# Gsm 2g.2.5g.2.75g



## عماد نبيه (19 يناير 2010)

*GSM *​*2G
Compared with 1G mobile communication system, 2G mobile communication system has the following advantages:
&#159; Provides high spectrum utilization and large system capacity. 
&#159; Provides diversified services (voice services and low-rate circuit-switched data services). 
&#159; Enables automatic roaming. 
&#159; Provides better voice quality. 
&#159; Provides good security. 
&#159; Can be interconnected with ISDN and PSTN. 
Basic structure of GSM network is shown in Fig 1.1‑1.
Discrepancies of 2G
2G mobile communication system has the following discrepancies:
&#159; Provides low-rate data services only and cannot support multi-media service. For example, Internet data access speed of GSM MS can reach 9.6 kbps theoretically. 
&#159; Different 2G mobile communication systems in the world use different frequencies, therefore it is difficult to implement global roaming. 
&#159; Internet, E-business, and multi-media communication is developing very rapidly. Failing to provide strong support to data communication has already constrained the development of 2G system. Demand for higher data rate and more diversified services leads to evolution from 2G to 3G. 
GSM 2.5G
GSM system (2.5G) Phase2 and Phase2+ were then developed, adopting high-rate adaptive coding solution. GPRS provides the data rate up to 171 kbps. Two high-rate data service options are:
&#159; High Speed Circuit Switched Data (HSCSD) based on high-speed data bit rate and circuit switching 
&#159; General Packet Radio Service (GPRS) based on packet switched data 
GSM 2.75G
Enhanced Data Rates for GSM Evolution (EDGE) developed by the European Telecommunications Standards Institute (ETSI) adopts 8-PSK (Phase Shift Keying) modulation. It supports data rate up to 384 kbps theoretically. EDGE is more advanced than GPRS. However, EDGE cannot provide rate up to 2 Mbps as 3G system does. Therefore EDGE is often called 2.75G.​*​​
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