CCM 4300 Lecture 5 Computer Networks: Wireless and Mobile Communication Systems Dr E. Ever

1. CCM 4300 Lecture 5 Computer Networks: Wireless and Mobile Communication Systems Dr E. Ever School of Computing Science

2. Lesson objectives • To acquire a basic understanding of GSM, GPRS, EDGE, Satellite systems, UMTS and Bluetooth and you will be able: - to make informative decision regarding which technology to use and why - explore the history and architecture of such technologies - identify some of the advantages and disadvantages of using these technologies.

3. Session Content • Introduction – what is GSM? • GSM and GPRS Components • Why the interest in 2G, 3G and 4G technologies? • UMTS • Bluetooth • Satellites: HEO, MEO, LEO

4. Wide Area mobile connectivity-GSM • Circuit-switched • Second generation (2G): • digital • GSM (2G): • digital • secure (?) • international roaming • 13Kb/s voice • 2.4kb/s - 9.6Kb/s data (uses FEC) • SMS: • up to 160 chars of text • GSM flavours: • GSM900 – vanilla GSM • GSM1800, PCN, (Europe) • GSM1900, PCS (US) • GPRS (2.5G) • UMTS (3G) • 4G systems: • 20Mb/s – 100Mb/s

5. GSM: An overview I GSM • formerly: Groupe Spéciale Mobile (founded 1982) • now: Global System for Mobile Communication • Pan-European standard (ETSI, European Telecommunications Standardisation Institute) • simultaneous introduction of essential services in three phases (1991, 1994, 1996) by the European telecommunication administrations (Germany: D1 and D2) seamless roaming within Europe possible • today many providers all over the world use GSM (more than 214 countries in Asia, Africa, Europe, Australia, America) • more than 2 billion subscribers • more than 70% of all digital mobile phones use GSM • Countries which are using GSM networks on larger scales are Russia, china Pakistan, United States, India. • over 360 billion SMS peryear worldwide

6. What happens within the network? ? GSM Network fixed network Fixed network subscribers GSM Subscriber Other mobile subscribers

7. GSM Physical layer 0 0 7 frame (8 bursts) (~4.615ms) 25 tail: 3 bits stealing: 1 bit data: 57 bits training: 26 bits guard: 8.25 bits multi-frame (26 frames) (120ms) frame 12 for signalling frame 25 unused • • Phy: • • 900MHz (1.8GHz, 1.9GHz) • • 2x25Mhz bands • 890-915MHz uplink • 935-960MHz downlink • • 124 carriers per band • • 200KHz bandwidth per • carrier • • Channel allocation: • • TDMA/FDMA • • multiple frequency channels • • TDMA in each channel • • (slow FH possible) S indicates user or network control data tail bits data bits stealing bit (S) training sequence Stealing bits data bits guard bits Tail bits

8. GSM Physical layer 8

9. GSM coding overhead • • 114 bits every 4.615ms  • ~31Kb/s • • So why do we only get • 13Kb/s speech and • 9.6Kb/s data? • • Error coding! • plus other overhead • • Large amount of error • correction coding: • • speech uses CRC + 1/2 rate convolutional coding for Forward Error Correction • • need better FEC for data • 260 bits of speech produces 456 bits for transmission! • 13Kbs  ~23Kb/s • “high-speed” data available now - HSCSD: • 14.4Kb/s or 28.8Kb/s on 2 channels • May be able to improve on this with 3G CDMA: • less overhead required?

10. FEC (simple example) A simple example would be an analog to digital converter that samples three bits of signal strength data for every bit of transmitted data. The simplest example of error correction is for the receiver to assume the correct output is given by the most frequently occurring value in each group of three. 10

11. GSM Network Structure I • Digital mobile service: • data/voice • extendable network • allows international roaming • Network topology: • cells • base-transceiver station (BTS) • GSM cell clusters: • 4, 7, 12, 21 cells • pattern repeats to cover area base-transceiver station (BTS) • • BTS network: • • interconnected by a • terrestrial network

12. GSM network structure II f3 f5 f2 f4 f6 f5 f1 f4 f3 f7 f1 f2 d Handoff region r • • d/r > 2.5 • • Network scaling: • • reduce cell-size • • increase number of cells

13. Handoff for Wireless Systems (cont`d) • Handoff!! • The process of transferring a mobile user from one channel or base station to another.

