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this chapter details about the evolution of wireless systems right from 150 BC

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What is communication??
What is Wireless communication??
What is Wireless mobile communication??
Mobile communication • Two aspects of mobility: • user mobility: users communicate (wireless) “anytime, anywhere, with anyone” • device portability: devices can be connected anytime, anywhere to the network • Wireless vs. mobile Examples   stationary computer   notebook in a hotel   wireless LANs in historic buildings   Personal Digital Assistant (PDA) • The demand for mobile communication creates the need for integration of wireless networks into existing fixed networks: • local area networks: standardization of IEEE 802.11, ETSI (HIPERLAN) • Internet: Mobile IP extension of the internet protocol IP • wide area networks: e.g., internetworking of GSM and ISDN
Evolution of wireless communication
• 1831 Faraday demonstrates electromagnetic induction • J. Maxwell (1831-79): theory of electromagnetic Fields, wave equations (1864) H. Hertz (1857-94): demonstrates with an experiment the wave character of electrical transmission through space (1888, in Karlsruhe, Germany, at the location of today’s University of Karlsruhe)
• 1895- Guglielmo Marconi • first demonstration of wireless telegraphy (digital!) • long wave transmission, high transmission power necessary (> 200kw) • 1907-Commercial transatlantic connections • 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) • 1926-Train-phone on the line Hamburg - Berlin • wires parallel to the railroad track
• 1928 many TV broadcast trials (across Atlantic, color TV, TV news) • 1933 Frequency modulation (E. H. Armstrong) • 1958 A-Netz in Germany analog, 160MHz, connection setup only from the mobile station, no handover, 80% coverage, 1971 11000 customers • 1972 B-Netz in Germany analog, 160MHz, connection setup from the fixed network too (but location of the mobile station has to be known) available also in A, NL and LUX, 1979 13000 customer in D • 1979 NMT at 450MHz (Scandinavian countries) • 1982 Start of GSM-specification goal: pan-European digital mobile phone system with roaming • 1983 Start of the American AMPS (Advanced Mobile Phone System, analog) • 1984 CT-1 standard (Europe) for cordless telephones
• 1986 C-Netz in Germany • analog voice transmission, 450MHz, hand-over possible, digital signaling, automatic location of mobile device • Was in use until 2000, services: FAX, modem, X.25, e-mail, 98% coverage • 1991 Specification of DECT • Digital European Cordless Telephone (today: Digital Enhanced Cordless Telecommunications) • 1880-1900MHz, ~100-500m range, 120 duplex channels, 1.2Mbit/s data transmission, voice encryption, authentication, up to several 10000 user/km2, used in more than 50 countries • 1992 Start of GSM • in D as D1 and D2, fully digital, 900MHz, 124 channels • automatic location, hand-over, cellular • roaming in Europe - now worldwide in more than 170 countries • services: data with 9.6kbit/s, FAX, voice, ...
• 1999 Standardization of additional wireless LANs • IEEE standard 802.11b, 2.4-2.5GHz, 11Mbit/s • Bluetooth for piconets, 2.4Ghz, <1Mbit/s • Decision about IMT-2000 • Several “members” of a “family”: UMTS, cdma2000, DECT, … • Start of WAP (Wireless Application Protocol) and i-mode • First step towards a unified Internet/mobile communicaiton system • Access to many services via the mobile phone • 2000 GSM with higher data rates • HSCSD offers up to 57,6kbit/s • First GPRS trials with up to 50 kbit/s (packet oriented!) • UMTS auctions/beauty contests • Hype followed by disillusionment (approx. 50 B$ payed in Germany for 6 UMTS licences!) • 2001 Start of 3G systems • Cdma2000 in Korea, UMTS in Europe, Foma (almost UMTS) in Japan
Evolution of Mobile Communication: From 1G to 5G The Journey of Mobile Networks Through Five Generations
Introduction to Mobile Communication Evolution • Brief overview of the evolution from 1G to 5G.
1G: The Birth of Mobile Communication • Era: 1980s • Technologies: AMPS (USA), NMT (Europe) • Key Features: Analog technology, voice-only service, poor call quality, lack of security.
2G: The Advent of Digital Communication • Era: 1990s • Technologies: GSM, D- AMPS, cdmaOne, PDC • Key Features: Digital signals, SMS introduction, improved capacity, smaller phones.
3G: The Era of Mobile Internet • Era: 2000s • Technologies: UMTS, CDMA2000 • Key Features: Mobile internet, video calling, rise of smartphones and app stores.
4G: The Rise of Mobile Broadband • Era: 2010s • Technologies: LTE, WiMAX • Key Features: High- speed data, low latency, real-time streaming, IoT development.
5G: More Than Just Faster Internet • Era: 2020s • Technologies: 5G NR (New Radio) • Key Features: Ultra-low latency, massive IoT connectivity, AR/VR, energy efficiency.
Key Use Cases for 5G • Massive IoT Connectivity: Smart cities, smart homes. • Mission-Critical Applications: Remote surgery, autonomous driving. • Enhanced Mobile Experiences: AR/VR applications. • Energy Efficiency: Sustainable and efficient technology.
What next ??
6G networks • For the first time, 6G networks will allow humans to move intuitively between virtual and physical realities, fusing the physical, digital, and human worlds.
Identify 5 wireless communication scenarios in your daily life??
Typical application: road traffic ad hoc UMTS, WLAN, DAB, GSM, cdma2000, TETRA, ... Personal Travel Assistant, DAB, PDA, laptop, GSM, UMTS, WLAN, Bluetooth, ... Universal Mobile Telecommunications System, a third generation (3G) mobile network standard that uses a group of radio technolo IMT-2000 stands for International Mobile Telecommunications-2000. It's a global standard for third-generation (3G) wireless
30 T L SINGAL : Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Applications of Wireless Communications  Office and household environments  Industrial control  Education sector  Health services  Government and military operations  Event and travel management  Home entertainment  Environmental and industrial research
Applications I • 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, ...
