Parallel PN code acquisition for wireless positioning in CDMA handsets

Abstract

This paper proposes a simplified acquisition system for finding and identifying Base Stations (BSs) in visibility in the framework of a CDMA wireless positioning system, based on IS-95 cellular standard. The problem of having more than one BS in the same PN code acquisition system makes it necessary to discriminate between correct detection and false alarm events. Since IS-95 uses the same PN sequence for all BSs, but with different code offsets, it is possible to use a cross-correlation technique to estimate both code and frequency offsets of several BSs at once. Time-Difference-Of-Arrival (TDOA) technique is used by the Mobile Station (MS) to geolocate itself. The positioning estimate is found to be stable in time and with a precision compatible with that required by emergency services, such as Enhanced 911 (E911).