Global Positioning Satellite Receivers Research Articles

A New Board-Integrated Single Microstripfed Circularly Polarized Monopole Antenna for Global Positioning Satellite Receivers

This article proposes a new single microstirp-fed circularly polarized printed antenna for global positioning satellite (GPS) receivers. The antenna consists of two orthogonal monopoles, generating two orthogonal linearly polarized waves of equal amplitudes with a 90-degree phase shift in the operation band. In contrast to typical GPS patch antennas, the proposed antenna has much wider axial ratio bandwidth. In addition, the antenna can be simply designed, cost-effectively manufactured, and easily merged with the related circuit board. A prototype antenna was created and investigated, and the experimental results obtained also demonstrate its low sensitivity to manufacturing uncertainty.

Near Real-Time Monitoring and Mapping of Specific Conductivity Levels Across Lake Texoma, USA

A submersible sonde equipped with a specific conductivity probe, linked with a global positioning satellite receiver was developed, deployed on a small boat, and used to map spatial and temporal variations in specific conductivity in a large reservoir. 7,695 sample points were recorded during 8 sampling trips. Specific conductivity ranged from 442,uS/cm to 3,378,uS/cm over the nine-month study. The data showed five statistically different zones in the reservoir: 2 different riverine zones, 2 different riverine transition zones, and a lacustrine zone (the main lake zone). These data were imported to a geographic information system where they were spatially interpolated to generate 8 maps showing specific conductivity levels across the entire surface of the lake. The highly dynamic nature of water quality, due to the widely differing nature of the rivers that flow into the reservoir and the effect of large inflows of fresh water during winter storms is easily captured and visualized using this approach.

Integrated electronic monitoring systems could revolutionize care for patients with cognitive impairment

Dementia and other causes of functional disability can create considerable burdens for families and society as a whole, but it may be possible to partially alleviate this strain through technical innovations that replace some functions of human caregivers. This article proposes the hypothesis that cell phones, internet communication and global positioning satellite receivers could be integrated into computer based care-giving systems to provide orientation and safety cues, daily reminders of activities, protection against wandering and direct links to medical assistance in case of incapacitation. Hypothetical case histories describe assistance systems for a patient with moderate Alzheimer's disease living at home, a patient in a nursing home with more advanced dementia and incontinence, an epileptic with intermittent transient postictal amnesia, and a head injury survivor with explosive disorder.

Hardware Simulator Models and Methodologies for Indoor Performance Assessment of High Sensitivity Global Positioning Satellite Receivers

High-sensitivity global positioning satellite (GPS)-enabled mobile telephones and personal digital assistants are being introduced for emergency-call location and location-based commercial services. Simulation of weak GPS signals received in various environments has been proposed as a cost-efficient method of verifying the positioning performance of such mobile telephones. Recent results have demonstrated both the success and limitations of weak-signal and multipath models implemented in an advanced GPS hardware simulator. In particular, the lack of variability of multipath delay, as a function of time, is suspected to be a major reason for the discrepancy between simulator and field test results. This paper discusses how these model limitations have been addressed recently and demonstrates the improvement in the correlation between the simulator results and field test results. A highsensitivity GPS receiver is used to collect data under two scenarios, near a building in an outdoor environment and inside a residence. These data are then used as a baseline to attempt to generate signals in the simulator that result in measurements with similar stochastic characteristics. An analysis of the results in terms of fading and position demonstrates the viability of this approach to test receivers under controlled environments. continued on page 152

Tomography of the lower troposphere using a small dense network of GPS receivers

The application of tomographic techniques to the troposphere with GPS signals was demonstrated in previous work using data from the Kilauea permanent network, Hawaii. Local orography of the network considered there, however, played a key role in the resolution capabilities of the technique. The authors explore the possibilities of tomographic reconstruction of the four-dimensional (4D) structure of water vapor using a very small network of global positioning satellite (GPS) receivers with virtually no height differences between the stations. The analyzed campaign consisted of seven GPS receivers located at the Onsala Space Observatory, Onsala, Sweden, and was carried out in August 1998. Traditional meteorological data sources and tools such as the numerical weather model NCAR Mesoscale Model (MM5), satellite data from the National Oceanic and Atmospheric Administration (NOAA), Washington, DC, and data and analysis from the European Center for Medium-Range Weather Forecasting (ECMWF), Reading, UK, have been used to evaluate the results. A good agreement is found between GPS tomography and classical methods, even in meteorological situations with complex vertical structure of water vapor.

57. Feasibility of the Global Positioning Satellite System for Rural Aeromedical Transport

Aeromedical navigation to the scene of an accident using navigational assistance computer mapping software (NACM) can be difficult in rural areas due to the lack of topographic landmarks. In these instances, navigation is made easier using the Global Positioning Satellite (GPS) system to determine latitude and longitude.Purpose: To determine the reliability and feasibility of portable GPS receivers compared with our current system of NACM (MAP EXPERT®) in the navigation of aeromedical transport flights.Design: A non-randomized prospective trial comparing flights using either GPS or NACM. Setting: Flight program at a Level I trauma center.Methods: GPS receivers (for transmitting location) were carried by half the helicopters and ground EMS units. The NACM system was used to transmit the location of the accident to the other flights. Data on flight time, distance, and accident location were collected. Pilots and EMS personnel using the portable GPS system completed a questionnaire regarding accuracy, reliability, and ease of use.Results: This study included 51 flights; GPS (n = 26) and NACM (n = 25). There was no difference in the miles flown per minute in the NACM group (1.69 miles/minute) compared with the GPS group (1.70 miles/minute). Pilots and EMS personnel rated the GPS reliable, accurate, and easy to use for navigation.