NTIA comments on efforts to implement the international Global Mobile Personal Communications by Satellite Memorandum of Understanding
FEDERAL COMMUNICATIONS COMMISSION
Washington, DC 20554
In the Matter of ) ) Amendment of Parts 2 and 25 to Implement ) IB Docket No. 99-67 the Global Mobile Personal Communications ) by Satellite (GMPCS) Memorandum ) of Understanding and Arrangements ) ) Petition of the National Telecommunications and) RM No. 9165 Information Administration to Amend Part 25 ) of the Commission's Rules to Establish Emissions) Limits for Mobile and Portable Earth Stations ) Operating in the 1610-1660.5 MHz Band ) COMMENTS OF THE NATIONAL TELECOMMUNICATIONS AND INFORMATION ADMINISTRATION Larry Irving Kathy Smith Assistant Secretary for Acting Chief Counsel Communications and Information William Hatch Acting Associate Administrator Office of Spectrum Management Edward Drocella David Anderson Electronics Engineers Office of Spectrum Management National Telecommunications and Information Administration U.S. Department of Commerce Room 4713 1401 Constitution Avenue, N.W. Washington, DC 20230 (202) 482-1816 June 21, 1999
Table of Contents
ANNEX A, ANNEX B (Annexes available in WordPerfect format only because of the large number of formulae)
The National Telecommunications and Information Administration (NTIA) applauds the Commission for its efforts in implementing the international Global Mobile Personal Communications by Satellite Memorandum of Understanding (GMPCS MOU) which will support the deployment of GMPCS service in the United States and around the world. As discussed in these comments, NTIA remains concerned about a number of issues vital to the future needs and operations of the Federal aeronautical radionavigation community and implementation of the Global Navigation Satellite System (GNSS) and its constituent elements the United States Global Positioning System (GPS) and the Russian Federation Global Navigation Satellite System (GLONASS).
The GPS Standard Positioning Service (SPS) Signal Specification has been amended in recognition that many civil GPS receivers utilize the entire transmitted bandwidth of the Coarse/Acquisition code signal to minimize tracking errors due to noise, interference, and multipath. NTIA requests that the Commission modify Section 25.213(b) of the Commission's Rules, 47 C.F.R. § 25.213(b), to reflect the amended SPS Signal Specification by replacing the current frequency range of 1574.397-1576.443 MHz with the new frequency range of 1563.42-1587.42 MHz.
In the study performed by RTCA Special Committee 159 (SC-159), it was concluded that GLONASS requires the same level of interference protection as GPS. This conclusion supports NTIA's recommendation that a wideband limit of -70 dBW/MHz and a narrowband limit of -80 dBW is required to protect aircraft reception of GLONASS signals in the 1597-1605 MHz portion of the band.
NTIA believes that as a result of the limited carrier-to-noise density margin, the higher interference levels associated with Category II/III precision approach landing, and the potential of multiple interfering sources, the susceptibility levels for GNSS receivers cannot be reduced from the level used to develop the proposed out-of-band emission limits for mobile-satellite service (MSS) terminals operating in the 1610-1660.5 MHz band. Moreover, NTIA does not believe that interference suppression techniques should be used as a substitute for GNSS receiver protection limits.
NTIA agrees with the Commission's proposal to specify the narrowband out-of-band emission limit for MSS terminals as an absolute level of -80 dBW. It is appropriate to specify narrowband emissions in terms of an absolute power level and it is consistent with the recommendation made by RTCA SC-159.
NTIA believes that it is beneficial to MSS operators and GNSS receiver manufacturers to establish out-of-band emission limits in the 1605-1610 MHz band instead of resolving interference on a case-by-case basis. Therefore, NTIA recommends that the Commission adopt the out-of-band emission limits established by the International Telecommunications Union - Radiocommunication Sector (ITU-R) and the European Testing and Standards Institute (ETSI) in the 1605-1610 MHz portion of the band.
NTIA agrees with the Commission that design decisions should be left to the MSS system providers. NTIA believes that if the Commission adopts rules that will require all MSS terminals operating in the 1610-1660.5 MHz band to meet the wideband limit of -70 dBW/MHz and the narrowband limit of -80 dBW in the 1559-1605 MHz by January 1, 2005, approval of hardware/software configurations would not be necessary.
The NTIA Petition proposed that out-of-band emission power levels should be averaged over a 20 millisecond time interval. This power level was based on the symbol duration of the GPS navigation message. Since the NTIA petition was filed, the Wide Area Augmentation System (WAAS) has continued to develop. The WAAS signal will augment GPS to obtain the required accuracy improvement for precision approaches, as well as integrity, continuity, and availability of navigation for all phases of flight. Because the WAAS transmits more data than GPS it has a symbol duration that is 10 times shorter than a GPS data symbol, making WAAS more susceptible to pulsed interfering signals. As a result of this increased susceptibility to pulsed interference, NTIA proposes that the out-of-band emissions for MSS systems employing Time Division Multiple Access (TDMA) techniques be averaged over a time interval of duration that is equal to the length of the transmission time slot. This would only apply to future MSS systems employing TDMA. For existing MSS systems employing TDMA the 20 millisecond averaging time interval should be used.
NTIA disagrees agree with the Commission's assertion that Little LEO terminals operating in compliance with Section 25.202(f) of the Commission's Rules, 47 C.F.R. § 25.202(f), will not exceed the wideband and narrowband limits proposed by NTIA in the 1559-1610 MHz band.
NTIA recommends that the Commission adopt a limit for the carrier-off state of an MSS earth terminal that is 10 dB lower than the carrier-on limit to account for a cumulative power effect.
NTIA believes that based on the continuing evolution of the 1559-1610 MHz band that it would be ill-advised to waive or postpone the 2002 compliance date for new non-geostationary MSS terminals that is proposed in NTIA's petition. However, NTIA does agree that there is some uncertainty for the date of domestic implementation of GLONASS. The status of GLONASS implementation should be reviewed in the 2005 timeframe and the date for invoking the final stages of compliance can be adjusted accordingly.
