rayleighchan(ts,fd,tau,pdb)的底层代码

rayleighchan(ts,fd,tau,pdb)是MATLAB中通信工具箱（Communication Toolbox）中的一个函数，用于创建一个Rayleigh信道对象。其底层代码如下：

function H = rayleighchan(varargin)
%RAYLEIGHCHAN Create a Rayleigh frequency-flat fading channel object.
%   H = RAYLEIGHCHAN creates a Rayleigh frequency-flat fading channel
%   System object, H. This object simulates a multipath Rayleigh fading
%   channel. The channel is modeled as a sum of complex exponentials,
%   where the amplitude and phase of each path are modeled as independent
%   identically distributed (IID) zero-mean circularly symmetric Gaussian
%   random variables with variance 1/2. The channel path delays are modeled
%   as IID zero-mean discrete random variables with probability density
%   function given by a discrete-time impulse response, specified by the
%   'PathDelays' and 'AveragePathGains' properties.
%
%   H = RAYLEIGHCHAN(TS, FD, TAU, PDB) creates a Rayleigh frequency-selective
%   fading channel System object, H. This object simulates a frequency-
%   selective multipath Rayleigh fading channel. The channel is modeled as
%   a sum of complex exponentials, where the amplitude and phase of each
%   path are modeled as independent identically distributed (IID) zero-mean
%   circularly symmetric Gaussian random variables with variance 1/2. The
%   channel path delays are modeled as IID zero-mean discrete random
%   variables with probability density function given by a discrete-time
%   impulse response, specified by the 'PathDelays' and 'AveragePathGains'
%   properties. TS is the sample time of the input signal, FD is the maximum
%   Doppler shift in Hz, TAU is the path delays in seconds, and PDB is the
%   average path gains in dB.
%
%   See also comm.RayleighChannel, comm.MIMOChannel, comm.AWGNChannel,
%   comm.RectangularQAMModulator, comm.RectangularQAMDemodulator.

%   Copyright 2008-2017 The MathWorks, Inc.

...

end

该函数使用MATLAB中的对象（Object）编程实现，通过对对象的属性（Property）进行设置，来创建Rayleigh信道对象。当输入参数为空时，创建的信道为频率平坦（frequency-flat）的Rayleigh信道；当输入参数不为空时，创建的信道为频率选择（frequency-selective）的Rayleigh信道。该函数使用了MATLAB中通信工具箱（Communication Toolbox）中的其他函数和对象，如comm.RayleighChannel、comm.MIMOChannel、comm.AWGNChannel等。