Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1992-10-02
2001-10-23
Le, Thanh Cong (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S067700, C375S357000
Reexamination Certificate
active
06308077
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to communication systems, and more specifically to synchronization of base-stations within communication systems.
BACKGROUND OF THE INVENTION
Some communications systems, and particularly a code-division multiple access (CDMA) digital cellular radiotelephone system, require that a fully functional base-station be synchronized within ±3 &mgr;S of Global Positioning System (GPS) time. In the event of a GPS failure, ±10 &mgr;S synchronization window is allowed. The present method of providing the required synchronization is through the use of the GPS satellite network and a GPS receiver. In the event of a GPS failure, a Rubidium oscillator is the present solution to providing redundancy. The use of the Rubidium oscillator for redundancy is a costly alternative for a limited amount of failure protection. A typical Rubidium oscillator will keep a previously synchronized base-station operational for a minimum of nineteen (19) hours, assuming the following:
Synchronization
⁢
⁢
Time
(
minimum
)
=
(
10
⁢
⁢
µS
-
3
⁢
⁢
µS
)
/
Osc
.
⁢
Accuracy
=
7
⁢
⁢
µS
/
1
×
10
-
10
=
19
⁢
⁢
Hrs
.
This extremely short time is obtained at an extremely high cost, approximately $4,000 per oscillator. To maintain the required synchronization between CDMA base stations, a central clocking source must be distributed to all base stations in the network. The use of a “Free Running” oscillator will allow a base-station to drift out of synchronization due to tolerances. The greatest difficulty in utilizing a central clocking source is the distribution of that signal with a consistent and predictable propagation delay throughout the network.
Thus a need exists for an apparatus and method that provides reliable redundancy for an extended period of time, while maintaining a cost-effective system design.
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patent: 4979191 (1990-12-01), Bond et al.
patent: 5016202 (1991-05-01), Seibel et al.
patent: 5023571 (1991-06-01), Fullmer et al.
patent: 5028886 (1991-07-01), Seibel et al.
patent: 5052028 (1991-09-01), Zwack
patent: 5052030 (1991-09-01), Ernst et al.
patent: 5245634 (1993-09-01), Averbuch
patent: 5261118 (1993-11-01), Vanderspool, II et al.
patent: 5331667 (1994-07-01), Izumi
patent: 0459039A1 (1990-05-01), None
patent: WO92011707 (1992-07-01), None
Cong Le Thanh
Motorola Inc.
Sonnetag Richard A.
Terry L. Bruce
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