rx_timed_to_freqd.m

MATLAB Simulation of OFDM System

function [freq_tr_syms, freq_data_syms, freq_pilot_syms] = rx_timed_to_freqd(time_signal, sim_options)
%freq_tr_syms  % n_rx_antennas*52*2
%freq_data_syms  % n_rx_antennas*48*n_data_syms
%freq_pilot_syms  % n_rx_antennas*4*n_data_syms
global sim_consts;

[n_tx_antennas, n_rx_antennas] = get_n_antennas(sim_options);

for rx_ant = 1:n_rx_antennas

   if ~sim_options.UseTxDiv
      long_tr_syms = time_signal(rx_ant,1:2*64);
   else
  %注意在生成preamble时，如下所示，在符号定时后，去除了前16个样值，
  %故两个接收天线上的长训练符号可以统一写作[time_signal(rx_ant,1:64) time_signal(rx_ant,81:144)]
 % long_trs_signal(1,:) = sqrt(2)*[long_tr_symbol(64-16+1:64) long_tr_symbol ...
 %     zeros(1,80)];
 %  long_trs_signal(2,:) = sqrt(2)*[zeros(1,80) ...
 %        long_tr_symbol(64-16+1:64) long_tr_symbol];
       
      long_tr_syms = [time_signal(rx_ant,1:64) time_signal(rx_ant,81:144)];
   end
   long_tr_syms = reshape(long_tr_syms, 64, 2);
   
   %FFT转至频域
   freq_long_tr = fft(long_tr_syms)/(64/sqrt(52)/sqrt(n_tx_antennas));
   reorder = [33:64 1:32];  %与tx_freqd_to_timed.m对应。
   freq_long_tr(reorder,:) = freq_long_tr;
   
   % 提取训练训练符号的子载波
   freq_tr_syms = freq_long_tr(sim_consts.UsedSubcIdx,:);
   
   % Take data symbols 提去数据部分，去除preamble.
   if ~sim_options.UseTxDiv
       %注意数据部分前面有长训练符号，回忆在tx_gen_preamble.m中有
       %if ~sim_options.UseTxDiv
       %long_trs_signal = [long_tr_symbol(64-2*16+1:64) long_tr_symbol long_tr_symbol];
       %else
       % long_trs_signal(1,:) = sqrt(2)*[long_tr_symbol(64-16+1:64) long_tr_symbol ...
        % zeros(1,80)];
        % 由于定时是在CP之后，故只需跳过长训练符号，若没有使用发射分集，长训练符号长64×2＝128；
        %若使用了发射分集，需跳过的长度为64+80=144。
      data_syms = time_signal(rx_ant,129:length(time_signal));
   else
      data_syms = time_signal(rx_ant, 145:length(time_signal));
   end
   
   data_sig_len = length(data_syms);
   n_data_syms = floor(data_sig_len/80);
   
   %使信号变成符号周期的整数倍
   data_syms = data_syms(1:n_data_syms*80);
   data_syms = reshape(data_syms, 80, n_data_syms);
   % 移除循环前缀
   data_syms(1:16,:) = [];
   
   % FFT
   freq_data = fft(data_syms)/(64/sqrt(52)/sqrt(n_tx_antennas));
   
   %Reorder 格式为 [33:64 1:32] 
   freq_data(reorder,:) = freq_data;
   
   %选择数据子载波 48个
   freq_data_syms = freq_data(sim_consts.DataSubcIdx,:);
   
   %选择导频子载波 4个
   freq_pilot_syms = freq_data(sim_consts.PilotSubcIdx,:);
   
   tmp_freq_tr(rx_ant,:,:) = freq_tr_syms;
   tmp_data_syms(rx_ant,:,:) = freq_data_syms;
   tmp_pilot_syms(rx_ant,:,:) = freq_pilot_syms;
end

freq_tr_syms = tmp_freq_tr;  % n_rx_antennas*52*2
freq_data_syms = tmp_data_syms; % n_rx_antennas*48*n_data_syms
freq_pilot_syms = tmp_pilot_syms; % n_rx_antennas*4*n_data_syms

%keyboard