Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1997-04-04
2001-03-06
To, Doris H. (Department: 2745)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S441000, C455S444000, C455S456500
Reexamination Certificate
active
06198927
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communications systems and methods, in particular, to systems and methods for controlling cellular communications systems.
BACKGROUND OF THE INVENTION
Cellular communications systems are commonly employed to provide voice and/or data communications to a plurality of subscribers within an array of defined geographical regions referred to as cells. Examples of voice applications include analog cellular radiotelephone systems such as AMPS, ETACS, NMT-450, and NMT-900, as well as digital cellular radiotelephone systems such as IS-54B in North America and GSM in Europe. These systems, and others, are described, for example, in the book titled
Cellular Radio Systems
by Balston, et al., published by Artech House, Norwood, Mass., 1993. Other types of cellular systems include data communications systems such as CDPD, a digital data transmission system designed to communicate data packets over an AMPS cellular infrastructure, and personal Air Communications Technology (pACT), a two-way paging and messaging protocol and system specification for narrow-band personal communications systems (PCS), a packet data system based on the widely used Internet Protocol (IP).
FIG. 1
illustrates a typical terrestrial cellular radiotelephone communication system
20
as in the prior art. The cellular radiotelephone system may include one or more subscriber units
21
, communicating with a plurality of cells
36
served by base stations
23
and a switching office, here shown as a Mobile Telephone Switching Office (MTSO)
25
. Although only three cells
36
are shown in
FIG. 1
, a typical cellular network may include hundreds of cells, may include several switching offices, and may serve thousands, if not millions, of subscriber units. The cells
36
generally serve as nodes in the communication system
20
, from which links are established between radiotelephones
21
and the MTSO
25
, by way of the base stations
23
serving the cells
36
. Thus, for example, a duplex communication link
32
may be effected between two subscriber units
21
or between a subscriber unit
21
and an end user connected to the cellular network
20
, for example, an end user
33
utilizing a conventional landline telephone connection through a public telephone switched network
30
. The base station
23
functions to relay communications between the cell and the mobile station
21
. Those skilled in the art will appreciate that similar cellular structures may be implemented using satellites or similar devices serving similar functions to the terrestrial base stations
23
illustrated in FIG.
1
.
FIG. 2
illustrates a typical cellular packet data communications system, specifically, an architecture typically employed in CDPD and pACT networks. An important element of the network is the pACT Data Intermediate System (PDIS)
210
, a specialized router that allows a subscriber unit
220
to move among cells
240
without losing connectivity within a fixed infrastructure network such as, for example, an internet. In particular, the PDIS
210
typically provides mobility management by constructing and continuously updating a directory/routing table that maps subscriber unit IP addresses to a temporary address and channel stream that identifies which base station
230
the subscriber unit
220
is currently connected. Typically, communication between a PDIS and a subscriber unit is transparent to a Fixed End Subscriber (FES)
250
communicating with the subscriber unit
220
. The FES
250
will issue an IP packet that is routed via an internet router
260
to the subscriber unit's home PDIS. The home PDIS may either route this packet to the subscriber unit via a specific base station
230
associated with the home PDIS or pass the packet to a different PDIS if the subscriber unit
220
has moved into a new radio coverage area served by the second PDIS, with the new PDIS taking on responsibility for routing the packet to the correct base station
230
.
One way in which the PDIS can track the location of a subscriber unit is to require the subscriber unit to announce its transfers between base stations by sending a location update message on the reverse or uplink, i.e., subscriber unit to base station, channel after a cell transfer has been performed. In systems with limited reverse channel bandwidth, however, a significant portion of the reverse channel may be consumed by the transmission of location updates by subscriber units. This typically results in a congested reverse channel and a decrease in network throughput. Also, mobiles with limited battery capacity sacrifice significant battery power to transmit their location updates as they traverse each cell boundary.
SUMMARY OF THE INVENTION
In light of the foregoing, it is an object of the present invention to provide communications systems and methods using mobility management techniques which more efficiently utilize system bandwidth than conventional mobility management techniques.
It is another object of the invention to provide cellular communications systems and methods using mobility management techniques which more efficiently utilize power resources of subscriber units than conventional mobility management techniques.
These and other objects, features and advantages are provided according to the present invention by cellular communications systems and methods in which cells of the communications system are characterized according to cell types based on mobility characteristics of the subscriber unit population within the cells. Districts are defined for the cells, and a cell identification message is broadcast in each cell, identifying the cell location, the cell type and the geographic extent of the one or more districts with which the cell is associated. The cell types preferably include geographic cells and transportation corridor cells. Geographic cells are characterized as having a subscriber unit population having a low aggregate mobility, such as hand-held pedestrian units in an urban area, while transportation corridor cells are characterized as having a subscriber unit population including a subpopulation of subscriber units having a higher aggregate mobility, such as vehicular-based units on a thorofare such as a freeway. A subscriber unit registers with the districts according to the cell type and district identified in a received cell identification message. For example, if a subscriber unit is currently registered with a geographic district but encounters a predetermined number of transportation corridor cells within a predetermined time interval, indicating that the subscriber unit is traveling at a relatively high speed in a transportation corridor, the subscriber unit may register with the transportation corridor district of the highway cells. The geographic districts are preferably mobile-centric, that is, a subscriber unit, upon exiting one geographic district, registers with a new geographic district which includes cells surrounding the cell in the new district with which the subscriber registers.
The present invention stems from the realization that the frequency of location updating by subscriber units may be reduced by taking advantage of the mobility characteristics of subscriber units. For a subscriber unit which tends to linger within a relatively small geographic area, e.g., a handheld unit being operated by a pedestrian in an urban area which has a densely packed cell pattern, the use of a mobile centric geographic district surrounding the subscriber unit can help reduce the number of transitions across district boundaries and thus the number of location updates required to track the subscriber unit in the area. For a subscriber unit which is passing along a transportation corridor, e.g., a vehicle-based unit traveling along a freeway such that it passes relatively quickly through several cells, using a transportation corridor district approximately constrained to the path of the transportation corridor can reduce the number of inter-district transitions and subsequent locatio
Chapman Randy G.
Wright Andrew S.
Kincaid Lester G.
Myers Bigel & Sibley & Sajovec
Telefonaktiebolaget L M Ericsson
To Doris H.
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