Browse Prior Art Database

ERROR DETECTION AND MITIGATION FOR IMBE PACKET AUDIO STREAMS

IP.com Disclosure Number: IPCOM000009843D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-23
Document File: 2 page(s) / 97K

Publishing Venue

Motorola

Related People

Tyrone Bekiares: AUTHOR [+3]

Abstract

There is a general trend within Motorola, and within the communications industry at large, to migrate away from circuit-based architectures toward those that are packet-based. This fundamental change in network design reopens the issue of vocoder audio quality.

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This is the abbreviated version, containing approximately 50% of the total text.

MOTOROLA

Technical Developments

ERROR DETECTION AND MITIGATION FOR IMBE PACKET AUDIO STREAMS

by Tyrone Bekiares, Gregory Feeney and Donald Newberg

BACKGROUND

There is a general trend within Motorola, and within the communications industry at large, to migrate away from circuit-based architectures toward those that are packet-based. This fundamental change in network design reopens the issue of vocoder audio quality.

In the world of dedicated circuit connections, compressed audio frames can, at worst, contain bit errors. Over shared packet connections, however, compressed audio frames may not only contain bit errors, but can be altogether lost. This is particularly true in the context of packet-based air interfaces.

Mechanisms must be in place to mitigate the effects of these errors and provide a graceful degradation of audio quality in their presenc~. Without mitigation, lost packets may cause time compression of the decompressed audio or complete loss of bit synch in the vocoder.

This invention presents a method for mitigating the effects of missing packets from a vocoded audio stream.

INVENTION

We have designed and implemented a new algorithm for concealing lost IMBE frames carried on a packet-based transport. The algorithm sits in front of the Project 25 IMBE vocoder. Together with packet reordering and jitter compensation, it presents the vocoder with a clean, circuit-like data stream even when packets have been lost. It is designed to operate at any endpoint in the packet-based network that must decode packetized IMBE audio.

The algorithm assumes that the IMBE frames will be streamed using a protocol that supports sequence numbers and/or timestamps (e.g. the RealTime Protocol). As packets are received by an end-

Motorola. lnc. 2000

point they are stored sequentially in a large array according to sequence number, not arrival time. To compensate for inter-arrival jitter, a fixed number of packet slots separate the read and write pointers.

The packet's timestamp and the host clock control movement of the read pointer through the array...