Softdec including the function poly2trellis-Viterbi Algorithm in soft decision

poly2trellis，程序清晰简单，容易阅读，matlab调用易实现-poly2trellis, procedures clear and straightforward, easy to read, matlab call easy to realize

采用卷积编码与维特比译码对通信过程进行了仿真，展示了卷积码的差错校正容量，调制方式采用QPSK-This demo shows how to use a convolutional encoder and decoder in a simulation of a communications link. It also shows the error correcting capability of convolutional co