Utility-Based Resource Allocation in OFDMA Relay Systems with Half-Duplex Transmission

Abstract

This paper considers resource allocation in an Orthogonal Frequency Division Multiple Access (OFDMA) relay system, which uses either direct transmission or nonregenerative relay transmission strategies in each subchannel. An optimization problem is developed to handle joint dynamic subchannel assignment (DSA), adaptive power allocation (APA), transmission strategy selection and relay selection in the downlink of OFDMA relay system exploiting half-duplex transmission. We aim to obtain the fair usage of the relays with the assumption that one relay’s maximum subchannels and the relay power in each subchannel are fixed. A suboptimal greedy algorithm is proposed to optimize all users’ overall sum utility, where resources are allocated to the user with the greatest utility increment potential one at a time. Simulation results illustrate that the proposed algorithm significantly outperforms the fixed resource allocation schemes.

Appendix

The water-filling power allocation problem for user i is given by

$$ \begin{array}{*{20}l} {\mathop {\hbox{max} }\limits_{{p_{0,n} }} \quad R_{i} } \\ \text{s.t.}\ \sum\limits_{{n \in S_{i} }} {p_{0,n} } = P_{i} , p_{0,n} \ge 0. \end{array} $$

(A.1)

Using the Karush–Kuhn–Tucker (KKT) conditions [11], after some algebraic manipulations, we get

$$ p_{0,n} = \left( {\lambda - \frac{{N_{0} W}}{{\left| {H_{0i,n} } \right|^{2} }}} \right)^{ + } , \, n \in A_{i} , $$

(A.2)

$$ p_{0,n} = \frac{{N_{0} W}}{{\left| {H_{0r,n} } \right|^{2} }}\left[ {\frac{{p_{r,n} \left| {H_{ri,0} } \right|^{2} }}{{2N_{0} W}}\left( {\sqrt {1 + \frac{{4\left| {H_{0r,n} } \right|^{2} }}{{\lambda p_{r,n} \left| {H_{ri,n} } \right|^{2} }}} - 1} \right) - 1} \right]^{ + } , \, n \in B_{i} , $$

(A.3)

where r denotes the relay in each subchannel, and constant λ is chosen to satisfy $\sum\nolimits_{{n \in S_{i} }} {p_{0,n} } = P_{i} .$