main.asv

运用matlab,实现16QAM调制与解调

clear all;
clc;

% % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %  %
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%       IEEE 802.11a based OFDM PHY program by You Li 2006.10.12         % 
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% % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %  % 

%%%  Program parameters are as following %%%%
% Working frequency: fc = 5.2GHz
% Bit rate: 24Mbps
% Number of data subcarriers: Nsd = 48
% Number of pilot subcarriers: Nsp = 4
% Number of total subcarriers: Nst = 52
% Subcarrier frequency spacing: fs = 0.3125MHz ( = 20MHz/64)
% Total bandwidth: ft = fs * Nst = 52 * 0.3125MHz = 16.25MHz
% IFFT/FFT period: T_FFT = 1/fs =1/0.3125M = 3.2us
% Guard interval: T_GI = T_FFT/4 = 3.2us/4 = 0.8us
% OFDM symbol period: T_sym = T_FFT + T_GI = 3.2+0.8 = 4us
% Coding: Convolutional code with coding rate R = 1/2
% Modulation: 16-QAM
% Coded bits per subcarrier: N_BPSC = 4;
% Coded bits per OFDM symbol: N_CBPS = 4 * 48 = 192
% Data bits per OFDM symbol: N_DBPS = N_CBPS * R = 192 * 1/2 = 96
% IFFT/FFT sampling point: 64, over sampling
% Sampling rate: f_s = 1/(T_FFT/64) = 1/(0.05us) = 20Msps 

diary IEEE802.11a_OFDM_PHY.txt

rand('state',sum(100*clock));%?
N_DBPS = 96;
N_SPF = input('Please enter the OFDM symbol number of each frame:\n');  % Number of OFDM symbols per fram 
frame_num = input('Please enter the number of frames: \n');
N_DBPF = N_DBPS * N_SPF - 6;   % Data bits per frame,minus the 6 tail bits to return the convolutional encoder to the "zero state"
fprintf('\nFrame size is %d OFDM symbols, and %d bits\n ',N_SPF, N_DBPF);
T_sym = 4 * 1e6;           % OFDM symbol period is 4us
fc = 5.2e9;                % Carrier frequency 5.2GHz
v = 2.7e3/3600;            % Vehicle speeed, 2.7km/h
f_max = v/3e8*fc;          % Maximum Dopper frequency, 13Hz 
T_start = rand(1) * 10^(-6);                    % A random starting time for simulation
channel_option = 1;
channel_response = channel_model(channel_option,f_max,frame_num,T_sym,T_start);   % Channel response of multipath Rayleigh fading channel during the simulation
                                                                                  % Assuming the channel response is invariant during one frame
pilot_sym = pilot_generator(128);               % Generate the pilot symbols, all in BPSK modulation
pilot_syms=pilot_sym';
pilot_syms=pilot_syms(:)';

for snr = 20:20
    nframe = 0;
    nerror = 0;
    while nframe < frame_num
        %======================
        %      Transmitter
        %======================
        info_bits = round(rand(1, N_DBPF));     % Generate the information bites randomly
        tail = zeros(1,6);                      % Tail bits for convolutional encoder
        info_bits = [info_bits tail];           % Append the tail bits to the infomation bits
        trl = poly2trellis(7,[133 171]);        % Trellis structure of convolutional encoder,
                                                % Constraint length K = 7,generator polynomial in octal g0 = 133, g1 = 171
        code_bits = convenc(info_bits, trl);    % Convolutional encoder,rate R = 1/2
        TX = tx_16qam_mod(code_bits); % 16-QAM modulation
        figure(1)
        a=real(TX);
        b=imag(TX);
        plot(a,b,'bx')
        pilot_num = 1;               % The start number of the cyclic pilot symbols 
        tx = tx_fre_to_time(TX,N_SPF,pilot_syms,pilot_num);    % Serial to parallel,Add pilot symbols, IFFT ( Oversampling),Add cyclic prefix                                      
        %======================
        %     Channel
        %======================
        temp_channel = channel_response(:,nframe+1).'; % Channel response at the current frame
        ry = channel_multipath(tx,temp_channel);      % Multi-path channel
        ry = awgn(ry,snr);                            % Add addictive white gaussian noise
        %======================
        %      Receiver
        %======================
        [RY,R_pilot] = ry_time_to_fre(ry,N_SPF,temp_channel); % Recover the time signal to frequency symbols of each subcarrier and Channel Equalization
        figure(2)
        a=real(RY);
        b=imag(RY);
        plot(a,b,'bx')
        axis([-2 2  -2 2]);
        hold on
        Rcode_bits = ry_16qam_demod(RY);                        % Demodulate the received symbols
        dec_bits = ry_sovadec(Rcode_bits, trl, N_DBPF,N_DBPF);  % Soft output viterbi decoding, out = ln( p(info_bits(i)=1)/p(info_bits(i)=0));
        %======================
        %   Error detection
        %======================      
        for i = 1:N_DBPF
            if dec_bits(i) >= 0
                hard_det(i) = 1;                                % hard_det refers to the hard decision   
            else 
                hard_det(i) = 0;
            end
            if hard_det(i) ~= info_bits(i)
                nerror = nerror+1;
            end
        end
        nframe = nframe + 1;
    end
    BER = nerror/(frame_num * N_DBPF);
    fprintf('\nSNR is %1.2f dB, BER is %e\n ',snr,BER);
end