NTIA proposes that geostationary MSS terminals operating in the 1626.5-1660.5 MHz band that are brought into service after January 1, 2002, be required to comply with the final emission limits of -70 dBW/MHz and -80 dBW. Geostationary MSS terminals that are currently in service or those brought onto service prior to January 1, 2002 should be permitted to operate at their current out-of-band emission levels until January 1, 2005. NTIA believes that this will lessen the burden on manufacturers allowing them adequate time to redesign their terminals to comply with the final emission limits.
NTIA believes that a user in need of emergency assistance should receive help independent of which type of wireless device that person is using. This should be independent of whether the network is terrestrially based like cellular or PCS or satellite-based like GMPCS. Since the ability to locate users in distress is in the public's best interest, NTIA supports position location capabilities for GMPCS terminals authorized for use in the United States.
NTIA requests clarification regarding the types of earth terminals that are to be exempted from the certification requirement proposed by the Commission in this NPRM. NTIA does not object to the Commission expanding the types of terminals considered under the GMPCS-MoU to include semi-fixed and fixed terminals. Such action, however, would require that national and international standards similar to those adopted for the MSS earth terminals be developed for the essential technical parameters of semi-fixed and fixed GMPCS earth terminals.
The United States Coast Guard (USCG) is considering developing interference susceptibility standards for maritime RNSS receivers. The results of the work performed by the USCG may have to be considered in a future rulemaking on the uses of RNSS other than aeronautical.
The National Science Foundation (NSF) requests that the Commission explicitly document in a Report and Order the protection of radio astronomy operations in the 1610-1613.8 MHz band. NSF is also concerned that the out-of-band emissions of MSS earth terminals operating below 1660 MHz may cause interference to radio astronomy observations in the 1660-1670 MHz band. Based on further studies and experience it may be necessary to revisit this issue and request tighter out-of-band emission standards or to introduce other measures.
FEDERAL COMMUNICATIONS COMMISSION
Washington, DC 20554
In the Matter of ) ) Amendment of Parts 2 and 25 to Implement ) IB Docket No. 99-67 the Global Mobile Personal Communications ) by Satellite (GMPCS) Memorandum ) of Understanding and Arrangements ) ) Petition of the National Telecommunications and) RM No. 9165 Information Administration to Amend Part 25 ) of the Commission's Rules to Establish Emissions) Limits for Mobile and Portable Earth Stations ) Operating in the 1610-1660.5 MHz Band )
AND INFORMATION ADMINISTRATION
The National Telecommunications and Information Administration (NTIA), an Executive Branch agency within the Department of Commerce, is the President's principal adviser on domestic and international telecommunications policy, including policies relating to the Nation's economic and technological advancement in telecommunications. Accordingly, NTIA makes recommendations regarding telecommunications policies and presents Executive Branch views on telecommunications matters to the Congress, the Federal Communications Commission, and the public. NTIA, through the Office of Spectrum Management, is also responsible for managing the Federal Government's use of the radio frequency spectrum. NTIA respectively submits the following Comments in response to the Commission's Notice of Proposed Rulemaking in the above-captioned proceeding.(1)
In October 1994, the Commission issued a Report and Order establishing rules for the "Big LEO" service, i.e., voice-and-data mobile satellite service (MSS) provided by non-geostationary satellites accessed by mobile terminals transmitting in segments of the 1610-1626.5 MHz band.(2) The rules included out-of-band emission limits to protect reception of the Global Positioning System (GPS) Coarse/Acquisition (C/A) signals.(3) Although U.S. consultations with Russian officials indicated a likelihood that the Global Navigation Satellite System (GLONASS) would shift to frequencies below 1605 MHz by the year 2005, the Commission acknowledged that emissions from Big LEO terminals could potentially interfere with GLONASS reception below 1610 MHz in the interim. The Commission refrained from adopting specific out-of-band limits to protect GLONASS, however, leaving the issue to be resolved after further study.
In November 1994, representatives of the Commission, the Federal Aviation Administration (FAA), and the NTIA signed a Memorandum of Understanding ("1994 MOU") concerning domestic implementation of a GPS/GLONASS Global Navigation Satellite System (GNSS).(4) The 1994 MOU declared that the Commission would consider adopting pertinent out-of-band emissions limits for MSS terminals recommended by the RTCA,(5) and that licenses for MSS terminals operating in the bands near the GPS and GLONASS bands issued prior to a U.S. decision to implement GLONASS domestically would indicate that the licensees would be bound by any such limits subsequently incorporated in the Commission's rules. The MOU pertained to all MSS terminals transmitting on assigned frequencies between 1610 and 1660.5 MHz.
In January 1997, Special Committee 159, the RTCA committee that had been commissioned pursuant to the 1994 MOU to study the potential for harmful interference with GNSS operation, issued its final report.(6) The aviation and MSS participants agreed that a wideband equivalent isotropically radiated power (EIRP) limit of -70 dBW/MHz and a narrowband EIRP limit of -80 dBW would protect aircraft reception of GPS signals, and the MSS participants agreed that it was feasible for them to meet those limits in the GPS Coarse/Acquisition signal band. No consensus, however, was reached regarding limits for the protection of GLONASS operations. The aviation representatives maintained that a -70 dBW/MHz wideband limit and a -80 dBW narrowband limit were necessary. The MSS representatives maintained that it was economically infeasible for them to suppress emissions in the GLONASS band to that extent and argued that limits of -54 dBW/MHz for wideband emission and -64 dBW for narrowband emissions would be adequate. As a result of this lack of consensus, RTCA SC-159 did not issue a recommendation for the out-of-band emissions to protect GLONASS.
After the release of the RTCA report, interested private sector parties and officials at the Commission, the NTIA, and the FAA conducted informal discussions concerning emission limits for the protection of GNSS in the United States. At the culmination of those discussions, NTIA filed the petition for rulemaking that is in part the subject of this GMPCS NPRM.(7) The NTIA Petition reflects a compromise proposal worked out by the NTIA, the FAA, and the representatives of Big LEO MSS systems. Under the proposal set forth in the NTIA Petition, the out-of-band emission standard that the aviation members of RTCA SC-159 had recommended would be adopted for the protection of aircraft reception of GLONASS signals between 1597 and 1605 MHz, but there would be an initial grace period during which less restrictive limits would apply for emissions in that portion of the band, and no specific limits were proposed for protection of GLONASS reception on frequencies above 1605 MHz.
