ofdmml.rar_OFDM symbol timing_OFDM 同步 matlab_ofdm 符号同步_ofdm循环前缀_

clear all; clc; N_symbol=4; N = 1024; %the number of carrier %N = 256; %the number of carrier %T=10^(-6); % Sampling time : 1us L=128; % the number of prefix SNR=15; % SNR of signal rx_pre2 = zeros(1,N+L); %buffer for symber i-1 rx_pre1 = zeros(1,N+L); %buffer for symbol i rx = zeros(1,N+L); %buffer for symbol i+1 ro = SNR/(SNR+1); %e=0.25; %abs(e)=0; delay=floor(rand*N); %generate delay cnt = 0; while cnt <= N_symbol+1 % Generate Signal input_stream = (sign(randn(1,N*2))+1)/2; % modulation to QPSK qpsk_str = QPSK(input_stream); % QPSK stream : 1024 % inverse fft : from frequency domain to time domain xn=ifft(qpsk_str,N); % add_prefix len_xn = length(xn); % for checking : len_xn=N sn=[xn(len_xn-L+1:len_xn) xn]; rx_pre2=rx_pre1; rx_pre1=rx; %############################ AWGN Channel ############################# e=0.25; for k=1:length(sn) rx(k)=sn(k)*exp(j*2*pi*e*(k-1)/N); end %rx= rx+add_noise(sn,SNR); % add noise %rx(delay:length(rx))=rx; %rx(1:delay-1)=0; obs_rx=[rx_pre2(N+L-delay+1:N+L) rx_pre1 rx(1:N-delay)]; % observe 2N+L obs_rx=obs_rx+add_noise(obs_rx,SNR); % add noise %################## Calculate gamma(m) & PI(m) ################### if cnt > 1 i=cnt-1; gamma =zeros(1,N); pii =zeros(1,N); for theta=1:N %Equation 2-(6),2-(7) for k=theta:theta+L-1 gamma(theta)= gamma(theta)+obs_rx(k)*conj(obs_rx(k+N)); pii(theta)=pii(theta)+0.5*( abs(obs_rx(k))^2 + abs(obs_rx(k+N))^2 ); end %equation 2-(5) %lamda(i,theta)=abs(gamma(theta))*cos( 2*pi*e+angle(gamma(theta)) ) - ro*pii(theta); lamda(i,theta)=abs(gamma(theta))- ro*pii(theta); gamma1(i,theta)=-angle(gamma(theta))/(2*pi); end %end loop_theta end %end if cnt= cnt+1; % increase counter end % end while % S/P for lamda lamda_str=[]; gamma1_str=[]; for i=1:N_symbol lamda_str=[ lamda_str lamda(i,]; gamma1_str=[ gamma1_str gamma1(i,]; end % for display clf; figure(1); grid on plot(lamda_str) %plot(abs(xn)*100) figure(2); plot(gamma1_str) error=gamma1_str(find(lamda_str==max(lamda_str)))-e