Applications II • 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 History Info
Potential Market Areas and Data Rates Limited broadcast video FAX SMS (text only) Credit Card Verificatio n E-banking, E- commerce Text + image Messaging Multimedia WWW Remote Office Web Clipping Large File Transfer Wireless postcar d Multimedi a Messages Interactive games and entertainment Mobile Computin g 10 Kbps 14.4 Kbps 44-64 Kbps 144Kbps 384 Kbps 2 Mbps
Mobile and wireless services – Always Best Connected UMTS, DECT 2 Mbit/s UMTS, GSM 384 kbit/s LAN 100 Mbit/s, WLAN 54 Mbit/s UMTS, GSM 115 kbit/s GSM 115 kbit/s, WLAN 11 Mbit/s GSM 53 kbit/s Bluetooth 500 kbit/s GSM/EDGE 384 kbit/s, WLAN 780 kbit/s LAN, WLAN 780 kbit/s
Location dependent services • Location aware services • what services, e.g., printer, fax, phone, server etc. exist in the local environment • Follow-on services • automatic call-forwarding, transmission of the actual workspace to the current location • Information services • „push“: e.g., current special offers in the supermarket • „pull“: e.g., where is the Black Forrest Cherry Cake? • Support services • caches, intermediate results, state information etc. „follow“ the mobile device through the fixed network • Privacy • who should gain knowledge about the location
Target Business Areas  The Automotive Industry Market  The Fleet Management  Vehicle Positioning Market  The Utilities Market  The Security Systems Market  Vending Machines
Challenges for Research Wireless communications – a major technological areas for research as well as industrial applications. True wireless multimedia services – required by highly mobile subscribers seamlessly on a global arena. Diverse IP multimedia applications.
Services offered by wireless technology??
Mobile devices performance Pager • receive only • tiny displays • simple text messages Mobile phones • voice, data • simple graphical displays PDA • simpler graphical displays • character recognition • simplified WWW Palmtop • tiny keyboard • simple versions of standard applications Laptop • fully functional • standard applications Sensors, embedded controllers
Wireless Data Communication Technologies Satellite & GPS 2G/2.5G/3G Cellular Phone/Data WiMAX 802.16 WLAN 802.11 UWB & Bluetooth RFID/Tag 0 – 100 m a few kms 50 km a few thousand kms several thousands of kms
@ McGraw-Hill Education 31 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Potential Market Areas and Data Rates Limited broadcast video FAX SMS (text only) Credit Card Verificatio n E-banking, E- commerce Text + image Messaging Multimedia WWW Remote Office Web Clipping Large File Transfer Wireless postcar d Multimedi a Messages Interactive games and entertainment Mobile Computin g 10 Kbps 14.4 Kbps 44-64 Kbps 144Kbps 384 Kbps 2 Mbps
Effects of device portability • Power consumption • limited computing power, low quality displays, small disks due to limited battery capacity • CPU: power consumption ~ CV2 f • C: internal capacity, reduced by integration • V: supply voltage, can be reduced to a certain limit • f: clock frequency, can be reduced temporally • Loss of data • higher probability, has to be included in advance into the design (e.g., defects, theft) • Limited user interfaces • compromise between size of fingers and portability • integration of character/voice recognition, abstract symbols • Limited memory • limited value of mass memories with moving parts • flash-memory or ? as alternative
Wireless networks in comparison to fixed networks 1. Higher loss-rates due to interference 1. emissions of, e.g., engines, lightning 2. Restrictive regulations of frequencies 1. frequencies have to be coordinated, useful frequencies are almost all occupied 3. Low transmission rates 1. local some Mbit/s, regional currently, e.g., 9.6kbit/s with GSM 4. Higher delays, higher jitter 1. connection setup time with GSM in the second range, several hundred milliseconds for other wireless systems 5. Lower security, simpler active attacking 1. radio interface accessible for everyone, base station can be simulated, thus attracting calls from mobile phones 6. Always shared medium 1. secure access mechanisms important
Introduction to radio wave propagation
3 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications  Introduction  The Radio Paths  The Propagation Attenuation  Basic Propagation Mechanisms  Mobile Radio Channel Simulation of Wireless Fading Channels Mobile Communication Engineering
4 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Introduction The mobile radio channel is  extremely random in nature  difficult to analyze places fundamental limitations on the performance of wireless communication systems
5 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Mobile Communication Engineering?  A study of signal propagation - vital to wireless communications  Basic Propagation Mechanisms  How wireless medium supports mobility of the users  Radio propagation characteristics
@ McGraw-Hill Education 6 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Mobile Radio Environment  Radio Propagation Paths  Propagation Attenuation  Multi-path Propagation  Basic Propagation Mechanisms  Mobile Radio Channel  Multipath Fading  Multipath Delay Spread  Effect of Mobility: Doppler Shift  Coherence Bandwidth and Time
7 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Radio Propagation Paths  Direct wave Path - a path which is clear form terrain contour.  Line of Sight (LOS) Path - a path clear form buildings. In the mobile radio environment, line of sight condition is generally not met.  Obstructive Path - a path when the terrain contour blocks the direct wave path. The signal may encounter diffraction resulting into shadow or diffraction loss.
