Browse Prior Art Database

ADAPTIVE DELAY REDUCTION OUTBOUND

IP.com Disclosure Number: IPCOM000008076D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-16
Document File: 3 page(s) / 115K

Publishing Venue

Motorola

Related People

Michael Kloos: AUTHOR [+2]

Abstract

Within the iDEN system, outbound audio data is transferred at lhkbps. Voice samples are VSELP encoded, HDLC encoded, and are then transmitted from the Transcoder within the Base Site Controller (BSC) to the Base Radio (BR). The packets are then sent out over the air to the mobile on an assigned timeslot. An algorithm in the iDEN system called Just in Time Audio (JITA) is implemented to reduce outbound audio delay. JITA works by having the BR Host make estimates of how much sooner pack- ets arrive at the BR than they are needed. This rep- resents excess delay in the system. The BR Host sends the Transcoder timing estimates to change the VSELP encode window so that packets are sent down to the BR just in time to go out over the air.

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@ MOTOROLA Technical Developments

ADAPTIVE DELAY REDUCTION OUTBOUND

by Michael Kloos and lrina Veksler

BACKGROUND

  Within the iDEN system, outbound audio data is transferred at lhkbps. Voice samples are VSELP encoded, HDLC encoded, and are then transmitted from the Transcoder within the Base Site Controller (BSC) to the Base Radio (BR). The packets are then sent out over the air to the mobile on an assigned timeslot. An algorithm in the iDEN system called Just in Time Audio (JITA) is implemented to reduce outbound audio delay. JITA works by having the BR Host make estimates of how much sooner pack- ets arrive at the BR than they are needed. This rep- resents excess delay in the system. The BR Host sends the Transcoder timing estimates to change the VSELP encode window so that packets are sent down to the BR just in time to go out over the air.

THE PROBLEM

  There is still another source of delay in the out- bound path. Originally, packets were sent out when they were formed by the HDLC encoding process. Delay reduction can further be implemented because outbound packets sent down a slow 16kbps link to the BR have a significant amount of trans- mission time. Packets can start to be transmitted before the entire packet is formed. This decreases delay in the outbound direction. However, the delay time is hardcoded in software and represents a con-

servative estimate of how much delay can safely be removed in all cases. This delay is not optimal for each and every call and will not be optimal for dif- ferent loading conditions either.

THE SOLUTION

  The solution is an algorithm which gives the optimal delay reduction under all loading conditions and calls. A timing buffer is kept which contains estimates of how much earlier a packet co...