Cellular System Technologies
Mobile phones send and receive radio signals with any number of cell site , base stations fitted with antennas. The communication between the handset and the cell site is a stream of digital data that includes digitized audio. The technology that achieves this depends on the system which the mobile phone operator has adopted. The Common Technologies used by operators in India are GSM and CDMA. With the advent of 3G technology systems a new era in Mobile technology in India is about to be born.
GSM (GLOBAL SYSTEM FOR MOBILE COMMUNICATION)
GSM is a widely used Second Generation cellular telecom network .Since the technology is fully digital it enables ...view middle of the document...
As there is never more than one person speaking in the room at any given moment, no one has to worry about being heard over the background.
Most GSM networks operate in the 900 MHz or 1800 MHz bands. GSM operators in India use the 900 MHz band. Operators like Hutch, Airtel, Idea etc use 900MHz in most areas and also use 1800Mhz in some areas.
One of the key features of GSM is the Subscriber Identity Module (SIM),a detachable smart card containing the user's subscription information and phonebook. This allows the user to retain his or her information after switching handsets. By changing SIM, users can change their sevice providers.
Major GSM operators in India are Airtel ,Vodafone Essar ,BSNL etc. Refer to Fig no 1 and Table 1 for market details.
Group Company Total Subscribers
Reliance (CDMA + GSM) 48696295
Vodafone Essar(GSM) 47466853
Tata (CDMA) 25476062
MTNL(GSM + WLL) 3350437
HFCL (CDMA) 326150
Shyam (CDMA) 108396
Total (All India) 272709111
Table no. 1
• Low Signal distortion inside buildings.
• Talk time is generally higher due to the pulse nature of transmission.
• The availability of SIM allows users to switch networks and handsets at will.
• GSM covers virtually all parts of the world so international roaming is not a problem.
• Large subscriber base creates better networking effect for GSM handset makers, carriers and end users.
• Since TDMA transmission is in pulse format ,it may result in interference with other electronics like high sensitive audio amplifiers.
• Competition among handset manufacturers is limited and there is a high entry barrier for new entrants.
• Technical limitations impose fixed maximum cell site range of 35 km.
CDMA (CODE DIVISION MULTIPLE ACCESS)
CDMA, a proprietary technology championed by Qualcomm, hailed as technology efficient in spectrum usage. About 17% of all global mobile connections is CDMA based.
CDMA also relies on multiplexing technique for multiple users to share the same frequency channel. The multiplexing is based on Spread spectrum technology and a special coding scheme, each transmitter with its own unique code, to allow multiple users use the same physical channel. Each transmitter in a cell site has its own unique code thus many codes occupy the same frequency channel, but only users associated with a particular code can understand others with different codes interprets the incoming data as a noise signal and rejects. The analogy by Qualcomm illustrates the technology
Imagine a room full of people, all trying to carry on one-on-one conversations. In CDMA each couple talks at the same time, but they all use a different language. Because none of the listeners understand any language other than that of the individual to whom they are listening, the background din doesn't cause any real problem.