ATIS 0500004-2005 Recommendation for the Use of Confidence and Uncertainty for Wireless Phase 2.pdf

1、 ATIS-0500004 Recommendation for the Use of Confidence and Uncertainty for Wireless Phase 2 1ATIS is a technical planning and standards development organization that is committed to rapidly developing and promoting technical and operations standards for the communications and related information tec

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3、05 Initial Release Recommendation for the Use of Confidence and Uncertainty for Wireless Phase 2 is an ATIS standard developed by the following committee of the ATIS User Interface functional group: Emergency Services Interconnection Forum (ESIF), Subcommittee C Published by Alliance for Telecommuni

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9、 DOCUMENT IS AT THE RISK OF THE USER. 3August 26, 2005 Recommendation for the Use of Confidence and Uncertainty for Wireless Phase 2 This is the Emergency Services Interconnection Forum (ESIF) recommendation for managing location confidence and uncertainty for Wireless Phase 2 calls. The Position In

10、formation for Emergency Services is defined in ANSI T1.628-2000, Emergency Calling Service. It defines confidence and uncertainty as follows. “uncertainty code: Information that indicates the level of uncertainty inherent to the associated longitude/latitude information.” “The uncertainty r, express

11、ed in meters (in the range 1m to 1800km)” “confidence: Information identifying the confidence by which it is known that the calling party lies within the associated shape description. The confidence by which the location is known to be within the shape description, C (expressed as a percentage) is d

12、irectly mapped from the binary number K, except for K=0 which is used to indicate no information, and 100 K 127 which are not used.” ESIF has a recommendation upon the use and interpretation of confidence and uncertainty. If confidence and uncertainty can be determined by the location technology, th

13、en the location technology should fix confidence and vary uncertainty to illustrate the probable location of the caller. As to delivery of confidence and uncertainty to the PSAP along with location information (i.e., latitude and longitude), ESIF recommends that uncertainty be delivered to the PSAP.

14、 Confidence can be optionally delivered across the E2 interface. If the option is to not send confidence, then the E2 confidence field will be populated with zero. As confidence will never be computed at zero percent, a value of zero implies “no information” (in accordance with T1.628). As to confid

15、ence being displayed at the PSAP, ESIF recommends that confidence not be displayed at the PSAP, regardless of whether the confidence comes across the E2 interface. BACKGROUND ESIF Subcommittee C explored the implementation of location determination with vendors developing this technology. All of the

16、 vendors use proprietary algorithms to determine the location of a wireless caller. In most cases the longer the sampling period the more accurate the location presented. All of the vendors surveyed fix confidence and let uncertainty vary as they refine the location fix. Each vendor sets the confide

17、nce at a different percentage value. The period of time to determine a satisfactory location is determined by making a statistically significant number of location fixes to meet the FCC requirements for location accuracy. Therefore, there is value to the PSAP in delivering uncertainty, but since the

18、 confidence value is fixed, it provides no additional information that would be of value to the PSAP in dispatching emergency resources. The PSAP community is cautioned in the use of uncertainty. Because uncertainty is expressed as a circle radius and the actual algorithms to produce the location do

19、 not produce circles (e.g., some produce ellipses), there are some inherent errors in the calculation of uncertainty. Therefore, the delivery uncertainty to the PSAP can only be used for the dispatch of responding agencies to the scene and not to verify compliance of the position information with the FCC mandate for accuracy.