards and Technology (NIST) will participate in the NTIA measurement and analysis effort. The NIST facilities will provide the opportunity to obtain measurements of the radiated time-domain waveform of the UWB transmission system. These accurate time-domain measurements along with digitized sampling of the time-domain information for Fast Fourier Transform analyses in the frequency-domain will permit NTIA to gain a greater understanding of UWB emissions.

As part of this measurement and analysis effort, the stated characteristics of typical or known UWB transmission systems will be examined from both a theoretical and analytical standpoint, to identify UWB parameters that need to be defined and measured for use in interference analyses. UWB signal generation, processing, and radiation methods in use and being developed will be investigated. The basic characteristics of the UWB pulses or signals needed to perform interference analyses will also be identified. The NIST time domain measurements and NTIA frequency domain analysis will be compared to measurements using commercial-off-the-shelf measurement equipment.

As can be seen, NTIA is taking steps to gain a more in-depth understanding of UWB transmission systems in order to make accurate assessments of these emissions. The GPS/UWB Measurement Plan will not duplicate this effort, but will use the results of these measurements as applicable. For more information on this measurement and analysis effort, the commenter is referred to <http://www.ntia.doc.gov/osmhome.uwbtestplan/>.

Comment: The U.S. GPS IC states that they are skeptical that NTIA, no matter how well intentioned, can conduct (on an extremely accelerated schedule using an admittedly incomplete sampling of UWB technology, no less) a study of sufficient comprehensiveness to allow it to avoid risk of permitting self-interested parties to draw partial and potentially grievously overgeneralized conclusions about the technology's impact on the GPS system and its millions of users in hundreds of applications across all sectors of our economy.(103)

Response: NTIA acknowledges the concerns raised by the commenter. The measurement schedule is extremely tight with little room to resolve any problems that may arise. The number of GPS receivers that can be measured and the UWB signal parameters that can be examined are also limited. Therefore, any conclusions drawn from this measurement effort may be limited depending on the outcome of the measurement results.

Comment: The U.S. GPS IC states that some military applications of UWB may involve co-site operation with GPS receivers, and that military GPS receivers should definitely be represented in NTIA's measurement effort.(104)

Response: Because of their experience in making measurements on the interference impact to GPS receivers, NTIA believes that the GPS Joint Program Office is in the best position to perform measurements on the potential impact from UWB transmission systems to military GPS receivers.

Comment: The U.S. GPS IC contends that although there is a representative timing receiver in the list, evidence should be provided that receivers, along with applications and specifications to support uses in the infrastructure of other systems, such as communication, power distribution, and finance, are taken into account in the measurement program.(105)

Response: NTIA has been working with the commenter to obtain candidate GPS receivers for this measurement effort. The problem regarding timing receivers is that there are no documented performance metrics and criterion. Furthermore, the commenter provided no additional information regarding the measurement procedures to be used in measuring the potential impact to GPS receivers used in timing applications. As indicated by the commenter, there is a timing receiver in the list of candidate GPS receivers. If time permits, the potential impact to the timing receiver will be measured using the procedures documented in this measurement plan.

Comment: The U.S. GPS IC states that NTIA's list of GPS receivers does not include products that will be coming on the market shortly (such as the E-911 cellular devices with network-assisted GPS receivers that will be introduced in 2001 pursuant to an FCC rulemaking mandate) and personal location GPS devices anticipated for market introduction this year.(106)

Response: Since the commenter does not provide specific performance requirements or specifications for these new receivers, any requirements that are not represented in the current list of candidate receivers cannot be taken into account in this measurement effort. There will always be a new implementation or application that is not completely represented in any study.

Comment: The U.S. GPS IC states that the NTIA Measurement Plan does not appear to encompass UWB waveform parameters that are representative of the UWB transmission systems that are envisioned for use by the public.(107)

Response: In the Federal Register Notice, NTIA requested comments on the list of UWB signal parameters to be considered in this measurement effort. The commenter did not make any specific recommendations for parameters to be included to represent UWB transmission systems to be used by the public. As part of the other NTIA measurement effort, actual UWB devices are being measured to obtain their technical characteristics that have been used to bound the envelope of possible UWB parameters.

Comment: The U.S. GPS IC asserts that if reliable results are to be obtained, NTIA must broaden the expected range of UWB waveforms and characterize them with respect to their envelope risetime, envelope damping, modulated harmonic components and time domain measurements of amplitude.(108)

Response: The measurements that are being performed by NIST as part of the other NTIA measurement effort will examine some of the more subtle effects of various UWB emissions. The full bandwidth time-domain measurements to be performed by NIST will provide the basis for determining and understanding the limitations and the accuracy for the laboratory measurements using commercial-off-the-shelf (COTS) equipment.

Comment: The U.S. GPS IC maintains that the testing proposed will not provide an understanding concerning the cumulative interference effects resulting from the enormous variety of choices of interpulse-interval timing (coding) of trains of such pulses.(109)

Response: It is impossible to develop a measurement plan that examines all possible interpulse-interval timing combinations that multiple UWB transmission systems can create. However, the expanded aggregate UWB interference measurement task can provide insight on the interference potential of multiple pulse trains created by UWB transmission systems. NTIA recognizes that the interference impact to a GPS receiver is very dependent on the C/A code spectral line. If a UWB spectral line falls on a dominate GPS C/A code spectral line the interference impact will be greater than if it falls between the C/A code spectral lines. In the UWB aggregate measurement, the PRFs will be selected such that multiple spectral lines will fall within the bandwidth of the GPS receiver. For higher values of PRF, at least one of the spectral lines will be located within 500 kHz of 1575.42 MHz.

