Time division duplex system utilizing global positioning system timing signals for access point synchronization

• US 20030048758A1
• Filed: 09/07/2001
• Published: 03/13/2003
• Est. Priority Date: 09/07/2001
• Status: Active Grant

• Current Assignee: L3 Technologies, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Simkins, James M., Jones, Delon K.
• Granted Patent: US 7,133,397 B2
• Time in Patent Office: Days
• US Class Current: 370/280
• CPC Class Codes: H03L 7/0993 and a circuit for adding and deleting pulses
• CPC Class Codes: H04J 3/0644 External master-clock
• CPC Class Codes: H04J 3/0688 Change of the master or reference, e.g. take-over or failure of the master

Abstract

A method and apparatus for Time Division Duplex (TDD) synchronization of Access Points (APEs) uses the 1 pulse-per-second timing pulses of the Global Positioning System (GPS) and synchronization state machines for its Time Division Multiple Access (TDMA) structure. As a result, the present invention obviates the need for expensive voltage-controlled oscillators used by the prior art, and achieves stable timing accuracy within approximately 7.5 minutes, as opposed to the 12 to 24-hour period needed by prior art methods.

Claims

1. In a Time Division Duplex (TDD) system, an apparatus for temporally aligning Access Points (APEs) and Customer Premises Equipment (CPE) in the system, said apparatus comprising:

a Global Positioning System (GPS) receiver adapted to receive GPS timing signals;

an APE local oscillator;

a timing generator having a dead time counter, said timing generator coupled to said local oscillator and adapted to generate a System Timing signal;

a phase error detector adapted to compare said GPS timing signals with a symbol clock signal derived from said System Timing signal; and

a synchronization state machine coupled to said phase error detector adapted to generate synchronization information in response to the output of said phase error detector, said synchronization information adapted to adjust said APE local oscillator frequency via said dead time counter.

2. The apparatus in claim 1, wherein said synchronization information comprises a symbol time correction signal adapted to be utilized by said dead time counter to add or subtract time units to or from said local oscillator frequency, and a time marker indicating when changes to said local oscillator frequency are to occur.

3. The apparatus in claim 1, wherein said apparatus subsumes a master APE, and said apparatus further comprises a synchronization output adapted to output said synchronization information to at least one slave APE in said TDD system, and to a master clock reference, wherein said at least one slave APE is adapted to adjust slave local oscillators in accordance with said synchronization information, and said master clock reference is adapted to adjust its local oscillator in accordance with said synchronization information.

4. The apparatus in claim 3, wherein said APE receivers have timing circuits comprised of an APE receiver synchronization circuit, said receiver synchronization circuit comprising:

an APE receiver synchronization information register adapted to store synchronization information received from said master APE;

an APE receiver timing generator having a dead time counter, said timing generator coupled to said APE receiver timing and adapted to generate a System Timing signal; and

an APE receiver synchronization state machine coupled to said synchronization information register adapted to, in response to said synchronization information, adjust the burst timing of said APE receiver via said dead time counter, to synchronize the APE receiver to the master APE burst timing.

5. The apparatus in claim 1, wherein said apparatus subsumes a slave APE, and said apparatus further comprises a synchronization information register for receiving synchronization information from a master APE, and said synchronization state machine is responsive to said synchronization information from said master APE.

6. The apparatus in claim 1 further comprising in each Customer Premises Equipment (CPE) serviced by said TDD system, a CPE synchronization circuit, said CPE synchronization circuit comprising:

a CPE synchronization information register adapted to store synchronization information received from an APE;

a CPE local oscillator;

a CPE timing generator having a dead time counter, said timing generator coupled to said CPE local recovered timing and adapted to generate a System Timing signal; and

a CPE synchronization state machine coupled to said synchronization information register adapted to, in response to said synchronization information, adjust the burst time of said CPE via said dead time counter, to synchronize the CPE local burst timing with the APE master burst timing.

7. The apparatus in claim 6, wherein said CPE synchronization circuit further comprises:

a confidence counter coupled to said CPE synchronization state machine and to said CPE synchronization information register, adapted to activate said CPE synchronization state machine when synchronization information is determined by said confidence counter to be accurate.

8. In a Time Division Duplex (TDD) system, a method for temporally aligning Access Points (APEs) in the system, said method comprising the steps of:

receiving Global Positioning System (GPS) timing signals;

via an APE local oscillator, generating an APE reference clock signal;

via a timing generator having a dead time counter, generating a System Timing signal;

detecting a phase error between said GPS timing signals and a symbol clock signal derived from said System Timing signal; and

via a synchronization state machine coupled to said phase error detector, generating synchronization information in response to the output of said phase error detector, said synchronization information adapted to adjust the system burst timing via said dead time counter.

9. The method in claim 8, wherein said synchronization information comprises a symbol time correction signal adapted to be utilized by said dead time counter to add or subtract time units to or from said system burst timing, and a time marker indicating when changes to said system burst timing are to occur.

10. The method in claim 8, wherein the steps are carried out by a master APE, and said method further comprises the step of outputting said synchronization information to slave APEs in said TDD system, wherein said slave APEs are adapted to adjust slave burst timing in accordance with said synchronization information.

11. The method in claim 8, wherein a slave APE carries out said method, and said method further comprises the steps of:

via a synchronization information register, receiving synchronization information from a master APE; and

controlling the operation of said synchronization state machine by said synchronization information from said master APE.

12. The method in claim 8 further wherein each Customer Premises Equipment (CPE) serviced by said TDD system adjusts its timing according to at least the following steps:

via a CPE synchronization information register, storing synchronization information received from an APE;

via a CPE recovered timing, generating a CPE reference signal;

via a CPE timing generator coupled to said CPE recovered timing and having a dead time counter, generating a System Timing signal; and

via a CPE synchronization state machine coupled to said synchronization information register, and in response to said synchronization information, adjusting the CPE burst timing via said dead time counter, to synchronize the CPE burst timing with the APE system burst timing.

13. The method in claim 12, further comprising the step of:

via a confidence counter coupled to said CPE synchronization state machine and to said CPE synchronization information register, activating said CPE synchronization state machine when synchronization information is determined to be accurate.