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Generation of subcarriers using the IFFT
 The time discrete equivalent of the complex based OFDM
signal is the inverse discrete Fourier transform (IDFT), which
is given by
N s 1
in
s(n)   d i exp( j 2 )
N
i 0
where the time t is replaced by a sample number n.
 In practice, this transform can be implemented very efficiently
by the inverse fast Fourier transform (IFFT).
 In the receiver, the desired complex symbols are recovered by
the fast Fourier transform (FFT), given as
1
di 
N
N 1
 s(n) exp(  j 2
n 0
in
)
N
Wireless Communication Technologies 2.5.2
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Example 2.5-1 IFFT operation
 Assume that the complex signals are denoted as

d  [1  1 j  j ]
please using Matlab to find the OFDM signal in discrete
form , s (n) .
【Sol.】
clear,
a=[1 -1 j -j];
b=ifft(a)
1 
 1 
 
j 
 
 j 
IFFT
0

  j / 2


 j/2 


1 / 2 
(1 0)
(0 0)
(1 1)
(0 1)
Wireless Communication Technologies 2.5.2
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