# US 2008/0187009 A1 · Automatic delay compensated simulcasting system and method

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- Number: US 2008/0187009 A1
- Document ID: US20080187009A1
- Status: Published application
- Kind: A1
- Application number: 11/540,301
- Filed: 2006-09-29
- Published: 2008-08-07
- Earliest claimed: 2006-09-29
- Assignees: Harris Corporation
- Inventors: Junius A. Kim; Keyur R. Parikh
- Web page: https://patentgrep.com/patent/US20080187009A1

## CPC

- H04J 3/0682: {by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging}
- H04H 20/67: Common-wave systems, i.e. using separate transmitters operating on substantially the same frequency
- H04J 3/0632: {Synchronisation of packets and cells, e.g. transmission of voice via a packet network, circuit emulation service [CES] (queuing arrangements in packet switching elements H04L49/90; synchronising systems for the synchronous transmission of a pulse code modulated video signal with one or more other pulse code modulated signals H04N7/56)}
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)
- H04H: BROADCAST COMMUNICATION (multiplex communication H04J; pictorial communication aspects of broadcast systems H04N)

## Abstract

A system and method of synchronizing transmissions in a simulcast system by continuously adjusting the signal transmission delay. Timing information that includes a GPS timestamp is continuously generated at a source site, encoded into a timing packet which along with a content signal can be transported over a network link such as T1/E1 or a packet switched network to multiple transmitter sites. Once received at a transmitter site, the timing packet along with the content signal is delayed by an adjustable delay. The GPS timestamp in the received timing packet is compared to a GPS timestamp that is generated at the transmitter site upon arrival of the timing packet. Based on a variance between that comparison and the value of a user-specified target delay, the delay of the received signal is adjusted to synchronize signal transmissions in the simulcast system.

## Claims

### Claim 1

A simulcast transmission system comprising:
a source site including:
a source generator for generating a timing packet, the timing packet containing a GPS timestamp associated with the source site;
a source transmitter for transmitting the timing packet and a content signal over a link to at least two transmitter sites;
a plurality of transmitter sites adapted to be coupled over the link to the source site, each transmitter site including:
a receiver for receiving the timing packet and content signal from the link;
a comparator for comparing the GPS timestamp contained in the received timing packet to a GPS timestamp associated with the transmitter site to determine a differential ΔT representative of the difference between said timestamps;
a delay processor responsive to the comparator for delaying the received content signal by an amount related to ΔT;
whereby the content signals at said plurality of transmitter sites are substantially synchronized.

### Claim 2 (depends on 1)

A system according to claim 1, wherein each transmitter site further includes a transmitter coupled to the delay buffer, the transmitter continuously transmitting the delayed received content signal.

### Claim 3 (depends on 1)

A system according to claim 1, wherein the source site further includes a GPS receiver for generating the GPS timestamp associated with the source site.

### Claim 4 (depends on 1)

A system according to claim 1, wherein the timing packet is a framed continuous bit stream adapted for transmission on a selectable TDM timeslot or fractional timeslot

### Claim 5 (depends on 1)

A system according to claim 1, wherein the timing packet is a UDP packet that is adapted for transmission on a packet switched network.

### Claim 6 (depends on 5)

A system according to claim 5,
wherein said delay buffer includes a jitter buffer adapted to receive said packets, and is responsive to an applied clock signal to provide an adjustable delay to said packets, and
wherein said delay processor includes a frequency locked loop for generating said clock signal, wherein said delay processor is responsive IP network delay determined from said comparison so that said clock signal;
(i) when the determined network delay is static, is adapted to drive said jitter buffer to clock said pockets at the same rate said packets are received at said jitter buffer,
(ii) when the determined network delay is increasing, is adapted to drive said jitter buffer to clock said packets at a rate reduced with respect to the rate said packets are received at said jitter buffer, and
(iii) when the determined network delay is decreasing, is adapted to drive said jitter buffer to clock said packets at a rate increased with respect to the rate said packets are received at said jitter buffer.

### Claim 7 (depends on 1)

A system according to claim 1, wherein said transmitter site is coupled to the source site by a TDM connection.

### Claim 8 (depends on 1)

A system according to claim 1, wherein each transmitter site is coupled to the source site by a T1/E1 connection.

### Claim 9 (depends on 1)

A system according to claim 1, wherein each transmitter site is coupled to the source site by a packet switched network.