14. Equations • The average number of calls in the systems, NS • However, since only i channels operative at any time, the MQL can now be represented by Ni where i is the number of operative channel. So overall MQL is as follows:

15. Performability Modelling of Handoff (cont`d) Why does no hand-off has the worst performance?

16. OMC, EIR, AUC fixed network HLR GMSC NSS with OSS VLR MSC VLR MSC BSC BSC RSS GSM Network Structure III AuC authentication centre BSC base-station controller BTS base-transceiver station EIR equipment identity register HLR home location register MSC mobile switching centre VLR visitor location register OMC Operation and maintenance systems

17. GSM network structure IV • MS: • • sends beacon to BTS • • BSC: • • talks to all BTS in an area • • assigns channels • • performs authentication • • sends updates for VLR • • communicates with other • BSCs and a single MSC • • Roaming: • • updates to VLR via MSC • • Hand-off: • • BTS BTS (same BSC) • • BSC BSC (same MSC) • • MSC  MSC • • Location information: • • mobile is tracked • • location registers kept • updated BSC base-station controller BTS base-transceiver station HLR home location register MSC mobile switching centre VLR visitor location register OMC Operation and maintenance systems MS Mobile station

18. GSM cell types • Hot spots: • • cell-within-a-cell • • Macro-cells: • • large, sparsely populated areas • • Micro-cells: • • densely populated areas. By splitting the existing areas into smaller cells, the number of channels available is increased as well as the capacity of the cells. The power level of the transmitters used in these cells is then decreased, reducing the possibility of interference between neighbouring cells. • • Selective cells: • • not-360° coverage • • special antenna give “shape” . e.g.Cells that may be located at the entrances of tunnels where a selective cell with a coverage of 120 degrees is used. • • Umbrella cells: • •covers several micro-cells • • used for “high-speed” MS • Umbrella cell fast-moving MS, many-hand-offs e.g. car, train, etc Umbrella cell

19. Power Management • Silence suppression • • DTX (Discontinuous transmission a • method of momentarily powering-down) • • No “speech” for ~40% of • call duration: • • perhaps more for data • • Background noise at MS: • • not easy to detect … • • detect “no speech” • • Switch off transmission: • • when “no speech”detected • • saves power • • Receiver: • • comfort noise • Hand-off • • Quality vs. power • • Maintain quality: • • mobile increases transmit • power • • maintains quality • • hand-off when quality is low • • Conserve power: • • set transmit power threshold • • hand-off when threshold • reached

20. Security • Network • • EIR: • • stores known IMEI numbers • • AuC: • • uses IMSI and IMEI (plus • interaction with EIR) • • authenticates user • • checks service subscription • • (updates VLR and other • location information) Terminal • SIM: • subscriber identity module • IMSI: • subscriber identity (on SIM) • IMEI: • MS identity (in MS) • Stream cipher used: • key+algorithm from SIM • random number XOR’d with data/voice bits

21. Security in GSM • Security services • access control/authentication • user  SIM (Subscriber Identity Module): secret PIN (personal identification number) • Security services • access control/authentication • user  SIM (Subscriber Identity Module): secret PIN (personal identification number) • SIM  network: challenge response method one party presents a question ("challenge") and another party must provide a valid answer ("response") to be authenticated. • 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 (standardised) • A8 for key generation (“secret”, open interface) • “between you and I”: • A3 and A8 available via the Internet • network providers can use stronger mechanisms

22. SIM mobile network RAND Ki RAND RAND Ki 128 bit 128 bit 128 bit 128 bit AC A3 A3 SIM SRES* 32 bit SRES 32 bit SRES SRES* =? SRES MSC SRES 32 bit Ki: individual subscriber authentication key SRES: signed response GSM - authentication