For protection of GPS reception, the NTIA Petition recommended requiring that all MSS terminals transmitting on frequencies between 1610 MHz and 1660.5 MHz conform to two restrictions: a wideband limit of -70 dBW/MHz, averaged over 20 milliseconds on the EIRP density of the out-of-band emissions in the 1559-1580.42 MHz frequency range; and a narrowband limit of -80 dBW/700 Hz, also averaged over 20 milliseconds on emissions in the 1559-1585.42 MHz frequency range.
The NTIA Petition also recommended a three-phased approach for protection of aircraft reception of GLONASS to ease the initial burden of compliance for MSS operators. In the first phase, MSS terminals transmitting on frequencies in the 1610-1626.5 MHz band that are placed into service prior to January 1, 2002 must, in addition to meeting the requirements described in the preceding paragraph, immediately meet an interim EIRP density limit of -64 dBW/MHz for wideband emissions in the 1580.42-1605 MHz range and a narrowband EIRP density limit of -74 dBW/700 Hz in the 1585.42-1605 MHz range. In the second phase, all MSS terminals licensed for operation on frequencies between 1610 and 1660.5 MHz commissioned after January 1, 2002 must meet limits of -70 dBW/MHz and -80 dBW/700 Hz throughout the 1559-1605 MHz band without relying on software restriction of operating frequencies. In the third phase, MSS terminals commissioned before January 1, 2002 must be deactivated as of January 1, 2005 unless they are altered by then, as necessary, to conform to the -70/-80 limits throughout the 1559-1605 MHz band.(8)
NTIA also recommended that any issue concerning potential interference with reception of GLONASS signals in the U.S. territory on frequencies above 1605 MHz should be addressed on a case-by-case basis.(9)
Since NTIA filed its petition for rulemaking, the Commission proposed voluntary interim equipment certification procedures to be used prior to adopting final rules to implement the Global Mobile Personal Communications by Satellite (GMPCS) MOU which was signed by the United States and over 120 additional parties in February 1997.(10) In this NPRM, the Commission proposed to certify all GMPCS-related terminal equipment that complies with the Commission's technical and other requirements for that service, including requirements governing emission limits. In addition, the Commission proposed that MSS terminals operating in the 1610-1626.5 MHz band would also have to meet the out-of-band emission limits recommended for implementation by the year 2005 by NTIA in its petition for rulemaking.
NTIA applauds the Commission for its efforts in implementing the international GMPCS-MOU which will support the deployment of GMPCS service in the United States and around world. These GMPCS systems will provide additional choices for delivery of seamless voice, data, and broadband services for consumers in all parts of the world. In particular, NTIA would like to commend the Commission for its decision to adopt rules governing the out-of-band emissions for MSS terminals essentially in accordance with NTIA's recommendation. The establishment of such rules strikes a reasonable balance between the public interest in fostering improvement in aeronautical radionavigation and providing GMPCS development. NTIA, however, offers the following comments to specific issues raised in the GMPCS NPRM that NTIA believes will likely have a direct and significant impact upon the future needs and operations of the Federal aeronautical radionavigation community.
The Commission describes the two GPS signals centered on a 1575.42 MHz (L1) carrier frequency: a C/A code signal primarily for civilian use and a 20 MHz wide Precision code signal for military and authorized civilian use.(11) Currently, Section 25.213(b) of the Commission's Rules, 47 C.F.R. § 25.213(b), provides that the bandwidth for the C/A code signal is 2.046 MHz wide extending from 1574.397 to 1576.443 MHz. This is consistent with the C/A code signal bandwidth definition in the 2nd Edition of the GPS Standard Positioning Service (SPS) Signal Specification that serves as the definitive reference source which delineates the GPS service provided to the civil community. Recently, however, the bandwidth definition of the GPS C/A code signal at 1575.42 MHz in the SPS Signal Specification was amended as follows:
The L-band SPS ranging signal is a 2.046 MHz null-to-null bandwidth
signal centered on L1. The transmitted ranging signal that comprises
the GPS-SPS is not limited to the null-to-null signal and extends through
the band 1563.42 to 1587.42 MHz.(12)
This amendment will be reflected in the upcoming 3rd Edition of the GPS SPS Signal Specification due for release later this year.
The SPS Signal Specification was amended in recognition that civil GPS receivers utilize the entire transmitted bandwidth of the C/A code signal to minimize tracking errors due to noise, interference, and multipath. The power dispersed over the bandwidth of a GPS signal is extremely important for high accuracy civilian safety-of-life applications for two reasons. First, the achievable tracking accuracy (in terms of ranging variance) of a signal is inversely proportional to the root-mean-square (RMS) signal bandwidth. The implication is that the further the signal power is dispersed from the carrier frequency, the more important it is in reducing nominal tracking errors. Second, the most effective multipath mitigation techniques for GPS rely on having a very sharp cross-correlation (between the incoming C/A code signal and the receiver replica) function. Sharpness of the cross-correlation function is provided by having a very wide bandwidth to capture the signal power well beyond the first lobe of the signal.
Since it is anticipated that many of the civilian applications that demand a higher degree of accuracy, including safety-of-life applications, will use the full transmitted bandwidth of the GPS C/A code signal, NTIA requests that the Commission conform Section 25.213(b) of its Rules to the amended SPS Signal Specification by replacing the current frequency range of 1574.397-1576.443 MHz with the new frequency range of 1563.42 - 1587.42 MHz.
The Commission requested comment on the assumptions underlying NTIA's recommendation to apply the -70 dBW/MHz limit in the 1597-1605 MHz band to protect aircraft reception of GLONASS signals.(13) The United States is making international commitments within the International Civil Aviation Organization (ICAO)(14) and the International Maritime Organization (IMO)(15) to participate in the development of GNSS. This entails providing protection to different elements of the GNSS, which include both GPS and GLONASS. The Russian Federation is implementing a three stage frequency transition plan for GLONASS.(16) After the year 2005, the GLONASS system will be in its final configuration where its highest carrier frequency will be 1604.25 MHz.(17) In the international frequency coordination process, the United States has committed to providing protection from interference to GLONASS in its final configuration. This protection from interference is to be consistent with standards established within the International Telecommunications Union-Radiocommunications Sector (ITU-R).(18)
User acceptance of the GNSS would be severely harmed if GLONASS availability was restricted by interference. It is therefore necessary that GLONASS receive the same protection from harmful interference that is afforded to GPS. RTCA Special Committee 159 (SC-159) determined that the out-of-band emission limits required to protect GPS would also be appropriate for GLONASS because:
1) GPS and GLONASS operate in the same frequency band with nearly identical hardware realizations.
