说明：  4. 试说明卷积编解码的工作原理： (1) 使用Simulink仿真卷积编码，并用Viterbi译码的方法进行解码，其中的编码、译码全部是自己编写代码(S-Function方式)，不是调用Simulink的已有编码、译码函数。 (2) 请在加性白高斯噪声信道中，画出比特信噪比与误码率的关系曲线。
(4. Try to explain the working principle of convolutional codec: (1) Simulink was used to simulate convolutional coding, and Viterbi decoding method was used for decoding. The coding and decoding were all written by oneself (s-function method), rather than calling the existing coding and decoding functions of Simulink. (2) in the additive white gaussian noise channel, please draw the curve of the relationship between bit signal-to-noise ratio and bit error rate.)