Optimal sequences for CDMA under colored noise: a Schur-saddlefunction property
Viswanath, P.; Anantharam, V.
Information Theory, IEEE Transactions on
Volume 48, Issue 6, Jun 2002 Page(s):1295 - 1318
Digital Object Identifier 10.1109/TIT.2002.1003823
Summary:We consider direct sequence code division multiple access
(DS-CDMA), modeling interference from users communicating with
neighboring base stations by additive colored noise. We consider two
types of receiver structures: first we consider the
information-theoretically optimal receiver and use the sum capacity of
the channel as our performance measure. Second, we consider the linear
minimum mean square error (LMMSE) receiver and use the
signal-to-interference ratio (SIR) of the estimate of the symbol
transmitted as our performance measure. Our main result is a
constructive characterization of the possible performance in both these
scenarios. A central contribution of this characterization is the
derivation of a qualitative feature of the optimal performance measure
in both the scenarios studied. We show that the sum capacity is a saddle
function: it is convex in the additive noise covariances and concave in
the user received powers. In the linear receiver case, we show that the
mini average power required to meet a set of target performance
requirements of the users is a saddle function: it is convex in the
additive noise covariances and concave in the set of performance
requirements
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