Comment: The U.S. GPS IC states that the NTIA GPS/UWB Measurement Plan is particularly deficient on the issue of the aggregation of UWB signals. The U.S. GPS IC further states that only one kind of UWB source is to be considered and the aggregated source are to consist of only three signals.(110)

Response: The UWB aggregate measurement task will be expanded to include up to six additional (a possible total of nine) UWB signal generators. This expansion will allow NTIA to measure the impact from different combinations of UWB signals, such as dithering, and gating. NTIA still maintains that in assessing the potential interference to GPS receivers from UWB transmission systems, the duration of the pulse is not a critical parameter. From an interference perspective, what is important is that the UWB signal level is constant across the bandwidth of the GPS receiver. The UWB generators used in this measurement effort will produce a constant signal level across the GPS receiver bandwidth. This flat characteristic will be verified through spectrum analyzer measurements. In a limited number of measurement cases, the UWB signal will not be flat (i.e., spectral lines) and steps will be taken to assure that at least one spectral line occurs within the bandwidth of the main lobe of the correlator. However, there will be no attempt made to align the UWB signal spectral line with a dominate spectral line of the C/A code.

Comment: The U.S. GPS IC states that the NTIA measurements will not demonstrate the degree of harm to the victim receiver from the synchronization effects of a communications network. The U.S. GPS IC contends that it is clear that the signal generator does not have the ability to replicate communication applications of UWB.(111)

Response: In the UWB aggregate measurements, there will no attempt to synchronize the transmissions of the UWB signal generators. NTIA is not aware of any application that uses simultaneous synchronized UWB transmissions. For example, through-the wall imaging radars transmit in bursts and wireless local area networks are packet radios that essentially transmit in bursts. Although the measurement configuration may be used to synchronize the transmissions from multiple UWB sources, NTIA believes that such a configuration is not of pratical interest. That is, the UWB system hardware cost and/or data overhead to synchronize emissions would seem to be prohibitive for what is envisioned for a low cost system. Furthermore, for the pulses from several synchronized UWB transmission systems to overlap at the GPS receiver would require the distance to each UWB transmission system be the same to within less than 1 meter (assuming a 1 nanosecond pulse width).

Comment: The U.S. GPS IC maintains that the generator described by NTIA is incapable of simulating a single high-duty-cycle UWB device or the aggregate of numerous devices.(112)

Response: NTIA disagrees with the commenter that the UWB signal generators used in the effort cannot simulate a single high duty cycle UWB device. The duty cycle as seen by the GPS receiver is the combination of the pulsewidth of the UWB signal and the PRF. The pulsewidth that should be used in the duty cycle calculation is based on the duration of the impulse response of the receiver filter which is inversely proportional to the filter bandwidth. For a 20 MHz GPS receiver filter bandwidth the duration of the filter impulse response is 0.05 microsecond (1/20x106). Assuming a PRF of 10 MHz (which is well within the range of the UWB signal generator to be used in this measurement effort), the duty cycle is 0.5 or 50%. NTIA also believes that the signal generators are sufficient to simulate the effects from multiple UWB transmission systems. The key point to remember is that the aggregate measurements are to demonstrate how multiple UWB emissions add within a receiver, which can be accomplished with the number UWB generators that NTIA has available.

Comment: The U.S. GPS IC states that there are several reasons why communication applications of UWB are, at present, inadequately represented with the use of the UWB generator described in the NTIA Measurement Plan: First, the maximum duty cycle of two percent is extremely low and would not take advantage of the large bandwidth potential of the system. The U.S. GPS IC contends that even if individual UWB transmitters in a larger network are fairly characterized by pulses with a low duty cycle, the aggregate of the transmissions from the individual units would probably appear at times like a high duty cycle emission.(113)

Response: NTIA disagrees with the commenter that the UWB signal generators to be used in this measurement effort cannot be used to represent a UWB transmission system representing a communication applications. The commenter states that the maximum duty cycle of the UWB signal generators to be used in this measurement effort is 2%. It appears that this duty cycle was computed using the pulsewidth and the maximum PRF given in Table 2 of the GPS/UWB Measurement Plan (e.g., 0.5x10-9 x 40 x 106 = .02 or 2%). However, to compute the duty cycle as seen by the GPS receiver, the pulsewidth of the UWB signal generator should not be used. The pulsewidth that should be used in the duty cycle calculation is based on the duration of the impulse response of the receiver filter, which is inversely proportional to the filter bandwidth. For a 20 MHz GPS receiver filter bandwidth, the duration of the filter impulse response is 0.05 microsecond (1/20x106). Assuming a PRF of 10 MHz (which is well within the range of the UWB signal generator to be used in this measurement effort) the duty cycle is 0.5 or 50%.

Comment: The U.S. GPS IC states that even with the properly phased combination of three UWB signal generators (the method pursuant to which this would be done is not described in the plan) it would produce an aggregate 6% duty cycle. The U.S. GPS IC maintains that a 6% duty cycle aggregate does not take advantage of the full potential for a local-area communication-network application. The U.S GPS IC further states that the limited duty-cycle test does not demonstrate the point where GPS receiver susceptibility to a pulsed signal increases markedly (at 20 to 30% duty cycle point).(114)

Response: NTIA disagrees with the commenter that the UWB signal generators to be used in this measurement effort cannot be used to represent a UWB transmission systems representing communications-network applications. Since the time that the GPS/UWB Measurement Plan was published, NTIA has obtained an additional six UWB signal generators to be used in this measurement effort. The additional UWB signal generators will allow NTIA to expand the scope of the aggregate measurements task. Modifications will be made to the GPS/UWB measurement plan to reflect the expanded aggregate measurement task.

