tion Figure 7.1 provides main motivations for the application of cooperative transmis- sion techniques for outdoor cellular mobile radio systems like LTE: Reuse of sites and HW. For incumbent mobile network operators, which already have a large installed base, it is important to reuse existing sites as well as installed HW as far and as effectively as possible. However, higher data rates, together with higher RF, will typically shrink possible cell sizes. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology Reuse of sites, reuse of installed HW Combine antenna elements of several sectors or eNBs Combine several UEs to a multiuser MIMO system Virtual MIMO Low rank, low SNR, Intercell Interference Use spatially distributed antenna elements Exploit rank enhancement and macro diversity Intercell interference cancellation by JT/JD Maximize gain due to spatial degree of freedom Diversity (DIV) Beam forming MIMO single link Spatial multiplexing (SMUX) COOPA Space division multiplexing (SDMA) Interference cancellation (JT/JD) Active IF management Interference rejection combining (IRC) Antenna tilting, IF coordination Figure 7.1 Rationale of COOPA systems. Cooperation between the antenna ports of different sites and sectors will enhance the existing cell sites SO that the original site structures might be reusable. Virtual MU-MIMO systems-sometimes also called spatial divi- sion multiple access (SDMA) [19]-allow for MIMO gains without requiring eNBs or UEs with large, costly, and space- and power-consuming antenna arrays as well as RF front ends (RF-FEs). Note that a significant part of HW costs of an eNB is contributed by the RF part, while, from a business perspec- tive, a doubling of RF chains does not translate into a doubling of spectral efficiency as can be seen from SL simulations for LTE release 8. Low SINR, low rank. For indoor single-link MIMO systems, typically the received power will be quite large. Rich scattering environments ensure high-rank radio channels, allow