The complexity impacts of this
technique are tremendous in that not only are two receivers needed, but also a more complicated
baseband receiver. Moreover, since a maximum of two spatial data streams can be multiplexed into
the spatial channel, two CQI estimators are required to drive the NodeB scheduler.
As discussed in earlier chapters, the usage of receive diversity with or without interference cancellation
(IC) can lead to a few dB of improvement. We leave it to the system designer where to use
this gain in order to have the largest impact. Currently, the two leading candidates are the dual receive
diversity with and without IC capability. A simplified receiver block diagram of the signal processing
blocks showing a reference receiver implementation is given in Fig. 9.22. The first block diagram uses
the MMSE cost function in the creation of the array weights, but only the desired signal??™s channel
matrix is estimated. In the second block diagram the desired and interference matrix is estimated to
form the true MMSE-based weights. The spreading and despreading functions have been removed in
order to generalize the operations and it is up to the system designer as to where the chips to symbol
conversion should take place.
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