8 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications The Propagation Attenuation  In general, the propagation path loss increases with frequency of transmission, fc and the distance between cell site and mobile, R.  In a real mobile radio environment, the propagation path-loss varies as Lp∞ Rγ, where γ is path-loss exponent which varies between 2 and 6, depending on the actual conditions.  γ= 2 is free-space condition and γ= 4 is typical value for mobile radio
@ McGraw-Hill Education 9 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Path Loss Exponent Values
10 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Signal Attenuation Rate  Free-Space conditions: Signal strength decays at the rate of 6 dB/octave or 20 dB/decade  Mobile Radio Propagation Environment condition: Signal strength decays at the rate of 12 dB/octave or 40 dB/decade
@ McGraw-Hill Education 11 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Radio Propagation Mechanisms (1) Direct Signal (2) Ground Reflected Signal (3) Reflected Signal (4) Scattered Signal (5) Diffracted Signal Building ht hr r (1) (3) (2) (5) (4) Cell-site Tx Mobile Rx
@ McGraw-Hill Education 12 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Propagation Mechanisms  Reflection : Propagating wave impinges on an object which is large compared to wavelength, such as the surface of the Earth, buildings, walls, etc.  Diffraction : Radio path between transmitter and receiver obstructed by surface with sharp irregular edges. Waves bend around the obstacle, even when LOS does not exist  Scattering : Objects smaller than the wavelength of the propagating wave, e.g. foliage, street signs, lamp posts.
13 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Effects of Reflection on Signal Propagation BS - Tx ) MS - Rx ) Building size >10m 120o Direct path Reflected path
14 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Diffraction  A change in wave pattern caused by interference between waves that have been reflected from a surface or a point  Causes regions of waves strengthening and weakening  Results in bending of the wave  Can occur in different situations when waves √ Pass through a narrow slit √ Pass the edge of a reflector √ Reflect off two different surfaces approximately one wavelength apart
15 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Diffraction of Radio Signal BS - Tx ) MS - Rx ) Direct path Diffracted path Object 33 ≈ cm
16 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Scattering of Radio Signal BS - Tx Object 33 ≈ cm Scattering of signals MS - Rx
17 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Blocking and Absorption  Some substances like trees and shrubs, clouds, mist and other atmospheric moisture and dust, metal screen, human body near a hand held absorb radio waves  Higher frequency radio waves are absorbed more than
18 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Refraction  Refraction is the bending of electromagnetic waves as they pass from medium of one density into medium of another density.  Radio waves typically bend due to changes in density of air caused by changes in humidity, temperature or pressure.  Dielectric constant describes how the wave will propagate through the material.
19 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Refraction of Radio Signal troposphere or ionosphere Earth reflected radio signal direct radio signal refracted radio signal
20 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Mobile Radio Channel  Mobile radio channels introduce noise, fading, interference, and other distortions into the signals that they transmit.  In mobile communication system, a signal experiences multipath propagation which causes rapid signal level fluctuations of the amplitude of a radio signal in a short time over a short distance called fading.
21 T L SINGAL : Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Impairment to Radio Channel - Fading  Multipath waves are generated because the antenna height of mobile is lower than its typical surroundings, and the operatingwave length is much less than the sizes of the surrounding structures at mobile.  The sum of multipath waves causes a signal fading phenomenon.  The signal may fade in range of about 40 dB (10 dB above and 30 dB below the average signal). If the mobile moves fast,
@ McGraw-Hill Education 22 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Multipath fading ~100λ Wireless Medium Radio path Multipath Fading in a Mobile Radio Environment Tx Antenna Cell Site Cell Site
23 T L SINGAL : Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Types of Fading  Fading effects due to multipath time delay spread  Flat (non-frequency selective) fading  Frequency selective fading  Fading effects due to Doppler spread  Fast fading (Rayleigh fading)  Slow fading (Rician fading)
24 T L SINGAL : Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Flat (Non-frequency Selective) Fading  When radio channel has a constant gain and linear phase response but its bandwidth is greater than that of the transmitted signal  All frequency components of the received signal fluctuates in the same proportions simultaneously  Described by Rayleigh distribution  Typical flat fading channels cause deep fades, (20 or 30 dB)
@ McGraw-Hill Education 25 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Frequency Selective Fading  When radio channel has a constant gain and linear phase response but its bandwidth is less than that of the transmitted signal  Affects the different spectral components of a radio signal unequally  Due to time dispersion of the transmitted symbols within the channel, the channel induces intersymbol interference  Frequency selective fading channels are also known as wideband channels
26 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Fast Fading (Rayleigh fading)  Rapid fluctuations in received signal strength occur over distances of about one-half a wavelength.  The channel impulse response changes rapidly within the symbol duration.  The coherence time of the channel is smaller than symbol period of the transmitted signal.  This causes frequency dispersion, also called time selective fading, due to Doppler spreading.
27 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Slow Fading (Rician fading)  Rapid fluctuations in received signal strength occur over distances of about one-half a wavelength.  The channel impulse response changes rapidly within the symbol duration.  The coherence time of the channel is smaller than symbol period of the transmitted signal.  This causes frequency dispersion, also called time selective fading, due to Doppler spreading.
28 T L SINGAL : Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 A Typical Fading Signal Received 0 5 25 30 -80 -90 -100 -110 -120 -130 10 15 20 Relative Position (m) Signal Level (dBm)
29 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Shadow Fading  The variation of the signal strength due to location  Similar to slow fading  Typically modeled by attenuation in signal amplitude that follows a log- normal distribution  The variation in shadow fading is specified by the standard deviation of the logarithm of this attenuation
30 T L SINGAL : Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Effects of Multipath Fading (as noticed by the listener)  Rapid change in volume  Random frequency modulation  Echoes  Distortion  Dropped call
31 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Multipath Delay Spread  Multipath propagation yields signal paths of different paths with different times of arrival at the receiver.  Spreads/smears the signal, could cause inter- symbol interference, limits maximum symbol rate  Delay Spread also occurs due to Rayleigh fading which results from the signal’s amplitude and phase being altered by reflections.
