Research On Ultra-wideband Techniques In Satellite Navigation System

The anti-jamming performance of navigation system is determined by signal system, terminal technology and other related links together. There has been a large number of antijamming technology in terminal. However, the update of signal system is relatively slow. This does not mean that we should not work on in signal system. Even if we can quickly keep up with developed countries in terminal technology, the overall performance of navigation system is deeply influenced by signal system. Ultra-wideband signal occupies 10 times more bandwidth than ordinary navigation signal, and it has an extreme low power spectral density that can improve the anti-jamming capability by an order of magnitude, which has a very important significance to navigation war. Therefore, the study of how to use ultra-wideband technology in satellite navigation is very necessary.In order to design the ultra-wideband navigation signal that can be adapted to the needs of navigation system, this paper introduces the existing ultra-wideband modulation techniques, through simulation and analysis we know it is difficult to use current modulation techniques in satellite navigation systems directly. On this basis, this paper proposes DS/FH constant envelope modulation scheme. This hybrid spread spectrum technology combines the advantages of frequency hopping technology and direct spread spectrum technology which greatly improves the processing gain of the system. However, the introduction of frequency hopping will bring great challenge to synchronization at the receiver. For example, it will cause Doppler shift hopping in different time slot, the initial phase of the carrier ambiguity problems. This paper proposes to use the frequency hopping pattern to assist carrier tracking, namely to use the internal relation of Doppler shift hopping to carrier frequency. We can use the last Doppler shift to predict next Doppler shift, which can minimize the Doppler agility at the input of tracking loop. To take full advantage of ultrawideband technology, this paper proposes a new code tracking algorithm which can combine signal of different frequency bands coherently. This will change the main lobe of the autocorrelation function of the signal greatly narrowed, which can improve the antijamming performance and tracking accuracy of the system. Finally, validity of the algorithms proposed is verified through the computer simulation. It is proven that the receive algorithm not only can keep tracking loop stability, but also can greatly improve the tracking accuracy and anti-multipath performance of the navigation system.