Wireless telephone user location capability for enhanced 911 application

Abstract

Base stations of a wireless telephone user location or position system are arranged in cell clusters and are mutually synchronized to provide very stable signal timing. A center cell or central base station (BSN) in a cluster of N cells acts as a cluster control center for purposes of user location or position finding and is provided with the capability to process information and derive user position. The other cells in a given cluster transmit received 911 data to the cluster control center. The handsets communicate with the respective cells in the normal fashion. However, when the handset dials '911', the enhanced 911 (ENH911) operation is initiated and the handset automatically changes its mode of operation: once per master frame there is included a 100 ms burst of a sequence of transmissions of unmodulated overlay PN sequence and Radamacher Walsh (RW) OCDMA code emanating from the handset only. However, other signalling formats may be used. The pattern is repeated once per master frame, the 540 ms interval between successive 100 ms bursts can be normal voice communication. When establishing a 911 call, a message is included in the handset to base station order wire data alerting the base station that a 911 call is in progress. The base stations are provided with matched filter receivers which can process the received OCDMA and overlay PN code spread signals so as to derive accurate time of arrival (TOA) data. At least three base stations within range of the handset are assigned to derive TOA data from the ENH911 signal from the handset and after processing these TOA signals are used to solve triangulation equations and obtain very accurate position or location information.