@ McGraw-Hill Education 32 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Delay spread of a received signal
@ McGraw-Hill Education 33 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Typical Delay Spread Values
34 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Doppler Shift  The relative motion between the cell site and mobile results in random frequency change due to different Doppler shifts on each of the multipath components.  The Doppler shift, fd is given by fd = (1/λc) Vm cos θ where λc is the wavelength of the carrier signal, Vm is the relative velocity of the mobile, the angle θ is between the motion of the mobile and direction of arrival of the scattered waves.
@ McGraw-Hill Education 35 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Doppler Spread Doppler shift will be positive or negative depending on whether the mobile receiver is moving towards or away from the cell site. In mobile radio applications, the Doppler spectrum or Doppler spread for a Rayleigh fading channel is usually modeled by D(λ) = (0.16/fdm) x [1-( λc / fdm)2]-0.5 for - fdm ≤ λc ≤ fdm where fdm is the maximum Doppler frequency possible fdm = Vm / λc
36 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Level Crossing Rate It is possible to relate the time rate of change of the received signal to the signal level and velocity of the mobile. The level crossing rate, NL is defined as the expected rate at which the Rayleigh fading envelope, normalized to the local RMS signal level, crosses a specified threshold level in a positive- going direction. NL = 2.5 fdm ρ e- ρ2 ρ is the value of the specified level L, normalized to the local rms amplitude of the fading envelope, that is, L/Lrms.
37 T L SINGAL : Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Fade Rate and Fade Duration Fade rate is defined as the number of times that the signal envelope crosses the threshold value in a positive going direction per unit time. Average fade rate = 2 Vm / λc  The average fade duration is defined as the average period of time for which the received signal is below a specified level L. Average fade duration, Ť = 0.4(eρ2 -1)/(fdm ρ)
38 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Coherence Bandwidth  The coherence bandwidth is a statistical measure of the range of frequencies over which the channel can be considered flat.  The coherence bandwidth, Bc represents the correlation between two fading signal envelopes at frequencies f1 and f2 and is a function of delay spread Ŧd. Bc ≈ 1 / (2 π Ŧd) Where Ŧd is the delay spread.
@ McGraw-Hill Education 39 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Coherence Time  Coherence time is the time duration over which two received signals have a strong potential for amplitude correlation.  It is used to characterize the time varying nature of the frequency dispersiveness of the channel in the time domain.  Coherence time, Ŧc is inversely proportional of Doppler spread. Ŧc ≈ 0.423 / fdm Where fdm is the maximum Doppler shift given by Vm /λc.
40 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Wireless Fading Channels  Simulating a wireless communication system involves modeling a mobile radio channel based on mathematical descriptions of the channel.  Even when a mobile receiver is stationary, the received signal may fade due to movement of surrounding objects in the radio channel.  Rayleigh and Rician fading channels are useful models of real-world phenomena in wireless communications.
41 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Impulse Response of Channel  The wireless channels can be characterized by a parameter U, defined as ratio of the power in the dominant path to the power in the scattered path.  When U = 0 (that is, power in the dominant path is zero), the channel is Rayleigh channel.  When U is equal to infinity (that is, power in the scattered path is zero), the channel is AWGN.  The impulse response is a wideband channel characterization and contains all information necessary to simulate any type of radio transmission through the channel.
@ McGraw-Hill Education 42 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Simulating a Fading Channel  The BERTool of Communications ToolBox of technical computing simulation software MATLAB implements a baseband channel model for multipath propagation conditions.  A mobile radio channel may be modeled as a linear filter with a time varying impulse response, where the time variation is due to receiver motion in space.  The Communications Toolbox models a fading channel as a linear Finite Impulse Response (FIR) filter.
43 @ McGraw-Hill Education McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications BER Plot for Fading Channels 0 5 10 20 25 30 35 10-1 1 (2) (3) (4) (5) (1) Frequency-selective or Fast fading (2) Flat and slow fading Rayleigh limit U=0 (3) Rician fading U=4 (4) Rician fading U=16 (5) Additive white gaussian noise U=∞ ((11 )) 15 Eb/N0 (dB) Bit Error Rate (B ER) 10-2 10-3 10-4
@ McGraw-Hill Education 44 T L SINGAL : Wireless Communications McGraw-Hill Education © 2010 Summary  Impairments to propagation include reflection, diffraction, scattering, and many other similar phenomena.  Channel impairments cause multipath propagation and mobile signal fading.  Multipath propagation results in delay spread, which causes intersymbol interference limiting the bandwidth of the channel, and irreducible error rates.

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Evolution of wireless mobile communication-1a.pptx

  • 3.
  • 4.
  • 5.
    What is Wirelessmobile communication??
  • 6.
    Mobile communication • Twoaspects of mobility: • user mobility: users communicate (wireless) “anytime, anywhere, with anyone” • device portability: devices can be connected anytime, anywhere to the network • Wireless vs. mobile Examples   stationary computer   notebook in a hotel   wireless LANs in historic buildings   Personal Digital Assistant (PDA) • The demand for mobile communication creates the need for integration of wireless networks into existing fixed networks: • local area networks: standardization of IEEE 802.11, ETSI (HIPERLAN) • Internet: Mobile IP extension of the internet protocol IP • wide area networks: e.g., internetworking of GSM and ISDN
  • 7.
  • 12.
