28)
where RI is the interference plus noise covariance matrix and is the cross-correlation vector
between the received signal and the desired or reference signal. It is common to define R to be the
covariance matrix of the received signal as the sum of the desired, interference and noise covariance
rxd
w R1
IN # rxd
I w* # x
matrices, as in Eq. (7.29). Here we have assumed the desired signal, interfering signals, and noise are
all uncorrelated from each other.
(7.29)
Suffice it to say that various combining or weight calculation options exist [8]. Let us briefly apply
the eigenanalysis to this receiver by providing the Eigen Canceler (EC) combining weights. First,
recall this interference plus noise covariance matrix can be written as [9]
(7.30)
The EC-based RAKE combiner is then expressed as
(7.31)
7.4.2 Predespread and Postdespread Combining
In this section, we will briefly mention a couple of options that are available to perform the multipath
combining in the RAKE functionality. The previous subsection had the despreading operations occurring
first and then the time-deskewing and combining operations being performed at the despread
symbol level. One can move the deskewing and combining into the chip level, prior to the actual
despreading operations.
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