The System: Second Report by LightSquared/GPS Technical Working Group Maps Terrain, Does Not Yet Explore

May 1, 2011  - By
Plus: GLONASS CDMA Tracked, Third Beidou-2 Launched

The second report from non‐governmental members of the LightSquared/GPS Technical Working Group (TWG) was filed with the Federal Communications Commission (FCC) on April 15. For those anxious to see actual results of interference/desensitization of GPS receivers by the proposed LightSquared terrestrial signal — or, conversely, absence of said results — the report does not contain any such hard news. It relates the set-up of TWG work sub-teams to test various categories of GPS devices and receivers.

The sub-teams have identified laboratories for testing activities, developed test plans, and identified devices, receivers, and systems to be tested. Attachments to the report include current draft test plans and the current list of devices and receiver models submitted for testing by companies.

The following sections summarize the testing laboratories and devices selected for testing by each sub-team:

  • aviation
  • cellular
  • general location/navigation
  • high precision, networks, and timing. These three sub-teams are collaborating to a large extent.
  • space-based receivers.

The full report also includes a “high-level description of test plan” by each sub-team.

Aviation Sub‐Team. The aviation sub‐team will rely primarily on testing, funded by the Federal Aviation Administration (FAA), that will be performed at Zeta Associates Incorporated of Fairfax, Virginia.

Additional testing is planned by the U.S. government at White Sands Missile Range and Holloman Air Force Base, both in New Mexico, for use by the National PNT Engineering Forum (NPEF) LightSquared Working Group. These results will be considered for inclusion in the TWG Final Report by the aviation sub‐team. Presumably, this group will test military receivers, under classified categorization.

The aviation receivers are representative of those in use today. Their selection was based mainly upon device availability (those already owned by the FAA Technical Center). They are: Canadian Marconi GLSSU 5024; Garmin 300XL; Garmin GNS 430W; Garmin GNS 480; Rockwell Collins GLU‐920 multimode receiver; Rockwell Collins GLU‐925 multimode receiver; Rockwell Collins GNLU‐930 multimode receiver; Symmetricomm timing card (used for an FAA automation system); WAAS NovAtel G‐II ground reference station; and Zyfer timing receiver (used for the WAAS ground network).

Cellular Sub‐Team. The cellular sub‐team is in the process of engaging PC TEST, Columbia, Maryland; CETECOM, Milpitas, California; InterTek, Lexington, Kentucky; and ETS Lindgren, Cedar Park, Texas, for device testing.

The cellular sub‐team expects to test approximately 50 different device models. The selections represent current and legacy devices and have been prioritized based on sales volumes. While it is expected that there will be some representation of data‐only devices and femtocells, the testing will focus largely on handheld devices.

Those designated for testing are: Apple iPhone 4 (GSM and CDMA); HTC A6366; HTC ADR6200; HTC ADR63002; HTC ADR63003; HTC ADR6400L; HTC Touch Pro 2; LG Lotus Elite; LG Rumor Touch; LG VN250; LG VS740; LG VX5500; LG VX5600; LG VX8300; LG VX8360; LG VX8575; LG VX9100; LG VX9200; Motorola A855; Motorola DROID X; Motorola VA76R; Motorola W755; Nokia 6650; Nokia E71x; RIM 8330C; RIM 8530; RIM 9630; RIM 9650; RIM 9800; Samsung Moment; Samsung SCH‐U310; Samsung SCH‐U350; Samsung SCH‐U450; Samsung SCH‐U640; Samsung SCH‐U750; Samsung SGHi617; Samsung SGHi917; Sierra Wireless 250 U USG 3G/4G; and Sony Ericsson W760a.

General Location/Navigation. This sub-team has chosen Alcatel/Lucent as its initial facility for testing. Twenty-six devices were selected based on nominations by manufacturers represented on the sub‐team, considering the percentage of the installed user base.

They include: Garmin Forerunner 110 and 305; Garmin ETREX‐H; Garmin Dakota 20; Garmin Oregon 550; Garmin GTU 10; BI Inc. ExacuTrack One; Garmin GPS 17X; Garmin GPSMAP 441; Hemisphere Vector MV101; GM OnStar (model TBD); Garmin GVN 54; TomTom XL335; TomTom ONE 3RD Edition; TomTom GO 2505; Garmin nűvi 2X5W, 13XX, 3XX, and 37XX; Garmin GPSMAP 496; Garmin aera 5xx; Honeywell Bendix/King AV8OR; Trimble iLM2730; Trimble TVG‐850; Trimble Placer Gold; and Hemisphere Outback S3.

