用matlab实现的曼彻斯特编码。50 占空比（可调）。绘制时域波形和频域功率谱密度。结果跟北邮的郭文斌的通信原理课件上的形状一模一样。-Manchester encoding with a matlab implementation. 50 duty cycle (adjustable). Draw time-domain waveform and frequency domain power spectral density. The results with the Beijing Un