21 August 2000

Mr. Steve Jones
Office of Spectrum Management
National Telecommunications and Information Administration
Room 6725 HCHB
1401 Constitution Avenue, NW
Washington, DC 20230

Reference: [Docket No. 000623194-0221-02] Notice; Request for Comments on Global Positioning System/Ultrawideband Measurement Plan

Dear Mr. Jones:

Multispectral Solutions, Inc. (MSSI) is pleased to provide the following comments on the GPS/UWB Measurement Plan (dated August 8, 2000) proposed by the Institute for Telecommunication Sciences (ITS) and the Office of Spectrum Management (OSM) of the National Telecommunications and Information Administration (NTIA).

In general, the GPS/UWB Measurement Plan is very well conceived and, if fully executed, will result in the generation of substantive engineering data which will greatly assist both UWB and GPS user communities in determining the potential interference impact to GPS from UWB transmission systems.

We would like to recommend two changes to the Measurement Plan – the first to more adequately consider the validation of test results through field testing; and the second to include two additional parametric values for the UWB signals under test:

  1. In Figure 1, "Flow Diagram of Measurement Plan", the block entitled "Measurement Procedures (Radiated)" does not appear to correspond to any identified Task.

    2. Section 3.1, however, 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." 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.

    One viable approach to field validation would be to utilize the techniques suggested in Task 4, "Development of Single Source UWB Interference Measurement Procedures," but to apply the output of the UWB Generator to a set of broadband antenna elements consisting of:

    1. Broadband dipole radiators (e.g., cylindrical dipole or biconical elements, cf. Y.T. Lo and S.W. Lee, Antenna Handbook, Van Nostrand Reinhold, New York, 1993, Chapter 3, pages 3-28 and 3-29) at a fixed set of center frequencies (e.g., 500, 1000, 1500, 2000 MHz, etc.). These antennas are easily constructed and have been used for UWB applications for nearly 40 years; and/or,
    2. Broadband antennas as provided by UWB manufacturers.

    For a fixed, measurable peak UWB transmitter power, measure the maximum range at which the selected GPS receiver (i) loses lock, and/or (ii) is unable to attain lock. In addition, measure the code and carrier pseudoranges (cf. Section 4.3) and the one-sigma pseudorange error as a function of separation distance between UWB emitter and GPS receiver. As a minimum, separation distances for the pseudorange measurements can be taken as those corresponding to CAT II/III and CAT I landing approaches (e.g., 70 or 100 feet, respectively). Measurements at such distances would be of critical value to both the GPS and aviation communities.

    While the University of Texas Applied Research Laboratory (ARL/UT) is also making field test measurements of UWB sources and GPS receivers, these tests are funded by a single UWB manufacturer and, hence, may not be perceived as totally impartial. Furthermore, since only raw, unprocessed measurement data will be provided by ARL/UT, validation of bench (conducted) tests via correlation with outdoor (radiated) measurements will not be performed. As such, the UT results will be of only limited value in an overall assessment of UWB interference on GPS.

  2. The following is a response to the NTIA's question 2, "Are the UWB transmission system parameters identified in the measurement plan representative of the parameters for UWB transmission systems envisioned for use by the public?"

It is recommended that Table 3, "UWB Signal Parameters" be modified to include a Pulse Repetition Frequency (PRF) of 10.0 MHz; and Continuous Pulse Transmissions (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. A revised Table 3 is provided below:

TABLE 3: UWB Signal Parameters (Revised)

UWB SIGNAL PARAMETER

RANGE

Average Power Density (dBm/20 MHz)

As needed to introduce effect in GPS receiver

Pulsewidth (nanoseconds)

0.5

Pulse Repetition Frequency (MHz)

0.1, 1.0, 5.0, 10.0, 20.0

Modulation

None, random OOK, 2% and 50% dithering

Gating (%)

None (i.e., continuous pulse transmissions), 20, 100, 1000 pulses per on cycle

Thank you for the opportunity to respond to the GPS/UWB Measurement Plan. As a company with over 15 years of experience in the development and fielding of UWB hardware and systems for the U.S. Government and military, we strongly believe that the full adoption of this Measurement Plan will result in the generation of data of significant importance to a thorough and technically sound assessment of the impact of UWB on GPS performance.

Sincerely,

/s/ Robert Fontana

Robert J. Fontana, Ph.D.
President