Browse Prior Art Database

POLITE VOICE CHANNEL ACCESS METHOD IN ANALOG FM TRUNKING SYSTEM

IP.com Disclosure Number: IPCOM000008958D
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2002-Jul-26
Document File: 1 page(s) / 79K

Publishing Venue

Motorola

Related People

Amiram Gores: AUTHOR [+2]

Abstract

This paper deals with a common problem which is inherent to any FM radio communication system: the ability of two or more radios to transmit on the same RF channel at the same time, and by that to prohibit any radio from being heard. This paper proposes a sig- naling scheme which enables any radio to monitor when the RF channel is busy, and to allow the radio user to transmit only if the channel is free. The pm- ferred application of this method is usage in FM tnml- ing system, such as Motorola Smartnet system.

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M-LA Technical Developments

POLITE VOICE CHANNEL ACCESS METHOD IN ANALOG FM TRUNKING SYSTEM

by Amiram Gores and Aaron Elmaleh

INTRODUCTION

  This paper deals with a common problem which is inherent to any FM radio communication system: the ability of two or more radios to transmit on the same RF channel at the same time, and by that to prohibit any radio from being heard. This paper proposes a sig- naling scheme which enables any radio to monitor when the RF channel is busy, and to allow the radio user to transmit only if the channel is free. The pm- ferred application of this method is usage in FM tnml- ing system, such as Motorola Smartnet system.

PROBLEM TO BE SOLVED

  Current FM trunking systems (such as Motorola Smartnet/Smartzone systems) use one RF channel as "control channel" to direct two way radios in the net- work to specific RF channels, known as "voice chan- nels," to communicate with each other in group call mode or in private call mode. Once a radio is directed to a voice channel as a receiver, the radio (or radio user) may start transmitting on the voice channel, regardless if somebody else is already transmitting on the same voice channel. When two (or more) FM modulated RF sources transmit simultaneously (with similar RF power), the modulation of each source interferes with the others, and none of the sources can be decoded properly (jamming situation).

The reasons for a radio to transmit "on top" of another radio may be

  The radio user did not notice that the channel is busy, or keyed the radio immediately after the first radio.

  The radio is used by automatic equipment (such as a modem) which has no ability to notice if another radio is transmitting on the channel.

The current tmnking systems maintain communi- cation link between the radios which participate in the

call and the RF repeater, which is used as voice chan- nel, but this link...