 edge Intra-site CoMP Inter-site CoMP CoMP with 1 CoMP with 3 macro + 4 pico macro + 12 pico Macro HetNet Figure 7.33 CoMP gains in uplink Small Cell Interference Management CoMP gains in uplink Average Cell edge CS + JP with 1 macro CS + JP with 3 macro + 4 pico + 12 pico Figure 7.34 CoMP gains in uplink in HetNet scenario with cell selection (CS) and joint processing the intra-site CoMP gives 60% of the benefit of the inter-site CoMP. The highest gains are obtained in HetNet scenario where CoMP set extends over multiple macro cells and pico cells. The average gains are 89% and cell edge gains 208% [9]. Figure 7.34 shows CoMP gains in HetNet scenario with cell selection (CS) and joint processing (JP). The first option uses just cell selection and can provide some gains: 31% for the average data rates and 65% for the cell edge data rates. The gains more than double when joint processing reception is applied between macro site and four pico cells under the macro coverage area. The gains further increase when CoMP set is extended over multiple macro sites. The uplink CoMP measurements are illustrated in Chapter 13. The downlink CoMP gains are expected to be lower than the uplink gains. The uplink CoMP uses multi-cell reception which can provide clear gains while the downlink CoMP gains rely on the selection diversity or joint transmission, which also adds interference. One challenge in downlink is the availability of the channel estimates at the eNodeB transmitter. UE first needs to estimate the multipath channel from all cells in CoMP set, and then UE can provide the CSI to the network in the uplink feedback channel. The feedback adds delay and quantization errors. A UE-specific measurement set is defined as a set of cells that a given UE performs measurement on to determine CSI feedback. The multi-cell CSI measurement requirements are defined in Release 11. Therefore, the downlink CoMP requires Release 11 UEs while the uplink CoMP benefits can also be obtained for the legacy UEs. The downlink CoMP can use joint t