Method for routing emergency calls during busy interface channel conditions

  • US 5,596,625 A
  • Filed: 09/28/1994
  • Issued: 01/21/1997
  • Est. Priority Date: 09/28/1994
  • Status: Expired due to Term
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First Claim
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1. For use in a wireless communication system including a plurality of base stations each operative to communicate with corresponding mobile units within its coverage area over air interface channels, the method of routing an E9-1-1 call from a mobile emergency user to a public safety answering point (PSAP) where all interface channels of the corresponding base station are busy, the method comprising:

  • for each of the base stations, determining in cooperation with a receiver, a plurality of RF measurements for the base station, including its link budget, for a predetermined plurality of arc segment regions;

    for each of the base stations, modeling its determined RF measurements as a scaled contour shape having minimum and maximum boundaries which is capable of being projected on a graphical information system (GIS) ;

    determining RF measurements from neighboring base stations;

    determining where the corresponding contours of the RF measurements from neighboring base stations intersect so as to define a bounding polygon area that describes the location of the mobile emergency user in terms of a minimum and maximum error estimate;

    identifying all mobile units currently communicating with the corresponding base station of the mobile emergency user and extracting predetermined uplink and downlink RF measurements for each unit;

    by reference to the uplink and downlink RF measurements, determining which mobile units are also within the coverage areas of neighboring base stations;

    determining which of the neighboring base stations can support additional mobile units;

    determining if Automatic Link Transfers (ALTs)/handoffs/handovers of one or more of the identified mobile units at one or more of the neighboring base stations will open an interface channel for the E9-1-1 call;

    if one or more ALTs/handoffs/handovers will not open an interface channel, generating a non-voice Emergency Alarm Call (EAC) for receipt by the PSAP, the EAC including the determined location of the mobile emergency user;

    if one or more ALTs/handoffs will open an interface channel, initiating the ALTs/handoffs/handover and allowing the mobile emergency user to have the opened channel for a provisioned period of time necessary to forward the E9-1-1 call to the PSAP along with its determined location.

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