GPRS (General Packet Radio Service) - an add-on technology, mobile GSM, performs packet data transmission. GPRS allows the user to the cellular network to exchange data with other devices in the GSM network and external networks, including the Internet. GPRS involves charging by volume of data sent / received data, and not on time spent online.
GPRS enables people to enjoy advanced, feature-rich data services, such as e-mail on the move, multimedia messages, social networking and location-based services(GSMA).
Architecture:
GPRS data service built over the existing network GSM. At a structural level, the GPRS system can be divided into two parts: a base station subsystem (BSS) and a core network GPRS (GPRS Core Network).In the BSS includes all base stations and controllers that support packet data transfer. To do this, BSC (Base Station Controller) is complemented by a control unit blocks - PCU (Packet Controller Unit), a BTS (Base Tranceiver Station) - encoder GSM formats, protocols used by TCP / IP.Gateways to external networks (Internet, intranet, X.25) called GGSN (Gateway GPRS Support Node). Exchange of information between the SGSN and GGSN are IP-based protocols.Also in the GPRS Core includes the DNS (Domain Name System) and the Charging Gateway (Gateway to communicate with the billing system).
Operation
When using GPRS information is collected and transmitted in packets through the currently unused voice channels. Such technology involves the use of more efficient network resource GSM. In this case, what is the priority of the transmission - voice traffic or data transfer - selected by the operator. Moso of the operatiors use the absolute priority of voice traffic over data, so the rate depends not only on the capabilities of the equipment, but also on the network load. The possibility of using multiple channels provides sufficiently high data rates, the theoretical maximum for all TDMA time slots employed is 171.2 kB/ s. There are different classes of GPRS, different data rates and the ability to combine data while a voice call.
This standard is currently maintained by the 3rd Generation Partnership Project (3GPP).
Subscribers connected to GPRS are provided with a virtual channel that is on the packet transmission time becomes real one, and in the rest of the time is used to transfer packets from other users. But a single channel can be used by some subscribers at one time that cause packet transmission queue and as a result, communication delay. For example, a modern version of the software base station controllers allow simultaneous use of a single time slot sixteen subscribers at different times to 5 (of 8) timeslots on the frequency, total - up to 80 subscribers using GPRS on one channel (the average maximum speed with 21, 4 * 5/80 = 1.3 kB / s per user). At the other extreme - packaging timeslots in one continuous with the exclusion of voice subscribers to other frequencies (if any, and taking into account the priority). The phone that works in the mode of GPRS, accepts all packets on the same frequency, and does not waste time to switch. In this case, the data transfer rate increases up to the maximum possible as described above, the two time slots 4 (class 10), or 4 +4 (class 12).The GPRS uses GMSK-modulation. The data are sent over the radio air and encoded by one of the 4 code schemes (CS1-CS4) all that strongly depends on the quality of signal. Each code scheme is characterized by redundant encoding and noise immunity, and is automatically selected depending on the quality of the radio signal. In the same way and using the same equipment, the EDGE technology works. But EDGE uses a different, more dense packing of information (modulation 8PSK) within the time slot.
GPRS Benefits
- high average data rate - 20-40 kbit / s.
- GPRS-billing service does not depend on the duration of the connection;
- Rapid and reliable GPRS-connection;
- Ability to talk on the phone and exchange SMS-messages not breaking GPRS-connection;
- efficient use of energy during a phone GPRS-connection.
References
"GPRS." About Us. N.p., n.d. Web. 20 Apr. 2013.
http://www.gsma.com/aboutus/gsm-technology/gprs
"3GPP - A Global Initiative." 3GPP. N.p., n.d. Web. 20 Apr. 2013.
http://www.3gpp.org/
