relaying operation in 3gpp lte challenges and solutions

I NTRODUCTION

Recent advancements in wide area cellular net-works provide high data rates for a variety of scenarios not relying on the availability of wire-less local area access networks or wired connec-tivity, and providing seamless mobility support.Mobile broadband networks deployments span scenarios from very dense urban areas to remote rural areas, operating in a large range of carrier frequencies with different propagation character-istics and different coverage levels.

The cost of the backhaul to the various net-work nodes has been identified as an essential cost component in the deployment of cellular networks, especially for future deployment of micro- and picocells for which the site acquisi-tion cost is expected to be lower than that for macrocells. Therefore, the ability to deploy net-work nodes not relying on a wired backhaul is an appealing option to reduce total network deploy-ment cost and operating costs. Relaying opera-tion provides the means to extend the coverage of broadband cellular networks coping with diverse radio propagation conditions without a wired backhaul.

With the help of relay nodes (RNs), the radio link between the base station (eNB) and user equipment (UE) is divided into two hops. The link between the eNB (also called the donor eNB or DeNB) and the RN is referred to as the backhaul link , while the link between the RN and the UE is referred to as the access link , as shown Fig. 1. Both links are expected to have better propagation conditions than the direct link from the DeNB to the UE.

An RN has a dual personality. On one hand,it communicates like UE with the DeNB. On the other hand, it communicates like an eNB with UE. Figure 1 illustrates how the RN and its respective physical links are integrated into the cellular concept.

Relaying has been a hot research topic for years [1]. The International Telecommunication Union — Radiocommunication Sector (ITU-R)has conferred IMT-Advanced status (fourth gen-eration, 4G) to two technologies: 3GPP Long Term Evolution (LTE) and IEEE 802.16m, both including relaying as one of their key features.Both technologies support fixed and two-hop relays [2].

This article describes relaying in 3GPP LTE and the challenges faced to define this new type of network node within the existing LTE struc-ture. One key requirement set forth at the begin-ning of the LTE relay study was the support of LTE UE of earlier and current releases (LTE Rel-8/9 and Rel-10, respectively). For these UE terminals, the RN is required to appear as a reg-ular eNB.

The article is organized as follows. We pre-sent various types of relays that were discussed as part of the LTE-Advanced study. Challenges and requirements for LTE relaying are provided.Detailed solutions for LTE relaying are given,focusing on architecture and protocols, and physical and medium access control (MAC)layer aspects, respectively. Simulation results are shown demonstrating the benefits of relaying

A BSTRACT

With the ever growing demand of data applica-tions, traditional cellular networks face the chal-lenges of providing enhanced system capacity,extended cell coverage, and improved minimum throughput in a cost-effective manner. Wireless relay stations, especially when operating in a half-duplex operation, make it possible without incur-ring high site acquisition and backhaul costs.Design of wireless relay stations faces the chal-lenges of providing backward compatibility, mini-mizing complexity, and maximizing efficiency. This article provides an overview of the challenges and solutions in the design of relay stations as one of the salient features for 3GPP LTE advanced.

Christian Hoymann, Ericsson Research

Wanshi Chen and Juan Montojo, Qualcomm Inc.Alexander Golitschek, Panasonic R&D Center Chrysostomos Koutsimanis, Ericsson Research Xiaodong Shen, China Mobile Research Institute

Relaying Operation in 3GPP LTE:Challenges and Solutions