wirelss channelpart 2無線信道

1、Wireless Channels,2024/3/21,2/58,Outline,Cell Wireless CommunicationsPhysical Modeling for Wireless ChannelsPass Loss ModelingShadow FadingStatistical Multipath Channel ModelsCapacity of Wireless Channels,2024/3/21,

2、3/58,Outline,Cell Wireless CommunicationsPhysical Modeling for Wireless ChannelsPass Loss ModelingShadow FadingStatistical Multipath Channel ModelsCapacity of Wireless Channels,2024/3/21,4/58,Cell Wireless Communica

3、tions,StructureBase StationWireless ChannelMobile Users,,,Wireless channels operate through electromagnetic radiation from the transmitter to the receiver.Its characteristic ? communication efficiency (Channel Ca

4、pacity)How to communicate effectively over wireless channels ?,2024/3/21,5/58,Cell Wireless Communications,System Design,2024/3/21,6/58,Outline,Cell Wireless CommunicationsPhysical Modeling for Wireless ChannelsPass L

5、oss ModelingShadow FadingStatistical Multipath Channel ModelsCapacity of Wireless Channels,2024/3/21,7/58,Physical Modeling for Wireless Channels,Mainly in the UHF(.3-3 GHz) and SHF(3-30GHz) bands,2024/3/21,8/58,Physi

6、cal Modeling for Wireless Channels,Frequency Bands for LTE,2024/3/21,9/58,Physical Modeling for Wireless Channels,Characteristics for wireless frequency bandsMultipathReflectScatterDiffract,,,2024/3/21,10/58,Physical

7、 Modeling for Wireless channels,Channel varies at two spatial scales,2024/3/21,11/58,Physical modeling for wireless channels,Modeling Problem？Approximation by using ray-tracing techniquesLarge scale fading? Pass loss m

8、odelLarge-scale propagation effects caused by transmit-receive distanceShadowing due to the obstacles Small scale fading? Statistical multipath channel modelsDeal with variation due to the constructive and destructi

9、ve addition of multipath signal components,2024/3/21,12/58,Physical modeling for wireless channels,,2024/3/21,13/58,Physical modeling for wireless channels,Fading caused by Multipath Channel,Real measurement courtesy(Pro

10、f. D Tse and Qualcom),2024/3/21,14/58,Outline,Cell Wireless CommunicationsPhysical Modeling for Wireless ChannelsPass Loss ModelingShadow FadingStatistical Multipath Channel ModelsCapacity of Wireless Channels,2024/

11、3/21,15/58,Pass loss modeling,Characterize the variation in received signal power over distance due to path loss and shadowing. Transmit-receive distanceCommunication environments Path loss models generally assume tha

12、t path loss is the same at a given transmit-receive distanceVariation occurs over large distances(100-1000 meters)Shadowing is caused by obstacles between the transmitter and receiver that absorb power.Variation occur

13、s over distances proportional to the length of the obstacles (10-100 meters in outdoor and less in indoor),,2024/3/21,16/58,Pass loss modeling,Path lossThe ratio of transmit power to receive powerPath gainDe?ned as

14、 the negative of the path loss in dB,,2024/3/21,17/58,Pass loss modeling,Free-space path loss exampleAssume there are no obstructions between the transmitter and receiver The signal propagates along a straight line(LOS

15、),Wave Length,,Transmit-receive distance,the product of the transmit and receive antenna gain,,,2024/3/21,18/58,Pass loss modeling,Ray-tracing--Two-Ray ModelThe two-ray model is used when a single ground re?ection dom

16、inates the multipath e?ectRural roads or highways,2024/3/21,19/58,Pass loss modeling,Ray-tracing--Ten-Ray ModelAlong a straight street or hallwayUrban area transmissions,The ground-re?ected (GR), the single-wall (SW)

17、re?ected, the double-wall (DW) re?ected, the triple-wall (TW) re?ected, the wall-ground (WG) re?ected and the ground-wall (GW) re?ected paths,2024/3/21,20/58,Pass loss modeling,General Ray-Tracing Model（GRT）For any prop

18、agation environmentUses geometrical optics to trace the propagation of the LOS and reflected signal components, as well as signal components from building diffraction and diffuse scattering,2024/3/21,21/58,Pass loss mo

19、deling,GRT-Diffraction model,2024/3/21,22/58,Pass loss modeling,Simplified Path Loss Model,K is a unitless constant which depends on the antenna characteristics and the average channel attenuationd0 is a reference dist

20、ance for the antenna far-?eld: typically assumed to be 1-10 m indoors and 10-100 m outdoors. γ is the path loss exponent,2024/3/21,23/58,Pass loss modeling,Typical Path Loss Exponent,2024/3/21,24/58,Pass loss modeling,

21、Empirical Path Loss ModelMost mobile communication systems cannot be accurately modeled by free-space path loss, ray tracing, or the simplified modelsEmpirical Path Loss Model: mainly based on empirical measurements o

22、ver a given distance in a given frequency range and a particular geographical area or building.,2024/3/21,25/58,Pass loss modeling,Empirical Path Loss ModelOkumura’s ModelHata ModelCOST231 Extension to Hata ModelWal?

