about the SampleRate of the comm.LTEMIMOChannel.

Hi: When the SampleRate is large, the result is error. But when the SampleRate is small, the result is likely correct.What is wrong with the following code? what happened to the large SampleRate value?

    numTx = 2;
    numRx = 2;
    SampleRate = 30.72e6;     %？？？？
    numBits = 2048*2;
    SNRdB = 0:20;
    lenSNRdB = length(SNRdB);
    bitErrors = zeros(1,lenSNRdB);

    hErrorCalc = comm.ErrorRate;
    hMod = comm.QPSKModulator(...
            'BitInput',true,...
            'SymbolMapping','Gray');
    hDemod = comm.QPSKDemodulator(...
            'SymbolMapping','Gray',...
            'BitOutput',true);

    hOSTBCEnc = comm.OSTBCEncoder(...
            'NumTransmitAntennas',numTx);

    hOSTBCCombine = comm.OSTBCCombiner (...
            'NumTransmitAntennas', numTx,...
            'NumReceiveAntennas', numRx);
    % 3GPP Long Term Evolution (LTE) Release 10 
    chanMode = 'EPA 5Hz'; %EPA 5Hz | EVA 5Hz | EVA 70Hz | ETU 70Hz | ETU 300Hz
    antconf = sprintf('%dx%d',numTx,numRx);%1x2 | 2x2 | 4x2 | 4x4

    hLTEMIMOChan = comm.LTEMIMOChannel(...
            'SampleRate',              SampleRate, ...   %？？？？
            'Profile',                 chanMode, ...  
            'AntennaConfiguration',    antconf, ...      
            'CorrelationLevel',        'Low',...       % Low | Medium | High
            'RandomStream',            'mt19937ar with seed',...
            'Seed',                    100,...
            'NormalizePathGains',      false, ...       %true | false
            'NormalizeChannelOutputs', false, ...       %true | false
            'PathGainsOutputPort',     true);           %true | false

    hAWGN = comm.AWGNChannel('NoiseMethod','Signal to noise ratio (SNR)');

    for ii = 1:lenSNRdB;

        iSNRdB = SNRdB(ii); 

        txData = randi([0 1],numBits,1);
        modData = step(hMod, txData); 

        encData = step(hOSTBCEnc, modData);

        %%用hLTEChan
        reset(hLTEMIMOChan);
        [LTEChanOut, pathGains] = step(hLTEMIMOChan, encData);
        sigPow = var(LTEChanOut);
        hAWGN.SNR = iSNRdB - 10*log10(numTx);%
    %    hAWGN.SNR = iSNRdB;%
        hAWGN.SignalPower = sigPow;
        rxSig = step(hAWGN,LTEChanOut);
        chEst = squeeze(sum(pathGains,2));
        combinedData = step(hOSTBCCombine, rxSig, chEst);
        rxData = step(hDemod,combinedData);
        reset(hErrorCalc);
        BitError = step(hErrorCalc, rxData, txData);
        bitErrors(ii) = BitError(1);

    end

    close all
    figure
    semilogy(SNRdB, bitErrors);
    axis([SNRdB(1) SNRdB(end) 1e-5 0.5]), grid on
    legend([sprintf('numTx = %d , numRx = %d,',numTx, numRx), 'OSTBC']);
    xlabel('SNR, dB');  ylabel('Bit Error Rate');
    title(['BER for QPSK modulation with', ...
        sprintf('numTx = %d , numRx = %d,',numTx, numRx), 'OSTBC ',chanMode]);

    scatterplot(combinedData)