function ofdm_out = ofdm_trans_freq(in_bits, n_point);

%this function is to do the ofdm of frequence field,
%   in_bits is the input v-blast symbols of frequence field,
%   in_bits is (m_transmitter * bits_len) array
%   n_point is the subcarrier number

%----------------------------------------------------------------
%!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
%   this function is used only in freqency field channel,where
%   the channel is convert to frequency field by DFT
%!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
%----------------------------------------------------------------

size_in = size(in_bits);
size_trans = size_in(1,1);  %   M-transmitter
size_len = size_in(1,2);    %   data length

antena_index_symbols(size_trans,n_point,size_len/n_point) = 0;

%   for every antena,  it need to do a series-parallel transformation
%   the 1st dimension stands for the first v-blast dimension
%   the 2nd dimension stands for the ith ofdm subchannel
%   the 3th dimension stands for the length of bits on each subchannel

for index_m = 1:size_trans
    antena_index_symbols = series2paralle(in_bits(index_m,:), n_point);
    for index_g = 1:n_point
        ofdm_sym_freq((index_m - 1) * n_point + index_g ,:) = ...
            antena_index_symbols(index_g,:);
    end;
end;

%save antena_index_symbols antena_index_symbols;     %   the symble after ofdm series-parallel 
ofdm_out = ofdm_sym_freq;