I need a MATLAB code that goes step-by-step in transmitting over time and frequency selective channels

1 次查看（过去 30 天）

Saed 2012-11-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/52737-i-need-a-matlab-code-that-goes-step-by-step-in-transmitting-over-time-and-frequency-selective-channe

Hello,

I need a MATLAB code that goes step-by-step in transmitting a bit sequence from the source to the destination over a time and frequency selective channel, considering into account the relative speed between the transceivers v, the propagation speed c, and the carrier frequency fc. The signal is Wide-band, i.e.: the ratio between the signal bandwidth and carrier frequency is not negligible. OFDM is used as a means to combat the multipath fading.

Thanks in advance

7 个评论
显示 5更早的评论隐藏 5更早的评论

Saed 2012-11-5

在 MATLAB Online 中打开

OK, let me explain the system:

I have a binary sequence {X[k]}, and I need to the following steps:

1- N-point IFFT is performed on N signal points to produce {x[n]}.

2- The last L symbols of each block consisting of N symbols are appended to the beginning to the block.

3- Each block is transmitted over a time varying frequency selective channel where the channel impulse response is \sum_{m=0}^L h_m \delta(t+at-\tau_m). {h_m} are i.i.d. Rayleigh fading channel gains, a=v/c is the Doppler effect where v is the relative speed of the transceivers, and c is the propagation speed, and \tau_m is the delay associated with the mth path.

4- At the receiver resampling is done at rate nT_s/(1+a) to transform the problem from wide-band to narrow-band.

5- The residual Doppler effect is carrier frequency offset (CFO) (We can ignore this by assuming that the receiver knows exactly the Doppler factor a).

6- OFDM demodulation and detection.

I wrote part of the code, but I do not know if it correct and how to continue beyond that:

if true clear all; clc;

    SNRdB=0:30;%SNR [dB]
    SNR=10.^(SNRdB./10);% SNR [Linear]
    f_o=15*10^3;% Carrier frequency
    R_s=5*10^3;% Symbol rate
    T_s=1/R_s;% Symbol Time;
    v=1.5;% Relative speed of the transceivers in m/s
    c=1500;% Sound speed in UWA channel
    a=v/c;% Doppler factor
    K=64;%Data subcarriers
    tau_t=[0 0.1*10^-3 0.2*10^-3 0.3*10^-3];% The delays of the resolvable    multipath compenets.
    L=ceil((tau_t(end)-tau_t(1))/T_s);% Find the channel length in symbols
    nErr=zeros(1,length(SNR));% Number of errors for each SNR value
    count=zeros(1,length(SNR));% Number of symbols generated to reach a   specific number of errors.
    Nerr=1;% A targer number of errors to be reached.
   for ii=1:length(SNR)
    while nErr(1,ii)<=Nerr
        count(1,ii)=count(1,ii)+K;% Each iteration K data symbols is generated
        b=rand(1,K)>0.5;% Generate a sequence of 0s and 1s
        X=2.*b-1;% Bipolar BPSK signal consisting of -1s and 1s
        x=ifft(X,K_s);% You said I need to do oversampling here, why? Is   this    correct
        xCP=[x(end-L+1:end) x];% Add a cycle prefix of L symb
        h=(1/sqrt(2*(L+1))).*(randn(L+1,1)+1i.*randn(L+1,1));% Multipath  channel gains
        n=(1/sqrt(2*SNR(ii))).*(randn(K+L,1)+1i.*randn(K+L,1));% AWGN
        %What is next
    end
end
  end