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Telecoms Systems (Week 1)

Telecoms Systems (Week 1). Prof. Laurie Cuthbert Dr. Michael Chai Dr Frank Gao. Staff. Prof Laurie Cuthbert – weeks 1 and 4 l aurie.cuthbert@eecs.qmul.ac.uk Dr Michael Chai – week 3 michael.chai@eecs.qmul.ac.uk Dr Frank Gao – week 2 frank.gao@eecs.qmul.ac.uk. Changes since last year.

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Telecoms Systems (Week 1)

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  1. Telecoms Systems (Week 1) Prof. Laurie Cuthbert Dr. Michael Chai Dr Frank Gao

  2. Staff Prof Laurie Cuthbert – weeks 1 and 4 laurie.cuthbert@eecs.qmul.ac.uk Dr Michael Chai – week 3 michael.chai@eecs.qmul.ac.uk Dr Frank Gao – week 2 frank.gao@eecs.qmul.ac.uk

  3. Changes since last year • Content has not changed • Exam format different – now 4 compulsory questions in 2 hours: • One on each week’s material • Remember: • QM rules on extenuating circumstances apply

  4. Assessment • Exam: 88% • Class tests: 12% • Class test every week of teaching on Friday • Each group split into 2 • You must be in the right group • Test is a question on anything taught that week • Roughly half an exam question • Each test counts 3% • Open book

  5. Emphasis on • Why • How • When you come to the lecture, bring: • Pen • Paper • Lecture notes • Calculator • You will have to do problems in the class!!

  6. Learning Outcomes • Explain the principles of operation and architectures of circuit-switched and packet/cell-switched network; wired and mobile. • Describe the operation of transmission and switching systems. • Calculate simple numerical problems on aspects of source coding, error-control coding, Queuing Theory and Information Theory.

  7. Extenuating circumstances • Must be for 'unplanned circumstances that outside of your control • These include medical and personal circumstances such as close family being ill, but not events such as: • planned holidays, • job interviews or internships • GRE or IELTS preparation or test • misreading timetables, • computer problems, • not being aware of rules or procedures. • Medical conditions must be sufficiently serious that they would have a major affect on your examination.

  8. QM rules • ECs for all QM modules will be treated under QM rules • If you want to claim EC for an exam or class test you must: • Complete a form in English (from Jing Liu) • Add supporting evidence (e.g. medical certificate) • Give everything back to Jing Liu at least 1 week before the examination board • Your BUPT tutor does NOT have the authority to approve ECs for QM modules

  9. modern telecommunications

  10. Telecommunication system – a system for conveying content • For example, the UK Telecommunications Act 1984, s.4(1) defines it as: “a system for the conveyance through the agency of electric, magnetic, electromagnetic, electro-chemical or electro-mechanical energy, of (a) speech, music or other sounds; (b) visual images; (c) signals serving the impartation (whether as between persons and persons, things and things or persons and things) of any matter otherwise than in the form of sounds or visual images; or (d) signals serving for the actuation or control of machinery or apparatus”.

  11. “More communications than we know how to use” • Many different technologies • Developed in parallel • Lead time to introduce new services decreasing • “Reliability” of software decreasing • Online patches for mobile phones • Remote working is now normal

  12. Legacy - wired communications using telephony fax analogue digital Analogue Dial-up modem Obsolete !!!! exchange Digital

  13. Mobile communications Tablet often a radio link to network WLAN 3G/HSDPA WLAN 2G/3G/HSDPA/LTE Cable / radio (Bluetooth)

  14. Dual cordless phone that connects to a normal phone line and the computer IP allows competition with telephony Webcam Headset SIP phone All telephony is going IP

  15. Now telephony is SIP based

  16. Transport modes • Traditionally telephony was circuit switched: • Call set up, conversation and clear-down phases • 64 kbit/s (in digital era) allocated in both directions • Much of the capacity wasted • Analogue to digital conversion in local exchange • Control very much centralised • Now IP-based • SIP sets up and clears down connections • Transport RTP • A-D conversion in the telephone • More distributed

  17. Traditional network hierarchy Local Exchange Local Exchange Core networkDigital Access networkAnalogue Trunk Exchange Trunk Exchange

