Introduction to Wireless Communication
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Introduction to basics of wireless networks such as • Radio waves & wireless signal encoding techniques • Wireless networking issues & constraints • Wireless internetworking devices
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Introduction to Wireless Communication
- 1. Introduction to Wireless Communication CS5440 Wireless Access Networks Dilum Bandara [email protected]
- 2. Outlines Elements of a wireless system Transmitter Frequency spectrum Modulation Antenna Medium Propagation Attenuation Receiver Antenna Demodulation Issues & constraints 2
- 3. Wireless Communication Transfer of data between 2+ points that aren’t connected by an electrical conductor Typically use electromagnetic waves Why wireless? Running cables not always possible Low footprint Rapid (re)configuration Low cost 3
- 4. Wireless History Ancient systems – Smoke Signals, Carrier Pigeons, etc. Radio invented in 1880s by Marconi Many sophisticated military radio systems developed during & after WW2 Exponential growth in Cellular systems since 1988 Ignited wireless revolution Voice, data, & multimedia ubiquitous 6.8 billion subscribers worldwide as of Feb. 2013 (source ITU) Use in 3rd-world countries growing rapidly 3.5 billion subscribers in Asia Pacific in 2013 Wi-Fi enjoying tremendous success & growth Wide area networks (e.g., WiMax) & short-range systems other than Bluetooth (e.g., UWB) less successful 4
- 5. 5
- 6. Future Wireless Networks Next-generation Cellular Wireless Internet Access Wireless Multimedia Sensor Networks Smart Homes/Spaces Automated Highways In-Body Networks IoT Ubiquitous communication among People & Devices Source: Andrea Goldsmith, “Cross Layer Design in Wireless Networks”, Stanford University 6
- 7. Wireless Services Telemetry control & traffic control systems Infrared & ultrasonic remote control devices Professional LMR (Land Mobile Radio) & SMR (Specialized Mobile Radio) Used by business, industrial & public safety entities Consumer 2-way radio Airband & radio navigation equipment Amateur Radio Service (Ham radio) Cellular telephones & pagers Global Positioning System (GPS) Cordless computer peripherals Cordless phones Satellite television 7 Source: www.access.kth.se
- 8. Medium Elements of a Wireless System 8 Transmitter Receiver 1 Receiver 2 Receiver n Source: www.mikroe.com/old/books/rrbook/chapter2/chapter2.htm
- 9. Transmitter Elements depend on transmission technology Frequency & wavelength, c = f λ Modulation Antenna 9 AM Transmitter
- 10. Exercise Wavelength of an electromagnetic wave travelling in space is 60 cm. What is its frequency? Assume speed of light is 3×108 m/s a) 500 MHz b) 3 GHz c) 5 GHz d) 15 GHz 10
- 11. Frequency Spectrum Range of available frequencies To avoid interference, various wireless technologies use distinct frequency bands Signal power is well controlled Assigned by regulatory agencies e.g., FCC, ITU, TRC 11 Source: www.cosmosportal.org
- 12. 12 Government license not required Industrial, Scientific, & Medical (ISM) band VLF – very low frequency LF – low frequency MF – medium frequency HF – high frequency VHF – very high frequency UHF – ultra-high frequency SHF – super-high frequency EHF – extremely high frequency Source: P. Zheng et al., Wireless Networking Complete
- 13. Key Frequency Bands AM – 520 - 1650.5 KHz FM – 87.5 - 108 MHz Direct broadcast satellite – 10.9 - 12.75 GHz Global System for Mobile (GSM) 890 - 960 MHz & 1710 - 1880 MHz Referred as 900 & 1800 bands Code Division Multiple Access (CDMA) 900 & 1800 bands 3G wideband CDMA (UMTS) 1900 - 1980, 2020 - 2025, & 2110 - 2190 MHz bands Wireless LAN (IEEE 802.11) 902 - 928 MHz, 2400 - 2483 MHz, 5.15 - 5.725 GHz ISM band – 2.4 GHz in US 13
- 14. Key Frequency Bands (Cont.) Bluetooth – 2.402 - 2.480 GHz in US WiMax – 2 - 11 GHz (includes both licensed & unlicensed) Ultra-wideband (UWB) – 1.1 - 10.6 GHz Radio-frequency IDentification (RFID) LF (120 – 140 KHz), HF (13.56 MHz), UHF (868 – 956 MHz), & Microwave (2.4 GHz) IrDA – 100 GHz Wireless sensors 300 - 1000 MHz & 2.4 GHz ISM band Global Positioning System (GPS) 1575.42 MHz (referred to as L1) & 1227.60 MHz (L2) 14
- 15. Antenna 15 Converts signal to electromagnetic waves Size must be consistent with wavelength Types Directional Satellite communication Omnidirectional Cell phones, car radios MIMO Wireless routers Source: www.flann.com
- 16. Antenna Gain How well an antenna converts input power into radio waves headed in a specified direction Depends on antenna's directivity & electrical efficiency Gain Ratio of power produced by antenna to power produced by a hypothetical lossless isotropic antenna Unitless Usually expressed in decibels (dB) Directional high gain Omnidirectional low gain 16
- 17. Attenuation Reduction in signal strength with distance, propagation medium, & atmospheric conditions Typically high for high frequencies Friis free-space equation PR, PT – Power at receiver (in Watts or Milliwatts) GT, GR – gain of antenna λ – wavelength (in meters) d – distance (in meters) 17 22 2 )4( =)( d GGP dP RTT R
- 18. Example Transmission frequency is 881.52 MHz & antenna gains are 8 dB & 0 dB for base station & mobile station What is the signal attenuation at a distance of 1,500 m? c = 299 792 458 m/s Solution c = f λ λ = 299 792 458/881.52×106 = 0.34 m 8 dB = 100.8 = 6.3 0 dB = 100 = 1 Loss = PT – PR Loss = 86.89 dB 18 8 9- 22 2 22 2 22 2 22 2 10×8788.4= )( 10×0497.2= )( 1500)4( 34.0×1×3.6 = )( 1500)4( 34.0×1×3.6 = )( )4( = )( )4( =)( dP P P dP P dP P dP d GG P dP d GGP dP R T T R T R T R RT T R RTT R
- 19. Attenuation (Cont.) Based on empirical evidence, more reasonable to model PR as a log-distance path-loss model np – path loss exponent Xσ – zero-mean Gaussian random variable with STD σ All power values are in dBm 19 )/log(10)()( 000 ddndPdP pR Source: S. Rao, “Estimating the ZigBee transmission-range ISM band,” EDN, May 2007.
