er technically feasible or cost-effective. The second special technology used in WLL is the creation of a single terminal equip- ment unit for multiple residences or offices. An apartment building, an office building, or even a development of multiple houses with local wiring within the development could all be served by a single multichannel terminal equipment unit. The air interface would have the functional role that a PSTN trunk group has from a private branch ex- change (PBX) at that location to the local exchange on a traditional landline network as described in Sec. 11.1. It would provide access for all the calls from that location. Just as is true of local landline trunks, the total capacity of the air interface might well be less than the total number of users in the building or complex being served. Since not everyone will be calling at once, it might be possible, for example, for a link that can support 10 simultaneous calls to serve 20 residences. In the case of large customer facilities, a directional antenna could be installed at the base station pointing toward that one customer group. This terminal equipment unit is not a base station because it is on the remote end of the air interface. Functionally, it is the opposite of a base sta- tion because itreceives the forward signal and transmits the reverse signal. However, in terms of components, a complex terminal equipment unit is very similar to a base 10 By nearest, we mean the one with the highest radio path gain. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. The User Terminal The User Terminal station, and many of the design issues that apply to the base station discussed in Chap. 4 apply to these terminal equipment units as well. Until recently, WLL seemed very promising. It seemed to be on the verge of explod- ing through the developing world. Its only competitor was la