Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1997-09-09
2001-11-27
Maung, Nay (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S012100, C455S427000, C455S431000, C455S558000
Reexamination Certificate
active
06324405
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to communications with a mobile user, and in particular to such communications in which the link to the mobile user is via a satellite or satellites.
This invention is particularly concerned with communications to mobile platforms carrying a number of potential subscribers or users; examples of such platforms are aircraft, ships or long range buses.
BACKGROUND ART
U.S. Pat. No. 4,189,675 proposes a satellite communications method and apparatus for communicating with mobile users using a satellite in a predetermined orbit.
EP 0562374 and EP 0568778 are believed to describe the “Iridium” proposed satellite cellular mobile communication system.
An alternative proposed satellite cellular system is described in EP 0536921 and EP 0506255.
GB-A-2295296 and WO-A-96/16488 describe a satellite communications network and in particular the ground segment thereof.
Communications to and from moving platforms such as aircraft or ships have traditionally been either ground based or satellite based.
One description of a satellite based system is given in “An airline passenger telephone system design development and early trials”; J. G. Schoenenberger and R. A. McKinlay, Fourth International Conference on Satellite Systems for Mobile Communications and Navigation, Oct. 17-19, 1988, pages 97-101, published by IEE.
In the system discussed, an aircraft carries equipment to allow two voice channels to carry passenger telephone conversations via a satellite to one or a number of ground stations. Four telephone handsets are provided in the aeroplane, and are assignable to the two channels.
U.S. Pat. Nos. 5,408,515 and 5,438,610 describe a satellite based system in which aircraft are equipped with a number of phones for use by customers. The customers register their seat numbers on check in, so that it is known which customer sits at which seat. Ground stations along the likely route to be taken by the aircraft are paged by the network on receipt of an incoming call by a party who knows on which aircraft and in which seat the customer is sitting, and when the page is successfully answered by the aeroplane, a call back is set up.
Dedicated ground to air systems are known which do not involve satellites, generally via dedicated HF ground stations. These systems, however, only give partial coverage over land and little coverage at sea.
U.S. Pat. No 4,399,330 discloses a communications system for a train, in which the train carries a number of telephones (one per compartment) and a mobile terminal concentrator device which communicates with the subscriber terminals and with a ground based radio connection station. The subscribers insert “smart cards” carrying ID codes or other data, and data indicating their presence or absence on the train is transmitted to the radio station.
Various terrestrial digital cellular communications systems are known or proposed. Of these, the GSM system is widely known.
In the GSM system, as in other cellular systems, in order to be able to direct incoming calls to a user, it is necessary to be aware of the location of the user (so called “mobility management”). In GSM, this is achieved by the provision of two layers of databases; so called “home location registers” (HLRs), and so called “visiting location registers” (VLRs), and by registration and location updating signalling processes.
Subscriber data on a given user and/or user terminal is stored in a specific HLR for that user. Each mobile switching centre (MSC) associated with a particular geographical area has an associated VLR, in which are temporarily stored details necessary for call management of all users currently thought to be within the area of that MSC.
Initially, a mobile terminal scans the broadcast common control channels (BCCHs) originating from all base stations (BSCs) within its reception, and attempts to register with one. The registration takes the form of an exchange of validation data, as described in “Security aspects and the implementation in the GSM-system”, Peter C. J. van der Arend, page
4
a,
Digital Cellular Radio Conference (DCRC) Conference Proceedings, Oct. 12-14, 1998, published by Deutche Bundespost, France Telecom and FernUniversitate.
If the data match, the mobile terminal is registered as being within the area of the VLR and MSC. On registration, the identity of the VLR is stored in the HLR for the mobile terminal.
Subsequently, when incoming calls arrive for the mobile terminal, the HLR is accessed to determine the VLR where the mobile is registered and calls are then routed to the MSC associated with that VLR.
Even in idle or “sleep” mode, mobile terminals will continually or periodically scan the broadcast control channels (BCCHs) which they can receive. Each BCCH of a cell carries, amongst other data, a location area identifier (LAI) indicating an individual cell or a group of cells within a certain area. When a new location area indicator is detected (indicating that the mobile terminal has moved into a new area), the mobile terminal transmits a location update request indicating the new LAI.
The exchange of authentication data is repeated, and if the mobile terminal is authenticated the new location area indicator is written into the VLR.
Thus, the VLR continually maintains an indication of which area (and, more specifically, which cell) the mobile terminal is within.
A mobile terminal may also move between the areas of two different VLRs.
In the GSM system, there is also a signalling procedure to secure periodic registration from mobile stations, to maintain information on the status of mobile stations.
Similar issues will arise in relation to satellite communications systems; see, for example, the paper “Study on network issues of medium earth orbit satellite communications systems”; Araki et al, Proceedings of the Third International Mobile Satellite Conference IMSC 1993 (JPL publication 93-009),pages 529-534, published by Jet Propulsion Laboratories (1993). In that paper it is described how either each land earth station may issue a location area identifier signal which is carried by spot beams of satellites within the area, or each spot beam of each satellite may carry a location area identifier.
Various attempts have previously been made to integrate cellular telephony and calls to aircraft. Naturally, mobile telephone users wish to use their telephones on board moving platforms such as a aircraft, but this leads to a number of problems.
Firstly, there may be interference with on board navigation systems or other equipment.
Secondly, there may be interference between aircraft systems and other systems through the coverage regions of which the aircraft is flying.
Thirdly, due to the relatively high speed with which the customer may be moving, terrestrial systems may be insufficient to cope with the number of handovers and the sudden transient loads as the moving platform passes through their coverage region.
U.S. Pat. No 5,444,762 discloses a system in which an aircraft monitors terrestrial channels and makes use of unused channels.
One approach is to provide a local cellular base station and switching centre on board the vehicle, to treat the vehicle as a microcell. Thus, the aircraft itself can deal with all signalling to and from the cellular telephones to handle location updating.
For example, “The provision of GSM cellular radio environments within passenger aircraft operating over Europe”, I. Casewell, Fifth International Conference on Mobile, Radio and Personal Communications (Dec. 11-14, 1989) pages 57-67 published by IEE, discloses a system in which an aircraft has a transponder which includes a first air interface for communicating with mobile telephones on board, and a second air interface for communicating with terrestrial base stations.
WO 94/28684 suggests providing an aircraft with a GSM station including both a base station and a mobile switching centre, linked to terrestrial networks by a dedicated HF network. The user terminals in this case are conventional cellular handsets coupled via their external antenna s
Lu Sze-Ching
Young Eddy Ka Ping
ICO Services Ltd.
Maung Nay
McDermott & Will & Emery
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