Browse Prior Art Database

FAULT DETECTION USING INFERRED AND DIRECT HANDOFF METRICS

IP.com Disclosure Number: IPCOM000007673D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2002-Apr-15
Document File: 2 page(s) / 126K

Publishing Venue

Motorola

Related People

Dr. Garry Hess: AUTHOR [+2]

Abstract

To date, systems featuring call handoff have com- monly selected their handoff destinations using inferred signal quality metrics. For example, talkout signal strength from candidate handoff destinations can be used to estimate the talkint signal strength that would be realized at that destination in the event a handoff to it is executed. Such estimates assume talkin and talkout path losses are compara- ble. Also, they require accurate knowledge of effec- tive radiated power and receive antenna gain for both talkin and talkout directions.

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MOlVROLA Technical Developments

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FAULT DETECTION USING INFERRED AND DIRECT HANDOFF METRICS

by Dr. Garry Hess and Mark Marsan

  To date, systems featuring call handoff have com- monly selected their handoff destinations using inferred signal quality metrics. For example, talkout signal strength from candidate handoff destinations can be used to estimate the talkint signal strength that would be realized at that destination in the event a handoff to it is executed. Such estimates assume talkin and talkout path losses are compara- ble. Also, they require accurate knowledge of effec- tive radiated power and receive antenna gain for both talkin and talkout directions.

ever, because the receiver has degraded, the actual signal-to-noise plus interference following the hand- off will probably be insufficient, prompting yet another handoff request.

  If the estimated talkin signal strength is much higher than actual signal strength, significant audio quality degradations may occur because ofunneces- sary handover flurries. Ifthe estimated talkin signal strength is much lower than actual signal strength, audio quality degradations (as well as dropped calls) may occur because of delayed or disallowed handoffs.

INTRODUCTION

PROPOSED SOLUTION

STATEMENT OF PROBLEM

  This selection methodology does not distinguish between destinations that are unusable for unavoid- able reasons, e.g., excessive path loss, or because equipmentfailures or incorrect parameter values. As an example of the latter, consider a time division multiplexed (TDM) cellular system site whose talkin capability is substantially degraded horn talkout capa- bility due to a mistuned receiver. If the base end detects insufficient talkin quality, a message report is requested from the subscriber unit. The best talkout strength observed by the subscriber unit may well

be from the current serving site; thus, the message reply would stimulate an intrasite handoffto another time slot. Because talkout is solid, the estimated talkin signal strength compared to the measured interference plus noise power on idle time slots will probably be high enough to allow the handoff How-

  By comparing the inferred talkin level to the level actually realized immediately aher handoff exe- cution, it is possible to detect equipment failures and incorrectly specified parameter values. In par- ticular, when the absolute difference between inferred and realized talkin signal strengths, averaged over a number of calls, becomes substantial, one can rea- sonably conclude that a problem exists. If system parameters are new or recently changed, they would be suspect. Otherwise, the likely explanation is equip- ment failure. Furthermore, logging such compari- sons over time provides a historical perspective of

performance which can assist scheduling preventa- tive maintenance.

  Next we will describe three different exampl...