rx_frequency_sync.m

ofdm系统仿真

%Frequency error estimation and correction
function [out_signal, freq_est] = rx_frequency_sync(rxsignal, thres_idx, sys_parm)

    global ofdm_data_parm_const;
    
    %Estimate the frequency error
    if sys_parm.FreqSync
        %Short training symbol periodicity
        D = (sys_parm.TotNumSubc * sys_parm.OverSamp + ofdm_data_parm_const.CPLength) * 2 / 10; 
        %Allows for error in packet detection
        pkt_det_offset = D;
        %Averaging length
        rlen = 8 * D;
        
        phase = rxsignal(pkt_det_offset: pkt_det_offset + rlen - D) .* ...
          conj(rxsignal(pkt_det_offset + D : pkt_det_offset + rlen));

        %Add all estimates 
        phase = sum(phase);   
        freq_est = - angle(phase) / (2 * D * pi / sys_parm.SampFreq);
        radians_per_sample = 2 * pi * freq_est / sys_parm.SampFreq;
    else
        %Magic number
        freq_est = sys_parm.FreqErr;
        radians_per_sample = 2 * pi * freq_est / sys_parm.SampFreq;
    end

% 	fprintf('The frequency estimation is : %d\n', freq_est);    
    
    %Now create a signal that has the frequency offset in the other direction
    siglen = length(rxsignal);
    time_base = [0 : siglen - 1];
    correction_signal = exp(- j * (radians_per_sample) * time_base);

    %And finally apply correction on the signal
    out_signal = rxsignal .* correction_signal;
end