Remote accurate frequency generation using a numerically controlled oscillator

• US 5,801,783 A
• Filed: 10/31/1996
• Issued: 09/01/1998
• Est. Priority Date: 10/31/1996
• Status: Expired due to Term

• Current Assignee: Avaya Incorporated
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Ross, Michael R.
• Primary Examiner(s): BRITTON, HOWARD W
• Application Number:
  US08/740,593
• Time in Patent Office: 670 Days
• Field of Search: 455/507, 455/502, 455/503, 455/13.2, 455/524, 455/71, 455/75, 455/76, 455/119, 455/192.1, 455/255, 455/259, 455/260, 455/265, 455/108, 455/109, 331/1 A, 331/10, 370/324, 370/350, 370/335, 370/503, 370/508, 370/337, 370/524, 370/349, 370/426, 370/512, 375/206, 375/355, 375/356
• US Class Current: 455/502
• CPC Class Codes: H04J 3/0647 Synchronisation among TDM nodes
• CPC Class Codes: H04J 3/0691 Synchronisation in a TDM node
• CPC Class Codes: H04W 56/0035 detecting errors in frequency or phase

Abstract

Within a communication system, driving a numerically controlled oscillator with a frequency of a precision frequency oscillator and adjusting the frequency of the numerically controlled oscillator by a calculated number to be equal to that of a frequency signal derived from an external source. The calculated number utilized to adjust the numerically controlled oscillator is then transmitted to each of a number of subunits. Each subunit has another numerically controlled oscillator that is driven by a frequency derived from an internal communication link connecting the subunit to the communication system; and the other numerically controlled oscillator is controlled by the calculated number so that its frequency matches the frequency of the precision oscillator. The frequency of the internal communication link is controlled by the precision oscillator. In a second embodiment, a frequency signal derived from an external source is used to drive a numerically controlled oscillator whose frequency is adjusted by a calculated number to be equal to that of a precision frequency oscillator. The calculated number utilized to adjust the numerically controlled oscillator is then transmitted to each of a number of subunits. Each subunit has another numerically controlled oscillator that is driven by a frequency derived from an internal communication link connecting the subunit to the communication system; and the other numerically controlled oscillator is controlled by the calculated number so that its frequency matches the frequency of the precision oscillator. The internal communication link is frequency locked to the external source.

Claims

1. An apparatus for generating a frequency in a system having a controller connected to subunits via communication links, comprising:

a first oscillator for generating a first frequency signal;

a second oscillator for generating a second frequency signal in responsive to the first frequency signal;

means for generating a third frequency signal;

means for calculating a number based on the difference between the first frequency signal and the third frequency signal;

the second oscillator further responsive to the number for generating the second frequency signal so as to minimize the difference;

the controller transmitting the number to one of the subunits via one of the communication links;

means in the one of the subunits for deriving a fourth frequency signal from the communication link where the fourth frequency signal is the transmission frequency of the communication link; and

a third oscillator in the one of subunits responsive to the derived fourth frequency signal and the transmitted number to generate a fifth frequency signal that is equal to first frequency signal within a predefined limit.

2. The apparatus of claim 1 wherein means for generating derives the third frequency signal from a transmission frequency signal of an external communication link interconnecting the system to another system.

3. The apparatus of claim 2 wherein the fourth frequency signal is derived from the second frequency signal.

4. The apparatus of claim 3 wherein the second oscillator is a numerically controlled oscillator.

5. An apparatus for generating a frequency in a system having a controller connected to subunits via communication links, comprising:

a first oscillator for generating a first frequency signal;

means for generating a second frequency signal;

a second oscillator for generating a third frequency signal in responsive to the second frequency signal;

means for calculating a number based on the difference between the first frequency signal and the second frequency signal;

the second oscillator further responsive to the number for generating the third frequency signal so as to minimize the difference;

the controller transmitting the number to one of the subunits via one of the communication links;

means in the subunit for deriving the fourth frequency signal from the communication link where the fourth frequency signal is the transmission frequency of the communication link; and

a third oscillator in the subunit responsive to the derived fourth frequency signal and the transmitted number to generate a fifth frequency signal that is equal to first frequency signal within a predefined limit.

6. The apparatus of claim 5 wherein means for generating derives the second frequency signal from a transmission frequency signal of an external communication link interconnecting the system to another system.

7. The apparatus of claim 6 wherein the second oscillator is a numerically controlled oscillator.

8. An apparatus in one of a plurality of subunits of a system where the one of the plurality of subunits is connected to a central controller of the system via communication links and the apparatus recovers a first frequency in response to a transmitted number from the system that defines the difference between a transmission frequency signal of one of the communication links connecting the one of the plurality of subunits to the system and a first frequency signal in the controller, the apparatus comprising:

a circuit for recovering the transmission frequency signal from the communication link;

an oscillator;

a subunit controller response to the transmission number for communicating control information to the oscillator; and

the oscillator responsive to the transmission frequency signal and the control information to generate a second frequency signal that is equal to the first frequency signal within a predefined limit.