23. MS with SIM mobile network (BTS) RAND Ki RAND RAND Ki AC SIM 128 bit 128 bit 128 bit 128 bit A8 A8 cipher key Kc 64 bit Kc 64 bit SRES data encrypteddata data BSS MS A5 A5 GSM - key generation and encryption

24. Beyond 2G systems: GPRS I • General Packet Radio Service (GPRS) • • Packet radio service: • • “always on” • • shared media access • Point-to-point (PTP) service: internetworking with the Internet (IP protocols) and X.25 networks. • Point-to-multipoint (PT2MP) service: point-to-multipoint multicast and point-to-multipoint group calls • Uses existing GSM infrastructure: • • requires some changes to • support new signalling • • Same RF spectrum as GSM • • multiple bursts per user • • one frame could carry voice • and data • • On demand allocation: • • user signals network for • channel/burst(s) allocation • • Requires new terminal: • • mobile phones may need to be • upgraded or replaced (done)

25. GPRS II • • Better network utilisation • • Good for general data: • • suits bursty applications • • GPRS + IP integration: • • How to charge? • • volume – per packet? • • flat rate? • • QoS: • • may not be suitable for real-time • applications • • “real-time extensions” in 3G

26. EDGE • Requires new RF spectrum: • • 2x50MHz • • 1.9GHz and 2.1GHz bands • being used in some parts of the world Enhanced Data-rates for Global Evolution: • builds on GPRS mechanism • packet interface • Available now in North America and some parts of Europe • “Peak rates” of 384Kb/s: • “pedestrian” rate • “Normal rate” of 144Kb/s: • “high mobility” rate High-Speed Packet Access (HSPA). Peak bit-rates of up to 1Mbit/s and typical bit-rates of 400kbit/s can be expected.

27. UMTS: universal mobile telecommunications services • 3G –• Voice: • • 2G GSM-like services • • Data: • • 64Kb/s – ~2Mb/s • • ISDN-like services • • WCDMA(Wideband Code Division Multiple Access) 10Mb/s • • Packet and circuit services • • International roaming • Needs new RF spectrum! • W-CDMA a pair of 5MHz frequency band, • for the uplink, 19000 MHz range, for the downlink, 2100 MHz range. • • Requires new or upgraded • infrastructure • • Potential for broadband wireless services • Since 2006, UMTS networks in many countries have been or are in the process of being upgraded with High Speed Downlink Packet Access (HSDPA), sometimes known as 3.5G. Up to 21 Mbit/s.

28. IMT-2000 • ITU’s approach to 3G wireless • • “Umbrella” activity from ITU: • • mainly European interest, though international in theory • • Intended to provide: • • coordination between different 2.5/3G systems • • harmonisation of services to allow use efficient of • Spectrum • • http://www.umts-forum.org/imt2000.html IMT: international Mobile Communications

29. Simplified Roadmap – one to another 2.5G 3G (IMT-2000) 2G GSM only (+SMS) EDGE UMTS GSM GSM + GPRS GSM only (+SMS)

30. Development of mobile telecommunication systems CT0/1 FDMA AMPS CT2 NMT IMT-FT DECT IS-136 TDMA D-AMPS EDGE IMT-SC IS-136HS UWC-136 TDMA GSM GPRS PDC IMT-DS UTRAFDD / W-CDMA IMT-TC UTRATDD / TD-CDMA IMT-TC TD-SCDMA CDMA IS-95 cdmaOne IMT-MC cdma20001XEV-DO cdma2000 1X 1XEV-DV (3X) 2G 3G 1G 2.5G

31. GLOBAL EVOLUTION TO 3G MULTIRADIO NETWORKS GSM PDC GSM/GPRS TDMA cdmaOne cdma2000 1x cdma2000 1xEV-DV cdma2000 1xEV-DO UMTS Multiradio Network GSM/GPRS/EDGE WCDMA(Wideband Code Division Multiple Access) Internet, multimedia, video and other capacity-demanding applications. ? 2G First Steps to 3G 3G Phase 1 Evolved 3G Networks

