receiver_lmmse.m

OFDM信道估计和均衡的仿真程序

%+----------------------------------------------------------------+
%|                                                                |
%|  Name: receiver_lmmse.m                                        |
%|  Author: James Shen                                            |
%|  Description: Takes ina signal and tries to demodulate it.     |
%|  We assume that we are receiving pilot signals so that the     |
%|  desired signal is know already. What happens in a real        |
%|  implementation is that the equalizer coefficients derived     |
%|  will continue to be used with data and the desired signal     |
%|  will then be the decovered signal. This will accumulate       |
%|  errors in the coefficients until the next batch of            |
%|  pilot symbols arrive. Receives one OFDM.                      |
%|                                                                |
%+----------------------------------------------------------------+
function[recovered_signal,w, error1] = ... 
    receiver_lmmse(desired_signal, noisy_signal, input_symbols, FFTLen, CPLen, M, w, SNRdB);

%============== Gaurd Interval Removal (GIR) ==================
% Remove cyclic extension from desired signal.
desired_time_serial = desired_signal((CPLen+1):FFTLen+CPLen); 
% Remove cyclic extension from noisy signal.
noisy_time_serial = noisy_signal((CPLen+1):FFTLen+CPLen);


%================= Serial To Parallel =================================
output_time_para = reshape(noisy_time_serial,FFTLen,1);

%================= FFT =================================
output_noisy_symbols = fft(output_time_para);

%============== Zero Forcing Equalizer ========================
% LS channel estimator in frequency domain
h_est = output_noisy_symbols ./ input_symbols;

% LMMSE equalizer
SNR = 10^(SNRdB/10);
new_w = conj(h_est) ./ ( abs(h_est).^2 + 1/SNR);
output_symbols = output_noisy_symbols .* w;

%================= Baseband Demodulation ===========================
output_para = qamdemod(output_symbols,FFTLen, M);

%================ Parallel to Serial ====================
output = reshape(output_para,1,FFTLen*M); % Time domain signal

%================ Returning output ===============================
recovered_signal = output;
w = new_w;

% The code below should be commented out when
% running for more than one iteration as it just
% shows graphs for one symbol
%================ Error Calculation ===========================
%figure(1);
%plot(abs(input_symbols), 'bx'); hold on;
%plot(abs(output_symbols), 'ro'), ...
%    title('Transmitted Symbols vs Equalized Symbols vs Unequalized Symbols');
%plot(abs(output_noisy_symbols), 'gd'), ...
%    legend('Tansmitted Symbols','Equalized Symbols','Unequalized Symbols') ...
%    ,ylabel('Amplitude'), xlabel('Symbol'); hold off;

error1= input_symbols - output_symbols;
%================ Graphs ===========================
%figure(2);
%semilogy(abs(desired_signal), 'b'); hold on;
%semilogy(abs(output_ext), 'r'); hold off;
%figure(3);
%semilogy(abs(e));

%=============== END FILE ================================