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GSM
Evolution of Cellular communication standards
• Analog standards
– Advanced Mobile Phone Service (AMPS)
• US, 800 MHz band
– Total Access Communication System (TACS)
• UK, based on AMPS in 900 MHz band
– Nordic Mobile Telephone System(NMT)
• Scandinavian, Both in 450 MHz and 900 MHz band
• Digital Standards
– Dual mode AMPS (D-AMPS)
• US, Analog signaling and Digital voice coding
– IS-95
• US, CDMA based
– Global Systems for mobile communications (GSM)
• European standard, 890 MHz - 960 MHz band
Why GSM?
• There were so many systems available need to consolidate ,Limitations of Analogue system,Incompatibility between systems.Moving towards PCN(Personal Communications Network)
• Mobility was the keyword in developing a new system to reach people on move between countries yet stay connected.
What are the types in GSM Network?
• GSM-900 (Channels 125 operating band 900Mhz carrier spacing 200khz spacing 45Mhz)
• GSM -1800 (Channels 374 spacing 95Mhz)
GSM in comparison with other Standards?
• GSM gives mobility without any loss in Audio quality
• Encryption techniques used gives high security in the air Interface and also use of SIM.
• Bit Interleaving for high efficiency in Transmission.
• Variable Power (Power budgeting- extend battery life)
• Minimum Interference.(Eq DTX )
• Features-CCS7 Signaling
– SMS (Short Message Services)
– Emergency Calls
– CELL Broadcast
GSM Concepts - Cellular Structure
• Cellular
– Networking technology that breaks geographic area into cells shaped like honey comb
• Cell
– Area of coverage provided by one or more Radio terminals
Cell Planning
• Traffic and Coverage Analysis
• Collection of data
• Traffic calculation
• Nominal Cell Plan
• Coverage and Interference Prediction
• Site Survey and Signal strength Measurement
• Evaluation, final Cell Plan
• Installation
• Optimization
Transmission Direction
• Uplink Transmission
– Transmission from Mobile to Radio Terminal
• Down Link Transmission
– Transmission from Radio Terminal to Mobile
– Uplink and Downlink channels separated by 45 MHz
Access Techniques
• Uplink 890 MHz to 915 MHz
• Down Link 935 MHz to 960 MHz
• 25 MHz divided into 125 channels of 200 KHz bandwidth
• Time Division Multiple Access
• Each carrier frequency subdivided in time domain into 8 time slots
• Each mobile transmits data in a frequency, in its particular time slot - Burst period = 0.577 milli secs.
• 8 time slots called a TDMA frame. Period is .577 * 8 = 4.616 milli secs
GSM System specifications
Frequency band
Uplink 890 MHz-915 MHz
Downlink 935 MHz-960MHz
Duplex distance 45MHz
Carrier separation 200KHz
Modulation GMSK
Air transmission rate 270Kbps
Access method FDMA/TDMA
Speech Coder RPE-LTP-LPC
(Regular pulse excitation
-Long Term predictive
-linear predictive Coder)
GSM - Network Structure
GSM Network
Mobile Station (MS)
• Hand portable unit
• Frequency and Time Synchronization
• Voice encoding and transmission
• Voice encryption/decryption functions
• Power measurements of adjacent cells
• Display of short messages
• International Mobile Equipment Identifier (IMEI)
Subscriber Identity Module (SIM)
• Portable Smart Card with memory (ROM-6KB to 16KB-A3/A8
algorithm, RAM- 128KB TO 256KB, EEPROM- 3KB to 8KB )
• Static Information
– International Mobile Subscriber Identity(IMSI) (MCC + MNC+MSIN
– Personal Identification Number (PIN)
– Authentication Key (Ki)
• Dynamic Information
– Temporary Mobile Subscriber Identity(TMSI)
– Location Area Identity (LAI)
– Phone memories, billing information
– Ability to store Short Messages received
Base Transceiver Station (BTS)
• Consists of one or more radio terminals for transmission and reception
• Each Radio terminal represents an RF Channel
• TRX and MS communicates over Um interface
• Received data transcoding
• Voice encryption/decryption
• Signal processing functions of the radio interface
• Uplink Radio channel power measurements
Base Station Controller (BSC)
• External Interfaces
– ‘Abis’ interface towards the BTS
– ‘A’ interface towards the MSC
• Monitors and controls several BTSs
• Management of channels on the radio interface
• Alarm Handling from the external interfaces
• Performs inter-cell Handover
• Switching from ‘Abis’ page link to the ‘A’ link
• Interface to OMC for BSS Management