2) GPS and GLONASS are both pseudo-random noise (PRN) modulated spread spectrum systems.
3) GPS is a code-division multiplex system with all satellites transmitting on the same frequency. GLONASS is a frequency division multiplex system with each satellite in view transmitting the same maximal length PRN code on a specific channel frequency. Neither method has any particular performance advantage over the other in principle.
4) The standard signal power received is similar (-160 dBW for GPS and -161 dBW for GLONASS) and both systems have the same data rate (50 Hz).
5) The code chipping rate for GPS is twice that of GLONASS (1.023 MHz for GPS and 0.511 MHz for GLONASS), and thus, GPS has a 3 dB higher theoretical spreading factor. The lower spreading factor for GLONASS is offset for wideband noise interference by its 3 dB narrower effective bandwidth.(19)
The net result is that the receiver susceptibility mask for GLONASS will be one-half the frequency scale of the GPS mask, but the broadband susceptibility will be the same on a per Hertz basis. Therefore, RTCA concluded that GLONASS requires the same level of interference protection as GPS.(20)
In addition to GPS and GLONASS, another radionavigation satellite service (RNSS) system that could be a component of the next generation of the GNSS has recently been Advanced Published with the ITU-R by the European Space Agency (ESA) for operation in the 1587.69-1609.17 MHz portion of the band. For this new RNSS system to be compatible with GPS and GLONASS, it must have a signal level at the surface Earth that is on the same order of magnitude as GPS and GLONASS, and therefore will require the same level of protection from interference. Given that the interference protection level is the same then the out-of-band emission limits required to protect the receivers using this new RNSS system would be the same.
Thus, NTIA's recommendation that a wideband limit of -70 dBW/MHz and a narrowband limit of -80 dBW should be adopted to protect aircraft reception of RNSS signals in the 1597-1605 MHz portion of the band.
The Commission requested comment concerning measures that might be employed to minimize the interference susceptibility limit of GNSS receivers used in the susceptibility analysis in Appendix F of the RTCA/DO-235 report.(21) The analysis in Appendix F only considered the interference susceptibility of a GNSS receiver and its ability to meet Category I accuracy and continuity requirements and did not address the more stringent requirements of Category II/III precision approach landings. It also emphasizes that the aviation community has accepted the burden of making GNSS receivers more robust so that these receivers can tolerate the current out-of-band emission limits and still meet Category II/III approach specifications.
The interference susceptibility levels of GNSS receivers used in the Appendix F susceptibility analysis represent the interference levels to which manufacturers must design to meet navigation performance requirements. It does not represent the allowable level of interference. For GNSS receivers the critical performance parameter is the carrier-to-noise density ratio (C/No). The C/No determines the performance of the GNSS receiver code and carrier tracking loops and directly impacts phase measurement accuracy, carrier cycle slip rate, navigation message bit/word error rate, and code tracking loop pseudorange accuracy. The GNSS receiver susceptibility level used in the Appendix F analysis results in only a 2.5 dB C/No margin, which is much smaller than the margins established for other ICAO approved navigation systems.(22) Moreover, unlike terrestrial radionavigation systems, the received GNSS satellite power is relatively fixed (e.g., cannot increase power to overcome interference), thus the receivers operate over a smaller dynamic range.(23) Given the limited dynamic range and small C/No margin any reduction in the interference susceptibility levels used to determine the out-of-band emission levels required to protect GNSS receivers is not possible.
In the development of the out-of-band emission limit for Category I operations, the Minimum Separation Distance (MSD) between the MSS terminal and the GNSS receiver based on the RTCA SC-159 "source-path-receiver" model was 100 feet.(24) For Category II/III operations the performance requirements (e.g., accuracy, continuity, integrity) are substantially increased and the MSD is reduced to 50 feet. Since freespace propagation loss is proportional to the square of the separation distance, this implies 6 dB higher interference levels that GNSS receiver manufacturers must tolerate to satisfy Category II/III specifications. RTCA SC-159 concluded that this 6 dB of additional tolerance to interference will be difficult to obtain solely by improving the receiver design.(25)
The interference susceptibility levels developed in Appendix F are based on the assumption that there is a negligible probability that a second transmitter will be operating in close proximity to a GNSS receiver. As new systems are deployed and transmitters proliferate, the probability of multiple sources of interference increases. Since the Appendix F analysis does not consider multiple sources of interference, an additional margin would be necessary , thereby reducing the allowable level of interference.
The use of interference suppression techniques to mitigate interference was also addressed in Appendix F. For the near future, the civil aviation and GNSS receiver manufacturing industries have rejected employing certain new, higher-risk interference mitigation techniques such as adaptive null-steering antennas and the vector tracking loop. These techniques have not been shown to have acceptable integrity and safety performance for civil aviation purposes. There is also a prohibitive cost associated with the implementation of these interference suppression techniques.(26)
NTIA believes that based on the existing limited C/No margin, the higher interference levels associated with Category II/III operations, and the potential of multiple sources of interference, the susceptibility levels for GNSS receivers cannot be reduced from the levels assumed in Appendix F that were used to develop the out-of-band emission limits for the MSS terminals. Furthermore, NTIA does not believe that interference suppression techniques should be used as a substitute for GNSS receiver protection limits.
The Commission is proposing to adopt an absolute power level of -80 dBW for the narrowband out-of-band emission limit to protect GNSS receivers instead of the spectral power density of -80 dBW/700 Hz recommended in the NTIA Petition.(27) The 700 Hz bandwidth was established in Appendix G of DO-235 as the breakpoint between narrowband and wideband interfering signals. NTIA agrees with the Commission's current proposal because it is appropriate to specify narrowband emissions (i.e., spurs) in terms of an absolute power level. Moreover, the narrowband out-of-band emission limit of -80 dBW is consistent with the value recommended by RTCA SC-159.
