Suppression Of Multi-Narrowband Interferences In Direct Sequence Spread Spectrum Signals

Adaptive interference suppression can improve further the anti-interference capacity of spectrum spreading (SS) systems, reduce the requirement of system processing gain, and thus is important to military communications system.This paper studies adaptive interference suppression technique for SS systems, especially for Direct Sequence SS (DS-SS) systems, emphasizing frequency domain adaptive algorithms and their implementation. In suppression of multi-narrowband interference, frequency domain adaptive filters have primarily two advantages compared to time domain implementations. The first one is that the frequency domain adaptive filter is perfect in resolving the exacerbation of the convergence properties caused by the eigenvalue spread. The frequency domain adaptive filter algorithm has a convergence rate that is independent of the number of interferences. The other advantage of the frequency domain adaptive filter is the potentially large savings in the computational complexity. Thus, the frequency domain adaptive filter is well suited to a multi-narrowband interference scenario, the paper studied frequency domain adaptive algorithms, carried out analysis and computer simulations. Simulation results: for GOLD codes DS-SS signal of length 63, 4 interferences of signal to interference ratio (SIR) 40 uB or 4 narrowband interferences of signal to interference ratio (SIR) 40 dB and frequency-spectrum bandwidth 12 percent of the whole bandwidth, the SIR improvement is better than 20dB.We built up an experimental adaptive interference suppression system, the paper emphasizes on base-band subsystem which used lots of advanced chips for the hardware design, including of high-speed DSP, dedicated DSP, CPLD and so on, and implemented DS-SS signal and interference generation, adaptive interference suppression, adaptive results analysis, etc. Experimental results: for m-sequence DS-SS signal of length 7, single interference of SIR 20 dB, the SIR improvement was 18dB; for m-sequence DS-SS signal of length 7, 4 interferences of SIR 20 dB, the SIR improvement was 15dB.