A novel type II relay-assisted retransmission scheme for uplink of LTE-advanced system
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RESEARCH
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A novel type II relay-assisted retransmission scheme for uplink of LTE-advanced system Anxin Li1*, Satoshi Nagata2, Atsushi Harada1 and Hirohito Suda1
Abstract Relay, which enables coverage extension and throughput enhancement, is a very promising technique for future wireless communication systems. Among different types of relay, type II relay is one kind of inband relays and is hotly discussed in LTE-Advanced system for throughput enhancement. In order to support type II relay, many challenges must be overcome. In this article, we focus on relay-assisted uplink data retransmission and propose a novel joint design of reference signal and data precoding for type II relay. The proposed method not only solves the problem of channel estimation mismatch for control information, but also achieves cooperative diversity gain for data transmission. Simulation results show the effectiveness of the proposed method over existing schemes. Keywords: Relay, Transparent relaying, Data retransmission, Channel estimation mismatch
Introduction Relay is a very promising technique for future wireless communication systems to extend coverage and enhance throughput, and has drawn increasing interest from both academia and industry [1-6]. There are many types of relays and some of them have been specified for future mobile systems, such as WiMax and LTE-Advanced system [5]. Two types of relays, i.e., type I and type II, are mainly discussed for LTE-advanced systems in the 3rd Generation Partnership Project (3GPP) [3,7-9]. The type I relay is a kind of non-transparent relay with wireless backhaul to the donor eNodeB cell. The type I relay terminates all layers 2 and 3 protocols and appears as a normal eNodeB to user equipment (UE). According to the backhaul, type I relay can be classified into inband (same frequency band for backhaul link and access link) and half-duplex (backhaul transmission and access transmission at different time), inband and full-duplex (backhaul transmission and access transmission at same time), and outband (different frequency band for backhaul link and access link). The type I relay has its own cell and physical cell identification (ID). It transmits synchronization signals and performs resource allocation. The typical usage scenarios of type I relay include coverage extension, e.g., hotspot and * Correspondence: [email protected] 1 DOCOMO Beijing Communications Laboratories Co, Ltd, 7/F, Raycom Infotech Park Tower A, No. 2 Kexueyuan South Road, Haidian District, Beijing 100190, China Full list of author information is available at the end of the article
deadspot, and group mobility, e.g., on a train or bus. On the other hand, the type II relay is a kind of inband transparent relay and works in a half-duplex mode. Usually, the type II relay only supports functions up to layer 2. Type II relay does not have a physical cell ID and is a part of a donor eNodeB cell. The eNodeB directly controls the UEs in the cell and performs resource allocation. The type II relay transparentl
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