On relay assignment strategy in wireless cellular environment

Relay assignment means assigning the proper relay nodes (RN) to cell-edge users (UE) in order to exploit the spatial diversity through relay nodes and improve cell-edge performance. An optimal algorithm, called ORA, is to maximize the minimum data rate among all users. ORA is shown to find the optimal objective regardless the initial relay node. Although the algorithm is shown to converge (the minimum data rate is maximized), there exist several different RN-to-UE assignment pairs for the remaining UEs assigned to RNs. This paper is motivated to enhance the performance of the relay assignment for the remaining UEs, provided that the minimum data rate is maximized. In this paper, we propose a new strategy whose main objective is to maximize the relative performance improvement, which is a ratio of the performance improvement to original direct transmission, under the max-min constraint. Under the new assignment algorithm, not only the original optimal property of ORA is preserved, but also the performance of remaining UEs assigned to RNs is maximized. Simulation results demonstrate the effectiveness of the proposed approach.