Research On The Acquisition For BOC Signals In Complex Conditions

With the rapid development of satellite navigation system,the number of navigation systems increases.The signal compatibility among the navigation systems is an urgent problem to be solved.In this case,the BOC(Binary Offset Carrier)modulation signals are addressed to solve the above problem.Therefore,the research scholars have launched an analytical research of BOC signals.But the actual communication condition is complex,there are a variety of interference factors.These interference factors make the research of BOC signals’ synchronization technology become more difficult and practical.Thus how to achieve the capture of BOC signals in complex conditions has become a hot and difficult point for domestic and foreign scholars.The main job of this thesis includes the following aspects:(1)Aiming at the problem that the transmission correctness of BOC signals is affected by the narrowband interference and the ambiguity in acquisition of the BOC modulation signals caused by the multi-peaks of auto-correlation function,this thesis studies an acquisition algorithm of BOC signal in narrowband interference condition.This algorithm combines frequency domain overlapping Transform with fractal-reconstruction method to remove ambiguity.Firstly,signal is processed by overlapping window processing technology to reduce the spectrum leakage and the loss of signal.And then according to feature that the spectrum of narrowband interference signal is very high and narrow,the value which is beyond the threshold is set zero through the frequency domain notch technology.The interference signal can be suppressed effectively.Finally,the processed BOC signal is captured by the fractal-reconstruction method to achieve the purpose of no fuzzy capture.(2)Aiming at the multimodality of the BOC signals can cause Fuzzy acquisition and the lack of research on the multipath suppression method for higher order BOC signals.This thesis proposes a multipath suppression algorithm of high-order BOC signals.It combines the parallel SCPC(Sub Carrier Phase Cancellation)with HRC(High-Resolution Correlator)to achieve multipath suppression.Firstly,the parallel SCPC acquisition algorithm is used to obtain the fuzzy function which is similar to the correlation function of the BPSK signal.It can remove the sidelobes of the correlation peak.Then,the multi-path components of the BOC signals are suppressed by a new correlator.This new correlator is obtained by the linear combination of ahead,lag,far ahead and far lagged correlators.(3)For the unambiguous general acquisition algorithm for BOC and its derivative signals is still scarce,a new unambiguous algorithm is studied for all types of BOC signals.Firstly,the common sub-carrier model is constructed according to the links of different sub-carrier modulations,and the general expression of BOC,MBOC(Multiplexed Binary Offset Carrier)and AltBOC(Alternate Binary Offset Carrier)signals can be obtained through the general subcarrier model.Then,the subcarrier is decomposed according to the period of the specific proportion based on the general subcarrier model,and the decomposed subcarrier is processed with the original received signal.Finally,a number of correlation values are got,and according to the method of correlation function synthesis a common capture method is builded.