Spectrum sensing using FFT Averaging Ratio (FAR) Algorithm

clc; clear; close all; Nu = 20; % Number Of Primary Users T = 200; % Number of frames N = 256; % FFT length w = rectwin(N); % Window function Tb = 0.4e-3; % Bit duration Ts = 1e-6/128; % Sampling time n_bits = 5; no_of_obs = n_bits; percentage_of_occupancy = 0.5; % Only 30 % of the Primary users are using channel SNR = -20; pf = 0.001; % Probability of false Alarm dt = ones(1,round(Tb/Ts)); t = Ts:Ts:Ts*round(n_bits*Tb/Ts); f = (20:1:20+((Nu-1)*1))*1e6; % band gap = 1 MHz carr = zeros(Nu,round(n_bits*Tb/Ts)); % Generate Carrier for each user for k = 1:Nu carr(k,:) = exp(1j*2*pi*f(1,k)*t); end % Generate Window function for each user for k = 1:T W(k,:) = w; end tt = rand(Nu,n_bits); PU_status = zeros(size(tt)); Sp = (sum(dt.^2)*Nu)/length(dt); No = Sp*10^(-0.1*SNR); Np = sqrt(No/2); data = double(rand(Nu,n_bits)>0.5); for k = 1:n_bits PU_status(:,k) = double(tt(:,k) < percentage_of_occupancy); end % PU_status = ones(size(tt)); data_1 = []; for k = 1:Nu temp = []; for p = 1:n_bits if data(k,p) == 1 temp = [temp PU_status(k,p)*dt]; else temp = [temp -PU_status(k,p)*dt]; end end data_1(k,:) = temp; end clear temp; data_up = zeros(size(carr)); % data_ch = zeros(size(carr)); for k = 1:Nu data_up(k,:) = data_1(k,:).*carr(k,:); % data_ch(k,:) = filter([1 randn(1,5)],1,data_up(k,:)); end data_rx = sum(data_up,1) + (Np*randn(1,length(data_up))); % no_of_obs = 1; temp = reshape(data_rx(1,1:no_of_obs*N*T),N*T,no_of_obs)'; for r = 1:no_of_obs temp1 = reshape(temp(r,:),N,T)'; % break the received sampled signal into T frames of N samples each P = abs(fft(temp1.*W,N,2)).^2; % Compute PSD P_avg = sum(P,1)/T; % Average power Pm = (2/(N+2))*sum(P_avg(1,1:round(N/2)+1)); % Mean Power Rk1 = P_avg/Pm; % Decision Parameter th =chi2inv(1-pf,Tb/Ts)*Ts/Tb; % Threshold % th = (max(Rk1) + min(Rk1))/2; status(r,:) = Rk1(1,41:2:40 + (2*Nu) - 1) > th; % status1(r,:) = Rk1(1,41:2:79) > th_2; thh = ones(1,length(status))*th; figure(1) subplot(no_of_obs,1,r) stem(f*1e-6,status(r,:),'*r') hold on stem(f*1e-6,PU_status(:,r),'k') xlabel(' Frequency in MHz'); ylabel(' Availability '); axis([19 40 -0.5 1.5]); title(' SNR = -40 dB'); hold off figure(2) subplot(no_of_obs,1,r) stem(f*1e-6,Rk1(1,41:2:40 + (2*Nu) - 1),'*r') hold on plot(f*1e-6,thh) xlabel('Frequency in MHz') ylabel(' Decision variable r(k) '); axis([19 40 -0.5 max(Rk1)]); title(' SNR = -40 dB'); hold off end