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DYNAMIC LENGTH REDUCTION OF DATA CHANNEL PREAMBLE ON A CHANNEL SCANNING INTEGRATED VOICE AND DATA SYSTEM

IP.com Disclosure Number: IPCOM000009229D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2002-Aug-13
Document File: 3 page(s) / 160K

Publishing Venue

Motorola

Related People

John A. Petterson: AUTHOR [+3]

Abstract

In an APCO 25, conventional (non-trunked), voice and data radio system a radio is able to listen to only one radio channel at a time. At times users have more than one channel that contains voice traf- fic of interest to them. Due to this need, radios uti- lize a scanning algorithm where the radio sequen- tially checks each frequency in its scan list to test for available voice traffic. This provides the users with an ability to listen to traffic on multiple chan- nels without a need to manually change the channel of the radio.

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m MOTOROLA v

Technical Developments

DYNAMIC LENGTH REDUCTION OF DATA CHANNEL PREAMBLE ON A CHANNEL SCANNING INTEGRATED VOICE AND DATA SYSTEM

by John A. Petterson, Michael L. Tanner and Thomas J. Senese

INTRODUCTION

  In an APCO 25, conventional (non-trunked), voice and data radio system a radio is able to listen to only one radio channel at a time. At times users have more than one channel that contains voice traf- fic of interest to them. Due to this need, radios uti- lize a scanning algorithm where the radio sequen- tially checks each frequency in its scan list to test for available voice traffic. This provides the users with an ability to listen to traffic on multiple chan- nels without a need to manually change the channel of the radio.

  It may take several seconds to complete a pass of the channels being scanned if all channels are idle. On average, a radio will be able to lock onto a channel which contains desired traflic approximate- ly l/2 of the radio's total scan cycle into the trans- mission that it is interested in. Voice messages are generally several seconds in length, allowing this type of sequential channel scanning to succeed. In contrast, data traffic is normally measured in frac- tions of a second.

PROBLEM TO BE SOLVED

  When a data message is sent to a mobile radio that is scanning for voice traffic, the mobile radio must be locked onto the channel where this data message will be transmitted prior to the start of the data message. In order to assure this, the system must transmit a preamble. The preamble must be long enough to assure the mobile radio will be locked onto the channel prior to the start of the data transmission. This means that the preamble must be longer than the maximum time it takes any mobile to complete its scan of all of the voice channels in its list. The problem addressed within this paper is the recapture of the channel bandwidth lost due to this long, fixed length preamble.

PROPOSED SOLUTION TO THE PROBLEM

  When a scanning radio detects a preamble sequence that contains that radio's ID, the radio will send an acknowledgement message to the infrastruc- ture. The infrastructure will then immediately stop sending the preamble sequence and start sending the data message. See Figure 2 for a message flow chart of this process.

  The mobile radios are half-duplex. This could cause a radio to miss the outbound data message if the radio was transmitting the preamble acknowl- edgement at the same time the preamble ended and the outbound data message was being transmitted by the infrastructure. To prevent this, each preamble block will contain the length of the remaining pre- amble sequence. The radio will use the remaining preamble length to determine whether to send a pre- amble acknowledgment. This decision will be based upon the remaining preamble length being greater then the time required for the radio to send an acknowledgement plus the time required for the infrastructure to process the acknowledge...