A signaling system is provided for rendering an alarm for an individual in distress combined with a locating and tracking system to thus alert and direct appropriate personnel to the needs of the individual in distress and to monitor the location of that individual. The system comprises a portable signaling unit, a remote alarm switch device, a central dispatch station, and makes use of a wireless communication system. The portable signaling unit and the remote alarm switch may be adapted to be worn at different locations on the person's body. The remote alarm switch way be concealed in the form of a wristband or in the form of any other object such as a broach, pendant, or keychain.

Personal Security and Tracking System

With the advances in wireless communications and low-power electronics, accurate position location may now be accomplished by a number of techniques which involve commercial wireless services. Emerging position location systems, when used in conjunction with mobile communications services, will lead to enhanced public safety and revolutionary products and services. The fundamental technical challenges and business motivations behind wireless position location systems are described, and promising techniques for solving the practical position location problem are treated.

Position location using wireless communications on highways of the future

Assisted GPS (A-GPS) has been developed to provide greatly improved capabilities, helping GPS work better and faster in almost any location. Offering a detailed look at all the technical aspects and underpinnings of A-GPS, this unique book places emphasis on practical implementation. The book reviews standard GPS design, helping you understand why GPS requires assistance in the first place. You discover how A-GPS enables the computing of a position from navigation satellites in the absence of precise time - a topic not covered in any other book. Moreover, you learn how to design and analyze a high sensitivity GPS receiver and determine the achievable sensitivity. The book provides detailed worksheets that show how to compute, analyze, and improve the processing gain from the input signal at the antenna to the signal after the correlators. These worksheets are used in the book to generate families of curves that completely characterize receiver sensitivity, parameterized in terms of front end noise figure, coherent and noncoherent integration times. From this work a law of achievable sensitivity is derived and explained in the book. This cutting-edge volume discusses special forms of assistance data, industry standards for A-GPS, and government mandates for location of mobile phones. You also find coverage of future global navigation satellite systems and how they can be designed specifically for instant-fixes and high sensitivity. The book features numerous tables, worksheets, and graphs that illustrate key topics and provide the equivalent of a technical handbook for engineers who design or use A-GPS.

A-GPS: Assisted GPS, GNSS, and SBAS

A goal in the software radio design philosophy is to place the analog-to-digital converter as near the antenna as possible. This objective has been demonstrated for the case of a single input signal. Bandpass sampling has been applied to downconvert, or intentionally alias, the information bandwidth of a radio frequency (RF) signal to a desired intermediate frequency. The design of the software radio becomes more interesting when two or more distinct signals are received. The traditional approach for multiple signals would be to bandpass sample a continuous span of spectrum containing all the desired signals. The disadvantage with this approach is that the sampling rate and associated discrete processing rate are based on the span of spectrum as opposed to the information bandwidths of the signals of interest. Proposed here is a technique to determine the absolute minimum sampling frequency for direct digitization of multiple, nonadjacent, frequency bands. The entire process is based on the calculation of a single parameter-the sampling frequency. The result is a simple, yet elegant, front-end design for the reception and bandpass sampling of multiple RF signals. Experimental results using RF transmissions from the US Global Positioning System-Standard Position Service (GPS-SPS) and the Russian Global Navigation Satellite System (GLONASS) are used to illustrate and verify the theory.

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Direct bandpass sampling of multiple distinct RF signals

A personal alarm system includes a monitoring base station and one or more remote sensing units in two-way radio communication. An electronic handshake between the base station and each remote unit is used to assure system reliability. The remote units transmit at selectable power levels. In the absence of an emergency, a remote unit transmits at a power-conserving low power level. Received field strength is measured to determine whether a remote unit has moved beyond a predetermined distance from the base station. If the distance is exceeded, the remote unit transmits at a higher power level. The remote unit includes sensors for common hazards including water emersion, smoke, excessive heat, excessive carbon monoxide concentration, and electrical shock. The base station periodically polls the remote units and displays the status of the environmental sensors. The system is useful in child monitoring, for use with invalids, and with employees involved in activities which expose them to environmental risk. Alternative embodiments include a panic button on the remote unit for summoning help, and an audible beacon on the remote unit which can be activated from the base station and useful for locating strayed children. In another embodiment, the remote unit includes a Global Positioning System receiver providing location information for display by the base station.