The Commission seeks comment on NTIA's recommendation to resolve potential interference problems between MSS terminals and GNSS receivers operating above 1605 MHz on a case-by-case basis.(28) Since the NTIA Petition was filed, the ITU-R has developed and approved Recommendation M.1343 and the European Testing and Standards Institute (ETSI) developed TBR-041.(29) Both of these international documents establish out-of-band emission limits in the 1559-1610 MHz bands for MSS terminals in the 1610-1626.5 MHz band and specifically require suppression of the out-of-band emission from these MSS terminals to be linearly interpolated from -70 dBW/MHz at 1605 MHz to a level of -10 dBW/MHz at 1610 MHz. NTIA believes that it is beneficial to MSS operators and GNSS receiver manufacturers to establish out-of-band emission limits in the 1605-1610 MHz band instead of resolving interference on a case-by-case basis. Therefore, NTIA recommends that the Commission adopt the out-of-band emission limits established by the ITU-R and ETSI in the 1605-1610 MHz band. However, it should be noted that these proposed limits are intended to protect GLONASS operations in the final frequency configuration (after 2005). At that time, GLONASS should be operating with all operational carrier frequencies below 1605 MHz. In the interim, harmful interference to aeronautical radionavigation transmissions on frequencies above 1605 MHz from MSS mobile earth terminals will be resolved on a case-by-case basis.
The NTIA Petition specified three options that could be used for MSS terminals that do not meet the -70 dBW/MHz and -80 dBW limits in the 1580.42-1605 MHz band by January 1, 2005. The MSS terminal had to be: (1) permanently deactivated; (2) modified in such a way that it would meet the wideband and narrow band limits in the 1559-1605 MHz band; or (3) constrained to operate only on frequencies in the upper end of the operating band, such that the wideband and narrowband limits were met in the 1559-1605 MHz band. The hardware/software implementation to restrict the operation of the MSS terminal had to be determined by the FAA as meeting air traffic control requirements. The FCC, with the concurrence of NTIA and the FAA, would incorporate the approved hardware/software implementation in the appropriate MSS licenses by January 1, 2002. If a negative finding was made, the licensing of the hardware/software will be denied by the FCC.(30)
NTIA agrees with the Commission that design decisions should be left to the MSS system providers and that requiring prior approval of hardware/software configurations could be unduly intrusive. Option 3 was included in NTIA's petition at the request of the geostationary MSS applicants with operations in the 1626.5-1660.5 MHz band. NTIA does not believe that Option 3 is necessary if the Commission adopts rules that will require all MSS terminals operating in the 1610-1660.5 MHz band to meet the wideband limit of -70 dBW/MHz and narrowband limit of -80 dBW in the 1580.42-1605 MHz band by January 1, 2005.
The FAA has initiated plans to transition from its present ground-based navigation and landing system to a satellite-based system. However, GPS alone will not meet all aviation positioning requirements. To meet the National Airspace System (NAS) requirements, the FAA has proposed two augmentations to GPS: a Wide Area Augmentation System (WAAS) and a Local Area Augmentation System (LAAS). The WAAS signal will provide the augmentation to GPS to obtain the required accuracy improvement for precision approaches, as well as integrity, continuity and availability of navigation for all phases of flight. A study performed by the Johns Hopkins University Applied Physics Laboratory (JHU/APL) concluded that GPS must be augmented to satisfy navigation performance requirements and that the WAAS and the LAAS can provide the required navigation performance.(31) The JHU/APL study also considered interference to GPS and its augmentation systems and recommended that regulations be developed for all licensed transmitters that explicitly limit radio frequency emissions at satellite radionavigation frequencies.(32)
As stated in the NTIA Petition, the out-of-band emission power levels are the average values to be measured over a 20 millsecond (msec) time interval. The 20 msec time interval is related to the 50 symbols/sec data rate of the GPS/GLONASS navigation message with a corresponding symbol duration of 20 msec (1/50). However, the WAAS transmitted data stream has a data rate of 500 symbols/second with a corresponding symbol duration of 2 msec (1/500).(33) As a result of the shorter symbol duration, WAAS receivers are more vulnerable to disruption by long duration pulsed signals. The longer duration pulses will overlap more of the shorter duration WAAS symbols resulting in an increase in bit error rate (BER) and the corresponding word error rate (WER) in the data demodulation performed in GPS and WAAS (GNSS) receivers. Annex A examines the BER and WER performance of GPS and WAAS receivers. As shown in Annex A, a WAAS receiver is more susceptible to increases in BER and WER than a GPS receiver.
The baseline data rate for WAAS is 250 bits/second. The data will be ½ rate convolutional encoded with a Forward Error Correction (FEC) code. Therefore, the symbol rate that the receiver must process is 500 symbols/second. The convolutional coding for WAAS will be constraint length 7 as standard for Viterbi coding. WAAS employs the convolutional code to partially make up for the degradation in bit energy due to its faster data rate as compared to GPS. Pulses that are longer than 2 msec will cause symbol erasures in the Viterbi decoder.(34) An erasure is a position in the demodulated sequence where the symbol value is unknown, thereby increasing the BER. The effects on the convolutional decoding will depend upon the nature of the pulsed signal (e.g., random, periodic, or other).
The MSS terminals operating in the 1610-1660.5 MHz band employ Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA) or Time Division Multiple Access (TDMA) multiple access techniques. For MSS terminals employing FDMA or CDMA, the level of out-of-band emission are constant and the 20 msec measurement interval is adequate. However, for MSS terminals employing TDMA the out-of-band emission levels will be related to the duration of the transmission time slot.(35) In order to provide protection to WAAS receivers, NTIA proposes that the out-of-band emissions of MSS terminals employing either FDMA or CDMA be averaged over a 20 msec time interval. For MSS terminals employing TDMA the out-of-band emissions should be averaged over a time interval of duration that is equal in length to the transmission time slot. This would only apply to future MSS systems employing TDMA. For existing MSS systems employing TDMA the 20 msec averaging time interval can be used.
Motorola recommends that the Commission allow licensees to use spectrum analyzer resolution bandwidths smaller than 1 MHz and integrate the measurements when testing for compliance with the wideband out-of-band power-density limits.(36) NTIA believes that the method of using smaller bandwidths to measure the wideband limits is consistent with ITU-R M.1343. Therefore, NTIA agrees that measurement of the wideband out-of-band emission levels in bandwidths of less than 1 MHz (e.g., 30 kHz, 100 kHz, or 300 kHz) is allowable provided the power of the narrow bandwidth is integrated over 1 MHz.