32. Performance characteristics of GSM (wrt. analog sys.) Communication • mobile, wireless communication; support for voice and data services Total mobility • international access, chip-card enables use of access points of different providers Worldwide connectivity • one number, the network handles localization High capacity • better frequency efficiency, smaller cells, more customers per cell High transmission quality • high audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g., from cars, trains) Security functions • access control, authentication via chip-card and PIN

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

34. GSM and 3G – more information can be found at ... • http://www.gsmworld.com/ • • http://www.umts-forum.org/ • • http://www.uwcc.org/ • Universal Wireless Communications Consortium • • http://www.3gpp.org/ • Third Generation Partnership Project • • Not covered in these notes, however, … • http://www.wapforum.org/ • Wireless Application Protocol Forum

35. Satellite systems • LEO and MEO: • • satellite constellations • • no terrestrial network • support • • “total” area coverage • • Very expensive: • • to construct and maintain • to use • • Complex: • • hand-off between satellites • • routing • Service providers finding • it hard to break into the market • • Safety concerns: • • MS power output • • Voice only systems • • Voice and data systems • • Broadband systems • • Will they succeed?

36. 4G Systems • Totally packet-based: • • IPv6 • • Higher data rates: • • up to 100Mb/s • • Better security • • Totally digital

37. Inter Satellite Link (ISL) Mobile User Link (MUL) MUL Gateway Link (GWL) GWL small cells (spotbeams) base station or gateway footprint GSM ISDN PSTN User data PSTN: Public Switched Telephone Network Classical satellite systems

38. Orbits I Four different types of satellite orbits can be identified depending on the shape and diameter of the orbit: • GEO: geostationary orbit, ca. 36000 km above earth surface • LEO (Low Earth Orbit): ca. 500 - 1500 km • MEO (Medium Earth Orbit) or ICO (Intermediate Circular Orbit): ca. 6000 - 20000 km • HEO (Highly Elliptical Orbit) elliptical orbits

39. Geostationary satellites Orbit 35,786 km distance to earth surface, orbit in equatorial plane (inclination 0°)  complete rotation exactly one day, satellite is synchronous to earth rotation • fix antenna positions, no adjusting necessary • satellites typically have a large footprint (up to 34% of earth surface!), therefore difficult to reuse frequencies • bad elevations in areas with latitude above 60° due to fixed position above the equator • high transmit power needed • high latency due to long distance (ca. 275 ms)  not useful for global coverage for small mobile phones and data transmission, typically used for radio and TV transmission

40. LEO systems Orbit ca. 500 - 1500 km above earth surface • visibility of a satellite ca. 10 - 40 minutes • global radio coverage possible • latency comparable with terrestrial long distance connections, ca. 5 - 10 ms • smaller footprints, better frequency reuse • but now handover necessary from one satellite to another • many satellites necessary for global coverage • more complex systems due to moving satellites Examples: Iridium (start 1998, 66 satellites) • Bankruptcy in 2000, deal with US DoD (free use, saving from “deorbiting”) Globalstar (start 1999, 48 satellites) • Not many customers (2001: 44000), low stand-by times for mobiles

41. MEO systems Orbit ca. 5000 - 12000 km above earth surface comparison with LEO systems: • slower moving satellites • less satellites needed • simpler system design • for many connections no hand-over needed • higher latency, ca. 70 - 80 ms • higher sending power needed • special antennas for small footprints needed Example: ICO (Intermediate Circular Orbit, Inmarsat) start ca. 2000 • Bankruptcy, planned joint ventures with Teledesic, Ellipso – cancelled again

42. Routing (Passing Information Between satellites) • One solution: inter satellite links (ISL) • reduced number of gateways needed • forward connections or data packets within the satellite network as long as possible • only one uplink and one downlink per direction needed for the connection of two mobile phones • Problems: • more complex focusing of antennas between satellites • high system complexity due to moving routers • higher fuel consumption thus shorter lifetime • Iridium and Teledesic planned with ISL • Other systems use gateways and additionally terrestrial networks

