北斗导航接收机高增益相干积分算法

近年来，针对弱信号的高灵敏度接收机已逐渐成为国内外的研究热点。加长相干积分时间可以提高信噪比，从而跟踪到更弱的信号。但是，北斗导航接收机跟踪环路并不可以无限加长相干积分时间，相干积分时间的长短和功效还受到卫星导航电文比特跳变的限制。为了消除导航电文比特跳变对相干积分的影响，提出了一种改进的基于最大似然估计的北斗信号位同步方法，完成位同步后再利用先猜后检的方法便可以实现长相干积分。利用软件接收机进行编程设计，仿真结果表明：该长相干积分算法能够稳定可靠地实现对弱信号的跟踪，20ms相干积分环路信噪比约提升12dB，40ms相干积分环路信噪比约提升15dB，80ms相干积分环路信噪比约提升17dB，提高了北斗导航接收机的灵敏度。

High Gain Coherent Integration Algorithm for Beidou Navigation Receiver

In recent years, high sensitivity receiver for weak signal has gradually become a research hotspot at home and abroad. The signal-to-noise ratio(SNR) can be improved by increasing the coherent integration time, and the weaker signal can be tracked. However, the tracking loop of Beidou navigation receiver can not increase the coherent integration time indefinitely. The length and efficiency of the coherent integration time are also limited by the bit jump of satellite navigation message. In order to eliminate the influence of navigation message bit jump on coherent integration, an improved maximum-likelihood bit synchronization algorithm is presented in this paper. A method of guessing and checking is used to achieve the longer coherent integration after completing bit synchronization. Simulation tests are carried out by using software receiver. The simulation results show that this coherent integration algorithm can track the weak signal stably and reliably. With 20ms coherent integration, the SNR of the loop is improved by 12dB, 15dB with 40ms and 17dB with 80ms. The simulation results show that this coherent integration algorithm can improve the sensitivity of Beidou navigation receiver.