The commenter states that the maximum aggregate duty cycle that can be generated from the three UWB signal generators is 6% (e.g., 2% for each UWB signal generator). This aggregate duty cycle is based on the erroneous calculation of the duty cycle for a single UWB signal generator as discussed in the response to the previous comment. The commenter specifically states that the signal generators to be used in this measurement effort cannot be used to determine the susceptibility to GPS receivers for high duty cycles on the order of between 20 to 30%. NTIA disagrees with the commenter. As shown in Measurement Case VI (previously Measurement Case IV) in Table 4 of the GPS/UWB Measurement Plan, the duty cycle from each of the UWB signal generators, assuming a 20 MHz bandwidth for the GPS receiver, is 15% (3x106 x .05x10-6). This results in an aggregate duty cycle from the four UWB signal generators of 60%. This will exceed the duty cycle of a local-area communications network as proposed by the commenter. Moreover, the additional UWB signal generators obtained by NTIA will provide greater flexibility and broaden the scope of the combinations of UWB signal parameters that can be considered in the aggregate measurement task of this measurement effort.

Comment: The U.S GPS IC states that they have serious difficulties with measuring the UWB signal power in a 20 MHz bandwidth, since this will provide a filtered, averaged, and therefore inaccurate measurement.(115)

Response: The power level of both the UWB and the broadband noise signals will be measured in a 20 MHz bandpass filter with the frequency and phase characteristics provided in Appendix B. A 20 MHz bandwidth filter is consistent with the maximum bandwidth of a GPS receiver. Therefore, from an interference perspective, measuring the UWB or broadband noise power levels in a bandwidth greater than 20 MHz is not necessary. Since the UWB and broadband noise signals will be measured in the same bandwidth, a direct comparison of the power levels can be made. Therefore, NTIA believes that it is appropriate to consider the interference as measured in a 20 MHz bandwidth filter. The measurements in a 20 MHz bandwidth made in this measurement effort will be compared to the COTS measurements, which is part of the other NTIA measurement effort. Therefore, the measurements made in this effort can be related to the NIST measurements.

Comment: The U.S. GPS IC asserts that the amplitude probability distribution ("APD") is only as good as the sampling rate of the test instrument taking the measurements required, and no definition of the referenced APD is provided in the Measurement Plan.(116)

Response: The use of APDs in this measurement effort will be limited to the characterization of the UWB signals. APDs provide a measure of the statistics of the UWB signal. APDs give a broader insight to the behavior of UWB signals in measurement systems (or victim receivers) of various bandwidths. An APD will provide information regarding whether a UWB signal at the output of a specific filter is CW, pulsed, or noise-like. This measurement effort will use APDs to gain a greater insight into the complicated and time varying characteristics of the UWB signal.

Comment: The U.S. GPS IC notes that a sampling rate of 20 MHz (typical of present day spectrum analyzers) is inadequate to provide a power measure of a 0.5 nanosecond signal. The U.S. GPS IC states that in order to provide an adequate measure of power, that NTIA should augment the spectrum analyzer with a time domain fast sample-and-hold oscilloscope that uses a 20 GHz sampling rate and samples at a Nyquist rate with respect to the UWB signal being analyzed. The U.S. GPS IC states that this must be done with each GPS receiver tested.(117)

Response: As shown in the measurement setup in Figure 4 and described in the measurement procedures, the UWB signal will be measured in a 20 MHz bandwidth filter using a power meter, not a spectrum analyzer. The UWB power measurements made in this effort will be compared with the results of the other NTIA measurement effort that is developing measurement procedures to characterize UWB emissions where COTS measurement equipment will be employed.

Comment: The U.S. GPS IC states that NTIA must embrace an understanding of UWB that moves from the outmoded notion that models for continuous wave signal apply to UWB, and focus on the pulsed, transient nature of the UWB signals.(118)

Response: The performance models that have been used in the past to analyze interference to GPS receivers include: CW, noise-like, and pulsed interference. The measurements performed by the DOT/SU measurement effort to date substantiate the use of these models for examining potential interference to GPS receivers from UWB transmission systems.(119) For example, the preliminary data shows that as UWB pulses are sent at very low rate compared to the front-end of the GPS receiver, the interference effects will be smaller than that due to UWB operation at high PRFs. Most GPS receivers have bandwidths between 2 MHz and 24 MHz. If the UWB PRF is less than 2 million pulses per second, then the pulses will still be distinct at the output of the receiver front end and interference is shown to be relatively small. If the UWB PRF is higher than the GPS receiver bandwidth, then the front end will smear the pulses and the interference effect is shown to be larger. GPS receivers are well known to have lower sensitivity to low PRF pulsed interference and higher sensitivity to continuous interference. NTIA recognizes the concern raised by the commenter and will take it into consideration during the analysis of the measured data.

Comment: The U.S. GPS IC states that other degradation metrics, which have differing significance depending on the application in which the GPS receiver is being used, include the following items, with proper units in parentheses: no fix, outage duration (seconds), cycle slips per second, cold start (seconds), reacquisition while tracking N or more satellites (seconds), pseudorange error, time of arrival, increase in standard deviation (seconds), position error, increase in standard deviation error (meters or centimeters, as appropriate), carrier-to-noise density ratio, and code - and carrier-residuals (where available). The U.S. GPS IC recommends that NTIA's measurements should report occurrences of each of these degradation metrics in the GPS receivers being analyzed.(120)

Response: NTIA agrees with the commenter that the list of metrics are important to examining the potential interference to GPS receivers. To the extent possible all of this information will be recorded, provided the GPS receiver manufacturers can provide guidance to the NTIA/ITS staff as to the procedure to be used to access this data (e.g., proprietary data streams). However, the commenter fails to provide criteria that would be associated with these metrics. Without a criteria it is not possible to use these metrics for assessing the potential for interference to GPS receivers from UWB transmission systems.