The Commission states that the frequency separation between the Little LEO 148-150.05 MHz band and the 1559-1610 MHz RNSS band is sufficient to ensure protection of GNSS receivers.(37) Furthermore, the Commission maintains that Little LEO terminals that operate in compliance with Section 25.202(f) of the Commission's Rules, 47 C.F.R. § 25.202(f), will not produce emissions, including harmonics, in the 1559-1610 MHz band that exceed the wideband and narrowband out-of-band emission limits established to protect GNSS receivers.(38)
NTIA disagrees with the Commission's assertion that frequency separation alone is enough to ensure protection of GNSS receivers from the unwanted emissions of Little LEO terminals. The Volpe National Transportation System Landing Systems Laboratory has performed tests to measure the unwanted emission levels that appear in the 1559-1610 MHz band from very high frequency (VHF) transceivers operating in the 118-136 MHz band.(39) Even though a frequency separation of over 1000 MHz exists the test results show that transmitter harmonics, transmitter spurious (non-harmonic frequency) emissions, and local oscillator harmonics were found to be at levels that could potentially interfere with GPS receivers.
It is important to recognize that the issue at hand is not the frequency separation that exists between the Little LEO terminals and the GNSS receivers, but the level of the interfering signal in the passband of a GNSS receiver, as well as the potential for close proximity to an aircraft in final approach. If the interfering signal exceeds the GNSS receiver susceptibility threshold, the location in frequency of the fundamental is irrelevant since it will still cause interference. Annex B examines the out-of-band emission levels of representative Little LEO terminals assuming they are in compliance with Section 25.202(f) of the Commission's Rules, 47 C.F.R. § 25.202(f). As shown in Annex B, the levels in Section 25.202(f) are 32 dB higher than required to protect GNSS receivers for wideband emissions and 37 dB for narrowband emissions. In practice it may well be that these levels of unwanted emissions will generally be present in well designed Little LEO terminals.(40) However, NTIA disagrees with the Commission's conclusion that Little LEO terminals operating in compliance with Section 25.202(f) will necessarily produce emissions in the 1559-1610 MHz band that are not in excess of the proposed wideband and narrowband limits.
The Commission also proposes to exempt Little LEO systems from the out-of-band emissions standards rather than require the licensees to incur the expense of establishing compliance with unnecessary restrictions.(41) It is unclear whether the Commission is proposing to exempt the Little LEO terminals from the out-of-band emission limits in Section 25.202(f) of its Rules, 47 C.F.R. § 25.202(f), or those proposed in the NTIA Petition. In any case licensees must make measurements to demonstrate compliance with the out-of-band emission limits adopted for the Little LEO terminals. In order to measure the out-of-band emissions to the limits proposed by NTIA in the 1559-1610 MHz band, the only additional test equipment that would be required is a suitable filter and low noise amplifier. Therefore, NTIA does not believe that measuring emissions in the 1559-1610 MHz band would present a significant expense to Little LEO licensees.
NTIA recognizes that a balance must be established between the development of emerging technologies and the protection of sensitive Government operations. The potential interference to GNSS receivers from little LEO MSS terminals touches upon the much broader issue of the protection of important Government operations (e.g., satellite navigation, search and rescue) from the unwanted emissions of emerging mobile systems. If the unwanted emission levels are too restrictive this could inhibit the development of emerging mobile technologies. On the other hand, if the unwanted emission levels are too high, sensitive Government operations, and likely many commercial services as well, will not be adequately protected as the use of the radio spectrum increases.
The protection of the spectrum used by GPS will be discussed in a report from the Secretary of Defense to the congressional defense committees.(42) The Secretary of Defense in coordination with the Secretaries of State, Commerce, and Transportation, the director of the Office of Science and Technology Policy, and interested user and industry representatives has been tasked to develop a national strategy to protect the integrity of the RNSS spectrum used by GPS against interference and disruption.(43)
Both ETSI and the ITU-R recognize that MSS terminals operating in the 1610-1626.5 MHz band have two operational states: carrier-on and carrier-off. In the carrier-on state an MSS terminal is transmitting a signal in a continuous or non-continuous mode. In the carrier-off state an MSS terminal is powered-on but not transmitting a signal. The emission limits proposed in the NTIA Petition only apply to the situation where an MSS terminal is in the carrier-on state. When an MSS terminal is in the carrier-off (e.g., stand-by) state, any emissions should be held to levels that are lower than those for the carrier-on state. While this is obvious, a provision still needs to be included in the Commission's rules, otherwise the probability of more than one MSS terminal being in a position to cause interference to an aircraft in a final approach landing could become unacceptably large. NTIA recommends a limit for carrier-off that is 10 dB lower than the carrier-on limit to account for a cumulative power effect. The cumulative power effect is attributed to the significant majority of MSS mobile earth terminals in the carrier-off state.
The Commission invites comment on the possibility of waiving or postponing the compliance deadline with respect to emissions in the 1597-1605 MHz band in the event that progress toward domestic implementation of GLONASS proves slower than expected.(44) As stated earlier, the NTIA Petition proposes a time-phased approach for GLONASS protection that considered: (1) MSS terminals commissioned prior to January 1, 2002; (2) MSS terminals commissioned after January 1, 2002; and (3) MSS terminals in operation after January 1, 2005.(45) The time-phased approach was proposed by NTIA as a way to ensure protection of GNSS operations, while allowing MSS providers to proceed with system implementation.
Since the NTIA Petition was filed, there have been several key developments regarding GNSS that have occurred in the 1559-1610 MHz band. In addition to GPS, GLONASS, and their augmentation systems, there are other RNSS systems proposed for operation in this band.(46) For example, the French Administration and ESA have advanced published RNSS systems with the ITU-R that are planned for operation in the 1559-1610 MHz band. The French Medium SATellite NAVagation (MSATNAV) and the ESA E-NSS-1 satellite navigation systems have been proposed for operation in the 1559.052-1563 MHz and 1587.696-1591.788 MHz portions of the 1559-1610 MHz band.
