Telecommunications – Transmitter and receiver at separate stations – Single message via plural carrier wave transmission
Patent
1995-04-12
1997-05-27
Eisenzopf, Reinhard J.
Telecommunications
Transmitter and receiver at separate stations
Single message via plural carrier wave transmission
455 341, H04B 100
Patent
active
056341970
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for establishing a high-priority individual call or group call to at least one subscriber in a mobile radio system participating in a first group call conducted on a given channel.
The method of the invention is specifically designed for use in what are known as trunked networks, which are typically company networks or government networks in which all channels are shared by one or several companies or governmental agencies. In such networks the subscribers have individual subscriber numbers and also group numbers indicating the group call group or subscriber group the subscriber belongs to, thus enabling calls intended for members of a given group to be switched to subscribers of said group.
The invention is suitable to be used in mobile radio systems with digital as well as analog radio paths. Analog mobile radio systems have been described for example in MPT 1327, January 1988, revised and reprinted November 1991, A Signalling Standard for Trunked Private Land Mobile Radio Systems, and MPT 1343, January 1988, revised and reprinted September 1991, Performance Specification, United Kingdom Department of Trade and Industry, Radiocommunications Agency.
BACKGROUND OF THE INVENTION
In public mobile radio networks, such as the NMT (Nordic Mobile Telephone) system, all calls have the same priority, i.e. none of the users have rights taking precedence over the rights of other users.
In private radio networks, some of which implement the trunked method, the situation is different. In such PMR (Private Mobile Radio) networks, it is possible to control the operation of the network in such a way that users carrying out specific tasks, e.g. emergency servicing or other urgent work, have a higher priority, i.e. their high-priority calls are the first to be switched in a heavily loaded traffic situation. It is even possible to define so high a priority that an existing call is cleared down before the new call if the new call cannot otherwise be switched. In most cases, the reason for switching being prevented is the fact that all radio channels are occupied, or the fact that the called subscriber is already engaged in a call. Other resources may also in fact be occupied and prevent switching of the call.
Where two-party calls are in progress in a mobile radio system, the system--for example its mobile exchange or a database in the mobile exchange--is aware of which radio units participate in the call. On this basis, when a high-priority call is to be established to a subscriber engaged in a call, the mobile exchange can terminate the ongoing call to disengage the subscriber to whom a new call is to be established. In a group call the situation is more difficult, as the mobile exchange in the mobile radio system is not necessarily aware of which group calls given subscribers belong to, and thus the mobile exchange is not aware of which radio channel said subscribers are listening to.
A group call is a call in which the system commands several, at least three, subscribers to the same call with a single command. The groups are formed of members of a company or other user organization, and often the groups are programmed into the mobile radio and the mobile exchange is not necessarily aware of which mobile radios belong to each group. Typically one mobile radio may belong to several groups. Part of the group numbers may even be such that they may be changed very often, if necessary every morning, and an indication of these changes is not necessarily sent to the mobile exchange. For example the MPT 1327 and MPT 1343 standards do not provide for means for communicating the group numbers from the mobile radios, i.e. subscriber stations, to the mobile exchange. This makes it especially difficult to include a subscriber who is already engaged in a previously initiated group call in a high-priority call. This situation is very common in mobile radio networks, as very often specifically those subscribers who are wanted in high-priority calls already participate in prior
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Patent Abstract of Japan, vol. 15, No. 195, E-1069, Abstract of JP, A, 3-50996 (Iwatsu Electric Co. Ltd.) 5 Mar. 1991.
Patent Abstracts of Japan, vol. 13, No. 366, E-806, Abstract of JP, A, 1-122244 (Hitachi Ltd.), 15 May 1989.
Armstrong Darnell R.
Eisenzopf Reinhard J.
Nokia Telecommunications Oy
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