What should I do if I am getting different output every time I run my code in MATLAB code to obtain Bit error rate of BPSK modulation for the given data-[1 0 0 0 0 1 1 1]

%BER of BPSK for given data=[1 0 0 0 0 1 1 1]

clc;

clear all;

close all;

%input data

N=8;

m=[1 0 0 0 0 1 1 1];

x=zeros(1, N); %preallocating variable

for i=1:N

if m(i)==0

x(i)=-1;

else

x(i)=1;

end

end

ber_sim=[]; %empty array for bit error rate

ber_theory_erfc=[]; %empty array for theoretical bit error rate

ber_theory_Q=[]; %empty array for Q equation

ber_chernoff=[]; % BER approximation for upper bound(chernoff bound)

for EbN0dB=0:1:15 %SNR value in dB

EbN0=10^(EbN0dB/10); %convert to normal scale

sigma=sqrt(1/(2*EbN0));

r=x+sigma.*randn(1,N); %AWGN channel with random numbers

m_cap=(r>0); %detected bits, threshold=0

%BER calculation

noe=sum(m~=m_cap); %number of errors, sum if m is not equal to m_cap

ber_sim1=noe/N; %bit error rate calculation with simulation values

ber_sim=[ber_sim ber_sim1];

ber_th_er=0.5*erfc(sqrt(EbN0)); %theoretical bit error rate calculation

ber_theory_erfc=[ber_theory_erfc ber_th_er];

ber_th_q=qfunc(sqrt(2*EbN0)); %bit error rate in terms of Q function

ber_theory_Q=[ber_theory_Q ber_th_q];

ber_cher=0.5*exp(-EbN0); %highest possible bit error rate

ber_chernoff=[ber_chernoff ber_cher];

end

EbN0dB=0:1:15;

semilogy(EbN0dB,ber_sim,'r*-',EbN0dB,ber_theory_erfc,'ko-',EbN0dB,ber_theory_Q,'g+-',EbN0dB,ber_chernoff,' m>-');

xlabel('Eb/N0(dB)');

ylabel('BER');

legend('Simulation','Theory(erfc)','Theory(Q)','Chernoff');

grid on;

Answer 1

[KALYAN ACHARJYA]

Because of the following line (function randn)you are getting different results each time, may be random noise addition

r=x+sigma.*randn(1,N); %AWGN channel with random numbers
%............^

[Nikshith Shetty]

I asked one of my matlab professor and he said the same thing, that i didn't need to change the code and for our level this much is enough.

[KALYAN ACHARJYA]

:)