Browse Prior Art Database

DIGITAL CONTROL SIGNALLING WITHOUT DEKEY

IP.com Disclosure Number: IPCOM000008545D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jun-21
Document File: 2 page(s) / 73K

Publishing Venue

Motorola

Related People

David Helm: AUTHOR

Abstract

Digital Simulcast systems are 2-way radio com- munications systems that utilize single frequency transmissions with multiple transmitters. This gives wide area coverage with a single frequency. A com- parator is the device that sources the simulcast signal and sends it to the multiple transmitters. A DekeyiRekey cycle in a Digital Simulcast system can take a long time (2-300ms). It is desirable to keep the transmitters keyed as long as possible to avoid this dekey/rekey delay.

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0 M MO-LA

Technical Developments

DIGITAL CONTROL SIGNALLING WITHOUT DEKEY

by David Helm

BACKGROUND

  Digital Simulcast systems are 2-way radio com- munications systems that utilize single frequency transmissions with multiple transmitters. This gives wide area coverage with a single frequency. A com- parator is the device that sources the simulcast signal and sends it to the multiple transmitters. A DekeyiRekey cycle in a Digital Simulcast system can take a long time (2-300ms). It is desirable to keep the transmitters keyed as long as possible to avoid this dekey/rekey delay.

PROBLEM

  The wireline bandwidth from the comparator to the station is the same as the on air bandwidth, so the station must dekey when it receives a control packet from the comparator. Even if the Control packet is short (15ms), the station must go through a complete dekey/rekey cycle to begin transmitting again. This causes large throughput delay for the subsequent signal.

  This problem occurs mainly when a console keys, interrupting a repeat signal, and sends positive indica- tion of its control parameters (positive mode control). The audio that follows the control information is

subsequently delayed for a large period of time.

SOLUTION

  There are defined Long Terminator frames (TERMLC) in the APCO 25 CA1 that are innocuous to the radio. These frames are 112 rate Reed- Soloman encoded. The comparator sends TERMLCs to the station without the Reed-Soloman parity bits, The station then adds the Re...