Opportunistic subcarrier allocation scheme for FFR-aided LTE networks

Abstract

This paper investigates the problem of Inter Cell Interference (ICI) in Orthogonal Frequency Division Multiplexing Access (OFDMA) aided Long Term Evolution (LTE) mobile systems. In OFDMA aided LTE systems the intra cell interference can be effectively suppressed by using orthogonal subcarriers within the same serving cell. However, the Inter Cell Interference (ICI) still exists, since the adjacent cells employ the same frequency subcarriers as the serving cell does, deteriorating the system performance especially at cell edge. Fractional Frequency Reuse (FFR) schemes have therefore proposed to mitigate the ICI issue for capacity improvements at cell edge regions. Nonetheless, the allocation of subcarriers in FFR reduces spectral efficiency in specific cell areas for cell edge scenarios, resulting in the decrease of the system throughput. In this paper, we propose a scheme to improve the system throughput by allocating subcarriers opportunistically to cell edge users. In the proposed Opportunistic Subcarrier Allocation (OSA) scheme, the same sub carriers are not allowed to be used by the adjacent cell edge users for ICI suppression purpose. In each scheduling period, each cell determines its own subcarriers for cell edge users based on the available Channel Quality Information (CQI). Thus, the spectrum bands are allocated opportunistically to the cell edge users of the multiple cells share the spectrum in cooperative way. Simulation results demonstrate that the proposed OSA scheme improves the spectrum utilization and achieves better performance in terms of edge users blocking probability and spectrum efficiency than its FFR counterpart.