The global satellite navigation technology (GPS) was created to be used for military purposes. The system was put into operation between the late 1980s and the early 1990s. However, until 2000, artificial positioning limitations considerably reduced the possibilities of using the system for civil purposes.

After limitations coordinate determination were eliminated, coordinate error was reduced from 100 to 20 meters (in an ideal scenario, the latest generations of GPS receivers, the error does not exceed 1-2 meters). These conditions enabled the use of this system for a wide range of both general and special tasks:

• Determination of the exact location
• Navigation and movement along the route with a map reference based on the actual location
• Time synchronization

GLONASS, a Russian analog of GPS, was unveiled in 1995, but because of lack of financing and a short life of the satellites, it did not receive a wide application. 2001 can be considered as a year of the system's second birth when a target program for the system's development was adopted, according to which GLONASS was scheduled to become a fully functional product by 2010.

Another popular navigation system is Galileo, a joint project of the European Union and the European Space Agency. Currently the system is under development, but it is expected to be put into operation by 2014—2016.

Review of GPS Modules

GPS modules by the most well-known manufacturers:

uBlox

• AMY-5M is a miniature GPS receiver (6.5 x 8 õ 1.2 mm), with A-GPS support.
• NEO-6 is a GPS receiver with a wide range of interfaces (UART, USB, I2C, SPI), with A-GPS support.
• LEA-6 is a GPS receiver in an enclosure, compatible with LEA-5 è LEA-4 receivers, which can receive signals from the European system GALILEO.
• LEA-6R is a GPS receiver based on uBlox 6 with dead reckoning support. Based on the information about the direction of movement and the distance covered (provided by additional sensors), the receiver can estimate its coordinates in absence of satellite signals (e.g., in tunnels, underground parking places and dense residential city areas).

Leadtek

• LR9548S is a 20-channel GPS module based on SiRF Star III.

SkyTraq

• Venus 634LPx is a miniature GPS module (10 x 10 õ 1,1 mm) with low power consumption (23 mÀ) and a short capture time (29 sec).

Transystem

• EB-270 is a GPS module based on the MTK chipset with 32 autonomous reception channels. It has high sensitivity (-158 dBm) and low current consumption (28 mA).

A Review of GLONASS/GPS Modules

Now we would like to compare combined GLONASS/GPS modules by the most well-known manufacturers:

* - at a confidence coefficient of 0,67

Linux Capabilities for Navigation Receivers

The GNU/Linux operating system, which is often used in development of embedded systems, includes the GPSD and NTPD packages, which are designed to work with navigation receivers.

GPSD includes a service that provides information about the device location (transmitted from navigation receivers to consumers over the TCP/IP connection, Port 2947). The package also has an embedded C library, a Ñ++ class and a Python module. Any of these components can be integrated into consumer software for GPSD connection.

The NTPD package gives an opportunity to input PPS exact time signals from a navigation receiver and provides information about the exact time for consumers over the UDP/IP connection (Port 123).