![GSM frequency bands
Type Channels Uplink [MHz] Downlink [MHz]
GSM 850
(Americas)
128-251 824-849 869-894
GSM 900
classical
extended
0-124, 955-1023
124 channels
+49 channels
876-915
890-915
880-915
921-960
935-960
925-960
GSM 1800 512-885 1710-1785 1805-1880
GSM 1900
(Americas)
512-810 1850-1910 1930-1990
GSM-R
exclusive
955-1024, 0-124
69 channels
876-915
876-880
921-960
921-925
- Additionally: GSM 400 (also named GSM 450 or GSM 480 at 450-458/460-468 or 479-486/489-496 MHz
- Please note: frequency ranges may vary depending on the country!
- Channels at the lower/upper edge of a frequency band are typically not used](https://image.slidesharecdn.com/mobilecomputingppt-231006043034-7aa9f147/85/Mobile-Computing_PPT-ppt-44-320.jpg)
Mobile Computing_PPT.ppt
- 1. The Future of Mobile Computing 1 Presented by Dr. M.Malathy, Professor, Department of CSE Vel Tech High Tech Dr.Rangarajan DrSakunthala Engineering College, Avadi, Chennai-62
- 2. Communication • Communication is a process of transferring information from one entity to another. Sender Receiver Information • Types of communication * One way communication (Eg.)Walkie talkie * * Two way communication (Eg.) Telephone. 2
- 3. Transmission media • Guided (or Wired)—waves are guided along a solid medium such as a transmission line. • Unguided (or Wireless)—transmission and reception are achieved by means of an antenna. – In Both, communication is in the form of electromagnetic waves. – With guided transmission media, the waves are guided along a physical path; examples of guided media include phone lines, twisted pair cables, coaxial cables, and optical fibers. – Unguided transmission media are methods that allow the transmission of data without the use of physical means to define the path it takes. Telephone line 3
- 4. • People are mobile • Devices are mobile Why Mobile Computing ? 4
- 5. Mobile devices performance Pager • receive only • tiny displays • simple text messages Mobile phones • voice, data • simple text displays PDA • simple graphical displays • character recognition • simplified WWW Palmtop • tiny keyboard • simple versions of standard applications Laptop • fully functional • standard applications Sensors, embedded controllers 5
- 6. Characteristics Wireless Mobile Examples X X Stationary computer X Notebook in a hotel X Wireless LANs in historic buildings Personal Digital Assistant (PDA) 6
- 7. Applications of Wireless Communication • Vehicles – transmission of news, road condition, weather, music via DAB – personal communication using GSM – position via GPS – local ad-hoc network with vehicles close-by to prevent accidents, guidance system, redundancy – vehicle data (e.g., from busses, high-speed trains) can be transmitted in advance for maintenance • Emergencies – early transmission of patient data to the hospital, current status, first diagnosis – replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc. – crisis, war, ... 7
- 8. Typical application: Road Traffic UMTS, WLAN, DAB, GSM, TETRA, ... Personal Travel Assistant, DAB, PDA, laptop, GSM, UMTS, WLAN, Bluetooth, ... 8
- 9. • Travelling salesmen – direct access to customer files stored in a central location – consistent databases for all agents – mobile office • Replacement of fixed networks – remote sensors, e.g., weather, earth activities – flexibility for trade shows – LANs in historic buildings • Entertainment, education, ... – outdoor Internet access – intelligent travel guide with up-to-date location dependent information – ad-hoc networks for multi user games Continuation..... 9
- 10. Origins of Wireless Communications • 1864: James Clark Maxwell – Predicts existence of radio waves • 1886: Heinrich Rudolph Hertz – Demonstrates radio waves • 1895-1901: Guglielmo Marconi – Demonstrates wireless communications over increasing distances • Also in the 1890s – Nikola Tesla, Alexander Stepanovich Popov, Jagdish Chandra Bose and others, demonstrate forms of wireless communications 10
- 11. First Mobile Radio Telephone, 1924 Courtesy of Rich Howard 11
- 14. Fundamentals of Wireless Transmission wave length , speed of light c 3x108m/s, frequency f i) Frequencies for communication 14
- 15. • VHF-/UHF-ranges for mobile radio – simple, small antenna for cars – deterministic propagation characteristics, reliable connections • SHF and higher for directed radio links, satellite communication – small antenna, beam forming – large bandwidth available • Wireless LANs use frequencies in UHF to SHF range – some systems planned up to EHF – limitations due to absorption by water and oxygen molecules (resonance frequencies) • weather dependent fading, signal loss caused by heavy rainfall etc. Frequencies for Mobile Communication 15
