 IRC delays the need to reorganize the CA in such cases because the UE can adapt to different local interference conditions. Zirwas et al. [18] achieved overall performance gains of several hundred percent in cer- tain environments by combining all techniques properly, as can be seen from the simulation results in Figure 7.3. The main and most important message of Figure 7.1 is that the newly introduced spatial dimension for LTE systems may be used for conventional MIMO techniques like DIV, BF, or SM; however, in the context of cellular radio systems with strong intercell interference (ICI), often suppression of a few of the strongest interferers (e.g., by IRC or by means of cooperation) will be far more beneficial. In this context, accu- rate closed-loop MIMO precoding will save valuable spatial degrees of freedom (SDF) for IF suppression of other cell interference (OCI) based on IRC at the UE side. With an active overall interference management scheme in mind, cooperation becomes much more effective because the IF management shapes the IF floor SO that only one interferer or a few of the strongest interferers remain for local IF can- cellation. Thus, the size of the CAs can be quite small-in the order of a few cells. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology 7.2.2 Theoretical Background and Motivation for Cooperative Strategies in Wireless Networks The single-user point-to-point link is relatively well understood, both in theory and in practice. With modern signal processing and coding, a large portion of the capacity can be achieved [44,52,54]. However, these results and techniques can- not always be transferred to communication networks, which possibly have several source-destination pairs and simultaneous transmission over multiple network nodes. There are various ways in which nodes can interact and cooperate. Due to the high dimensionality of the problem, it is typically not possible to arrive at closed-form expressions or even to handle the problem a