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METHOD OF ASSISTING A SUBSCRIBER UNIT WITH GEOGRAPHIC DATA FOR BETTER LOCATION FINDING ACCURACY

IP.com Disclosure Number: IPCOM000004644D
Original Publication Date: 2001-Mar-14
Included in the Prior Art Database: 2001-Mar-14
Document File: 2 page(s) / 12K

Publishing Venue

Motorola

Related People

Slim Souisisi: AUTHOR

Abstract

METHOD OF ASSISTING A SUBSCRIBER UNIT WITH GEOGRAPHIC DATA FOR BETTER LOCATION FINDING ACCURACY

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METHOD OF ASSISTING A SUBSCRIBER UNIT WITH GEOGRAPHIC DATA FOR BETTER LOCATION FINDING ACCURACY

by Slim Souisisi

INTRODUCTION

The process of locating a mobile unit consists of two main functions:

Measurement of time of arrival (TOA): This could be done by the mobile unit (downlink method) or by the infrastructure (uplink method). Without loss in generality, we assume that a downlink approach is used. TOA measurements represent the time it takes for the signal to travel between a given transmitter and the subject mobile unit.

Fusion of TOA measurements: Knowledge of TOA estimates from multiple sources along with the location of the transmitting sources, leads to a set of linear equations to which the solution is the actual position of the subscriber unit.

The fusion function may reside either at the mobile unit (GPS) or at the infrastructure (Assisted GPS). Because of the lack of DSP/memory resources on the mobile side, subscriber based fusion algorithms are kept simple. Their accuracy performance is usually lower than sophisticated fusion technology used on the infrastructure side.

The availability of computational and memory resources at the infrastructure side allows for the use of enhanced fusion techniques. These techniques are based on advanced multipath rejection algorithms as well as topography based ambiguity resolution techniques.

PROBLEM TO BE SOLVED

Because of the complexity of the fusion process, current location systems architecture uses a fusion server which resides at the infrastructure side. An important fusion feature uses geographic data bases to resolve the ambiguity on the subscriber position. The use of geographic data bases is restricted to infrastructure based positioning solutions.

It is believed that in the future, the mobile units will have large enough memory and computation power to perform enhanced fusion algorithms.

SOLUTION

We suggest to transmit a geographic data base to the mobile unit in order to provide assistance in the calculation of the subscriber position. The geographic data base may include terrain, building, roads, rivers etc.

The operation of the proposed technique is as follows:

1. The subscriber unit attempts to locate itself.

2. The system knowing the approximate location of the unit (from cell id), sends a geographic file that describes the local area.

3. The subscriber unit uses the geographic data base to enhance the accuracy on the position by using geographic weighting factors to eliminate unlikely solutions.

Acronyms

TOA: Time of arrival

GPS: Global positioning system

AGSP: Assisted GPS

EOTD: Enhanced Observed Time difference. Suggested new elements

SUGGESTED NEW ELEMENTS

The transmitted data base is sent over the air to the mobile unit. The data base can be compressed to minimize air time usage.

The transmitted ge...