| It is based on the TT&C system. The current TT&C system has adopted DS spread spectrum. As the development of signal examination technique and the mathematical model of period steady and random processing and spectrum related theories, TT&C system has met serious menace. To improve the ability of anti-jamming and anti-intercepting, it is a trend to develop DS/FH hybrid spread spectrum.This thesis studied DS/FH hybrid spread spectrum on that background, including the designing of sequence, the synchronization and the performance of system when existing jamming.The primary content of this thesis is as follows:(1) Analyzed and compared the form of TT& C signal.It is been discussed in two aspects. First, modulate and demodulate in consider of the power ratio, signal enveloping and the necessity of TT&C.Second, designed and analyzed the PN sequence.Designed and analyzed the PN sequence based on m sequence and Gold sequence, including DS (Direct Spectrum) sequence and hopping sequence. Firstly, designed a long DS sequence and a short DS sequence with equal-speed and times-period. And then analyzed and simulated the character of the sequence. Secondly, designed a long space frequency hopping head-sequence by the choosing of frequency point, and designed a long space frequency hopping sequence based on m sequence and non-liner modulus. And then analyzed and simulated the character of the frequency hopping sequence, including hamming correlation, equality and randomicity. The simulating result shows that the design has satisfied the requirement.(2) Researched on the method of synchronization of DS/FH hybrid spread spectrum. This project combined DS synchronization with FH synchronization for discussing closely, and provided a method of DS/FH synchronization. Designed the format of synchronization signal. And through the DS signal's acquisition tracking and demodulation processing, to get the FH synchronization information, the hybrid DS/FH system's synchronization was completed. The DS acquisition based on FFT for the acquisition of carrier frequency and PN code phase. It is a process of one-dimension search instead of two-dimension one. Then simulated and validated the character and the parameter of it. This thesis has also put forward a modified method of capturing the long PN code, which has largely reduced the capturing time.In addition, this thesis has advanced an improved long sequence capturing method with the lead of short sequence's'entire one'pulse. The two sequences are equal-speed and times-period. The capturing of long sequence has adopted cluster-parallel hybrid searching, which has largely reduced the capturing time.For the Frequency synchronization, this project has considered the factors of the ability to anti-jamming, capturing time and power lose and so on, and then combined the synchronization-head with shift-waiting-synchronization. And then discussed the method of tracking and keeping method of frequency hopping.(3) Studied the performance of anti-jamming of DS/FH hybrid spread spectrum, and compared the effect of jamming. On the condition of BPSK modulation and DS spread spectrum bandwidth is equal to the frequency hopping space, discussed the bit error rate in presence of broad band jamming, narrow band jamming, multi-tone jamming and partial band jamming with the added Gauss white noise. The analysis was performed for various system parameters such as signal-to-noise ratio, jamming-to-signal ratio and the ratio of signal bandwidth and system bandwidth. It was a reference for the design of spread spectrum TT&C system. |
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