High Precision-Networks-Timing. The HPN&T sub‐teams are collaborating extensively to develop joint test plans and procedures. The joint sub-teams have chosen the U.S. Navy’s NAVAIR facility for testing.

To be tested are: Hemisphere R320; Hemisphere A320; Deere iTC; Deere SF‐3000; Deere SF‐3050; Trimble MS990; Trimble MS992; Trimble AgGPS 252, AgGPS 262, AgGPS 442, and AgGPS EZguide 500; Trimble CFX 750; Trimble FMX; Trimble GeoExplorer 3000 series GeoXH and GeoXT; Trimble GeoExplorer 6000 series GeoXH and GeoXT; Trimble Juno SB; Trimble NetR9 and NetR5; Trimble R8 GNSS; Trimble 5800; Leica SR530; Leica GX1200 Classic; Leica GX1230GG; Leica GR10; Leica Uno; Leica GS15; Topcon HiPer Ga and HiPer II; Topcon GR‐3 and GR‐5; Topcon MC‐R3; Topcon NET‐G3A; Topcon TruPath/AGI‐3; NovAtel PROPAK‐G2‐Plus; NovAtel FLEXG2‐STAR; NovAtel FLEXPAK‐G2‐V1, FLEXPAK‐G2‐V2 and FLEXPAK6; NovAtel PROPAK‐V3; NovAtel DL‐V3; Septentrio PolaRx3e; and Septentrio AsteRx3.

Timing receivers: FEI‐Zyfer UNISync GPS/PRS; TruePosition GPS timing receiver; Symmetricom SSU 2000 (Motorola M12M); Symmetricom Time Provider 1000/1100 (Furuno GT‐8031); Symmetricom TimeSource 3500 (XR5 (Navstar/Symmetricom); Trimble Resolution T; Trimble Accutime Gold; Trimble Resolution SMT; Trimble MiniThunderbolt; NovAtel OEMStar; NovAtel OEM4; and NovAtel OEMV3.

Space‐Based Receivers. Lab testing has been conducted at the NASA Jet Propulsion Laboratory (JPL) in California. The receivers are used by NASA for space‐based missions and high-precision science applications. The TWG agreed that these would be tested at JPL by NASA, with participation by LightSquared personnel, and the results provided to the TWG; see Appendix G

The devices tested are current or representative of GPS receivers in use by NASA or planned for use in the near future for space and science applications: TriG (NASA Next‐generation Space Receiver) and IGOR (Space Receiver).

NASA/JPL also tested the following high-precision receivers and shared the results with the HPT&N sub‐team: JAVAD Delta G3T (High Precision‐IGS) and Ashtech Z12 (High Precision‐IGS).

Conclusion. For all sub-teams, analyses will consider both LightSquared’s expected transmit power of 62 dBm per channel and its maximum authorized transmit power of 72 dBm per channel.

The WG co‐chairs will update the Commission on its progress in a subsequent report on May 16.

The April 15 TWG report contains these appendices: Working Group Roster; List of Receivers and Devices; Aviation Test Procedure; Cellular Test Plan Draft; General Location/Navigation Test Plan Draft; High Precision/Networks/Timing Test Plans Draft; Space‐Based Receivers Test Process.

GLONASS CDMA: New Era’s Dawn Glimpsed from Multiple Receivers

The newest Russian satellite, launched on February 26, began transmitting its new code-division multiple-access (CDMA) signal on April 7. In a clear break from all previous GLONASS signals, which are frequency-division multiple-access (FDMA), the new signal is expressly designed to be interoperable with current and future GPS signals, and with the coming Galileo signals, all of which have a CDMA structure. Thus, a new era of GNSS, truly global navigation satellite systems, began on April 7.

JAVAD GNSS was the first company to announce that it had tracked CDMA signals of the GLONASS-K satellite in
the L3 GLONASS band. Data was logged at the company’s Moscow office on April 8 from 02:30 until 07:30 UTC. The satellite’s pseudorange (in chips) and signal-to-noise ratio (in relative numbers) are shown in Figures 1 and 2.

Figure 1. GLONASS-K’s pseudorange in chips, courtesy of JAVAD GNSS. The y-axis goes from 0 to 12,000 in increments of 2,000; the x-axis goes from 0 to 500 in increments of 100. (Click to enlarge.)

Figure 2. GLONASS-K’s signal-to-noise ratio (in relative numbers), courtesy of JAVAD GNSS. The y-axis goes from 0 to 10,000 in increments of 2,000; the x-axis goes from 0 to 500 in increments of 100. (Click to enlarge.)

