To solve the LightSquared versus GPS controversy, Javad Ashjaee, president and CEO of JAVAD GNSS, has appealed directly to President Obama to discontinue the encryption of P-code, the restricted military GPS signal. His comments came in the context of the LightSquared/GPS interference imbroglio, as part of his solution to the conflict over spectrum. “This policy is not helping national security. It is hurting both precision users and the broadband project. We need more broadband, for global, fast, and inexpensive real-time kinematic (RTK) GPS.”
Ashjaee, a longtime leader in high-precision GNSS equipment, made the remarks during a panel discussion at the Esri Survey Summit, and expands upon them in a video posted on his company’s website: “A Solution for LightSquared.” In the video, he calls the LightSquared saga “a good thing, because it brings the issue of in-band interference to many GPS users, especially surveyors and high-precision users.”
He goes on to address three issues: collateral damage, why high-precision receivers are more affected by the LightSquared attack, and finally a proposed solution to the problem.
In the first section, he disputes the assertion that LightSquared interference to 5 percent (surveyors) and 1 percent (military) of GPS users should be tolerated as collateral damage. “When you add substance to the numbers, you see how quickly this argument fails. The military is the backbone of our national security, and high-precision users are the backbone of our financial security and growth.”
On the second topic, he gives two reasons why high-precision receivers are more affected by the LightSquared signal, briefly summarized here as:
- the crucial importance of the arrival time of the signal edges; the edges are first to be distorted by interference. Narrow filters, proposed as a solution by LightSquared, also blur the signal-edge shape.
- the encryption of P-code on L1 and L2 bands, degrading their effectiveness by a factor of 1,000, according to Ashjaee. “Encryption does not do any good to anybody.”
As his solution to the problem, Ashjaee says Lightsquared should stay further away from the GPS signal, and use a cascade of filters; secondly, he calls on President Obama to discontinue P-code encryption, at least until the new L2 signal is operable in 8 or 10 years. “This would make GPS less vulnerable to the LightSquared project and others like it.”
In a subsequent conversation with GPS World, Ashjaee likened the P-code situation to that of selective availability (SA), another U.S. government effort to restrict use of high precision. Ashjaee recalled campaigning vigorously against SA in 1991, with full-page ads in GPS World depicting the Mona Lisa painting with many missing parts. “Selective availability is a step backward in providing the best of this excellent work [GPS] of science and art. As the leader in GPS technology, we consider selective availability as being neither good science nor good politics,” the ad copy reads.
Ashjaee adds with a twinkle, “[A former director of the GPS Wing] told me that a high general in the Air Force had that ad pinned to the wall behind his desk. Why? Who knows. Perhaps he agreed with it.”
SA was discontinued in May 2000.
(As an interesting historical side-note, in an adjacent ad in the same January 1991 issue, the company advertised “Ashtech’s True P-Code Advantage.” At that time, P-code was not encrypted. The copy reads:
“GPS was designed as a dual-frequency system and the Ashtech P-12 GPS receiver enables users to take full advantage of GPS capabilities. Dual-frequency reception eliminates ionospheric refraction effects, so medium-to-longer baselines can be measured more accurately.
“High-quality P-code measurements on both bands also enable shroter station occupation time, further increasing productivity for survey crews.”
“P-code correlation produces carrier-phase measurements of higher accuracy because of significantly higher SNR over conventional codeless techniques. This, combined with the P-12 receiver’s ability to measure full-wavelength L2 carier-phase, allows nearly instantaneous integer cycle-phase ambiguity resolution for kinematic survey, precision navigation, and other applications.
“Unlinke conventional codeless techniques, ‘true P-code’ tracking provides inherent immunity from jamming for uninterrupted tracking in areas of high interference.”)
“The U.S. policy of national security and P-code is 30 years old,” Ashjaee resumes. “This policy was devised at the time we were head-to-head in the Cold War with Soviet Union. They had missiles targeted at us, we had missiles targeted at them. That’s why we encrypted the P-code. But this situation is gone. There is now an agreement between Obama and [Russian president] Medvedev that citizens of the two countries can have 3-year visas to visit each other. Our missiles are not targeted at each other.”
“Since the inception of GPS, there is no shred of evidence that GPS has ever been used to attack any U.S. national security, let alone its P-code signals.”
Further, Ashjaee pointed out, “At that time, GLONASS did not exist, and we did not want them to use our system. Now GLONASS exists, and its signal is arguably more robust than GPS.”
Ashjaee called on President Obama to turn off P-code encryption. “This policy is not helping national security. It is hurting both precision users and the LightSquared project, which we all desperately need. We need more broadband. They know the system is not good, and they want to put another clear code [on L2]. It will take 8 or 10 years. Turn off encryption temporarily until we have it. Encryption can be turned on in a fraction of a second whenever needed.”
“Turning off P-code encryption not only makes the GPS signalmore robust to LightSquared, but also protects it against all kind of other interferences, including harmonics of innocent signals like harmonics or radio stations.”
He embraced the use of wideband communication between base and rovers for RTK GPS. “We have base and rovers, with VRS networks. The corrections must be transmitted from base to rovers. Now we have a mess of communications: UHF (different in every country, difficult to certify in every country), spread-spectrum, VHF, Ethernet, WiFi. These are kludgey communications. If we have broadband, similar to Lightsquared, we have RTK globally, fast, and inexpensive.”
In a separate conversation with GPS World, another expert in high-precision use confirmed that “we have worked very hard in the past, when bandwidth was much more expensive, to minimize the bandwidth required to send differential GPS corrections with minimal latency. Sensor fusion has mitigated the latency issue as well. As robotics applications increase, not only base-rover communications but tons of data relevant to precise positioning, sensor fusion, including vision, RF ranging, path planning, mission planning, obstacle detection, and so on, will be needed. Industrial, scientific, and medical (ISM) band spread-spectrum and ultra-wideband (UWB) ranging systems have a lot of problems that 4G systems could alleviate.”
“We need a coalition to save GPS and Lightsquared,” concluded Ashjaee. “It’s a nice complement.”
“Broadband would be a good help to our industry, and to our technology. We want global, universal wideband communication, either through towers or satellites, or through any means to transmit base station or VRS network corrections to rovers.”
Ashjaee offered to debate the P-code encryption issue with representatives from the GPS Wing, State Department, Department of Defense, PNT ExCom, and others, at the annual GPS World Leadership Dinner, held during the ION-GNSS conference each September. “It will be a very lively debate,” he said. “Add Tom Stansell, too. And representative of LightSquared.”