(4.36)
(4.37)
(4.38)
Hence phase derotation was accomplished by the use of the complex conjugation operation on the
channel estimate. Assume we normalize by the power of the channel and the SNR is at a reasonable
value then we have the following:
(4.39)
This compensated symbol clearly shows the amplitude and phase distortion (introduced by the channel)
has been removed. We have chosen to normalize the channel estimate for the purposes of supporting
our explanation; however is it not a requirement. The decision to perform such an operation
should be based on the signal processing functions that follow the detector, such as forward error correction,
and so on.
If the channel is time varying then using the channel estimate throughout the entire time slot is
incorrect and can prove to cause detrimental effects on system performance. In order to obviate the
risk of degraded performance a solution is to update the channel estimate as it is applied in the time
slot. This is accomplished with the assistance of two blocks: Delay first-in first-out (FIFO) and
Interpolation. The Delay FIFO buffer allows us to use noncausal signal processing algorithms, by this
we mean using the channel estimates of not only the past and present, but also the future to make a
more accurate estimate of the present channel.
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