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MULTI-STAGE FULL SPECTRUM CONTROL CHANNEL SCAN FOR APCO PROJECT 25 SUBSCRIBERS

IP.com Disclosure Number: IPCOM000008557D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jun-24
Document File: 4 page(s) / 174K

Publishing Venue

Motorola

Related People

Richard Svienty: AUTHOR [+2]

Abstract

With the advent of wide area trunked systems, the number of frequencies a subscriber unit must maintain has increased significantly. To circumvent this problem, possible solutions include the following: * Frequency reuse is employed between sites and a wide area trunked system is meticulously con- structed such that as few as possible frequencies are allocated for control channel use while pre- venting interference among sites, . Status information about adjacent sites and their respective frequencies are broadcast out at each site and tracked by the subscriber unit.

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MOTOROLA Technical Developments

MULTI-STAGE FULL SPECTRUM CONTROL CHANNEL SCAN

FOR APCO PROJECT 25 SUBSCRIBERS

by Richard Svienty and Gary Gutknecht

1 BACKGROUND

With the advent of wide area trunked systems,

the number of frequencies a subscriber unit must maintain has increased significantly. To circumvent this problem, possible solutions include the following:

* Frequency reuse is employed between sites and a wide area trunked system is meticulously con- structed such that as few as possible frequencies are allocated for control channel use while pre- venting interference among sites,

. Status information about adjacent sites and their respective frequencies are broadcast out at each site and tracked by the subscriber unit.

* Subscriber units may attempt to find control channel synchronization via an exhaustive search through the entire band of the spectrum once other means have failed.

2 PROBLEM

  Each of the frequency tracking solutions discussed above has associated disadvantages. For example, frequency re-use among sites may be impossible, undesirable, or inefficient. This is espe- cially true as systems continue to grow in size (both in number of overall sites as well as in number of channels per site). Adjacent site broadcasts may not be sent often enough to be received by all sub- scriber units in all situations. Exhaustively scanning each frequency in the spectrum is extremely slow.

  Furthermore, the new APCO Project 25 standard proposes a method to roam to any system anywhere. Subscriber units need a better way to specify the frequencies of a single system while also providing for inter-system roaming.

3 SOLUTION

  The solution proposed by this paper will provide a means to alleviate some of the problems associated with the need for frequency reuse requirements while striving to minimize the time a subscriber unit spends finding a suitable control channel. It is geared towards subscriber units operating on APCO Project 25 systems, but could be extrapolated to work in any trunked protocol.

  This algorithm will separate the exhaustive control channel search (Full Spectrum Scan) into three different stages. The first two stages will be designed to guarantee coverage of the customer's particular system. The third stage will be designed to provide inter-system roaming. Stage 1 will place its emphasis on speed. Stage 2 will place its empha- sis on reliability. Stage 3 will be a fast, efficient search of the entire frequency band of the radio.

  The algorithm places emphasis on those frequencies important to a customer's own system through the use of (up to three) frequency ranges stored in the subscriber unit's codeplug. First, the subscriber unit will check these ranges with a quick algorithm that has approximately 95% reliability of finding the channel on the given frequency. If that search fails, the radio will check the ranges in a more reliable, somewhat slower manner that guar- antees at least 99.5% reliability. If that sea...