    • 1831 Faradaydemonstrates electromagnetic induction • J. Maxwell (1831-79): theory of electromagnetic Fields, wave equations (1864) H. Hertz (1857-94): demonstrates with an experiment the wave character of electrical transmission through space (1888, in Karlsruhe, Germany, at the location of today’s University of Karlsruhe)
  • 13.
    • 1895- GuglielmoMarconi • first demonstration of wireless telegraphy (digital!) • long wave transmission, high transmission power necessary (> 200kw) • 1907-Commercial transatlantic connections • huge base stations (30 100m high antennas) • 1915-Wireless voice transmission New York - San Francisco
  • 14.
    • 1920 -Discoveryof 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) • 1926-Train-phone on the line Hamburg - Berlin • wires parallel to the railroad track
  • 15.
    • 1928 manyTV broadcast trials (across Atlantic, color TV, TV news) • 1933 Frequency modulation (E. H. Armstrong) • 1958 A-Netz in Germany analog, 160MHz, connection setup only from the mobile station, no handover, 80% coverage, 1971 11000 customers • 1972 B-Netz in Germany analog, 160MHz, connection setup from the fixed network too (but location of the mobile station has to be known) available also in A, NL and LUX, 1979 13000 customer in D • 1979 NMT at 450MHz (Scandinavian countries) • 1982 Start of GSM-specification goal: pan-European digital mobile phone system with roaming • 1983 Start of the American AMPS (Advanced Mobile Phone System, analog) • 1984 CT-1 standard (Europe) for cordless telephones
  • 16.
    • 1986 C-Netzin Germany • analog voice transmission, 450MHz, hand-over possible, digital signaling, automatic location of mobile device • Was in use until 2000, services: FAX, modem, X.25, e-mail, 98% coverage • 1991 Specification of DECT • Digital European Cordless Telephone (today: Digital Enhanced Cordless Telecommunications) • 1880-1900MHz, ~100-500m range, 120 duplex channels, 1.2Mbit/s data transmission, voice encryption, authentication, up to several 10000 user/km2, used in more than 50 countries • 1992 Start of GSM • in D as D1 and D2, fully digital, 900MHz, 124 channels • automatic location, hand-over, cellular • roaming in Europe - now worldwide in more than 170 countries • services: data with 9.6kbit/s, FAX, voice, ...
  • 17.
    • 1999 Standardizationof additional wireless LANs • IEEE standard 802.11b, 2.4-2.5GHz, 11Mbit/s • Bluetooth for piconets, 2.4Ghz, <1Mbit/s • Decision about IMT-2000 • Several “members” of a “family”: UMTS, cdma2000, DECT, … • Start of WAP (Wireless Application Protocol) and i-mode • First step towards a unified Internet/mobile communicaiton system • Access to many services via the mobile phone • 2000 GSM with higher data rates • HSCSD offers up to 57,6kbit/s • First GPRS trials with up to 50 kbit/s (packet oriented!) • UMTS auctions/beauty contests • Hype followed by disillusionment (approx. 50 B$ payed in Germany for 6 UMTS licences!) • 2001 Start of 3G systems • Cdma2000 in Korea, UMTS in Europe, Foma (almost UMTS) in Japan
  • 18.
    Evolution of Mobile Communication:From 1G to 5G The Journey of Mobile Networks Through Five Generations
  • 19.
    Introduction to MobileCommunication Evolution • Brief overview of the evolution from 1G to 5G.
  • 20.
    1G: The Birthof Mobile Communication • Era: 1980s • Technologies: AMPS (USA), NMT (Europe) • Key Features: Analog technology, voice-only service, poor call quality, lack of security.
  • 21.
    2G: The Adventof Digital Communication • Era: 1990s • Technologies: GSM, D- AMPS, cdmaOne, PDC • Key Features: Digital signals, SMS introduction, improved capacity, smaller phones.
  • 22.
    3G: The Eraof Mobile Internet • Era: 2000s • Technologies: UMTS, CDMA2000 • Key Features: Mobile internet, video calling, rise of smartphones and app stores.
  • 23.
    4G: The Riseof Mobile Broadband • Era: 2010s • Technologies: LTE, WiMAX • Key Features: High- speed data, low latency, real-time streaming, IoT development.
  • 24.
    5G: More ThanJust Faster Internet • Era: 2020s • Technologies: 5G NR (New Radio) • Key Features: Ultra-low latency, massive IoT connectivity, AR/VR, energy efficiency.
  • 25.
    Key Use Casesfor 5G • Massive IoT Connectivity: Smart cities, smart homes. • Mission-Critical Applications: Remote surgery, autonomous driving. • Enhanced Mobile Experiences: AR/VR applications. • Energy Efficiency: Sustainable and efficient technology.
  • 27.
  • 28.
    6G networks • Forthe first time, 6G networks will allow humans to move intuitively between virtual and physical realities, fusing the physical, digital, and human worlds.
  • 30.
    Identify 5 wirelesscommunication scenarios in your daily life??
  • 31.
    Typical application: roadtraffic ad hoc UMTS, WLAN, DAB, GSM, cdma2000, TETRA, ... Personal Travel Assistant, DAB, PDA, laptop, GSM, UMTS, WLAN, Bluetooth, ... Universal Mobile Telecommunications System, a third generation (3G) mobile network standard that uses a group of radio technolo IMT-2000 stands for International Mobile Telecommunications-2000. It's a global standard for third-generation (3G) wireless
  • 32.
    30 T L SINGAL: Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Applications of Wireless Communications  Office and household environments  Industrial control  Education sector  Health services  Government and military operations  Event and travel management  Home entertainment  Environmental and industrial research
  • 33.
    Applications I • 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, ...
