UMTS: Alive and Well - 4G Americas

Figure 7.9. Potential Gain of DL CoMP.7.8.5 RELAYINGRecently, there has been an upsurge of interest on multi-hop relay in LTE-Advanced. The concept ofRelay Node (RN) has been introduced to enable traffic/signaling forwarding between eNB and UE toimprove the coverage of high data rates, group mobility, cell edge coverage, and to extend coverage toheavily shadowed areas in the cell or areas beyond the cell range. It provides throughput enhancementespecially for the cell edge users and offers the potential to lower the CAPEX and OPEX by keeping thecell sizes relatively large.The relay nodes are wirelessly connected to the radio access network via a donor cell. The RN isconnected to the donor eNB via the Un interface and the UEs are connected to the RN via the Uuinterface as shown in Figure 7.10. The Un connections that are currently under study can be either inbandor out-band. In an in-band connection, the eNB to relay link shares the same band with the directeNB to UE link within the donor cell. In this case, Rel-8 UEs should have the ability to connect to thedonor cell. For out-band connection, on the other hand, the eNB to relay connection is at a different bandfrom that of the direct eNB to UE link.www.3GAmericas.org February 2010 Page 105