2 research outputs found
Opportunistic Communications in Fading Multiaccess Relay Channels
The problem of optimal resource allocation is studied for ergodic fading
orthogonal multiaccess relay channels (MARCs) in which the users (sources)
communicate with a destination with the aid of a half-duplex relay that
transmits on a channel orthogonal to that used by the transmitting sources.
Under the assumption that the instantaneous fading state information is
available at all nodes, the maximum sum-rate and the optimal user and relay
power allocations (policies) are developed for a decode-and-forward (DF) relay.
With the observation that a DF relay results in two multiaccess channels, one
at the relay and the other at the destination, a single known lemma on the
sum-rate of two intersecting polymatroids is used to determine the DF sum-rate
and the optimal user and relay policies. The lemma also enables a broad
topological classification of fading MARCs into one of three types. The first
type is the set of partially clustered MARCs where a user is clustered either
with the relay or with the destination such that the users waterfill on their
bottle-neck links to the distant receiver. The second type is the set of
clustered MARCs where all users are either proximal to the relay or to the
destination such that opportunistic multiuser scheduling to one of the
receivers is optimal. The third type consists of arbitrarily clustered MARCs
which are a combination of the first two types, and for this type it is shown
that the optimal policies are opportunistic non-waterfilling solutions. The
analysis is extended to develop the rate region of a K-user orthogonal
half-duplex MARC. Finally, cutset outer bounds are used to show that DF
achieves the capacity region for a class of clustered orthogonal half-duplex
MARCs.Comment: Submitted to the IEEE Trans. on Information Theor
Opportunistic Communications in Fading Multiaccess Relay Channels
The problem of optimal resource allocation is studied for ergodic fading orthogonal multiaccess relay channels (MARCs) in which the users (sources) communicate with a destination with the aid of a half-duplex relay that transmits on a channel orthogonal to that used by the transmitting sources. Under the assumption that the instantaneous fading state information is available at all nodes, the maximum sum-rate and the optimal user and relay power allocations (policies) are developed for a decode-andforward (DF) relay. With the observation that a DF relay results in two multiaccess channels, one at the relay and the other at the destination, a single known lemma on the sum-rate of two intersecting polymatroids is used to determine the DF sum-rate and the optimal user and relay policies. The lemma also enables a broad topological classification of fading MARCs into one of three types. The first type is the set of partially clustered MARCs where a user is clustered either with the relay or with the destination such that the users waterfill on their bottle-neck links to the distant receiver. The second type is the set of clustered MARCs where all users are either proximal to the relay or to the destination such that opportunistic multiuser scheduling to one of the receivers is optimal. The third type consist