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AUTOMATIC ISW DECODE WINDOW ALIGNMENT

IP.com Disclosure Number: IPCOM000007073D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2002-Feb-22
Document File: 1 page(s) / 89K

Publishing Venue

Motorola

Related People

Jane Kellenberger: AUTHOR

Abstract

This paper describes a method for automatically setting the Inbound Signaling Word (ISW) decode window opening time in an Intellirepeater. The ISW decode window is the window in time during which an ISW must arrive in the station for proper decoding. Time is measured with respect to Word Frame Inter- rupt (WFI), the timing signal to which all control channel signaling is synchronized in Motorola trunking systems. The ISW decode window is sup- posed to occur 13.66 ms after WFI, but because of variations in signal time delay in the base station transmitters and receivers for different bands, the actual time at which this window is opened needs to be adjusted for each band. Currently, delay meas- urements must be made for each band. These meas- urements are converted into constants which are then hard coded into the DSP sohware of the Station Con- trol Board. Ifat any time a receiver or transmitter is redesigned, then these measurements need to be repeated, and the DSP code modified.

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MOlOROLA Technical Developments Volume 21 February 1994

AUTOMATIC ISW DECODE WINDOW ALIGhMENT

by Jane Kellenberger

with the Intellirepeater and storing the result in non- volatile memory. If all types of subscriber units that will be used are available, then this measurement can be performed with each, and the resulting min- imum time can be stored. This procedure would be performed as part ofstation alignment.

INTRODUCTION

  This paper describes a method for automatically setting the Inbound Signaling Word (ISW) decode window opening time in an Intellirepeater. The ISW decode window is the window in time during which an ISW must arrive in the station for proper decoding. Time is measured with respect to Word Frame Inter- rupt (WFI), the timing signal to which all control channel signaling is synchronized in Motorola trunking systems. The ISW decode window is sup- posed to occur 13.66 ms after WFI, but because of variations in signal time delay in the base station transmitters and receivers for different bands, the actual time at which this window is opened needs to be adjusted for each band. Currently, delay meas- urements must be made for each band. These meas- urements are converted into constants which are then hard coded into the DSP sohware of the Station Con- trol Board. Ifat any time a receiver or transmitter is redesigned, then these measurements need to be repeated, and the DSP code modified.

  Another source ofvariability in ISW arrival time, is the time at which the subscriber unit launches the ISW All models of subscriber units are supposed to launch their ISWs at the same time with respect to their own perception ofWFI. Unfortunately, this is not the case. This fact became painfully apparent during Intellirepeater system testing. An ISW decode window opening time that was found to work with one type of subscriber unit, would not necessarily work with all types. The setting for the window open- ing that worked with all subscribers had to be found by trial and error, since there is currently no way of meas...