Browse Prior Art Database

RECOGNITION OF INVALID SIGNALS IN SCAN WHEN USING APCO-25 COMMON AIR INTERFACE

IP.com Disclosure Number: IPCOM000009344D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2002-Aug-19
Document File: 2 page(s) / 111K

Publishing Venue

Motorola

Related People

John D. Hamrick, Jr.: AUTHOR

Abstract

Unmme delays in conventional scan represent a significant customer concern. Unmute delays can be minimized by decreasing the time required to verify that received RF activity does not meet the qualification rules for a given channel. By decreas- ing the time scan spends on a channel with unquali- tied activity the time to reach a channel with quali- tied activity is decreased. When digital activity is detected, the existing scanner always waits 360 milli seconds to allow recovery of both LDUl and LDU2 (defined below). There are cases in which recovery of both LDU's is not necessary, and the scanner can leave the channel 180 milli seconds faster. This will decrease voice umnute delays.

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Developments Technical 0 M MOTOROLA

 RECOGNITION OF INVALID SIGNALS IN 'SCAN WHEN USING APCO-25 COMMON AIR INTkRFACE

by John D. Hamrick, Jr.

ABSTRACT

  Unmme delays in conventional scan represent a significant customer concern. Unmute delays can be minimized by decreasing the time required to verify that received RF activity does not meet the qualification rules for a given channel. By decreas- ing the time scan spends on a channel with unquali- tied activity the time to reach a channel with quali- tied activity is decreased. When digital activity is detected, the existing scanner always waits 360 milli seconds to allow recovery of both LDUl and LDU2 (defined below). There are cases in which recovery of both LDU's is not necessary, and the scanner can leave the channel 180 milli seconds faster. This will decrease voice umnute delays.

STANDARDS BACKGROUND

  Voice is transmitted in TIA Project 25 Common Air Interface in 180 milli second voice data units. Two voice data units form a superframe, which takes 360ms to transmit. The fast voice data unit of a superframe is called Logical Link Data Unit 1 (LDUl); the second data unit is called Logical Link Data Unit 2(LDU2).

  LDUl contains 180 milli-seconds of vocoded voice along with several embedded data fields: Talkgroup ID, Destination ID, Network ID, and Manufacturer's ID.

  LDU2 contains 180 milli-seconds of vocoded voice along with several embedded data fields: NetworkID,AlgorithmID,andKeyID.

  Four tmmute rules are defined for qualifying the data contained in LDUl and LDU2:

  1. Digital Carrier Squelch: The data contained in LDU2 is sufficient to qualify a signal with this unmute rule. The Algorithm ID and Key lD fields

are needed to determine if the received call is NOT encrypted. If the call is encrypted, the Algorithm ID and Key ID fields are used to determine if the speci- tied algorithm and key are available for decryption.

  2. Normal Squelch: The data contained in LDU2 is sufficient to qualify a~i signal with this unmute rule. The Network ID, Algorithm ID, and Key ID fields are needed.

  3. Selective Squelch: The data contained in LDUl and LDU2 is necessary to qualify a signal under this unmute rule.: The relevant fields are Network ID, Manufactmer's ID, Talkgroup ID, Destination ID,Algorithm ID, and Key ID.

  4. AND Squelch: The data contained in LDUl and LDU2 is necessary to;qualify a signal under this unmute rule. The relevant fields are Network ID, Manufacturer's ID, Destination ID, Algorithm ID,...