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ADAPTIVE WINDOWING FOR DIGITAL SYNCHRONIZATION

IP.com Disclosure Number: IPCOM000005683D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2001-Oct-25
Document File: 1 page(s) / 77K

Publishing Venue

Motorola

Related People

Kenneth J. Crisler: AUTHOR

Abstract

In many digital communications systems, synchronization is achieved by detection of adigital pattern which is repeated regularly. An enable signal or "window" can be used to reduce the likelihood of a false detection by disabling the detector circuits between transmissions of the sync pattern. However, prior to acquisition of synchronization, a narrow window can significantly hamper efforts to detect sync. Thus it is desirable to generate a window signal which is open until sync is acquired and then narrows while the sync is locked.

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MOTOROlA Technical Developments Volume 7 October 1987

ADAPTIVE WINDOWING FOR DIGITAL SYNCHRONIZATION

by Kenneth J. Crisler

   In many digital communications systems, synchronization is achieved by detection of adigital pattern which is repeated regularly. An enable signal or "window" can be used to reduce the likelihood of a false detection by disabling the detector circuits between transmissions of the sync pattern. However, prior to acquisition of synchronization, a narrow window can significantly hamper efforts to detect sync. Thus it is desirable to generate a window signal which is open until sync is acquired and then narrows while the sync is locked.

   In a mobile radio environment, however, fades can cause failure to detect the sync pattern when in fact synchronization itself has not been lost. If upon failure to detect sync, the window is completely opened, the odds of a false detection are greatly increased. An adaptive window signal solves this problem by providing a detection period of increasing length in response to sync detection failures.

   The adaptive window works as follows: while the receiver is successfully detecting synchronization on every opportunity, a window is generated that is only long enough to allow for the time delay difference ex- pected in one synchronization period. One source of timing skew is due to vehicle movement. For example, avehicle moving at 60 mph could experience a datadelay change of 5 I set over aone minute period. Another factor which must be considered here is the possible offset between the base and transmit clock frequencies. If the mobile clock is significantly different than the base, the apparent delay skew could be much greater. If during one of these narrow windows, sync is not detected, a slightly larger window is generated...