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OFDM_RX.m
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OFDM_RX.m
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function [M_n,Threshold_graph,H_est_time,RX_Payload_1_no_Equalizer,RX_Payload_2_no_Equalizer,RX_Payload_1_no_pilot,RX_Payload_2_no_pilot,BER] = OFDM_RX(RX,Parameters_struct)
%% Debug mode
Debug_mode = 'off';
if strcmp(Debug_mode,'on')
clearvars -except Debug_mode;close all;clc;
Global_Parameters;
load('RX');
end
%% j Parameter
j = 1i;
%% Root Raised Cosine filter
rolloff = 0.5;
L_RRC = 6;
OVR = 2;
RRC = rcosdesign(rolloff,L_RRC,OVR,'sqrt'); % [1x13]
RX_signal = conv(RX,RRC); % [1x3012]
%% Packet Detection
D = 16;
L = 32;
C_n = zeros(1,length(RX)-D+1-L);
P_n = zeros(1,length(RX)-D+1-L);
C_k = zeros(1,L);
P_k = zeros(1,L);
for n=1:length(RX)-D+1-L
for k=1:L
C_k(k) = RX(n+k-1)*complex(RX(n+k-1+D));
P_k(k) = abs(RX(n+k-1+D))^2;
end
C_n(n) = sum(C_k);
P_n(n) = sum(P_k);
end
M_n = (abs(C_n).^2)./(P_n.^2);
%% Packet_select
Threshold = 0.75;
loc = find(M_n>Threshold);
temp_1 = [loc,0];
temp_2 = [0,loc];
temp_3 = temp_1-temp_2;
Packet_Front = find(temp_3>300);
Packet_Front_idx = loc(Packet_Front);
Length_over_Threshold = 230;
for x=1:length(Packet_Front_idx)-1
if M_n(Packet_Front_idx(x)+Length_over_Threshold)>Threshold;
idx = Packet_Front_idx(x)+L_RRC+1;
end % if Loop
end % for Loop
Threshold_graph = Threshold*ones(1,length(M_n));
Threshold_graph(idx-L_RRC-1) = 1.15;
%% Downsampling
Frame_DWN_sampling = RX_signal(idx:OVR:OVR*480+idx-1); % [1x480] Frame length
%% Coarse CFO Estimation
Short_preamble_slot_length = 16;
z = Frame_DWN_sampling(Short_preamble_slot_length*5+1:Short_preamble_slot_length*6)*Frame_DWN_sampling(Short_preamble_slot_length*6+1:Short_preamble_slot_length*7)'; % [1x16]*[16x1]
f_Coarse_est = (-1/(2*pi*Short_preamble_slot_length*Parameters_struct.Ts))*angle(z);
Frame_After_Coarse = Frame_DWN_sampling.*exp(-j*2*pi*f_Coarse_est*Parameters_struct.Ts*(0:480-1)); % [1x480]
%% Fine CFO Estimation
z = Frame_After_Coarse(Short_preamble_slot_length*12+1:Short_preamble_slot_length*16)*Frame_After_Coarse(Short_preamble_slot_length*16+1:Short_preamble_slot_length*20)'; % [1x64]*[64x1]=[1x1]
f_Fine_est = (-1/(2*pi*64*Parameters_struct.Ts))*angle(z);
Frame_After_Fine = Frame_After_Coarse.*exp(-j*2*pi*f_Fine_est*Parameters_struct.Ts*(0:480-1)); % [1x160]
%% Symbol Timing Estimation
%% Channel Estimation
Long_preamble_1 = Frame_After_Fine(Short_preamble_slot_length*12+1:Short_preamble_slot_length*16); % [1x64]
Long_preamble_2 = Frame_After_Fine(Short_preamble_slot_length*16+1:Short_preamble_slot_length*20); % [1x64]
Long_preamble_1_After_FFT = fftshift(fft(Long_preamble_1)); % [1x64]
Long_preamble_2_After_FFT = fftshift(fft(Long_preamble_2)); % [1x64]
H_est = 0.5*(Long_preamble_1_After_FFT+Long_preamble_2_After_FFT).*conj(Parameters_struct.Long_preamble_slot_Frequency); % [1x64]
H_est_time = ifft(ifftshift(H_est)); % [1x64]
%% One tap Equalizer
RX_Payload_1_time = Frame_After_Fine(320+1:400); % [1x80]
RX_Payload_1_no_CP = RX_Payload_1_time(17:end); % [1x64]
RX_Payload_1_Frequency = fftshift(fft(RX_Payload_1_no_CP)); % [1x64]
RX_Payload_1_Frequency_Equalizer = RX_Payload_1_Frequency./H_est; % [1x64]
RX_Payload_2_time = Frame_After_Fine(400+1:480); % [1x80]
