What’s up with GPS?

Interference is moving at the speed of LightSquared

If you haven’t been paying attention during the past year, a threat to the accuracy of Global Positioning System (GPS) signals has been growing at almost the speed of light. Thankfully, some light has been shed on the issue, and it has at least been slowed so pertinent information can be introduced into the discussion, evaluation and final decision.

LightSquared is a broadband wireless communications company located in Reston, Va., a Washington, D.C. suburb. In January 2011, the Federal Communications Commission (FCC) granted LightSquared a conditional waiver to explore using several of the band spectrums near the one used by GPS. The provisions of the conditional waiver required that special consideration be given to the possibility of interference with GPS signals. Even given a rush-rush timetable not typical of such waivers, numerous incidents of interference have arisen.

Concerns are building world-wide as the total amount of interference can only be estimated currently, as LightSquared plans to build 40,000 land- based transmitters to use bands that were initially approved only for land-to-satellite communications. The interference can also cross to the Russian Glonass, Chinese Compass and European Galileo satellite navigation systems, and they are not pleased.

Still, LightSquared refuses to see the light and continues to push forward with the idea. A comment period that ended in late July showed overwhelmingly opposition by almost all end users of GPS, but somehow the issue has not gone away. Several fixes have been proposed, but none have been proven effective independently, and LightSquared continues to decline any financial responsibility for retrofitting existing equipment if any of the fixes prove effective.

As boaters and fishermen, we think of GPS as a marine navigation system, and it has morphed into a good one, but not without some inherent problems and issues. We also need to consider the other users of GPS. The aviation industry concerns me most. Thousands of planes are in the air at almost any time. Even minor interference that creates small errors could have devastating consequences.

The military is probably the next-heaviest user of GPS. It figures in their precision positioning of ships, planes, artillery, troop movements and almost every facet. Smart bombs and other precision strikes rely on GPS. First responders often rely on GPS to locate their destinations and render aid. Ground transportation services, such as trains, busses and commercial trucks use GPS and it has enhanced their service. To the general population, GPS in their personal vehicle is almost considered standard equipment.

The survey and mapping industry has come to rely heavily on GPS; surveys are much more precise and maps more correct. With their specialized receivers, GPS is accurate to within inches. There are many more uses, too. The bottom line is that we have become very dependent on precise GPS information and it is beyond comprehension why anyone would consider allowing that to be compromised.

Our situation in the United States is particularly tense as early in his presidency, President Obama signed off on shutting down a recently refurbished e-Loran system that was a very capable alternative to GPS.

Do any of you remember the first marine GPS units that we used before Selective Availability (SA) was discontinued? SA was a military system that altered the timing of GPS signals and created errors of up to a quarter mile for non-military users. By altering the induced error different amounts on different days, there was no consistent accuracy in GPS positioning and many end users hesitated to accept it.

Eventually, GPS manufacturers worked with government agencies to create Differential GPS (DGPS), which used a second receiver to recalculate the timing error and increased the accuracy and consistency to within about 15 to 30 feet. Wide Area Augmentation System (WAAS) was developed by the Federal Aviation Authority (FAA) to be even more accurate and was introduced to the public short after DGPS. Finally, President Clinton signed an executive order to discontinue SA and everyone had access to GPS that is accurate within a few feet.

Now, with the potential interference from LightSquared’s transmissions, we face the possibility of having to revert to accuracy similar to the days of SA. As another slap in the face, LightSquared says it has created receivers and filters that will eliminate the interference, but it insists any financial accountability for retrofits and increased costs of new units is not theirs. While these units may actually work, as of 45 days ago, they had not been independently tested and certified.

Chris Freeman, the senior coastal geologist and president of Geodynamics LLC in Pine Knoll Shores, said the potential interference from LightSquared using a frequency so close to GPS has potential to be devastating. He had a much longer list of end users of GPS than mine, but suffice it to say it affects everyone on an everyday basis. A simple, everyday device that everyone has that uses GPS is a cell phone.

“My line of work is high-resolution hydrographic surveying, which is using a variety of sonar systems to map the seafloor,” Freeman said. “We use a system called an Applanix POS , which is a positioning and orientation system for marine vessels. The same system is used in guiding missiles and in aviation. This is a $150,000 system that calculates not only our Lat/Lon for positioning our soundings, but also uses GPS tied to the motion sensor to calculate complex vessel motion so that we can tie all of our soundings to a vertical datum.Our data is used in mapping inlets for safe navigation, sediment transport modeling to understand how inlets work, precise calculation of dredge volumes, mapping beaches to determine erosion, flood plain maps so we know where potential areas will flood and a variety of other public safety / scientific data streams.

“The Light Squared issue is a major one in the survey industries,” Freeman said. “Any error caused by interference is too much, especially when that interference is known and can be easily avoided by not allowing it.”

While there is significant opposition in the U.S. to allowing LightSquared to continue, there is hedging, and a decision has not yet been made. An article in the November issue of GNSS Signals, a newsletter by the publishers of Inside GNSS (http://www.insidegnss.com/), states that LightSquared has at least temporarily ceased seeking approval to operate a similar broadband 4G network from the International Telecommunications Union. International opposition was very high.

That article in GNSS Signals cites letters sent to the FCC by the International Air Transport Association and the European Commission as expressing grave concerns about the LightSquared network. The Commission said its own testing confirmed the interference in the radionavigation band used by GPS – the same set of frequencies the Europeans plan to use for their satellite navigation system.

The GPS Council in Japan, one of the United States’ closest partners on navigation issues, underscored in an Aug. 1 letter to the FCC that any policy allowing the degradation of the GPS signal would “raise question[s] as to the integrity of the stated U.S. commitment to maintain GPS as a stable and reliable global standard for positing, navigation and timing.”

The bottom line is that both from within the U.S. and from the international community, there are many serious questions regarding LightSquared access to this spectrum of broadband and that interference with GPS and other countries similar navigational signals has been documented. Many knowledgeable persons raise the question of why this is even being discussed.

If you have concerns regarding allowing LightSquared to operate on these frequencies that are known to interfere with GPS signals, our avenue for preventing this now is only through legislative means. We should also be sure our congressmen are aware how this affects us as boaters and how widespread the use of GPS is in everyday life.

Sen. Richard Burr (R-NC) signed a Senate letter requesting further review, but Sen. Kay Hagan (D-NC) did not. Some members of the House of Representatives have forwarded a similar letter. These letters are available for review at the website of the Coalition to Save Our GPS at http://www.saveourgps.org/ and you can check to verify if your representative has joined the group requesting further review. Contact information is available at http://www.senate.gov/ and http://www.house.gov/.