用matlab画出α=0,0.5,1的余弦滚降系统的频谱，并画出各自对应的时域波形。以α=1的余弦滚降系统为例，进行二进制双极性数字基带信号传输，试画出接收端的基带信号波形及眼图。-Matlab draw α = 0,0.5, 1 cosine roll-offs system of spectrum, and draw their corresponding time domain waveform. To α = 1 cosine roll-offs system as an example