基于恒模特性的QPSK-DSSS信号扩频序列估计

 针对非合作低信噪比条件下的QPSK-DSSS信号,提出一种基于恒模特性的扩频序列估计算法。该算法首先将单用户QPSK-DSSS信号等效为两用户的BPSK-DSSS信号,其次通过对信号协方差矩阵进行特征分解,估计出由同相与正交两路扩频序列张成的二维信号子空间,最后利用扩频序列的恒模特性消除特征分解带来的酉阵模糊问题,实现扩频序列的精确估计。本文提出算法实现简单,相对目前现有传统算法具有较低的计算复杂度,而且计算机仿真表明:本文提出算法在低信噪比条件下具有优良的估计性能。

Spreading Sequence Estimation Based on Constant Modulus Property for QPSK-DSSS Signals

In this paper, a spreading sequence estimation algorithm based on constant modulus property is proposed for the QPSK-DSSS signals in low signal to noise ratio and non-cooperative scenarios. First, the single-user QPSK-DSSS signal can be equivalently represented as a two-user BPSK-DSSS signal, and then the two-dimensional signal subspace spanned by the in-phase and quadrature binary spreading sequences is estimated by the eigen-decomposition of the covariance matrix. Finally, to estimate the spreading sequences accurately, its constant modulus property is exploited to cope with the unitary matrix ambiguity resulting from eigen-decomposition. The proposed algorithm is simple and easy to implement, and has a lower computational complexity compared to existing methods. And simulation results demonstrate the significant performance gains of the proposed algorithm in low signal to noise ratio situations.