  18. Transmission • Connections are carrying little traffic are served with low capacity links • Up to 120Mbps in UK for broadband • Very high speed optical fibre links between major cites • In excess of 500 Mbps and support over 7000 voice calls

  19. Switching used to be manual

  20. Then relays, then electronic – but specialised Electromechanical exchange picture courtesy of Nortel 1960s Private electronic exchange 1983

  21. Now just boxes of electronics – high volume IP router WLAN AP Servers All of these are just “boxes” of Electronics IP switch IP phone

  22. Wireless (GSM) network architecture PSTN Gateway MSC Mobile switching centre Base station controller BTS BTS=Base transceiver station BS

  23. History of wireless communications • 1865 James Clerk Maxwell published his equations • 1887 Heinrich Hertz demonstrated EM wave propagation • 1893 Nicola Tesla demonstrated communication by radio • 1895 Aleksandr Popov demonstrated a wireless system • 1896 Guglielmo Marconi demonstrated wireless telegraphy • 1901 First wireless signal sent across the Atlantic Ocean from Cornwall to St. John’s, Newfoundland (Canada) • Marconi was not the ‘inventor’, but appreciated the commercial opportunities offered by the new medium.

  24. Why wireless? • No more cables • No cost for installing wires or rewiring • Wiring is infeasible or costly in some areas, e.g.. rural areas, old buildings… • Mobility and convenience • Allows users to access services while moving: walking, in vehicles… • Flexibility • Roaming allows connection any where and any time • Scalability • Easier to expand network coverage compared to wired networks.

  25. Challenges of wireless • Limited resources: finite radio spectrum • Frequency reuse, breaking cells into smaller cells, more efficient medium access technology, e.g. CDMA… • Supporting mobility - Location management, handover, … • Maintaining Quality of Service (QoS) over unreliable wireless links • Radio propagation attenuation: path loss, shadowing, multipath fading. • Connectivity and coverage - roaming and internetworking • Security • Wireless channels are “open” • Certification and authentication • Integrated services (voice, data, multimedia, etc.) over a single network • service differentiation, priorities, resource sharing,... • Mobile terminal battery life • You will learn more about all of this later

  26. Mobile Wireless: 2G: GSM, TDMA, CDMA 2.5G EDGE, GPRS 3G W-CDMA, HSDPA, HSUPA 4G - LTE Fixed Wireless: MMDS, LMDS, Satellite dish, Microwave Wireless LAN: IEEE 802.11, Ad-hoc, Bluetooth, WiMax Wireless LAN Point-Point/ Multipoint Wireless Mobile cellular Satellite wireless Emerging and existing wireless technology

  27. Types of wireless network • WPAN (Wireless Personal Area Network) • typically operates within about 30 feet • WLAN (Wireless Local Area Network) • operates within 300 yards • WMAN (Wireless Metropolitan Area Network ) • operates within tens of miles • WWAN (Wireless Wide Area Network ) • operates over a large geographical area, mobile phone, …

  28. Features of mobile communications • Mobile phones are portable, convenient, move with people. • By their nature, they are location aware. • Limited frequency bandwidth • Low power: max mobile transmit power • 125mW for WCDMA • 2W peak for GSM900 • 1W for GSM1800/1900 • Point to multi-point, not broadcast

  29. Cellular concept • Late 40s: AT&T developed cellular concept for frequency re-use • Break the service area into cells • Shrink the cell size; adopt intensive frequency re-use • Add more cells to add more capacity • Mobility management is required

  30. Evolution of mobile networks “It is dangerous to put limits on wireless” Guglielmo Marconi in 1932……. 1G 2G 2.5 G 3G 1970’s Proposed late 1980’s GSM launched in 1992 1990’s –present Proposed in 1998 Launched in UK 2003

  31. W-CDMA (3GSM) TD-SCDMA cdma2000 GPRS HSCSD EDGE IS-95B GSM IS-136 IS-95 PDC NTT TACS NMT AMPS 4G ? 3G 2.5G 2G 1G • Higher bit rate ? • New applications ? • Speech & low rate data service • Digital transmission • Speech, data, multimedia services • Bit rate up to 2 Mbit/s • Digital transmission • Speech service • Analogue transmission Evolution of mobile networks

