To find the rms value

%Generate bit sequence
bit_seq=[1 0 0 1 1 0 1 1];
%Consider bit period. This also defines the bit frequency/data rate
%Data rate=1MHz
bit_period=0.000001; 

%There are 8 bits in the sequence. The period for each bit is 0.000001
%Hence the time scale will be in the range of 0 to 8*10^-6 for 8 bits

t1=bit_period/1000:(bit_period/1000)*1:1000*length(bit_seq)*(bit_period/1000);
bit=[]; 
for n=1:1:length(bit_seq)
    if bit_seq(n)==1;
       se=ones(1,1000);
    else bit_seq(n)==0;
        se=zeros(1,1000);;
    end
     bit=[bit se];
end

subplot(3,1,1)
plot(t1,bit,'g','linewidth',1)
xlabel('Time')
ylabel('Amplitude')
title('Bit Sequence')

t2=0:0.001:1-(0.001);
sigma=.1;
mymean=0.5;
b=2*(sigma)^2;
g=exp((-(t2-mymean).^2)/b);

%Generation of gaussian signal for the bits
bit1=[]; 
for n=1:1:length(bit_seq)
    if bit_seq(n)==1;
       se=exp((-(t2-mymean).^2)/b);
    else bit_seq(n)==0;
        se=0*exp((-(t2-mymean).^2)/b);
    end
     bit1=[bit1 se];
end
     
subplot(3,1,2)
plot(t1,bit1,'r','linewidth',1)
xlabel('Time')
ylabel('Amplitude')
title('Gaussian signal')

y1=(bit1.^2)
b=length(y1)
sum1=0; for i=1:b
    sum1= sum1+i;
end
disp(sum1)
mean1=sum1/b;
rms=sqrt(mean1)


%y2=mean(y1,'all')
%Finding the RMS Value of the gaussian signal
RMS1=sqrt(mean(bit1.^2));
disp(RMS1)

%Addition of noise. We need to add the noise to the gaussian 
%signal. Consider the vector of the gaussian signal=bit1

L=length(bit1);
disp(L)
SNR_dB=13.6;
SNR = 10^(SNR_dB/10); %SNR to linear scale
disp(SNR)
Esym=sum(abs(bit1).^2)/(L)%Calculate actual symbol energy
disp(Esym)
N0=Esym/SNR; %Find the noise spectral density
disp(N0)
if(isreal(bit1)),
 noiseSigma = sqrt(N0);%Standard deviation for AWGN Noise when x is real
 n = noiseSigma*randn(1,L);%computed noise
 else
 noiseSigma=sqrt(N0/2);%Standard deviation for AWGN Noise when x is complex
 n = noiseSigma*(randn(1,L)+1i*randn(1,L));%computed noise
 end
 y = bit1 + n; %received signal
 
subplot(3,1,3)
plot(t1,y,'o','linewidth',1)
xlabel('Time')
ylabel('Amplitude')
title('Gaussian signal with noise')

Iam getting an error at line 73 saying,

Array indices must be positive integers or logical values.

Error in ask_gaussian_rms (line 73)

Esym=sum(abs(bit1).^2)/(L)%Calculate actual symbol energy

[KSSV]

It should no tthrow any error actually. Check did you define any variable with the name sum?

What does which sum show?

Answer 1

[Adam Danz]

My bet is that you have a variable in the worksapace named "abs" which overrides Matlab's abs() function.

When you run the line below, abs(bit1) is not taking the absolute value of bit1. Instead, it's treating bit1 like a vector of indices and indicies must be positive integers or logical values as the error indicates. Instead, bit1 contains floating point decimals.

Esym=sum(abs(bit1).^2)/(L)

Solution: remove the variable 'abs' using clear('abs') or rename the variable.