Radio Resource Management for a Two-hop OFDMA Relay System in Downlink

In this paper, we propose two radio resource control (RRC) schemes where both base station (BS) and relay station (RS) perform dynamic resource allocation. The target system is a two-hop mobile communication system employing OFDMA technique. These schemes operate in such a distributed manner that both BS and RS control the mobile stations directly connected to each of them. However, the mobile station (MS) connected to RS is influenced by BS-RS and RS-RS links as well in addition to RS-MS link. To solve this problem, a BS-RS link control mechanism based on the information from RS should be supplemented into the system. The proposed mechanism, a semi-distributed method, is that BS allocates resources to the directly connected mobile stations and relay stations, first. Then RS allocates resources to the connected mobile stations in two ways; RS uses the assigned subcarriers from BS or all system subcarriers independently. The former method is called the `separate and sequential allocation (SSA)' and the latter the `separate and reuse allocation (SRA)'. The SSA method yields a superior quality without regard to the location of RS, but the SRA method reveals performance results depending on the location of RS. Computer simulations show that the two proposed methods have almost the same performance as the existing centralized method but lower complexity and higher flexibility compared to the centralized method.