- 20. Complex Attenuation When signal encounters obstacles High-frequency signals experience 1. Absorption 2. Shadowing When object >> λ 3. Reflection When object >> λ 4. Refraction 5. Diffraction 6. Scattering When object ≤ λ 20
- 21. Complex Attenuation (Cont.) 21 Source: http://computer-help- tips.blogspot.com/2011/04/radio-frequency- behaviors.html Absorption Source: http://elmag.org/en/propagation-modeling- of-shadowing-by-vegetation-for-mobile-satcom-%26- satnav-systems Shadowing
- 22. Complex Attenuation (Cont.) 22 Reflection Source: http://wireless.navigator.co.uk/radio_link.htm Refraction Source: http://computer-help- tips.blogspot.com/2011/04/radio-frequency- behaviors.html
- 23. Complex Attenuation (Cont.) 23Scattering Diffraction Source: http://newhorizons.bg/blog/2010/12/wireless- 101-terminology-part-2-implementing-cisco-unified- wireless-networking-essentials-iuwne/ Source: http://www.astrosurf.com/luxorion/qsl- propa.htm
- 24. Example – Attenuation Experienced by Mobile Phones 24 Source: www.intechopen.com/books/matlab-a-fundamental-tool-for-scientific-computing-and-engineering- applications-volume-2/mobile-radio-propagation-prediction-for-two-different-districts-in-mosul-city
- 25. Exercise Reflection of wireless signals occurs when a) wavelength is constant b) object size << wavelength c) object size ≈ wavelength d) object size >> wavelength 25
- 26. Noise Disturbances introduced to wireless signals 26Source: www.cisco.com/en/US/prod/collateral/video/ps8806/ps5684/ps2209/prod_white_paper0900aecd805738f5.html
- 27. Noise (Cont.) Sources Thermal (white) noise From electronic circuit PThermal = KTB K – Boltzmann constant, T - Ambient temperature, B - receiver BW Intermodulation noise When 2 frequencies of signals are transmitted over same medium 27 2 signals at 270 & 275 MHz Source: http://en.wikipedia.org/wiki/Inter modulation
- 28. Noise (Cont.) Crosstalk between channels Impulse noise Due to instantaneous electromagnetic changes 28 Source: http://volpefirm.com/impact-of- impulse-noise-on-adaptive-pre-equalization- part-ii/impulse-noise/ Source: www.chalmers.se/en/departments/s2/research/ Pages/Hardware-constrained-communication.aspx
- 29. Signal-to-Noise Ratio To cope with noise, transmitted signal > noise High Signal-to-Noise Ratio (SNR) Or use spread spectrum technology Embed signal over wide range of frequencies with low power 29
- 30. Example PT = 10 W, free space loss 117 dB, antenna gains 8 dB & 0 dB, total system losses 8 dB, receiver antenna temperature 290 K, & receiver bandwidth 1.25 MHz Find PR Find thermal noise, K = 1.38×10-23 W/Kelvin-Hz Find SNR at receiver Solution PR = -107 dBW PThermal = KTB = 1.38×10-23 × 290 × 1.25×106 = -143 dBW SNR = -107 + 143 = 36 dB 30
- 31. Multipath Propagation Receive same signal through different paths Different arrival times Inter Symbol Interference (ISI) Different levels of attenuation Different levels of distortion 31 Source: http://www.ni.com/white-paper/6427/en/
- 32. Signal Propagation Amplitude domain Amplitude change with time Frequency domain Frequency change with time Phase domain Phase change with time Frequency & phase modulation require high- frequency carriers 32 Source: www.ni.com/white-paper/4805/en
- 33. AM & FM 33 Amplitude Modulation Frequency Modulation
- 35. Phase Modulation (Cont.) Amplitude-Shift Keying (ASK) Binary ASK 1 – By presence of a signal 0 – No signal Pros Bandwidth efficient Simple to implement Cons Low power efficiency Susceptible to noise & multipath propagation Unclear absence of a signal vs. binary 0 35
- 36. Phase Modulation (Cont.) Frequency-Shift Keying (FSK) Binary FSK 1 – High frequency 0 – Low frequency Pros Better SNR Simple decoding Long distance Cons Slightly less bandwidth efficient than ASK & PSK More complicated circuitry than ASK 36
- 37. Phase Modulation (Cont.) Phase-Shift Keying (PSK) Encode based on phase of carrier wave Binary PSK 1 – 180o 0 – 0o Quadrature PSK 0o, 90o, 180o, 270o Pros Power efficient Cons Low-bandwidth efficiency More complicated circuitry than FSK 37
