基于长时间差分相关/最大似然法的北斗信号位同步算法  

BeiDou signal bit synchronization algorithm based on long-time differential correlation and maximum likelihood

作　　者：韩志凤[1] 刘建业[1] 李荣冰[1] 王翌[1] HAN Zhi-feng, LIU Jian-ye, LI Rong-bing, WANG Yi(Navigation Research Center, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, Chin)

机构地区：[1]南京航空航天大学导航研究中心,南京210016

出　　处：《中国惯性技术学报》2017年第6期765-769,775,共6页Journal of Chinese Inertial Technology

基　　金：国家自然科学基金资助项目(61374115;61328301);南京航空航天大学博士学位论文创新与创优基金(BCXJ14-06);江苏省研究生培养创新工程(KYLX_0283);中央高校基本科研业务费专项资金资助

摘　　要：北斗信号二次编码调制了速率为1 kbps的NH码,频繁的比特跳变将相干积分时间限制在1 ms,需要对信号实现位同步获得比特边缘信息和NH码相位信息。为了实现弱信号、大频偏条件下北斗信号的位同步,解决频繁比特跳变和大频偏对传统位同步算法的性能影响问题,提出了一种基于长时间差分相关的最大似然位同步算法。首先,采用差分相关运算去除剩余频率误差的影响,并将差分延迟时间设定为整数倍比特周期以去除NH码的影响;其次,基于最大似然函数进行差分相关后的相干和非相干检测,提高弱信号条件下的位同步检测概率。最后,采用蒙特卡洛仿真测试分析了载噪比为20~40 d B·Hz、不同频率误差的条件下,此算法与传统位同步算法的检测性能。结果表明在频率误差为50 Hz的条件下,传统位同步方法无法工作,本文提出的算法仍具备较好的检测性能。该算法能够有效地去除北斗NH码频繁相位变化对位同步的影响、减弱频率误差对位同步性能的衰减作用,以及通过相干/非相干累积获得弱信号能力,该算法适用于弱信号、大频率偏差条件下的北斗信号位同步。BeiDou navigation message is modulated with a secondary code of NH code of 1 kbps, and the frequent bit jumps limit the coherent integration time to be 1 ms. So a bit synchronization algorithm is necessary to obtain bit edge and NH code phase information. In order to realize bit synchronization for weak signals with large frequency error and solve the problem that the frequent bit jumps and large frequency errors affect the performance of traditional bit synchronization algorithm, a bit synchronization algorithm based on long-time difference correlation and maximum likelihood is proposed. Firstly, the difference correlation is used to remove the effect of residual frequency error, and the differential delay time is set to be integer of bit cycle to remove the influence of NH code. Secondly, based on coherent and non-coherent integration, the maximum likelihood function detection can improve the detection probability of weak signals. Finally, the Monte Carlo simulation is used to analyze the detection performance of this algorithm comparing with traditional algorithm under the carrier-to-noise ratio of 20-40 d B×Hz and different frequency errors. Simulation results show that, under the condition that the frequency error is 50 Hz, the proposed algorithm presents a good detection performance, while the traditional method does not work. This algorithm can effectively remove the effect of BeiDou NH code, weaken the influence of frequency error, and realize bit synchronization of weak signals based on coherent and non-coherent integration. It is suitable for BeiDou weak signal bit synchronization with large frequency error.

关 键 词：位同步 NH码 弱信号 北斗 

分 类 号：V249.3[航空宇航科学与技术—飞行器设计]