Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
2001-04-12
2002-10-22
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S442000, C342S457000
Reexamination Certificate
active
06469665
ABSTRACT:
The invention relates to a method of estimating the time of arrival of a radio signal and to an apparatus operating in accordance with the method, and has particular, but not exclusive, application to location systems for mobile radio devices.
Location systems for mobile radio have a variety of applications, for example for use in conjunction with emergency calls made from mobile telephones, as many people making emergency calls are unaware of their precise location, making it difficult for the emergency services to reach them. A variety of technologies have evolved for determining the location of a mobile radio. A review of location technology is contained in “An Overview of the Challenges and Progress in Meeting the E-911 Requirement for Location Service” by J. H. Reed et al, published in the IEEE Communications Magazine, Apr. 1998, pp. 30-37.
The location of a mobile radio may be determined by calculating its distance from three or more radio base stations situated at known locations. The location of the mobile radio will be at the intersection of circles (or spheres in three dimensions) about each base station, each circle having a radius corresponding to the distance of the mobile radio from that base station. Such distances may be readily determined from the propagation delay of a radio signal travelling between the mobile radio transmitter and base station receiver, assuming that radio signals propagate at the constant speed of light (3×108 m/s). For example, a propagation delay of 10 &mgr;s will correspond to a distance of 3 km. The propagation delay can be determined by combining what is commonly referred to as a TOA (Time Of Arrival) measurement with knowledge of the time at which the radio signal was emitted from the transmitter.
A more practical method of determining propagation delay, in which knowledge of the emission time is not required, is to measure the difference in time of a signal emitted by the mobile radio transmitter arriving at each base station receiver. Instead of the circular location trajectory about each base station which results from an absolute TOA measurement, for each pair of base stations there is calculated a hyperbolic trajectory corresponding to the difference in distance of the mobile from each base station in the pair, and the location of the mobile radio will be at the intersection of these hyperbolae. Measurement of the difference in time of arrival is commonly referred to as a TDOA (Time Difference Of Arrival) measurement.
Methods of calculating location using TOA and TDOA measurements are discussed in “Position Location Using Wireless Communications on Highways of the Future” by T. S. Rappaport et al, published in the IEEE Communications Magazine, Oct. 1996, pp. 33-41.
Whether TOA or TDOA measurements are used, the accuracy of the location calculation is very dependent on the accuracy of the time of arrival measurements. In the present specification and claims the term “time of arrival” is used to encompass both TOA and TDOA.
Time of arrival can be measured by using the correlation properties of a pseudo-noise (PN) sequence, transmitted from a transmitter to a receiver. The correlation of the received signal with a replica of the transmitted signal will produce a peak in the correlation function when the two are synchronised. The peak can be detected even in the presence of severe distortion caused by multipath propagation and noise. Therefore, the problem of measuring time of arrival is equivalent to the accurate detection of the position of the peak in the correlation function between the distorted, received signal and a replica of the transmitted signal. It is known that correlation of the received signal with the replica can be performed in either the time domain or in the frequency domain, for example see T. S. Rappaport et al referenced above.
In emergency situations, the speed and accuracy of location calculation can be critical. The speed and accuracy of the location calculation is dependent on the speed and accuracy of the time of arrival measurement, which, in turn, depends on the processing power available and the algorithms used. In order to address a mass market, equipment cost should be low, so a low processing power requirement is important.
An object of the invention is to provide improvements in location systems for mobile radio by providing improvements in the time of arrival estimation.
According to one aspect of the invention there is provided a system for determining the location of a mobile radio station relative to radio base stations, comprising a plurality of radio base stations, each equipped to transmit a signal; and a mobile radio station equipped to receive the signal transmitted by each radio base station and having means for estimating the time of arrival of each received signal and means for computing the location of the mobile radio station from the estimated time of arrival of each received signal, wherein the means for estimating the time of arrival further comprises a means for making a first estimate of time of arrival having a first resolution and a means for making a second estimate of time of arrival having a second resolution, the first estimate of time of arrival contributing to defining the scope of the means for making the second estimate of time of arrival, and the second resolution being more refined than the first resolution.
According to a second aspect of the invention there is provided a system for determining the location of a mobile radio station relative to radio base stations, comprising a mobile radio station equipped to transmit a signal, a plurality of radio base stations, each equipped to receive the signal transmitted by the mobile radio station and having means for estimating the time of arrival of the received signal, and means for computing the location of the mobile radio station from the estimated time of arrival of the signal received at each radio base station; wherein the means for estimating the time of arrival further comprises a means for making a first estimate of time of arrival having a first resolution and a means for making a second estimate of time of arrival having a second resolution, the first estimate of time of arrival contributing to defining the scope of the means for making the second estimate of time of arrival, and the second resolution being more refined than the first resolution.
According to a third aspect of the invention there is provided a method of determining the location of a mobile radio station relative to radio base stations, comprising transmitting a signal from a plurality of radio base stations; receiving at a mobile radio station the signal transmitted by each radio base station; estimating the time of arrival of each received signal; and computing from the time of arrival estimates the location of the mobile radio station; wherein the time of arrival estimation further comprises making a first stage of estimation having a first resolution and which yields a first estimate of time of arrival, and making a second stage of estimation having a second resolution and which yields a second estimate of time of arrival; the first estimate of time of arrival contributing to defining the scope of the second stage of estimation, and the second resolution being more refined than the first resolution.
According to a fourth aspect of the invention there is provided a method of determining the location of a mobile radio station relative to radio base stations, comprising transmitting a signal from a mobile radio station; receiving at a plurality of radio base stations the signal transmitted by the mobile radio station; estimating the time of arrival of each received signal; and computing from the time of arrival estimates the location of the mobile radio station; wherein the time of arrival estimation further comprises making a first stage of estimation having a first resolution and which yields a first estimate of time of arrival; and making a second stage of estimation having a second resolution and which yields a second estimate of time
Koninklijke Philips Electronics , N.V.
Phan Dao
Slobod Jack D.
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