- 38. Phase Modulation (Cont.) Quadrature Amplitude Modulation (QAM) Combines ASK & PSK Widely used 38 Source: www.physics.udel.edu/~watson/scen103/projec ts/96s/thosguys/qam.html Source: www.scicos.org/ScicosModNum/modnum_web/sr c/modnum_421/interf/scicos/help/eng/htm/MODQ AM_f.htm
- 39. Multiplexing Transmitting multiple signals simultaneously Maximize capacity Time Division Multiplexing (TDM) Multiple channels occupy same frequency in alternating slices Frequency Division Multiplexing (FDM) Use different carrier frequencies Code Division Multiplexing (CDM) Same frequency & same time but different codes Code – like Tx & Rx speak different languages 39
- 42. Exercise Which of the following multiplexing technique allow signals to use different frequencies at the same time? a) Amplitude Division Multiplexing b) Frequency Division Multiplexing c) Code Division Multiplexing d) Time Division Multiplexing 42
- 43. Narrowband Transmission Pros Efficient use of frequency Cons Require regulation Easier to intercept & jam 43 Source: www.tapr.org
- 44. Spread Spectrum Spread signal over a large range of frequencies Low power density (power per frequency) Signal appear as background noise 44 www.intercomsonline.com/Spread-Spectrum-Technology_a/162.htm
- 45. Spread Spectrum (Cont.) Only receivers that know the spreading scheme can reconstruct original signal Spreading scheme defined by a code Only designated receiver knows the code Pros Improved channel capacity Resistance against interference Security against tapping & jamming Cons Complex circuits 45
- 46. Signal With & Without Noise 46 Source: www.sciencedirect.com/science/article/pii/S0888327009003756
- 47. Types of Spread Spectrum Systems 1. Direct Sequence Spread Spectrum (DSSS) 2. Frequency-Hopping Spread Spectrum (FHSS) 3. Orthogonal Frequency-Division Multiplexing (OFDM) 47
- 48. Direct Sequence Spread Spectrum (DSSS) Spread signal over broader frequency band Chipping technique to spread signal Transmitter & receiver needs to be synchronized Used in WiFi 48 Source: www.maximintegrated.com/app-notes/index.mvp/id/1890
- 49. Frequency-Hopping Spread Spectrum (FHSS) Hoping sequence of frequencies Only subset of the available frequencies are used to hop Transmitter & receiver needs to be synchronized Relatively simple to implement than DSSS Relatively easier to recover Tx signal than DSSS Relatively less robust to signal distortion & multipath effects Used in Bluetooth 49 Source: www.maximintegrated.com/app- notes/index.mvp/id/1890
- 50. Orthogonal Frequency-Division Multiplexing (OFDM) Utilize orthogonal multiple subcarriers in parallel Much higher data rates Low multipath interference Used in IEEE 802.11 a/g 50 Source: http://wiki.hsc.com//Main/OFDM
- 51. Challenges Wireless channels are a difficult & capacity- limited communications medium Typically less efficient Traffic patterns, user locations, & network conditions are constantly changing Applications are heterogeneous with hard constraints that must be met by networks 51
- 52. More Challenges Network challenges Scarce spectrum Demanding/diverse applications Reliability Ubiquitous coverage Seamless indoor/outdoor operation Device challenges Size, power, cost Multiple antennas in Silicon Multi-radio Integration Coexistance Cellular Apps Processor BT Media Processor GPS WLAN Wimax DVB-H FM/XM 52
- 53. Growth in mobile data, massive spectrum deficit & stagnant revenues require technical & political breakthroughs for ongoing success of cellular Careful what you wish for… 53 Source: Unstrung Pyramid Research 2010Source: FCC
- 54. Software-Defined (SD) Radio Wideband antennas & A/Ds span BW of desired signals DSP programmed to process desired signal: no specialized HW Cellular Apps Processor BT Media Processor GPS WLAN Wimax DVB-H FM/XM A/D A/D DSP A/D A/D Is this the solution to the device challenges? Today, this isn’t cost, size, or power efficient 54
- 55. Summary Bandwidth & QoS is in demand Many applications & services Spectrum is scare Many elements & solutions Still not enough It’s only going to be even more interesting... 55