ALGORITHM TO SMOOTH TIME ADVANCE CORRECTIONS

Publishing Venue

Motorola

Related People

Abstract

During co-channel interference conditions where the desired and interfering BR signals are subject to log-normal fading such that the subscriber is periodically locking into the interfering BR, the iDEN subscriber is not discarding sync timing infor- mation from the BR with the incorrect color code. Instead, the subscriber changes its timing reference to the interfering BR. When this occurs the desired BR attempts to correct any timing errors. The cor- rections, however, are not received by the subscriber since it is locked onto the interfering signal. This can lead to rapid increases in the time correction value. Consequently, when the log-normal fade sub- sides, the subscriber's time correction is erroneous. The result is an audio artifact or a dropped call.

MOTOROLA Technical Developments

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ALGORITHM TO SMOOTH TIME ADVANCE CORRECTIONS

by Tim Dickinson, Peter Hamot, Scott Zielke

  During co-channel interference conditions where the desired and interfering BR signals are subject to log-normal fading such that the subscriber is periodically locking into the interfering BR, the iDEN subscriber is not discarding sync timing infor- mation from the BR with the incorrect color code. Instead, the subscriber changes its timing reference to the interfering BR. When this occurs the desired BR attempts to correct any timing errors. The cor- rections, however, are not received by the subscriber since it is locked onto the interfering signal. This can lead to rapid increases in the time correction value. Consequently, when the log-normal fade sub- sides, the subscriber's time correction is erroneous. The result is an audio artifact or a dropped call.

  The proposed disclosure suggests implementing a delay algorithm whose purpose would be to slow down the subscriber's reaction time to rapid and/or large changes in received outbound sync symbols. The delayed reaction need only be long enough to accomodate a typical log-normal fade. See Figure 1.

Proposed time advance smoothing algorithm for subscriber active on a TCH/RACH:

If (sync detect without color-code match): time advance remains fixed (i.e. flywheel) else

If (sync detect with color-code match): time advance correction allowed with incre- menting steps no greater than 1 click betw...