Delay equalization detector

• US 5,105,439 A
• Filed: 08/11/1989
• Issued: 04/14/1992
• Est. Priority Date: 08/11/1989
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Narayanan, Venkat, Bennett, Richard L.
• Primary Examiner(s): Safourek, Benedict V.
• Assistant Examiner(s): Tse, Young
• Application Number:
  US07/392,689
• Time in Patent Office: 977 Days
• Field of Search: 375/10, 375/11, 375/106, 375/107, 375/113, 333/18, 333/28 R, 455/51
• US Class Current: 375/224
• CPC Class Codes: H04H 20/67 Common-wave systems, i.e. using separate transmitters operating on substantially the same frequency

Abstract

An improved method for detecting that a facility delay has changed is provided. According to the invention, a facility having a delay that may change is coupled to a transmitter and a receiver. The transmitter is coupled to a first clock that transmits a first signal based on its current reading (the first clock signal) from time to time to the receiver via the facility. The receiver is coupled to a second clock that generates a second signal based on its current reading (the second clock signal) responsive to receiving the first clock signal. In operation, the first clock signal is fed downstream (via the facility having the delay), thereby triggering the second clock signal. The two clock signals are then detected and the difference in the two clock readings computed, thereby forming Δ_n. The process is then repeated for successive first and second clock signals, thereby forming Δ_n+1. The absolute value of Δ_n -Δ_n+a is then compared with a predetermined value to determine whether the facility time delay has changed. This method is particularly useful in simulcast broadcast systems.

Claims

1. In a communication system (100) comprising a transmitter (107) coupled to a receiver (111) via a channel (101) having a time delay (102) whose value may change, the transmitter (107) having a transmitter clock (109) and arranged to periodically send a transmitter signal including the transmitter clock (109)'"'"'s current reading to the receiver (111) via the channel (101), the receiver (111) having a receiver clock (113) and arranged to send a receiver signal including the receiver clock (113)'"'"'s current reading upon the transmitter signal arriving at the receiver (111), and a detector (115) coupled to the receiver (111) and arranged for recovering the transmitter signal and the transmitter clock (109) reading included therewith, and further arranged for recovering the receiver signal and the receiver clock (113) reading included therewith,

a method for the detector (115) determining when the time delay (102) has changed, comprising the steps of:

at the detector (115);

(a) recovering a transmitter signal_n and the transmitter clock reading_n included therewith;

(b) recovering a receiver signal_n and the receiver clock reading_n included therewith;

(c) calculating Δ

_n equal to the transmitter clock reading_n minus the receiver clock reading_n ;

(d) recovering a transmitter signal_n+1 and the transmitter clock reading_n+1 included therewith;

(e) recovering a receiver signal_n+1 and the receiver clock reading_n+1 included therewith;

(f) calculating Δ

_n+1 equal to the transmitter clock reading_n+1 minus the receiver clock reading_n+1 ;

(g) calculating the absolute value of Δ

_n minus Δ

_n+1 ; and

,

(h) determining when the time delay has changed by comparing the value calculated in step (g) with a predetermined value ("K"),

where n is a non-zero positive integer such as, for example, 1, 2, 3, 4, 5, . . . , and so forth.

2. The method of claim 1, where K is based on the transmitter clock and the receiver clock.

3. The method of claim 2, where K is based on the drift and stability of the transmitter clock and the drift and stability of the receiver clock.

4. The method of claim 1, wherein the detector and the receiver are located at the same site.

5. The method of claim 1, wherein the detector and the receiver are located at different sites.

6. The method of claim 1, where the communication system comprises a simulcast system.

7. In a simulcast system (300) comprising a controller (301) coupled to a transmitter (305) via a channel (303) having a time delay whose value may change, the controller (301) having a controller clock (311) and arranged to periodically send a controller signal including the controller clock'"'"'s current reading to the transmitter via the channel, the transmitter having a transmitter clock (313) and arranged to send a transmitter signal including the transmitter clock'"'"'s current reading upon the controller signal arriving at the transmitter, and a detector (325) coupled to the transmitter and arranged for recovering the controller signal and the controller clock reading included therewith, and further arranged for recovering the transmitter signal and the transmitter clock reading included therewith,

a method for the detector determining when the time delay has changed, comprising the steps of:

at the detector;

(a) recovering a controller signal_n and the controller clock reading_n included therewith;

(b) recovering a transmitter signal_n and the transmitter clock reading_n included therewith;

(c) calculating Δ

_n equal to the controller clock reading_n minus the transmitter clock reading_n ;

(d) recovering a controller signal_n+1 and the controller clock reading_n+1 included therewith;

(e) recovering a transmitter signal_n+1 and the transmitter clock reading_n+1 included therewith;

(f) calculating Δ

_n+1 equal to the controller clock reading_n+1 minus the transmitter clock reading_n+1 ;

(g) calculating the absolute value of Δ

_n minus Δ

_n+1 ; and

,

(h) determining when the time delay has changed by comparing the value calculated in step (g) with a predetermined value ("K"),

where n is a non-zero positive integer such as, for example, 1, 2, 3, 4, 5, . . . , and so forth.

8. The method of claim 7, where K is based on the controller clock and the transmitter clock.

9. The method of claim 8, where K is based on the drift and stability of the controller clock and the drift and stability of the transmitter clock.

10. The method of claim 7, wherein the detector and the transmitter are located at the same site.

11. The method of claim 7, wherein the detector and the transmitter are located at different sites.