How GPS Tracking Device works

Январь 11th, 2016 by homesecuirtycameras and tagged , , ,

Navigation employing GPS and inertial sensors is a synergistic relationship. The integration of these two types of sensors not only overcomes performance issues found in each individual sensor, but also produces a system whose performance exceeds that of the individual sensors. portable GPS tracking provides bounded accuracy, while inertial system accuracy degrades with time. Not only does the GPS sensor bound the navigation errors, but the GPS sensor calibrates the inertial sensor. In navigation systems, GPS receiver performance issues include susceptibility to interference from external sources, time to first fix, interruption of the satellite signal due to blockage, integrity, and signal reacquisition capability. The issues related to inertial sensors are their poor long-term accuracy without calibration and cost.

Today digital advancements make it possible to pre-program asset GPS tracking device on common routes you usually tread on with the vehicle and the trackers will also bookmark your work and home GPS coordinates. This allows the tracker to automatically notice changes to common routes and begin emitting readings that raise alerts well in advance. vehicle GPS locator tend to be very discrete and will have unique and personalized beepers and sounds alerting the driver or owner regarding an unplanned reroute and they are required to respond by accepting the same by pressing a secret hidden button.

One primary concern with using GPS as a stand-alone source for navigation is signal interruption. Signal interruption can be caused by shading of the GPS antenna by terrain or manmade structures (e.g., buildings, vehicle structure, and tunnels) or by interference from an external source. Each vertical line in this figure indicates a period of shading while driving 460 Integration of GPS with Other Sensors and Network Assistance in an urban environment. The periods of shading (i.e., less than three-satellite availability) are caused by buildings and are denoted by the black lines in the lower portion. (This experiment was conducted when five to six satellites above a 5º mask angle were available for ranging.)

GPS tracker works by the process of triangulation. (Technically, it is called trilateration because it calculates your position using distances rather than angles, but the concept is similar, and the terms are often used interchangeably.) When only three usable satellite signals are available, most receivers revert to a two-dimensional navigation mode by utilizing either the last known height or a height obtained from an external source. If the number of usable satellites is less than three, some receivers have the option of not producing a solution or extrapolating the last position and velocity solution forward in what is called dead-reckoning (DR) navigation. Inertial navigation systems (INSs) can be used as a flywheel to provide navigation during shading outages. The discrete-time nature of the GPS 3G in some equipment is also of concern in real-time applications, especially those related to vehicle control. if a vehicle’s path changes between updates, the extrapolation of the last GPS measurement produces an error in the estimated and true position. This is particularly true for high-dynamic platforms, such as fighter aircraft. In applications where continuous precision navigation is required, inertial sensors can be employed. An alternative solution is the use of a GPS receiver that provides higher rate measurement outputs.

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Electronic tracking devices - about Multipath error

Январь 5th, 2016 by homesecuirtycameras and tagged , , ,

Multipath is a major error source for both the carrier-phase and pseudorange measurements. Multipath error occurs when the GPS ( personal GPS tracking devices ) signal arrives at the receiver antenna through different paths. These paths can be the direct line of sight signal and reflected signals from objects surrounding the receiver antenna. Multipath distorts the original signal through interference with the reflected signals at the GPS antenna. It affects both the carrier-phase and pseudorange measurements; however, its size is much larger in the pseudorange measurements. The size of the carrier-phase multipath can reach a maximum value of a quarter of a cycle. The pseudorange multipath can theoretically reach several tens of meters for the C/A-code measurements. However, with new advances in 32 Introduction to GPS receiver technology, actual pseudorange multipath is reduced dramatically. With these multipath-mitigation techniques, the pseudorange multipath error is reduced to several meters, even in a highly reflective environment.

