Visualization of Doppler in comm.RicianChannel not showing impulsive peak due to LOS component.

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Abhay Mohan
Abhay Mohan 2020-12-6
评论： Abhay Mohan 2020-12-17
Hello,
I am simulating a rician channel as per the following MWE.
Fs=6192000; %Sampling frequency
pdbs = [-0.2000,-13.50,-18.80,-21,-22.80,-17.90,-20.10,-21.90,-22.90,-27.80,-23.60,-24.80,-30,-27.70]; %Power profile in dB
Kfactor = 10.^(13.3/10); % Set K factor of LOS path. 13.3 dB is converted to linear scale
fd_LOS = 100; % Set Doppler of LOS path
fdmax = 120; %Set maximum doppler shift of NLOS paths.
delays = (1e-6)*[0,0,0.03500,0.6120,1.363,1.405,1.804,2.596,1.775,4.042,7.937,9.424,9.708,12.525];
chan = comm.RicianChannel('SampleRate',Fs, 'PathDelays',delays, 'AveragePathGains',pdbs, 'MaximumDopplerShift',fdmax,'KFactor',Kfactor,...
'DirectPathDopplerShift',fd_LOS,'DirectPathInitialPhase',zeros(size(Kfactor)));
xblock = randn(100000,1);
chan.Visualization='Doppler Spectrum';
for ii = 1:1000
yblock = chan(xblock);
end
As per my understanding of Rician Channels and Matlab, this should generate a Jakes Doppler spectrum that ranges from -120 Hz to 120 Hz, with an impulsive peak at 100 Hz corresponding to the Line of Sight component. This follows from Clarke's landmark paper which mentions that the line of sight component of Doppler spectrum shows up as an impulse. Please refer to Fig. 7 in [1]. However, I do not see this impulse in the theoretical or emperical plot that results from this MWE. Can someone help me understand what I'm doing wrong? Thank you!
[1] Clarke, Richard Hedley. "A statistical theory of mobile‐radio reception." Bell system technical journal 47.6 (1968): 957-1000.

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Deepak@Mathworks
Deepak@Mathworks 2020-12-16
Hi Abhay,
Yes, you are right about theory of Rician Channel model and you should get an impulse for the direct path component in your frequency spectrum.
But when you plot using comm.RicianChannel, you only get plot for Jakes Doppler spectrum means multipath component of your signal and not the direct path component. So doesn't matter if you plot using comm.RayleighChannel or comm.RicianChannel, both will give you same plots.
"The frequency response scope displays the multipath Rayleigh fading channel spectrum by taking a discrete Fourier transform of the channel filter coefficients." This info is given on the documentation page of comm.RicianChannel
Hope this helps.
Cheers,
Deepak

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