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METHOD OF UTILIZING IDLE TIME IN A DSMA SLOT AFTER AN INBOUND TRANSMISSION BY INTRODUCING A SLOT PHASE SHIFT

IP.com Disclosure Number: IPCOM000009306D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2002-Aug-15
Document File: 2 page(s) / 113K

Publishing Venue

Motorola

Related People

Stan Knapczyk: AUTHOR [+2]

Abstract

The Association of Public-Safety Communi- cations Officers (APCO) Project 25 Common Air Interface (CAI) specifications call for the use of the Digital Slotted Multiple Access (DSMA) method for subscriber radio inbound data t&tic. Inbound traffic refers to data packets transmitted by a subscriber radio and received by a base station. The base sta- tion then routes the' received data packets to a Data Controller connected via wire-line to the base sta- tion.

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MOTOROLA Technical Developments

  METHOD OF UTlLlZlNG IDLE TIME IN A DSMA SLOT AFTER AN INBOUND TRANSMISSION BY INTRODUCING A SLOT PHASE SHIFT

by Stan Knapczyk and George Popovich

PROBLEM SOLVED BY THE INVENTION

  The Association of Public-Safety Communi- cations Officers (APCO) Project 25 Common Air Interface (CAI) specifications call for the use of the Digital Slotted Multiple Access (DSMA) method for subscriber radio inbound data t&tic. Inbound traffic refers to data packets transmitted by a subscriber radio and received by a base station. The base sta- tion then routes the' received data packets to a Data Controller connected via wire-line to the base sta- tion.

  The DSMA method defines a protocol to be used for channel access that minimizes collisions on the inbound channel. To be effective. in avoiding collisions, this method requires that a subscriber unit, with a data packet queued for transmit, check the status of the inbound channel and only transmit if the inbound channel is idle. This is done by moni- toring channel status symbols transmitted by the base station on the outbound channel. These channel status symbols indicate the status of the inbound channel. The time between transmitted channel sta- tus symbols is determined first by how quickly a subscriber unit can transition from detecting an idle inbound channel to being on the air and second by how quickly the station can detect the subscriber's transmission and indicate BUSY on the outbound channel. This time is referred to as the window of vulnerability or slot time. For Motorola's APCO/ASTRO conventional integrated voice/data systems, valid channel status symbols are every 90 ms.

  Since the DSMA method requires a subscriber to wait for the next channel status symbol just in case it indicates BUSY, the subscriber's data trans- mission may be delayed up to a slot time (90 ms in Motorola's system) even if the channel is IDLE. Furthermore, if a subscriber completes transmission of a dam packet on the inbound channel just after a channel status symbol has been transmitted by the

base station, it will be nearly an entire slot time until the IDLE channel status is indicated.

DESCRIPTION OF THE INVENTION

  APCO Project 25 Common Air Interface (CAD specifications call for transmission of channel status symbols every 7.5 ms. However, since the slot time in Motorola's APCO/ASTRO conventional integrat- ed voice/data systems is 90 ms, only every 12th channel status symbol is used. The other 11 channel status symbols in the slot are not used and are assigned...