Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Hardware Architecture for Channel Measurement and TDOA Based Locating in WLAN Systems

IP.com Disclosure Number: IPCOM000198271D
Original Publication Date: 2010-Aug-23
Included in the Prior Art Database: 2010-Aug-23
Document File: 7 page(s) / 155K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

RTLSs (RTLS: Real Time Locating System), also known as RF locating systems (RF: Radio Frequency), are used to determine the position of a tagged object within a given area. This kind of locating is based on the analysis of RF propagation between the tag and dedicated infrastructure components. Evaluating the TDOA (Time Difference Of Arrival) of a tagged signal at several spatially separated APs (Access Point) achieves very good location accuracy. The disadvantages of RTLS solutions based on TDOA are the high costs due to their low production volume and the additional hardware needed for the required signal processing. Currently various RTLS approaches exist. The most common ones are based on RSSI (Received Signal Strength Indication), i.e., the field strength of radio signals received by a tag is measured, or based on measuring the propagation delays of RF signals exchanged between the tag and some reference stations at known positions, e.g., according to the ISO 24730 standard. If using an RSSI based RTLS, the field strength of the radio signals emitted by the tags and received by the infrastructure can be evaluated alternatively.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 16% of the total text.

Page 1 of 7

Hardware Architecture for Channel Measurement and TDOA Based Locating in

WLAN Systems

Idea: Mattias Lampe, Ph.D., CN-Beijing; Ji Feng Tian, Ph.D., CN-Beijing

RTLSs (RTLS: Real Time Locating System), also known as RF locating systems (R Frequency), are used to determine the position of a tagged object within a given
locating is based on the analysis of RF propagation between the tag and dedica components. Evaluating the TDOA (Time D
separated APs (Access Point) achieves very good location accuracy. The disad
solutions based on TDOA are the high costs due to their low production volume and the ad hardware needed for the required signal processing.

Currently various RTLS approaches exist. The most common ones are ba
Signal Strength Indication), i.e., the
based on measuring the propagation delays of R
reference stations at known positions, e.g., according to the ISO 24730 standard. If using an RSSI based RTLS, the field strength of the radio signals emitted by the tags and receive
infrastructure can be evaluated alternatively.

RSSI based approaches can be grouped in two categories:

• Multilateration techniques which are based on the known relationship between path loss, e.g., based on the assumption of free-space propagation; here received signal is directly translated into an estimated distance. RSSI measu
a tag and a number of APs, at least three for a 2D-location (2D: Two-Di
four for a 3D-location (3D: Three-Dimensional), provide distance estimates s deriving the tag position.

• Fingerprinting techniques which also work in environments where line-o and APs cannot be guaranteed; here the RSSI measurement values o
tag position are compared to a database or reference map of previou measurement results. This happens for a sufficiently large number of fixed estimate of the final location is obtained by taking into account the known p similar reference measurement.

These approaches do not require any special hardware support, since almost all av cards (WLAN: Wireless Local Area Network) are capable to deliver RSSI measurem higher-layer software.

TDOA based locating is currently limited to dedicated RTLSs, e.g., according to the standard. Correlation techniques in combination with reference tags for time synchr to measure the relative delays of the received tag signal at several access points. IS operate in the 2.4 GHz ISM band (ISM: Industrial, Scientific and Medical) an
with WLAN systems operating in the same band. There have been claims in lit
shelf WLAN cards can be used without modification in a TDOA-based locating schem the time stamp data attached to the received data frames by the receiver. Howev
rely on some rather optimistic assumptions regarding the internal time synchroni WLAN hardware, e.g., timing differences between hardw

typically 1μs, is acknowledged by the corresponding publications. The most important dra scheme, even if the practical issue
esired tim
h efficienc

1 A. Guenther, Ch. Hoene: "Measuring Round Trip Times to Determine...