Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
2000-07-18
2002-08-20
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S422000, C342S423000, C342S153000
Reexamination Certificate
active
06437740
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a target tracking system. In particular, the present invention relates to a single receiver wireless locating and tracking system.
BACKGROUND OF THE INVENTION
Wireless locating and tracking systems are often used to identify the location of a target object. Conventional wireless locating systems typically employ two or three wireless receivers positioned at known co-ordinates for the identification a target object's location. For instance, two-dimensional global positioning systems (GPS) employ three satellites which transmit their respective co-ordinates and transmission times to a GPS receiver. Typically, additional satellite are used for redundancy purposes, to increase accuracy and for three-dimensional imaging. The GPS receiver receives the transmitted information, and then determines its position from the transmitted co-ordinates and from the transmission interval of the wireless transmissions from the satellites to the GPS receiver. Signal strength locating systems typically employ two wireless receivers positioned at known co-ordinates for receiving wireless transmissions from a wireless transmitter. The co-ordinates of the wireless transmitter, relative to the wireless receivers, are calculated from the signal strength of the wireless transmission received at each receiver. Although both forms of locating systems, particularly signal strength locating systems, are widely used, they suffer from a number of deficiencies.
For instance, GPS satellites intermittently transmit erroneous information to the GPS receivers. Although military users of GPS receivers are provided with an encryption key for identifying and removing the erroneous information, the encryption key is not available to non-military GPS users. As a result, GPS systems do not provide non-military GPS users with particularly accurate co-ordinate identification. Further, triangulation by RF signal strength is limited by the effects of co-channel interference, multi-path distortion, tropospheric scatter, phase distortion and signal phase cancellation. Additionally, the multiple satellites/receivers required of both forms of wireless systems constitute significant barriers to market entry. Attempts have been made to improve upon the conventional wireless locating systems.
For example, Jarvis (U.S. Pat. No. 3,665,312) teaches a wireless locating system comprising a multiple frequency wireless transmitter, an entry detector for activating the wireless transmitter upon detection of unauthorized entry, and a plurality of directional receivers. Once unauthorized entry is detected, the wireless transmitter transmits a unique coded signal to the directional receivers for co-ordinate identification using signal triangulation. To thwart jamming of the wireless transmitter, the transmitter sequentially shifts its transmission frequency at predetermined time intervals. However, Jarvis is limited by the need for multiple directional receivers.
Regan (U.S. Pat. No. 4,177,466 assigned to Lo-Jack Corporation) teaches an auto theft detection system comprises a wireless transceiver configured with the vehicle identification number of the vehicle in which the transceiver is fitted, and a plurality of mobile radio direction finders for determining the direction of a transmission from the target transceiver. If the vehicle fitted with the target transceiver is reported stolen, a transmitter station transmits a continuous locator signal encoded with the vehicle identification number assigned to the subject transceiver. Upon receipt of the continuous locator signal, each transceiver decodes the signal to determine whether the transmitted vehicle identification code matches its assigned vehicle identification number. The transceiver having the matching vehicle identification number transmits a responsive output signal which the radio direction finders use to triangulate on the subject vehicle. Although the use of multiple mobile radio direction finders reduces the sensitivity of the system to co-channel interference, multi-path distortion, phase distortion and signal phase cancellation, the system can be defeated by jamming the transmission of the wireless transmitter with an RF transmitter tuned to the appropriate transmitting frequency. Further, recourse to multiple mobile direction finders unnecessarily increases the cost of locating a stolen vehicle.
Rackley (U.S. Pat. No. 4,742,357) teaches a vehicle locating system comprising a target wireless transceiver configured with the vehicle identification number of the vehicle in which the transceiver is fitted, and a single conventional directional receiver for receiving a transmission from the target transceiver. Each wireless transceiver is capable of operating in a direction-triangulation mode, a distance-triangular mode, a distance-direction mode, and long range navigation (LORAN) mode. If the vehicle fitted with the target transceiver is reported stolen, a base station transmits to the target transceiver a data packet containing the subject vehicle's vehicle identification number, a location mode code identifying distance-direction mode as the operating mode for the transceiver, and a code identifying the transmission frequency at which transceiver is requested to transmit. Upon receipt of the base station message, the transceiver configured with the subject vehicle identification number activates its echo channel. The base station then transmits an echo pulse to the transceiver and activates a timer. After the transceiver receives the echo pulse, it returns the echo pulse back to the directional receiver through the echo channel, after a precise fixed delay. The directional receiver calculates the distance of the vehicle relative to the receiver from the propagation delay of the echo pulse, after subtracting the fixed delay of the transceiver. Simultaneously, the directional receiver measures the angle of transmission of the echo pulse from the transceiver, and converts the calculated range and angle measurements to map coordinates. Although Rackley is advantageous in that it only requires a single directional receiver, the need for the wireless transceiver to operate in a number of different operation modes increases the cost and complexity of each transceiver. Further, as the delay of the transceiver can vary with temperature and humidity, the accuracy of the calculated co-ordinates is limited. In addition, the use of a single conventional directional receiver exposes the locating system to further inaccuracy from multi-path distortion, signal phase cancellation, and ambient noise.
Therefore, there remains a need for a target tracking and locating system which does not rely on a plurality of wireless directional receivers for accurate target co-ordinate location. Further, there remains a need for a target tracking and locating system whose accuracy is not sensitive to RF jamming, multi-path distortion and changes in environmental conditions.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a single receiver wireless tracking system which addresses deficiencies of the prior art wireless target tracking and locating systems. The wireless tracking system includes a wireless target including a wireless communication system for transmitting a data packet over a communication path, and a locating station for determining a position of the target. The data packet transmitted from the target includes an identification code uniquely associated with the target. The locating station includes a configurable directional antenna, a communication interval processing system, a direction processing system, and a position processing system. The communication interval processing system is in communication with the directional antenna and determines the transmission interval (elapsed transmission time) of the transmitted data packet over the communication path. The direction processing system determines the transmission angle (angular direction) of the communication path, and is in c
De Champlain Brian
Gerlach Frank
Blum Theodore M.
Stelx Inc.
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