运行一个Matlab程序，完成一个M＝4的PAM通信系统的仿真。仿真对10000个符号（2万个比特）进行。测量在噪声方差为0,0.1,1.0和2.0时的符号差错概率。通过低通滤波器。画出理论误码率和由Monte Carlo仿真测得的误码率，并比较这些结果。(平均符号能量为1)-Running a Matlab program, complete a M = 4 PAM communication system simulation. The simulation of 10000 symbols (20000 bits). Measurement in the noise variance is 0,0.1, 1.0 and 2.0 when the symbol error probability. Through the low pass filter. Draw the theoretical error rate and Monte Carlo simulation by measured error rate, and compare these results. (average symbol energy for 1)