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Browse Prior Art Database

ADAPTIVE ENCODE DELAY TO REMOVE PACKET TIMING JITTER

IP.com Disclosure Number: IPCOM000008638D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jun-28
Document File: 2 page(s) / 88K

Publishing Venue

Motorola

Related People

Michael Kloos: AUTHOR [+2]

Abstract

In the current iDEN 3:l system, because the VSELP encode process runs at a background priority and can be interrupted by the decode process and because the VSELP encode inherently has a wide CPU loading depending on the type of voice stream being encoded, there exists a substantial timing variation in the encode times of various voice frames. These types of processes (i.e. 6: 1 or 3: I VSELP) are usually data-driven and a packet is generated whenever the VSELP encode is complete. For the iDEN 3:1 system, this variation is some- times too much and results in the Base Radio (BR) dropping voice packets over the air causing very choppy audio. The variation also makes JITA lock- ing either slow or non-converging, also causing choppy audio. The iDEN 6:l system sends out packets whenever the VSELP encode process is fin- ished. In Figure I, the encoded packets are sent out whenever the encode is finished. In the diagram, an example is shown of decode and encode timing in a worst case type of situation. This results in extreme timing variation.

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MOTOROLA Technical Develapnmts

ADAPTIVE ENCODE DELAY TO REMOVE PACKET TIMING JITTER

by Michael Kloos and Michael Loos

BACKGROUND

  In the current iDEN 3:l system, because the VSELP encode process runs at a background priority and can be interrupted by the decode process and because the VSELP encode inherently has a wide CPU loading depending on the type of voice stream being encoded, there exists a substantial timing variation in the encode times of various voice frames. These types of processes (i.e. 6: 1 or 3: I VSELP) are usually data-driven and a packet is generated whenever the VSELP encode is complete. For the iDEN 3:1 system, this variation is some- times too much and results in the Base Radio (BR) dropping voice packets over the air causing very choppy audio. The variation also makes JITA lock- ing either slow or non-converging, also causing choppy audio. The iDEN 6:l system sends out packets whenever the VSELP encode process is fin- ished. In Figure I, the encoded packets are sent out whenever the encode is finished. In the diagram, an

example is shown of decode and encode timing in a worst case type of situation. This results in extreme timing variation.

PROBLEM SOLUTION

  An easy solution to the problem would be to just hold all packets produced for some time to remove the jitter. This method is simple but would result in a worst case delay on all calls which is not optimal. A better approach is to use an algorithm to allow packet timing to be stabilized w...