Comment: The U.S GPS IC states that public safety applications of GPS often rely on reacquisition time as a key criterion of integrity. The U.S. GPS further contends that a one-second time-to-alarm requirements for intelligent transportation systems has been cited by NTIA.(121)

Response: The commenter refers to an NTIA report that specifies time to alarm requirements for vehicle navigation, railroad navigation, marine navigation, and air navigation.(122) The performance metric proposed in the measurement plan is reacquisition time. Reacquisition time is used to characterize the ability of a receiver to reacquire a GPS satellite signal that was being tracked but, momentarily interrupted and then the signal is restored. The momentary interruption could be caused by shielding of the GPS signal by a building, by passing under a bridge, by going through a tunnel, etc. The reacquisition time is measured from the time of signal restoration until the receiver has regained lock and then resumes tracking the interrupted GPS satellite signal. The time-to-alarm is a GPS receiver performance metric that was not proposed in this measurement plan. Time-to-alarm is the elapsed time from the onset of a positioning failure until the equipment annunciates an alarm, which is quite different than time to reacquire.

3.0 NTIA MODIFICATIONS TO THE GPS/UWB MEASUREMENT PLAN

After reviewing the public comments the following changes shown in italics will be made to the GPS/UWB Measurement Plan.

3.1 Section 2.0 Modifications

Modify the fourth paragraph as follows:

 

… D.C., and the National Institute of Standards and Technology (NIST), also located in Boulder Colorado.

3.2 Section 4.0 Modifications

Modify the second line of the first paragraph as follows :

6) the development of procedures to determine UWB radiated signal effects when received by a GPS antenna; and 7) data recording and reporting methods.

3.3 Section 4.1 Modifications

In the third paragraph third sentence insert the following sentence:

For the GPS receivers that employ an active antenna, the following information will be requested from the engineering points of contact: noise figure at the input to the receiver, receiver sensitivity, the minimum signal-to-noise ratio, and the dynamic range of the receiver. Using this information, a matching preamplifier/attenuator configuration can be included in the measurement setup to simulate the front-end of the GPS receiver.

3.3 Section 4.2 Modifications

In Table 3 modify the entry for Gating(%) Range as follows:

4 millisecond on-cycle with a 16 millisecond off-cycle (20% gating)

continuous stream of pulse transmissions (100 % Gating)

Insert the following sentence after Table 3:

For the nominal PRFs shown in Table 3, the PRF will be adjusted such that a spectral line is located within 500 kHz of 1575.42 MHz (i.e., 3 dB bandwidth of the C/A code signal).

3.4 Section 4.3 Modifications

 

Insert the following sentence after the sixth sentence of the fourth paragraph:

If the estimated pseudo-range error changes by 50% over the interval defined by a 3 dB increase in UWB signal level, then this will be considered a significant deviation.

In the fifth paragraph modify the fifth sentence as follows:

Based on a minimum guaranteed GPS signal power specification for the C/A code of

-130 dBm (C) into a 0 dBic gain antenna10 and a 2 dB implementation loss (Limp)11, the maximum broadband noise density level at which satellite acquisition can be ensured is:

N0 = C - Limp - C/N0 = -130 - 2 - 34 = -166 dBm/Hz.

Modify the second equation for N0 as follows:

N0 = -166 + 10 log (20x106/1) = -93 dBm/20 MHz

Modify footnote 9 as follows:

See Generally Section 3 of Recommendation ITU-R M.1477…

Add a new footnote 11 with the following text:

11. The implementation loss takes into account the loss due to IF filtering, the loss due to the analog-to-digital conversion, correlation loss due to modulation imperfections in the GPS signal and other miscellaneous losses.

3.5 Section 4.4 Modifications

In the third paragraph modify the fifth sentence as follows:

This broadband noise is introduced to account for sky noise, cross-correlation noise generated by GPS satellites other than the one being tracked, satellites from GPS augmentation systems, and satellites from other RNSS systems (e.g., Galileo).

 

Delete the last two sentences in the third paragraph.

Add the following text to the end of the third paragraph:

The number of trials for determining the standard deviation of the pseudo-range error is 200. This will result in a 68% confidence level that the true standard deviation is within

± 5% of the measured value. The 50 meter step in pseudo-range for the reacquisition measurements will be accomplished by simulating receiver motion of 5 meters/second and removing a satellite to cause loss of receiver lock for a period of 10 seconds.

Insert the following text after the third paragraph as a new paragraph:

A GPS simulator will be used to simulate the output of the GPS satellites. In order to maintain synchronization between the oscillators in the simulator and the GPS receiver, three additional satellites signals will be simulated. The space vehicle (SV) number, satellite power level at the surface of the Earth, and the satellite elevation angle are provided below:

SV 20 -125 dBm 10 degrees

SV 22 -125 dBm 0 degrees

SV 25 -130 dBm 90 degrees

SV 30 -125 dBm 15 degrees

The GPS Almanac Week is 1075. During the static scenario, the GPS receiver is held at a simulated constant coordinate position of latitude: 32 degree 0 minute and longitude:

-106 degree 0 minute, and 1000 meter elevation. The constellation starts at 21:30:00 on August 16, 2000 . The duration of the simulation is 1 hour and 15 minutes. Although there are four satellites used only the impact to SV 25 will be considered in this measurement effort. For the simulated moving GPS receiver that is required for the reacquisition measurements, the same constellation is used and the starting latitude, longitude, and elevation are the same as the static scenario. However, the receiver is simulated as moving at a constant rate of 5 meters/second.

