Channel coefficients using Matlab's Rayleigh channel function

[serhannn]

Hi, I'm trying to obtain the Channel matrix (H) and code matrix for a cdma simulation. Basically, I need the channel responses h_i's for each user i=1,...,K. But when I use the Matlab's Rayleighchan function it gives me the path gains for every symbol I transmit. What does that mean? I want to get the channel response for every user and say, if each user transmits 100 symbols and I have 10 users and channel has 3 taps, then I get a PathGains matrix of 100x3 for every one of the 10 users. But I think, for each user I should only have one channel response. Am I not correct? I am a little bit confused about this channel response thing, so forgive me if I am making any fundamental mistakes here.

My code is as follows:

K = 10;     % Number of users
L = 3;      % Number of multipath fingers for each user
M = 100;    % Number of symbols transmitted by each user in each frame
G = 64;     % Spreading gain = Chip rate / Symbol rate

sampleTime = 2.0e-006;
maxDopplerShift = 200;                  % = v*f/c [Hz]
maxDelay = 0.16;
%delayVec = 1.0e-006 * [0 0.04 0.08];                % delays of three-path channel
delayVec = 1.0e-004 * rand([K L-1]) * maxDelay;      % create avg. path delays for each user (each has 3 paths)
delayVec = [zeros(K,1) delayVec];                    % First path is direct path, hence 0 delay for all users
%gainVec = [0 -3 -6];                    
gainVec = -delayVec*10^6;                            % average path delays [dB], decay exponentially with delay (linearly in dB)
%%

% Modulation
hMod = comm.BPSKModulator;
bitsPerFrame = M;                                    % Number of bits transmitted per frame = M , due to BPSK modulation
                                          

S = zeros(bitsPerFrame,K);                           % Create data matrix for K users, each having M symbols
modulated_S = zeros(bitsPerFrame,K);                 % Modulated data matrix
nFrames = 100;                                       % Number of frames   

% Create K impulse responses for each user
for i=1:K  
    h(i) = rayleighchan(sampleTime, maxDopplerShift, delayVec(i,:), gainVec(i,:));
    h(i).StoreHistory = 1;                                   %
    h(i).ResetBeforeFiltering = 0;                           % preserve the continuity of fading process 
    for n=1:nFrames
        S(:,i) = randi([0 1],bitsPerFrame,1);                % Create the message bits for i-th user
        modulated_S(:,i) = step(hMod, S(:,i));               % Modulate the message of i-th user into BPSK symbols
        Y(:,i) = filter(h(i),modulated_S(:,i));              % Apply the channel of i-th user to the modulated message
    end
end

So as you see I have a multidimensional array h(i) to store the channel responses and when I type for example:

h(1).PathGains

I get a 100x3 matrix containing path gains for 100 symbols transmitted by the user 1 with 3 multipath fingers. At least, that's what I think what is happening. My question is: Am I not supposed to get one single channel response for each user? Or how do I obtain that channel response for this path gains matrix.

Thanks a lot.

 

[serhannn]

I think I might have solved the problem. I removed the part of the code:

h(i).StoreHistory = 1;

After this, when I type h(8) meaning that I would like to see the channel of user 8, I get the following:

             ChannelType: 'Rayleigh'
       InputSamplePeriod: 2.0000e-06
         DopplerSpectrum: [1x1 doppler.jakes]
         MaxDopplerShift: 200
              PathDelays: [0 5.4140e-06 7.3073e-06]
           AvgPathGaindB: [0 -5.4140 -7.3073]
      NormalizePathGains: 1
            StoreHistory: 0
          StorePathGains: 0
               PathGains: [0.4047 - 0.1857i 0.2528 - 0.6938i -0.2452 + 0.1236i]
      ChannelFilterDelay: 4
    ResetBeforeFiltering: 1
     NumSamplesProcessed: 100

So for each user, the parameter PathGains is the respective impulse response as far as I could understand. It has three components since my multipath channel has three fingers. I think when I set the StoreHistory parameter to 1, the rayleighchan function stored evolution of the channel response throughout the transmission of all 100 symbols and the last value was actually what I desired.

 

[arushim]

error in code--??? Undefined function or variable 'comm'.
Error in ==> rayl2 at 17
hMod = comm.BPSKModulator;

Ques)How to generate h(64 by 1 matrix),channel impulse response for a rayleigh fading channel(speed-120km/hr)..relative delays[0 781 1563 2344],avg power[0 -3 -6 -9]..max doppler shift 150 HZ,carrier freq-1 GHZ..
no.of users-8, no.of path for each user-8 or 16

plz help :roll: