How to compute Eb/No

Hello, I am trying to compute the Eb/No of a signal after an AWGN channel. I use a known Eb/No value on the AWGN channel and in the end I need to check that the AWGN is working as expected by confirming that the Eb/No value set is the same as the one I compute after it. The system is just a M-QAM modulator, an AWGN channel and this Eb/No computation. Why is not working? Thank you very much in advance.

clear all
M=4;
k=log2(M);
n=1000;% #_symbols
EbNo=20;
snr_ = EbNo+3+10*log10(k);
h  = comm.RectangularQAMModulator(M);
for jj = 1:1:512
    k = log2(M);
    x = randi([0 M-1],n,1);

      y = step(h,x);
          ypower(jj)=10*log10((y' * y)/ length(y));

      y2=awgn(y,snr_,ypower(jj));
          y2power(jj)=10*log10((y2' * y2)/ length(y2));

          SNR2(jj) = snr(y,y2);

          EbNo(jj)=SNR2(jj)-(10*log10(k))-3;
  end

[VIVEK JOSHI]

SNR = Eb/No + 10*log10(k)- 10*log10(nsamp),, clearly you are using some particular form of this formula