The GPS simulator used in this measurement effort is a Nortel Model STR 2760. Calibrations are performed on a annual basis. There is no official GPS Joint Program Office certification process for the simulator. However, this simulator was made available from the 746th Test Squadron at Holloman Air Force Base. One of their responsibilities for the Department of Defense is to compare simulated data from GPS simulators against real world data to verify the consistency of the simulators. The STR 2760 has proven to meet their requirements. In Appendix A, Section A.2 calibration procedures are provided for the GPS simulator to be used in this measurement effort.

Insert the following text as the last paragraph is this section:

Since there will be some energy that passes through the filter outside of the 20 MHz bandwidth, a power correction factor will be applied to each specific signal measured through the 20 MHz filter. The power correction factor will be determined by taking a trace on a spectrum analyzer for each type of UWB signal as it is passed through the 20 MHz filter. The power is then integrated between the outside edges of the filter skirts. The difference between these two values (in dB) is subtracted from the measured power of each of the signals, giving a spectral power density in the 20 MHz bandwidth.

 

3.6 Section 4.4.1 Modifications

Replace measurement Step 2 with the following text:

2) The GPS signal power at the LNA input should be adjusted to -130 dBm.12

Add footnote 12:

12. If there is a separate LNA the gain of the LNA will be duplicated in the measurement setup.

Replace measurement Step 3 with the following text:

3) Add broadband noise to the simulated GPS satellite signal at the LNA input. The initial broadband noise level should to set to -96 dBm/20 MHz (3 dB below the -93 dBm/20 MHz described in Section 4.3). The broadband noise to be recorded is that measured at the output of the 20 MHz bandpass filter with appropriate calibration corrections, to reference this value at the LNA input.

In measurement Step 5, replace the first sentence with the following text:

Measure the pseudo-range values described in Section 4.3 and estimate the one-sigma pseudo-range error.

In measurement Step 6, replace the second sentence with the following text:

Record the median C/N0 as reported by the receiver, the pseudo-range values, and the broadband noise level at each increment. The one-sigma pseudo-range error will be estimated from the pseudo-range values.

In measurement Step 7, replace the third sentence with the following text:

At each increment record the median C/N0 as reported by the receiver, the pseudo-range values, and estimate the one-sigma pseudo-range error.

In measurement Step 8, delete the parenthetical statement (C=-130 dBm + GLNA).

Replace measurement step 12 with the following text:

12) Decrease the broadband noise power level from NBL - 2 dB in 1-dB increments to -93 dBm/20 MHz. Repeat Steps (8) through (11) for a total of 10 trials at each broadband noise power level setting. Record the reacquisition time and the broadband noise power level for each trial.

3.7 Section 4.4.2 Modifications

 

Replace measurement Step 2 with the following text:

2) The GPS receiver is operated at a GPS signal level of -130 dBm, compensated for calibration corrections relative to the LNA input.

Replace measurement Step 4 with the following text:

4) Add the broadband noise and UWB signal to the simulated GPS satellite signal. Set the broadband noise signal to -93 dBm as measured in the 20-MHz filter with necessary calibration corrections to reference the value at the LNA input. The UWB signal is similarly measured in the 20-MHz filter and appropriately referenced to the LNA input. The initial UWB signal level should be set to -96 dBm/20 MHz (3 dB below the -93 dBm/20 MHz described in Section 4.3).

In measurement Step 8, delete the parenthetical statement (C=-130 dBm + GLNA).

 

In measurement Step 9, change -91 dBm/20 MHz to -93 dBm/20 MHz.

Replace measurement Step 14 with the following text:

14) Decrease the UWB signal power level from NBL - 2 dB, or N'UWB , in 1-dB increments to -93 dBm/20 MHz. Repeat Steps (8) through (13) for a total of 10 trials at each UWB signal power level setting. Record the reacquisition time and the UWB power level for each trial.

 

3.8 Section 4.5 Modifications

 

Replace the third paragraph with the following text:

The aggregate measurements in this plan will consider one of the widest bandwidth receivers used in the measurements performed in Section 4.4. Table 4 provides a list of the UWB signal parameters to be considered in the aggregate measurements. There will be no attempt made to synchronize the transmissions of the UWB signal generators.

Add the following subsection heading:

4.5.1 Measurement Procedures for Measurement Case I Through V

In measurement Step 2, delete and GLNA.

Replace measurement Step 4 with the following text:

4) Add the broadband noise and UWB signal to the simulated GPS satellite signal. The broadband noise signal will be set at -93 dBm as measured in the bandwidth of the 20-MHz filter with calibration corrections to reference the value at the LNA input. Set the power level of each UWB signal generator (with the signal parameters of Table 4) such that they are equal at the UWB signal combiner as measured in a 20 MHz bandwidth. The PRF of each UWB signal generator is to be adjusted to assure that: 1) one spectral line from each generator is within 500 kHz of 1575.42 MHz and 2) the spectral lines are not coincident in frequency. If the signal is dithered, then the signal around one spectral line, from each dithered UWB signal generator is to be within 500 kHz of 1575.42 MHz. The pulses of the individual UWB signal generators are not to be synchronized.

