Gsm architecture
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- GSM is a standard for 2G digital cellular networks that uses narrowband TDMA. It describes protocols for features like GPRS, EDGE, authentication, encryption, and more. - The GSM architecture consists of mobile equipment (handsets), a base station subsystem for radio network management, a network switching subsystem for call routing, and a network management subsystem. - Key aspects include the SIM card for user identification, base transceiver stations for radio signals, transcoding between speech formats, home and visitor location registers for subscriber data, and authentication/equipment databases.
Gsm architecture
- 1. GSM Architecture By: •Hassan Amjad •Bilal Waheed •Mohsin Amin
- 2. Intro to GSM: • GSM (Global System for Mobile Communication) • It is a standard set developed by the ETSI. • It describe protocols for 2G digital cellular networks. • Full duplex. • GPRS & EDGE facilities.
- 3. GSM Variants : Variant Uplink Downlink Total Duplex- Channels (MHz) (MHz) Bandwidth frequency GSM-400 451-458 and 461-468 and Twice 14 MHz 10 MHz Twice 72 479-486 489-496 GSM-900 890-915 935-960 Twice 25 MHz 45 MHz Twice 124 (primary band) Extended 880-915 925-960 Twice 35 MHz 45 MHz Twice 174 GSM-900 GSM-R 876-880 921-925 Twice 4 MHz 45 MHz Twice 19 DCS-1800 1,710-1,785 1,805-1,880 Twice 75 MHz 95 MHz Twice 373 PCS-1900 1,850-1,910 1,930-1,990 Twice 60 MHz 80 MHz Twice 300
- 4. GSM Architecture What so ever the variants are the basic architecture of GSM network remains the same as elaborated below: • BSS (Base Station Subsystem) • NSS ( Network Switching Subsystem ) • NMS ( Network Management Subsystem )
- 6. ME: • Mobile equipment • Handset + SIM +
- 7. Handset: • is a device that can make and receive telephone calls • over a radio link • Can moving around a wide geographic area.
- 8. SIM: Subscriber identification module It contains • IMSI ( international mobile subscriber identity ) • PIN (personal identification number ) • PUK ( personal un blocking code ) • ICCID ( integrated circuit card identification )
- 9. • IMSI ( used by operators to identify user) • IMSI = MCC+MNC+MSIN i. MCC ( mobile country code) ii. MNC ( mobile network code) iii. MSIN ( mobile user identification number ) • ICCID (SIM is internationally recognized by this number ) • Usually printed on SIM
- 10. Base Station Subsystem: • The Base Station Subsystem is responsible for managing the radio network, and it is controlled by an MSC. • A BSS itself may cover a considerably large geographical area consisting of many cells (a cell refers to an area covered by one or more frequency resources).
- 11. BSS consists of three element • BTS ( Base transceiver station) • BSC ( Base station controller ) • TC ( Tran coder)
- 12. Base transceiver station: • Encoding, encrypting, multiplexing, modulating, and feeding the RF signals to the antenna. • Time and frequency synchronizing • Decoding, decrypting, and equalizing received signals • Random access detection • Uplink channel measurements
- 13. Base station controller : • The BSC manages the radio resources for one or more BTSs. It handles radio channel setup, frequency hopping, and handovers. • The BSC is the connection between the mobile and the MSC. • Control of frequency hopping • Performing traffic concentration to reduce the number of lines from the MSC • Reallocation of frequencies among BTSs • Time and frequency synchronization • Power management
- 14. Transcoder: • In the air interface (between MS and BTS), the media carrying the traffic is a radio frequency. • To enable an efficient transmission of digital speech information over the air interface, the digital speech signal is compressed. • We must however also be able to communicate with and through the fixed network, where the speech compression format is different. • Somewhere between the BTS and the fixed network, we therefore have to convert from one speech compression format to another, and this is where the Transcoder comes in.
- 15. • For transmission over the air interface, the speech signal is compressed by the mobile station to • 13 k bit/s (Full Rate and Enhanced Full Rate), • 5.6 k bit/s (Half Rate), • 12.2 k bit/s (Enhanced Full Rate). • AMR (Adaptive Multirate Coding) which is more flexible since it produces speech with bitrates similar to older solutions but adapted to link conditions. • However, the standard bit rate for speech in the PSTN is 64 Kbits/s. The modulation technique is called "Pulse Code Modulation" (PCM). This requires the GSM network to perform bit rate adaptation of speech.
