Lecture II Agenda Lecture II Agenda Radio Propagation 無線網路多媒體系統 • Physical of radio propagation • Two types of propagation models Wireless Multimedia System • Outdoor vs. Indoor Radio Propagation Model • How to do simple “ link budget” calculation • Combating the radio channel impairment Radio Propagation:Issues & Models Wireless Modem Design Modern Application: 911 services Dr. Eric Hsiaokuang Wu http://wmlab.csie.ncu.edu.tw/course/wms Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Path Loss Model (Large Scale) Path Loss Model (Large Scale) Multi Multi- -path fading (Small Scale) path fading (Small Scale) d ( ) ( ) 10 log( ) PL d PL d n 0 d 0 Telco Core Telco Core Telco Core Telco Core Network or Network or Network or Network or Private (Fiber) Private (Fiber) Private (Fiber) Private (Fiber) Network Network Network Network INTERNET INTERNET INTERNET INTERNET d0 d BACKBONE BACKBONE BACKBONE BACKBONE Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Reading list for This Lecture Reading list for This Lecture Required Reading: The mystery of the Radio Propagation The mystery of the Radio Propagation (Jorgen95) J. B. Andersen, T. S. Rappaport, “Propagation Measurements and Models for Wireless Communications channels”, (IEEE Communication Magazine), pp. 42~49 (Jeffrey H98) Jeffrey H. Reed, Kevin J. Krizman, Brian D. Woerner, and T. S. Rappaport, “An Overview of the Challenges and Progress in Meeting the E-911 Requirement for Location Service, (IEEE Communication Magazine) pp 30~37 Magazine), pp.30~37 Further Reading (Rappaport97) T. S. Rappaport, K. Blankenship, H. Xu, “Propagation and Radio System Design Issues in Mobile Radio Systems for the GloMo Project Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory 1
How to deal with Radio Propagation How to deal with Radio Propagation Where are you from? Where are you from? IP backbone Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory QoS and Multimedia Traffic Support Simplified View of a Digital Radio Link Simplified View of a Digital Radio Link Application Source OS, MiddleWare Coder Multiple Channel Power Multiplex Modulator Access Coder Amplifier Source RTP, TCP, UDP Coder Carrier f c Adaptive RSVP Mobility “Limited b/w” Radio Algorithm Unpredictable IP, Mobile IP “Highly variable b/w” Channel channel channel “Random & Noisy” “R d & N i ” by QoS Wireless Network Layer “Spurious Disconnections” Requirement by QoS Clustering(optional) Information Data Link Source MAC Coder Multiple Channel Demodulator RF Demultiplex Access Decoder & Equalizer Filter Source Coder Radio Carrier f c Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Digital to Analog Modulation Digital to Analog Modulation Digital Digital- -Digital Digital- -Analog Modulation Analog Modulation Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory 2
Digital Correlator Digital Correlator Multiple correlators Multiple correlators Multiple correlators in each receiver At any instant of time, the signal carriers in the different correlators are synchronize to signal paths with different propagation times A search circuit examines the arriving signal in order to detect the appearance of a new path, then assign a correlator to synchronize the signal on the path Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Key role for the radio propagation Key role for the radio propagation Radio Propagation determines • the area which could be covered • The maximum data rate in a system • Battery power requirement for mobile transceivers Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory 3
Radio Channel Radio Channel Some Distributions Some Distributions Free Space Normal (Gaussian) Land Mobile Log-normal Distribution Multi-path Propagation Rayleigh Distribution Shadow Rician Distribution • Dominant path Impulse Response Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Propagation Mechanisms in Space with Propagation Mechanisms in Space with Reflection, Diffraction, and Scattering in Reflection, Diffraction, and Scattering in Objects Objects Real Real- -Life Life Reflection (with Transmittance and Absorption) • Radio wave impinges on an object • Surface of earth, walls, buildings, atmospheric layers • If perfect (lossless) dielectric object, then zero absorption • If perfect conductor, then 100%reflection Diffraction • Radio path is obstructed by an impenetrable surface with sharp irregularities (edges) • Secondary waves “bend” around the obstacle (Huygen’s principle) • Explain how RF energy can travel without LOS • “shadowing Received signal often a sum of contributions from different directions Scattering (diffusion) Random phases make the sum behave as noise (Rayleigh Fading) • Similar principles as diffraction, energy reradiated in many directions Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Small Small- -scale and Large scale and Large- -scale Fading scale Fading Signal fades rapidly as receiver moves, but the local average signal changes much more slowly Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory 4
Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory 5
Analysis of the Propagation Analysis of the Propagation Large Scale - Large Scale -> Link Budget > Link Budget Large Scale Effect • The variation of the mean received signal strength over large distance or long time intervals Small Scale Effect • The fluctuations of the received signal strength about a local mean, where these fluctuations occur over small distances or short time interval th fl t ti ll di t h t ti i t l Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Free Space Propagation Model Free Space Propagation Model Used when Transmitter and Receiver have a clear, unobstructed, line of sight (LOS) path • e.g. satellite channels, microwave LOS radio links Free space power at a receiver antenna at a distance d from transmitter antenna is 2 P G G ( ) t t r P d 2 2 where, w e e, r ( ( 4 ) ) d L G t and G r are antenna gains L >= 1 is the system loss factor not related to propagation (e.g. loss due to filter losses, hardware Path loss = signal attenuation as a positive quantity in dB P ( ) 10 log t Pl dB Pr ( ) 10 log[ ( ) / 1 ] P dBm P mW mW t t Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory Wireless & Multimedia Network Laboratory 6
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