Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Patent
1995-09-18
1999-05-04
Urban, Edward F.
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
455512, 455518, H04B 714
Patent
active
059013630
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for assigning in a mobile exchange speech items requested by subscribers belonging to the same group call group substantially simultaneously through interfaces to the mobile exchange, in which method a subscriber belonging to a group call group and wishing to speak requests a speech item through an interface to the mobile exchange.
BACKGROUND OF THE INVENTION
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 several companies or government organizations and in which the subscribers have, in addition to their own subscriber numbers, group numbers indicating the group call group or subscriber group the subscriber belongs to, thus enabling calls intended for members of a predefined group to be switched to subscribers of the group.
A group call is one of the essential functions of a private mobile radio system. A group call is used, for example, in all kinds of operations involving more than one participant, particularly when an entire group must be constantly aware of the progression of events. Typically, subscribers participating in a group call are directed one by one to speak on the same logical radio channel, and in that situation it would be desirable that several subscribers were not switched to speak simultaneously on the same channel.
Traffic in a group call in trunked networks of this kind is nearly always of the semiduplex type, i.e. listening is not possible during transmitting. This affords a significant advantage in that, within the area of one base station, all participants in a call can share the same channel irrespective of the number of participants. Only one subscriber, however, is able to speak at a time. Neither is a subscriber aware upon speaking that another subscriber is speaking at the same time.
In known, particularly analog, trunked radio networks realization of a group call is based on the use of a pressel or PTT (push-to-talk button) as a transmitter switch: by pressing the PTT, the transmitter is switched on, and the subscriber can communicate on the channel. Pressing the PTT also mutes the receiver of the subscriber unit. Each subscriber may attempt to communicate whenever he or she so wishes, and thus it is possible that several subscribers attempt to communicate simultaneously without being aware of one another. If, in a conventional system, more than one participants attempt to speak simultaneously on the same channel, the instantaneous signal strength determines which one will be heard through. If the signals have sufficiently equal power levels, none of them will be distinct enough to be audible. Furthermore, since the receiver of each speaker is muted, the speakers are not aware that the channel they are using is already in use.
The problem becomes more complex if more than one base station is connected to the same group call. In such a case, the normal solution is to add up the speech paths of the base stations in the system, for example by means of a conference connection in the mobile exchange. If two subscribers are speaking simultaneously in the service areas of different base stations, the other subscribers will hear the speech of both parties concurrently. Such a solution is typical of analog networks, but a conference connection can also be employed in digital systems with special arrangements.
The problems presented above can be solved in a digital trunked system, as a solution is known in which concurrent transmission by two subscribers in a group call is prevented, but this occurs only in the area of one base station. Yet the problem exists in practice also between subscribers located within the coverage areas of different base stations, and further between subscribers who are located within the service areas of several exchanges in a trunked network and who belong to the same group call group and participate in the same group call.
The above described
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patent: 5463617 (1995-10-01), Grube et al.
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Nokia Telecommunications Oy
Urban Edward F.
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