Drop channel pre-alert for trunked radio communication system

• US 5,086,507 A
• Filed: 05/25/1989
• Issued: 02/04/1992
• Est. Priority Date: 05/25/1989
• Status: Expired due to Term

• Current Assignee: General Electric Company, Globe-Union Inc., Pine Valley Investments, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: Ericsson GE Mobile Communications Inc (Telefonaktiebolaget LM Ericsson)
• Inventors: Mela, Samuel S.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Charouel, Lisa
• Application Number:
  US07/356,353
• Time in Patent Office: 985 Days
• Field of Search: 455/32, 455/33, 455/34, 455/54, 455/38, 379/58, 379/59, 379/60, 379/63, 370/92-93
• US Class Current: 455/509
• CPC Class Codes: H04W 84/08 Trunked mobile radio systems

Abstract

To help prevent call bridging and increase the reliability of channel de-assignment in a trunked radio repeater system, the working channel sends a drop channel "pre-alert" message to on-channel mobile units just before sending the drop channel signal. This "pre-alert" message instructs the mobile units to continue to receive but to not attempt to access the channel by transmitting. The pre-alert message thus makes the overall trunked communications system more forgiving of coincident mobile transmissions during drop channel signalling. Under good signalling conditions there are two possibilities: (1) all mobile units detect the pre-alert, nothing is transmitted to the repeater during the pre-alert message, and a drop channel message is transmitted by the repeater following the pre-alert signal to successfully de-assign the channel; or (2) a mobile unit transmits during the pre-alert to thereby prevent the repeater from ever transmitting the drop channel message but to instead permit all mobile units to stay on the channel and continue communications. Thus, no mobile will attempt channel access during the drop channel message, and either; (a) all mobile units leave the working channel and return to the control channel, or (b) all mobile units remain on the working channel and continue to communicate.

Claims

1. In a trunked radio communications system, a method of operating plural radio frequency transceivers presently assigned for use of a radio frequency communications channel, said method comprising the following steps:

(a) monitoring said assigned channel for a period of non-use by said assigned transceivers and in response to the detection of said period of non-use;

(b) transmitting a pre-alert signal on said assigned channel;

(c) receiving said pre-alert signal present on said assigned radio frequency communications channel at each of said transceivers;

(d) inhibiting further transmission of RF signals over said assigned communications channel by each of said transceivers but with each said transceiver continuing to monitor said assigned channel in response to receipt of said pre-alert signal;

(e) subsequent to said receiving step (c), receiving a drop channel signal present on said assigned channel; and

(f) each said transceiver ceasing to monitor said assigned channel in response to receipt of said drop channel signal.

2. A method as in claim 1 wherein said step (f) includes the step of monitoring a further radio frequency communications channel instead of said assigned radio frequency communications channel.

3. A method as in claim 1 wherein said step (f) includes the step of monitoring a radio frequency control channel instead of said assigned radio frequency communications channel.

6. A method as in claim 1 further comprising the steps of:

(g) subsequent to said transmitting step (b) determining whether any of said transceivers is transmitting over said assigned channel, and

(h) inhibiting said ceasing step (f) if said determining step (g) detects that at least one of said transceivers is transmitting.

4. In a trunked radio communications system, a method of operating a radio frequency repeater system comprising the following steps:

(a) assigning an RF communications channel for use by a radio frequency transceiver;

(b) subsequent to said assigning step, commanding said radio frequency transceiver to cease transmitting on said assigned channel;

(c) confirming whether said radio frequency transceiver has ceased to transmit over said assigned channel in response to said commanding step (b);

(d) promptly de-assigning said channel if said confirming step (c) reveals said radio frequency transceiver has ceased to transmit; and

(e) continuing to enable said radio frequency transceiver to communicate on said RF communication channel if said conforming step (c) reveals said radio frequency transceiver has not ceased to transmit in response to said commanding step (b).

5. In a trunked radio communications system, a method of operating a radio frequency repeater system comprising the following steps:

(a) assigning an RF communications channel for use by a plurality of radio frequency transceivers;

(b) monitoring said use of said assigned channel by said plurality of radio frequency transceivers;

(c) detecting termination of use of said assigned channel use by said plurality of radio frequency transceivers;

(d) transmitting a pre-alert signal present over said assigned radio frequency communications channel in response to said detected use termination;

(e) subsequent to said transmitting step (d), determining whether any of said plurality of radio frequency transceivers is transmitting over said assigned channel;

(f) de-assigning said channel if said determining step (e) reveals none of said plurality of radio frequency transceivers is transmitting subsequent to said transmitting step (d); and

(g) inhibiting said de-assigning step (f) from being performed if said determining step (e) reveals at least one of said plurality of radio transceivers is transmitting.