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How to add multipath fading to a signal using tap?

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barithegreat

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hi
I want to add multipath fading(frequency selective) in my signal. can any body help me for doing this using tap.
bari
 

cheggy

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multipath fadding

You can create Rayleigh channel by generating taps of channel as x+i*y, where x and y are Gaussian with mean zero and variance that you choose.
 

barithegreat

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multipath fading matlab

Thanks for reply but i can understand. can u give me example. taps mean paths.
lets I want to creat 4 paths and there power as well.
taps=4
delays[0 10 20 30];
pdb=[1 0.1 0.2 0.5];
signal= rand(1,100);
now how i added fadding.
Thanks and take care.
 

cheggy

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multipath fading wiki

If you generate amplitudes for paths (or taps) directly - you won't get proper distribution.

Let's say you actually need 4-tap Rayleigh channel with variance 0.01 - it can be generated with:

for m=1:4
h(m)=sqrt(0.01/2)*randn+i*sqrt(0.01/2)*randn;
end;

And that's it. You can find on Wikipedia how random variable with Rayleigh distribution can be generated from two variables with normal distribution in quadrature - that's exactly our approach in given code.
 

barithegreat

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multipath fading wikipedia

hi
why u take variance 0.01 and how we pass signal through this channel, is just multiplying it or something else.
Please give me some detail.
Thanks and take care
bari
 

cheggy

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taps in rayleigh channel

Hi,

I took var. 0.01 only for example, you may use any value that you find to be appropriate for your simulation. To pass signal through this channel just use convolution of transmitted signal and channel impulse response created above. If you are using MATLAB, all you need is function "filter":

output=filter(h,1,input)

Best Regards
 

Communications_Engineer

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frequency selective multipath fading

You can also use Matlab command raychan for this purpose. Just write this command in the Help browser for Matlab and you'll know what to do next
 

van_ptithcm

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multipath with frequency

Communications_Engineer said:
You can also use Matlab command raychan for this purpose. Just write this command in the Help browser for Matlab and you'll know what to do next
I have use the Matlab help browser for rayleighchan command to generate frequency selective Rayleigh fading channel. However, I wonder the chan.PathGains are the impulse response? If this is true, is the channel's frequency response found by this command: freq_response=fft(chan.PathGains)?
I am doing my thesis on MC-CDMA, and need Channel State Information matrix, which list all the subchannel gain corresponding to each user. Can you help me how to obtain this matrix?
Thanks in advance.
 

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