Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Patent
1995-11-20
1998-11-17
Blum, Theodore M.
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
324329, G01S 302
Patent
active
058382798
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a navigation and tracking system which can be used in shielded spaces.
EP-B-0 303 371 describes a navigation and tracking system (CURSOR.TM.) in which the signals from several independent point signal sources (eg. radio transmitters) are received at two locations, one being at a fixed and known location (the "base station"), and the other being attached to the roving object whose position is to be determined (the "rover"). A representation of the signals received at one of the locations, A, is sent by any convenient means (e.g., a narrow-band radio link) to the other, B, where the said representation is used in a computer program to calculate the position of the rover, together with a similar representation derived from the same signal sources at B.
In cases where location in real time is not required, the link may be the transmission of data by physical means such as a floppy disk.
This system has particular advantages over other (radio) navigation and tracking systems but, in common with all such systems, it suffers from the drawback that the signals do not usually penetrate far into tunnels and other shielded spaces, and hence the continuous tracking of a roving object is interrupted whilst it is inside such a space.
The CURSOR.TM. system already incorporates a tunnel-recovery procedure whereby the correct operation of the system may be quickly re-established after such an interruption (P J Duffett-Smith & G Woan, 1991 Journal of Navigation Vol.45 No.2 pages 157-165, 1992). However, this is different from maintaining tracking of the rover within the tunnel or the like and some additional means is required if this is necessary for the particular purposes of the system.
According to a first aspect of the present invention there is provided apparatus for use with a navigation and tracking system having a base station and a roving receiver both of which receive signals from a plurality of transmission sources, and between which a link signal is passed to enable the relative location of the roving receiver to be determined, the apparatus enabling the determination of the position of the roving receiver within a space shielded from direct receipt of signals from the transmission sources and comprising means for producing substitute or replica signals, each signal being locked in phase with a signal from a respective one of the transmission sources; a curvilinear transmission element, extending within the shielded space for generating fields in the shielded space; means for propagating at least two of the substitute signals in opposite directions along the curvilinear transmission element for receipt by the roving receiver; and means for passing the link signal between the roving receiver and the base station.
If necessary in a particular application, the signals propagated along the curvilinear transmission element may also be received by the base station.
The invention also includes a navigation and tracking system having a base station and a roving receiver both of which are capable of receiving signals from a plurality of transmission sources, and between which a link signal is passed to enable the relative location of the roving receiver to be determined, and including such apparatus.
The means for passing the link signal between the roving receiver and the base station may includes means for receiving signals from the rover within the shielded space.
As described in EP-B-0 303 371, the transmission signals may be modulated and timing delays between the respective signals may be determined in order to enable the relative location of the roving receiver to be determined, in which case the substitute signals may replicas of the transmitted signals, the system including means for comparing the signals received by the base station and roving receiver, which includes means for correlating the signals to produce estimates of the cross-correlation function to determine the time delay between the signals.
Alternatively, the signals may be modulated or unmodulated and the phase difference
REFERENCES:
patent: 5430379 (1995-07-01), Parkinson et al.
Patent Abstracts of Japan, vol. 16, No. 125 (P-1331), Dated Mar. 30, 1992, and Japanese Patent Publication No. 3-291,582, Dated Dec. 20, 1991.
Patent Abstracts of Japan, vol. 12, No. 111 (E-598), Dated Apr. 8, 1988, and Japanese Patent Publication No. 62-242427, Dated Oct. 23, 1987.
P.J. Duffett-Smith & G. Woan, "The CURSOR Radio Navigation and Tracking System", Journal of Navigation, vol. 45, No. 2, pp. 157-165 (1992).
Duffett-Smith Peter James
Woan Graham
Blum Theodore M.
Cambridge Positioning Systems Limited
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