基于Viterbi算法的扩频码与信息序列联合估计

针对短码DSSS（Direct Sequence Spread Spectrum,直接序列扩频）信号扩频码MLE（Maximum Likelihood Estimation,最大似然估计）问题,提出了一种基于Viterbi算法的扩频码搜索方法,并将其应用到同步CDMA（Code Division Multiple Access,码分多址）信号的扩频码估计中.该算法利用了扩频码码元为±1的先验知识,以向量的2-范数平方或1-范数作为度量值;每次判决扩频码码元时,计算2条可能路径的度量值,并选择使度量值最大的那条路径作为幸存路径,最终的幸存路径即为估计的扩频码;所提算法不仅计算复杂度低,而且能同时估计扩频信号的扩频码和信息序列.仿真实验表明,本算法在低信噪比时同样具有较好的性能.

Joint Blind Estimation of Spreading Code and Information Sequence Based on Viterbi Algorithm

A new blind estimation algorithm based on Viterbi search is proposed to solve the problem of MLE （Maxi- mum Likelihood Estimation） of spreading codes of DSSS （Direct Sequence Spread Spectrum） signals. The algorithm is also adaptable to estimation of the spreading codes of synchronous CDMA （Code Division Multiple Access） signals. It makes use of the priori knowledge that each chip of a spreading code must be -t-1 and takes the square of 2- norm of a vector or 1-norm of a vector as path metrics. At each decision of one chip of a spreading code, path met- rics of 2 possible paths are computed and the path which has bigger path metric is chosen as the survived path. The final survived path is the estimation of the spreading code. The algorithm not only has lower computational complex- ity but also can simultaneously estimate spreading codes and information sequences. Simulation results show that the algorithm performs well at lower SNR （Signal-to-Noise Ratio）.