- 16. • Physical representation of data • Function of time and location • signal parameters of periodic signals: period T, frequency f=1/T, amplitude A, phase shift . ii) Signals iii) Antenna • Antenna couples the energy to and from the space and from other conductor. iv) Signal Propagation • Propagation is always free space always like light.(Line of straight) 16
- 17. • Transmission range – communication possible – low error rate • Detection range – detection of the signal possible – no communication possible • Interference range – signal may not be detected – signal adds to the background noise distance sender transmission detection interference Signal Propagation Ranges 17
- 18. The propagation effects leads to channel impairment called multipath propagation. Multipath propagation signal at sender signal at receiver LOS pulses multipath pulses
- 19. • Multiple user share the medium with minimum or no interference. • Multiplexing in 4 dimensions – space (si) – time (t) – frequency (f) – code (c) • Important: guard spaces needed! s2 s3 s1 v)Multiplexing f t c k2 k3 k4 k5 k6 k1 f t c f t c channels ki 19 Space division Multiplexing
- 20. Frequency Division Multiplexing • Separation of the whole spectrum into smaller frequency bands • A channel gets a certain band of the spectrum for the whole time • Advantages – no dynamic coordination necessary – works also for analog signals • Disadvantages – waste of bandwidth if the traffic is distributed unevenly – inflexible k2 k3 k4 k5 k6 k1 f t c 20
- 21. f t c k2 k3 k4 k5 k6 k1 Time Division Multiplexing • A channel gets the whole spectrum for a certain amount of time • Advantages – only one carrier in the medium at any time – throughput high even for many users • Disadvantages – precise synchronization necessary 21
- 22. f Time and Frequency Multiplexing • Combination of both methods • A channel gets a certain frequency band for a certain amount of time • Example: GSM • Advantages – better protection against tapping – protection against frequency selective interference • but: precise coordination required t c k2 k3 k4 k5 k6 k1 22
- 23. Code Division Multiplexing • Each channel has a unique code • All channels use the same spectrum at the same time • Advantages – bandwidth efficient – no coordination and synchronization necessary – good protection against interference and tapping • Disadvantages – varying user data rates – more complex signal regeneration • Implemented using spread spectrum technology k2 k3 k4 k5 k6 k1 f t c 23
- 24. Cell structure • Implements space division multiplex – base station covers a certain transmission area (cell) • Mobile stations communicate only via the base station • Advantages of cell structures – higher capacity, higher number of users – less transmission power needed – more robust, decentralized – base station deals with interference, transmission area etc. locally • Problems – fixed network needed for the base stations – handover (changing from one cell to another) necessary – interference with other cells • Cell sizes from some 100 m in cities to, e.g., 35 km on the country side (GSM) - even less for higher frequencies 24
- 25. Frequency planning • Frequency reuse only with a certain distance between the base stations • Standard model using 7 frequencies: • Fixed frequency assignment: – certain frequencies are assigned to a certain cell – problem: different traffic load in different cells • Dynamic frequency assignment: – base station chooses frequencies depending on the frequencies already used in neighbor cells – more capacity in cells with more traffic – assignment can also be based on interference measurements f4 f5 f1 f3 f2 f6 f7 f3 f2 f4 f5 f1 25
- 26. Cell breathing • CDM systems: cell size depends on current load • Additional traffic appears as noise to other users • If the noise level is too high users drop out of cells 26
- 27. Media Access Control(MAC) • Can we apply media access methods from fixed networks? • Example CSMA/CD – Carrier Sense Multiple Access with Collision Detection – send as soon as the medium is free, listen into the medium if a collision occurs (legacy method in IEEE 802.3) • Problems in wireless networks – signal strength decreases proportional to the square of the distance – the sender would apply CS and CD, but the collisions happen at the receiver – it might be the case that a sender cannot “hear” the collision, i.e., CD does not work – furthermore, CS might not work if, e.g., a terminal is “hidden” 27