On April 11, the satellite’s code-minus-phase and signal-to-noise ratio were tracked (Figures 3 and 4). Data quality is quite similar to GPS, according to the company.

Figure 3. GLONASS-K satellite’s code-minus-phase data (courtesy of JAVAD GNSS). (Click to enlarge.)

Figure 4. GLONASS-K satellite’s signal-to-noise ratio (courtesy of JAVAD GNSS). (Click to enlarge.)

Future GLONASS satellites of the K1 and subsequent K2 generations will broadcast CDMA signals in multiple frequency bands. GLONASS-K satellites are markedly different from their predecessors. They are lighter, use an unpressurized housing (similar to that of GPS satellites), have improved clock stability, and a longer, 10-year design life. There will be two versions: GLONASS-K1 will transmit a CDMA signal on a new L3 frequency, and GLONASS-K2 will in addition feature CDMA signals on L1 and L2 frequencies. The CDMA signal in the L3 band has a center frequency of 1202.025 MHz.

The new generations of GLONASS signals and satellites are described in detail in the April “Innovation” column of GPS World, edited by Richard Langley.

Septentrio Navigation of Leuven, Belgium, also tracked GLONASS CDMA L3 signal with its AsteRx3 receivers. Figure 5 shows the C/N0 in dB-Hz of the legacy L1-C/A signal and of the data component of the new L3 CDMA signal. The graph covers the time span starting at 20:30 (UTC) on April 10 and ending at 02:00 on April 11. Figure 6 shows the de-trended code minus phase from L1-C/A and L3 signals. Such a plot provides a glimpse of the code measurement multipath and noise, according to the company.

Figure 5. GLONASS-K1 AsteRx3 measurements; C/N0 in dB-Hz of L1-C/A and L3 CDMA (courtesy of Septentrio Navigation).

Figure 6. GLONASS-K1 AsteRx3 measurements; de-trended code minus phase of L1-C/A and L3 CDMA (courtesy of Septentrio Navigation).

Topcon Positioning Systems (TPS) also released data on the new signal, stating that signals from the new satellite “provide an additional accuracy advantage over older satellites.” Figures 7 and 8 show data from the company’s Moscow office.

Figure 7. Pseudorange-phase of four signals transmitted by the new K1 satellite (courtesy of Topcon Positioning Systems). (Click to enlarge.)

Figure 8. Signal-to-noise ratios of four signals transmitted by the new K1 satellite (courtesy of Topcon Positioning Systems). (Click to enlarge.)

Finally, the German Aerospace Center’s Institute of Communications and Navigation recorded the spectrum of the GLONASS CDMA signal, captured with a 25-meter dish antenna, Raisting Satellite Earth Station, near Munich.

The signal spectrum spans at least 40 MHz (Figure 9). It contains additional sidelobes not shown in the plot. The plot indicates total power of all components of the transmitted signal.

Figure 9. GLONASS CDMA signal’s power over frequency (courtesy of the German Space Agency, DLR).

Third Beidou-2 IGSO Launched

China’s BeiDou-2 (Compass) satellite launched on April 9 has attained a circularized orbit, joining two inclined geosynchronous orbit (IGSO) satellites to form a mini-constellation centered on an east longitude of about 120 degrees. While BeiDou-IGSO-3’s orbit might still be tweaked slightly, it is clear that the orbits of the three satellites are arranged so that there will always be one satellite with a high elevation angle over China, according to the CANSPACE news service operated by the University of New Brunswick.

The latest spacecraft joins four geostationary satellites, a middle-Earth orbiting vehicle, and the two other IGSO satellites now on orbit. As the first Chinese launch in 2011, the new arrival presages much activity to come. With eight now flying, six more spacecraft are scheduled to rise by 2012, completing a 14-satellite constellation to provide a regional service over eastern Asia. The regional system will consist of five geostationary or GEO, five IGSO, and four medium-Earth orbit satellites.

Long-range plans envision a 35-satellite constellation providing global service by 2020: 27 MEOs, 5 GEO satellites, and 3 IGSOs. The satellites will transmit signals on the 1195.14–1219.14 MHz, 1256.52–1280.52 MHz, 1559.05–1563.15 MHz, and 1587.69-1591.79 MHz carrier frequencies.

Compass satellites have an announced lifespan of eight years.

Three IGSO satellite tracks over China (image courtesy of CANSPACE).


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About the Author:

Alan Cameron is editor-in-chief and publisher of GPS World magazine, where he has worked since 2000. He also writes the monthly GNSS Design & Test e-Newsletter and the Wide Awake blog.

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