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Performance Evaluation of WiMAX/IEEE 802.16 OFDM Physical Layer - page 51 / 107

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S( f )

0 7 8 5 . 0 7 2 . 1 1 0 2 0 f 4 f

1 1 0 0 f f

(4.13)

Where,

the

function

is

parameterized

by

a

maximum

Doppler

e q u e n c y m f

a n d f 0

f

fm

.

To generate a set of channel coefficients with this PSD function, the original coefficients are correlated with a filter which amplitude frequency response is:

H ( f ) S( f )

(4.14)

For efficient implementation, a non­recursive filter and frequency­domain overlap­add method has been used.

T h e r e a r e n o f r e q u e n c y c o m p o n e n t s h i g h e r t h a n f m ( f o r t h e c o n s t r u c t i o n f o r m u l a o f S ( f ) ) : s o t h e c h a n n e l c a n b e r e p r e s e n t e d w i t h a m i n i m u m s a m p l i n g f r e q u e n c y o f f m a c c o r d i n g t o t h e N y q u i s t t h e o r e m . F o r t h i s r e a s o n w e c h o s e t h e s a m p l i n g f r e q u e n c y e q u a l t o 2 f m .

The power of the filter has to be normalized to 1, so that the total power of the output signal is equal to the input one.

40

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