Presentation On Study Of GSM BTS Guided by :- Mr. Suresh Dhruwey JTO(CMTS), Bhilai. Submitted By:- Amit Kumar Singh Priya Rajput Soumya Vaishnava Amit Kumar Patel

GSM Definition Global system for mobile communication(GSM) is globally accepted standard for digital cellular communication. GSM is the name of a standardization group established in 1982 to create European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz. It is estimated that many countries outside of Europe will join the GSM partnership. Overview This tutorial provides an introduction to basic GSM concept, specification, networks, and services. A short history of network evolution is provided in order set the context for understanding GSM.

INTRODUCTION Global System for Mobile Communication (GSM) Currently ~ 670 networks in 213 countries and territories Frequency bands (MHz) –450, 850, 900, 1800, 1900 Very rapid growth in subscribers (1275M-2/05, 1600M-12/05, 2000M-12/06) Aggressive evolution to 3G –EDGE, Wideband CDMA Air Interface Based on FDD –TDMA Raw bit rate: kbps Each physical channel is shared (TDMA) by 8 users Data service: HSCSD (Circuit-Switched) & GPRS (Packet-Switched)  The GSM standard was developed as a replacement for first generation (1G) analog cellular networks, and originally described a digital, circuit switched network optimized for full duplex voice telephony.1G

GSM – The idea of a common European mobile communications system. 1982: A Nordic group is considering the next generation of mobile telephone. – NMT (Nordisk Mobil Telefon), the analogue first generation system has only just been started These ideas are presented to CEPT (European Conference of Postal and Telecommunications Administrations) in June 1982 September 1982: The first meeting in CEPT GSM – Groupe Spécial Mobile In 1988 ETSI (European Telecommunications Standards Institute) is established and the work is continued under a new name: SMG – Special Mobile Group

Advantages of GSM over Analog system Capacity increases Reduced RF transmission power and longer battery life. International roaming capability. Better security against fraud (through terminal validation and user authentication). Encryption capability for information security and privacy. Compatibility with ISDN,leading to wider range of services

Disadvantages of GSM There is no perfect system!! no end-to-end encryption of user data. no full ISDN bandwidth of 64 kbit/s to the user, no transparent Bchannel. reduced concentration while driving. electromagnetic radiation. abuse of private data possible. roaming profiles accessible. high complexity of the system. several incompatibilities within the GSM standards.

GSM Architecture SIM – Subscriber Identity Module. Allows you to switch phones. Stores your phonebook and ringtones. ME – Mobile Equipment. Your cellphone UM – User Mobile Frequency The actual radio frequency you are using.

GSM Architecture BTS – Base Transceiver Stations. – The radio antennas. – In GSM, 1 sends and 1 receives. Only 2 are necessary. BSC – Base Station Controller. – Packages up all the radio signals and sends them to the switch. – Handles handoffs and some other low-level functionality. – Manages up to 50 or so radio antennas Provides better network segmentation. Abis – Typically a T1 SS7 connection using ISUP

GSM Architecture MSC – Mobile Switching Center – Has several databases that perform call validation, call routing to the PSTN, and roaming validation. – Some of the databases: HLR: Home Location Register – Main customer database – Motorola only has 60 HLRs in the United States. VLR: Visitor Location Register – Works in tandem with the HLR. Roamer database. EIR: Equipment Identity Register – Deny stolen mobile phones service. Has all valid serials. AuC: Authentication Center – Stores encryption keys necessary for secure communications.

GSM Frames The frame length in time is ms –.577 ms times 8 Each frame carries 164 bits – 114 are for voice – The rest are for synchronization and CRC checks Each frame can carry up to 8 voice samples, or, the frame can be dedicated to other necessary information.

GSM Frames Different frames mean different things. – For instance, this data structure contains information about the cell site. The cell phone scans for this information when it is turned on. This is the burst that occurs when the mobile transmits its access key back to the base station.

Speech Coding GSM uses LPC – Linear Predictive Coding. – Uses interpolation. – Basically, previous samples, which don’t change very quickly, are used to predict current samples. So, instead of actually sending the voice sample, the delta in the voice sample is sent. Also, silence is not transmitted. – This increases throughput by about 40%. – This bits can be used for other conversations.

BTS ABC protocol is used in BTS system. The whole BTS matures calls. Bandwidth of a call is 9.6kbps. BTS works in MHz. TRA The signal received by the antenna is connected with TRA. A signal TRA matures 7/8 calls. A BTS system contains 4 TRA by which it matures calls. If 91 calls occurs, then it show busy to the subscriber then it is connected with SUMA card which tells us about the compiler, then it goes to BSC through PCM and the call gets matched.

Block Diagram of BTS

Base Transceiver Station - BTS The BTS has the equipment needed to transmit and receive on the radio channels allocated to take care of traffic and signalling in one cell. The main responsibility is to provide connections with the MSs over the air interface. The BTS can consist of several TRXs (one per carrier) whose functions can be divided into Control, Signal processing, Transmitting part, Receiving part and Synchronisation. Other functions commonly, but not necessarily, used are combining and dividing the signals to and from the antenna(s), and a battery backup in case of power failure.

GSM BTS Specification Single TRX (Single carrier). Low power. Supports multiple bands –GSM 900, 1800 and Standard compliant. Remote monitoring capability. Low cost. Spectrum efficient. Compatible with ISDN.

GSM conclusion Widely used. – Upwards of 70% of phones. Uses SIM cards so customers can use any phone and for security. Allows more customers than analog. Worse voice quality than analog. Purely digital. Open source, very complex standard. Uses TDMA. Will be replaced by CDMA in the near future.