There are a number of ways to improve GPS accuracy.
Use a network of fixed, ground-based reference stations.
These stations broadcast the difference between the measured satellite pseudoranges and actual (internally computed) pseudoranges. Receiver stations correct their pseudorangesm by the same amount.
This method is called Differential GPS, or DGPS. DGPS was especially useful when GPS was still degraded (via the "Selective Availability" described below). DGPS provided 5-10 meter accuracy. Primarily, the DGPS network has been developed by the Finnish, and Swedish, maritime administrations. The goal was to improve safety, in the archipelago between the two countries. tomtom full serial number and activation code
Exploitation of DGPS, for Guidance Enhancement (EDGE).
This is an effort to integrate DGPS, into precision guided munitions. This includes the Joint Direct Attack Munition (JDAM).
Wide-Area Augmentation System (WAAS).
It uses a series of ground reference stations, to calculate GPS correction messages. These are uploaded, to a series of additional satellites. These satellites are in geosynchronous orbit, for transmission to GPS receivers. This includes information on ionospheric delays, individual satellite clock drift, and similar.
The expectation of WAAS is to provide sufficient reliability, and accuracy, for critical applications. One use is for GPS-based instrument approaches, in aviation (landing an airplane in conditions of little or no visibility).
The current WAAS system only works, for North America (where the reference stations are located). Due to the satellite location, the system is only usable in the eastern and western coastal regions.
Variants of the WAAS system are being developed, in Europe (EGNOS, the Euro Geostationary Navigation Overlay Service), and Japan (MSAS, the Multi-Functional Satellite Augmentation System). They are virtually identical to WAAS.
Local-Area Augmentation System (LAAS).
It uses similar correction data, to WAAS. But, in this case, the correction data is transmitted from a local source. This is typically at an airport, or another location where accurate positioning is needed. Correction data is typically useful for only a thirty to fifty kilometer radius, around the transmitter. tomtom full serial number and activation code
Wide Area GPS Enhancement (WAGE).
This is an attempt to improve GPS accuracy. It provides more accurate satellite clock and ephemeris (orbital) data, to specially-equipped receivers.
Relative Kinematic Positioning (RKP).
This is an approach for a precise, GPS-based positioning sytem. Using this approach, accurate determinination of range signal is resolved to an accuracy of less than 10 centimeters.
It resolves the number of cycles the signal is transmitted, and received, by the receiver. This is accomplished using a combination of differential GPS (DGPS) correction data, transmitting GPS signal phase information and ambiguity resolution techniques. This is done via statistical tests. Sometimes, there is processing in real-time (real-time kinematic positioning, RTK). tomtom full serial number and activation code
Many GPS systems in automobiles combine the GPS unit with a gyroscope, and speedometer pickup.
This allows the computer to maintain a continuous navigation solution. Buildings, terrain, or tunnels blocking the satellite signals are not problems. This is similar, in principle, to the combination of GPS and inertial navigation, used in ships and aircraft. However, it is less accurate, and less expensive, because it only works for short periods.