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IP.com Disclosure Number: IPCOM000007842D
Original Publication Date: 1996-Nov-01
Included in the Prior Art Database: 2002-Apr-29

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Rafael Diaz


In today's SmartZone systems, the subscriber units use RSSI (Received Signal Strength Indica- tion) sampling algorithms in order to determine what the received signal strength ofadjacent RF sites are. This allows the subscriber units to rank adjacent sites ahead of time and allow it to switch to the next best adjacent site to provide seamless roaming between sites. The way the radios perform this task is as follows. The radio periodically will switch off the current control channel frequency and change its frequency to the next control channel frequency it haa in its control channel list. The control chan- nel list represents the control channels of the other sites in the SmartZone system. Note while the radio is sampling this other control channel, it is no longer listening to data coming horn its selected site's con- trol channel. After switching hequencies to the next control channel, the radio does a simple RSSI read- ing on that channel. The RSSI circuit just measures RF energy and converts this horn analog to digital and inputs this data to the microprocessor. The soft- ware then converts this data into a number between O-256. This number represents a particular micro- volt reading which easily translates into a dR (Deci- bel) level. The radio then stores this value into its database for this particular frequency so that it can later use it in its filtering algorithms. The radio con- tinues this sampling for each control channel in ita list multiple times in order to take a running aver- age of the measurements. The Eltering algorithms take into account RR fades, RF shadowing, tempo- rary tides due blocked signals, etc.