MATLAB code for QAM constellation

 

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MATLAB Script

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clc;clear all;close all;

M = 4;  % Number of levels after quantization / size of signal constellation

k = log2(M);  % Number of bits per symbol

rng(1)  %assaining the value of seed integer

N =5000;  % Number of bits to process

dataIn = randi([0 1],1,N);   % Generating randon bits

dataInMatrix = reshape(dataIn,length(dataIn)/k,k); % Reshape data into binary k-tuples, k = log2(M)

dataSymbolsIn = bi2de(dataInMatrix);  % Convert binary to decimal

for n= 1:N/k

    if dataSymbolsIn(n)==0

        QAM(n)= complex(1,1);

    elseif dataSymbolsIn(n)==1

        QAM(n)= complex(-1,1);

    elseif dataSymbolsIn(n)==2

        QAM(n)= complex(1,-1);

    else

        QAM(n)= complex(-1,-1);

    end

  

end

display(dataIn,'First fifty bits');

display(QAM,'first twenty-five4-QAM symbols');

%Transmission of 4QAM data over AWGN channel

snrdB =8;

Y=awgn(QAM,snrdB); %received signal

%Threshold Detection

    for n= 1:N/k

        if (real(Y(n))>0 && imag(Y(n))>0)

            Z(n)=complex(1,1);

    elseif (real(Y(n))>0 && imag(Y(n))<0)

            Z(n)=complex(1,-1);

    elseif (real(Y(n))<0 && imag(Y(n))>0)

            Z(n)=complex(-1,1);

        else

            Z(n)=complex(-1,-1);

        end

    end

sPlotFig = scatterplot(Y,1,0,'g.');

hold on

scatterplot(QAM,1,0,'k*',sPlotFig)

legend('received','transmitted')

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Output