Enhanced Cooperative Relaying Transmission for LTE-Advanced System

Relay has been identified as a fundamental feature in LTE-Advanced in order to achieve LTE-A requirements. The conventional straightforward relaying scheme named decode-and-forward (DF) protocol is used at relay station (RS) to decode the data received from mobile station (MS) and forward the decoded data to the base station (BS) to improve the spatial diversity gain. It is not efficient and optimal since the traditional DF scheme has not considered the unequal bit reliability within each QAM symbols. In this paper, a bit rearrangement technique is used at RS to improve the performance of the cooperative relaying system, in which the bit remapping employed at RS is different from the one used at MS. At BS, the soft information combining technique with maximum a posteriori (MAP) is used to demodulate the data before turbo decoding. Simulation results show that the proposed cooperative transmission scheme obtains a significant performance gain in terms of block error rate (BLER) compared to the traditional DF relaying scheme.