Under the same environment, the presence of multipath errors can be verified using a day-to-day correlation of the estimated residuals. This is because the satellite-reflector-antenna geometry repeats every sidereal day. However, multipath errors in the undifferenced pseudorange measurements can be identified if dual-frequency observations are available. A good general multipath model is still not available, mainly because of the variant satellite-reflector-antenna geometry. There are, however, several options to reduce the effect of multipath. The straightforward option is to select an observation site with no reflecting objects in the vicinity of the receiver antenna. Another option to reduce the effect of multipath is to use a chock ring antenna (a chock ring device is a ground plane that has several concentric metal hoops, which attenuate the reflected signals). As the GPS signal is right-handed circularly polarized while the reflected signal is lefthanded, reducing the effect of multipath may also be achieved by using an antenna with a matching polarization to the GPS signal. The disadvantage of this option, however, is that the polarization of the multipath signal becomes right-handed again if it is reflected twice.

When a cell phone operator calls 911 to report emergency situation, it is desirable to locate the caller automatically. Often the caller is inside a building. If the building is equipped with a geolocation system, the caller’s location inside the building can be identified. The location of the building must also be identified. This combination of information is sent to the emergency unit receiving the call. Another approach is to use the GPS signal to locate the caller. However, inside a building the GPS ( GPS Tracking Device ) signal strength may be very weak.

One of the approaches is to use a GPS base station in the neighborhood to receive signals at normal strength. The GPS signals of normal strength are acquired and tracked. In other words, the initial phase of the C/A code, the carrier frequency, and the navigation data can all be obtained from the signals of normal strength. This information can be transmitted through the cell system to the cell phone users in the vicinity. The cell phone unit will include a GPS receiver. This GPS tracker can perform acquisition based on the received GPS information. Since the carrier frequency of the GPS is known only a very narrow frequency range need to be searched.

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GPS tracking solutions —— basic knowledge about GPS system

Декабрь 28th, 2015 by homesecuirtycameras and tagged , , ,

Today, GPS (  GPS for vehicle ) is causing a renaissance of the navigation, surveying and mapping professions and may, within only a few years, completely replace conventional methods of transportation navigation and land surveying. The uses and implications of the GPS system are yet to be fully realized, and new applications are being found at an ever-increasing rate. There are three parts to the GPS system: the satellite segment, the user segment, and the control segment.

Control segment

This part keeps the whole system running smoothly. Satellites need to be kept in their proper orbits and their signal transmissions kept up-to-date. The Air Force operates a series of five ground stations around the globe, typically at exotic tropical locations: Hawaii, Ascension Island, Diego Garcia, Kwajalein, and the decidedly nontropical master station in Colorado Springs. You’ll probably never think about the control segment, but without it, the entire system would quickly fall into disrepair.

Satellite segment

Satellites are the heart of the Global Positioning System. They broadcast the signals your receiver uses to determine your position. At least 24 satellites are in operation at all times, each orbiting the earth every 12 hours (or 11 hours and 58 minutes, if you want to be precise). Their orbits are designed so that, theoretically, at least 6 and as many as 12 satellites are above the horizon virtually all the time, regardless of where you are. “Theoretically” is the key word here—the satellite signals don’t travel through mountains, buildings, people, or heavy tree cover, so unless you’re on a flat plain or body of water, some signals probably will be blocked. Since your receiver must lock onto at least four satellites to accurately determine its position, you may have to move around to get better reception. (By the way, it’s a little-known fact that all GPS satellites perform a second duty: Each includes an X-ray detector that lets the U.S. government monitor nuclear explosions anywhere in the world.)

User segment

Your handheld receiver makes up the user segment. There’s a lot of power inside that little package. Not only does it contain a sensitive receiver capable of detecting signals less than a quadrillionth the power of a light bulb, it also includes a powerful computer that converts the raw data into such useful information as your position and speed. A GPS magnetic tracker doesn’t include any kind of transmitter, meaning it is a passive positioning system—you can determine your own position, but there’s no way for anyone else to use it to track you.

However, accuracy can be improved by combining the electronic tracker with a Differential GPS (or DGPS) receiver, which can operate from several possible sources to help reduce some of the sources of errors described above. Differential GPS works by placing a GPS receiver (called a reference station) at a known location. Since the reference station knows its exact location, it can detennine the errors in the satellite signals. It does this by measuring the ranges to each satellite using the signals received and comparing these measured ranges to the actual ranges calculated from its known position. The difference between the measured and calculated range.

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