扩频码速率异步时直扩系统码分多址能力

摘要

Direct Sequence CDMA system has the widest application in spread spectrum communication system at present. Multiple access interference (MAI) is the main interference factor in the system.The analysis of MAI in asynchronous direct sequence spread spectrum system using Gold sequence is made,and Matlab simulation is completed both in the condition of extended and single integration period.Simulation results show that asynchronous Gold sequence is not three valued,MAI will decrease as the integration period extended and MAI is related to code deviation,in some code deviation,the value of cross correlation function is almost single. If the integration period is single,the variation trend of MAI is not related to the length of Gold sequence,but if the code deviation is fixed,MAI will decrease as the length of Gold sequence increases.%直接序列扩频码分多址系统是目前应用最广泛的扩频系统，影响系统容量的主要因素是系统内多址信号的干扰。分析了采用Gold码的码速率异步直扩系统多址干扰，对扩展积分周期和单一积分周期均进行了数值仿真。仿真结果表明，码速率异步的Gold序列互相关函数不再具有三值特性；随着积分长度的扩展，互相关函数的统计值逐渐递减，即多址干扰减小；多址干扰与码偏移量大小有关，在某些特定码偏移量，积分长度为最小公倍数周期时，互相关函数接近为单值，而这些码偏移量正负对称出现；积分长度为单一周期时，多址干扰随码偏移量的变化趋势与扩频码长度无关；在相同码偏移量的情况下，随着扩频码的长度增加而减小。