Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
2001-02-06
2004-10-05
Maung, Nay (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S506000, C455S065000, C455S277200, C455S456100, C455S457000, C375S347000, C342S457000
Reexamination Certificate
active
06801782
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a position location system for determining the position of a mobile communication device, and, more particularly, to a system employing two-way transmission of spread spectrum ranging signals between the mobile communication device and reference communication devices having relatively low accuracy clocks, to rapidly and accurately determine the position of the mobile communication device in the presence of severe multipath interference.
2. Description of the Related Art
The capability to rapidly and accurately determine the physical location of a mobile communication device would be of great benefit in a variety of applications. In a military context, it is desirable to know the location of military personnel and/or equipment during coordination of field operations and rescue missions, including scenarios where signals of conventional position-determining systems, such as global position system (GPS) signals, may not be available (e.g., within a building). More generally, appropriately equipped mobile communication devices could be used to track the position of personnel and resources located both indoors or outdoors, including but not limited to: police engaged in tactical operations; firefighters located near or within a burning building; medical personnel and equipment in a medical facility or en route to an emergency scene, including doctors, nurses, paramedics and ambulances; and personnel involved in search and rescue operations. An integrated position location communication device would also allow high-value items to be tracked and located, including such items as personal computers, laptop computers, portable electronic devices, luggage, briefcases, valuable inventory, and stolen automobiles. In urban environments, where conventional position determining systems have more difficulty operating, it would be desirable to reliably track fleets of commercial or industrial vehicles, including trucks, buses and rental vehicles. Tracking of people carrying a mobile communication device is also desirable in a number of contexts, including, but not limited to: children in a crowded environment such as a mall, amusement park or tourist attraction; location of personnel within a building; and location of prisoners in a detention facility.
The capability to determine the position of a mobile communication device also has application in locating the position of cellular telephones. Unlike conventional land-based/wire-connected telephones, the location of conventional cellular telephones cannot automatically be determined by emergency response systems (e.g., the 911 system in the United States) when an emergency call is placed. Thus, assistance cannot be provided if the caller is unable to speak to communicate his or her location (e.g., when the caller is unconscious, choking or detained against will). The capability to determine the position of cellular telephones could be used to pinpoint the location from which an emergency call has been made. Such information could also be used to assist in cell network management (for example, by factoring each mobile communication device's location into message routing algorithms).
Naturally, in cases where a mobile communication device is being used primarily to transmit or receive voice or data information, it would be desirable to incorporate position location capabilities such that the device can communicate and establish position location at the same time without disruption of the voice or data communication.
Among conventional techniques employed to determine the position of a mobile communication device is the reception at the mobile communication device of multiple timing signals respectively transmitted from multiple transmitters at different, known locations (e.g., global positioning system (GPS) satellites or ground-based transmitters). By determining the range to each transmitter from the arrival time of the timing signals, the mobile communication device can compute its position using trilateration.
The accuracy and operability of such position location techniques can be severely degraded in the presence of multipath interference caused by a signal traveling from a transmitter to the receiver along plural different paths, including a direct path and multiple, longer paths over which the signal is reflected off objects or other signal-reflective media. Unfortunately, multipath interference can be most severe in some of the very environments in which position location techniques would have their greatest usefulness, such as in urban environments and/or inside buildings, since artificial structures create opportunities for signals to be reflected, thereby causing signals to arrive at the receiver via a number of different paths.
Attempts have been made in position location systems to mitigate the effects of multipath interference. An example of a system reported to provide position location in a multipath environment is presented by Peterson et al. in “Spread Spectrum Indoor Geolocation,” Navigation: Journal of The Institute of Navigation, Vol. 45, No 2, Summer 1998, incorporated herein by reference in its entirety. In the system described therein (hereinafter referred to as the Peterson system), the transmitter of a mobile radio continuously transmits a modulated pseudorandom noise (PRN) sequence, with a carrier frequency of 258.5 MHz and a chipping rate of 23.5 MHz. The transmitter is battery powered and therefore can be easily transported inside a building. Four wideband antennas located on the roof of a test site receive the signal transmitted by the mobile radio. The signals are conveyed from the antennas to four corresponding receivers via low loss cable that extends from the roof to the receivers disposed in a central location. The receivers demodulate the signal transmitted by the mobile radio using an analog-to-digital (A/D) converter board disposed inside a host personal computer (PC), which samples the signal at 1.7 s intervals for 5.5 ms and processes the raw data to determine the Time of Arrival (TOA). The system uses two receiver computers, each with a dual channel A/D board inside. The output from the receiver boxes is fed into a dual channel A/D board on two host computers. Each of the host computers processes the signal on each channel of the A/D board to determine the TOA for each channel relative to a trigger common to both channels on the A/D board. The TOA algorithm is based on finding the leading edge of the cross correlation function of the PRN sequence that is available at the output of the correlator using frequency domain techniques. TOAs are transferred via wireless local area network to the RAM-drive of a third computer acting as the base computer. From the TOAs, the base computer calculates time differences (TDs) and determines the two-dimensional position of the transmitter. This position is then plotted in real time on a building overlay.
The Peterson system suffers from a number of shortcomings. The range between the target radio and each reference radio is determined by measuring the duration of time required for a signal to travel between the radios. This information can be determined from a one-way communication only if the target radio and the reference radios remain synchronized to the same time reference. That is, the transmitting radio establishes the time of transmission of the signal based on its local clock, and the receiving radio determines the time of arrival of the signal based on its local clock which must constantly be synchronized to the same time reference as the clock of the transmitter. The signal propagation duration can then be determined essentially by subtracting the time of transmission from the time of arrival.
Because the Peterson system uses this one-way measurement technique, the system requires synchronization between the clocks of the transmitter and the four receivers. Unfortunately, the precise time synchronization required to accurately measure the duration of the signal propaga
Cummiskey Peter
Doyle Lawrence J.
Forstrom Howard
McCrady Dennis D.
Edell Shapiro & Finnan LLC
ITT Manufacturing Enterprises Inc.
Maung Nay
Sobutka Philip J.
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