Communications: directive radio wave systems and devices (e.g. – Radar transponder system
Reexamination Certificate
2002-12-20
2004-08-31
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar transponder system
C342S463000, C342S453000
Reexamination Certificate
active
06784827
ABSTRACT:
TECHNICAL FIELD
The present invention is related to an apparatus, method, and system for determining a time of arrival, hereinafter abbreviated to TOA, of a transmitted or emitted signal receivable at different locations of known spatial coordinates. More particularly, the invention allows to determine time differences of arrival, hereinafter abbreviated to TDOA. Furthermore, the present invention relates to location-aware or location-based applications built upon wireless networking systems or wireless tag tracking systems.
BACKGROUND OF THE INVENTION
Newly emerging indoor wireless systems supporting precise and nearly real-time localization and tracking of multiple mobile radio terminals or radio tags require capabilities for accurate measurement of TOA and TDOA of a radio signal receivable at different spatial locations. In particular, wireless local area networks known today have not been designed to sufficiently accommodate these required capabilities and thus often provide insufficient support for location-aware or location-based applications. It would be an advantage if TOA and TDOA measurements could be performed without need for absolute time synchronization between system components located at different spatial positions.
A well-known technique for locating a signal source is based on measuring the difference in time for a signal to travel to a pair of spatially separated receivers of known position. When using a sufficient number of different pairs of receivers ambiguous location solutions can be avoided and the location of the signal source can be found at the corresponding intersection of hyperbolas or hyperboloids. Besides the specific geometric constellation of the receivers and observed signal source as well as the accuracy with which the fixed receiver locations have been measured, the accuracy with which the location of the signal source can be determined depends also critically on the achievable accuracy of the TDOA measurements. Moreover, the timeliness of the obtained location solution is dictated by the delay between time of emission of the signal and time of availability of the location solution. In some cases, it may also be desirable to determine the absolute TOA of the signal at the individual receivers. A plurality of techniques and applications exist that use either radio signals, optical signals, or acoustic signals, and perform TDOA measurements for the determination of the spatial coordinates of the respective sources emitting any such signals.
The paper entitled “Hyperbolic location errors due to insufficient numbers of receivers,” by John L. Spiesberger, published in
Journal of the Acoustical Society of America,
109 (6), June 2001, is related to location techniques based on the difference in travel time of acoustical sources at pairs of widely separated receivers. Therein, the author demonstrates that ambiguous location solutions based on TDOA measurements for two and three spatial dimensions can generally only be avoided by using four and five receivers, respectively. This paper provides a theoretical method to compute the location of an acoustic signal source based on TDOA measurements from up to four independent pairs of receiving stations. However, the paper does not discuss nor disclose any practical solution that could be used for useful TDOA measurements.
U.S. Pat. No. 6,054,950 is related to an ultra wideband precision geolocation system. The system includes N>2 untethered ultra wideband transceivers, hereinafter abbreviated to UWB transceivers, located at fixed positions, an untethered UWB transceiver at the unknown target location (herein also called the unknown location of the signal source), and a processor at the target location. The latter resolves time-of-flight measurement ambiguities of received pulses to determine the geolocation by solving a set of equations according to time-of-flight measurements and surveyed positions of N−1 receivers. To eliminate a clock distribution system, self-synchronizing of pulse timing is achieved by generating a start pulse at one of the untethered transceivers. As an alternate means, a timing source may be provided at the transceivers by a Global Positioning System, hereinafter abbreviated to GPS, or other timing generator, in order to synchronize emissions of their pulses. The system has the disadvantage that it is restricted to situations where both the signal source and the processor estimating the a priori unknown location of the signal source must be located at the same spatial position. Thus, the system is restricted to the known “mobile-based architecture”. Also, to eliminate a clock distribution system for time synchronization, the system described in U.S. Pat. No. 6,054,950 has the disadvantage that self-synchronization of pulse timing is achieved in a sequential fashion. An alternate synchronization method as disclosed in U.S. Pat. No. 6,054,950 has the disadvantage that each reference transceiver is required to provide its own GPS-derived absolute timing source.
U.S. Pat. No. 6,028,551 describes a micro-miniature beacon transmit-only geolocation emergency system for personal security, which can operate synergistically with existing or newly designed satellite or ground-based wireless communication networks. The document also discloses a program procedure to calculate the geolocation of the micro-miniature beacon from TDOA measurements at the satellites and initial estimates of the location. The
FIGS. 2 and 9
in U.S. Pat. No. 6,028,551 show a configuration or mode of operation of a system architecture that is commonly identified by those knowledgeable in the field as a “network-centric architecture.” The document proposes in general terms the use of a traditional and well-known radio-astronomy technique, called auto-correlation, to determine the time difference of signals detected at three or more satellites.
The paper entitled “Performance of ultrawideband SSMA using time hopping and M-ary PPM,” by Fernando Ramirez-Mireles, published in
IEEE Journal on Selected Areas in Communications
, Vol. 19, No. 6, June 2001, analyzes multiple-access performance in free-space propagation conditions, in terms of the number of users supported by the system for a given bit error rate, the signal-to-noise ratio, the bit transmission rate, and the number of signals in a set of pulse position modulated signals.
In the paper entitled “Indoor Geolocation using OFDM Signals in HIPERLAN/2 Wireless LANs,” by Xinrong Li, et al, published in
Proceedings of the
11
th
International Symposium on Personal, Indoor and Mobile Radio Communication
(
PIMRC
2000), Vol. 2, London, Sep. 18-21, 2000, the authors study and describe new methods to integrate geolocation functionalities into next generation wireless LANs based on OFDM (orthogonal frequency division multiplexed) signals. In particular, the authors propose a method to measure geolocation metrics by exploiting the HIPERLAN/2 MAC frame structure with a focus on geolocation methods for network-based architectures. This paper reports results from computer simulations to show the performance of the investigated geolocation system. The HIPERLAN/2 system is specified to operate in the 5 GHz frequency range and support short-range broadband wireless access within 30 m in typical indoor environments. The authors conclude that their system has the disadvantage of a large mean ranging error of 3 m to 7.5 m, depending on channel conditions. They further conclude that some other timing method is needed to improve the accuracy in real multi-path indoor environments.
The paper entitled “An Overview of Wireless Indoor Geolocation Techniques and Systems,” by Kaveh Pahlavan, et al, published in
Proceedings of Mobile and Wireless Communications Networks
(
MWCN
2000), Paris, France, May 2000, provides an overview of various indoor geolocation systems, including results on predicted performance of such systems. The paper points out that compared to the TOA method, the main advantage of the TDOA method is that knowledge of the transmit time from the transmittin
Andrea Brian K
International Business Machines - Corporation
Jennings Derek S.
Tarcza Thomas H.
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