Weak Signal Acquisition Technology Research For The New BeiDou Navigation Signals

With the development of GNSS modernization, Chinese BeiDou satellite navigation system is also stepping up upgrade to implement high interoperability with other GNSS, and improve the anti interference ability between different signals. The received satellite signal will be weakened in urban canyons and mountain environment it presents a new challenge to the design of the BeiDou receiver.This paper analyzed the current status of GNSS, and in this context, we focus on the BOC modulation, the existing GNSS weak signal acquisition technology and the elimination technique of BOC signal acquisition ambiguity. The followings were the main research results in this dissertation.(1) “First data accumulation, then coherent accumulation” approach was proposed, according to the fast acquisition requirement of GNSS signal. And PMF-FFT technology is used to improve the speed of GPS and BeiDou weak signal acquisition. Proposed method can overcome the influence of BeiDou NH code, and the error is small between the phase and the Doppler frequency estimate and the real value.(2) In order to acquisition the BeiDou signal modulated by NH code, a generalized difference method was improved, and two fine frequency acquisition strategy will be used. The Improved Generalized Difference Method(IGDM) is not affected by NH code. Compared with the traditional coherent difference method, IGDM can effectively improve detection capacity and improve the ability for acquisition weak signal.(3) An BeiDou weak signal acquisition algorithm based on estimate the current combination of NH code sequence was proposed. The algorithm can effective solve that reduction the accumulated value because of NH code phase uncertainty. In the same acquisition sensitivity,compared to traditional 20 ms coherent accumulation, the proposed algorithm can effectively reduce the amount of calculation and acquisition weak signal.(4) In order to solve the ambiguity problem of BOC signal acquisition, an improved method for BOC(n, n) was proposed, the method only retain the autocorrelation function(ACF) main peak of the BOC(n, n) signal. Then two kind of new structure function was proposed, according the improved BOC(n, n) ACF. Both of two new structure function can retain main peak of BOC(m, n)ACF and improve the ratio of primary and secondary peaks.