Browse Prior Art Database

IMPROVED VOICE TRANSPORT OVER A HEAVILY ERRORED CHANNEL

IP.com Disclosure Number: IPCOM000007967D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-09
Document File: 3 page(s) / 186K

Publishing Venue

Motorola

Related People

Dean Banwart: AUTHOR

Abstract

Traditional land-mobile radio users occasionally experience areas of extremely poor RF coverage. In such areas, voice messages can neither be transmit- ted nor received with readable clarity. Users who forego the real-time nature of a voice message can use more robust signaling and control methods to increase the odds of a successful message and per- haps even guarantee its delivery. Such an option might he useful in public safety or other emergency situations where voice message delivery is critical and the notion of moving to a better transmit loca- tion is not feasible.

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MOTOROLA Technical Developments

IMPROVED VOICE TRANSPORT OVER A HEAVILY ERRORED CHANNEL

by Dean Banwart

ABSTRACT

  Traditional land-mobile radio users occasionally experience areas of extremely poor RF coverage. In such areas, voice messages can neither be transmit- ted nor received with readable clarity. Users who forego the real-time nature of a voice message can use more robust signaling and control methods to increase the odds of a successful message and per- haps even guarantee its delivery. Such an option might he useful in public safety or other emergency situations where voice message delivery is critical and the notion of moving to a better transmit loca- tion is not feasible.

BACKGROUND

  Those who have used a two-way land mobile communications system are aware of what happens at the fringe of coverage - speech messages become broken, noisy, and garbled. Users may repeat mes- sages several times, but still the message may be unreadable by other system users. Modem digital communications systems employing digital vocoders use forward error correction and error mit- igation techniques to enhance the apparent range of the signal. But regardless of range extension tech- niques or digital modulation improvements, cover- age issues remain due to fading, shadow-loss, multi-path, signal-to-noise issues, and a host of other RF anomalies.

  Imagine a radio system user who is undergoing an emergency or duress situation or perhaps forced to leave the radio for some reason, Consider a police officer equipped with only a mobile radio who has stopped in an area of poor RF coverage to engage in a foot pursuit. This individual may need to urgently send a voice message, but repeated attempts at voice communications are likely to fail. A mode of operation would be useful whereby this user could send a voice message with greater relia-

bility and without needing to be present to make iterative call attempts.

A POTENTIAL SOLUTION

  Modem communications systems transport a variety of signals including voice, data, images, and control signaling. Each type of payload may be transported with different methods depending on the type and specific needs of the payload contents. Voice is usually a time-sensitive payload requiring real-time processing. Special attention is usually paid to voice messages to minimize any voice trun- cation or delay.

  Because of this sensitivity to time, voice sys- tems are limited in the types of forward error-cor- rection schemes which they can employ. However, if the real-time requirements of a voice message are relaxed, other options begin to arise which provide more robust transport. Such alternative schemes can alleviate some issues which arise in poor coverage or in highly-errored channel situations.

USING DATA SYSTEMS AS A TEMPLATE

  Systems which transport data messages are not as time-intensive as voice systems and therefore typically use different transport schemes. Data sys- tems typically employ RF re-try mechanisms an...