problem to make an ofdm modulation

hello if i have a 4qam symbols and i want to make ofdm modulation to them is that corect to make that before i make the ifft: symbols=rand (1,1000)

for n =length(symbols)
 s=(cos(2*pi*n*t)+j*sin(2*pi*n*t))*symbols
end
thanks!

Answer 1

[Yella]

Hi I think u want to transmit an ofdm symbol.

Generate random data.('randn'in matlab) Modulate it with QAM('qammod' in matlab) Create a preamble of known data. Create ofdm sysmbols using cyclic prefix method. Form an ofdm frame using preamble and ofdm symbols

Then do ifft and transmit them...that is ofdm modulation..

[itsik]

how do i do the cyclic prefix method?

thanks!!

Answer 2

[Yella]

http://en.wikipedia.org/wiki/Cyclic_prefix

Cyclic prefix is used to eliminate ISI and IBI. Read the link u get to know to how to code 'CP'