ore, uplink CoMP works fine also with Release 8-10 UEs while the downlink CoMP requires Release 11 UEs. 13.4 Downlink Interference Management Table 7.2.3-1 in [2], shown as a graph in Figure 13.30, specifies the connection between UE-reported downlink channel quality indicator (CQI) and spectral efficiency in a network where no reference signal power boosting is used. The higher the average reported downlink CQI value in a cluster of cells the better the downlink spectral efficiency. Figure 13.30 Connection between channel quality indicator per stream (CQI) and downlink spectral efficiency (bits per second per hertz) Capacity Optimization The CQI reports from the UEs, together with other indicators such as HARQ feedback, are used by eNodeB algorithms to decide the downlink modulation and coding scheme (MCS) and number of control channel elements (CCEs) (i.e. aggregation level) used to deliver the downlink control information (DCI) (i.e. uplink and downlink capacity grants) on PDCCH. Once the radio conditions for a UE worsens, due to higher inter-cell interference or poor coverage, the eNodeB needs to use more robust MCS as well as higher aggregation level is required to deliver the DCI i.e. more CCEs are used. 13.4.1 PDSCH Spectral Efficiency Spectral efficiency is a factor of large number of variables, for example, layer 1 design, system bandwidth, cell density, traffic load, UE measurement and reporting accuracy and UE distribution across the network. Spectral efficiency is not constant in a network, but varies during the day. As the traffic increases and inter-cell interference increases the average reported CQI falls which means loss in spectral efficiency. Highest spectral efficiency in any network can measured when the UEs are under favourable radio conditions (close to the eNodeB) and there is very low inter-cell interference (low traffic) from surrounding cells. Often this is visible during the night time when UEs are least active and tend to be distributed more evenly across the large geographical area c