SYSC5606-4 - The Small-Scale Ppropagation Iimpairments...

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SYSC 5606 - 4 Copyright © 1995-2009 by R.H.M. Hafez 1 (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 SYSC 5606 - 4 Copyright © 1995-2009 by R.H.M. Hafez 2 Definition When a signal arrives to a receiver by means of several (many) rays RX TX Each ray arrives with different : Amplitude Phase Delay Angle of arrival Multipath causes : Fading Delay spread Random phase distortion Inter-symbol-interference Multipath Multipath
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SYSC 5606 - 4 Copyright © 1995-2009 by R.H.M. Hafez 3 Definition Fading occurs when multipath rays are added destructively such that the resultant signal is weaker than its average value by a specified limit RMS signal level threshold level non fade interval fade interval distance Relative motion between the transmitter and receiver converts the distance axis into a time axis Fading Fading SYSC 5606 - 4 Copyright © 1995-2009 by R.H.M. Hafez 4 Definition A drop in the signal strength due to the presence of a large object between the transmitter and receiver. Objects (large and small) form a complex shadowing patters fading fluctuations shadowing fluctuations transmitter object object Shadowing Shadowing
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SYSC 5606 - 4 Copyright © 1995-2009 by R.H.M. Hafez 5 Definition Relative motion between the transmitter and receiver causes Doppler frequency shifts. In a multipath channel, the frequency shift of each ray is different and the sum of all these shifts causes what is known as random FM freq. δ( f-f o ) f o Freq. Doppler spread f o TX Single tone transmitted Many tones received one for each ray Random FM (Doppler) Random FM (Doppler) SYSC 5606 - 4 Copyright © 1995-2009 by R.H.M. Hafez 6 Definition Different multipath rays arrive at the receiver at different times. The delay spread is a measure of the time interval over which significant rays arrive. RX TX time δ( t) 0 delay Delay spread Short pulse transmitted Many pulses received Delay Spread Delay Spread
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SYSC 5606 - 4 Copyright © 1995-2009 by R.H.M. Hafez 7 PRACTICAL CONSIDERATIONS PRACTICAL CONSIDERATIONS • WHAT DO WE NEED TO KNOW ABOUT THE CHANNEL? - Statistical description of all six parameters as a function of the environment • HOW ACCURATE SHOULD THE MODELS BE ? - Loss of accuracy means loss of capacity (and loss of revenue) • CURRENT STATUS ?
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This note was uploaded on 10/24/2009 for the course SCE Sysc5606 taught by Professor Roshdy during the Spring '09 term at Carleton CA.

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SYSC5606-4 - The Small-Scale Ppropagation Iimpairments...

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