Browse Prior Art Database

Continuous APCO 25 Control Channel Hunt

IP.com Disclosure Number: IPCOM000004581D
Original Publication Date: 2001-Feb-22
Included in the Prior Art Database: 2001-Feb-22
Document File: 1 page(s) / 9K

Publishing Venue

Motorola

Related People

Stephen Fenwick: AUTHOR

Abstract

Continuous APCO 25 Control Channel Hunt

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Continuous APCO 25 Control Channel Hunt

by Stephen Fenwick

BACKGROUND

Whenever a Motorola APCO Project 25 compliant trunked subscriber is powered on, changes trunking systems, or goes out of range, it enters a control channel hunt algorithm in order to lock onto a control channel on a valid site. If a valid control channel is not found, the algorithm will search for a Failsoft channel (a digital channel broadcast by sites in a failure condition which enable radios to fall back to Conventional operation).

PROBLEM

The objective of the control channel hunt algorithm is to find a control channel rather than a Failsoft channel so the radio can operate in trunking mode. To maximize the chance of finding a control channel over a Failsoft channel, the algorithm is designed so that most of the search time is spent looking for a control channel, and a small amount of time is spent looking for a Failsoft channel. However, while the radio is in the "Failsoft Search" portion of the algorithm, it will ignore any control channels it detects. This is an opportunity for the radio to go into Failsoft mode for a short period of time even when there is a valid control channel available to the radio. This could impact the trunking availability of the subscriber in time-critical situations.

SOLUTION

The control channel hunt algorithm described above was originally designed for Motorola Type II trunked subscribers. In the older Type II protocol, the Failsoft channel is digital whereas the control channel is analog. This required the Type II subscribers to have a separate period of time when the radio would search for a control channel and a separate period of time when the radio would search for a Failsoft channel, because the subscriber was unable to detect these two types of channels at the same time. The same algorithm was implemented in the newer APCO Project 25 radios. However, in the newer APCO Project 25 protocol, both the Failsoft and control channels are digital and can be detected at the same time.

The solution to this problem is to modify the control channel hunt algorithm to take advantage of the fact that both the APCO Project 25 control channel and the Failsoft channel are digital channels. The Continuous APCO 25 Control Channel Hunt algorithm would accept control channels as a valid channel to lock onto as well as a Failsoft channel while in the "Failsoft Search" stage. This would maximize the chance of a APCO Project 25 subscriber locking onto a system which is fully operational (i.e., broadcasting a control channel and not broadcasting Failsoft) in the shortest amount of time, furthering Motorola's five-nines goals. This change is a small Subscriber-only enhancement which takes advantage of the newer, more robust APCO Project 25 protocol.