On the Application of Directional Antenna to Two Hop Relay System

The concept of relaying is a candidate solution for the challenging throughput and high data rate coverage requirements of future wireless cellular networks. In this paper, we demonstrate that to fully exploit the benefit of relaying it is crucial to ensure good quality of the hop from base station (BS) to relay station (RN). In multi-cell environment RN may suffer strong inter-cell interference in downlink, which largely diminishes the profit of deploying RNs. By applying directional antenna to RN towards BS, the interference at RN could be effectively suppressed and the benefit from RN could be more adequately exploited. In particular we considered an OFDM/TDMA network where six digital fixed RNs are placed evenly in each cell. The evaluation shows that with directional antenna equipped for the RN to BS link the performance gain substantially increases in both capacity and coverage especially in multi-cell environment. Moreover, applying directional antenna makes it easier to tune the favorable RN positions where both capacity and coverage are considerably improved. With single cell, however, by proper deployment RN can have line of sight (LOS) transmission to BS, which eases the requirement of directional antenna.