一个四用户的扩频通信系统，扩频增益为N=16，采用Walsh码进行直接序列扩频，BPSK调制，无线信道为AWGN(加性高斯白噪声信道)信道(AWGN信道：不考虑通信信道信号时，由宽频范围描述的统计随机无线噪声。)。在接收端进行解扩，解调，判决，通过仿真得到其中一个用户的误比特率与信噪比的仿真结果。,A four-user spread spectrum communication system, spreading gain for N = 16, using Walsh code Direct

qpsk解调与调制 包括滤波器 环路滤波器等多个过程内容-carrier frequency for modulation and demodulation

利用BPSK, DBPSK, QPSK, OQPSK, 16QAM, PAM， 信号进行基带，通带调制解调，分析频域，时域波形，误码率等-Using BPSK, DBPSK, QPSK, OQPSK, 16QAM, PAM for modulation and demodulation. Analyzing the spectrum, wave forms, and bit error rate

实现随机信号序列的QPSK调制和相干解调，观察信号的星座图，计算误比特率和误码率。-this code is designed for the signal s QPSK modulation and demodulation exactly. Meanwhile, the BER and SER were estimated and drawed.