A Scheduling Algorithm for QoS Support in OFDMA Relay Networks

For supporting the high quality of service (QoS) in relay network, this paper proposes a new scheduling scheme that can be adopted in the orthogonal frequency division multiple access (OFDMA) cellular systems. In relay-aided network, a relay station should receive data from base station for forwarding data to its serving mobile stations. In addition, since the channel quality of each hop cannot be the same, the transmission time of each hop should be adjusted to harmonize the achievable transmission rate on each hop. In this paper, we first formulate the optimal scheduling problem and suggest a simple and fast heuristic scheme that provides enough subchannels to each hop for guaranteeing QoS and also adjusts the transmission time of each hop. With the proposed scheme, the QoS of each mobile station can be guaranteed and the channel utilization is increased. By using the simulation, we show that the throughput of the proposed scheme is higher than that of the scheme with fixed transmission time and the scheme not using relay stations. Moreover, since the proposed scheme not only allocates subchannels adequately but also adjusts the transmission time of each hop, the lowest outage rate can be achieved.