09-02-2013, 11:29 AM
Relay Selection and Power Allocation in Cooperative Cellular Networks
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Abstract
We consider a system with a single base station
communicating with multiple users over orthogonal channels
while being assisted by multiple relays. Several recent works
have suggested that, in such a scenario, selection, i.e., a single
relay helping the source, is the best relaying option in terms of
the resulting complexity and overhead. However, in a multiuser
setting, optimal relay assignment is a combinatorial problem. In
this paper, we formulate a related convex optimization problem
that provides an extremely tight upper bound on performance
and show that selection is, almost always, inherent in the solution.
We also provide a heuristic to find a close-to-optimal relay
assignment and power allocation across users supported by a
single relay. Simulation results using realistic channel models
demonstrate the efficacy of the proposed schemes, but also raise
the question as to whether the gains from relaying are worth the
additional costs.
INTRODUCTION
IN distributed wireless systems wherein each node possesses
only a single antenna, relays can be used to provide
spatial diversity and combat the impact of fading. Relaying
has been an extremely active research area, especially since
Sendonaris et al., in [1], proposed the idea of user cooperation
wherein mobile users cooperate by relaying each others’
data. Many cooperation schemes have now been studied,
e.g., [1]–[6]. The work in [3] and [4] proposed repetition-based
cooperation schemes including fixed amplify-and-forward
(AF) and decode-and-forward (DF) using orthogonal channels
(time/frequency slots). In networks with multiple relays, the
traditional strategy has been to let all the relays forward their
messages to the destination. However, having relays transmit
on orthogonal channels is bandwidth inefficient.
SYSTEM MODEL
Our system model consists of a cellular network with a
single BS, communicating with