GSM Technology

* GSM : 

>>     GSM( Global System For Mobile Communication) is an open, digital cellular technology used for transmitting mobile voice and data services.

   >>   GSM network is mainly used for speech.  Basic gsm planning is called Green field planning.These are two types :

•      Capacity planning : depends on traffic
•      Coverage planning: depends on coverage Area.

>> Capacity sites are divided into two:

1.  Micro  (1 sector, 2 sector site)
2.  Macro (3 sector site)

GPRS :  GPRS(General Packet Radio Services) is an extension of the GSM architecture. packet data runs on a new backbone Ip network and is seperate from the existing Gsm core network. that is used mainly for speech.
* EDGE : GSM networks upgraded with Enhanced Data rates for GSM Evolution (EDGE)  technology can provide up to three times the data capacity of GPRS. It is a new modulation method.Enabling higher data bit rates. 

GSM WORLD: 

>>   Basic cell planning process :

1.   Traffic and Coverage Analysis.
2.   Nominal cell plan
3.   Surveys
4.   Implementation ( installation, comissioning& Testing )
5.   System tuning.

>>  Different frequency bands Gsm ( 450/800/900/1800/1900 )

  In India following Bands are used :

                                 Uplink (MHz)                Down link(MHz)
GSM - 800                   8xx-8xx                       8xx-8xx
GSM - 1900                 17xx-17xx                   18xx-18xx
P-GSM   900                8xx-9xx                       9xx-9xx
E- GSM  900                8xx-9xx                        9xx-9xx



GSM ARCHITECTURE:






















* MSC ( Mobile Servicing Switching Center ) :
                             The MSC is responsible for set-up, routing and supervision of calls to and from mobile subscribers. other functions are also implemented in the Msc, such as authentication.

* VLR ( Visitor Location Register ) : 
                             VLR is a data base containing information about all MSc's that currently are located in the Msc service area. when MS roams into a new Msc Service area.the VLR connected to that Msc requests data about the MS from the HLR and stores it.

* SMS-GM SC(Short message service-Gateway Msc) :
                          A SMS-GMSC is capable of receiving a short message from a service center, interrogating an HLR for routing information and message waiting data and delivering the short message to MSC of the receiving MS.

* SMS- IWMSC (Short message service-interworking MSC) :
                         It is capable of receiving a mobile oriented message from Msc and submitting the message to the receipents sc.

* GMSC (Gateway Msc) : 
                        The GMSC supports the function for routing incoming calls to the Msc where the mobile subscriber is currently registered.

* IWU (Inter Working Unit) : 
                       The IWU provides an interface to various networks for data communication. Its main functions include modem and fax adapter. This functionality is implemented in DTI ( Data Transmission Interworking unit).

* HLR (Home Location Register) : 
                        HLR is a database holding information about all subscribers belonging to PLMN (Public Land Mobile Network). In PLMN there is one or more HLRs.

* AUC (Authentication center) : 
                       The AUC provides authentication and encryption parameters required for subscriber verification and to ensure call confidentially. AUC stores the 

• a RANDom number (RAND)
• a Signed RESponse (SRES)
• a Ciphering Key (Kc)

* FNR (Flexible Numbering Register ) : 
                          The number portability enables a subscriber to change an GSM operator without changing his MSISDN number.

* BSS (Base Station System ) : 
                         The base Station System is composed of two major components.

•        Base Station Controller (BSC)
•        Radio Base Station (RBS)

* BSC / TRC :
                         The BSC can manage entire radio network and performs the following funcs:
          

•          Handling MS connection and Handover
•          Radio Network Management
•          Trans coding and rate adaptation.
•          Traffic Concentration
•          Transmission management of the BTS
•          Remote Control of the BTS

*  BTS or RBS ( Base Transceiver Station ) : 
                             It includes all radio and transmission interface equipment needed in one cell. Each BTS operates at one or several pairs of frequencies. One frequention is used to Transmit signal to MS and one to receive signal from MS.

*CHANNEL CONCEPT : 

The Carrier Seperation in GSM, is 200 KHz.

• In GSM 900 band carriers are 124
• In GSM 1800 band carriers are 374
• In GSM 1900  band carriers are 299

>> Each carrier can be shared by eight MSs.

• The number of channels in Gsm 900 band 124*8 = 992 channels
• The number of channels in Gsm 1800 band 374*8 = 2952 channels

* Logical channels : 
                         There are eleven logical channels in the GSM system, two of which are used for Traffic and nine for control signaling.

* Traffic Channels (TCH) : 
                         Two types of TCHs are used :

•  Full rate channel, Bm-  This channel is used for full rate speech
•  Half rate channel, Lm -This channel can be used for half rate speech.

 CONTROL CHANNELS :

 * Broad Cast Channel (BCH) : 

• FCCH ( Frequency correction channel ) : It is used for frequention correction of the MS, downlink only.
• SCH ( Synchronization Channel ) : It carries information about TDMA frame number and BSIC ( Base station identity code ) of the BTS, downlink only.
• BCCH (Broad cast control channel ) : Broad casts cell specific information to MS, dwonlink only.

 * Common Control Channels ( CCCH ) : 

• PCH ( Paging channel ) : It is used to page the MS, downlink only.
• RACH ( Random Access Channel ) : Used by the MS to request SDCCH or an access to MS call origination / registration.......etc. up link only.
• AGCH ( Access Grant Channel ) : It is used to allocate SDCCH to an MS, downlink only.