  • 34.
    Applications II • Travellingsalesmen • 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 History Info
  • 35.
    Potential Market Areasand Data Rates Limited broadcast video FAX SMS (text only) Credit Card Verificatio n E-banking, E- commerce Text + image Messaging Multimedia WWW Remote Office Web Clipping Large File Transfer Wireless postcar d Multimedi a Messages Interactive games and entertainment Mobile Computin g 10 Kbps 14.4 Kbps 44-64 Kbps 144Kbps 384 Kbps 2 Mbps
  • 36.
    Mobile and wirelessservices – Always Best Connected UMTS, DECT 2 Mbit/s UMTS, GSM 384 kbit/s LAN 100 Mbit/s, WLAN 54 Mbit/s UMTS, GSM 115 kbit/s GSM 115 kbit/s, WLAN 11 Mbit/s GSM 53 kbit/s Bluetooth 500 kbit/s GSM/EDGE 384 kbit/s, WLAN 780 kbit/s LAN, WLAN 780 kbit/s
  • 37.
    Location dependent services •Location aware services • what services, e.g., printer, fax, phone, server etc. exist in the local environment • Follow-on services • automatic call-forwarding, transmission of the actual workspace to the current location • Information services • „push“: e.g., current special offers in the supermarket • „pull“: e.g., where is the Black Forrest Cherry Cake? • Support services • caches, intermediate results, state information etc. „follow“ the mobile device through the fixed network • Privacy • who should gain knowledge about the location
  • 38.
    Target Business Areas  TheAutomotive Industry Market  The Fleet Management  Vehicle Positioning Market  The Utilities Market  The Security Systems Market  Vending Machines
  • 39.
    Challenges for Research Wirelesscommunications – a major technological areas for research as well as industrial applications. True wireless multimedia services – required by highly mobile subscribers seamlessly on a global arena. Diverse IP multimedia applications.
  • 40.
    Services offered bywireless technology??
  • 41.
    Mobile devices performance Pager • receiveonly • tiny displays • simple text messages Mobile phones • voice, data • simple graphical displays PDA • simpler graphical displays • character recognition • simplified WWW Palmtop • tiny keyboard • simple versions of standard applications Laptop • fully functional • standard applications Sensors, embedded controllers
  • 42.
    Wireless Data Communication Technologies Satellite& GPS 2G/2.5G/3G Cellular Phone/Data WiMAX 802.16 WLAN 802.11 UWB & Bluetooth RFID/Tag 0 – 100 m a few kms 50 km a few thousand kms several thousands of kms
  • 43.
    @ McGraw-Hill Education 31 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Potential Market Areas and Data Rates Limited broadcast video FAX SMS (text only) Credit Card Verificatio n E-banking, E- commerce Text + image Messaging Multimedia WWW Remote Office Web Clipping Large File Transfer Wireless postcar d Multimedi a Messages Interactive games and entertainment Mobile Computin g 10 Kbps 14.4 Kbps 44-64 Kbps 144Kbps 384 Kbps 2 Mbps
  • 44.
    Effects of deviceportability • Power consumption • limited computing power, low quality displays, small disks due to limited battery capacity • CPU: power consumption ~ CV2 f • C: internal capacity, reduced by integration • V: supply voltage, can be reduced to a certain limit • f: clock frequency, can be reduced temporally • Loss of data • higher probability, has to be included in advance into the design (e.g., defects, theft) • Limited user interfaces • compromise between size of fingers and portability • integration of character/voice recognition, abstract symbols • Limited memory • limited value of mass memories with moving parts • flash-memory or ? as alternative
  • 45.
    Wireless networks incomparison to fixed networks 1. Higher loss-rates due to interference 1. emissions of, e.g., engines, lightning 2. Restrictive regulations of frequencies 1. frequencies have to be coordinated, useful frequencies are almost all occupied 3. Low transmission rates 1. local some Mbit/s, regional currently, e.g., 9.6kbit/s with GSM 4. Higher delays, higher jitter 1. connection setup time with GSM in the second range, several hundred milliseconds for other wireless systems 5. Lower security, simpler active attacking 1. radio interface accessible for everyone, base station can be simulated, thus attracting calls from mobile phones 6. Always shared medium 1. secure access mechanisms important
  • 46.
    Introduction to radiowave propagation
  • 50.
    3 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications  Introduction  The Radio Paths  The Propagation Attenuation  Basic Propagation Mechanisms  Mobile Radio Channel Simulation of Wireless Fading Channels Mobile Communication Engineering
  • 51.
    4 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Introduction The mobile radio channel is  extremely random in nature  difficult to analyze places fundamental limitations on the performance of wireless communication systems
  • 52.
    5 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Mobile Communication Engineering?  A study of signal propagation - vital to wireless communications  Basic Propagation Mechanisms  How wireless medium supports mobility of the users  Radio propagation characteristics
  • 53.
    @ McGraw-Hill Education 6 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Mobile Radio Environment  Radio Propagation Paths  Propagation Attenuation  Multi-path Propagation  Basic Propagation Mechanisms  Mobile Radio Channel  Multipath Fading  Multipath Delay Spread  Effect of Mobility: Doppler Shift  Coherence Bandwidth and Time
  • 54.
    7 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Radio Propagation Paths  Direct wave Path - a path which is clear form terrain contour.  Line of Sight (LOS) Path - a path clear form buildings. In the mobile radio environment, line of sight condition is generally not met.  Obstructive Path - a path when the terrain contour blocks the direct wave path. The signal may encounter diffraction resulting into shadow or diffraction loss.
  • 55.
