The System: Third Report by LightSquared/GPS Technical Working Group

June 1, 2011  - By
Plus: Locata as Alternative PNT, Indian SBAS, Galileo Launch

Slow but steady progress of the Working Group (WG) convened by the Federal Communications Commission (FCC) to study the GPS overload/desensitization issue is related in the group’s Third [monthly] Pogress Report, filed with the FCC on May 16. For the third consecutive time, the report contains little in terms of actual results of testing for interference/desensitization of GPS receivers by the proposed LightSquared terrestrial signal. It continues to carefully lay out the ground rules adopted by several subteams for testing the particular receivers in their domain. As of the date of filing, it reported, “testing is underway for six device categories and has been completed for the Space-Based Receivers category.”

As related in May’s The System, the Working Group has self-divided into sub-teams.

Aviation Sub‐Team. Laboratory testing was scheduled to be completed by May 20, conducted by Zeta Associates. The team’s report is being compiled, and some receivers were to be made available for field testing near Las Vegas.

The Federal Aviation Administration (FAA) issued a flight advisory warning pilots that GPS service in one area of Nevada could be “unreliable or unavailable” May 16–27, during LightSquared testing. Tests were to be conducted in six-hour blocks.

“Pilots are strongly encouraged to report anomalies during testing to the appropriate ARTCC to assist in the determination of the extent of GPS degradation during tests,” said the advisory.

Cellular Sub‐Team. Two of the three laboratories engaged to perform radiated and conducted testing have added work shifts to complete their processes by the TWG’s deadline; the third lab is being configured. Forty-five models of GPS-enabled cell phones will undergo testing, following a detailed procedure described in Appendix D to the report.

General Location/Nav Sub‐Team. This team recently added new members representing public safety users at the request of the National Public Safety Telecommunications Council (NPSTC). See related article, “LightSquared Interference with Emergency Service.“ The sub‐team has accumulated live‐sky GPS test data for use in dynamic testing scenarios, and plans further field tests in the Las Vegas, Nevada, area, described in Appendix G.

High-Precision, Networks, Timing. The sub teams have completed testing of all devices in the NAVAIR lab facility. Some team members expect to have some receivers of the same models that have been tested by NAVAIR available for field testing in Las Vegas, and are working to develop test procedures for the field tests.

Space-Based Receivers. The team completed its laboratory testing activities as reported on April 16, and is now reviewing the initial draft analysis of the impacts.

Senate Letter

Meanwhile, the U.S. Senate is showing increasing signs of life in response to the problem. As of May 23, a total of 32 senators had signed a letter to the FCC initially drafted on April 15 by two U.S. senators from the heartland, Pat Roberts (Republican, Kansas) and Ben Nelson (Democrat, Nebraska). The joint public letter urges action in the form of “asking the FCC to take all necessary steps to protect GPS.”

What sway, if any, the Senate holds over the FCC, which forms part of the executive (presidential) branch of government, remains unclear. However, the letter does signal some heightened interest in Washington, presumably as a result of hearing from constituents. Kansas and Nebraska, of course, have large-scale farming activity, in which precision agriculture driven by GPS plays a significant role.

The two original authors state that “the International Bureau, a sub-organization within the FCC, granted a conditional waiver to allow a single company, called LightSquared, to build tens of thousands of ground stations that may cause widespread interference to neighboring GPS signals.”

The letter goes on to outline the many key roles that GPS plays in economic activity and specifically in “economic recovery,” public safety, aviation, and national defense. “Reliable GPS affects virtually every American,” Nelson and Roberts assert.

They close by “calling on the FCC to ensure that GPS is not compromised in any way. To do so, the full commission must be involved and require LightSquared to objectively demonstrate non-interference as a condition prior to any operation of its proposed service. Anything less is an unacceptable risk to public safety.”

The latest signer, Senator Chuck Grassley of Iowa, writes on his website that “Given the FCC’s haste so far, I worry that LightSquared will not have interference problems resolved before given the green light to become fully operational. Farmers shouldn’t have to worry that they’re planting the correct seed or applying the precise amount of fertilizer needed for the soil to optimally produce the crop, and ambulance drivers shouldn’t have to weather taking a wrong turn or driving into a ditch because a new system is scrambling their existing navigational technology.”

Grassley adds, “If anything, the shadows around the LightSquared project should have led the FCC to proceed with caution rather than step on the gas. Yet the opposite happened. The agency originally planned to take public comment on a key regulation necessary for green-lighting the project for only one week. The commission relented and held the comment period open longer only after consumers and affected businesses protested.”

