function [p_MMSE]=MMSE_Q(snr_in_dB)
% Wireless Communications   
% ZF & MMSE : Simulation
E=1;
tap=2;
SNR=10^(snr_in_dB/10);
sgma=E/sqrt(SNR);
p_MMSE=0;
N=5000;
for i=1:N,
    x=1/sqrt(2)*(sign(randn(2,1))+sqrt(-1)*sign(randn(2,1)));
    h0=(randn(2,1)+j*randn(2,1))*sqrt(1/2);
    h1=(randn(2,1)+j*randn(2,1))*sqrt(1/2);
    % pass the channel
    H=diag(h0)+diag(h1(1:tap-1),-1);
    y=H*x;
    % add AWGN
    y=y+(randn(2,1)+j*randn(2,1))*sgma/sqrt(2);
 
    % MMSE equalizer
    Ryy=H*H'+sgma^2*eye(tap);
    Ryx=H;
    C=(inv(Ryy)*Ryx)';
    d=1/sqrt(2)*(sign(real(C*y))+sign(imag(C*y))*sqrt(-1));
    p_MMSE=p_MMSE+sum(x~=d);
end;
p_MMSE=p_MMSE/tap/N;