    8 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications The Propagation Attenuation  In general, the propagation path loss increases with frequency of transmission, fc and the distance between cell site and mobile, R.  In a real mobile radio environment, the propagation path-loss varies as Lp∞ Rγ, where γ is path-loss exponent which varies between 2 and 6, depending on the actual conditions.  γ= 2 is free-space condition and γ= 4 is typical value for mobile radio
  • 56.
    @ McGraw-Hill Education 9 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Path Loss Exponent Values
  • 57.
    10 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Signal Attenuation Rate  Free-Space conditions: Signal strength decays at the rate of 6 dB/octave or 20 dB/decade  Mobile Radio Propagation Environment condition: Signal strength decays at the rate of 12 dB/octave or 40 dB/decade
  • 58.
    @ McGraw-Hill Education 11 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Radio Propagation Mechanisms (1) Direct Signal (2) Ground Reflected Signal (3) Reflected Signal (4) Scattered Signal (5) Diffracted Signal Building ht hr r (1) (3) (2) (5) (4) Cell-site Tx Mobile Rx
  • 59.
    @ McGraw-Hill Education 12 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Propagation Mechanisms  Reflection : Propagating wave impinges on an object which is large compared to wavelength, such as the surface of the Earth, buildings, walls, etc.  Diffraction : Radio path between transmitter and receiver obstructed by surface with sharp irregular edges. Waves bend around the obstacle, even when LOS does not exist  Scattering : Objects smaller than the wavelength of the propagating wave, e.g. foliage, street signs, lamp posts.
  • 60.
    13 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Effects of Reflection on Signal Propagation BS - Tx ) MS - Rx ) Building size >10m 120o Direct path Reflected path
  • 61.
    14 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Diffraction  A change in wave pattern caused by interference between waves that have been reflected from a surface or a point  Causes regions of waves strengthening and weakening  Results in bending of the wave  Can occur in different situations when waves √ Pass through a narrow slit √ Pass the edge of a reflector √ Reflect off two different surfaces approximately one wavelength apart
  • 62.
    15 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Diffraction of Radio Signal BS - Tx ) MS - Rx ) Direct path Diffracted path Object 33 ≈ cm
  • 63.
    16 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Scattering of Radio Signal BS - Tx Object 33 ≈ cm Scattering of signals MS - Rx
  • 64.
    17 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Blocking and Absorption  Some substances like trees and shrubs, clouds, mist and other atmospheric moisture and dust, metal screen, human body near a hand held absorb radio waves  Higher frequency radio waves are absorbed more than
  • 65.
    18 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Refraction  Refraction is the bending of electromagnetic waves as they pass from medium of one density into medium of another density.  Radio waves typically bend due to changes in density of air caused by changes in humidity, temperature or pressure.  Dielectric constant describes how the wave will propagate through the material.
  • 66.
    19 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Refraction of Radio Signal troposphere or ionosphere Earth reflected radio signal direct radio signal refracted radio signal
  • 67.
    20 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Mobile Radio Channel  Mobile radio channels introduce noise, fading, interference, and other distortions into the signals that they transmit.  In mobile communication system, a signal experiences multipath propagation which causes rapid signal level fluctuations of the amplitude of a radio signal in a short time over a short distance called fading.
  • 68.
    21 T L SINGAL: Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Impairment to Radio Channel - Fading  Multipath waves are generated because the antenna height of mobile is lower than its typical surroundings, and the operatingwave length is much less than the sizes of the surrounding structures at mobile.  The sum of multipath waves causes a signal fading phenomenon.  The signal may fade in range of about 40 dB (10 dB above and 30 dB below the average signal). If the mobile moves fast,
  • 69.
    @ McGraw-Hill Education 22 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Multipath fading ~100λ Wireless Medium Radio path Multipath Fading in a Mobile Radio Environment Tx Antenna Cell Site Cell Site
  • 70.
    23 T L SINGAL: Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Types of Fading  Fading effects due to multipath time delay spread  Flat (non-frequency selective) fading  Frequency selective fading  Fading effects due to Doppler spread  Fast fading (Rayleigh fading)  Slow fading (Rician fading)
  • 71.
    24 T L SINGAL: Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Flat (Non-frequency Selective) Fading  When radio channel has a constant gain and linear phase response but its bandwidth is greater than that of the transmitted signal  All frequency components of the received signal fluctuates in the same proportions simultaneously  Described by Rayleigh distribution  Typical flat fading channels cause deep fades, (20 or 30 dB)
  • 72.
    @ McGraw-Hill Education 25 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Frequency Selective Fading  When radio channel has a constant gain and linear phase response but its bandwidth is less than that of the transmitted signal  Affects the different spectral components of a radio signal unequally  Due to time dispersion of the transmitted symbols within the channel, the channel induces intersymbol interference  Frequency selective fading channels are also known as wideband channels
  • 73.
    26 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Fast Fading (Rayleigh fading)  Rapid fluctuations in received signal strength occur over distances of about one-half a wavelength.  The channel impulse response changes rapidly within the symbol duration.  The coherence time of the channel is smaller than symbol period of the transmitted signal.  This causes frequency dispersion, also called time selective fading, due to Doppler spreading.
  • 74.
    27 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Slow Fading (Rician fading)  Rapid fluctuations in received signal strength occur over distances of about one-half a wavelength.  The channel impulse response changes rapidly within the symbol duration.  The coherence time of the channel is smaller than symbol period of the transmitted signal.  This causes frequency dispersion, also called time selective fading, due to Doppler spreading.
  • 75.
    28 T L SINGAL: Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 A Typical Fading Signal Received 0 5 25 30 -80 -90 -100 -110 -120 -130 10 15 20 Relative Position (m) Signal Level (dBm)
  • 76.
