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Browse Prior Art Database

SINGLE FREQUENCY RE-USE WITH AUTOMATIC VEHICLE LOCATION

IP.com Disclosure Number: IPCOM000006500D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-09
Document File: 2 page(s) / 113K

Publishing Venue

Motorola

Related People

William D. Haymond: AUTHOR

Abstract

This publication describes a method of improving the Motorola Single Frequency Re-use algorithm by incorporating Automatic Vehicle Location information into the selection ofthe best outbound transmitter site.

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MOTOROLA INC. Technical Developments Volume 16 August 1992

SINGLE FREQUENCY RE-USE WITH AUTOMATIC VEHICLE LOCATION

by William D. Haymond

  This publication describes a method of improving the Motorola Single Frequency Re-use algorithm by incorporating Automatic Vehicle Location information into the selection ofthe best outbound transmitter site.

  Single frequency re-use is used for data radio net- works which must cover a large geographical area with few radio channels. In the simplest case one radio chan- nel is used to cover a large metropolitan area with as many as thirty or forty transmitter base sites, with overlapping and interfering coverage. The critical prob- lem, particularly in areas where four or five transmitters may overlap in spots, is determining which of the trans- mitters has the best probability of reaching the portable or mobile terminal in question.

  This problem is made more difficult with portable terminals, which are affected by very slow multipath fad- ing when moving at walking speeds. When stationary a portable or mobile terminal may be in a total fade for one base transmitter site but in good coverage for another base transmitter site.

  In the present Ardis network the network control processor attempts to determine the location ofthe trans- mitting terminal based on the received signal strength indication from each of the base sites receiving the trans- mission. The acknowledgement or reply outbound trans- mission is attempted via what appears to be the nearest base site, and a calculation is performed to determine which other interfering base sites can be keyed simul- taneously (with other messages) without disrupting the transmission to the terminal in question.

  Present operation ignores the effects of multipath fading, particularly the case where the terminal may be stationary,

  Since with the existing system the signal strength measurement is made on the inbound frequency which is 45 MHz offset from the outbound frequency, there is no guarantee that the outbound frequency will be sub- ject to the same path conditions. Also the base site which

receives the best signal may not be the closest site-it is simply the site which has the best propagation path for the inbound transmission. The outbound transmission, due to the 45 MHz offset, will likely follow a different path and may experience quite different conditions. In fact the best propagation path for that outbound trans- mission may be provided by a different base site.

  Since the received signal strength measurements are confused by multipath fading, the proposed technique begins by performing a path loss calculatioh to deter- mine which base site should have the clearest path in the absence of multipath fading.

  The proposed technique is based on the increasing awilabiity of small, relatively inexpensive automatic vehi- cle loca...