This paper proposes an efficient multiuser relaying scheme in OFDMA systems. In the proposed scheme, multiple terminals transmit packets simultaneously in the same subband and multiple relay stations retransmit their received signals in dif- ferent subbands after subband conversion. The base station (BS) extracts each packet from multi-dimensional signals received at the different subbands. In advance of data transmission, the BS's scheduler selects appropriate terminals for packet transmission such that the BS can detect each packet correctly. Numerical results show that the proposed relaying scheme achieves much higher system throughput than the conventional relaying scheme. 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)-(4) to this problem. So far, various types of relaying schemes have been inves- tigated for future wireless systems. These relaying schemes can be basically categorized into analog repeater, amplify-and- forward (AF) or decoding-and-forward (DF) relaying in digital fields, and higher-layer relaying. Although clear comparison of different categories would be an issue for future study, AF relaying in digital fields has advantages in simple structure, low cost, and capability of frequency selection for relaying. Meanwhile, it has drawbacks in causing delay at baseband processing and spending double radio resources compared to direct transmission. Therefore, more efficient digital AF relaying scheme would be needed towards future wireless systems. In this paper, we propose an efficient multiuser relaying scheme to support low-mobility terminals in uplink of orthog- onal frequency division multiple access (OFDMA) systems. In the proposed scheme, multiple terminals transmit their data packets simultaneously in the same subband and multiple RSs retransmit their received signals in different subbands after subband conversion. A base station (BS) extracts individual data packets from multi-dimensional signals received at the different subbands. In advance of data packet transmission, the BS's scheduler selects appropriate terminals for data packet transmission so that the BS can receive individual data packets successfully. The proposed scheme can reduce radio resources Fig. 1. Conventional relaying scheme (a) with 1 relay station (b) with multiple relay stations. required for a packet transmission, since multiple terminals transmit their packets simultaneously in a subband. In perfor- mance evaluation, we show that the proposed scheme achieves higher system throughput than the conventional scheme. It should be noted that the proposed scheme can multiplex more packets than the number of the BS's antennas, apart from (5)(6). The proposed scheme does not use channel state information at relay stations, apart from (7). Furthermore, this paper presents flexible subband conversion at a relay station depending on the number of relay stations and link capacity.
['Yoshitaka Hara', 'Hiroshi Kubo']
An Efficient Multiuser Relaying Scheme for OFDMA Systems