Converting 4 QAM to 16 QAM - 16 QAM produces error when generating signal

clear all close all clc T=10000; dB=40; % SNR value(dB)

N=12; Lh=5; M=2; % fractional (Ts/M)

h=randn(M,Lh+1)+sqrt(-1)*randn(M,Lh+1); for i=1:M, h(i,:)=h(i,:)/norm(h(i,:)); end

 s=round(rand(1,T))*2-1;  % QPSK or 4 QAM symbol sequence
 s=s+sqrt(-1)*(round(rand(1,T))*2-1);

% Produce a noisy signal x=zeros(M,T); SNR=zeros(1,M); for i=1:M x(i,:)=filter(h(i,:),1,s); vn=randn(1,T)+sqrt(-1)*randn(1,T); vn=vn/norm(vn)*10^(-dB/20)*norm(x(i,:)); SNR(i)=20*log10(norm(x(i,:))/norm(vn)); x(i,:)=x(i,:)+vn; end SNR=SNR;

Lp=T-N; X=zeros((N+1)*M,Lp); for i=1:Lp for j=1:M X((j-1)*(N+1)+1:j*(N+1),i)=x(j, i+N:-1:i).'; end end

e=zeros(1,Lp); f=zeros((N+1)*M,1); f(N*M/2)=1; R2=2.0; mu=0.0012; for i=1:Lp e(i)=abs(f'*X(:,i))^2-R2; % Momentary error f=f-mu*2*e(i)*X(:,i)*X(:,i)'*f; % Equalizer update equation end

sb=f'*X;

    figure 
    plot(s,'s');  
    grid,title('Gonderilen semboller');  xlabel('Reel'),ylabel('Sanal')
    axis([-2 2 -2 2])

    figure 
    plot(x,'o');  % kanal ve gürültü ile bozulmuþ alýnan sembollerin çizimi
    grid, title('Alinan ornekler');  xlabel('Reel'), ylabel('Sanal')

    figure 
    plot(sb,'o');   % denkleþtirilen sembollerin çizimi
    grid, title('Denklestirilen Semboller'), xlabel('Reel'), ylabel('Sanal')

    figure 
    plot(abs(e)/100);   % show the convergence
    %semilogy(abs(e)/100,'b-p');
    grid, title('Kor Ogrenme Egrisi'), xlabel('Ogrenme Adimi'), ylabel('MSE')