- 28. Motivation - Hidden and Exposed Terminals • Hidden terminals – A sends to B, C cannot receive A – C wants to send to B, C senses a “free” medium (CS fails) – collision at B, A cannot receive the collision (CD fails) – A is “hidden” for C • Exposed terminals – B sends to A, C wants to send to another terminal (not A or B) – C has to wait, CS signals a medium in use – but A is outside the radio range of C, therefore waiting is not necessary – C is “exposed” to B B A C 28
- 29. Motivation - near and far terminals • Terminals A and B send, C receives – signal strength decreases proportional to the square of the distance – the signal of terminal B therefore drowns out A’s signal – C cannot receive A • If C for example was an arbiter for sending rights, terminal B would drown out terminal A already on the physical layer • Also severe problem for CDMA-networks - precise power control needed! A B C 29
- 30. Access methods SDMA/FDMA/TDMA • SDMA (Space Division Multiple Access) – segment space into sectors, use directed antennas – cell structure • FDMA (Frequency Division Multiple Access) – assign a certain frequency to a transmission channel between a sender and a receiver – permanent (e.g., radio broadcast), slow hopping (e.g., GSM), fast hopping (FHSS, Frequency Hopping Spread Spectrum) • TDMA (Time Division Multiple Access) – assign the fixed sending frequency to a transmission channel between a sender and a receiver for a certain amount of time 30
- 31. Global System for Mobile Communication (GSM) – formerly: Groupe Spéciale Mobile (founded 1982) – now: Global System for Mobile Communication – seamless roaming within Europe possible – today many providers all over the world use GSM (more than 200 countries in Asia, Africa, Europe, Australia, America) – more than 1.2 billion subscribers in more than 630 networks 31 Source: Wireless Intelligence / GSM Association GSM Subscribers
- 32. Performance characteristics of GSM (wrt. analog sys.) • Communication • Total mobility • Worldwide connectivity • High capacity • High transmission quality • Security functions 32
- 33. 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 B-channel 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 33
- 34. GSM: Mobile Services GSM offers – several types of connections • voice connections, data connections, short message service – multi-service options (combination of basic services) Three service domains – Bearer Services – Tele Services – Supplementary Services GSM-PLMN transit network (PSTN, ISDN) source/ destination network TE TE bearer services tele services R, S (U, S, R) Um MT MS 34
- 35. Bearer Services Telecommunication services to transfer data between access points Specification of services up to the terminal interface (OSI layers 1-3) Different data rates for voice and data (original standard) – data service (circuit switched) • synchronous: 2.4, 4.8 or 9.6 kbit/s • asynchronous: 300 - 1200 bit/s – data service (packet switched) • synchronous: 2.4, 4.8 or 9.6 kbit/s • asynchronous: 300 - 9600 bit/s 35
- 36. Tele Services Telecommunication services that enable voice communication via mobile phones All these basic services have to obey cellular functions, security measurements etc. Offered services: Mobile telephony Emergency number Multinumbering Short Message Service (SMS) Enhanced Message Service Multimedia Message Service Voice Mailbox 36
- 37. Supplementary services – User identification – Call Redirection or forwarding of caller number – automatic call-back – conferencing with up to 7 participants – locking of the mobile terminal (incoming or outgoing calls) 37
- 38. Architecture of the GSM system GSM is a PLMN (Public Land Mobile Network) – several providers setup mobile networks following the GSM standard within each country – components • MS (mobile station) • BS (base station) • MSC (mobile switching center) • LR (location register) – subsystems • RSS (radio subsystem): covers all radio aspects • NSS (network and switching subsystem): call forwarding, handover, switching • OSS (operation subsystem): management of the network 38
- 39. GSM: Elements and Interfaces NSS MS MS BTS BSC GMSC IWF OMC BTS BSC MSC MSC Abis Um EIR HLR VLR VLR A BSS PDN ISDN, PSTN RSS radio cell radio cell MS AUC OSS signaling O 39
- 40. Radio subsystem The Radio Subsystem (RSS) comprises the cellular mobile network up to the switching centers Components – Base Station Subsystem (BSS): • Base Transceiver Station (BTS): radio components including sender, receiver, antenna - if directed antennas are used one BTS can cover several cells • Base Station Controller (BSC): switching between BTSs, controlling BTSs, managing of network resources, mapping of radio channels (Um) onto terrestrial channels (A interface) BSS = BSC + sum(BTS) + interconnection – Mobile Stations (MS) 40