  32. Analogue Speech Some data at 1.2kbit/s Designed for car use First handportable – Motorola “Brick” (DynaTAC 8000X ) 1983 800g 30 mins talk time USD 3995 Insecure Eavesdropping Cloning Almost no roaming 1G systems

  33. Some 1G systems • No real roaming apart from NMT

  34. 2G Systems • Speech and low bit rate data service • Digital transmission • Designed to be more secure • Almost exclusively handportable

  35. 2G Systems

  36. GSM • Officially launched in 1992 • Multiple access: TDMA 8 channels (frames of 8 time slots) on each carrier • FDD (Frequency Division Duplex) – different frequencies for uplink and downlink • 200kHz carrier bandwidth • 9.6kb/s net data (13kb/s encoded voice) • (Almost) worldwide availability with multi-band handset • Useful link www.gsmworld.com

  37. GSM worldwide success • Over 860 networks in 220 countries/areas • Still growing: No of GSM + 3 GSM subscribers • 11/9/2011 00.55 (CN time) 5,231,269,752 • In the next 5 mins an increase of: 7,106 !!!!! • World Population at same time: 6.914 billion • Penetration 59%

  38. GSM network architecture – core components AuC • BTS: Base Transceiver Station • BSC: Base Station Controller • BSS: Base Station Subsystem • MSC: Mobile Switching Centre • HLR: Home Location Register • VLR: Visitors Location Register • AuC: Authentication Centre • GMSC: Gateway MSC • PSTN: Public Switched Telephone Network PSTN HLR VLR MSC GMSC BSC BSC BTS MT BSS

  39. GSM network architecture – other elements • EIR: Equipment Identity Register • Record of status of phone • White / grey /black (stolen) • SMS-C: Short Message Service Centre • OMC: Operation and Maintenance Centre BS

  40. Locating a Mobile terminal When a MT moves from one location area to another: • MT initiates the location updating procedure. • HLR is notified by the new MSC/VLR. • HLR removes old MSC/VLR information • HLR confirms and updates the new MSC/VLR. • location area update is confirmed with the MT.

  41. PSTN Mobile Terminating call HLR Location area GMSC VLR BSC MSC MSC BTS BSC VLR traffic signalling

  42. PSTN Roaming incoming call Home network HLR Location area Visited network GMSC VLR VLR MSC BSC MSC MSC BTS BSC VLR BTS Roaming leg paid by recipient

  43. PSTN Roaming outgoing call Home network HLR Location area Visited network GMSC VLR VLR MSC BSC MSC MSC BTS BSC VLR Billing centre BTS

  44. GSM Mobility Management: Authentication Mobile Terminal Randomnumber Challenge: RAND Key Ks in SIM Key Ki in MSC A3 algorithm A3 algorithm SRESMSC If equal, then authenticated Response: SRESMT If results match, Ks=Ki and the user is genuine Only information transmitted over the air is RAND and SRESMT

  45. How does communications everywhere affect the global economy? • Increasingly reliant on communications technology for business • Variety of actors with competing interests • Communications systems becoming the target of cyber-terrorist attacks • Communications networks now part of the national large-scale critical infrastructure.

  46. Information Conversion

  47. Transmission of analogue information Multiplexing Demultiplexing Information: ‘Hello! How are you?’ You and I understand but not the telephone! Analogue signal can be understood by electrical systems but problematic! So all new systems digital

  48. Information Conversion • Different sources of information are presented with different formats at the input of transmitter. • Formatting transforms the source information to a compatible digital format for digital processing. • Four basic stages of information conversion

  49. Overview of Digital Communication System Format Source encode Encrypt Channel encode Multiplex Pulsemodulate Bandpassmodulate Freq.spread Multipleaccess Transmitter Receiver Format Source decode Decrypt Channel Decode Demultiplex PulseDetect Demodulate Freq.despread Multipleaccess

  50. Transmission side Format Source encode Encrypt Channel encode Multiplex Pulsemodulate Bandpassmodulate Freq.spread Multipleaccess Transmitter Transform the source information into bits, assuring compatibility between the information and the signal processing within the DCS. Digital Information Pulsemodulate Encoder Textual Information Sample Quantise Analogue Information

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