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S-72.227 Digital Communication Systems Multipath Radio Channel Addendum (extracts from J-P Linnartz: Wireless Communication CDROM)

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Presentation on theme: "S-72.227 Digital Communication Systems Multipath Radio Channel Addendum (extracts from J-P Linnartz: Wireless Communication CDROM)"— Presentation transcript:

1 S Digital Communication Systems Multipath Radio Channel Addendum (extracts from J-P Linnartz: Wireless Communication CDROM)

2 Timo O. Korhonen, HUT Communication Laboratory Multipath radio channels u Physical backgrounds u Channel modeling: statistical, semi-statistical, deterministic (empirical) u Characterizing channel: –channel responses –figures of merit, as RMS-delay spread and coherence bandwidth u Reception techniques to cope with multipath –diversity t antenna t power control t selection of modulation scheme: GSM, OFDM, UWB –coding: FEC / ARQ –interleaving

3 Timo O. Korhonen, HUT Communication Laboratory Modeling radio channels statisticalsemi-deterministicdeterministic + Wideband modeling * Narrowband modeling + + +*+* Radio channel modeling targets: - narrow band : averaged path loss - wide band : impulse response Mapping electromagnetic fields based on physical structures Ray tracing Playback modeling Simplified physical environment modeled by statistical parameters increasing accuracy-> +*+*

4 Timo O. Korhonen, HUT Communication Laboratory Effect of mobility in communication systems

5 Timo O. Korhonen, HUT Communication Laboratory Effect of mobility in communication systems (cont.)

6 Timo O. Korhonen, HUT Communication Laboratory Effect of mobility in communication systems (cont.)

7 Timo O. Korhonen, HUT Communication Laboratory Multipath fading characterization

8 Timo O. Korhonen, HUT Communication Laboratory Multipath fading characterization (cont)

9 Timo O. Korhonen, HUT Communication Laboratory

10 Radio channel's physical backgrounds multipath shadowing Path loss reflection scattering diffraction free space loss plane earth loss Rayleigh Rice dispersion variation as a function of time

11 Timo O. Korhonen, HUT Communication Laboratory Physical propagation: case A: free space B: reflection C: diffraction D: scattering

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15 Free space loss

16 Timo O. Korhonen, HUT Communication Laboratory Semi-empirical channel modeling u Egli's model takes into account –loss per distance –antenna high –fits to measurements u Okimura-Hata have made a model that fits the model into empirical average path loss measurements

17 Timo O. Korhonen, HUT Communication Laboratory Shadowing u Received signal power fluctuates due to objects obstructing the propagation path between transmitter and receiver. u These fluctuations are experienced on local-mean powers, that is, short-term averages to remove fluctuations due to multipath fading.

18 Timo O. Korhonen, HUT Communication Laboratory Example of average path loss in different cities

19 Timo O. Korhonen, HUT Communication Laboratory Typical delay spreads

20 Timo O. Korhonen, HUT Communication Laboratory Scatter functions u Effects of path delays & Doppler spread combined in a single plot u Each path can be described by angle of arrival, complex power attenuation, Doppler shift and excess delay u Thus a plot can be made for instance to show the received wave with Doppler & Delay in x-plane and power at z plane

21 Timo O. Korhonen, HUT Communication Laboratory Distribution of the angle of arrival

22 Timo O. Korhonen, HUT Communication Laboratory Doppler spectra <- Theoretical spectra for an omni-directional sinusoidal

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25 Diffraction loss (single knife)

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27 Antenna diversity u A signal transmitted at a particular carrier frequency and at a particular instant of time may be received in a multipath null. u Diversity reception reduces the probability of occurrence of communication failures (outages) caused by fades by combining several copies of the same message received over different channels. u In general, the efficiency of the diversity techniques reduces if the signal fading is correlated at different branches.


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