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Timing and Synchronization over Packet Networks



Mobile networks fall into two categories, Frequency Division Duplexing (FDD), which uses two separated frequency bands to transmit/receive, and Time Division Duplexing (TDD), which transmits and receives on a single frequency band. Time synchronization (in addition to frequency synchronization) is needed for LTE-TDD, WiMAX TDD, CDMA networks (popular in North America), TD-CDMA and TD-SCDMA, while only frequency synchronization is required for LTE-FDD, GSM (global system for mobile communications), W-CDMA, and other wireless technologies. Even with the use of LTE-FDD, new LTE mobile services such as network MIMO and location-based services will demand accurate time synchronization.

This project deals with clock synchronization (both time and frequency) over packet networks, specifically with the synchronization of telecom networks. Unlike IT computing systems and sensor networks, which require millisecond level accuracies to operate well, telecom networks require sub microsecond (in fact, nanosecond) level accuracies. Such stringent clock quality levels have traditionally been provided by GPS, atomic clocks, and TDM timing links. For these reasons, the ITU-T, IEEE, and other standards bodies have defined special standards to allow packet networks to support the special synchronization needs of telecom networks. One such recent standard that is now widely accepted and adopted by the telecom industry is the IEEE 1588 Precision Timing Protocol (PTP).