Radio communications system

Details Radio communications system Radio communications system

1998-05-11

2001-06-26

Olms, Douglas (Department: 2661)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S348000, C455S450000

Reexamination Certificate

active

06252859

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to radio communications systems, particularly radio communications systems including a plurality of talkgroups.
BACKGROUND OF THE INVENTION
In a typical application, the radio communications system might include as many as 100 different talkgroups, each containing 50 or so individual radio units e.g. mobile and/or hand-portable radios. The talkgroups may be of the ‘all informed’ type in which data transmitted by each radio unit in a talkgroup will be received by all the other radio units in the same talkgroup.
The management of such a large number of talkgroups presents a significant technical problem. In one approach, a separate communications channel is assigned to each talkgroup. However, in practice, it is unlikely that the required number of channels would be available. Moreover, this approach would require excessive duplication of the system hardware.
In a preferred approach, the talkgroups share a relatively small number of channels. However, in existing systems, a finite set-up time is required in order to assign a communication channel to a talkgroup. More specifically, a radio unit must transmit, on a dedicated control channel, a request that one of the communication channels be assigned to its talkgroup. A finite set-up time is undesirable especially in the case of high priority communications for which delays must be kept to the minimum. Furthermore, the use of a dedicated control channel reduces the number of communication channels available to the talkgroups.
It is an object of this invention to provide a radio communications system which at least alleviates these shortcomings.
SUMMARY OF THE INVENTION
According to the invention there is provided a radio communications system including control means and a plurality of talkgroups, each talkgroup comprising a number of individual radio units having the capability to communicate with each other on one of a number of discrete communication channels temporarily assigned to that talkgroup by the control means, wherein said control means is arranged to identify a said communication channel (the selected channel) which is currently idle and to transmit a ‘Free Channel’ signal on that channel, said radio units which are not in communication are tuned to said selected channel in response to the ‘Free Channel’ signal, a said radio unit initiating communication with the other radio units in the same talkgroup will start to transmit on said selected channel to which it is already tuned, and said control means assigns the selected channel to the respective talkgroup in response to said transmission to enable all the radio units in the talkgroup to communicate with each other on the selected channel.
According to another aspect of the invention there is provided a radio communications system including a plurality of different groups of talkgroups, each talkgroup comprising a number of individual radio units having the capability to communicate with each other, a corresponding plurality of groups of communications channels, each said group of communications channels (a home group) being allocated to a different said group of talkgroups, another group of communications channels (the reserve group) which is not allocated to any particular group of talkgroups, and control means, wherein the control means is arranged to identify in each said home group of communications channels a communications channel (the selected channel) which is currently idle and to transmit a ‘free channel’ signal on that channel, the control means transmits a different ‘free channel’ signal for each said group of talkgroups and the radio units in each group of talkgroups are responsive to the ‘free channel’ signal for that group of talkgroups and are unresponsive to the ‘free channel’ signal for any other group of talkgroups, whereby a radio unit initiating communication with other radio units in the same talkgroup will start to transmit on a said selected channel carrying the ‘free channel’ signal for that talkgroup's group of talkgroups and the control means assigns the selected channel to that talkgroup in response to this transmission to enable all radio units in the talkgroup to communicate with each other on the selected channel, and the control means has the capability to transmit a said ‘free channel’ signal on an idle channel of the reserve group of communications channels and to assign that idle channel to a talkgroup if all the communications channels in the corresponding home group of communications channels have already been assigned. According to yet another aspect of the invention there is provided a method for operating a radio communications system including a plurality of talkgroups, each talkgroup comprising a number of individual radio units having the capability to communicate with each other on one of a number of discrete communication channels, the method including identifying a said communication channel (the selected channel) which is currently idle and transmitting a ‘free channel’ signal on that channel, said radio units which are not in communication being tuned to said selected channel in response to the ‘free channel’ signal so that a radio unit initiating communication with other radio units in the same talkgroup will start transmitting on the selected channel to which it is already tuned, and assigning the selected channel to the respective talkgroup in response to said transmission to enable all the radio units in the talkgroup to communicate with each other on the selected channel.


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