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说明：  modem.qammod对象实现M-QAM调制器，本示例中M为16。其输入参数是从0到15的整数而不是4bits二进制数据。因此，在利用此对象的modulate方法之前需要对二进制数据序列x进行预处理。特别地, 先采用MATLAB中的reshape函数将x沿着矩阵的行方向重新整理成每行4bit数据，然后应用bi2de函数将4bit数据转换成相应的整数。(modem.qammod object implements M-QAM modulator M in this example is 16. Input parameter is an integer from 0 to 15 instead of 4bits binary data. Therefore, before using the method of this object needs to modulate the binary data sequence x pretreatment. In particular, the first use of MATLAB reshape function x 4bit rearranged into each row of data in the row direction of the matrix, and then apply bi2de 4bit function to convert the data into the corresponding integer.)