The Key Techniques Of Practical Satellite Navigation Anti-jam Receivers

Satellite navigation and position system, as a critical element in national economic development and military security safeguard, is likely to be attacked by lots of strong jammers especially for its military use. The receiver with an anti-jamming unit, which is an effective solution to interference mitigation by space-domain processing, time-domain processing, frequency-domain processing or integration of these methods, can greatly suppress narrowband disturbing signals. Currently, several brands of well-developed anti-jamming receiver products have been created and some of them have been employed for military motives abroad. On the contrary, there is a long way to go at home because the anti-jam receiver is usually on the hypothesis that channels are ideal and the impact of isolation between RF channels usually being ignored in bad jamming environment. Also, the IF output power and ADC effective number of bits are also the key factors which effect the performance of anti-jam receiversFirstly, in this paper, the impact of RF channels isolation on the anti-jam performance of receivers is discussed. A model to analyze the RF channel isolation is proposed, aiming to find the relationship between RF channels isolation and receiver output SINR in the conditions of different signal azimuth, signal elevation, jamming intensity and magnitude of the isolation. Simulative analyses show that the output SINR degrade rapidly as the isolation decrease, especially, when JSR is 20dB and the isolation exceeds 20dB, the output SINR decreases slightly, about 0.2dB, but when the isolation has been reduced to the 15dB level, the change of the output SINR is about 2dB. The design demands of isolations in different jamming conditions are also introduced.Secondly, the optimum IF output power of anti-jam receivers is described. Based on the operation principles of AGC, a model used for the ADC quantization loss analysis is proposed. The optimum IF frequency is obtained at different interference environments by theoretical derivation and numerical simulation. When the IF output power is 0.23 times (one fifth) of the square of the full scale of the quantizer, receivers can adapt to different interference environments which can be verified by using real data.Finally, some problems related to ADC effective number of bits are analyzed. Based on the characteristics of satellite navigation and positioning system, an efficient ADC effective number of bits measurement method which based on despread output CNR is proposed. Then comparison is made between the proposed solution and the traditional measurement method by using real data, validating the effectiveness of the proposed method. At the same time, the influence of the DC bias on ADC effective number of bits is described by theoretical derivation and the collected real data, then the relationship between DC bias and ADC effective number is achieved. Lastly, the influence of the ADC effective number of bits on the anti-jam performance of receivers, by given the threshold of quantization loss, this paper find out how many ADC effective number of bits is need in different strong jammers environment.The work of this paper can be used as a design reference to practical anti-jam receivers in our satellite navigation and positioning system.