Answer:

• The group of special mobile is sometimes known as global system for mobile and it is a second generation cellular mobile standard. Actually in 1980's many mobile systems with closer carrier frequencies under analog mobile phone systems faced many interferences and other problems, in European counters.
• A better approach which is a second generation digital system is the global system for mobile with acronym '(SM'. In the age before GSM European countries used various cellular mobile standards which were not much efficient. CSM was initially functioning in 900 hIllz band of frequency.
• The group of special mobile committee was a functioning group of CEPT. In the year of 1992 GSM modified its name to "Global system for mobile communications". The standards setting for CSM was under European Technical Standards Institute (E1S1).
• In European countries GSM was first marketed in the year 1991. After two years other countries also evinced interest in this digital standard used for cellular communications technology.
• The main aim of GSM was to provide 'roaming facility' for subscribers and to follow ISDN guidelines. It provides voice services that are compatible with ISDN standards.

• GSM lies under second generation systems, that replaced first generation analog systems. Considering satellite uplink and downlinks, GSM was deployed using 890-915 MHz for uplinks and 935 to 960 MHz for downlink transmissions. GSM system used in United States in the band of 1900 MHz was called as personal communications services (PCS). There are many GSM solutions known as GSM 900, GSM 1800 etc.

   

• The global system for mobile (group of special mobile) GSM phone functional block diagram is shown in Fig.The transceiver antenna system receives or transmits RE signal. The analog to digital conversion and digital to analog conversions are done in opposite directions depending upon transmission or reception. Microphone and loudspeakers are used in similar two directional ends.

• The channel coding is done with interleaving technique. Modulation and demodulation for transmission and reception. Equalization technique is also applied. Modulation scheme adopted is gaussian minimum shift keying digital modulation. The antenna is of MIMO (Multiple Input and Multiple Output) nature. User authentication is possible with GSM phones.

Depending upon the services provided by this standard there are size important category/examples. 

| 1) Transactional sante ShoppingBooking | | 2) Travelling related services RoamingWeather | | 3) Personal Service Health monitoringBudgeting | | --- | --- | --- | | 4) Mobile office EmailModemFax | | 5) Fun GamblingOnline games | | 6) Security services Emergency callsAlarm provisions |