gusucode.com > MIMO与SISO仿真程序 > MIMO-OFDM/results_SISO_v1.m
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% Student: Benjamin Pham
% ID: 25957066
%
% Version: Final
% Changes:
% Description: a 1x1 SISO OFDM System
%
% Simulates a 1x1 SISO OFDM system. This system includes the
% Transmitter:
% QAM Modulation, S/P converter, Pilot Insertion IFFT, Add Cyclic Prefix,
% P/S converter
% Channel:
% Frequency flat fading Channel modelled by Complex number, AWGN,
% Time Offset
% Receiver:
% S/P converter, Removal of Cyclic Prefix, DFT, Channel estimation,
% Channel equalisation, 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 138 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
% Pilot Symbols
PS = 1;
% Data Symbols
DS = n_fft - PS;
% OFDM frame length
OFDM = n_fft + n_cp;
% Signal to Noise Ratios for AWGN
snr = [0:1:30];
% Channel modelled by random complex number
h = [randn()+randn()*1i];
% Initialise variables
errors = zeros(size(snr));
ber = zeros(size(snr));
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%% TRANSMITTER %%
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% Generate binary data
binary_data = round(rand(data,1));
%% 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
pilot = [0 1]';
% Padding for symbol mapping
while floor(length(binary_data)/symbols) ~= length(binary_data)/symbols
binary_data = [binary_data; zeros(1,1)];
end
% Padding for subcarriers mapping
while floor(length(binary_data)/symbols/DS) ~= length(binary_data)/symbols/DS
binary_data = [binary_data; zeros(1,1)];
end
elseif mod_type == 2 % Modulation Type: 16QAM
symbols = 4;
pilot = [0 0 0 1]';
% Padding for symbol mapping
while floor(length(binary_data)/symbols) ~= length(binary_data)/symbols
binary_data = [binary_data; zeros(1,1)];
end
% Padding for subcarriers mapping
while floor(length(binary_data)/symbols/DS) ~= length(binary_data)/symbols/DS
binary_data = [binary_data; zeros(1,1)];
end
elseif mod_type == 3 % Modulation Type: 64QAM
symbols = 6;
pilot = [0 0 0 0 0 1]';
% Padding for symbol mapping
while floor(length(binary_data)/symbols) ~= length(binary_data)/symbols
binary_data = [binary_data; zeros(1,1)];
end
% Padding for subcarriers mapping
while floor(length(binary_data)/symbols/DS) ~= length(binary_data)/symbols/DS
binary_data = [binary_data; zeros(1,1)];
end
end
% Mapping binary data onto constellation maps
mod_method = 2^symbols;
mod_data = qammod(binary_data,mod_method,'unitaveragepower',true,'inputtype','bit');
pilot = qammod(pilot,mod_method,'unitaveragepower',true,'inputtype','bit');
Tx1 = mod_data;
%% Serial to Parallel Conversion
% serial stream into subcarriers
Xk1 = reshape(Tx1,DS,length(Tx1)/DS);
%% Pilot Insertion
Xk1_p = [ones(1,length(Xk1))*pilot;Xk1];
%% Inverse Fast Fourier Transform
Xn1 = ifft(Xk1_p);
%% Cyclic prefix
Xn1_cp = [Xn1((end - n_cp + 1):end,:);Xn1];
%% Parallel to Serial Conversion
xn1 = Xn1_cp(:);
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%% Channel %%
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%% BER test for different SNR
for k = 1:length(snr)
%% Data passing through Channel
% y time, receiver
yn11 = xn1*h(1,1); % Tx1 to Rx1
%% add noise
dB = snr(k);
yn11 = awgn(yn11,dB,'measured');
%% offset added to between transmitter 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 Tx1 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
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
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%% RECEIVER %%
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%% Serial to Parallel Conversion
yn1_sp = reshape(yn11,OFDM,size(Xn1_cp,2));
%% Remove cyclic prefix
yn1_rcp = yn1_sp((n_cp + 1):end,:);
%% Discrete fourier transform
Yk1_block = fft(yn1_rcp);
%% Channel Estimation
% because we send pilot symbols, we can estimate the channel. symbols that
% are known beforehand. So its the received signal divided by the pilot
% symbol.
Yk1_DS = Yk1_block(2:64,:);
Yk1_pilot = Yk1_block(1,:);
H_hat = Yk1_pilot./pilot;
%% Channel equalisation
% zero forcing / Least Squares method
H_hate = mean(H_hat); % average of estimated channel
Yk1_block2 = Yk1_DS./H_hate; % cancelling out the channel effects
%% Parallel to serial conversion
Yk1 = Yk1_block2(:);
%% QAM demodulation
X_demod = qamdemod(Yk1,mod_method,'unitaveragepower',true,'outputtype','bit');
output = X_demod(:).';
%% Calculating BER
errors(mod_type,k) = 0;
for i = 1:length(binary_data)-n_fft*symbols
if output(i+n_fft*symbols) ~= binary_data(i+n_fft*symbols)
errors(mod_type,k) = errors(mod_type,k) + 1;
end
end
ber(mod_type,k) = errors(mod_type,k)/length(binary_data);
end
% Plotting BER vs Eb/No
semilogy(snr-10*log10(symbols),ber(mod_type,:),'-');
title('Single transmitter Single Receiver'); legend('4QAM','16QAM','64QAM');
xlabel('E_b/N_o (dB)'); ylabel('BER'); grid on; hold on
end