SYSC5606-4-with-notes

SYSC5606-4-with-notes - Small Scale Radio Propagation The...

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Knowledge of the details of small scale propagation mechanisms is useful in designing efficient mechanisms for modulation, error correcting codes, equalizers, diversity techniques and so on. SYSC 5606 - 4 Copyright © 1995-2009 by R.H.M. Hafez 1 Small Scale Radio Propagation D Small area P average The average power is determined by a propagation model and shadowing statistics ± Within the small area, different points could have vastly different power level due to fading ± The analysis of these variations is called the small scale propagation
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Notes The five propagation mechanisms listed on this slide have a profound impact on the design and performance of wireless systems. Each of these mechanisms will be treated in some details later. We need to start by a brief description of the propagation mechanics (the bare essentials). This is covered in the next few slides. SYSC 5606 - 4 Copyright © 1995-2009 by R.H.M. Hafez 2 (1) REFLECTION AND SCATTERING (MULTIPATH) (2) VECTORIAL SUM OF MANY WAVES (FADING) (3) OBSTRUCTION BY LARGE OBJECTS (SHADOWING) (4) RELATIVE TX / RX MOTION (DOPPLER) (5) MULTIPLE COPIES OF SIGNALS (DELAY SPREAD) The he Small Small -Scale Scale Ppropagation propagation Iimpairments impairments CHANNEL IMPAIRMENTS ARE CAUSED BY 6 INTER-RELATED MECHANISMS
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Notes This slide is the start of a group of slides that deals with the small scale signal statistics. The analysis is still elementary, but enough to understand the basic mechanisms. This subject will be visited later in the course in the context of multiple access methods, transmission techniques and signal improvement techniques. SYSC 5606 - 4 Copyright © 1995-2009 by R.H.M. Hafez 3 MULTIPATH MULTIPATH WITHOUT MOTION MULTIPATH WITH MOTION (1) FADING IN SPACE maxima and minima in the coverage area) (2) DELAY SPREAD time distortion Inter-Symbol-Interference (ISI) (1) FADING IN SPACE AND TIME. motion converts distance into time. The moving unit samples different field points at different times (2) DELAY SPREAD motion has little impact on the delay spread or time distortion (3) DOPPLER SPREAD frequency distortion and random phase
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Notes The term multipath applies that there is more than the transmitted signal reaches the receiver through reflections and scattering. Several versions od the transmitted signal arrives at the receiver. We call the different versions “Rays”. Each ray follows a different path, therefore rays arrive to the receiver at differenr times and with different magnitudes and phases. In that sense, all radio channels are multipath channels. In personal wireless environment, the number of rays is large (in most scenarios) and often we assume that the number of rays is infinite. This leads to simple statistical models (such as Rayleigh). This slide depicts the situation where 4 rays arrive with different magnitudes and phases.
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SYSC5606-4-with-notes - Small Scale Radio Propagation The...

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