Resource allocation for maximizing weighted sum of per cell min-rate in multi-cell DF relay aided downlink OFDMA systems

This paper considers a multi-cell relay aided orthogonal frequency division multiple access (OFDMA) downlink system, in which all stations are coordinated by a central controller for resource allocation (RA). The decode-and-forward (DF) protocol with selection relaying (SR) is applied. The problem considered is the maximization of the weighted sum of per cell min-rate (WSMR) with a total power constraint in each cell. An iterative RA algorithm is proposed to optimize mode selection (decision whether the relay should help or not), subcarrier assignment (MSSA) and power allocation (PA) alternatively. Each iteration is composed of the MSSA stage and the PA stage. During the MSSA stage, instead of the original objective function, a lower bound is maximized leading to lower complexity. The lower complexity problem is decoupled into mixed integer linear programs (MILP) that can easily be solved by typical MILP solvers. During the PA stage, an algorithm based on single condensation and geometric programming PA (SC-GPPA) is designed to optimize PA with the tentative MSSA results. The convergence of the proposed RA algorithm is proven. Finally, the performance of the RA algorithm and the benefit of using SR are illustrated through numerical experiments.