The United States is also engaged in discussions with the European Union (EU) regarding implementation of the second generation GNSS (GNSS-2) and the development of RNSS systems that are compatible and interoperable with GPS. Subsequently, the EU has proposed the Galileo RNSS system.(47) At this time, it is unknown what portion of the 1559-1610 MHz band it will operate in. One option being considered is to build Galileo from the base of the existing GLONASS system which would enable the EU to take advantage of Russia's expertise in space operations and lead to an early deployment of a European GNSS-2 satellite system.(48)
It is envisioned that one of these RNSS systems will be included in the GNSS-2. Since all of the RNSS systems operating or proposed for operation in the 1559-1610 MHz band are being designed to be compatible with each other they have similar characteristics which include a low signal level at the surface of the Earth (e.g., 1 x10-16 Watts). This is why the out-of-band emission limits proposed in the NTIA Petition were developed. As a result of the continuing evolution of the 1559-1610 MHz band NTIA believes that it is ill-advised to waive or postpone the 2002 compliance date for new MSS terminals proposed in the NTIA Petition. However, NTIA does agree that there is some uncertainty for the date of the domestic implementation of GLONASS. The status of GLONASS implementation should be reviewed in the 2005 timeframe and the date for invoking the final stages of compliance can be adjusted accordingly.
The Commission invites comment on whether the interim wideband limit of -64 dBW/MHz (in the 1580.42-1605 MHz band) and the narrowband limit of -74 dBW (in the 1585.42-1605 MHz band) proposed in the NTIA Petition should also apply to geostationary MSS terminals operating in the 1626.5-1660.5 MHz band.(49) NTIA does not believe that it would be appropriate to apply the interim standards to such geostationary MSS terminals.
When the NTIA Petition was filed, there were no MSS terminals operating in the 1610-1626.5 MHz band; thus, there was an opportunity for such terminals to be designed to meet the interim limits prior to being placed into service. On the other hand, there are a large number of geostationary MSS terminals already in operation that could exceed the proposed out-of-band emissions levels. In recognition of this fact, NTIA proposes that geostationary MSS terminals currently in service or brought into service prior to January 1, 2002, be permitted to operate at their current out-of-band emission levels in the 1597-1605 MHz portion of the band until January 1, 2005. Geostationary MSS terminals operating in the 1626.5-1660.5 MHz band that are brought into service after January 1, 2002, however, should be required to comply with the final emission levels of -70 dBW/MHz and -80 dBW. NTIA believes that this two-fold approach will both protect current equipment investments and lessen the burden on manufacturers by allowing them adequate time to redesign their terminals to comply with the final emission limits.
The Commission seeks comment on whether to require GMPCS terminals authorized for use in the United States to have position location capabilities.(50) NTIA notes that the Commission has acted to require wireless carriers to deliver 911 and to meet a schedule for introducing the features of Enhanced 911 (E 911) calls from wireless devices such as cellular and personal communication services (PCS), whose networks are terrestrially based.(51) Effective April 1, 1998, wireless carriers are required to implement Phase I of this schedule, provided certain conditions were met.(52) Under Phase I rules, carriers must provide Automatic Number Identification (ANI) and cell site information for 911 calls to Public Safety Answering Points (PSAP).(53) Phase II, which requires the deployment of the capability to determine the location of callers, by latitude and longitude, is scheduled for October 1, 2001.(54) NTIA believes that a user in need of emergency assistance should receive help independent of which type of wireless device that person is using. This should be independent of whether the network is terrestrially based like cellular or PCS or satellite-based like GMPCS. Since the ability to locate users in distress is in the public's best interest, NTIA supports position location capabilities for GMPCS terminals authorized for use in the United States.
The United States Coast Guard (USCG) has stated that MSS systems should be included in the requirements for wireless providers to provide compatibility with E 911 emergency calling systems. It is envisioned that GMPCS terminals could be used by persons in distress in remote maritime areas. To provide effective search and rescue support it is essential that the USCG know the location of individuals in distress and be able to confirm the existence of a distress situation. In order to do this, the USCG must be able to immediately determine ANI and Automatic Location Identification (ALI) information. The ALI information is necessary to ensure that the call is routed to the proper response agency. Many of the MSS systems currently operating or planned for operation in the near future are capable of providing position accuracy within 125 meters as required in Phase II of the Commission's E911 Order.(55) For example, GPS contained in the MSS handset will provide a horizontal accuracy of 100 meters with selective availability activated.(56)
The Commission appears to propose that handheld or portable GMPCS terminals, such as those permanently installed on ships, boats or planes, not be required to obtain FCC certification under Part 2 of the Commission's Rules.(57) It is unclear, however, whether the Commission seeks comment on this proposal or if the Commission proposes to exempt such terminals from the out-of-band emission limits proposed in the NTIA Petition.
If the Commission's intent is to exempt handheld or portable GMPCS terminals on ships, boats or planes from the process of obtaining the certification with the associated eligibility to use the "GMPCS-MOU ITU REGISTRY" mark, NTIA has no objection. If the intent, however, is to exempt these terminals from the emission limits proposed in the NTIA Petition, NTIA strongly disagrees. These terminals could be located in the vicinity of a GNSS receiver and pose a potential interference threat. Thus, the emission limits should be a requirement of all earth terminals.
The Commission also requests comment on whether the certification process should encompass all varieties of earth terminals, including such fixed services as Very Small Aperture Terminals (VSATs).(58) This proposal would expand the types of satellite terminals considered under the GMPCS-MoU to include semi-fixed (transportable) and fixed (village pay phones) and to include such terminals operating in the fixed-satellite service. In general, NTIA has no objection to such a certification process, but notes that it could require the development of national and international standards and recommendations for the essential technical parameters of semi-fixed and fixed GMPCS earth terminals similar to those adopted for the MSS earth terminals. In addition, operation of these terminals within the U.S. must be in accordance with the national allocation table.
