Application And Research On Weak Signal Detection By LOD For DS/SS

The direct-sequence spread spectrum system is widely applied in kinds of radio and satellite navigation system (GPS, GALILEO, BeiDou) because of its virtue of strong secrecy, code divided multiple address and precise measurement. Through its spread spectrum gain, DSSS has ability of interference rejection. But because of the relatively crowded electromagnetic circumstance and the existence of intentional hostile interference, the influence by interference can cause the receiver work weakly. So the research of weak signal detection technique and anti-jamming technique for DSSS is very exigent.The paper gradually expands research based on the application of locally optimal detector(LOD) in weak signal detection for DSSS, mainly including the following aspects:Aiming at the phenomenon that the additive noise model is difficult to describe the actual complicated channel accurately and cause the detection performance of common detectors greatly decrease, the paper establishs additive non-Gaussian noise model, correlated first order moving average noise model and multiplicative noise model respectively. Then, under the above three noise models, the paper proposes adopting LOD to deduce the coherent and non-coherent optimal acquisition configuration. The corresponding simulation analysis verifies the superiority of LOD compared to common detectors.Aiming at the situation of unknown actual noise model, the paper proposes combining fractional maximum entropy PDF estimation algorithm and LOD to obtain the simply optimal pseudo code acquisition configuration under unknown noise model for DSSS. Through corresponding simulation analysis, we verify the improvement of LOD compared to common detectors. In order to compare the acquisition performance of LOD acquisition methods under the above kinds of noise models, the paper adopts the actual sea testing data of some radio navigation system to carry out acquisition performance simulation, finding:under this experimental data, the acquisition performance of LOD for non-Gaussian noise model is best, and it is a practical acquisition method.Considering the character of resisting non-Gaussian jamming for LOD acquisition configuration in DSSS, the paper obtains a non-Gaussian jamming resisting technology based on amplitude domain processing(ADP), and proposes adopting fractional maximum entropy PDF estimation algorithm to obtain PDF of observed noise, so as to improve ADP technology. Simulation analysis shows:the ADP technology can suppress strong non-Gaussian jamming existing in DSSS, and meanwhile damage little to the nearly Gaussian distributive DS signal, so it is a simply nonlinear digital processing technology.Considering the limitation of ADP for multiple jamming sources, the paper proposes frequently amplitude domain processing (FADP) technology, which transforms time-domain amplitude processing to frequency-domain amplitude processing and adopts fractional maximum entropy PDF estimation algorithm to obtain PDF of observed noise. Then the paper gives out the detail structure frame of DS receiver inserted with FADP technology. The corresponding simulation analysis verifies the superiority of LOD compared to ADP, and FADP can be used as a plug-in nonlinear filter module inserted in the front of correlation processing of receiver, and compatible to any present DS regime receivers.