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GPS System
GPS System (Global Positioning System) works based on NAVSTAR satellite technology made available by the U.S. Department of Defense for civilian needs.
This system consists of 24 active satellites (on six orbits), circling the Earth twice a day (24h). On each orbit, there are four satellites at the altitude of more than 20 thousand kilometres above the Earth.
Orbits are distributed around the whole earth and have the angle of 55 degrees to the equator. Each of these satellites transmits two types of signals: L1 (frequency 1575.42 MHz) and L2 (frequency 1227.60 MHz). Signal L1 is processed with two pseudo-random jamming signals: P code protected and C/A code protected. L2 signal only contains the P code. Each satellite contains other signal, which enables the receivers to recognise from which satellite the signal comes.
Civilian receivers for navigation use only C/A code at L1 frequency. P code is used by the Army or specialised geodesic centres.
GPRS System
General Packet Radio Service (GPRS) – the technology which is used in GSM networks for packet data transmission. The actual transmission speed of 30-80 kb/s enables using the Internet or audio/video streaming transmission. Another advantage of the technology is the fact that the user pays for the actually sent or received amount of bites and not the time in which the connection was active. GPRS is often referred to as 2.5 G technology, because it is an element of GSM evolution (as the second generation mobile telephony) into the 3G standard network.
There is also the notion of “GPRS network”. It is referred to in the context of telecommunication infrastructure, which enables packet transmission. It consists of base stations used in the classic GSM network for voice transmission and of an independently developed backbone, which connects the radio network with external IP or X.25 networks and with other cell phone networks.
GPRS specification is developed as part of GSM standard by the 3GPP standardization consortium.
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