get_ofdm_preamble.m

国外大学的同志作出来的好程序

function preamble=get_ofdm_preamble(ofdm_sim);
%
%
%
if strcmp(lower(ofdm_sim.preamble_type), 'ieee802_11a'),

    ShortTrainingSymbols= sqrt(13/6)*[0 0 1+j 0 0 0 -1-j 0 0 0 1+j 0 0 0 -1-j 0 0 0 -1-j 0 0 0 1+j 0 0 0 0 0 0 -1-j 0 0 0 -1-j 0 0 0 ...
        1+j 0 0 0 1+j 0 0 0 1+j 0 0 0 1+j 0 0].';
    LongTrainingSymbols=[1 1 -1 -1 1 1 -1 1 -1 1 1 1 1 1 1 -1 -1 1 1 -1 1 -1 1 1 1 1 ...
        1 -1 -1 1 1 -1 1 -1 1 -1 -1 -1 -1 -1 1 1 -1 -1 1 -1 1 -1 1 1 1 1].';
    %Generate first ten short training symbols
    short_training_symbols = tx_freqd_to_timed(ShortTrainingSymbols, ofdm_sim.Nfft);

    % Pick one short training symbol
    Strs = short_training_symbols(1:16);

    % extend to ten short training symbols
    short_preamble=repmat(Strs, 10, 1);

    % next generate the long training symbols
    long_training_symbol = tx_freqd_to_timed(LongTrainingSymbols, ofdm_sim.Nfft);

    %double size prefix and the long training symbols
    index=ofdm_sim.Nfft-2*ofdm_sim.Ncp+1: ofdm_sim.Nfft;
    long_preamble = [long_training_symbol(index); long_training_symbol; long_training_symbol];

    preamble=[short_preamble; long_preamble];

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
elseif ~isempty(findstr(lower(ofdm_sim.preamble_type), 'mseq')),
    preamble_len=ofdm_sim.Nu;
    freqd_symbols=get_preamble(ofdm_sim.preamble_type, preamble_len);

    %note for MIMO, pilot info should be a matrix.
    %a matrix to store OFDM symbols
    OFDMsymbols=zeros(ofdm_sim.Nfft, ofdm_sim.tx_num);

    for ic_tx=1: ofdm_sim.tx_num,
        %merge the OFDM data and the pilot info
        OFDMsymbols([ofdm_sim.UsedSubcIndex], ic_tx)=freqd_symbols;
    end
    timed_symbols=freqd_to_timed(OFDMsymbols, ofdm_sim.Nfft);

    ofdm_preamble1=add_ofdm_prefix(timed_symbols, ofdm_sim.Nfft, ofdm_sim.Ncp);
    preamble=[ofdm_preamble1; ofdm_preamble1; ofdm_preamble1];

else
    disp('Other types of preambles not supported.');
    return;

end

if ofdm_sim.tx_num>1,
    disp('MIMO support is coming soon...');
    return;
end