9. The apparatus of claim 8 wherein the oscillator is a numerically controlled oscillator.

10. An apparatus for generating a frequency including a switch node which is providing telecommunication service to a plurality of wireless handsets via a plurality of base stations each connected to the switch node via a plurality of internal telecommunication links with the switch node being interconnected to a telecommunication switching system via a plurality of external telecommunication links, comprising:

a first oscillator in the switch node for generating a first frequency signal;

a second oscillator in the switch node responsive to the first frequency signal for generating a second frequency signal;

a telecommunication interface connected to one of the plurality of external telecommunication links and recovering the transmission frequency signal of the one of the plurality of external telecommunication links;

a frequency comparator in the switch node in the switch node responsive to the second frequency signal and transmission frequency signal for determining a difference;

a controller in the switch node responsive to the determined difference for generating a number for controlling the second oscillator to modify the second frequency signal to minimize the determined difference;

the second oscillator further responsive to the number for modifying the second frequency signal;

the controller further transmitting the number to one of the plurality of base stations via one of the plurality of internal telecommunication links;

a circuit in one of the plurality of base stations for recovering another transmission frequency signal from the one of the plurality of internal telecommunication links;

a third oscillator in the one of the plurality of base stations;

a base station controller in the one of the plurality of base stations responsive to the transmitted number for communicating control information to the third oscillator; and

the third oscillator responsive to the other transmission frequency signal and the control information to generate a third frequency signal that is equal to the first frequency signal within a predefined limit.

11. The apparatus of claim 10 wherein the other transmission frequency signal is derived from the second frequency signal.

12. The apparatus of claim 11 wherein the controller responsive to loss of the one of the plurality of external telecommunication links to cease generating a number for controlling the second oscillator.

13. The apparatus of claim 12 wherein the second oscillator is a numerically controlled oscillator.

14. An apparatus for generating a frequency including a switch node which is providing telecommunication service to a plurality of wireless handsets via a plurality of base stations each connected to the switch node via a plurality of internal telecommunication links with the switch node being interconnected to a telecommunication switching system via a plurality of external telecommunication links, comprising:

a first oscillator in the switch node for generating a first frequency signal;

a telecommunication interface connected to one of the plurality of external telecommunication links and recovering the transmission frequency signal of the one of the plurality of external telecommunication links;

a second oscillator in the switch node responsive to the transmission frequency signal for generating a second frequency signal;

a frequency comparator in the switch node in the switch node responsive to the second frequency signal and transmission frequency signal for determining a difference;

a controller in the switch node responsive to the determined difference for generating a number for controlling the second oscillator to modify the second frequency signal to minimize the determined difference;

the second oscillator further responsive to the number for modifying the second frequency signal;

the controller further transmitting the number to one of the plurality of base stations via one of the plurality of internal telecommunication links;

a circuit in one of the plurality of base stations for recovering another transmission frequency signal from the one of the plurality of internal telecommunication links;

a third oscillator in the one of the plurality of base stations;

a base station controller in the one of the plurality of base stations responsive to the transmitted number for communicating control information to the third oscillator; and

the third oscillator responsive to the other transmission frequency signal and the control information t o generate a third frequency signal that is equal to the first frequency signal within a predefined limit.

15. The apparatus of claim 14 wherein the other transmission frequency signal is derived from the transmission frequency signal.

16. The apparatus of claim 15 wherein the second oscillator is a numerically controlled oscillator.

17. An apparatus in a base station is interconnected to a switch node via a telecommunication link and the base station is providing telecommunication service to a plurality of wireless handsets for recovering a first frequency in response to a transmitted number from the switch node that defines the difference between a transmission frequency signal of the telecommunication link and a first frequency signal in the switch node, comprising:

a circuit for recovering the transmission frequency signal from the telecommunication link;

an oscillator;

a base station controller responsive to the transmitted number for communicating control information to the oscillator; and

the oscillator responsive to the transmission frequency signal and the control information to generate a second frequency signal that is equal to the first frequency signal within a predefined limit.

18. The apparatus of claim 17 wherein the oscillator is a numerically controlled oscillator.

19. An apparatus for generating a frequency in a switch node which is providing telecommunication service to a plurality of wireless handsets via a plurality of base stations each connected to the switch node via a plurality of internal telecommunication links with the switch node being interconnected to a telecommunication switching system via a plurality of external telecommunication links, comprising:

a first oscillator in the switch node for generating a first frequency signal;

a second oscillator in the switch node responsive to the first frequency signal for generating a second frequency signal;

a telecommunication interface connected to one of the plurality of external telecommunication links and recovering the transmission frequency signal of the one of the plurality of external telecommunication links;

a frequency comparator in the switch node in the switch node responsive to the second frequency signal and transmission frequency signal for determining a difference;

a controller in the switch node responsive to the determined difference for generating a number for controlling the second oscillator to modify the second frequency signal to minimize the determined difference;

the second oscillator further responsive to the number for modifying the second frequency signal; and

the controller further transmitting the number to the plurality of base stations via the plurality of internal telecommunication links whereby the each of the plurality of base stations recovers the first frequency signal using the transmitted number and transmission frequency signal of each of the plurality of internal telecommunication links.

20. The apparatus of claim 19 wherein the controller responsive to loss of the one of the plurality of external telecommunication links to cease generating a number for controlling the second oscillator.

21. The apparatus of claim 20 wherein the second oscillator is a numerically controlled oscillator.