Telecommunications – Radiotelephone system – Special service
Reexamination Certificate
1998-06-05
2001-11-13
Bost, Dwayne (Department: 2681)
Telecommunications
Radiotelephone system
Special service
C455S426100, C455S450000, C455S517000, C379S215010, C370S329000
Reexamination Certificate
active
06317595
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of communications in general, and to radio communications in particular.
BACKGROUND OF THE INVENTION
A trunked digital radio communications system may be used to provide point to point radio communications between single users or groups of users. A user may access the trunked digital radio communications system by placing a call with a radio or user terminal and transferring voice or data information to another user terminal or group of user terminals. The information may be transferred between the user terminals on communications channels (working channels). The trunked digital radio communications system may provide multiple working channels to enable multiple users to share the trunked digital radio communications system. Free working channels may be assigned as calls are initiated within the trunked digital radio communications system. When a call is completed, the assigned working channel may be released and subsequently may be assigned to a new call.
In some trunked digital radio communications systems, a control channel may provide the working channel assignment for a particular call. For example, when a call is initiated, the working channel assignment for the call may be transmitted on the control channel. Consequently, user terminals within the trunked digital radio communications system may monitor the control channel.
A user terminal may have a user terminal identifier that identifies the user terminal within the trunked digital radio communications system. Similarly, multiple user terminals may be designated as part of a group with a corresponding group identifier. A call may, therefore, be placed to a particular user terminal or group of user terminals within the trunked digital radio communications system by indicating the proper identifier. For example, the user terminal may include a keypad to enter the user terminal identifier of the particular user terminal to be called. Alternately, the group identifier may be entered, thereby broadcasting the call to the group. A user may then initiate a call within the trunked digital radio communications system by pressing a push-to-talk (PTT) button on the user terminal. The call is then transmitted using the identifier entered by the user.
Some existing trunked digital radio communications systems may allow an on-going call between user terminals to be interrupted by a higher priority call that is transmitted to at least one of user terminals participating in the call. For example, a user terminal may include a priority switch so that the user can select the priority of the call. Subsequently, a call transmitted to a user terminal has the selected priority. Accordingly, when the high priority call is transmitted, the identified user terminal (or group of user terminals) is interrupted with the higher priority call.
When the identified user terminal (or group of user terminals) receives the interruption, the identified user terminal (or group of user terminals) switches or transfers to the higher priority call, wherein the higher priority call is transmitted on a different working channel. The user terminal typically returns to the control channel to receive the working channel assignment for the higher priority call and then transfers to the assigned working channel. However, by the time the user terminal transfers to the control channel, receives the assigned working channel, and transfers to the assigned working channel (such as in TDMA systems that use FDMA control channels), the higher priority call may have ended. Moreover, some control channels may not be synchronized to the assigned working channel, thereby possibly increasing the time to transfer to the higher priority call. In view of the above discussion, there exists a need for improved trunked digital radio communications systems.
SUMMARY OF THE INVENTION
In view of the above discussion, it is an object of the invention to provide improved trunked digital radio communications systems.
It is another object of the present invention to provide improved call transfer in trunked digital radio communications systems.
These and other objects of the present invention are provided by methods, user terminals, and base stations that allow a receiving user terminal to transfer out of a first call to a second higher priority call addressed to the user terminal using transfer data that is transmitted on a working channel. In particular, a user terminal may transfer from a first call on a first working channel to a second call on a second working channel by transmitting from the base station to the receiving user terminal transfer data in the first call on the first working channel, the transfer data identifying a second call and the second working channel. The receiving user terminal detects the transfer data in the first call on the first working channel and transfers to the second call on the second working channel based upon the transfer data.
The user terminal transfers to the second call on the second working channel by detecting that the second call from the transmitting user terminal on the second working channel is a higher priority call than the first call to the receiving user terminal. Transfer data is generated on the first working channel that identifies the second call and transmitted to the receiving user terminal within a control frame on the first working channel downlink, wherein the first working channel downlink links the base station to the receiving user terminal on the first working channel.
Improved reliability may be provided by comparing a first color code that corresponds to a higher priority call (the second call) to which the user terminal has been instructed to transfer and a second color code that corresponds to the call to which the user terminal actually transferred (the current call). Comparing the color codes may indicate that the current call is not the higher priority call to which the user terminal was instructed to transfer. For example, if the higher priority call ends and the working channel and the time slot originally assigned to the higher priority call are reassigned to a new call before the user terminal completes the transfer to the higher priority call, the user terminal may transfer to the new call, not the higher priority call. The color codes may thereby ensure that the user terminal transfers to the higher priority call.
The first color code is included within the verification data and identifies the current call within the trunked digital radio communications system. The second color code is included within the transfer data and identifies the second (higher priority) call within the trunked digital radio communications system. Comparing the first and second color code may allow the user terminal to verify that the higher priority call has not ended and that the transfer has been made to the correct call. According to the prior art, verification may not occur after the transfer from the first call to the higher priority call. The receiving user terminal of the prior art may, therefore, transfer to a call that was not intended for the receiving user terminal.
In one aspect, a user terminal that communicates with a trunked digital radio communications system includes a transceiver that receives calls from the base station on the first and second working channels. A detector, responsive to the transceiver, detects transfer data within a first call on the first working channel and a switcher, responsive to the detector, transfers to a second call on the second working channel based on the transfer data.
In another aspect, a base station within a trunked digital radio communications system includes a transceiver that relays a first call from the first transmitting user terminal to a receiving user terminal on a first working channel and receives a second call from a second transmitting user terminal on a second working channel, the first call including transfer data. A processor, responsive to the transceiver places the transfer data in the first call on the
Janky William O.
St. John James T.
Beusse Brownlee Bowdoin & Wolter P.A.
Beusse, Esq. James H.
Bost Dwayne
COM-NET Ericcson Critical Radio Systems, Inc.
Craver Charles
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