New Standards for Wireless LANs

Transcription

1 New Standards for Wireless LANs Summer Term 2014 Dr.-Ing. Andreas Könsgen Dr.-Ing. Koojana Kuladinithi Communication Networks TZI University of Bremen

2 Organisational Issues How to reach us? Andreas Könsgen Room S2310 Tel: Koojana Kuladinithi Room N2240 Tel:

3 Organisational Issues Exam: Oral Exam (30min) after the end of the term Questions, Critics etc.: always welcome Exercises: After the lecture, N 1250, 12:00 to 12:45 deepen understanding, open discussion, some labs/demos/simulation Slides available on under Education Lectures & Tutorials New Standards for Wireless LANs -3-

4 Acknowledgement This lecture is based on material by Prof. Dr.-Ing. Andreas Timm-Giel Institute of Communication Networks Technical University of Hamburg-Harburg Germany -4-

5 Objective of the Lecture Understand wireless technologies: how do they work? Give an overview on existing and emerging wireless standards Give an idea what is coming up in the future in Wireless Communications -5-

6 Course Overview (1) Overview: History of Wireless Communication Mobile and Wireless Communications Basics radio propagation modulation and coding multiple access, duplex schemes, access protocols IEEE (Wireless LAN) Overview a, b, g, h... Physical Layer MAC Layer Security -6-

7 Course Overview (2) IEEE Wireless Regional Area Network (WRAN) IEEE Wireless Personal Area Network (WPAN): Bluetooth and Zigbee Sensor Networks (Dr. Koojana Kuladinithi) -7-

8 Literature Jochen Schiller: Mobile Communications, Pearson/Addison-Wesley, 2003 James F. Kurose, Keith W. Ross, Computer Networking A top-down Approach, 4th Edition, 2008, Pearson International Edition Matthew Gast: Wireless Networks, O'Reilly, 2005 Bernhard H. Walke Mobile Radio Networks, J. Wiley & Sons, 1999 Brent Miller, Chatschik Bisdikian: Bluetooth Revealed, Prentice Hall 2001 Holger Karl, Andreas Willig, Protocols and Architectures for Wireless Sensor Networks, John Wiley and Sons, 2007 Zach Shelby, Carsten Bormann, 6LoWPAN: The Wireless Embedded Internet, John Wiley and Sons, 2009 IEEE Standardisation documents (link on website) -8-

9 Chapter 1: First Mobile and Wireless Communication Systems

10 Definition of Wireless and Mobile Wireless Communication without wires, can be mobile and fixed Mobile Portable devices (laptops, notebooks etc.) connected at different location to wired networks (e.g. LAN or PSTN) Portable devices (phones, notebooks, PDAs etc.) connected to wireless networks (UMTS, GSM, WLAN.)

11 Early History of Wireless Communications In history first light and sound have been used to transmit messages over wide distances - 11 Pics from

12 Transmission of Electromagnetic Waves 1831: Faraday demonstrates magnetic induction 1865: Maxwell theory of electromagnetic fields, wave equation 1876 Patent on phone, Alexander Graham Bell (Antonio Meucci 1849) 1888: H. Hertz: demonstrates the wave character of electrical transmission through space Nikola Tesla extends the transmission range Pics from

13 History of Wireless Communication 1895 Guglielmo Marconi first demonstration of wireless telegraphy (digital!) 1901 transatlantic transmission long wave transmission, high transmission power necessary (> 200kW) 1907 Commercial transatlantic connections Photo from huge base stations (30 100m high antennas) 1915 Wireless voice transmission New York San Francisco 1920 Discovery of short waves by Marconi reflection at the ionosphere smaller sender and receiver, possible due to the invention of the vacuum tube (1906, Lee DeForest and Robert von Lieben)

14 Beginning of Mobile Communications 1911 mobile transmitter on Zeppelin 1926 train (Hamburg Berlin) 1927 first commercial car radio (receive only) First Mobile Communication Systems started in the 40s in the US and in the 50s in Europe. CONCEPTS: Large Areas per Transmitter Mobiles large, high power consumption Systems low capacity, interference-prone Expensive!!!

