Adaptive Resource Allocation in OFDMA Relay-Aided Cooperative Cellular Networks

Adaptive resource allocation to exploit multiuser diversity and spacial diversity in OFDMA relay-aided cooperative cellular networks is studied. Assuming that the BS has all the channel state information (CSI), an optimization problem for subcarrier assignment, relay selection and power allocation that maximizes downlink capacity of the system is formulated. Since the optimal solution is complex to obtain, a suboptimal solution dividing the problem into two sub-problems is proposed. Assuming equal power allocation in BS and each relay, the first sub-problem for joint subcarrier assignment and relay selection is a combinatorial optimization problem, for which an iterative algorithm derived from necessary optimality condition is proposed. Given the results from the first sub- problem, the second sub-problem for power allocation becomes a convex optimization problem and can be solved by an iterative method which optimizes the power of BS and each relay separately. Numerical results showed that two iterative algorithms can converge in reasonable steps and achieve significant improvement on system capacity due to two diversity schemes and power fully exploited.