The Commission states that the purpose of this proceeding is to adopt out-of-band emission limits for protection of only aeronautical uses of RNSS.(59) As noted earlier, however, the International Maritime Organization (IMO) has also recognized GPS and GLONASS as elements of their GNSS.(60) There are currently numerous mariners operating in-land and coastal waterways, including recreational and commercial vessels, who depend upon GPS for navigation and safety. In many instances these mariners operate their vessels with GPS receivers interconnected to automatic pilots. Both the U.S. Coast Guard (USCG) and the IMO are considering mandating that vessels required to carry radios must also carry Automatic Identification System (AIS) equipment, ship-to-ship transponders incorporating GPS receivers to aid navigation in restricted waterways and areas of heavy traffic. GMPCS compliant terminals used by operators and passengers on these vessels could cause interference to GPS receivers if adequate out-of-band emission limits are not adopted. The USCG currently supports the limits proposed by the Commission in the GMPCS NPRM. However, the USCG is considering developing interference susceptibility standards for maritime GPS receivers within the Radio Technical Commission for Maritime Services (RTCM). The results of the work performed by USCG may have to be considered in a future rulemaking on uses of RNSS other than aeronautical.
The 1610-1613.8 MHz band is shared on a co-primary basis with the radio astronomy service. Radio astronomy operations are protected from MSS earth terminal emissions in Part of the Commission's Rules.(61) The National Science Foundation (NSF) requests that these rules be explicitly referenced in a Report and Order so that they are easily accessed by foreign MSS operators who may not be familiar with the Commission's Rules.(62)
The band 1660-1660.5 MHz was allocated to the generic mobile-satellite service at WRC-97, on the condition that it not cause interference to radio astronomy stations operating in this band. There is a concern that the out-of-band emissions from MSS earth terminals operating below 1660 MHz may interfere with radio astronomy observations conducted in the 1660-1670 MHz radio astronomy band. At this time the issue has not been adequately studied. Based on further studies, and experience with MSS earth terminals below 1660 MHz, it may be necessary to revisit this issue, in order to protect radio astronomy operations in the 1660-1670 MHz band, and request a tightening of the out-of-band emission standards or to introduce other measures.(63) XVIII. CONCLUSION
NTIA urges the Commission to consider carefully the issues raised in these comments in an effort to develop a workable arrangement that would greatly facilitate global roaming of MSS terminals while protecting sensitive Government operations.
For the foregoing reasons, NTIA submits these comments.
Larry Irving Kathy Smith Assistant Secretary for Acting Chief Counsel Communications and Information William Hatch National Telecommunications and Acting Associate Administrator Information Administration Office of Spectrum Management U.S. Department of Commerce Room 4713 Edward Drocella 1401 Constitution Avenue, N.W. David Anderson Washington, DC 20230 Electronics Engineers (202) 482-1816 June 21, 1999
1. Amendments of Parts 2 and 25 to Implement the Global Mobile Personal Communications by Satellite (GMPCS) Memorandum of Understanding and Arrangements and Petition of the National Telecommunications and Information Administration to Amend Part 25 of the Commission's Rules to Establish Emissions Limits for Mobile and Portable Earth Stations Operating in the 1610-1660.5 MHz Band, IB Docket No. 99-67 and RM No. 9165, FCC 99-37 (rel. March 5, 1999) (hereinafter "GMPCS NPRM").
2. Amendment of the Commission's Rules to Establish Rules and Policies Pertaining to a Mobile Satellite Service in the 1610-1626.5/2483.5-2500 MHz Frequency Bands, Report and Order, CC Dkt. No. 92-166, 9 F.C.C. Rcd. 5936 (1994).
4. The GNSS also includes the Space Based Augmentation Systems (SBAS) and Ground Based Augmentation Systems (GBAS). In the United States the SBAS is the Wide Area Augmentation System (WAAS) and the GBAS is the Local Area Augmentation System (LAAS). These augmentation systems are capable of supporting both GPS and GLONASS signal formats.
5. RTCA, Inc., formerly known as the Radio Technical Commission for Aeronautics, is a voluntary government/industry group that performs studies and makes recommendations pertaining to radio use for aviation.
7. NTIA Petition for Rulemaking, Amendment to the Commissions Rules to Incorporate Mobile Earth Station Out-of-Band Emissions, RM No. 9165 (Sept. 19, 1997)(placed on Public Notice, Report No.2227 (Sept. 23, 1997)).
10. 1998 Biennial Regulatory Review - Amendment of Parts 2, 25, and 68 of the Commission's Rules to Further Streamline the Equipment Authorization Process for Radio Frequency Equipment, Modify the Equipment Authorization Process for Telephone Terminal Equipment, Implement Mutual Recognition Agreements and Begin Implementation of the Global Mobile Communications by Satellite (GMPCS) Arrangements, Notice of Proposed Rulemaking, GEN Dkt. No. 98-68, 13 F.C.C. Rcd. 10683 (1998).
12. Letter from James R. Beale, Brig Gen, USAF Acting Deputy Assistant Secretary of Defense (C3ISR and Space Systems) to Mr. Joseph F. Canny, Deputy Assistant Secretary for Transportation Policy (Sept. 11, 1998).
14. The requirements for civil aircraft operating precision approach phases of flight are defined in the ICAO GNSS Standards and Recommended Practices (SARPs). The SARPs establish the requirements necessary to protect GPS and GLONASS (GNSS) receivers from harmful interference.
16. Recommendation ITU-R M.1317, Considerations for Sharing Between Systems of Other Services Operating in Bands Allocated to the Radionavigation-Satellite and Aeronautical Radionavigation Services and the Global Navigation Satellite System (GLONASS-M).
24. The source-path-receiver model is the traditional method by which frequency management ensures electromagnetic compatibility. Applications of the model to specific environmental sources results in a determination of the conditions under which interference remains below an acceptable level at the receiver.
29. European Testing and Standards Institute TBR-041, Satellite Personal Communications Networks (S-PCN); Mobile Earth Stations (MESs), Including Handheld Earth Stations, For S-PCN in the 1.6/2.4 GHz Bands Under the Mobile-Satellite Service (MSS) Terminal Essential Requirements (Feb. 1998).
46. In a contribution to the Eighth meeting of Working Party 8D, the Russian Federation provided the technical characteristics for space based and ground based augmentation systems that will operate in the 1559-1610 MHz band.
51. See generally, Revisions of the Commission's Rules to Ensure Compatibility with Enhanced 911 Emergency Calling Systems, Memorandum Opinion and Order, CC Docket No. 94-102, 12 F.C.C. Rcd. 22665 (1997).