15 Today's Wireless Communication (1) 1984 CT-1 standard (Europe) for cordless telephones In Germany selling no longer permitted since DECT Digital European Cordless Telephone (today: Digital Enhanced Cordless Telecommunications) MHz, ~ m range, 120 duplex channels, 1.2Mbit/s data transmission, voice encryption, authentication, up to several user/km2, used in more than 50 countries 1996 HiperLAN (High Performance Radio Local Area Network) ETSI, standardization of type 1: GHz, 23.5Mbit/s recommendations for type 2 and 3 (both 5GHz) and 4 (17GHz) as wireless ATM-networks (up to 155Mbit/s) Did not enter market

16 Today's Wireless Communications (2) In the 1990s: many proprietary products for wireless networks 1997 Wireless LAN IEEE standard GHz and infrared, 2Mbit/s 1999 IEEE b, 2.4 GHz, 11Mbit/s 1999 IEEE a, 5 GHz, 54 Mbit/s 1999/2001 Bluetooth/IEEE for piconets, 2.4 GHz, < 1Mbit/s 2003 IEEE g, 2.4 GHz, 54 Mbit/s 2003/2004 Zigbee/IEEE for sensor networks 2009 IEEE n, 2.4 and 5 GHz, 600 Mbit/s 2012 IEEE ad, 60 GHz, 7 Gbit/s

17 Chapter 2 Mobile Communications Definitions & Basics

18 Chapter 2 - Overview Part 1 (today) Digital Transmission System Frequencies, Spectrum Allocation Radio Propagation and Radio Channels Part 2 (next week) Modulation, Coding, Error Correction Part 3 (in 2 weeks) Capacity limits Duplexing schemes Media Access Protocols

19 Acknowledgement Pictures and some slides of this chapter are taken from: B. Walke, P. Seidenberg, M. P. Althof, UMTS: the fundamentals, Wiley Schiller: Mobilkommunikation (Mobile Communications), Pearson Studium/Addison Wesley, 2003/2002 David/Benkner: Digitale Mobilfunksysteme, Teubner 1996 Proakis/Saleh, Grundlagen der Kommunikationstechnik, Pearson Studium

20 Simple Reference Model Application Application Transport Transport Network Network Network Network Data Link Data Link Data Link Data Link Physical Physical Physical Physical Radio Wired Medium

21 More Detailed Reference Model Application layer Transport layer Network layer Data link layer Physical layer Web, mail service location multimedia adaptive applications congestion and flow control quality of service addressing, routing, device location hand-over media access multiplexing media access control modulation interference cancellation compensation of fading frequency channel selection

22 More Detailed Reference Model Application layer Transport layer Network layer Data link layer Physical layer Web, mail service location multimedia here adaptive applications congestion and flow control quality of service addressing, routing, device location hand-over media access multiplexing media access control here in the framework of this lecture here modulation interference cancellation compensation of fading frequency channel selection Authentication and encryption

23 Structure of Digital Transmission System Digital Source Sink

24 Structure of Digital Transmission System Digital Source Sink

25 Frequencies for Communication twisted pair 1000 km 300 Hz VLF coax cable 10 km 30 khz LF optical transmission 100 m 3 MHz MF HF 1m 300 MHz 10 mm 30 GHz VHF SHF UHF VLF = Very Low Frequency LF = Low Frequency MF = Medium Frequency HF = High Frequency VHF = Very High Frequency EHF 100 μm 3 THz infrared 1 μm 300 THz visible light UV UHF = Ultra High Frequency SHF = Super High Frequency EHF = Extra High Frequency UV = Ultraviolet Light Frequency and wave length: λ = c /f With wave length λ, speed of light c m/s, frequency f

26 Frequencies for Mobile Communication 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, focusing large bandwidth available Wireless LANs use frequencies in UHF to SHF spectrum 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

27 Frequency Regulations Frequency assignments are managed by the International Telecommunication Union Radiocommuncation Sector (ITU-R) holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences) National regulation authorities Germany: Bundesnetzagentur (Federal Network Agency) USA: Federal Communications Commission (FCC)

28 Important Frequency Assignments Cellular Phones Cordless Phones Wireless LANs Others Europe USA Japan GSM , / ,489496, /935960, / UMTS (FDD) , UMTS (TDD) , CT , CT DECT IEEE HIPERLAN , RF-Control 27, 128, 418, 433, 868 AMPS, TDMA, CDMA , TDMA, CDMA, GSM , PDC , , , PACS , PACS-UB PHS JCT IEEE , IEEE RF-Control 315, 915 RF-Control 426,

29 ISM Bands: General facts Industrial, scientific, and medical (ISM) radio bands originally reserved internationally by ITU-R for non-commercial use of RF electromagnetic fields for industrial, scientific and medical purposes Individual countries' use may differ due to variations in national radio regulations In recent years permission for license-free short-range communication applications such as walkie-talkies, remote controls, Wireless LANs, Bluetooth Source: ITU, FCC

