channel.m

ofdm系统仿真

% Channel model
function rx_signal = channel(tx_signal, cir, sys_parm)
    
    global ofdm_data_parm_const;

    %Channel effect
    if sys_parm.ChannelMode == 2
        rx_signal = filter(cir, tx_signal);
    else
        rx_signal = conv(cir, tx_signal);
    end
    
    len = length(rx_signal);
    
    %Add noise
    %Calculate noise variance
    noise_var = sys_parm.TotNumSubc * sys_parm.OverSamp / ofdm_data_parm_const.UsedNumSubc / (10 ^ (sys_parm.SNR / 10)) / 2;
    noise = sqrt(noise_var) * (randn(1, len) + j * randn(1, len));

    begin_noise = sqrt(noise_var) * (randn(1, ofdm_data_parm_const.StartNoiseSamples) + ...
       j * randn(1, ofdm_data_parm_const.StartNoiseSamples));

    %End noise is added to prevent simulation from crashing from incorrect timing in receiver
    end_noise = sqrt(noise_var) * (randn(1, ofdm_data_parm_const.EndNoiseSamples) + ...
       j * randn(1, ofdm_data_parm_const.EndNoiseSamples));

    %Add noise
    rx_signal = rx_signal + noise;

    %Begin noise samples are inserted before the packet to test the packet search algorithm
    rx_signal = [begin_noise, rx_signal, end_noise];

    %Create frequency offset
    rx_signal = create_freq_offset(rx_signal, sys_parm.FreqErr);
end