REDUCCIÓN DEL MARGEN DE ERROR DE POSICIÓN EN SISTEMAS BASADOS EN GPS
Ing. Martínez Pérez, César Adrian
This paper is referred to the different positional errors associated with GPS systems, and it suggests an error correction model where the most significant multipath effects can be mitigated; the navigation message information from satellites and the concept of Differential GPS (DGPS) is used for this purpose. At first, the theoretical framework concerning to the operation of GPS systems is presented; then, the different segments of the system as well as the foundation upon which is based on GPS positioning method are studied. Subsequently, an analysis of the different GPS errors and how they affect the entire system is included. For the practical stage, a GPS was installed at a known point, in order to simulate a differential correction station. This GPS calculates its position and subtracts it from the original one, for calculating the error introduced in the area. For this point, an application that could read and interpret NMEA sentences delivered by the GPS was developed. A database for recording all information also was implemented. For field testing, another GPS that could communicate with the reference station for differential correction was needed. A GPS on a cell phone, which sends NMEA sentences to a laptop via a USB connection, was implemented; a program similar to the reference station was implemented for communication between them. Finally, the information concerning to the direction and signal-to-noise levels (SNR) of the GPS satellites is analyzed, in order to determine which signals have multipath effects.