30 ISM Bands: Assignments Some typical ISM bands Frequency Comment MHz MHz MHz MHz Europe MHz America GHz WLAN/WPAN GHz WLAN GHz

31 Signal Propagation Propagation in free space always like light (straight line) Receiving power in free space proportional to 1/d² (d = distance between sender and receiver) Sources of distortion Reflection/refraction bounce of a surface; enter material Scattering multiple reflections at rough surfaces Diffraction start new wave from a sharp edge Doppler fading shift in frequencies (loss of center) Attenuation energy is distributed to larger areas with increasing distance reflection refraction scattering diffraction

32 Signal Propagation Propagation in free space always like light (straight line) Receiving power in free space proportional to 1/d² (d = distance between sender and receiver) Sources of distortion Reflection/refraction bounce of a surface; enter material Scattering multiple reflections at rough surfaces Diffraction start new wave from a sharp edge Doppler fading shift in frequencies (loss of center) Attenuation energy is distributed to larger areas with increasing distance reflection refraction scattering diffraction

33 Attenuation results in path loss Effect of attenuation: received signal strength is a function of the distance d between sender and transmitter Captured by Frii's free-space equation Describes signal strength at distance d relative to some reference distance d0 < d for which strength is known d0 is far-field distance, depends on antenna technology

34 Pathloss in Free Space Received power depends on frequency, transmitted power, antenna gains, distance and constants only 2 λ PR = PT GT GR 4πd PT / R : transmitted / received Power GT / R : Antenna Gain Transmitter/Receiver λ: d: f: PR LF (db) = 10 log PT Wavelength [m] Distance [m] Frequency [Hz] LF (db) = 10 log GT + 10 log GR 20 log f 20 log d EIRP: effective isotropic radiated power: EIRP = PTGT

35 Attenuation of different frequencies Attenuation depends on the used frequency Attenuation strong rain fog / clouds Can result in a frequency-selective channel If bandwidth spans frequency ranges with different attenuation properties molecular dispersion moderate rain frequency

36 Attenuation in Atmosphere vapor Atmospheric attenuation (db/km) 10 David Benkner: Digitale Mobilfunksysteme oxygen f (GHz) - 36

37 Multipath Propagation Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction multipath LOS pulses pulses signal at sender signal at receiver Time dispersion: signal is dispersed over time interference with neighbor symbols, Inter Symbol Interference (ISI) The signal reaches a receiver directly and phase shifted distorted signal depending on the phases of the different parts

38 Multipath Propagation Channel characteristics change over time and location signal paths change different delay variations of different signal parts different phases of signal parts quick changes in the power received (short term/fast fading) power Additional changes in distance to sender obstacles further away slow changes in the average power received (long term/slow fading) All fading effects are frequency-dependent long term fading t short term fading

39 Radio Channel Characteristics Superposition of numerous direct and reflected multipath components with different attenuation and phasing time variant Differentiation of fast and slow fading A B Fast fading due to superposition of different phases Slow fading is due to the change of propagation environment Both fading types depend on the frequency

40 Real World Example: Propagation

41 Real World Example: Time variation Signal amplitude Carrier frequency: 5.2 GHz Channel bandwidth: 40 MHz 5.18 Frequency (GHz) time (s)

42 Walfish-Ikegami UMTS Mostly shown in db (attenuation) Okumura-Hata 40 Pathloss [db] Received power of a sender is decreasing with the distance between sender and receiver Depends on Frequency Many models, e.g. 160 Real World Example: Path Loss Distance [m] UMTS Vehicular From Walke: UMTS - the fundamentals

43 Noise and Interference So far: only a single transmitter assumed Only disturbance: self-interference of a signal with multi-path copies of itself In reality, two further disturbances Noise due to effects in receiver electronics, depends on temperature Typical model: an additive Gaussian variable, mean 0, no correlation in time Interference from third parties Co-channel interference: another sender uses the same spectrum Adjacent-channel interference: another sender uses some other part of the radio spectrum, but receiver filters are not good enough to fully suppress it Effect: Received signal is distorted by channel, corrupted by noise and interference

44 Channel models Simplest model: assume transmission power and attenuation are constant, noise an uncorrelated Gaussian variable Additive White Gaussian Noise model Situation with no line-of-sight path, but many indirect paths: Amplitude of resulting signal has a Rayleigh distribution (Rayleigh fading) One dominant line-of-sight plus many indirect paths: Signal has a Rice distribution (Rice fading) Raytracing model Given location of transmitters, receivers, obstacles Calculate current SINR for each transmission path