IFFT in OFDMA

[helee4]

I am hoping someone can rescue me from the dark....

I have been puzzling how a serial data stream can be mapped into subcarrier.

Say if I have a 8 bit data stream modulated with QPSK, and I am only using 256 point IFFT (sampling rate of 3.84Mps).

Each OFDMA symbol has a duration of 66.67 ms and sampling rate of 3.84Mps, one OFMDA symbol could fit 256 symbol.

Now is that mean S/P converted modulated stream, will fit within a symbol and perform a 256 point IFFT with the symbol? My confusion has always been since a OFDMA symbol can fit many bits within its duration, then why many article showing only 1 modulated symbol mapped to one OFDMA symbol? Sorry for the very confusing question...

[muneer]

clc;
close all;
clear all;
BW=1.92*10^6;
M=12;N=128;Ns=N+L-1;%D= no:of data blocks in between
F=1*BW/N;
Ts=1/(F*N);
Np=2;
% fs=1.92*10^6;
% fs= 2.5*BW;
% Ts=1/fs;
T=1/F;
Tss=1/(M*Ns);
K=4; %four users
N_k=N/K;
Nfg=0;r=3;

x1=(1/sqrt(2))*((2*randint(N_k,M)-1)+1i*(2*randint(N_k,M)-1));
x2=(1/sqrt(2))*((2*randint(N_k,M)-1)+1i*(2*randint(N_k,M)-1));
x3=(1/sqrt(2))*((2*randint(N_k,M)-1)+1i*(2*randint(N_k,M)-1));
x4=(1/sqrt(2))*((2*randint(N_k,M)-1)+1i*(2*randint(N_k,M)-1));

x11 =zeros(N,M);x22 =zeros(N,M);x33 =zeros(N,M);x44 =zeros(N,M);

for i = 1:N_k
x11(carr_perm(i), = x1(i,;
x22(carr_perm(N_k+i), = x2(i,;
x33(carr_perm((2*N_k)+i), = x3(i,;
x44(carr_perm((3*N_k)+i), = x4(i,;
end;

x_txd1=ifft(x11);x_txd2=ifft(x22);x_txd3=ifft(x33);x_txd4=ifft(x44);


x_txd_cp1=[x_txd1(N-L+2:N,;x_txd1];
x_txd_cp2=[x_txd2(N-L+2:N,;x_txd2];
x_txd_cp3=[x_txd3(N-L+2:N,;x_txd3];
x_txd_cp4=[x_txd4(N-L+2:N,;x_txd4];