Replace measurement Step 5 with the following text:

5) Set the initial combined power level of UWB signal generators #1 through #4 at -96 dBm as measured in the bandwidth of the 20-MHz filter, with appropriate calibration corrections to reference this value at the LNA input.

In measurement Step 9, change -91 dBm/20 MHz to -93 dBm/20 MHz.

Replace measurement Step 14 with the following text:

14) Decrease the combined UWB signal power level in 1-dB increments to -93 dBm/20 MHz. Repeat Steps (8) through (13) for a total of 10 trials at each combined UWB signal power level setting. Record the reacquisition time and the UWB power level for each trial.

Add a new measurement Step 15:

15) Turn on UWB signal generators #5 and #6 and repeat Steps (5) through (14) with the initial combined UWB signal level at -96 dBm/20 MHz including the appropriate corrections to reference this value at the LNA input.

 

Add the following subsection heading:

4.5.2 Measurement Procedures for Measurement Case VI

Replace measurement Step 2 with the following text:

2) The GPS receiver is operated at a signal level of -130 dBm, compensated for calibration relative to the LNA input.

Replace measurement Step 4 with the following text:

4) Add the broadband noise and UWB signal to the simulated GPS satellite signal. The broadband noise signal is to be set at -93 dBm as measured in the bandwidth of the 20-MHz filter with calibration corrections to reference the value at the LNA input. Set the power level of each UWB signal generator (with the signal parameters of Table 4) such that they are equal at the UWB signal combiner as measured in a 20 MHz bandwidth. The PRF of each UWB signal generator is to be adjusted to assure that: 1) one spectral line from each generator is within 500 kHz of 1575.42 MHz and 2) the spectral lines are not coincident in frequency. The pulses of the individual UWB signal generators are not to be synchronized.

 

Replace measurement Step 5 with the following text:

5) With the UWB signal generator #1 turned on, the initial power level at the output of the UWB combiner is set at -96 dBm as measured in the bandwidth of the 20-MHz filter with calibration corrections to reference the value at the LNA input.

Replace measurement Step 7 with the following text:

7) Increase the combined UWB signal power in 3-dB increments until the receiver reaches break-lock, or the UWB signal generator power at the input to the GPS receiver is maximized. Either the break-lock point or the maximum UWB signal power level, as appropriate, will be used as the break-lock point in the remainder of these measurement procedures. Record the median C/N0 as reported by the receiver, the code and carrier pseudo-range values and estimate the one-sigma pseudo-range error.

In measurement Step 9 replace -91 dBm/20 MHz with -93 dBm/20 MHz.

Replace measurement Step 14 with the following text:

14) Decrease the combined UWB signal power level in 1-dB increments to -93 dBm/20 MHz. Repeat Steps (8) through (13) for a total of 10 trials at each combined UWB signal power level setting. Record the reacquisition time and the UWB power level for each trial.

 

Replace measurement Step 15 with the following text:

15) With UWB signal generators #1 and #2 turned on, the initial power level at the output of the UWB signal combiner is set to -96 dBm/20 MHz with calibration corrections to reference the value at the LNA input. Repeat Steps (6) through (14).

 

Replace measurement Step 16 with the following text:

16) With UWB signal generators #1, #2, and #3 turned on, the initial combined power level at the output of the UWB signal combiner is set to -96 dBm/20 MHz with calibration corrections to reference the value at input. Repeat Steps (6) through (14).

Add measurement Step 17:

17) With UWB signal generators #1, #2, #3, and #4 turned on, the initial combined power level at the output of the UWB signal combiner is set to -96 dBm/20 MHz with calibration corrections to reference the value at the LNA input. Repeat Steps (6) through (14).

Modify Table 4 as follows:

TABLE 4. UWB Signal Parameters for Aggregate Measurements

Measurement Case

UWB Signal Parameters

I

Combined Power Level Range: -96 dBm/20 MHz to break-lock point

PRF: 10 MHz (#1); 20 MHz (#2); 20 MHz (#3); 10 MHz (#4); 10 MHz (#5); 10 MHz (#6)

Gating: 100 %

II Combined Power Level Range: -96 dBm/20 MHz to break-lock point

PRF: 10 MHz (#1); 10 MHz (#2); 10 MHz (#3); 10 MHz (#4); 10 MHz (#5); 10 MHz (#6)

Gating: 100 %

Dithering: 2%

III Combined Power Level Range: -96 dBm/20 MHz to break-lock point

PRF: 10 MHz (#1); 10 MHz (#2); 10 MHz (#3); 10 MHz (#4); 10 MHz (#5); 10 MHz (#6)

Gating: 20 %

Dithering: 2%

IV Combined Power Level Range: -96 dBm/20 MHz to break-lock point

PRF: 10 MHz (#1); 10 MHz (#2); 3 MHz (#3); 3 MHz (#4); 3 MHz (#5); 3 MHz (#6)

Gating: 100 % (#1, #2, #3); 20% (#4, #5, #6)

Dithering: 2% (#4, #5, #6)

V Combined Power Level Range: -96 dBm/20 MHz to break-lock point

PRF: 3 MHz (#1); 3 MHz (#2); 3 MHz (#3); 3 MHz (#4); 3 MHz (#5); 3 MHz (#6)

Gating: 20 %

Dithering: 2% (#5, #6)

VI Combined Power Level Range: -96 dBm/20 MHz to break-lock point

PRF: 3MHz (#1); 3 MHz (#2); 3 MHz (#3); 3 MHz (#4)

Gating: 100 %

Introduce each UWB signal generator separately

3.9 Section 4.6 Modifications

Insert a new Section 4.6 as shown below:

4.6 Task 6: Determine UWB Radiated Signal Effects When Received by a GPS Antenna

The objective of this task is to investigate the effects observed at the output of a GPS antenna when a radiated UWB signal is received. This task is important to determine if UWB signals will have an adverse impact on GPS receivers whose performance would be degraded by the occurrence of phase dispersion.