- 41. possible radio coverage of the cell idealized shape of the cell cell segmentation of the area into cells Cellular Network – use of several carrier frequencies – not the same frequency in adjoining cells – cell sizes vary from some 100 m up to 35 km depending on user density, geography, transceiver power etc. – hexagonal shape of cells is idealized (cells overlap, shapes depend on geography) – if a mobile user changes cells handover of the connection to the neighbor cell 41
- 42. Network and switching subsystem NSS is the main component of the public mobile network GSM – switching, mobility management, interconnection to other networks, system control Components – Mobile Services Switching Center (MSC) – Databases (important: scalability, high capacity, low delay) • Home Location Register (HLR) • Visitor Location Register (VLR) 42
- 43. Operation subsystem The OSS (Operation Subsystem) enables centralized operation, management, and maintenance of all GSM subsystems Components – Authentication Center (AUC) – Equipment Identity Register (EIR) – Operation and Maintenance Center (OMC) 43
- 44. GSM frequency bands Type Channels Uplink [MHz] Downlink [MHz] GSM 850 (Americas) 128-251 824-849 869-894 GSM 900 classical extended 0-124, 955-1023 124 channels +49 channels 876-915 890-915 880-915 921-960 935-960 925-960 GSM 1800 512-885 1710-1785 1805-1880 GSM 1900 (Americas) 512-810 1850-1910 1930-1990 GSM-R exclusive 955-1024, 0-124 69 channels 876-915 876-880 921-960 921-925 - Additionally: GSM 400 (also named GSM 450 or GSM 480 at 450-458/460-468 or 479-486/489-496 MHz - Please note: frequency ranges may vary depending on the country! - Channels at the lower/upper edge of a frequency band are typically not used
- 45. Mobile Terminated Call PSTN calling station GMSC HLR VLR BSS BSS BSS MSC MS 1 2 3 4 5 6 7 8 9 10 11 12 13 16 10 10 11 11 11 14 15 17 1: calling a GSM subscriber 2: forwarding call to GMSC 3: signal call setup to HLR 4, 5: request MSRN from VLR 6: forward responsible MSC to GMSC 7: forward call to current MSC 8, 9: get current status of MS 10, 11: paging of MS 12, 13: MS answers 14, 15: security checks 16, 17: set up connection 45
- 46. Mobile Originated Call PSTN GMSC VLR BSS MSC MS 1 2 6 5 3 4 9 10 7 8 1, 2: connection request 3, 4: security check 5-8: check resources (free circuit) 9-10: set up call 46
- 47. Handover • Handing over the Mobile from one cell to another cell. • There are 4 types, – Intra cell – Inter cell – Inter BSC – Inter MSC 47
- 48. 4 Types of Handover MSC MSC BSC BSC BSC BTS BTS BTS BTS MS MS MS MS 1 2 3 4 48
- 49. Handover Procedure HO access BTSold BSCnew measurement result BSCold Link establishment MSC MS measurement report HO decision HO required BTSnew HO request resource allocation ch. activation ch. activation ack HO request ack HO command HO command HO command HO complete HO complete clear command clear command clear complete clear complete 49
- 50. Security in GSM Security services – access control/authentication • user SIM (Subscriber Identity Module): secret PIN (personal identification number) • SIM network: challenge response method – confidentiality • voice and signaling encrypted on the wireless link (after successful authentication) – anonymity • temporary identity TMSI (Temporary Mobile Subscriber Identity) • newly assigned at each new location update (LUP) • encrypted transmission 3 algorithms specified in GSM – A3 for authentication (“secret”, open interface) – A5 for encryption (standardized) – A8 for key generation (“secret”, open interface) 50
- 51. GSM - Authentication A3 RAND Ki 128 bit 128 bit SRES* 32 bit A3 RAND Ki 128 bit 128 bit SRES 32 bit SRES* =? SRES SRES RAND SRES 32 bit mobile network SIM AC MSC SIM Ki: individual subscriber authentication key SRES: signed response 51
- 52. GSM - Key Generation and Encryption A8 RAND Ki 128 bit 128 bit Kc 64 bit A8 RAND Ki 128 bit 128 bit SRES RAND encrypted data mobile network (BTS) MS with SIM AC BSS SIM A5 Kc 64 bit A5 MS data data cipher key 52
- 53. GPRS (General Packet Radio Service) – packet switching – using free slots only if data packets ready to send (e.g., 50 kbit/s using 4 slots temporarily) – standardization 1998, introduction 2001 – advantage: one step towards UMTS, more flexible – disadvantage: more investment needed (new hardware) GPRS network elements – GSN (GPRS Support Nodes): GGSN and SGSN – GGSN (Gateway GSN) • interworking unit between GPRS and PDN (Packet Data Network) – SGSN (Serving GSN) • supports the MS (location, billing, security) – GR (GPRS Register) • user addresses 53