Multi-hazard alarm system using selectable power-level transmission and localization

This paper describes the architecture of a fully digital receiver well suited for Global Positioning System (GPS) satellite radio-navigation and other spread-spectrum applications. The unique design of this receiver allows phase coherent measurements to be made across a broad range of frequencies, enabling optimal combination of a set of measurements from signals on different frequencies, for example GPS L1, L2, and L3, GLONASS or ground-based pseudolites. The receiver methodology provides precise absolute positioning measurements by maintaining phase coherency between frequencies of interest by direct L-band digital sampling. A one-bit sampler head is discussed that is suitable for navigation and digital communications applications. Surveillance applications can be accommodated with an expanded, multi-bit sampler. The design is particularly suited for chip set integration leading to a miniaturized and low cost receiver. Design of the receiver's digital front-end provides coherency between the code and carrier phase of the measurements across a 400 MHz bandwidth with down-conversion effected by digital techniques. In addition, it features a software configurable topology that enables filter parameters to be loaded dynamically, allowing rapid change of tracking frequency. The flexible "software receiver" architecture has been developed to allow the receiver to be dynamically reconfigured for different applications. This allows the receiver channels to be used for GPS navigation, ionospheric calibration, attitude determination, or even GLONASS navigation simply through software commands. Sampler performance criteria are discussed as well as test data demonstrating the effect of sampler performance on the receiver correlation loss. >

Digital L-band receiver architecture with direct RF sampling

NAVSYS High Gain Advanced GPS Receiver (HAGR) uses a digital beam-steering antenna array to provide additional gain in the direction of the GPS satellite signals. This increases the received signal/noise ratio on the satellites tracked and also improves the accuracy of the pseudo-range and carrier-phase observations. The directivity of the digital beams created from the antenna array also reduces the effect of jamming and interference. This paper describes the operation of the HAGR digital beam steering array in a jamming environment and includes test data collected from the HAGR at the Electronic Proving Grounds, Fort Huachuca, that demonstrate the performance of a digital, beam-steering receiver against interference sources.

Test Results of a Digital Beamforming GPS Receiver in a Jamming Environment

This paper presents and proves two new theorems that provide deeper understanding of receiver autonomous integrity monitoring (RAIM) methods. The theorems answer the following two questions about RAIM and the least squares navigation solution. (i) Given one set of GPS measurements (a "snapshot"), is it ever possible to determine the navigation error from the parity vector? (ii) Consider a set of measured satellite ranges. All the measurements are subject to noise and one of the measurements is biased by an unknown amount. Three navigation solutions may be obtained. (A) All the measurements are used. (B) Solution A is corrected using standard RAIM techniques for estimating the bias and its effect on the navigation solution. (C) The biased measurement is excluded and a navigation solution is obtained with the remaining measurements. The first theorem reveals the surprising result that the navigation solution is independent of the parity vector, given any single set of measurements. It indicates that accumulation of measurements is essential for an accurate integrity solution. Based on this result, NAVSYS Corporation has developed the NAVSAFE software package which verifies navigation precision by accumulating sets of measurements. The second theorem states that Solution B and Solution C are equivalent. The NAVSAFE software package uses Solution B to correct biased measurements with excellent success. The proof presented in this paper gives sound theoretical foundation to the results observed in practice. Both theorems are proved by employing the singular value decomposition of the observation matrix. >

Mathematical aspects of GPS RAIM

The development of an effective motorist mayday system for travelers in rural and urban parts of the United States and Canada has been hampered by the lack of an infrastructure to receive and process emergency requests and by the inability of most motorists to precisely define the location of their vehicle. The development of intelligent vehicle-highway systems and an expanded network of computer-switched radio systems will greatly improve the ability of highway agencies, both public and private, to respond to emergency requests. The missing element is still an inexpensive and reliable means of determining the location of vehicles in distress. GPS has been proposed as a potential method of providing location in support of a mayday service. NAVSYS has developed a low cost GPS sensor, the TIDGET, for a GPS mayday service. The TIDGET sensor does not track the GPS signals, but instead captures a brief "snapshot" of raw GPS sampled data. This "snapshot" is transmitted to the emergency dispatch facility where it is processed to compute the location of the motorist. The processing also includes aiding data from a map database to allow the vehicle's location to be determined when fewer than four satellites are in view of the sensor. In large quantities, the TIDGET sensor cost is reduced to less than $50 a unit (not including the communications link). The sophisticated software used to process this message at the dispatch center allows the solution to be derived in many cases when only two GPS satellites are in view. The paper includes a description of the TIDGET mayday system and presents preliminary test results. >

TIDGET mayday system for motorists

Inertial navigation with low-cost IMU’s can be an acceptable sole navigation source during short periods of GPS signal dropout due to intentional or unintentional interference. However, as the dropout period continues, the inertial navigation error reach unacceptable levels. In this paper, a technique is presented where relative or absolute position estimates derived from onboard captured image data are used to update the inertial navigation solution during GPS dropouts. This optical aiding technique is described and test results shown from aircraft and ground-based navigation trials.

Alison Brown

Papers

Digital L-band receiver architecture with direct RF sampling

Test Results of a Digital Beamforming GPS Receiver in a Jamming Environment

Mathematical aspects of GPS RAIM

TIDGET mayday system for motorists

Inertial Navigation Electro-Optical Aiding During GPS Dropouts