PRFs to be used for this measurement procedure were chosen to represent noise-like, pulse-like, and continuous wave-like UWB signals as observed in a 20-MHz bandwidth. These PRFs are 3 MHz, 10 MHz, and 20 MHz respectively. The 3-MHz PRF signals will also contain dithering of 2% and 50%, to add up to a total of 4 permutations of UWB parameters. All UWB permutations used for this measurement procedure will employ 100% gating (always on).

The following procedures will be used by NIST personnel to perform the radiated measurements:

1) Setup the measurement equipment shown in Figure 6.

 

Figure 6

2) For the first permutation of UWB parameters, use a broadband antenna to capture and record the following data:

  • One single UWB pulse
  • Spectral Plot measured with a spectrum analyzer with a 1 MHz resolution and a 1 MHz video bandwidth, across a 20 MHz bandwidth centered on 1575.42 MHz
  • Fast Fourier Transform as computed from the single UWB pulse measurement
  • APD

3) Repeat Step (2) using the GPS antenna under consideration.

4) Repeat Steps (2) and (3) for the remaining UWB permutations to be considered.

3.10 Section 4.7 Modifications

 

Modify the title of this section as follows:

4.7 Task 7: Data Recording and Reporting

Add a new subsection title:

 

4.7.1 GPS Receiver Measurements

Add the following new subsection:

4.7.2 GPS Antenna Measurements

NIST personnel will provide data from the radiated measurements to be included in the data product to be provided to OSM. This data should include a gain curve at the bearing of the UWB antenna (across the 20 MHz GPS band) of the antenna under consideration. The data should also include any LNA gain, if the LNA is integral to the antenna. This data should be available from the manufacturer's engineering point of contact. If the individual antenna and LNA gain information is not available, then the combined gain (antenna plus LNA) should be determined at the bearing of the UWB antenna and across the 20 MHz GPS band.

At a minimum, the following UWB signal parameters will be recorded:

One single UWB pulse

    • Spectral Plot measured with a spectrum analyzer with a 1 MHz resolution and a 1 MHz video bandwidth, across a 20 MHz bandwidth centered on 1575.42 MHz
    • Fast Fourier Transform as computed from the single UWB pulse measurement
  • APD

This data will also be incorporated into the CD containing the GPS receiver data measured during this effort.

3.11 Addition of Appendix B

Add a new appendix (Appendix B) that provides the frequency and phase characteristics of the 20 MHz filter used in the single source and aggregate measurements.


APPENDIX A

4.6 Task 6: Determine UWB Radiated Signal Effects When Received by a GPS Antenna

The objective of this task is to investigate the effects observed at the output of a GPS antenna when a radiated UWB signal is received. This task is important to determine if UWB signals will have an adverse impact on GPS receivers whose performance would be degraded by the occurrence of phase dispersion.

PRFs to be used for this measurement procedure were chosen to represent noise-like, pulse-like, and continuous wave-like UWB signals as observed in a 20-MHz bandwidth. These PRFs are 3 MHz, 10 MHz, and 20 MHz respectively. The 3-MHz PRF signals will also contain dithering of 2% and 50%, to add up to a total of 4 permutations of UWB parameters. All UWB permutations used for this measurement procedure will employ 100% gating (always on).

The following procedures will be used by NIST personnel to perform the radiated measurements:

1) Setup the measurement equipment shown in Figure 6.

 

Figure 6

 

 

2) For the first permutation of UWB parameters, use a broadband antenna to capture and record the following data:

  • One single UWB pulse
  • Spectral Plot measured with a spectrum analyzer with a 1 MHz resolution and a 1 MHz video bandwidth, across a 20 MHz bandwidth centered on 1575.42 MHz
  • Fast Fourier Transform as computed from the single UWB pulse measurement
  • APD

3) Repeat Step (2) using the GPS antenna under consideration.

4) Repeat Steps (2) and (3) for the remaining UWB permutations to be considered.


APPENDIX B

20 MHz BANDPASS FILTER CHARACTERISTICS

As discussed in the GPS/UWB measurement plan, a 20 MHz filter will be used to measure the power of the broadband noise and the UWB signal. The filter is a TTE 315-1575.42-24M-50 bandpass filter. Figure B-1 is the frequency response of the filter used in this measurement effort. As it can be seen from Figure B-1, within the GPS band, the frequency response of this filter is relatively flat. Furthermore, the frequency response of the filter is also steep enough to avoid additional energy outside of the 20 MHz filter which would present erroneous readings. Figure B-2, gives the phase characteristics of the filter used in this measurement effort.

 

Figure B-2

 

Figure B-2

Endnotes

1. National Telecommunications and Information Administration, Notice, Request for Comments on Global Positioning System/Ultrawideband Measurement Plan, Federal Register, Vol. 65, No. 157 (Aug. 14, 2000), at 49544.

2. Air Transport Association Comments Dkt. No. 000623194-0221-02, Request for Comments on Global Positioning System/Ultrawideband Measurement Plan (Aug. 29, 2000) at 1.

3. Anro Engineering, Inc. Comments Dkt. No. 000623194-0221-02, Request for Comments on Global Positioning System/Ultrawideband Measurement Plan (Aug. 28, 2000) at 1.

