frame_timing.m

OFDM的详细仿真代码

function [recv_frame, err_frame_timing] = frame_timing( recv_signal ,Window1, Threshold1, Delay1 , ...
    PreNoiseLen, PostNoiseLen, N_subc,PrefixRatio,N_sym,FrameTiming ,N_tran_sym, N_Rx_ant, TurnOn)

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% 实现OFDM的接收机帧定时(包检测,粗定时)算法
% 如果有多天线, 则有两种处理方法:
% 1) 每条天线分别进行帧定时. 
% 2) 取多条天线的帧定时位置的加权平均值

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

% 有2个OFDM符号长度的训练序列, 加上噪声样点

signal_len = size(recv_signal,2);
recv_frame = zeros(size(recv_signal));

if TurnOn
    
    for ant = 1: N_Rx_ant
        recv_tmp = recv_signal(:,:,ant);
        
        switch FrameTiming              % 帧定时算法
            
        case 1                          % 1--单窗口能量检测方法
            
            for start_idx = 1:PreNoiseLen*2       
                timing_metric(start_idx) = sum( recv_tmp(start_idx : start_idx + Window1 - 1).*...
                    conj( recv_tmp(start_idx :start_idx + Window1 - 1)) )/ Window1;
                %                 if timing_metric(start_idx) >= Threshold1  % 固定门限的方法，效果不好
                %                     timing_idx = start_idx;
                %                     %break;
                %                 end
            end
            max_value = max(timing_metric);       % 求得最大的估计值，然后取其比例(ratio值)得到门限
            ratio = 0.8 ;
            threshould = max_value*ratio;         % 门限由最高延时相关值确定,以防止出现漏判
            timing = find(timing_metric >= threshould);
            timing_idx = timing(1);
            
        case 2                          %  2--双窗口能量检测方法
            
            for start_idx = 1:PreNoiseLen*2
                timing_A_window = sum(recv_tmp(start_idx : start_idx+Window1 - 1).*...
                    conj(recv_tmp(start_idx :start_idx + Window1 - 1)));
                timing_B_window = sum(recv_tmp(start_idx + Window1: start_idx + 2*Window1 - 1).*...
                    conj(recv_tmp(start_idx + Window1:start_idx + 2*Window1 - 1)));
                timing_metric(start_idx) = timing_B_window/timing_A_window;
            end
            [max_value,max_idx] = max(timing_metric);
            timing_idx = max_idx + Window1;
            
        case 3                          % 3--延时相关方法帧定时
            
            for start_idx = 1:PreNoiseLen*2
                correlation = sum(recv_tmp(start_idx : start_idx + Window1 - 1).*...
                    conj(recv_tmp(start_idx + Delay1 : start_idx + Window1 + Delay1 - 1)));
                power = sum(recv_tmp(start_idx + Delay1 : start_idx + Window1 + Delay1 - 1).*...
                    conj(recv_tmp(start_idx + Delay1 : start_idx + Window1 + Delay1 - 1)));
                timing_metric(start_idx) = (correlation.*conj(correlation))/(power.*conj(power));               
                %                 if timing_metric(start_idx) >= threshould     % 固定门限的方法，效果不好
                %                     timing_idx = start_idx;
                %                     break;
                %                 end
            end          
            max_value = max(timing_metric);      % 求得最大的估计值，然后取其比例(ratio值)得到门限
            ratio = 0.6 ;
            threshould = max_value*ratio;        % 门限由最高延时相关值确定,以防止出现漏判
            timing = find(timing_metric >= threshould);
            timing_idx = timing(1);
        otherwise
        end
        
        idx_cnt(ant) = timing_idx ;         %   最佳定时值 ： PreNoiseLen + 1
        
        % 多天线帧定时处理方法1:  各条天线分别进行定时
        recv_frame( 1,1:signal_len - idx_cnt(ant) + 1,ant ) = recv_signal( 1, idx_cnt(ant):end , ant );
        
    end
    

%     多天线帧定时处理方法2:
%      多条天线使用平均的定时位置
      idx = round(sum(idx_cnt)/N_Rx_ant);
%      截取得到接收信号
      recv_frame = recv_signal( 1,idx : end ,: );


% 计算误差的样点数
err_frame_timing = sum( ( PreNoiseLen + 1) - idx_cnt )/N_Rx_ant ;


else
    delay = 0; 
    recv_frame = recv_signal(1,PreNoiseLen + 1 + delay:end ,:);
    err_frame_timing = 0;
end