A Novel Downlink Adaption Scheme for TDD Type-II Relay Systems

In a LTE-A relay-enhanced system, Type-II relay does not transmit CRS (Common Reference Signal), which prevents UE from estimating channel quality of relay-UE link and feeding back to eNB. Without knowledge of relay-UE link quality, eNB cannot select appropriate MCS (Modulation and Coding Scheme) for downlink transmission. In this paper, a novel downlink adaption scheme for a TDD (Time Division Duplex) relay-enhanced system is proposed. The procedure, transmit and receive algorithms of the proposed adaption scheme are also presented. Simulation results show that proposed link adaption scheme improves system spectrum efficiency significantly in various situations.