RX_Payload_2_no_CP = RX_Payload_2_time(17:end); % [1x64]
RX_Payload_2_Frequency = fftshift(fft(RX_Payload_2_no_CP)); % [1x64]
RX_Payload_2_Frequency_Equalizer = RX_Payload_2_Frequency./H_est; % [1x64]
%% De-Mapping
RX_Payload_1_no_Equalizer = [RX_Payload_1_Frequency(7:11),RX_Payload_1_Frequency(13:25),RX_Payload_1_Frequency(27:32),RX_Payload_1_Frequency(34:39),RX_Payload_1_Frequency(41:53),RX_Payload_1_Frequency(55:59)]; % [1x48]
RX_Payload_1_no_pilot = [RX_Payload_1_Frequency_Equalizer(7:11),RX_Payload_1_Frequency_Equalizer(13:25),RX_Payload_1_Frequency_Equalizer(27:32),RX_Payload_1_Frequency_Equalizer(34:39),RX_Payload_1_Frequency_Equalizer(41:53),RX_Payload_1_Frequency_Equalizer(55:59)]; % [1x48]
RX_Payload_1_Final = qamdemod(RX_Payload_1_no_pilot,16,0); % [1x48]
RX_Payload_2_no_Equalizer = [RX_Payload_2_Frequency(7:11),RX_Payload_2_Frequency(13:25),RX_Payload_2_Frequency(27:32),RX_Payload_2_Frequency(34:39),RX_Payload_2_Frequency(41:53),RX_Payload_2_Frequency(55:59)]; % [1x48]
RX_Payload_2_no_pilot = [RX_Payload_2_Frequency_Equalizer(7:11),RX_Payload_2_Frequency_Equalizer(13:25),RX_Payload_2_Frequency_Equalizer(27:32),RX_Payload_2_Frequency_Equalizer(34:39),RX_Payload_2_Frequency_Equalizer(41:53),RX_Payload_2_Frequency_Equalizer(55:59)]; % [1x48]
RX_Payload_2_Final = qamdemod(RX_Payload_2_no_pilot,16,0); % [1x48]
%% BER calculation
Error_bits = sum([abs(sign(Parameters_struct.data_Payload_1-RX_Payload_1_Final)),abs(sign(Parameters_struct.data_Payload_2-RX_Payload_2_Final))]);
BER = Error_bits/(length(Parameters_struct.data_Payload_1)+length(Parameters_struct.data_Payload_2));
%% Plot
if strcmp(Debug_mode,'on')
subplot(2,4,1),plot(RX,'.');title('RX-Raw');axis([-1.5 1.5 -1.5 1.5]);axis square;
%--------------------------------------------------------------------------------%
subplot(2,4,2),plot(real(RX));title('I');axis([1 3000 -1.5 1.5]);axis square;
subplot(2,4,3),plot(imag(RX));title('Q');axis([1 3000 -1.5 1.5]);axis square;
%--------------------------------------------------------------------------------%
[Spectrum_waveform,Welch_Spectrum_frequency] = pwelch(RX,[],[],[],1/Parameters_struct.Ts,'centered','power');
subplot(2,4,4),plot(Welch_Spectrum_frequency,pow2db(Spectrum_waveform));
title('Welch Power Spectral Density');axis square;
%--------------------------------------------------------------------------------%
subplot(2,4,5),plot(1:length(M_n),M_n,1:length(M_n),Threshold_graph);title('Packet Detection');axis([1,length(M_n),0,1.2]);axis square;
subplot(2,4,6),plot(abs(H_est_time));title('Channel Estimation');axis([1 64 0 4]);axis square;xlabel('Time');
%--------------------------------------------------------------------------------%
subplot(2,4,7),plot(RX_Payload_1_no_Equalizer,'*');
hold on
subplot(2,4,7),plot(RX_Payload_2_no_Equalizer,'*');
title('Before Equalizer');axis([-18 18 -18 18]);axis square;
hold off
%--------------------------------------------------------------------------------%
subplot(2,4,8),plot(RX_Payload_1_no_pilot,'*');
hold on
subplot(2,4,8),plot(RX_Payload_2_no_pilot,'*');
title({'Demodulation';['BER = ',num2str(BER)]});axis([-5 5 -5 5]);axis square;
hold off
set(gcf,'Units','centimeters','position',[1 2 49 24]);
end % Plot end
%% End function
end