CDMA MATLAB Code for Simulation

This section provides MATLAB source code related to CDMA (Code Division Multiple Access).

CDMA MATLAB simulation code

As shown in the figure, CDMA employs codes to modulate user data, thereby spreading it in the transmitter. The same code is used at the receiver for despreading. In an actual CDMA system, the base station allocates different codes to different users. Only the user possessing the correct code can retrieve their information.

The block diagram covers the CDMA transmitter and receiver. The CDMA transmitter consists of an FEC encoder (convolution encoder), a BPSK modulator, and a spreading module. The CDMA receiver consists of reverse modules of the transmitter part, namely despreading, BPSK demodulator, and Viterbi decoder.

Following is the CDMA MATLAB code and BER curve. The BER curve is obtained after passing the data through AWGN (Additive White Gaussian Noise).

CDMA MATLAB Code for 1 User

n1=1;
n2=14;
FFT_SIZE=256;
%CP=16;
conv_in=[];

%% Data Generator
Data_gen = randint(1,11,255)
Data_IN=dec2bin(Data_gen);
s=0;

%% BER PARAMETERS
EbNo=0:1:15;
BER = zeros(1,length(EbNo));
numPackets=15;
frmLen = 1000;

for idx = 1: length(EbNo)
    for packetidx = 1 : numPackets

        %% Convolution Encoder
        conv_in=[];
        for index =1:11
            conv_in=[conv_in double(Data_IN(index,:))-48];
        end
        conv_in=[conv_in 0 0 0 0 0 0 0 0]; %%8 bits padding
        DIN=conv_in;
        trel = poly2trellis(7, [171 133]); % Define trellis.
        code = convenc(conv_in,trel);
        inter_out=code;

        %% BPSK Data Mapping
        mapper_out=mapping(inter_out',1,1);
        clear inter_out;
        D=mapper_out;

        %% CDMA MATLAB TRANSMITTER
        % encode bits and transmit
        % CDMA specific parameters
        C = [  -1  1 -1  1 ]; % code for the user which will be multiplied with %data stream of the user#1 i.e.mapper_out
        M = length(C); % length (number of bits) of code
        Y = size(mapper_out);
        N = Y(1); % number of unique senders / bit streams
        I = Y(2); % number of bits per stream
        T = []; % sum of all transmitted and encoded data on channel
        RECON = []; % vector of reconstructed bits at receiver
        G = zeros(I,M);
        for n = 1:N
            Z = zeros(I,M);
            for i = 1:I
                for m = 1:M
                    Z(i,m) = [D(n,i)*C(n,m)];
                end
            end
            G = G + Z; %G is the data to be transmitted after IFFT
        end

        %% Adding AWGN
        G = awgn(G./sqrt(16), EbNo(idx) , 'measured');
        G = awgn(G./sqrt(16), EbNo(idx) , 'measured');
        G = awgn(G./sqrt(16), EbNo(idx) , 'measured');

        %% CDMA MATLAB RECEIVER
        for n = 1:N
            TOT = zeros(1,I);
            R = zeros(I,M);
            for i = 1:I
                for m = 1:M
                    R(i,m) = G(i,m) * C (n,m);
                    TOT(i) = TOT(i) + R (i,m);
                end
            end
            RECON = [RECON ; TOT / M];
        end
        RECON
        rx_data1=RECON;
        Demap_out=demapper(rx_data1,1,1);

        %%viterbi decoder
        vit_out=vitdec(Demap_out,trel,7,'trunc','hard');
        DOUT=vit_out;
        [number,ratio] = biterr(DIN,vit_out);
        error(packetidx) = biterr(DIN,vit_out);

    end % End of for loop for numPackets
    BER21(idx) = sum(error)/(log2(4)*numPackets*frmLen);
end

h=gcf;clf(h);
grid on;
hold on;
set(gca,'yscale','log','xlim',[EbNo(1), EbNo(end)],'ylim',[0 1]);
xlabel('Eb/No (dB)');
ylabel('BER');
set(h,'NumberTitle','off');
set(h,'Name','BER Results');
set(h, 'renderer', 'zbuffer');
title('CDMA alone BER PLOTS');
semilogy(EbNo(1:end),BER21(1:end),'b-*');

CDMA BER curve