一种基于序列最大似然的多进制扩频捕获算法

针对多进制扩频系统的伪码捕获问题,通过分析多进制最小频移键控(MSK)正交扩频调制信号的组成规律,提出一种适合MSK调制系统的快速捕获算法.该方法将似然函数的计算分成两部分,分别用两个匹配滤波器实现,得到的似然函数计算单元实现结构简单,适合现场可编程逻辑门阵列(FPGA)实现.后级的多码元累加结构可提高系统低信噪比下的捕获性能.分析了该算法在MSK调制的多进制正交扩频系统中的捕获性能以及频差、信噪比等因素对检测概率的影响.仿真实验结果和性能推导验证了该方法的可行性.

An N-MLBE Based Fast Code Acquisition Method for Spread Spectrum System

Aimed at dealing with the acquisition of PN phase in direct-sequence spread-spectrum system (DSSS) system, by analyzing the construction of the modulated signal, a novel non-coherent approach to PN code acquisition technique for M-ary orthogonal signals in a DSSS system, based on non-coherent maximum-likelihood block estimator (N-MLBE), is proposed. The integrated maximum likelihood function is turned to two parts, which are realized with two matched filters. The proposed acquisition method is suitable to FPGA implementation. Combined with the multi-codes accumulation cell, the performance at low signal-to-noise ratios (SNR) is improved obviously. Its performance in M-ary MSK system, as well as its impact on factors such as frequency shift, signal noise ratio (SNR) have also been shown. Simulation results and analysis show that this algorithm is able to capture PN code at low SNR.