transmit.m

L. Dong and A. P. Petropulu, 揗ultichannel ALLIANCES: A Cross-layer Cooperative Scheme for Wireless

% This code is to generate the transmitted packets and symbols 
% active_ii
% h: channel
% subch: the subchannel used to transmit 
% G: number of total subchannels

% trs_bit: transmitted bits
% transmitted signal

function [trs_bit,Y]=transmit(active_ii,h,subch,G)

J = 32; % total number of users

NF=64;  % total number of carriers
Ng=48/G; % the number of carriers of each subchannel

NP=8;       % the length of prefix
Pref=NP;    % the length of CP


L=3;    % the length of FIR channel

NN=1000*1;    % block size

N=NN*Ng;    % total symbol number of one packet in one slot

N1 = N - Ng*J; %number of data symbols per packet (QPSK)

ID = hadamard(J)+j*hadamard(J); 

pack=sign(rand(N1,1)-0.5)+j*sign(rand(N1,1)-0.5);
trs_bit=[];

%To guarantee the performance of channel estimation, 
%sd here used pilots in each carrier (even though it is not necessary 
%because there is a lot of frequency redundancy
for ii=1:J
    temp=[ID(ii,active_ii)* ones(Ng,1)];
    trs_bit=[trs_bit; temp];
end

trs_bit=[trs_bit; pack];

trs_bit1=reshape(trs_bit,Ng,floor(length(trs_bit)/Ng));
x=zeros(NF,floor(length(trs_bit)/Ng));
x(8+((subch-1)*Ng+1:subch*Ng),:)=trs_bit1;  % information symbols only occupy some positions

% IFFT
X=ifft(x,NF)*sqrt(NF); 

% .add cyclic prefix
X1=[X(NF-(Pref-1):NF,:); X];

X1=reshape(X1,1,prod(size(X1)));

%.....convolution with the FIR channel - channel changes between blocks.....
Y=filter(h,1,X1);