oposals that is given based on the schematics in Figure 7.10. All cooperation schemes have in common that they form a distributed MU-MIMO or virtual MIMO system, where antenna ele- ments (AEs) from different radio stations transmit simultaneously to different UEs. Intra-NB or intersector cooperation is the simplest form of cooperation in a cel- lular network because all cells are located at the same site, avoiding any back- bone interconnections between NBs. One of the channel cards can easily perform the CU functionality, given that it has enough processing capability. Intra-NB cooperation combats intersector IF, which typically reduces overall performance by about 20%. At a first glance, 20% performance gain seems to be small, but one has to keep in mind that, in conventional cellular sys- items, very narrow sector antennas-for example, 60° beam width for 120° sectors-have to be used to minimize intersector IF. In the case of COOPA systems, we face a paradigm shift as IF is turned into useful signal energy. Therefore, with wider antenna patterns, greater overlap areas and larger per- formance gains will be possible. This opens the door for an interesting first system deployment of LTE, where, with only one AP per sector, UEs may be © 2009 by Taylor & Francis Group, LLC Intra eNB Cooperation Center Simplest and must basic Locally restricted to a few NodeBs element for cooperation Requires fast backbone connection (a) Intra-eNodeB Cooperation Requires central processing unit (b) Inter-eNodeB Cooperation Intra eNB Cooperation Diversity No backbone included Requires deployment of fibers d,d,d3 (c) DAS or use of RRH PMICU2,3 eNodeB as central processing unit d1,d2, d3 PMICU2 NB 1 Combines MIMO capacity as well as multi-hop coverage gains d,d,d3 d1, d, d3 Low backbone requirements RMICU1,3 CSI estimation & scheduler Includes backbone functionality PMICU3 synchronization challenging (e) Cooperative Relaying PMICU2 CU2 PMICU1,2 (d) Distributed/self-organizing Figure 7.10 Main COOPA proposals. Long Term Evolution: 3GPP 