to_freq_channel.m

来自「OFDM的详细仿真代码」· M 代码 · 共 28 行

function H_freq = to_freq_channel(h_time,ch ,N_subc,N_sym, N_Tx_ant, N_Rx_ant,N_tran_sym)

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% 得到频域信道响应,为自适应调制算法提供数据,也为接收机的信道估计器提供已知的频域信道响应.
% 这两类算法,在我们的B3G系统设计中,都是假设一帧/数据包中信道不变进行的. 因此我们只需要提供
% 第一个OFDM符号内的信道响应即可.
% 然而在频域加信道响应时, 最好把时变也考虑进去, 所以此处还是产生了所有OFDM符号内的频域响应.

% 时域信道响应H_freq的产生方法如下:
% 1) 按照ch.Delay_sample调整列元素的位置,并使得列长为N_subc
% 2) 矩阵第三维仍然表示不同天线对之间的信道参数, 共N_Tx_ant * N_Rx_ant个
% 3) 把列变换到频域, 并按照频域信道位置, 用fftshift进行重排, 得到频移信道响应

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    H_freq = zeros(N_subc ,N_sym + N_tran_sym, N_Tx_ant * N_Rx_ant );

    H_freq(ch.Delay_sample + 1,:,:) = h_time;
    
    % 我们假设频域的样点是在[-fs/2  fs/2]中的, fs是采样频率
    % fftshift目的是使得变换后的频域样点在[-fs/2  fs/2]中,而不是[0 2*pi]中

    %H_freq = fftshift( 1/(sqrt(N_subc)) * fft( H_freq ), 1 ) ;
    H_freq = fftshift( fft( H_freq ), 1 ) ;
    
%     eps = 1e-9;
%     H_freq = fftshift( 1/(sqrt(N_subc)) * fft( H_freq ) ) + eps ;