Global Positioning System Use In Telecommunications

Phil Mann, Ed Butterline

Abstract:	Precision timing throughout the public and private digital networks is a must and thus the objective. Every telecommunications service depends on continuous, error- free transmission of information that is only possible through the use of precision synchronization systems. Today, the Global Positioning System (GPS) is the most frequently selected technology used in the United States and throughout national networks world wide. This paper describes the use of GPS within the telecommunications infrastructure today. The method to ensure each network element for modern digital communications is synchronized, is typically to procure two attributes: (1) generation of a frequency source suitable for all services and technologies; and (2) distribute that signal throughout the entire network. In the U.S. the concept is called BITS - Building Integrated Timing Supply, first defined by Bellcore and AT&T, and now prescribed by ANSI Standards for all national and regional carriers for their central office nodes. GPS with its long term frequency accuracy, ubiquitous availability, and decreasing costs over the last 6-8 years makes it very suitable to serve as the BITS source in some manner. It can serve either as the network timing source or simply as an overlay synchronization distribution network. The greatest difficulty for the telecommunications infrastructure is currently distribution of the network timing and synchronization source. Network impairments such as jitter and wander that can constantly impact data flow must be controlled. Complex network architectures such as SONET that utilize the high speed fiber bandwidth create many new demands on the network synchronization infrastructure. One concern being the large number of clocks cascaded or chained together. Digital wireless network needs, be it GSM, CDMA, TDMA, or DECT impose similiar yet different demands. The use of GPS in a direct or combined manner can reduce cost while maintaining the performance required. This is what GPS has provided today at CDMA base stations and BITS nodes. The cost of GPS timing receivers has been coming down in price while maintaining high reliability and performance. The practicality of GPS in the telecommunications infrastructure is seen in both the acceptance and cost advantages, as evidenced by the thousands GPS timing devices used in networks today. The purpose being to serve as an overlay synchronization network - either as the source, distribution framework, or both. In most cases GPS is used as the primary source and in others as the backup. The last driver for putting GPS into the infrastructure is then to gain the other benefits a local GPS source provides, network frequency verification, and Time of Day.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	1449 - 1454
Cite this article:	Mann, Phil, Butterline, Ed, "Global Positioning System Use In Telecommunications," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 1449-1454.
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