Публикация:Болденков 2012 In-car GNSS Jammers Tracking System Evaluation Results

E.N. Boldenkov, I.V. Korogodin, I.V. Lipa In-car GNSS Jammers Tracking System Evaluation Results // Proc. ION GNSS. — 2012. — Pp. 901-906.

BibTeX:

@article{ion2012, author = "E.N. Boldenkov and I.V. Korogodin and I.V. Lipa", title = "In-car GNSS Jammers Tracking System Evaluation Results", journal = "Proc. ION GNSS", pages = "901-906", year = "2012", language = english }

Abstract

GNSS equipment is widely utilized nowadays in a lot of fields. One of the major threat is that GNSS equipment is vulnerable to radio interferences. The most dangerous are active jammers. Anti-jamming capabilities are different in equipment of different class. For some applications special techniques makes the problem to be more or less solved. Several approaches known to provide high anti-jamming capabilities which includes spatial processing, integration with additional sensors and reception of wide-band signals like GPS L5. These techniques provides receiver a possibility to "survive" in jamming environment. The game in this field focuses on maximizing the distance between jammer and navigation receiver when the latter is able to operate for given jammer power. An obligatory condition of success is that application scenario suggest a considerable distance between jammer and receiver where needed jammer power would be inappropriate high.

Absolutely different situation is in automotive navigation field. The major threat here is availability of hand-held and in-car jammers which today are very easy to buy. The key difference of this application scenario is that the distance from jammer and receiver is very small. Given the fact that both jammer and navigation receiver are in the same car, this distance can be from one to three meters. So even high-linear receiver front-end can be easily overdriven with relatively low-power jammer. In this mode the navigation signal would be suppressed on a front-end non-linearity which makes no sence for any latter processing. More than that, advanced anti-jamming techniques usually can´t be implemented in automotive navigation due to economical reasons, power consumption and other issues. So in real one had to rely on standard receiver with low anti-jamming capabilities.

Vulnerability of automotive GNSS receiver makes them difficult to trust in car alarm systems. These systems became popular several years ago which raised demand for in-car jammers. This demand has been completely fulfilled - now it is very easy to buy GNSS jammer. Future applications comprise intellegent transport systems where GNSS are suggested to be used for driving car which is impossible with current jammer threat. If it is not possible to provide appropriate antijamming capabilities to "survive" in jamming environment another way is to "fight" against jammers itself. Jammer can be located by the signal it generates. So we need an interference monitoring system. To be effective this system should provide real-time jammer location with accuracy of tens of meters. As for car alarm application, despite to the fact that car alarm will not be able to report it´s coordinates, the position (and even entire track) of stolen vehicle would be possible to determine by jammer signal.

There are several jammer location techniques exist. A promising approach is the same pseudorange method as in GNSS system itself. Despite some difficulties this method can provide a high-accurate position and velocity determination as well as simple hardware similar to that from usual GNSS receiver.

The key difference from usual position determination in GNSS is the fact that jammer signal regarded to be unknown. The only things we suggest is that it has considerable power and the band of jamming signal is same as one of navigation signal. Jammer signal can be extracted with cross-correlation technique. The quality of this algorithm would determine performance of the system as whole.

The aims of this study includes experimental evaluation of pseudorange-based jammer location technique, investigation of cross-correlation jammer detection method and maximum achievable jammer detection distance.

The method under consideration is almost the same as in GNSS systems - a pseudorange method. In GNSS systems several navigation satellites with known coordinates synchronously transmit navigation signals. User equipment having received these signals can calculate it´s position. Jammer location system operates vice versa. One jammer source transmits its signal which should be received synchronously with several monitoring receivers placed at known positions. If the bandwidth of jamming signal is the same as one of navigation signal while its power is higher we can expect comparable level of positioning accuracy.

The main problem is in unknown jammer signal. To implement proposed monitoring system we need a way to detect jammer signal and measure its relative delays in every monitoring receiver. For the situation considered an optimal synthesis revealed cross-correlation technique to be the best choise. The monitoring system find a correlation between observations from several receivers and determine relative delays.

Both computer simulation and experiments were used to test jammer monitoring system. As a result of study we have shown that pseudorange-based jammer location technique can be implemented in practice. An analysis of maximum jammer detection distance dependence from jammer power is provided. It is shown for typical today -15 dBm chirp-signal jammer the maximum detection distance is 2 km. The accuracy of jammer location also have been evaluated. For standard -15 dBm jammer positioning error is less than 15 m. These figures were obtained for chirp jamming signal with 2 MHz bandwidth.

Suggested monitoring system is distributed in space and contains several antennas, standard GNSS receivers to determine control antennas positions and time synchronization, monitoring receivers, baseband processing block and communication links between monitoring receivers and processing block. Baseband block implements cross-correlation delay determination and calculates jammer position. The result is converted into usual NMEA-0183 protocol and displayed on map.

Monitoring receivers we are using are based on typical GNSS receiver architecture. It comprises single-stage frequency conversion to low intermediate frequency 4.092 MHz and quadrature analog-to-digital conversion with sampling frequency 16.369 MHz and 3 quantization bits. Prototype system is build with standard computers. Digitized signal transferred to memory via High-speed USB connection. Communication between receivers are based on standard TCP/IP networks.