Defense. Congressman Mike Turner included language in the National Defense Authorization Act (NDAA) that requires the Secretary of Defense to notify Congress if he determines there is widespread interference with the military’s use of GPS caused by a commercial communications service. Turner, the House Armed Services Subcommittee chairman on Strategic Forces, has legislative jurisdiction over space and satellite systems, and included the provision in his Mark of the NDAA.

LightSquared Interference with Emergency Services, Public Safety

Law enforcement, emergency medical service (EMS), and fire first-responders in the state of New Mexico who participated in LightSquared/GPS interference testing at Holloman Air Force Base have submitted reports verifying a negative effect of LightSquared transmissions on their GPS equipment.
A cover letter from the New Mexico E-911 program director states that the reports “substantiate concerns that the LightSquared network will . . . jeopardize 911 and public safety nationwide.”

The director of emergency services for Otero County, New Mexico, writes that “during the testing process the [ambulance’s automatic vehicle location] unit was limited to only being able to see 7 satellites at any location and upon moving just 50 yards from our position at the test site towards the [LightSquared] tower were diminished to 3 or 4 satellites and at 60 yards unable to establish any satellite connections. This is still approximately 1/8 of a mile from the tower.”

The tests were conducted on April 15 and 16 of this year at Holloman Air Force Base, in a live sky environment.

Locata Flight Results; ICAO to Weigh for Alternative PNT

“The Need for an Alternative PNT” was presented to the International Civil Aviation Organization’s (ICAO) 10th meeting in Montreal, Canada, on May 19 by the Australian delegation, proposing a new method for alternative position, navigation, and time (APNT). ICAO accepted the paper, and the Locata technology it describes, placing it on the table as a potential back-up to GPS. The organization will take up the discussion at its next meeting in October.

Locata Corporation of Griffith, Australia, also released preliminary post-processing analysis on data collected during its APNT flight trial on May 9. An aircraft fitted with a Locata receiver and several truth-reference devices recorded data for three hours while flying at approximately 7,000 feet. The Locata receiver tracked a ground-based network of six LocataLites, which provided positioning signals to cover an area of approximately 1,500 square kilometers. The aircraft flew pre-defined patterns that gave varying distances to LocataLites (3–49 kilometers) during the test.

During this trial, the Locata first acquired and tracked LocataLite signals at a range of 51.9 kilometers, according to the company, which provided an early-stage assessment of the performance of the Locata pseudorange-based (code) solution against a high-precision carrier-phase differential GPS solution. Figure 1 shows the difference in East, North, and Height between the high-precision GPS truth carrier solution and the Locata code solution. Relative to the high-precision GPS, the Locata code solution has a 95 percent RMS in horizontal of 2.1 meters and 3.2 meters in vertical. The company attributed the larger difference in the vertical to worse dilution of precision in the vertical component for this specific physical deployment of its network. Over this test data analysis, the Locata’s average VDOP of 3.3 compared to an average HDOP of 1.5.

One test objective, the company stated, was to obtain information on the significant tropospheric effects inherent in a ground-based system over these sorts of ranges. Further detailed analysis is now underway to measure and then reduce the residual biases present in the Locata code solution. For this first-pass data analysis these biases are approximately –0.8 meters in North and –1.1 meters in height. When these residual biases are further analyzed and reduced, Locata anticipates that the 95 percent RMS code-solution accuracies will improve to better than 1 meter horizontal and 2.5 meters vertical.

Locata emphasized that this is an early-stage analysis of first flight tests, expressly designed to provide data for a better understanding of the Locata system’s performance characteristics in ICAO-type APNT applications, and for a USAF-contracted LocataNet deployment at White Sands Missile Range that will cover more than 6,500 square kilometers. Further flight trials are planned in the near future to refine the system.

In Q3/2011 Locata expects papers to be published on carrier-phase performance observed over multiple flights, with presentations during ION 2011 Conference in Portland, Oregon.

Figure 1. Difference in East, North, and Height between preliminary Locata pseudorange-based solution and high-precision differential carrier-phase GPS solution.

Indian SBAS Aloft

The Indian Space Research Organisation successfully launched a GSAT-8 satellite, carrying a GPS-Aided Geo Augmentation Navigation (GAGAN) satellite-based augmentation system (SBAS) transponder, on May 21, aboard an Ariane-V launch vehicle, from Kourou, French Guiana. The satellite will be stationed at 55 degrees east longitude.

Galileo Picks October 20

The first two operational/validation satellites of the Galileo project received a launch date of October 20 of this year. Antonio Tajani, European Commission vice-president for industry and entrepreneurship, predicted that this will keep the system on track for provision of “three early services in 2014/2015 based on an initial constellation of 18 satellites.”

This article is tagged with , and posted in Augmentation & Assistance, Galileo, GPS Modernization, The System
Alan Cameron

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 System Design e-mail newsletter and the Wide Awake blog.

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