23、sch/Bertoni ModelPiecewise Linear (Multi-Slope) ModelIndoor Propagation Models,2024/3/21,26/58,Pass loss modeling,Okumura’s Modellarge urban macrocellsover distances of 1-100 Km frequency ranges of 150-1500 MHzBase

24、d on extensive measurements of base station-to-mobile signal attenuation throughout TokyoHata ModelExtend Okumura’s model by adding correction factor for the mobile antenna height and different frequency.The Hata mode

25、l well-approximates the Okumura model for distances d> 1 Km.,2024/3/21,27/58,Pass loss modeling,COST231 Extension to Hata ModelThe Hata model was extended by the European cooperative for scientific and technical rese

26、arch (EURO-COST) to 2 GHz1.5GHz <fc < 2GHz, 30m<ht < 200 m1m <hr < 10 m, 1Km <d< 20 Km,0 dB for medium sized cities and suburbs, and 3 dB for metropolitan areas,,the same correction factor as

27、 Hata Model,,2024/3/21,28/58,Outline,Cell Wireless CommunicationsPhysical Modeling for Wireless ChannelsPass Loss ModelingShadow FadingStatistical Multipath Channel ModelsCapacity of Wireless Channels,2024/3/21,29/5

28、8,Shadow Fading,Experience random variation due to blockage from objects, giving rise to a random variation about the path loss at a given distance,2024/3/21,30/58,Shadow Fading,The log-normal shadowing modelThe path lo

29、ss ψ is assumed random with a log-normal distribution,ξ =10/ ln 10,,,the mean of ψdB (10log10ψ),the standard deviation of ψdB,,2024/3/21,31/58,Combined Path Loss and Shadowing,Cell Coverage Area,2024/3/21,32/58,Outline,C

30、ell Wireless CommunicationsPhysical Modeling for Wireless ChannelsPass Loss ModelingShadow FadingStatistical Multipath Channel ModelsCapacity of Wireless Channels,2024/3/21,33/58,Statistical Multipath Channel Models

31、,Small scale fadingExamine fading models for the addition of different multipath componentsConstructiveDestructive,Sum of multipath components,,2024/3/21,34/58,Statistical Multipath Channel Models,Narrowband fading mo

32、delsThe delay spread of a channel is small relative to the inverse signal bandwidth B,in-phase components,,quadrature components,,2024/3/21,35/58,Statistical Multipath Channel Models,The power spectral densities (PSDs)

33、the Fourier transform of their respective autocorrelation functions relative to the delay parameter τ,U form,,2024/3/21,36/58,Statistical Multipath Channel Models,Relationship,2024/3/21,37/58,Statistical Multipath Chann

34、el Models,Envelope and Power DistributionsFor any two Gaussian random variables X and Y , both with mean zero and equal variance σ2, the envelope of Z = sqrt(X^2 + Y^2) is Rayleigh-distributed and the power of Z^2 is ex

35、ponentially distributedRayleigh-distributedExponentially-distributed,2024/3/21,38/58,Statistical Multipath Channel Models,Rician distributionFor multipath with a ?xed LOS componentRician Factor:,Power of LOS,,

36、Power of NLOS,,Bessel Function,,2024/3/21,39/58,Statistical Multipath Channel Models,More General DistributionNakagami fading distributionm=1: Rayleigh fadingM=∞: no fading,2024/3/21,40/58,Statistical Multipath C

37、hannel Models,Define,lowpass time-varying channel impulse responseτ: multipath delay,,depends only on the frequency di?erence ?fand time separation ?t,2024/3/21,41/58,Statistical Multipath Channel Models,Coherence Ba

38、ndwidth: BcAc(?f) ≈ 0 for all ?f>Bc:Channel varies (B is the signal bandwidth)Flat fading: B>BcSignificant ISIOFDM…Between ?at and frequency-selective fading: B ≈ Bc.,2024/3/21,42/58,Statistical Multipath Cha

39、nnel Models,Channel Coherence Time：Tc Ac (?t) ≈ 0 for all ?t>Bc Doppler spread: BD|Sc(ρ)|≈ 0 for all ρ>BD,Doppler power spectrum,,,2024/3/21,43/58,Outline,Cell Wireless CommunicationsPhysical Modeling for Wirel

40、ess ChannelsPass Loss ModelingShadow FadingStatistical Multipath Channel ModelsCapacity of Wireless Channels,2024/3/21,44/58,Capacity of Wireless Channels,Information TheoryInformation theory provides a fundamental

41、characterization of coded performance.It succintly identifies the impact of channel resources on performance as well as suggests new and cool ways to communicate over the wireless channel.It provides the basis for the

42、 modern development of wireless communication.,2024/3/21,45/58,Capacity of Wireless Channels,Capacity of AWGN Channel,2024/3/21,46/58,Capacity of Wireless Channels,Power and Bandwidth Limited Regimes,,2024/3/21,47/58,Cap

43、acity of Wireless Channels,Power and Bandwidth Limited Regimes,2024/3/21,48/58,Capacity of Wireless Channels,Frequency-selective AWGN Channel,2024/3/21,49/58,Capacity of Wireless Channels,Slow Fading Channel,,2024/3/21,5

44、0/58,Capacity of Wireless Channels,Outage for Rayleigh Channel,2024/3/21,51/58,Capacity of Wireless Channels,Fast Fading Channel,2024/3/21,52/58,Capacity of Wireless Channels,WaterfillingTransmit More when Channel is Go

45、od,2024/3/21,53/58,Capacity of Wireless Channels,Waterfilling Capacity,2024/3/21,54/58,Capacity of Wireless Channels,Transmitter side information,2024/3/21,55/58,Capacity of Wireless Channels,Transmitter side information

46、At high SNR, waterfilling doesn’t provide any gain,2024/3/21,56/58,Capacity of Wireless Channels,Capacity with Receive Diversity,2024/3/21,57/58,Capacity of Wireless Channels,Capacity with Transmit Diversity,2024/3/21,5