This paper mainly focuses on the noise limiting by means of the direct sequence spread spectrum ( dsss ) and the analysis of the transmission performance of the plc and some digital modulation technology . the contents of the paper is as follows : 1 ) the technical feasibility is proved after simulating noise limiting principle of dsss by means of systemview , the simulation software ; 2 ) a kind of band pass filter ( bpf ) is realized according to the requirement of filter and the principle of butterworth approximation , which satisfies the index of performance of dsss . 3 ) the low voltage plc system includes the sc1128 , the specific modulation / demodulation ic , the bpf filter and other circuit components , furthermore , the control function of system is realized by means of the personal computer and the microcontroller 本课题在对低压电力线的传输特性和数字调制技术进行分析的基础上，将通信理论中的直接序列扩频技术( dsss )用于解决低压电力线通信的干扰问题，主要研究内容如下： ( 1 )用通信仿真软件systemview对dsss技术的通信和抗干扰原理进行仿真分析，分别对时域和频域下采用dsss技术前后接收信号的频谱进行分析，验证dsss技术在本系统中的可行性； ( 2 )由dsss技术对滤波系统的要求，根据滤波理论分析了巴特沃思型滤波器的逼近原理并设计了合适的滤波电路； ( 3 )用调制解调芯片sc1128和自行设计的滤波器加之辅助外围电路，构造出低压电力线载波通信系统，并采用atmel公司的单片机设计了接收和发射电路的微控制器； ( 4 )分别对采取抗干扰措施前后输入和输出信号进行对比实验，并对结果进行分析，验证了dsss技术对干扰信号的抑制作用。
