Communications: electrical – Continuously variable indicating – With meter reading
Reexamination Certificate
1998-02-12
2001-03-06
Horabik, Michael (Department: 2635)
Communications: electrical
Continuously variable indicating
With meter reading
C455S434000, C340S870030
Reexamination Certificate
active
06198406
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to messaging systems, and more specifically to a method and apparatus for providing a predictable upper bound for a channel search time of a portable subscriber unit.
BACKGROUND OF THE INVENTION
Until recently, most one-way pager users either had service in a single simulcast area or had nationwide service. For the first type of service, messages are simulcast from a single group of transmitters. For nationwide service the messages are replicated on all simulcast areas across the nation. Obviously, nationwide service is very expensive for the service providers.
Recently, “Follow Me Roaming” (FMR) has become available. Under FMR, the user normally has service in only one simulcast area, i.e. the user's “home” area. When the user plans to travel outside the home area, he notifies the service provider of his planned itinerary, including departure and arrival times so that his messages can follow him.
FMR is becoming the method of choice by the service providers for providing nationwide coverage, because messages do not have to be sent in all coverage areas. They just have to be sent to the area where the user is. The most thoughtfully implemented FMR systems operate with an “overlap interval” around the departure and arrival times. During the overlap interval, messages are replicated both in the area being departed and in the arrival area. This is done to provide a “grace period” having upper and lower limits for accommodating temporal variations in the departure and arrival times. Additional time generally is put into the upper limit of the overlap interval to accommodate uncertainty in the channel search time required for the pager to find a new messaging system in each arrival area.
Uncertainty in the channel search time occurs because prior art subscriber units do not search for a new system until they lose the signal from a currently received system. Because system coverage areas can overlap, it is possible for a subscriber unit that has visited, for example, a second system adjacent to the home system to remain locked to the second system for a long time—possibly hours or days—after the subscriber unit has returned to the home area. If message replication is halted before the subscriber unit has switched back to the home area, messages transmitted only in the home area will be missed. On the other hand, message replication costs air time, causing the service provider to want to keep message replication time as short as possible.
A related problem affects a prior art two-way subscriber unit which has switched to one-way operation with a one-way system, due to the unavailability of a usable two-way system. If the subscriber unit remains within range of the one-way system, it may not search for a more appropriate two-way system for a long time, even when a usable two-way system becomes available.
Thus, what is needed is a method and apparatus for providing a predictable upper bound for a channel search time during which a portable subscriber unit searches for a more appropriate system for its message delivery. The method and apparatus preferably will allow the portable subscriber unit to find the more appropriate system even when monitoring a currently selected system, and without missing any messages.
SUMMARY OF THE INVENTION
An aspect of the present invention is a method in a plurality of messaging systems for providing a predictable upper bound for a channel search time of a portable subscriber unit. The method comprises in the portable subscriber unit the steps of selecting a first messaging system to monitor for messages; and initiating background scanning in accordance with a scan list, comprising a plurality of system parameters ranked by appropriateness for the portable subscriber unit, at a rate not slower than the rate established by a predetermined set of rules known to a controller which sends the messages to the portable subscriber unit, in an attempt to find a system identifier identifying a second messaging system more appropriate for the portable subscriber unit than the first messaging system. The method further comprises the step of concurrently monitoring the first messaging system for receiving messages until identifying the second messaging system.
Another aspect of the present invention is a portable subscriber unit operating in a plurality of messaging systems for providing a predictable upper bound for a channel search time. The portable subscriber unit comprises a receiver for receiving messages and control information, and a processing system coupled to the receiver for controlling the receiver and for processing the messages and control information. The processing system is programmed to select a first messaging system to monitor for messages, and to initiate background scanning in accordance with a scan list, comprising a plurality of system parameters ranked by appropriateness for the portable subscriber unit, at a rate not slower than the rate established by a predetermined set of rules known to a controller which sends the messages to the portable subscriber unit, in an attempt to find a system identifier identifying a second messaging system more appropriate for the portable subscriber unit than the first messaging system. The processing system is further programmed to concurrently monitor the first messaging system for receiving messages until identifying the second messaging system.
Another aspect of the present invention is a controller in a messaging system of a plurality of messaging systems for providing a predictable upper bound for a channel search time of a portable subscriber unit assigned to the controller. The controller comprises a network interface for receiving a message from a message originator and for conducting communications with others of the plurality of messaging systems, and a processing system coupled to the network interface for processing the message and the communications. The controller further comprises a base station interface coupled to the processing system for controlling a base station. The processing system is programmed to control the base station to transmit, during a plurality of predetermined time periods, a system identifier. The processing system is further programmed with information about a scan list in the portable subscriber unit, comprising a plurality of system parameters ranked by appropriateness for the portable subscriber unit, and with information defining for the portable subscriber unit a predetermined set of rules by which the portable subscriber unit initiates background scanning. The processing system is further programmed to cooperate with others of the plurality of messaging systems, with regard to message delivery to the portable subscriber unit, in accordance with the information about said scan list and said predetermined set of rules, thereby providing said predictable upper bound for the channel search time.
REFERENCES:
patent: 5652783 (1997-07-01), Keba et al.
patent: 5682147 (1997-10-01), Eaton et al.
Breeden R. Louis
Horabik Michael
Motorola Inc.
Shimizu M
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