CDMA MATLAB Code

This section of MATLAB source code covers CDMA MATLAB code. CDMA stands for Code Division Multiple Access.

As shown in the figure, CDMA uses codes to modulate the user data for spreading in the transmitter. The same code is used at the receiver for despreading. In actual CDMA system base station allocates different codes to different users. Only the user having the correct code can only retrieve its information back.

The block diagram covers CDMA transmitter and CDMA receiver. CDMA transmitter consists of FEC encoder(convolution encoder), BPSK modulator and spreading module. CDMA receiver consists of reverse modules of transmitter part viz. despreading, BPSK demodulator and viterbi decoder.

Following is the CDMA matlab code and BER curve. BER curve is obtained after passing the data through the AWGN.

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-*');

BER Curve

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