OFDM system with channel estimation code error in modulate

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albin k
albin k 2021-3-30
回答： vidyesh 2024-2-19
getting ab error in modulate can any figure this out
%% OFDM system with channel estimation:
clear all; close all; clc;
global W
%% define parameters
m=10 ;
N=1000 ; %length of OFDM symbols N
M=16 ; %Constellation Order M
pilotFrequency=5 ;
E=1; %Pilot Energy
Ncp=100 ; %Cyclic Prefix length
L=8; %channel Length (number of taps)
typ=1; %Constellation Family Type is [1 for M-QAM, 2 for M-PSK]:-
%% ----------------------------------------------------------------------
%% define the modems Tx/Rx
switch typ
case 1
Tx=qammod(W,M);
Rx=qamdemod (W,M);
case 2
Tx=pskmod(W,M);
Rx=pskdemod (W,M);
otherwise
error('Error, Constellation Family not Defined');
end
%% data generation
D=randi ([0 M-1],m,N);
%% mapping (baseband modulation )
D_Mod=modulate(Tx,D);
%% serial to parallel
D_Mod_serial=D_Mod.';
%% specify Pilot & Date Locations
PLoc = 1:pilotFrequency:N; % location of pilots
DLoc = setxor(1:N,PLoc); % location of data
%% Pilot Insertion
D_Mod_serial(PLoc,:)=E*D_Mod_serial(PLoc,:);
figure;
imagesc(abs(D_Mod_serial ))
%% inverse discret Fourier transform (IFFT)
% Amplitude Modulation
d_ifft=ifft(D_Mod_serial);
%% parallel to serail
d_ifft_parallel=d_ifft.';
%% Adding Cyclic Prefix
CP_part=d_ifft_parallel(:,end-Ncp+1:end); % this is the Cyclic Prefix part to be appended.
ofdm_cp=[CP_part d_ifft_parallel];
%% generating random channel
h= randn(1,L) + 1j * randn(1,L);
h = h./norm(h); % normalization
H = fft(h,N); % Frequency-Domain Channel
d_channelled = filter(h,1,ofdm_cp.').'; % channel effect
channel_length = length(h); % True channel and its time-domain length
H_power_dB = 10*log10(abs(H.*conj(H))); % True channel power in dB
%% add noise
count=0;
snr_vector=0:4:40;
for snr=snr_vector
SNR = snr + 10*log10(log2(M));
count=count+1 ;
disp(['step: ',num2str(count),' of: ',num2str(length(snr_vector))])
ofdm_noisy_NoCH=awgn(ofdm_cp,SNR,'measured' ) ;
ofdm_noisy_with_chann=awgn(d_channelled,SNR,'measured' ) ;
%% receiver
%Remove Cyclic Prefix
ofdm_cp_removed_NoCH=ofdm_noisy_NoCH(:,Ncp+1:N+Ncp);
ofdm_cp_removed_with_chann=ofdm_noisy_with_chann(:,Ncp+1:N+Ncp);
% serial to parallel
ofdm_parallel_NoCH=ofdm_cp_removed_NoCH.';
ofdm_parallel_chann=ofdm_cp_removed_with_chann.';
%% Discret Fourier transform (FFT)
% Amplitude Demodulation
d_parallel_fft_NoCH=fft(ofdm_parallel_NoCH) ;
d_parallel_fft_channel=fft(ofdm_parallel_chann) ;
%% channel estimation
% Extracting received pilots
TxP = D_Mod_serial(PLoc,:); % trnasmitted pilots
RxP = d_parallel_fft_channel(PLoc,:); % received pilots
% Least-Square Estimation
Hpilot_LS= RxP./TxP; % LS channel estimation
% MMSE Estimation:-
for r=1:m
H_MMSE(:,r) = MMSE(RxP(:,r),TxP(:,r),N,pilotFrequency,h,SNR);
end
% Interpolation p--->N
for q=1:m
HData_LS(:,q) = interpolate(Hpilot_LS(:,q).',PLoc,N,'spline'); % Linear/Spline interpolation
end
%% parallel to serial
HData_LS_parallel1=HData_LS.';
HData_MMSE_parallel1=H_MMSE.';
%% demapping
d_received_NoCH=demodulate(Rx,(d_parallel_fft_NoCH.')) ; % No Channel
d_received_chann_LS=demodulate(Rx,(d_parallel_fft_channel.')./HData_LS_parallel1) ; % LS channel estimation
d_received_chann_MMSE=demodulate(Rx,(d_parallel_fft_channel.')./(HData_MMSE_parallel1)) ; % MMSE channel estimation
%% Removing Pilots from received data and original data
D_no_pilots=D(:,DLoc); % removing pilots from D
Rec_d_NoCH=d_received_NoCH(:,DLoc); % removing pilots from d_received_NoCH
Rec_d_LS=d_received_chann_LS(:,DLoc); % removing pilots from d_received_chann_LS
Rec_d_MMSE=d_received_chann_MMSE(:,DLoc); % removing pilots from d_received_chann_MMSE
%% Calculating BER
[~,r_NoCH(count)]=symerr(D_no_pilots,Rec_d_NoCH) ;
[~,r_LS(count)]=symerr(D_no_pilots,Rec_d_LS) ;
[~,r_MMSE(count)]=symerr(D_no_pilots,Rec_d_MMSE) ;
end
figure;
semilogy(snr_vector,r_NoCH,'-+');hold on
semilogy(snr_vector,r_LS,'-o');
semilogy(snr_vector,r_MMSE,'-s');
legend('orig. No Channel','LS CE','MMSE CE');
grid ;
hold off;
H_power_esti_dB_LS = 10*log10(abs(HData_LS_parallel1.*conj(HData_LS_parallel1))); % Estimated channel power in dB
H_power_esti_dB_MMSE = 10*log10(abs(HData_MMSE_parallel1.*conj(HData_MMSE_parallel1))); % Estimated channel power in dB
figure;hold on;
plot(H_power_dB(1:8:end),'+k','LineWidth',3);
plot(H_power_esti_dB_LS(1,(1:8:end)),'or','LineWidth',3);
plot(H_power_esti_dB_MMSE(1,(1:8:end)),'Sb','LineWidth',1);
title('ACTUAL AND ESTIMATED CHANNELS');
xlabel('Time in samples');
ylabel('Magnitude of coefficients');
legend('Actual','estimated LSE','estimated MMSE')

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回答（1 个）

vidyesh
vidyesh 2024-2-19
Hi albin,
The issue you're encountering with the modulate function is due to an incorrect number of input parameters. The modulate function in MATLAB requires at least three arguments: the message signal ‘x’, the carrier frequency ‘fc’, and the sampling rate ‘fs’.
For more information on how to use the modulate function, refer to the MATLAB documentation page: https://www.mathworks.com/help/signal/ref/modulate.html
Hope this helps.

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