“北斗二号”B2频段信号直接多普勒频移估计

Direct Doppler shift estimation for compass-M1 B2 signal

为了实现卫星信号的快速捕获,考虑到'北斗二号'B2频段采用的AltBOC(15,10)调制方式由两路QPSK组成,每一路QPSK都包含数据通道和与其正交的导频通道两部分,导频通道没有数据调制,因此可以通过对周期数据进行累加提高信号的信噪比来进行检测.为此采用了基于FFT的'频率补偿和同步块累加'的方法直接确定信号的多普勒频移,同时为了减小搜索空间提出了双数据块的方法,在不改变频率敏感性的前提下,使速度加倍.仿真结果表明,虽然双数据块累加造成了一定的幅值损失,当信噪比为-24 dB时,20ms的数据可以有效完成多普勒频移的估计.

＂COMPASS-M1＂（Beidou2） satellite navigation system broadcasts civil signals on B2 band with A ltBOC（15,10） modulation which contains two QPSK （quadrature phase shift keying）channel separately, one in phase data channel and one quadrature pilot one. To realize fast signal acquisition for software receiver, one can accumulate pilot signal periodically for its dataless feature to improve signal＇ SNR （signal to noise ratio） and make a direct detection. ＂Phase complementation and synchronized data block accumulation＂ method was adopted to acquire Doppler shift directly. To shorten the acquisition time, the paper proposes a improvement of double data blocks accumulation, which can shorten the acquisition time twice without frequency sensitivity lost. The simulation results show that the double data blocks accumulation method can acquire Doppler shift with some amplitude degradation directly and effectively.