UMTS: Alive and Well - 4G Americas

• RN → eNB and UE → RN links are time division multiplexed in a single frequency band and onlyone is active at any one timeWith respect to the multiplexing of backhaul links, the current understandings are:• The eNB → RN transmissions and RN → eNB transmissions are carried out in the DL frequencyband and UL frequency band respectively for FDD systems• The eNB → RN transmissions and RN → eNB transmissions are carried out in the DL subframesof the eNB and RN and UL subframes of the eNB and RN respectively for TDD systemsThe exact procedure for allocating the backhauling resources and the supporting channels needed arestill being investigated in 3GPP.Cooperative relaying is principally a distributed MIMO system in multi-hop relay environments. The sametime-frequency resource block is shared by multiple RNs and these distributed deployed RNs operatecollaboratively to form virtual MIMO transmissions. Additionally, cooperative relaying potentially simplifiesthe implementation of inter-RN handover due to the concept of the “virtual cell” (i.e., every UE is alwaysserved by one or more RNs which provide the best performance). Therefore, smooth handover isexpected in multi-hop relay-based networks. The collaborative transmission and reception of multiple RNscan improve signal quality due to spatial diversity or increase the spectrum efficiency as a result of SM.7.8.5.1 PERFORMANCEFigure 7.11 shows the possible system performance gain determined from system simulation from usingrelays in an LTE-Advanced system. The assumptions of the simulations were consistent with that agreedto in 3GPP. 133 The simulation scenario considered is Case One: 2x2 MIMO, three Type 1 RNs per celland with 25 UEs per cell. The eNB can schedule the RNs on six subframes and schedule UEs on 10subframes while the RN can schedule UEs on four subframes. The results show that significant gain inboth the cell edge and cell average throughputs are possible with only three relay nodes per cell. Notethat additional gain is possible with additional relay nodes in the system with more antennas at the eNBand/or the relay and a better backhauling design.133 3GPP TR 36.814, Further Advancements for E-UTRA, Physical layer Aspects.www.3GAmericas.org February 2010 Page 108