写一个MATLAB程序，实现4个时间同步的CDMA用户的仿真，其中每个用户都使用长度为L=31的不同的Gold序列。每个用户都采用它们代表的Gold序列的二进制（+-1）调制。每个用户的接收端将这个复合的CDMA接收信号相关，而这个复合的信号都在它们各自的序列上受到AWGN的污损（基于按码片相加）。在N=10000信息比特下，仿真估值并画出作为SNR的函数的CDMA通信系统的差错概率。-Write a MATLAB program, the realization of the four time synchronization of the simulation of CDMA users, including the length of each user for use of the L = 31 different Gold sequences. They are used for each user on behalf of the Gold sequence of binary (+-1) modulation. Each user' s receiver will receive the composite CDMA signal, and this composite signal in the sequence of their respective defaced by the AWGN (additive based on the chip by). Information in the N = 10000 bits, the simulation value and draw as a function of SNR of the CDMA communication system the probability of error.