www.gusucode.com > MIMO与SISO仿真程序 > MIMO-OFDM/results_MISO_OFDMA_v1.m
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% Student: Benjamin Pham
% ID: 25957066
%
% Version: Final
% Changes:
% Description: a two user one receiver OFDM System
%
% Simulates a multi-user OFDM system. This system includes the
% Transmitter:
% QAM Modulation, S/P converter, IFFT, Add Cyclic Prefix,
% Sub-carrier allocation, P/S converter
% Channel:
% Frequency flat fading Channel modelled by Complex number, AWGN,
% Time Offset
% Receiver:
% S/P converter, Sub-carrier Demux, Removal of Cyclic Prefix, DFT,
% P/S converter, QAM Demodulation
%
% Simulation performs a BER test vs SNR when various time offsets are
% inputted by sending binary data through the system and measuring the
% amount of errors at the receiver. Time offsets can be changed beginning
% on line 140 for different channels.
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clc; clear all;close all; warning off
%% Input parameters
% data points
data = 2^16;
% fft size
n_fft = 64;
% cyclic prefix length
n_cp = 0.25*n_fft; % CP length 25% of FFT size
% OFDM frame length
OFDM = 2*n_fft+2*n_cp;
% Signal to Noise Ratios for AWGN
snr = [0:1:30];
% Channel modelled by random complex number
% 1 for same channels or any other number different channels
channel = 1;
% Simulate users with same channel or different channels
if channel == 1
h = [randn() + randn()*1i];
h = [h h];
else
h = [randn()+randn()*1i , randn()+randn()*1i];
end
% Initialise variables
errors1 = zeros(size(snr));
ber1 = zeros(size(snr));
errors2 = zeros(size(snr));
ber2 = zeros(size(snr));
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%% TRANSMITTER %%
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% Generate binary data
binary_data1 = round(rand(data,1)); % User 1
binary_data2 = round(rand(data,1)); % User 2
%% Run BER test for 4QAM, 16QAM and 64 QAM
for mod_type = 1:3
% Quadrature Amplitude Modulation
if mod_type == 1 % Modulation Type: 4QAM
symbols = 2; % Bits per symbol
% Padding for symbol mapping
while floor(length(binary_data1)/symbols) ~= length(binary_data1)/symbols
binary_data1 = [binary_data1; zeros(1,1)];
end
while floor(length(binary_data1)/symbols/(2*n_fft)) ~= length(binary_data1)/symbols/(2*n_fft)
binary_data1 = [binary_data1; zeros(1,1)];
end
% Padding for subcarriers mapping
while floor(length(binary_data2)/symbols) ~= length(binary_data2)/symbols
binary_data2 = [binary_data2; zeros(1,1)];
end
while floor(length(binary_data2)/symbols/(2*n_fft)) ~= length(binary_data2)/symbols/(2*n_fft)
binary_data2 = [binary_data2; zeros(1,1)];
end
elseif mod_type == 2 % Modulation Type: 16QAM
symbols = 4;
% Padding for symbol mapping
while floor(length(binary_data1)/symbols) ~= length(binary_data1)/symbols
binary_data1 = [binary_data1; zeros(1,1)];
end
while floor(length(binary_data1)/symbols/(2*n_fft)) ~= length(binary_data1)/symbols/(2*n_fft)
binary_data1 = [binary_data1; zeros(1,1)];
end
% Padding for subcarriers mapping
while floor(length(binary_data2)/symbols) ~= length(binary_data2)/symbols
binary_data2 = [binary_data2; zeros(1,1)];
end
while floor(length(binary_data2)/symbols/(2*n_fft)) ~= length(binary_data2)/symbols/(2*n_fft)
binary_data2 = [binary_data2; zeros(1,1)];
end
elseif mod_type == 3 % Modulation Type: 64QAM
symbols = 6;
% Padding for symbol mapping
while floor(length(binary_data1)/symbols) ~= length(binary_data1)/symbols
binary_data1 = [binary_data1; zeros(1,1)];
end
while floor(length(binary_data1)/symbols/(2*n_fft)) ~= length(binary_data1)/symbols/(2*n_fft)
binary_data1 = [binary_data1; zeros(1,1)];
end
% Padding for subcarriers mapping
while floor(length(binary_data2)/symbols) ~= length(binary_data2)/symbols
binary_data2 = [binary_data2; zeros(1,1)];
end
while floor(length(binary_data2)/symbols/(2*n_fft)) ~= length(binary_data2)/symbols/(2*n_fft)
binary_data2 = [binary_data2; zeros(1,1)];
end
end
% Mapping binary data onto constellation maps
mod_method = 2^symbols;
mod_data1 = qammod(binary_data1,mod_method,'unitaveragepower',true,'inputtype','bit');
mod_data2 = qammod(binary_data2,mod_method,'unitaveragepower',true,'inputtype','bit');
%% splitting data up between the users
Tx1 = mod_data1;
Tx2 = mod_data2;
%% Serial to Parallel Conversion
% serial stream into 64 subcarriers
Xk1 = reshape(Tx1,n_fft,length(Tx1)/(n_fft)); % 64 sub carriers, per user
Xk2 = reshape(Tx2,n_fft,length(Tx2)/(n_fft));
%% Inverse Fast Fourier Transform
Xn1 = ifft(Xk1);
Xn2 = ifft(Xk2);
%% Cyclic prefix
Xn1_cp = [Xn1((end - n_cp + 1):end,:);Xn1];
Xn2_cp = [Xn2((end - n_cp + 1):end,:);Xn2];
%% Sub-carrier allocation
Xn1_pad = [ Xn1_cp ; zeros(size(Xn1_cp)) ];
Xn2_pad = [ zeros( size(Xn2_cp)) ; Xn2_cp ];
%% Parallel to Serial Conversion
xn1 = Xn1_pad(:);
xn2 = Xn2_pad(:);
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%% Channel %%
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%% BER test for different SNR
for k = 1:length(snr)
%% Data passing through Channel
yn11 = xn1*h(1);
yn21 = xn2*h(2);
%% add noise
db = snr(k);
yn11 = awgn(yn11,db,'measured');
yn21 = awgn(yn21,db,'measured');
%% offset added to between User and receiver
% CP length is 16, input time offset of 15 to match CP length of 16
% offset greater than CP length, 15, introduces ISI and increased BER
% time offset is equal to duration of one symbol length
delay11 = 0; % offset between User1 and Rx1
delay21 = 0; % offset between User2 and Rx1
% next OFDM symbol becomes superposition of delayed previous symbol
% tail of previous symbol added to front of next symbol - ISI
%% inter-symbol interference
for i = 0:(length(yn11)/(OFDM))-2
% ISI between transmitter 1 and receiver 1
if delay11 ~= 0
if delay11 == 1
yn11(1+OFDM+OFDM*i) = yn11(1+OFDM+OFDM*i) + yn11(OFDM-delay11+OFDM*i);
else
yn11(1+OFDM+OFDM*i:1+OFDM+delay11+OFDM*i) = yn11(1+OFDM+OFDM*i:1+OFDM+delay11+OFDM*i) ...
