s presented in this chapter, giving a clear view of the high potential of cooperative antenna systems and promising performance gains on the order of several hundred percent or even more. Different implementation strate- gies have been presented and some important issues for the core element of any cooperation area have been addressed for the example of intersector cooperation. The newly proposed COOPA HARQ (hybrid automatic repeat request) concept allows reducing feedback overhead and, at the same time, solves the critical issue of feedback delay. In recent years, the interest in multihop-augmented, infrastructure-based net- works has grown because relaying techniques help improve coverage and capacity without too much cost for infrastructure. Recently, radio technologies from indus- try and academia, such as IEEE 802.16 (WiMAX-worldwide interoperability for microwave access), HiperLAN/2, and the Winner-II system, have included multi- hop support right from the start. Chapter 8 ("Multihop Extensions to Cellular Networks-the Benefit of Relaying for LTE") describes how relaying can be introduced into the LTE pro- tocol stack, the basic blocks, and the extensions. Different approaches are covered for exploiting the benefits of multihop communications, such as solutions for radio range extension (trading coverage range for capacity) and solutions to combat shad- owing at high radio frequencies. It is shown that relaying can also enhance capac- ity (e.g., through the exploitation of antenna gains, spatial diversity, or by suitable placement against shadowing due to obstructions). Further, multihop is presented as a means to reduce infrastructure deployment costs. The performance is presented and studied in several scenarios here. In the 3GPP WCDMA/HSPA (high-speed packet access) standards, the radio link control (RLC) sublayer is defined on top of the MAC sublayer and under other, higher sublayers such as RRC (radio resource control) and PDCP (packet data convergence protocol). Its main function is to guarantee relia