Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-09-30
2002-07-09
Bost, Dwayne (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S515000, C455S452200
Reexamination Certificate
active
06418313
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to communication systems and more particularly to acquisition of communication systems by mobile terminals.
BACKGROUND OF THE INVENTION
Public wireless radiotelephone systems are commonly employed to provide voice and data communications to subscribers. For example, analog cellular radiotelephone systems, such as designated AMPS, ETACS, NMT-450, and NMT-900, have long been deployed successfully throughout the world. Digital cellular radiotelephone systems such as those conforming to the North American standard IS-54 and the European standard GSM have been in service since the early 1990's. More recently, a wide variety of wireless digital services broadly labeled as PCS (Personal Communications Services) have been introduced, including advanced digital cellular systems conforming to standards such as IS-136 and IS-95, lower-power systems such as DECT (Digital Enhanced Cordless Telephone) and data communications services such as CDPD (Cellular Digital Packet Data). These and other systems are described in
The Mobile Communications Handbook
, edited by Gibson and published by CRC Press (1996).
FIG. 1
illustrates a conventional terrestrial wireless public communication system
20
that may implement one of the aforementioned wireless communication standards. The wireless system may include one or more wireless mobile terminals
22
that communicate within a plurality of cells
24
served by base stations
26
and a mobile telephone switching office (MTSO)
28
. Although only three cells
24
are shown in
FIG. 1
, a typical cellular radiotelephone network may comprise hundreds of cells, and may include more than one MTSO
28
and may serve thousands of wireless mobile terminals
22
.
The cells
24
generally serve as nodes in the communication system
20
, from which links are established between wireless mobile terminals
22
and a MTSO
28
, by way of the base stations
26
servicing the cells
24
. Each cell
24
will have allocated to it one or more dedicated control channels and one or more traffic channels. Through the communication system
20
, a duplex radio communication link
30
may be effected between two wireless mobile terminals
22
or between a wireless mobile terminal
22
and a landline telephone user
32
via a public switched telephone network (PSTN)
34
. The function of the base station
26
is commonly to handle the radio communications within the cell
24
to and from the wireless mobile terminal
22
. In this capacity, the base station
26
functions chiefly as a relay station for data and voice signals.
As mobile terminals in cellular radio communication systems may cross geographic regions served by different base stations, it is known in the prior art that means should be provided to select the appropriate base station to service a mobile terminal. In the U.S. AMPS system, the mobile terminal would typically use signal strength measurements (such as RSSI) to determine the strongest base station to which it should listen for calls during standby (idle) mode. This determination of which base station to communicate with may be referred to as site scanning (reselection) as periodically the radiotelephone determines the RSSI for other base station sites. Also in the U.S. AMPS system, base stations belonging to the cellular network typically listen to the signal strengths received from mobile telephones that are actively transmitting during calls, and the network uses its measurements to determine an optimum base station for handling a call in progress. When a call in progress is switched from one base station to another, it is commonly known as “handover” or “handoff.”
Cellular telephones using a Time Division Multiple Access (TDMA) method conforming to the TDMA cellular standards, for example, those known respectively as GSM, D-AMPS, IS54, IS136 or PCS1900, may use spare time between transmit and receive timeslots to change frequency and monitor the signal strengths of other base stations. The mobile telephone may make measurements of the signal strengths received from surrounding base stations. Mobile Assisted Handover (MAHO) may be implemented using these measurements. The measurements are typically reported to the currently serving base station, which determines if a handoff or reselection should be made to another base station.
The control channel as described above is a dedicated channel used for transmitting cell identification and paging information often referred to as a broadcast control channel (BCCH). Identification information in, for example, an IS-136 system may be referred to as a Public Service Profile (PSP) and may include frequency information on various channels as well as the cell's associated Digital Voice Color Code (DVCC), System Identification (SID), System Operator Code (SOC) and Mobile Country Code (MCC). The traffic channels carry the voice and data information. The dedicated control channels are generally broadcast using a different radio frequency in each cell to allow frequency reuse for greater system capacity while limiting the problems caused by interference. The traffic channels are also typically allocated among a plurality of radio frequencies to reduce and preferably eliminate interference using conventional frequency allocation techniques that are well known to those having skill in the art. However, capacity problems may still be encountered, such as in high population density areas.
Capacity limitations and cost and service considerations have been addressed by using private wireless communication systems, which use low power cellular transmissions that provide coverage over a smaller area. These private communication systems may be located within the coverage area of a public communication system such as one of the cellular systems described above. An indoor cellular communication system typically includes one or more mobile stations or units, one or more base stations, a radio control interface, and a mobile switching center. A typical indoor cellular network may have one or more cells.
It is desirable for mobile terminals having access rights to both public and private communication systems to determine the availability of both systems when in operation. Accordingly, it is known, for example under the IS-136, Rev. A standard, to provide mobile terminals which monitor not only for alternate base stations within the public network but also to monitor for transmissions from private communication systems. It is also known to provide transmission of identification information from private communication systems for use by the mobile terminal in its monitoring operations.
Under the IS-136 standard, the private communication system transmits identification information referred to as Private Operating Frequencies (POF). The POFs retained by a mobile terminal are a set of private communication system control frequencies previously identified by the mobile terminal as being actively in use by a private communication system within the vicinity of a public cell (associated by the mobile terminal with a specific control channel frequency) for which the mobile terminal has retained a PSP. Upon acquisition of a particular control channel (CCH) transmission, the mobile terminal may recognize the control channel as corresponding to a PSP retained by the mobile terminal and declare a PSP match. When a PSP match is declared, any stored associated POFs are treated as reselection candidates for the mobile terminal. If the mobile terminal then finds a satisfactory POF candidate (for example, with acceptable signal strength), the mobile terminal typically registers for service on the private communication network (which has an associated private system identification or PSID) and switches to a non-public mode of operation.
A mobile terminal supporting PSP/POF pursuant to the IS-136 Rev. A. standard typically stores at least 4 PSPs and 4 POFs per private communication system (PSID) as shown in Table 1 below. Each private system has an associated identifier (PSID). The PSP/POF info
Bost Dwayne
Ericsson Inc.
Myers Bigel & Sibley & Sajovec
Trinh Sonny
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