Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Patent
1996-07-10
1998-12-22
Le, Thanh Cong
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
455514, 455519, H04B 7155
Patent
active
058527818
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This application claims benefit of international application PCT/FI95/00614, filed Nov. 10, 1995.
The invention relates to a method for establishing a group call extending to service areas of a plurality of exchanges in a mobile radio system comprising at least a first and a second exchange, telecommunication media for establishing communication connections between at least the first and the second exchange, and mobile stations communicating via said exchanges; the method comprising the step of selecting a second exchange to which the group call is routed from the first exchange.
The invention relates to a mobile radio system in which group calls are to be established between subscribers that may be located in areas of a plurality of exchanges.
BACKGROUND OF THE INVENTION
The invention is intended for use especially in so-called trunking networks that are typically company networks or private mobile radio networks used by authorities, all the channels of such networks being used by one or more companies or authority organizations. In addition to subscriber numbers, the subscribers of these networks have group numbers indicating the group call group or subscriber group that the subscriber belongs to. This makes it possible to transmit calls addressed to the members of a certain group to the subscribers of the group.
The invention is suitable for use in mobile radio systems having either a digital or an analog radio paths. The digital mobile radio systems may comply, e.g., to the TETRA system (Trans European Trunked Radio System). Analog mobile radio systems are described, e.g. in MPT 1327, A Signalling Standard for Trunked Private Land Mobile Radio Systems, January 1988, revised and reprinted November 1991, and MPT 1343, Performance Specification, January 1988, revised and reprinted September 1991, both issued by the Radiocommunications Agency, published by the British Department of Trade and Industry.
One essential feature of, e.g., the above mentioned mobile radio systems is that they allow and are designed for the implementation of a group call between several subscribers.
A group call is a conference call during which all the participants are able to both speak and listen to one another, in turns. In group calls, the entire group is called by a single call number. An individual mobile station (e.g. radio phone), or a subscriber station, may belong to several groups programmed in the respective mobile station. The system contains a file storing information about base stations associated with the number of each group. A group call may cover one, more one of or all base stations located within the area of a mobile exchange, or a plurality of mobile exchanges. To establish a group call, each base station belonging to the group allocates a traffic channel and transmits a group call request containing a group number and information about the traffic channel allocated. If a mobile station identifies as being one of a group to which it belongs the group number contained in the group call request, it switches to the traffic channel indicated by the group call request. In principle, a mobile station is thus always able to enter a group call, if it is located within the predetermined operation area of the group and if the request to enter the call originates in that area.
A group call is usually a characteristic of networks designed for special purposes. Such networks do usually not comprise many exchanges. Conventionally, the area for setting up a group call has been limited, e.g., to the area of one exchange. The problem of establishing a group call in a network of several free-connected exchanges has thus arisen as mobile radio systems have become larger in size and as one has started to establish group calls extending to service areas of several exchanges.
The conventional way of establishing a group call to service areas of several exchanges is to try and route the group call as a whole and not branch it until as close to the destination exchanges as possible.
The known methods for
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Cong Le Thanh
Nokia Telecommunications Oy
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