Control channel timing detection and self correction for digitally trunked simulcast radio communications system

• US 5,594,761 A
• Filed: 06/03/1994
• Issued: 01/14/1997
• Est. Priority Date: 06/30/1992
• Status: Expired due to Term

• Current Assignee: Pine Valley Investments, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Brown, Thomas A.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): PHAN, HAI
• Application Number:
  US08/253,600
• Time in Patent Office: 956 Days
• Field of Search: 375/356, 375/354, 375/359, 370/105.1, 370/100.1, 455/51.1, 455/51.2, 371/67.1, 371/68.1, 371/68.2, 371/71, 371/61
• US Class Current: 375/356
• CPC Class Codes: H04B 7/2684 Synchronisation of a mobile station with more than one base station
• CPC Class Codes: H04H 20/67 Common-wave systems, i.e. using separate transmitters operating on substantially the same frequency
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 56/00 Synchronisation arrangements

Abstract

A control channel timing monitor for a simulcast radio frequency (RF) digitally trunked mobile radio communications system continually monitors the outbound control channel timing of each of plural simulcasting transmitting sites. The timing of such monitored signals obtained "over the air" is compared relative to one another and/or to a reference. Fault indications identifying specific sites having faulty synchronization are produced when such comparison indicates lack of synchronization within a programmable tolerance. Appropriate corrective action (e.g., bringing down the control channel and transferring its function to a frequency formerly used for working channel functions) is taken.

Claims

1. In a simulcast radio frequency (RF) communications system that simulcasts the same signals from at least first and second RF transmission sites to portable or mobile radio transceivers over a same outbound RF control channel and same RF working channels specified by digital trunking control signals simulcasted over the same outbound RF control channel which are divided into a continuous series of frames with each frame having a synchronization portion including repetitive synchronization signals for obtaining frame and bit synchronization and a message port, ion including a digital thinking control message, wherein at least one of said radio transceivers obtains frame and bit synchronization with said first RF transmission site using the repetitive synchronization signals transmitted over said outbound RF control channel by said first transmission site, a control channel timing monitoring system, comprising:

an RF receiver other than said radio transceiver and corresponding to said first RF transmission site that receives said series of frames transmitted over said outbound RF control channel by said first RF transmission site and generates a first pulse timing signal base detection of said repetitive synchronization signals included in each frame;

a reference timer for providing a reference timing signal; and

a fault detector, connected to receive said reference timing signal and said first pulse timing signal, for determining whether said first pulse timing signal is synchronized to a least within a predetermined tolerance with said reference timing signal and for generating a fault indication if said determination reveals that said first pulse timing signal is not synchronized with said reference timing signal to at least within said predetermined tolerance.

2. The control channel timing monitoring system as in claim 1, further comprising:

a further radio receiver that receives said series of frames, along with the repetitive synchronization signals included in each frame, transmitted on said outbound RF control channel by said second RF transmission site and generates a further pulse timing signal based on a predetermined timing specified by said repetitive synchronization signals received by said further radio receiver, and said fault detector is connected to receive said further pulse timing signal and produces said fault indication when said further pulse timing signal is not synchronized with said reference timing signal to at least within said predetermined tolerance.

3. The control channel timing monitoring system as in claim 1 wherein said reference timer comprises a time base providing a timing for frame synchronization of said simulcast system, and said fault detector provides the fault indication when the timing of said first pulse timing signal differs from the timing provided by said time base.

4. The control channel timing monitoring system as in claim 1 further including means for automatically generating calibration data in response to comparison, during a calibration routine, of timing of said first pulse timing signal with the timing of said reference signal.

5. In a simulcast radio frequency (RF) communications system that simulcasts identical signals as a sequence of frames, each frame including a portion containing digital control signals and a portion containing frame synchronization signals, from at least first and second transmission sites having corresponding geographical coverage areas over a same outbound RF control channel, where a portable or mobile radio monitors the digital control signals in each frame transmitted by said first transmission site and obtains synchronization with said first transmission site using said frame synchronization signals transmitted by said first transmission site, a method of monitoring control channel timing comprising the steps of:

(a) receiving at a receiver other than said portable or mobile radio said sequence of flames transmitted over the air by said first transmission site;

(b) providing a reference timing signal;

(c) determining whether the timing of frame synchronization signals included in said sequence of frames received by said receiver in step (a) is synchronized to at least within a predetermined tolerance with said reference timing signal; and

(d) generating a fault indication if said determining step (c) reveals that said received frame synchronization signals are not synchronized with said reference timing signal to at least within said predetermined tolerance.

