o the centralized element which would then coordinate the scheduling of the individual eNodeBs. These two architecture options are shown in Figure 7.25. This kind Distributed multi-cell New network element for scheduler centralized scheduler Centralized scheduler Cell A Cell B Cell A Cell B Figure 7.25 Multi-cell coordination architectures Small Cell Interference Management of coordination is called enhanced coordinated multipoint (eCoMP). The 3GPP term for the feature is CoMP with non-ideal backhaul. The multi-cell scheduler has become more attractive since it can utilize the 3GPP Release 11 UE features that allow more accurate reporting of the neighbour cell channel conditions. We will analyse the differences of these two implementations. We assume that there is some latency in X2 interface between eNodeBs and between centralized scheduler and eNodeBs. The algorithms need to be designed in such a way that latencies at least up to 10 ms can be tolerated. The distributed multi-cell scheduler can access the local scheduler information without any delay while the information from adjacent cells includes some delay. The centralized scheduler can access local scheduler information only with some delays. Therefore, the distributed multi- cell scheduler can have a benefit compared to the centralized solution because the distributed solution can take the local instantaneous scheduler information into account when optimizing the multi-cell scheduling. The distributed solution is also compatible with earlier 3GPP features like intra-frequency load balancing, also known as mobility load balancing (MLB), which uses distributed solution for balancing the loading between two adjacent cells. We also need to consider the amount of signalling needed in the information exchange. The distributed solution can be designed SO that exchanging raw information, such as CSI of all users, is not required. Each eNodeB can access the CSIs of its own UEs and exchange only cell-level metrics between adjacent eNodeBs. Each eNodeB makes a local