m-qam调制解调系统仿真，包含调制解调的所有步骤-m-qam modulation and demodulation system simulation, including all steps of modulation and demodulation

/* A C++ version of Matlab's qamdemod(y, M, varargin) * Align each symbol to the nearest constellation points by minimum Euclidean distance. * The function only consider rectanglular constellation diagram and grey code. * The input is assum