Research On Unambiguous Tracking Technique Of BOC Modulated Signals

The Binary Offset Carrier modulated technique is a new satellite signal modulated method and it is proposed to meet increasing needs in terms of frequency bands. A BOC signal is defined as BPSK modulated code multiplied by a binary- valued (1 or -1)square-ware subcarrier with larger frequency. The main idea behind the BOC modulation is to shift the power spectrum of the radio frequency signal away from the center frequency in order to share a given frequency bands with the pre-existing signals and minimize the interference with other signals. Besides,it has been recognized that the BOC signals can achieve enhanced robustness against multipath and increase the precision of the range measurement, thus it being widely adopted in the satellite navigation system.Compared with the traditional modulation methods, the BOC has many advantages while also presents some drawbacks, the most severe being the ambiguity problem in tracking since its autocorrelation function has multiple peaks. To expatiate on the problem clearly, the BOC modulation method and its basic characters are given and the acquisition and tracking principles of the satellite signals are introduced. Then the exact reasons of the ambiguity problems in acquisition and tracking are expounded.To solve the ambiguity problem in the BOC signals tracking, the Autocorrelation Side-peak Cancellation Technique (ASPeCT) and the Pseudo-correlation-function based Unambiguous Delay Lock Loop (PUDLL) method are given. By theoretical deduction and performance simulation, the advantages and drawbacks of the two ambiguity mitigation methods are analyzed clearly. To solve the ambiguity problem completely, the Composed Correlation Function (CCF) is proposed. Firstly, two local auxiliary signals are designed,which correlate with the received BOC signal respectively to form two cross-functions. Then,the two cross-functions are used to obtain a CCF. The side-peaks are removed completely in the CCF, thus solving tracking ambiguity completely.The theoretical and numerical results have shown that the CCF technique is applicable to arbitrary order sine-BOC signals and derives better performance on robustness against the noise interference and multipath effect than the ASPeCT and PUDLL.