an operator's lack of high quality coverage. During the course of writing this book, many operators were still using femtocells. There is little marketing for the service, and the equipment cost is usually borne by the operator. As network coverage matures it is expected that the need for femtocells will diminish. However, universal high quality coverage is very difficult to achieve and there remains a business case for femtocells in the foreseeable future. Case Study Questions Why are femtocells necessary? How are coverage imperfections discovered? Can it be automatic? Why are femtocells usually marketed and sold under operator brands? How can a mobile operator compensate for the traffic carried over a subscriber's fixed network? Why are femtocells an economical solution for coverage defects? Network Topologies, Design and Convergence Repeaters Two other cell figurations are used in practice. One is a repeater as illustrated in Figure 13.11. Repeaters are simple devices consisting of an outdoor receiving/transmitting antenna, an amplifier, and an indoor transmitting/receiving antenna. The function of a repeater is to increase the signal power within a confined area in the same way that a microcell or a pico- cell base station does. However, a repeater is simpler as it does not carry any signal processing itself. It only bridges a well-covered outdoor environment with an isolated, often under- ground, environment through a receiver and transmitter antenna pair. They are also used to increase signal power inside buildings. One example is the Mobile Smart Antenna offered by Telstra [14]. Femtocells and repeater configurations show that no coverage can be perfect, and 'band- aids' are necessary to fix remaining areas after a network has been rolled out. Distributed Antenna Systems Another solution for indoor building coverage is illustrated in Figure 13.12. Here the radio signal is sent inside a building using fixed links such as fibre or cable. The radio signal is connected to distributed antenna systems throughout