he interference to other neighboring users, while increasing the served users' signal strength. For joint processing/transmission, the transmission to a single UE is simultaneously transmitted from multiple transmission points, in practice cell sites. The multipoint transmissions will be coordinated as a single transmitter with antennas that are geographically separated. This scheme has the potential for higher performance, compared to coordination in scheduling only, but at the expense of more stringent requirement on backhaul communications [101]. Network and collaborative MIMO have been studied for the 4th generation of cellular systems. Their application depends on the geographical separation of the antennas, coor- dinated multipoint processing method, and the coordinated zone definition. Depending on whether the same data to a UE is shared at different cell sites, collaborative MIMO includes single-cell antenna processing with multi-cell coordination, or multi-cell antenna processing. The former technique can be implemented via precoding with interference nulling by exploiting the additional degrees of spatial freedom at a cell site. The latter technique includes collaborative precoding and closed-loop macro diversity. In collaborative precoding, each cell site performs multi-user precoding towards multiple UEs, and each UE receives multiple streams from multiple cell sites. In closed-loop macro diversity, each cell site performs precoding independently, and multiple cell sites jointly serve the same UE. As shown in Figure 10-46, uplink coordinated multipoint reception implies reception of the transmitted signal at multiple geographically separated points. Scheduling decisions can be coordi- nated among cells to control interference. It should be noted that in different instances, the cooperating units can be separate base station's remote radio units, relays, etc. Moreover, since uplink CoMP mainly impacts the scheduler and receiver, it is primarily an implementation issue. As shown in Figure 10-47, the sin