AC = 6 16 mW 12 dBm VMAC = 7 8 dBm 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. Analog Wireless Telephony (AMPS) Key Radio Concepts a U.S. patent to be issued for it. In Sec. 25.6 we discuss the strategy issues of power control on the AMPS channel. 6.6.2 AMPS handoff When the signal goes below some level, called the primary threshold in the AMPS lan- guage, the base station decides to look for a handoff. There are three kinds of AMPS handoffs: to another server group on the same face, to another face on the same cell, and to another cell. Server groups are different cell sizes served by the same base sta- tion, as described in Sec. 5.2.3. Once the call has been below primary threshold for a few measurements, all the an- tenna faces at the serving base station and some nearby neighbor base stations mea- sure the signal strength of the reverse channel. If there is a logical face where the call is above primary threshold, the base station tries to put the call onto the strongest face (best radio path) and the innermost server group that can handle the call. If the mobile telephone reverse signal is not above primary threshold on the primary neighbor list, then there is a secondary threshold and a larger secondary neighbor list. If the signal is below secondary threshold, then this wider survey of measurements is taken, and a more intense search is done for a suitable handoff. When other cells measure the signal strength of a call, they can be instructed only to return a measurement when the signal at the requested frequency has the correct SAT. We want to avoid doing a handoff based on measuring the wrong call. This is the basic outline of handoff search we designed at AT&T. Different cellular equipment vendors use different selection rules. And different cellular service pro- viders set their system parameters differently. Notice, please, t