How can I simulate the MIMO section only?

I am using the example found here: https://uk.mathworks.com/help/phased/ug/improve-snr-and-capacity-of-wireless-communication-using-antenna-arrays.html?searchHighlight=ULA%20MIMO&s_tid=srchtitle_support_results_24_ULA%2520MIMO

How can I just simulate the MIMO section without using the helperMIMOBER function in the example? as the version of MATLAB I am using does not support the function nargin.

I need to simulate this so I can compared existing SISO results which I have obtained previously.

[Sam Chak]

Hi @Liam, I couldn't locate the custom helperMIMOBER() function in the provided link. However, @Star Strider shared the function in this comment, and the nargin command is not a new command or function.

function nber = helperMIMOBER(chan, x, snr_param, wt, wr) 
    Nsamp   = size(x,1);
    Nrx     = size(chan,2);
    Ntx     = size(chan,1);
    
    if nargin < 4
        wt = ones(1,Ntx);
    end
    
    if nargin < 5
        wr = ones(Nrx,1);
    end 
    
    xt      = 1/sqrt(Ntx)*(2*x-1)*wt; % map to bpsk
    nber    = zeros(Nrx,numel(snr_param),‘like’,1); % real
    
    for m = 1:numel(snr_param)
        n   = sqrt(db2pow(-snr_param(m))/2)*(randn(Nsamp,Nrx)+1i*randn(Nsamp,Nrx));
        y   = xt*chan*wr+n*wr;
        xe  = real(y)>0;
        nber(:,m) = sum(x~=xe);
    end
end

[Liam]

But what I am stuck with is how this: xt = 1/sqrt(Ntx)*(2*x-1)*wt maps to BPSK. and how would i map it to QPSK? would I square it or multiply it all by 2?

[Hengrun]

Hello Liam,

I'm afraid you cannot. QPSK is different in mapping."(2*x-1)"is used to map 1s,0s to 1 and -1. You can for sure use 1/sqrt(Ntx). For the mapping part, you can choose to use pskmod or qammod.

Answer 1

[Sam Chak]

While I'm not an expert in BPSK and QPSK, I haven't encountered any problems when running the script in the link you provided and 'helperMIMOBER()' code on this MATLAB Answers forum.

%% The Script:
c           = 3e8;      % propagation speed
fc          = 60e9;     % carrier frequency
lambda      = c/fc;     % wavelength
txcenter    = [0;0;0];
rxcenter    = [1500;500;0];
[~,txang]   = rangeangle(rxcenter,txcenter);
[~,rxang]   = rangeangle(txcenter,rxcenter);
txsipos     = [0;0;0];
rxsopos     = [0;0;0];
g           = 1;        % gain for the path
sisochan    = scatteringchanmtx(txsipos,rxsopos,txang,rxang,g);
Nsamp       = 1e6;
x           = randi([0 1],Nsamp,1);
ebn0_param  = -10:2:10;
Nsnr        = numel(ebn0_param);

% Now, we call the helperMIMOBER() function:
ber_siso    = helperMIMOBER(sisochan,x,ebn0_param)/Nsamp

ber_siso = 1x11

0.3274 0.2866 0.2396 0.1861 0.1310 0.0789 0.0374 0.0123 0.0023 0.0002 0.0000

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%% the helperMIMOBER() function
function nber = helperMIMOBER(chan, x, snr_param, wt, wr) 
    Nsamp   = size(x,1);
    Nrx     = size(chan,2);
    Ntx     = size(chan,1);
    
    if nargin < 4
        wt = ones(1,Ntx);
    end
    
    if nargin < 5
        wr = ones(Nrx,1);
    end 
    
    xt      = 1/sqrt(Ntx)*(2*x-1)*wt; % map to bpsk
    nber    = zeros(Nrx,numel(snr_param), 'like', 1); % real
    
    for m = 1:numel(snr_param)
        n   = sqrt(db2pow(-snr_param(m))/2)*(randn(Nsamp,Nrx)+1i*randn(Nsamp,Nrx));
        y   = xt*chan*wr+n*wr;
        xe  = real(y)>0;
        nber(:,m) = sum(x~=xe);
    end
end