can anyone help please? i am trying to simulate the BER in OFDM

% the code is without the addition of the cyclic prefix. the results is not as i am expecting, can anyone help please?

clear all;
N=24;% size of fft
N1 = 6 ;% number of bits or symbols
SNR_db = [1: 20]; % multiple Eb/N0 values
SNR= 10.^(SNR_db./10);
errors = zeros(1,length(SNR_db));


%Transmitter
d = rand(1,N)>0.5; % generating 0,1 with equal probability
Signal = 2*d - 1; % BPSK modulation 0 -> -1; 1 -> 1

for k=1:N1

for i=1:length(SNR_db)
R=zeros(1,length(Signal));%Detected Signal size

x= ifft(Signal);

%for k=1:N1

%channel
W = awgn(x,SNR_db(i));


%receiver

b= fft(W);

for j=1:length(Signal)
if b(j)>=0
R(j)=1;
else
R(j)=-1;
end;
end;


errors(i) = errors(i) + size(find(Signal - R),2) ; %errors(i) + nnz(Signal-R);%number of non-zero elements

end

errors = errors./N1;

end;

BER = errors/(length(b)) ; % practical ber

a = 0.5*erfc(sqrt(SNR)); % theoretical ber

%theoretical
figure(1)
semilogy(SNR_db, a,'b.-');
hold on;

%practical
semilogy(SNR_db, BER,'or');
axis([0 20 10^-5 0.5])

hold on;
grid on;

legend('theory', 'practical');
xlabel('SNR, db');
ylabel('BER');
title('Bit error probability for ofdm using bpsk');