Planning of Frequency Reuse and Relay Station's Location for Cellular Relaying Networks

This paper investigates an amplify and forward (AF) relaying scheme compatible with a legacy wireless system in cellular environments. In the proposed scheme, terminals and relay stations use different frequency bands for signal transmission. The two frequency bands for terminals and for relay stations are used by individual frequency reuse factors in cellular environments. We study frequency planning and a relay station's location for high spectral efficiency. The numerical results show that the spectral efficiency of a relaying scheme is enhanced by deploying a relay station close to the base station (BS) and using frequency reuse factor 1 for a relay station to BS link. I. INTRODUCTION Future wireless systems envisaged to support high data rate communications create transmit power problems since high data rate transmission requires large transmit power at a terminal of limited power capability. A relaying scheme, which can extend coverage area saving the transmit power, has been considered as an attractive solution (1)-(3) to this problem. When a relaying scheme is newly introduced into a legacy wireless system, a smooth migration from the legacy wireless system to an advanced wireless system with relaying has been envisaged. For smooth migration, it is essential to maintain compatibility between the legacy and advanced systems. For instance, in 3rd Generation Partnership Project (3GPP), Long Term Evolution (LTE)-advanced system with relay functions is expected to support LTE terminals which follow control procedure of LTE specifications ((4) etc.). It is also important for the advanced system to achieve high spectral efficiency. In this paper, we investigate an amplify and forward (AF) relaying scheme compatible with a legacy wireless system in an uplink of orthogonal frequency division multiple access (OFDMA) system. In the presented scheme, a relay station (RS) retransmits the received signal after changing a subband of the received signal. Thus, terminals and RSs use differ- ent frequency bands for signal transmission. The proposed relaying scheme can be applied to a legacy system by adding extra bandwidth for relaying. The proposed relaying scheme is compatible with legacy terminals, because it does not change any frame format of the legacy system. In the presented system, terminals can transmit signals without being aware of relaying transmission. We further study planning of frequency reuse factor (FRF) and appropriate location of a RS in cellular environments. In the presented scheme, frequency band for Fig. 1. A relay transmission model. terminals and that for RSs are used by individual frequency reuse factors. We analyze spectral efficiency under various FRFs and RS's locations to find a good FRF and RS's location. Although this paper assumes an OFDMA system on uplink, the proposed scheme can be straightforwardly applied to SC- FDMA scheme (4) by adding DFT processor at a terminal's transmitter part.