How to generate TDL path gains for different subcarriers in a frequency selective channel?

I would like to generate different path gains for different subcarriers in order to simulate a frequency selective channel. How can I achieve this by using nrTDLChannel object? I previously used nrCDLChannel and understand frequency-selectivity cannot be achieved by this model. If my goal can be achieved by stting the correlation matrices and xpr of the nrTDLChannel object, how would I need to set these parameters for each subcarrier? Thank you.

Answer 1

[Suraj Kumar]

Hi Elcinur,

To simulate a frequency-selective channel using the ‘nrTDLChannel’ object in MATLAB, you can refer the following steps and the attached code snippets:

1. Initialize the TDL channel model using the ‘nrTDLChannel’ function and set the parameters like DelayProfile, DelaySpread, and MaximumDopplerShift to define the channel's characteristics.

% Define the channel 
channel = nrTDLChannel; 
channel.DelayProfile = 'TDL-C'; 
channel.DelaySpread = 30e-9; 
channel.MaximumDopplerShift = 5; 
channel.NumTransmitAntennas = 1; 
channel.NumReceiveAntennas = 1; 
channel.SampleRate = 15.36e6; 

2. Simulate the channel by generating a random signal and passing it through the ‘nrTDLChannel’.

% Generate random signal 
numSubcarriers = 1024; 
txWaveform = randn(numSubcarriers, 1); 
% Pass through channel 
[rxWaveform, pathGains] = channel(txWaveform); 

3. Use the Fast Fourier Transform (FFT) function to convert time-domain path gains to the frequency domain, which helps us analyze frequency selectively.

% Transform path gains to frequency domain 
pathGainsFreqDomain = fft(pathGains, numSubcarriers, 1); 

4. Examine the frequency-selective nature by displaying path gains for each subcarrier

figure; 
plot(1:numSubcarriers,   20*log10(abs(pathGainsFreqDomain))); 
xlabel('Subcarrier Index'); 
ylabel('Path Gain (dB)'); 
title('Frequency Response of the Channel'); 
grid on; 

You may refer to the output below for better understanding:

To know more about ‘nrTDLChannel’ object or ‘fft’ function in MATLAB, kindly refer the following documentations:

• https://www.mathworks.com/help/5g/ref/nrtdlchannel-system-object.html
• https://www.mathworks.com/help/matlab/ref/fft.html

Happy Coding!