i'm using comm.MIMOChannel. i have problem varying 4x4,8x8 in [chanOut,pathGains] = step(hChan,encData); this...help me... how to rectify that

clc close all clear all % rng default warning off %% input decleration numTx =4; % Number of transmit antennas numRx =4; % Number of receive antennas Rs = 1e6; % Sampling rate (Hz) tau = [0 2e-6]; % Path delays (sec) pdb = [0 -10]; % Average path gains (dB) maxDopp = 30; % Maximum Doppler shift (Hz) numBits = 16; % Number of bits SNR= 25; % Signal-to-noise ratio (dB) block_size = 16; % fixing the block size for cyclic prefix data = randi([0 1],numBits,1); %generating random input data hMod = comm.QPSKModulator(... 'BitInput',true,... 'SymbolMapping','Gray'); hDemod = comm.QPSKDemodulator(... 'SymbolMapping','Gray',... 'BitOutput',true); hOSTBCEnc = comm.OSTBCEncoder(... 'NumTransmitAntennas',numTx); hOSTBCComb = comm.OSTBCCombiner(... 'NumTransmitAntennas',numTx,... 'NumReceiveAntennas',numRx); hChan = comm.MIMOChannel('SampleRate',Rs,... 'PathDelays',tau,... 'AveragePathGains',pdb,... 'MaximumDopplerShift',maxDopp,... 'NumTransmitAntennas',numTx,... 'NumReceiveAntennas',numRx,... 'PathGainsOutputPort',true); hAWGN = comm.AWGNChannel(... 'NoiseMethod','Signal to noise ratio (SNR)',... 'SNR',SNR,... 'SignalPower',1); modData = step(hMod,data);

    %Qpsk modulation
    cp_len = floor(0.5 * length(modData));                       %Length of the cyclic prefix fixing
    ofdm_signal=ofdm_transmission(modData,cp_len);               %initilization cyclic prefix & ifft
    encData = step(hOSTBCEnc,ofdm_signal);                       %STBC encoder
    [chanOut,pathGains] = step(hChan,encData);
    [rxSignal] = step(hAWGN,chanOut);                              %applying in channel
    % rxSignal = chanOut;
    chEst = squeeze(sum(pathGains,2));                           %channel estimation
    combinedData = step(hOSTBCComb,rxSignal,chEst);              %STBC decoder
    recvd_serial_data=ofdm_reciving(combinedData,cp_len);        %removing cyclic prefix & ifft
    receivedData = step(hDemod,recvd_serial_data);               %demodulation
    [numErrors,ber] = biterr(data,receivedData); 
    numErrors