Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
2001-11-14
2003-09-09
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C342S442000, C342S463000
Reexamination Certificate
active
06618010
ABSTRACT:
ORIGIN OF THE INVENTION
The invention described herein was made by employee(s) of the United States government and may be manufactured and used by or for the Government of the United States of America for governmental purpose without payment of any royalties thereon or therefor.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to signal tracking systems and, more specifically, to a passive system for tracking/locating a transmitter.
2. Background of the Invention
Determining the location and/or tracking a moveable transmitter is useful for many purposes. For instance, there frequently exists an urgent need for locating the source of an emergency 911 telephone call from a mobile phone. Previous options for this application included utilizing GPS location devices but these require additional circuitry, additional antennas, do not necessarily operate indoors, and may be slow to obtain a location fix.
Other tracking requirements might include tracking an astronaut in space during extravehicular activity. Another desirable use might be to track small vehicles in space such as, for instance, a small one-foot diameter autonomous vehicle for flying anywhere around the Space Station and transmitting video from an onboard camera.
It is also increasingly important to be able to locate, track, communicate with or activate vehicle systems wirelessly, and/or otherwise monitor fleets or individual trucks, automobiles, containers, and other moveable targets. Such monitoring is increasingly utilized and has, for instance, become a standard feature on many automobiles. Previous prior art options to perform this function typically include utilizing GPS location devices with the same problems as listed above. It would be very useful to somehow provide such monitoring in a low cost, reliable, high-speed manner that avoids/alleviates the problems associated with presently existing GPS location systems.
The above are only a few specific uses, and it will be understood that a small, inexpensive system that is capable of passively tracking a transmitter by utilizing the transmitter's data modulated signal, and which may operate in a noisy environment with mulitpath signals, may be useful for a myriad of applications and systems.
Tracking objects by receiving signals therefrom is well known. For instance, radar has been utilized for most of the last century to track objects. However radar is nonpassive, requires high power, and also requires a recognizable signature at the target for identification.
Various types of signal processing for estimation of signal parameters have been used as far back as 1795. A more recent signal processing method is that of ESPRIT (Estimation of Signal Parameters using Rotational Invariance Techniques) which is discussed in at least one of the subsequently listed patents. However, the ESPRIT technique is based on relatively complicated mathematics. The inventors believe that using the ESPRIT technique for the purposes of the present invention may require at least four antennas, the generation of complex matrices, the calculation of complex eigenvalues and eigenvectors, and the estimation of noise level. The complexity of these requirements effectively renders the ESPRIT technique unacceptable for many applications requiring low weight and power and small size.
It might also be noted that techniques exist for locating the source of a magnetic field but such techniques require a powerful magnetic pulse generator at the source.
The following patents show attempts to solve problems related to the present invention but do not show the solution provided by the present invention:
U.S. Pat. No. 5,987,016, issued Nov. 16, 1999, to R. He, discloses a method for tracking a mobile communication signal, which operates in a code division multiple access wireless communication system including an antenna, and a base site receiver having at least two receiver tracking fingers, includes receiving at the antenna a first multipath signal arriving at an on-time pn-offset with an associated advanced pn-offset value and retard pn-offset value and receiving at the antenna a second multipath signal arriving at an on-time pn-offset with an associated advanced pn-offset value and retard pn-offset value. The method further includes determining a spacing between the first multipath signal and the second multipath signal, and adjusting the at least two receiver tracking fingers based on the advanced pn-offset value of one of the multipath signals and the retard pn-offset value of the other multipath signal.
U.S. Pat. No. 5,691,974, issued Nov. 25, 1997, to Zehavi et al., discloses a method and apparatus for tracking the frequency and phase of signals in spread spectrum communication systems that makes more efficient use of available carrier frequency and phase information by utilizing a substantial portion or all of the energy occupying the frequency spectrum of a received carrier signal, including energy from communication signals intended for other system users. Multiple spread spectrum communication signals are input in parallel to data receivers where they are despread using preselected despreading codes at an adjustable phase angle and decoded over multiple orthogonal codes active within the communication system. Multiple decoded signals are then combined to form a single phase detection signal which is used by at least one tracking loop to track frequency and phase of the carrier signal for the received communication signals. The tracking loop generates a timing signal which is used to adjust the phase angle used during despreading. In further embodiments, the communication signals are despread using appropriate PN codes and separated into in-phase (I) and quadrature channels (Q) where data symbols are processed by fast Hadamard transformers to generate corresponding data bits. The data is formed into pairwise products between the channels and summed over multiple or all active subscriber orthogonal codes. This sum indicates a degree to which the estimated phase differs from the actual phase of received communication signals and is used to adjust the phase of application for the PN codes.
U.S. Pat. No. 5,621,752, issued Apr. 15, 1997, to Antonio et al., discloses a system and method for adaptively sectorizing channel resources within a digital cellular communication system is disclosed herein. The system includes an antenna arrangement for providing at least first and second electromagnetic beams for receiving a first information signal transmitted by a specific one of a plurality of users, thereby generating first and second received signals. A first set of beam-forming signals are then generated from the first and second received signals. A demodulating receiver is provided for demodulating at least first and second beam-forming signals included within the first set of beam-forming signals, thereby producing first and second demodulated signals. The system further includes a tracking network for tracking multipath information signals, received from various positions and angles of incidence, based on comparison of the first and second demodulated signals.
U.S. Pat. No. 6,147,641, issued Nov. 14, 2000, to J. Issler, discloses a process for the autonomous reduction of acquisition and tracking thresholds of carriers received in orbit by a receiver accessing an orbital navigator inside or outside said receiver, the latter having at least one phase loop. The phase loop, which is responsible for the acquisition and/or tracking of the carrier, is “pushed” by the fine speed aid and takes up the error between the real speed and the calculated speed. The search for the Doppler frequency of the carrier received takes place around a frequency prediction maintained by the fine speed aid coming from the orbital navigator.
U.S. Pat. No. 5,914,949, issued Jun. 22, 1999, to G. Y. Li, discloses a finger tracking circuit for a rake receiver, a method of tracking a carrier signal and a wireless infrastructure. The finger tracking circuit includes: (1) a timing err
Arndt G. Dickey
Bourgeois Brian A.
Chen Henry A.
Dusl John
Hill Brent W.
Mull F H
Ro Theodore U.
Tarcza Thomas H.
United States of America as represented by the Administrator of
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