Problem with Maximum Likehood Detector's (for MIMO systems) Code!

Hi everyone, I wrote a code of a ML Detector for MIMO systems:

function sML= MLDet (x,H,C,N,M)

SNR=rand*40-10;

j=sqrt(-1);

iModulation=randi(3) %1=BPSK, 2=QPSK , 3=16QAM

mymodalalphabet = {[1,-1,1,-1], [1+j, 1-j, -1+j, -1-j], [1+j, 1-j, -1+j, -1-j, 3+j, 3-j, -3+j, -3-j,1+3j, 1-3j, -1+3j, -1-3j, 3+3j, 3-3j, -3+3j, -3-3j]}

symbset=mymodalalphabet{iModulation}

M= numel(symbset)

Eta= sqrt((1/SNR)/2)*(randn(4,1)+1j*randn(4,1)) ; % Eta= noise % sigma^2= 1/SNR

y= symbset(randi(3,4,1)); y=y'

H=randn(4,4)+j*randn(4,4);

x=H*y+Eta ;

v=[1/SNR 1/SNR 1/SNR 1/SNR];

C=diag (v);

mini= inf;

N= 4; % N=Number of the symbols

 for i=1:2^N
    for j= 1:N
        k= N-j+1;
        a=i-1;
        s(j)= a/2^(M*k);
        a= a-s(j)*2^(M*k);

    end
    end

    s= qammod(s,M);

    s=s'
    f=(x-H*s)'*inv(C)*(x-H*s);

     if f< mini
        mini=f;
         sML=s;
     end

sML

end

So if I run this programm , matlab says: ''Error using qammod (line 38) Elements of input X must be integers in the range [0, M-1].

Error in MLDet (line 40) s= qammod(s,M);''

I just tried to convert the vector s which is double according to Matlab to integers with s= int8(s), but it didn't work either. Because it gave me the error message: ''Error using *

Inner matrix dimensions must agree.

Error in MLDet (line 43) f=(x-H*s)'*inv(C)*(x-H*s);'' But i checked and s, x H etc. do have the right dimension. Not matter if I use s or s', this error message always comes.

So can you see where the actual problem is? Would be great if you can help me! Thank you. Ruifei

[Yu Jiang]

Hi Ruifei

Can you let me know what are the test inputs for the function? (What are the x,H,C,N,M you use when running the function)?

-Yu

[Ruifei]

Hi Yu,

H is the channel matrix

x is the received signal vector (x= Hy+Eta)

C is the covariance matrix

N is as I wrote in the code the number of the symbols,(number of channel inputs)

M is the alphabet size , e.g. M would be 16 if you have 16-QAM .

Ruifei

[Yu Jiang]

Can you provide a minimum code that can generate the input arguments and can be used to test the function? That would be really helpful.

-Yu