- 16. Network switching subsystem (NSS) NSS typically consists of following elements • MSC (Mobile switching center) • HLR (Home location register ) • VLR ( visitor location register ) • AUC (Authentication center ) • EIR ( Equipment identity register) • GMSC ( Gate way mobile switching center )
- 17. HLR: • centralized network database • stores and manages all mobile subscriptions belonging to a specific operator. • a permanent store for subscriber until that subscription is canceled. It stores 1. Subscriber identity 2. Subscriber supplementary services 3. Subscriber location information 4. Subscriber authentication information
- 18. VLR : • It is a temporary database . • Stores only information of subscriber those are in that MSC. • Every MSC has its own VLR • When a subscriber roams into a new MSC service area, the VLR connected to that MSC requests information about the subscriber from the subscriber's HLR.
- 19. EIR : • Data base used to store mobile identity • Help us blocking calls from stolen MS
- 20. AUC: • AUC is a database connected to the HLR • Function is to authenticate the subscribers attempting to use a network.
- 21. MSC & GMSC: • MSC performs the telephony switching functions for the mobile network. • controls calls to and from other telephony and data systems, such as the Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN). • In GMSC Gateway functionality enables an MSC to interrogate a network's HLR in order to route a call to a Mobile Station (MS). • Any MSC can be GMSC
- 22. NMS: NMS consists of two element 1. OMC ( Operation and maintenance center ) 2. NMC (Network management center )
- 23. OMC & NMC • OMC a computerized monitoring & maintenance center which is connected MSCs and BSCs. • OMC is local. • In NMC centralized control of a network is done. • One NMC per network to control many OMCs. • OMC and NMC functionality can be combined in the same physical network node.
- 24. GSM GEOGRAPHICAL NETWORK STRUCTURE Local area (LA) • LA is as a group of cells. • Within the network, a subscriber’s location is known by the LA. • The identity of the LA in which an MS is currently located is stored in the VLR.
- 25. MSC SERVICE AREA • An MSC service area is made up of a number of LAs and • MSC use LA to route a call to MS
- 26. Hardware view of a sample network
- 27. Software view of a sample network
- 28. GMSK: • Gaussian Minimum Shift Keying. • Gaussian Minimum Shift Keying (GMSK) is a form of continuous-phase FSK in which the phase change is changed between symbols to provide a constant envelope. Consequently it is a popular alternative to QPSK. • The RF bandwidth is controlled by the Gaussian low-pass filter.
- 29. continuous-phase : continuous-phase • In CPM the carrier phase is modulated in a continuous manner in contrast to QPSK .
- 30. • CPM is typically implemented as a constant- envelope waveform. • QPSK requires a relatively large percentage of the power to occur outside of the intended band. • CPM is attractive because the phase continuity yields high spectral efficiency. • The primary drawback is the high implementation complexity required for an optimal receiver.
- 31. MSK: • Minimum shifting keying . • It is similar to OQPSK • OQPSK gives us square wave which is difficult to handle. • MSK gives us half cycle sinusoidal wave for a symbol
- 32. GMSK: • Gaussian minimum shifting keying • MSK with Gaussian filter. •
- 33. Gaussian filter • Gaussian filters are designed to give no overshoot to a step function input while minimizing the rise and fall time. • Gaussian filter has the minimum possible time delay
- 34. Example The filter smoothes the binary pulses
- 35. signal is integrated over time to obtain a continuous waveform which captures the bit transition information
- 36. • Send this wave to IQ modulator . • Integrate out put and send it
- 37. ADVANTAGES DISADVANTAGES • High spectral efficiency. • Higher power level than • Reducing sideband QPSK. power. • Requiring more complex • Excellent power channel equalization efficiency due to constant algorithms such as an envelope. adaptive equalizer at the • Good choice for voice receiver. modulation. • Inter symbol interference
- 38. Interleaving • Interleaving rearranges a group of bits in a parti cular way. • Improve the performance of the error correction mechanisms • The interleaving decreases the possibility of losing whole bursts during the transmission.
- 39. Interleaving