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Letter From Javad Ashjaee to FCC Regarding LightSquared Interference and Receiver Standards Print E-mail
Written by Dr. Javad Ashjaee   
Wednesday, 14 December 2011

The Honorable Julius Genachowski
Chairman
Federal Communications Commission
445 12'h Street, SW
Washington, DC 20554

RE: LightSquared-GPS Interference Debate and Receiver Standards

Chairman Genachowski,

When the interference issues first surfaced between LightSquared and GPS, I looked into the problems and realized the deficiency was in existing receiver designs. Our filter systems had little protection against interference and were wide enough to invite in undesirable signals, resulting in degraded performance. We started to tackle this problem, and a few weeks ago produced a new filter system, which we offered to interested parties to test for themselves.

We showed that this new filter system has much better protection – in particular it has protection against LightSquared (10L) and its handset (10R). The new filter proved that the PNT Advisory Board’s letter from August 3, 2011 to you was full of false claims and misleading information, including that it would take many years and billions of dollars to fix this problem.

That was all nonsense designed to confuse the debate and stifle the innovation that would disrupt the GPS status quo. After our success in the design of a filter system which protected against LightSquared 10L signal, we have recently developed another new filter system which protects against LightSquared 10H too, without losing any properties of the GPS signal. We will put this filter system into production soon. We have proved that technology to protect against LightSquared 10L, 10H, and 10R does exist today and once again showed that the PNT letter of August 3, 2011 was completely false.

Given the technical and modest financial resources of my small company, Javad GNSS, compared to giant organizations like Trimble, John Deere, Stanford University, NASA, and many others whose representatives who make up the PNT Advisory Board, one might question their true motivation. Did they try to develop a filter that protects against 10L, 10H, and 10R? Or did they not try at all?

Either they lacked technical competence, or they intentionally misled the debate with false claims. Either way, I have lost faith in the credibility of the PNT Advisory Board when it comes to their judgement about GPS interference.

When we proved the GPS establishment wrong about the high-precision interference issue, they turned to low-precision and leaked false accusations that 75% of tested receivers failed the tests. It’s important to note that their definition of “failure” was 1-dB reduction in signal to noise ratio of the unit under test – not the complete failure of the unit to track satellites, and was clearly meant to mislead a discussion that has no technical merit.

It is much easier this time to prove them wrong with this latest accusation because the problem is in the design of the GPS receivers that were tested. The truth is that any GPS receiver that “failed” the test against the LightSquared signal, will also “fail” against many existing transmitting systems. Anyone can test this. Take any low-end GPS receiver similar to those they claim “failed” the test and get close to an FM radio transmitting stations, for example.

One may not see the degradation of 1-dB because low-end receivers do not report signal-to-noise numbers and usually have about 20-dB of margin. This is even more true for low-end narrow band C/A code devices. Get close enough to many FM radio stations, for example, and you will see the receiver will completely stop functioning. There are tens of thousands of interfering transmitters which the “failed” GPS receivers have no protection against. One can start such tests by getting close to FM radio stations 92.7, 98.5, and 105.

Again, please note that one may not be able to notice the 1-dB reduction in signal-to-noise, but so-called GPS experts advising the government call this “failure” and leaked it to news reporters. What sort of expertise is that? Under this same principal, one will see that all of the tested receivers will “fail” against almost all transmitting stations when close enough (within 100 meters, for example).

The PNT Advisory Board should do this test as well and it will see that the receivers they tested will “fail” against not only LightSquared but also against thousands of other existing signals that have been in existence for decades. Therefore, such receivers should not be used in critical applications.

Electrons do not have political party affiliation and are not influenced by PNT letters, titles of “professor emeritus”, and stars of generals. Any child can take his/her GPS navigation receiver close to many number of existing transmitting towers (like many FM radio stations) and prove that most current GPS receivers (high precision and low precision) do not have protection against many existing transmitting systems, yet they are still being manufactured and used in critical applications.

Your honor, it is time for FCC to act to establish guidelines for GPS receivers that we increasingly depend on.

The FCC should mandate that any receiver used for critical applications must show its signal-to-noise numbers, so every user can see degradation when they encounter interference. High precision receivers, and all those which use P-code, should have 8- to 10-dB suppression for every MHz away from the edges of the GNSS wide band (P-code). Low-end C/A-code-only receivers should have 2-dB suppression for every MHz away from the edges of the C/A code. These standards are important. The filter technology to achieve these (without negatively affecting performance) exists today and should be applied because the cost and size of such filters are even less than what was used before.

Had the FCC established and enforced receiver standards to begin with, we could have avoided this entire interference debate between LightSquared and the GPS industry.

Respectfully,

Javad Ashjaee, Ph.D.
CEO and President
JAVAD GNSS
900 Rock Ave.
San Jose, California, 95131
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
 

 
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