Matlab实现基于OFDM信号的能量频谱感知算法

clear; close all; clc; % OFDM Simulation % % - ECE 5664 Project % - Erich Cosby % - December 4, 2001 % - Virginia Tech, Nothern Va. Center % % Based on the matlab work of Eric Lawrey in his 1997 BSEE thesis, % "The suitability of OFDM as a modulation technique for wireless % telecommunications, with a CDMA comparison", % refer to www.eng.jcu.edu.au/eric/thesis/Thesis.htm. % % % Basic OFDM system parameters % - choice of defaults or user selections % fprintf ('OFDM Analysis Program\n\n'); defaults = input('To use default parameters, input "1", otherwise input "0": ');%default if defaults == 1 IFFT_bin_length = 1024; % IFFT bin count for Tx, FFT bin count for Rx carrier_count = 200; % number of carriers bits_per_symbol = 2; % bits per symbol symbols_per_carrier = 50; % symbols per carrier SNR = 10; % channel signal to noise ratio (dB) else IFFT_bin_length = input('IFFT bin length = '); carrier_count = input('carrier count = '); bits_per_symbol = input('bits per symbol = '); symbols_per_carrier = input('symbols per carrier ='); SNR = input('SNR = '); end % % Derived parameters % baseband_out_length = carrier_count * symbols_per_carrier * bits_per_symbol; carriers = (1:carrier_count) + (floor(IFFT_bin_length/4) - floor(carrier_count/2)); conjugate_carriers = IFFT_bin_length - carriers + 2; % TRANSMIT >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> % % % Generate a random binary output signal % - a row of uniform random numbers (between 0 and 1), rounded to 0 or 1 % - this will be the baseband signal which is to betransmitted. % baseband_out = round(rand(1,baseband_out_length)); % % Convert to 'modulo????? N' integers where N = 2^bits_per_symbol % - this defines how many states each symbol can represent % - first, make a matrix with each column representing consecutive bits % from the input stream and the number of bits in a column equal to the % number of bits per symbol % - then, for each column, multiply each row value by the power of 2 that % it represents and add all the rows % - for example: input 0 1 1 0 0 0 1 1 1 0 % bits_per_symbol = 2 % convert_matrix = 0 1 0 1 1 % 1 0 0 1 0 % % modulo_baseband = 1 2 0 3 2 % convert_matrix = reshape(baseband_out, bits_per_symbol, length(baseband_out)/bits_per_symbol); for k = 1:(length(baseband_out)/bits_per_symbol) modulo_baseband(k) = 0; for i = 1:bits_per_symbol modulo_baseband(k) = modulo_baseband(k) + convert_matrix(i,k)*2^(bits_per_symbol-i); end end % Serial to Parallel Conversion % - convert the serial modulo N stream into a matrix where each column % represents a carrier and each row represents a symbol % - for example: % % serial input stream = a b c d e f g h i j k l m n o p % % parallel carrier distribution = % C1/s1=a C2/s1=b C3/s1=c C4/s1=d % C1/s2=e C2/s2=f C3/s2=g C4/s2=h % C1/s3=i C2/s3=j C3/s3=k C4/s3=l % . . . . % . . . . % carrier_matrix = reshape(modulo_baseband, carrier_count, symbols_per_carrier)'; % % Apply differential coding to each carrier string % - append an arbitrary start symbol (let it be 0, that works for all % values of bits_per_symbol) (note that this is done using a vertical % concatenation [x;y] of a row of zeros with the carrier matrix, sweet!) % - perform modulo N addition between symbol(n) and symbol(n-1) to get the % coded value of symbol(n) % - for example: % bits_per_symbol = 2 (modulo 4) % symbol stream = 3 2 1 0 2 3 % start symbol = 0 % % coded symbols = 0 + 3 = 3 % 3 + 2 = 11 = 1 % 1 + 1 = 2 % 2 + 0 = 2 % 2 + 2 = 10 = 0 % 0 + 3 = 3 % % coded stream = 0 3 1 2 2 0 3 % % carrier_matrix = [zeros(1,carrier_count);carrier_matrix]; for i = 2:(symbols_per_carrier + 1) carrier_matrix(i,:) = rem(carrier_matrix(i,:)+carrier_matrix(i-1,:),2^bits_per_symbol); end % % Convert the differential coding into a phase % - each phase represents a different state of the symbol % - for example: % bits_per_symbol = 2 (modulo 4) % symbols = 0 3 2 1 % phases = % 0 * 2pi/4 = 0 (0 degrees) % 3 * 2pi/4 = 3pi/2 (270 degrees) % 2 * 2pi/4 = pi (180 degrees) % 1 * 2pi/4 = pi/2 (90 degrees) % carrier_matrix = carrier_matrix * ((2*pi)/(2^bits_per_symbol)); % % Convert the phase to a complex number % - each symbol is given a magnitude of 1 to go along with its phase % (via the ones(r,c) function) % - it is then converted from polar to cartesian (complex) form % - the result is 2 matrices, X with the real values and Y with the imaginary % - each X column has all the real values for a carrier, and each Y column % has the imaginary values for a carrier % - a single complex matrix is then generated taking X for real and % Y for imaginary [X,Y] = pol2cart(carrier_matrix, ones(size(carrier_matrix,1),size(carrier_matrix,2))); complex_carrier_matrix = complex(X,Y); % Assign each carrier to its IFFT bin % - each row of complex_carrier_matrix represents one symbol period, with % a symbol for each carrier % - a matrix is generated to represent all IFFT bins (columns) and all % symbols (rows) % - the phase modulation for each carrier is then assigned to the % appropriate bin % - the conjugate of the phase modulation is then assigned to the % appropriate bin % - the phase modulation bins and their conjugates are symmetric about % the Nyquist frequency in the IFFT bins % - since the first bin is DC, the Nyquist Frequency is located % at (number of bins/2) + 1 % - symmetric conjugates are generated so that when the signal is % transformed to the time domain, the time signal will be real-valued % - example % - 1024 IFFT bins % - bin 513 is the center (symmetry point) % - bin 1 is DC % - bin 514 is the complex conjugate of bin 512 % - bin 515 is the complex conjugate of bin 511 % - .... % - bin 1024 is the complex conjugate of bin 2 (if all bins % were used as carriers) % - So, bins 2-512 map to bins 1024-514 % IFFT_modulation = zeros(symbols_per_carrier + 1, IFFT_bin_length); IFFT_modulation(:,carriers) = complex_carrier_matrix; IFFT_modulation(:,conjugate_carriers) = conj(complex_carrier_matrix); % % PLOT BASIC FREQUENCY DOMAIN REPRESENTATION % figure (1) stem(0:IFFT_bin_length-1, abs(IFFT_modulation(2,1:IFFT_bin_length)),'b*-') grid on axis ([0 IFFT_bin_length -0.5 1.5]) ylabel('Magnitude') xlabel('IFFT Bin') title('OFDM Carrier Frequency Magnitude') figure (2) plot(0:IFFT_bin_length-1, (180/pi)*angle(IFFT_modulation(2,1:IFFT_bin_length)), 'go') hold on stem(carriers-1, (180/pi)*angle(IFFT_modulation(2,carriers)),'b*-') stem(conjugate_carriers-1, (180/pi)*angle(IFFT_modulation(2,conjugate_carriers)),'b*-') axis ([0 IFFT_bin_length -200 +200]) grid on ylabel('Phase (degrees)') xlabel('IFFT Bi