UMTS: Alive and Well - 4G Americas

freedom at a cell site. The latter technique includes collaborative precoding and CL macro diversity. Incollaborative precoding, each cell site performs multi-user precoding towards multiple UEs, and each UEreceives multiple streams from multiple cell sites. In CL macro diversity, each cell site performs precodingindependently and multiple cell sites jointly serve the same UE.7.8.4.4 UL COMPUplink coordinated multi-point reception implies reception of the transmitted signal at multiplegeographically separated points. Scheduling decisions can be coordinated among cells to controlinterference. It is important to understand that in different instances, the cooperating units can beseparate eNBs’ remote radio units, relays, etc. Moreover, since UL CoMP mainly impacts the schedulerand receiver, it is mainly an implementation issues. The evolution of LTE, consequently, will likely justdefine the signaling needed to facilitate multi-point reception.7.8.4.5 INTER-CELL INTERFERENCE COORDINATIONAnother simple CoMP transmission scheme which relies on resource management cooperation amongeNBs for controlling inter-cell interference is an efficient way to improve the cell edge spectral efficiency.The Inter-Cell Interference Coordination (ICIC) enhancement currently being studied for LTE-Advancedcan be classified into dynamic Interference Coordination (D-ICIC) and Static Interference Coordination (S-ICIC). In D-ICIC, the utilization of frequency resource, spatial resource (beam pattern) or power resourceis exchanged dynamically among eNBs. This scheme is flexible and adaptive to implement the resourcebalancing in unequal load situations. For S-ICIC, both static and semi-static spatial resource coordinationamong eNBs are being considered.7.8.4.6 PERFORMANCE RESULTSFigure 7.9 shows the possible system performance gain determined from system simulation with thevarious CoMP techniques in the downlink. The simulations assumptions were consistent with that agreedto in 3GPP. 132 The CoMP techniques investigated include:• Coordinated Beam Switching (CBS)• Non-Coherent Joint Processing (JP-Nco)• Coherent Joint Processing (JP-Co)• CBF• Intra-Site Coherent JPQuantized feedbacks were assumed for CBS with SU-MIMO and Intra site JP with MU-MIMO whileidealized feedbacks were assumed for the other schemes. Figure 7.9 illustrates that significant cell edgeand cell average throughput gain is possible.132 3GPP TR 36.814, Further Advancements for E-UTRA, Physical layer Aspects.www.3GAmericas.org February 2010 Page 104