Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Patent
1995-08-23
1999-03-16
Bost, Dwayne D.
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
455442, H04Q 700
Patent
active
058841733
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a mobile radio system comprising at least a first base station, at least a further base station and at least a switching centre.
The invention further relates to a base station, switching equipment and a detection and control arrangement for such a mobile radio system.
2. Discussion of the Related Art
In a mobile radio system there are provided a plurality of base stations for maintaining radio links to mobile subscriber units. A switching centre also referenced switching system in the following is used for establishing connections to the base stations allocated to the switching system. For a handover, the switching system comprises, for example, means which hand over, as required, a connection between the switching system and a mobile subscriber station existing via a first base station (call handover base station) to a second base station (call take-over base station).
Modem mobile radio systems currently comprise many individual radio cells which have each a limited coverage area. Each cell is supplied with radio signals by a base station, while the transmitter power of the base stations and of the mobile subscriber stations is adapted to the size of a radio cell. In this manner the same radio parameters (for example, frequencies, time slots or codecs) can be used in radio cells which are a specific distance apart, without having to take mutual interference into account.
While a base station is connected to mobile subscriber stations that are located inside its cell via a radio channel, the base stations themselves are connected to switching systems, for example, via cable transmission paths. The switching systems on their part are again connected to at least one fixed network, for example, the public telephone network (PSTN=Public Switched Telephone Network, or ISDN=Integrated Services Digital Network). Via the switching systems a mobile subscriber station can be linked to an arbitrary subscriber of the respective network (mobile originating call), or a subscriber of the respective network to an arbitrary subscriber of the mobile radio network (mobile terminating call). In the case of such a link, this may conventionally relate to a call link, but also to a data link, for example, for a facsimile transmission.
The moment a mobile subscriber station leaves the coverage area of a radio cell assigned thereto, there should be provided that the radio link to the mobile subscriber station is taken over by another radio cell i.e. by another base station. The occurrence of such a change of radio cells may be detected, for example, by measuring the signal field strength, the signal-to-noise ratio, the error probability, the distance between base station and mobile subscriber unit and so on. If such a situation is detected, both the radio link is to be handed over from one base station to the take-over base station and the transmission path between a network subscriber and the handover base station is to be switched to the take-over base station.
In a call handover method which is implemented, for example, in a GSM system, first a free radio channel is to be selected by the take-over base station. This channel is announced to the mobile subscriber station, so that the mobile subscriber station can maintain the radio link along the channel announced thereto. In other systems, for example, in DECT (Digital European Cordless Telecommunication), the selection of the new radio channel is made by the mobile station.
When the mobile station is changed to the new radio channel, also the link in the cabled part of the mobile radio system is to be switched over by appropriately driving the switching systems concerned. Then there is the problem that the radio channel and the switching systems are to be switched over substantially simultaneously, so that no perceivable pauses, for example, caused by clicking sounds, or even longer pauses, occur.
For this purpose, there has also been proposed to build up a conferencing circuit of the mobile subsc
REFERENCES:
patent: 5090051 (1992-02-01), Muppidi et al.
patent: 5289525 (1994-02-01), Issenman et al.
patent: 5291544 (1994-03-01), Hecker
patent: 5483668 (1996-01-01), Malkamaki et al.
Bost Dwayne D.
Lucent Technologies
Wyche Myron K.
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