In fact, depending on the SF of the desired physical channel, the number of multicodes, the channel
model, and the amount of interference in the system, this can be an inaccurate assumption. In other
words, the IPI should be taken into account in the receiver.
This approach is also called generalized RAKE or GRAKE for short [7]. In the first public appearance
of this technique, the time delay between adjacent fingers was not specified and the interference
plus noise matrix was used in the weight calculation. Applying the same principles provided in [3]
can result in performance improvement.
The optimal combiner includes the IPI statistics in the finger weight calculation. The effects of the
IPI become more apparent as the SF of the desired physical channel decreases. Let us present the
derivation for the statistical signal properties of the RAKE finger output, assuming QPSK modulation.
This will give us insight into the signal characteristics. For the sake of illustrative purposes, we
will assume a two-ray channel model with an arbitrary time delay separation between the arriving two
multipaths.
The first RAKE finger output is assumed to be tracking the first arriving ray and is given as
follows:
(7.97)
The second RAKE finger output is written as
(7.
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