4. Joint Spectrum Center Comments Dkt. No. 000623194-0221-02, Request for Comments on Global Positioning System/Ultrawideband Measurement Plan (Aug. 21, 2000) at 1.

5. Id.

6. Multispectral Solutions, Inc. Comments Dkt. No. 000623194-0221-02, Request for Comments on Global Positioning System/Ultrawideband Measurement Plan (Aug. 21, 2000) at 1.

7. Id at 2.

8. National Aeronautics and Space Administration Glenn Research Comments Dkt. No. 000623194-0221-02, Request for Comments on Global Positioning System/Ultrawideband Measurement Plan (Aug. 28, 2000) at 1.

9. Id.

10. Id.

11. RAND Science and Technology Policy Institute Comments Dkt. No. 000623194-0221-02, Request for Comments on Global Positioning System/Ultrawideband Measurement Plan (Aug. 25, 2000) at 1 (hereinafter "RAND Comments").

12. National Telecommunications and Information Administration, Notice of Public Meeting to Develop Global Positioning System/ Ultrawideband Operational Scenarios, Vol. 65, No. 170 (Aug. 31, 2000), at 52989 (hereinafter "Public Meeting Notice").

13. RAND Comments at 1.

14. Id.

15. Id. at 2.

16. U.S. Department of Commerce, National Telecommunications and Information Administration, and U.S. Department of Transportation, A Technical Report to the Secretary of Transportation on a National Approach to Augmented GPS Services, (Dec. 1994) (hereinafter "NTIA/DOT Report").

17. RAND Comments at 2.

18. Integrity is the ability of a system to provide timely warnings to users when the system should not be used for navigation.

19. NTIA/DOT Report at 9-12.

20. RAND Comments at 2.

21. Id. at 4.

22. Id.

23. National Telecommunications and Information Administration, Ultra-Wideband Signals for Sensing and Communication: A Master Plan for Developing Measurement Methods, Characterizing the Signals and Estimating Their Effects on Existing Systems, (June 15, 2000) at 6.

24. RAND Comments at 5.

25. Id.

26. Id.

27. Id.

28. Id.

29. Id.

30. Id. at 6.

31. Id.

32. Id.

33. Id.

34. Id.

35. Id.

36. Id.

37. Time Domain Corporation Comments Dkt. No. 000623194-0221-02, Request for Comments on Global Positioning System/Ultrawideband Measurement Plan (Aug. 29, 2000) at 1 (hereinafter "TDC Comments").

38. Id at 3.

39. Id. at 4.

40. Id.

41. Id. at 5.

42. Id.

43. Id.

44. Id. at 4.

45. Id. at 5.

46. As shown in Tables 1 through 3 of ITU-R Recommendation M.1477 the interference threshold for narrowband (CW) interfering signals is 10 dB lower than the threshold for wideband interfering signals.

47. TDC Comments at 6.

48. Id. at 7.

49. Id.

50. Id.

51. Id. at 8.

52. Id.

53. Id. at 9.

54. Id. at 10.

55. Id.

56. Per Enge, Konstantin Gromov and Jaewoo Jung Stanford University and G. Roberto Aiello and Gerald D. Rogerson, Interval Research Corporation, A Cooperative Program to Assess Interference from Ultra Wide Band Technologies to the Global Positioning System, 1999 UWB Conference for Radio and Radar Technology, Washington D.C. (Sept. 29, 1999).

57. Ex Parte Notification, ET Docket No. 98-153, David E. Hilliard, Counsel for Time Domain Corporation (Feb. 17, 2000).

58. TDC Comments at 11.

59. See, Public Meeting Notice.

60. TDC Comments at 11.

61. Id. at 12.

62. Id at 13.

63. Id.

64. Id.

65. Id. at 14.

66. Id. at 15.

67. Id.

68. Id.

69. Id.

70. Id.

71. Id.

72. Id. at 16.

73. Id.

74. Id.

75. Id.

76. Id.

77. Id.

78. Id. at 17.

79. Id.

80. Id.

81. Id.

82. Id.

83. Id.

84. Id.

85. Id. at 18.

86. Id.

87. Id.

88. Id.

89. Id.

90. Id.

91. Id. at 19.

92. Id.

93. The actual number of UWB signal generators available for the aggregate measurements will depend on scheduling conflicts with the other NTIA measurement effort.

94. TDC Comments at 19.

95. Id.

96. Id.

97. Id. at 20.

98. Id.

99. Id.

100. Id.

101. U.S. GPS Industry Council Comments Dkt. No. 000623194-0221-02, Request for Comments on Global Positioning System/Ultrawideband Measurement Plan (Aug. 29, 2000) at 3 (hereinafter "U.S. GPS IC Comments").

102. National Telecommunications and Information Administration, Notice of Publication and Solicitation of Comments, Federal Register, Vol. 65, No. 127 (June 30, 2000) at 40614-40615.

103. U.S. GPS IC Comments at 4.

104. Id. at 6.

105. Id.

106. Id.

107. Id.

108. Id.

109. Id. at 7.

110. Id.

111. Id.

112. Id.

113. Id.

114. Id.

115. Id. at 8.

116. Id.

117. Id.

118. Id.

119. Ming Luo, Dennis Akos, Sam Pullen, Per Enge, Stanford University, Sally Frodge, Department of Transportation, UWB Interference Test Preliminary Results (Aug. 4, 2000).

120. U.S. GPS IC Comments at 8.

121. Id.

122. NTIA/DOT Report at 9-12.


Go to UWB into GPS Home Page.