+ yn11(OFDM-delay11+OFDM*i:OFDM+OFDM*i);
end
end
% ISI between transmitter 1 and receiver 2
if delay21 ~= 0
if delay21 == 1
yn21(1+OFDM+OFDM*i) = yn21(1+OFDM+OFDM*i) + yn21(OFDM-delay21+OFDM*i);
else
yn21(1+OFDM+OFDM*i:1+OFDM+delay21+OFDM*i) = yn21(1+OFDM+OFDM*i:1+OFDM+delay21+OFDM*i) ...
+ yn21(OFDM-delay21+OFDM*i:OFDM+OFDM*i);
end
end
end
% Time offset transmitter 1 and receiver 1
if delay11 ~= 0
if delay11 == 1
yn11(1:OFDM) = [zeros(delay11,1);yn11(1:OFDM-delay11)];
else
yn11(1:OFDM) = [zeros(delay11+1,1);yn11(1:OFDM-delay11-1)];
end
end
% Time offset transmitter 1 and receiver 2
if delay21 ~= 0
if delay21 == 1
yn21(1:OFDM) = [zeros(delay21,1);yn21(1:OFDM-delay21)];
else
yn21(1:OFDM) = [zeros(delay21+1,1);yn21(1:OFDM-delay21-1)];
end
end
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%% RECEIVER %%
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% superposition of two received signals at receiver
%% y(1) = h1*x1 + h2*x2
yn = yn11 + yn21; % combined signal at receiver 1
%% Serial to Parallel Conversion
yn_sub = reshape(yn,OFDM,size(Xn1,2));
%% Sub-Carrier Demux
Yn_sub1 = yn_sub(1:80,:);
Yn_sub2 = yn_sub(81:160,:);
%% Remove cyclic prefix
yn_sub_rcp1 = Yn_sub1((n_cp+1):end,:);
yn_sub_rcp2 = Yn_sub2((n_cp+1):end,:);
%% Discrete fourier transform
Yk_block1 = fft(yn_sub_rcp1);
Yk_block2 = fft(yn_sub_rcp2);
%% Serial to parallel conversion
Yk1_s = Yk_block1(:);
Yk2_s = Yk_block2(:);
%% Channel estimation
% assume perfect channel estimation through pilot symbols and using
% zero forcing
Xhat1 = Yk1_s./h(1);
Xhat2 = Yk2_s./h(2);
%% QAM demodulation
X_demod1 = qamdemod(Xhat1,mod_method,'unitaveragepower',true,'outputtype','bit');
X_demod2 = qamdemod(Xhat2,mod_method,'unitaveragepower',true,'outputtype','bit');
output1 = X_demod1(:).';
output2 = X_demod2(:).';
%% Calculating BER
% BER for User 1
errors1(mod_type,k) = 0;
for i = 1:length(binary_data1)-n_fft*symbols
if output1(i+n_fft*symbols) ~= binary_data1(i+n_fft*symbols)
errors1(mod_type,k) = errors1(mod_type,k) + 1;
end
end
ber1(mod_type,k) = errors1(mod_type,k)/length(binary_data1);
% BER for User 2
errors2(mod_type,k) = 0;
for i = 1:length(binary_data2)-n_fft*symbols
if output2(i+n_fft*symbols) ~= binary_data2(i+n_fft*symbols)
errors2(mod_type,k) = errors2(mod_type,k) + 1;
end
end
ber2(mod_type,k) = errors2(mod_type,k)/length(binary_data2);
end
% Plotting BER vs Eb/No
semilogy(snr-10*log10(symbols),ber1(mod_type,:),'-',snr-10*log10(symbols),ber2(mod_type,:),'-')
title('Two users One receiver'); legend('4QAM user1','4QAM user2','16QAM user1','16QAM user2','64QAM user1','64QAM user2');
xlabel('E_b/N_o (dB)'); ylabel('BER'); grid on;hold on
end