Simulcast transmitter apparatus having automatic synchronization capability

• US 4,696,052 A
• Filed: 12/31/1985
• Issued: 09/22/1987
• Est. Priority Date: 12/31/1985
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Breeden, Robert L.
• Primary Examiner(s): NG, JIN FAY
• Application Number:
  US06/815,432
• Time in Patent Office: 630 Days
• Field of Search: 455/18, 455/33, 455/51, 455/53, 455/54, 455/56, 455/57, 375/107, 370/108
• US Class Current: 455/503
• CPC Class Codes: H04H 20/67 Common-wave systems, i.e. using separate transmitters operating on substantially the same frequency

Abstract

A simulcast transmitter apparatus having automatic synchronization capability is disclosed which utilizes a signal readily available from any one of a number of available master timing sources to maintain a constant, uniform time delay to the transmitter via its interconnect link, even though the time delay corresponding to this interconnect link is susceptible to variation. Each interconnect link may consist of a phone line or other radio link which exhibits a relatively fixed, but unstable, delay. Each base station includes at least a transmitter and an adaptive-delay device which operates as a remotely-adjustable delay network upon receipt of a resync signal from a central controller to readjust and automatically maintain a uniform amount of time delay to each transmitter in the base stations. A master timing signal receiver, such as a suitable radio navigation receiver, is coupled to a suitable fixed delay network and provides the reference sync signal for each remotely-sited base station throughout the designated geographical area. This transmitter is therefore able to be compensated for varying amounts of delay caused by utilizing alternate links which may be necessary to maintain system reliability while overcoming inclement weather, interference, or other equipment difficulties.

Claims

1. In a plurality of base stations, each having a transmitter connected to a central controller via an interconnect link having an associated time delay and forming one branch of a simulcast transmission system for transmitting message signals in a synchronized first mode, apparatus for providing automatic synchronization capability, the apparatus comprising in combination:

adaptive delay means, inserted between said interconnect link and said transmitter, having a first input electrically connected to said interconnect link and a second input for utilizing a reference sync signal; and

master timing signal receiving means electrically connected to said second input of said adaptive delay means for providing said reference sync signal thereto,

said adaptive delay means having a first and a second mode of operation, with said second mode activated upon detecting a re-sync command from said central controller at said first input and utilizing said reference sync signal at said second input for varying an adjustable time delay therein in opposite fashion to said associated delay, for re-adjusting, during said second mode and automatically maintaining during said first mode, a constant total delay from said central controller to each of said transmitters, for sending message signals from said base stations in precise time synchronization.

2. The automatic synchronization apparatus according to claim 1, wherein said adaptive delay means comprises an adjustable delay and an intelligent syn comparator.

3. The automatic synchronization apparatus according to claim 2, wherein said intellligent sync comparator comprises a re-sync detector, a timing pulse detector, and a processor-controller for controlling said adjustable delay.

4. The automatic synchronization apparatus according to claim 2, wheien said adjustable delay comprises:

a bidirectional counter having add and substract inputs;

a variable frequency clock formed by a fixed clock and a programmable divider controlled by said counter; and

a plurality of shift registers operatively controlled by said variable frequency clock to effect a delay in said message signal.

5. The automatic synchronization apparatus according to claim 1, wherein said master timing signal receiving means includes suitable radio navigation receiving means and a fixed delay network for providing said reference sync signal.

6. The automatic synchronization apparatus according to claim 5, wherein said radio navigation receiving means comprises a radio navigation receiver electronically tunable to at least one of a plurality of radio navigation signals such as a Loran-C master timing signal.

7. A method for use in a plurality of base stations, each having a transmitter connected to a central controller via an interrconnect link having an associated time delay and forming one branch of a general communication system which has a normal, synchronized first mode for transmitting message signals, the method briefly interrupting the normal mode in order to automatically re-synchronize all transmitters, the method comprising the steps of:

receiving, at each transmitter, a reference sync signal;

receiving from said central controller, a re-sync command coinciding with said reference sync signal, for switching from said first mode to a second mode;

comparing, during said second mode, the time occurrence of said re-sync command and said sync signal; and

adjusting an amount of time delay, based upon a time difference measured between said re-sync command and said sync signal, utilizing adaptive delay means included in each transmitter, so as to automatically maintain, during said first mode, a constant total delay to each of said transmitters which is equal to each and every branch time delay.

8. The method according to claim 7, wherein the step of receiving a reference sync signal includes the steps of receiving a master timing signal such as a radio navigation signal and providing a fixed time delay in order to convert said master timing signal into a suitable reference sync signal.

9. The method according to claim 7, wherein the step of comparing, during said second mode, the time occurrence of said re-sync command and said sync signal includes the steps of computing a time difference between said re-sync command and said reference sync signal in a processor-controller and outputting a delay control signal.

10. The method according to claim 7, wherein said step of adjusting an amount of time delay includes the steps of:

accepting a delay control signal from an included processor-controller to modify a previous value of time delay maintained by an included bidirectional counter which controls a variable frequency clock; and

utilizing asid variable frequency clock related to the delay control signal to effect the proper amount of time delay presently needed.

11. The method according to claim 7, wherein the step of receiving a re-sync command includes the step of activating a re-sync detector, which in turn initiates a re-synchronization mode at said transmitter by enabling a timing pulse detector.