低信噪比下超长PN码的快速捕获技术

直扩系统中,为了硬件实现上的简便,PN码的捕获一般都采用串行搜索的方法。但当PN码很长时,由于要搜索的相位点很多,串行搜索法将使捕获时间过长。并且当信噪比较低时,会有较高的虚警概率。这些都会使系统的捕获性能下降。文献6]针对长码提出了分布采样的快速捕获方案(DSA)。本文就此提出了改进,利用积累使之能够适应低达-50dB的低信噪比环境。仿真结果表明,改进后的算法改善了原算法在极低信噪比下的性能,降低了平均捕获时间。

Fast Acquisition Technique of Long PN Code With Low Signal-to-Noise Ratio

In DS-CDMA systems, in order to simplify the hardware implementation, people usually adopt serial search ( SSA) to synchronize PN code . But when PN code is very long,SSA will spend more time because there are many phase position to be cmopared. Specially,when the signal-to-noise is very low,the false alarm probability will be very high. All these factor will strongly debase acquisitive performance. Literature 6] proposed a new acquisition scheme called distributed sample acquisition(DSA) which is applicable to a long period PN code. We improve the scheme by accumulator, and make it available in -50dB' s Low SNR environment. The result of simulation proves that our improvement meliorates the old scheme' s performance with low SNR, and reduces the average acquisitive time.