### Claim 10 (depends on 1)

A system according to claim 1, wherein each transmitter site further includes a GPS receiver for generating the GPS timestamp associated with the transmitter site.

### Claim 11

A method for synchronizing signal transmission in a simulcast system, the method comprising:
a) generating a timing packet at a source site, the timing packet containing a GPS timestamp associated with the source site;
b) transmitting the timing packet and a content signal over a link to a plurality of transmitter sites;
c) delaying transmission of the received content signal by an adjustable amount of delay at the transmitter site;
d) at each transmitter site, comparing the GPS timestamp in the received timing packet to a GPS timestamp associated with the transmitter site to determine a differential ΔT representative of the difference between said timestamps; and
e) at each transmitter site and in response to the comparison delaying the received content signal by an amount related to ΔT;
whereby the content signals at the plurality of transmitter sites are substantially synchronized.

### Claim 12 (depends on 11)

A method according to claim 11, further comprising the step of continuously repeating steps a) through e).

### Claim 13 (depends on 11)

A method according to claim 11, wherein the step of generating includes encoding the GPS timestamp in the timing packet.

### Claim 14 (depends on 11)

A method according to claim 11, wherein the step of generating includes obtaining the GPS timestamp from a GPS receiver located at the source site.

### Claim 15 (depends on 11)

A method according to claim 11, wherein the step of transmitting includes transmitting the timing packet as a framed continuous bit stream to the transmitter sites on a selectable TDM timeslot or fractional timeslot.

### Claim 16 (depends on 11)

A method according to claim 11, wherein the step of transmitting includes transmitting the timing packet to the receiver at the transmitter site on a single timeslot in a T1/E1 connection.

### Claim 17 (depends on 11)

A method according to claim 11, wherein the step of transmitting includes transmitting the timing packet and content signal to the transmitter sites in IP packets over a packet switched network.

### Claim 18 (depends on 17)

A method according to claim 17, wherein said delaying stop includes receiving said IP packets, and in response to an applied clock signal, adjustably delaying said packets, and
wherein said delaying step uses a frequency locked loop for generating said clock signal,
wherein said delaying step is responsive to an IP network delay determined from said comparing step:
(i) when the determined network delay is static, drives said jitter buffer to clock said packets at the same rate said packets are received at said jitter buffer,
(ii) when the determined network delay is increasing, drives said jitter buffer to clock said packets at a rate reduced with respect to the rate said packets are received at said jitter buffer, and
(iii) when the determined network delay is decreasing, drives said jitter buffer to clock said packets at a rate increased with respect to the rate said packets are received at said jitter buffer.

### Claim 19 (depends on 11)

A method according to claim 11, wherein the step of delaying includes sending the received signal through a digital buffer.

### Claim 20 (depends on 11)

A method according to claim 11, wherein the step of comparing includes obtaining the GPS timestamp from a GPS receiver located at the transmitter site.

### Claim 21

A simulcast transmitter site comprising:
a receiver for receiving a timing packet and a content signal from a link, the timing packet containing a GPS timestamp;
a comparator for comparing the GPS timestamp in the received timing packet to a GPS timestamp associated with the transmitter site to determine a differential ΔT representative of the difference between the compared timestamps; and
delay processor responsive to the comparison for delaying the received content signal by an amount related to ΔT.

### Claim 22 (depends on 21)

A system according to claim 21, wherein the transmitter site further includes a transmitter coupled to the delay buffer, the transmitter continuously transmitting the delayed received content signal.

### Claim 23 (depends on 21)

A system according to claim 21, wherein the transmitter site further includes a GPS receiver for obtaining the GPS timestamp at the transmitter site.

### Claim 24 (depends on 21)

A system according to claim 21, wherein said receiver includes a jitter buffer adapted to receive said packets, and is responsive to an applied clock signal to provide an adjustable delay to said packets, and wherein said delay processor includes a frequency locked loop for generating said clock signal, wherein said delay processor is responsive to an IP network delay determined from said so that said clock signal:
(i) when the determined network delay is static, is adapted to drive said jitter buffer to clock said packets at the same rate said packets are received at said jitter buffer,
(ii) when the determined network delay is increasing, is adapted to drive said jitter buffer to clock said packets at rate reduced with respect to the rate said packets are received at said jitter buffer, and
(iii) when the determined network delay is decreasing, is adapted to drive said jitter buffer to clock said packets at a rate increased with respect to the rate said packets are received at said jitter buffer.