6. A method as in claim 5 wherein the step (b) of providing a reference timing signal comprises a step of generating a master timing signal that controls the timing of said frame synchronization signals transmitted over the air by said first transmission site.

7. A method as in claim 5 further including a step of automatically generating calibration data by comparing the timing of received frame synchronization signals with said reference timing signal.

8. In a simulcast radio frequency (RF) communications system of the type that simulcasts identical sequential frames of signals, with each frame including a portion containing digital trunking control signals and a portion containing frame synchronization signals, from at least first and second transmission sites over a same outbound RF control channel, where a portable or mobile radio monitors the digital control signals in each frame transmitted by said first transmission site and obtains synchronization with said first transmission site using said frame synchronization signal transmitted by said first transmission site, a control channel timing monitoring system comprising:

a first radio receiver other than said portable or mobile radio that receives said sequential frames transmitted by said first transmission site over said outbound RF control channel and generates a first timing signal in response to frame synchronization signals included in said sequential frames received by said first radio receiver;

a second radio receiver other than said portable or mobile radio that receives said frame synchronization signals transmitted by said second transmission site over said control channel and generates a second timing signal in response to said frame synchronization signals received by said second radio receiver; and

a timing comparator, coupled to said first and second receivers, for comparing the timing of said first timing signal with the timing of said second timing signal and for generating a fault indication if said comparison reveals the timing of said first timing signal differs by more than a certain amount from the timing of said second timing signal.

9. In a simulcast radio frequency (RF) communications system of the type that simulcasts digital control signals and frame synchronization signals from at least first and second transmission sites over the same outbound RF control channel, a method of monitoring control channel timing comprising:

receiving, at a first timing, said frame synchronization signals transmitted by said first transmission site over said RF control channel;

receiving, at a second timing, said frame synchronization signals transmitted by said second transmission site over said RF control channel;

comparing said first timing with said second timing; and

generating a fault indication if said comparison reveals said first timing differs from said second timing by more than a predetermined amount.

10. A radio frequency control channel timing monitor comprising:

a radio frequency receiver that continually monitors frame synchronization signals included in each frame of control signals transmitted over the air on a digital radio frequency control channel and generates a timing signal indicating a timing of said transmitted frame synchronization signals; and

a timing comparator connected to receive said timing signal, said timing comparator comparing said timing indicated by said timing signal with a reference timing and selectively generating a fault indication or not generating a fault indication depending on said comparison.

11. A radio frequency control channel timing monitor as in claim 10 wherein:

said radio frequency receiver monitors frame synchronization signals transmitted by a first simulcasting transmission site over said digital radio frequency control channel such that the timing signal generated thereby indicates the timing of said frame synchronization signals transmitted by said first simulcasting transmission site; and

said radio frequency control channel timing monitor further includes a further radio frequency receiver that continually monitors frame synchronization signals transmitted by a further simulcasting transmission site over the air on said digital radio frequency control channel and generates a further timing signal indicating the timing of said frame synchronization signals transmitted by said further simulcasting transmission site.

12. A radio frequency control channel timing monitor as in claim 11 wherein said timing comparator compares the timing of said timing signal generated by said radio frequency receiver with the further timing signal generated by said further radio frequency receiver and produces a fault indication if said compared timings are not identical within a predetermined tolerance.

13. A radio frequency control channel timing monitor as in claim 11 wherein said timing comparator compares the timing of each of the timing signal and the further timing signal with the reference timing.

14. A radio frequency control channel timing monitor as in claim 10 wherein said timing comparator includes delay means for introducing a delay to compensate for inherent time delays between said timing signal and said reference timing.

15. A radio frequency control channel timing monitor as in claim 10 wherein said reference timing comprises a frame timing reference, and said timing comparator includes gating means for passing said timing signal only during a time window beginning a programmable time period after occurrence of said frame timing reference.

16. A radio frequency control channel timing monitor as in claim 10 wherein said radio frequency receiver includes means for generating a digital pulse each time a frame synchronization signal is received.

17. A radio frequency control channel timing monitor as in claim 10 wherein said radio frequency receiver includes means for detecting an occurrence of said frame synchronization signals and for producing a digital pulse in response to detection of frame synchronization signals.