43. Localisation of Mobile Stations • Mechanisms similar to GSM • Gateways maintain registers with user data • HLR (Home Location Register): static user data • VLR (Visitor Location Register): (last known) location of the mobile station • SUMR (Satellite User Mapping Register): • satellite assigned to a mobile station • positions of all satellites • Registration of mobile stations • Localisation of the mobile station via the satellite’s position • requesting user data from HLR • updating VLR and SUMR • Calling a mobile station • localization using HLR/VLR similar to GSM • connection setup using the appropriate satellite

44. Handover in Satellite Systems • Several additional situations for handover in satellite systems compared to cellular terrestrial mobile phone networks caused by the movement of the satellites • Intra satellite handover • handover from one spot beam to another • Spot beams are used so that only earth stations in a particular intended reception area can properly receive the satellite signal. • mobile station still in the footprint of the satellite, but in another cell • Inter satellite handover • handover from one satellite to another satellite • mobile station leaves the footprint of one satellite • Gateway handover • Handover from one gateway to another • mobile station still in the footprint of a satellite, but gateway leaves the footprint • Inter system handover (VERTICAL?) • Handover from the satellite network to a terrestrial cellular network • mobile station can reach a terrestrial network again which might be cheaper, has a lower latency etc.

45. Bluetooth: “Personal Area” wireless connectivity • Universal radio interface for ad-hoc wireless connectivity • Interconnecting computer and peripherals, handheld devices, PDAs, cell phones – replacement of IrDA • Embedded in other devices, goal: £5/device (2002: £50/USB bluetooth), (Mini Bluetooth Network adapter USB £6) • Short range (10m), low power consumption, license-free 2.45 GHz ISM • Voice and data transmission, approx. 1 Mbit/s gross data rate • Bluetooth 2.0 Enhanced Data Rate (EDR) 2.1 Mbit/s

46. Inter-device connections Scenario 1: • PDA, mobile phone, laptop • PDA  mobile phone: 1 cable • PDA laptop: another (different) cable • mobile phone laptop: yet another (different) cable Scenario 2: • desktop computer, PDA, laptop all need to use printer • again, more cables, hard to configure • standard wireless inter-device communication?

47. Bluetooth: The Rational • Standard, convenient device inter-connectivity • • Mobile phones, headsets, PDAs, laptops: • • coffee machines, utility meters, hi-fi equipment, etc. • • Simple, low-cost, radio-based system: • • simple, “wire-replacement” system, re-use existing • standards • • aiming for cost of ~£5 to build into a device • • uses ISM radio band (2.4000-2.4835GHz) • • http://www.bluetooth.com/ • • Named after a Viking called Harald Bluetooth

48. Bluetooth: Characteristics • 2.4 GHz ISM band, 79 (23) RF channels, 1 MHz carrier spacing • Channel 0: 2402 MHz … channel 78: 2480 MHz • G-FSK modulation, 1-100 mW transmit power • FHSS and TDD • Frequency hopping with 1600 hops/s • Hopping sequence in a pseudo random fashion, determined by a master • Time division duplex for send/receive separation • Voice link – SCO (Synchronous Connection Oriented) • FEC (forward error correction), no retransmission, 64 kbit/s duplex, point-to-point, circuit switched • Data link – ACL (Asynchronous Connectionless) • Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/s symmetric or 723.2/57.6 kbit/s asymmetric, packet switched • Topology - Overlapping piconets (stars) forming a scatternet

49. Bluetooth Architecture: An overview • Two link types: • • synchronous, connection oriented (SCO) • • asynchronous, connection-less (ACL) • • Bi-directional link (symmetric and asymmetric data rates) • • Can use existing protocols, e.g. IP • • Several profiles defined: • • e.g. dial-up networking, headset, fax, LAN access • • Products now becoming available in all almost all new mobile phones and some laptops

50. Bluetooth: Basic Components • Four basic components to architecture: • 1. RF component: for receiving and transmitting • 2. Link control: for processing information to/from RF component • 3. Link management: manages transmission process • (media access) • 4. Supporting applications: uses other three • components through a well-defined interface