channel.m

OFDM的详细仿真代码

function recv_signal = channel( transmit_signal,h_time, ch, N_Tx_ant, N_Rx_ant ,...
                        PreNoiseLen,PostNoiseLen, var_noise,N_subc,PrefixRatio,N_sym,...
                        delta_fc,T_sample,N_tran_sym,TurnOn)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 多径多天线信道

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

len = length(transmit_signal) + max(ch.Delay_sample) + PreNoiseLen + PostNoiseLen;

recv_signal = zeros(1,len ,N_Rx_ant);
tmp_recv = zeros(1,length(transmit_signal) + max(ch.Delay_sample),N_Rx_ant);

% 对每条接收天线的信号, 是N_tx_ant个数据的叠加
for n_r = 1:N_Rx_ant
    tmp_signal = zeros(1,length(transmit_signal) + max(ch.Delay_sample) );
    for n_t = 1:N_Tx_ant
        
        % 对单天线信道, 是N_path条径的延时叠加. h_time是时域信道的系数矩阵
        % 首先取一对天线,h_time(:,:,(n_t-1)*N_Tx_ant + n_r)是N_path行, N_sym列的矩阵
        % 把h_time扩展为每个OFDM符号有N_subc*(1 + PrefixRatio)个衰落系数
        % 乘上对应的时域样点.
        
        max_d = max(ch.Delay_sample);
        for p = 1:ch.N_path
            if (N_Rx_ant == 1) & (N_Tx_ant ~= 1)
                ch_coeff = h_time(p,:,n_t);
            else
                ch_coeff = h_time(p,:,(n_t-1)*N_Tx_ant + n_r);
            end
            ch_coeff = reshape( repmat(ch_coeff, N_subc*(1 + PrefixRatio),1) ,...
                                1,N_subc*(1 + PrefixRatio)*(N_sym+N_tran_sym) );
                            
            delay = ch.Delay_sample(p);
            
            % 然后把N_path条路径延时叠加,得到长度为length(transmit_signal) + max(ch.Delay_sample)的向量
            tmp_signal = tmp_signal + ...
                    [zeros(1, delay)  transmit_signal(1,:,n_t).*ch_coeff  zeros(1,max_d - delay)];
       end

    % 把不同发送天线的信号叠加
    tmp_recv(1,:,n_r) = tmp_recv(1,:,n_r) + tmp_signal;
 
    end
end

% 在每条接收天线的信号加噪声,并加前噪声和后噪声,用于定时同步算法
recv_signal = [ zeros(1,PreNoiseLen,N_Rx_ant) tmp_recv zeros(1,PostNoiseLen,N_Rx_ant) ];
noise = sqrt(var_noise)*( randn(1,len,N_Rx_ant) + j*randn(1,len,N_Rx_ant) );
recv_signal = recv_signal + noise;

% 加载波频偏
if TurnOn
    idx = repmat([0:length(recv_signal)-1],[1,1,N_Rx_ant]);
    recv_signal = recv_signal.*exp(j*2*pi*delta_fc*idx*T_sample);
end

% 加抽样频偏, 下一步完成