procedures as described in the previous chapters. In the context of next-generation mobile networks (NGMNs) and the LTE SAE trial initiative (LSTI) [8], the single-link performance of LTE for 2 X 2 MIMO systems has been validated based on existing real-time hardware (HW) [5]. Outdoor multiuser measurement campaigns for single sites as described in this book more than proven the high benefits of MIMO and OFDMA, provid- ing a user data rate of more than 100 Mb/s in a significant part of the radio cell. The logical next step will be the optimization of the multicell network, which includes the transmission from more than one sector as well as from more than one site. As known very well, cellular radio systems in general (and specifically LTE) suffer significantly from interference in urban areas, reducing overall spectral effi- ciency from an ideal of about 10 to a few bits per second per hertz per cell. System- level simulations as well as the NOMOR [9] LTE emulator proved that MIMO in combination with OFDMA as an early form of adaptive resource coordination helps to overcome interference issues better than 1 X 1 or 1 X 2 OFDM systems like wireless local area networks (WLANs). Other common techniques, like frequency reuse greater than one [10], are already known from the global system for mobile communications (GSM) or from 3G systems like the universal terrestrial radio access (UTRA) frequency division duplex (FDD) system [11] and are quite easy to implement. But the resulting spectral efficiencies are in the order of 1 b/s/Hz/cell and thus far below the theoretical optimum of a COOPA system. Downlink (DL) LTE baseline (2,2) systems with two antenna ports (APs) at the narrowband (eNB) and two receive antennas at the UE achieve spectral efficiencies in the order of 2-3 b/s/Hz/cell according to system-level (SL) simulations; this is sig- nificantly smaller than what is predicted in the theory for full cooperation among all eNBs of a network. A factor of 10-15 in terms of spectral efficiency can be expected [6], if o