    29 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Shadow Fading  The variation of the signal strength due to location  Similar to slow fading  Typically modeled by attenuation in signal amplitude that follows a log- normal distribution  The variation in shadow fading is specified by the standard deviation of the logarithm of this attenuation
  • 77.
    30 T L SINGAL: Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Effects of Multipath Fading (as noticed by the listener)  Rapid change in volume  Random frequency modulation  Echoes  Distortion  Dropped call
  • 78.
    31 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Multipath Delay Spread  Multipath propagation yields signal paths of different paths with different times of arrival at the receiver.  Spreads/smears the signal, could cause inter- symbol interference, limits maximum symbol rate  Delay Spread also occurs due to Rayleigh fading which results from the signal’s amplitude and phase being altered by reflections.
  • 79.
    @ McGraw-Hill Education 32 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Delay spread of a received signal
  • 80.
    @ McGraw-Hill Education 33 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Typical Delay Spread Values
  • 81.
    34 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Doppler Shift  The relative motion between the cell site and mobile results in random frequency change due to different Doppler shifts on each of the multipath components.  The Doppler shift, fd is given by fd = (1/λc) Vm cos θ where λc is the wavelength of the carrier signal, Vm is the relative velocity of the mobile, the angle θ is between the motion of the mobile and direction of arrival of the scattered waves.
  • 82.
    @ McGraw-Hill Education 35 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Doppler Spread Doppler shift will be positive or negative depending on whether the mobile receiver is moving towards or away from the cell site. In mobile radio applications, the Doppler spectrum or Doppler spread for a Rayleigh fading channel is usually modeled by D(λ) = (0.16/fdm) x [1-( λc / fdm)2]-0.5 for - fdm ≤ λc ≤ fdm where fdm is the maximum Doppler frequency possible fdm = Vm / λc
  • 83.
    36 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Level Crossing Rate It is possible to relate the time rate of change of the received signal to the signal level and velocity of the mobile. The level crossing rate, NL is defined as the expected rate at which the Rayleigh fading envelope, normalized to the local RMS signal level, crosses a specified threshold level in a positive- going direction. NL = 2.5 fdm ρ e- ρ2 ρ is the value of the specified level L, normalized to the local rms amplitude of the fading envelope, that is, L/Lrms.
  • 84.
    37 T L SINGAL: Wireless Communications @ McGraw-Hill Education McGraw-Hill Education © 2010 Fade Rate and Fade Duration Fade rate is defined as the number of times that the signal envelope crosses the threshold value in a positive going direction per unit time. Average fade rate = 2 Vm / λc  The average fade duration is defined as the average period of time for which the received signal is below a specified level L. Average fade duration, Ť = 0.4(eρ2 -1)/(fdm ρ)
  • 85.
    38 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Coherence Bandwidth  The coherence bandwidth is a statistical measure of the range of frequencies over which the channel can be considered flat.  The coherence bandwidth, Bc represents the correlation between two fading signal envelopes at frequencies f1 and f2 and is a function of delay spread Ŧd. Bc ≈ 1 / (2 π Ŧd) Where Ŧd is the delay spread.
  • 86.
    @ McGraw-Hill Education 39 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Coherence Time  Coherence time is the time duration over which two received signals have a strong potential for amplitude correlation.  It is used to characterize the time varying nature of the frequency dispersiveness of the channel in the time domain.  Coherence time, Ŧc is inversely proportional of Doppler spread. Ŧc ≈ 0.423 / fdm Where fdm is the maximum Doppler shift given by Vm /λc.
  • 87.
    40 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Wireless Fading Channels  Simulating a wireless communication system involves modeling a mobile radio channel based on mathematical descriptions of the channel.  Even when a mobile receiver is stationary, the received signal may fade due to movement of surrounding objects in the radio channel.  Rayleigh and Rician fading channels are useful models of real-world phenomena in wireless communications.
  • 88.
    41 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications Impulse Response of Channel  The wireless channels can be characterized by a parameter U, defined as ratio of the power in the dominant path to the power in the scattered path.  When U = 0 (that is, power in the dominant path is zero), the channel is Rayleigh channel.  When U is equal to infinity (that is, power in the scattered path is zero), the channel is AWGN.  The impulse response is a wideband channel characterization and contains all information necessary to simulate any type of radio transmission through the channel.
  • 89.
    @ McGraw-Hill Education 42 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Simulating a Fading Channel  The BERTool of Communications ToolBox of technical computing simulation software MATLAB implements a baseband channel model for multipath propagation conditions.  A mobile radio channel may be modeled as a linear filter with a time varying impulse response, where the time variation is due to receiver motion in space.  The Communications Toolbox models a fading channel as a linear Finite Impulse Response (FIR) filter.
  • 90.
    43 @ McGraw-HillEducation McGraw-Hill Education © 2010 T L SINGAL : Wireless Communications BER Plot for Fading Channels 0 5 10 20 25 30 35 10-1 1 (2) (3) (4) (5) (1) Frequency-selective or Fast fading (2) Flat and slow fading Rayleigh limit U=0 (3) Rician fading U=4 (4) Rician fading U=16 (5) Additive white gaussian noise U=∞ ((11 )) 15 Eb/N0 (dB) Bit Error Rate (B ER) 10-2 10-3 10-4
  • 91.
    @ McGraw-Hill Education 44 TL SINGAL : Wireless Communications McGraw-Hill Education © 2010 Summary  Impairments to propagation include reflection, diffraction, scattering, and many other similar phenomena.  Channel impairments cause multipath propagation and mobile signal fading.  Multipath propagation results in delay spread, which causes intersymbol interference limiting the bandwidth of the channel, and irreducible error rates.