Contributions in Radio Channel Sounding, Modeling, and Estimation

Troels Pedersen

Contributions in Radio Channel Sounding, Modeling, and Estimation

Troels Pedersen

Institut for Elektroniske Systemer

Publikation: Ph.d.-afhandling

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Abstract

Denne Ph.D. afhandling omhandler tre stærkt forbunde emner: måling, modellering og estimering af radiokommunikationskanaler. Tre hovedproblemer behandles: optimering af rum-tid sampling i radiokanalmålesystemer, enkeltvis estimering af effektspektre af signalkomponenter i radiokanaler med flervejsudbredelse samt modellering af efterklangsfænomener.

Der udvikles en teori for optimering of rum-tid aperturer i multi-input multi-output (MIMO) målesystemer. Der fokuseres først på samlet bestemmelse af dopplerfrekvens og udstrålings/indstrålings retninger ud fra tidsmultiplexede målinger af MIMO kanaler. Derefter indføres en `ambiguityfunktion' for dette estimeringsproblem. Analyse af ambiguityfunktionen viser, at den højeste dopplerfrekvens, der kan bestemmes entydigt, afhænger af rum-tid aperturet. Ved passende design af målesystemets rum-tid apertur er den øvre grænse for den estimerbare dopplerfrekvens for MIMO systemer lige så høj som for traditionelle målesystemer med en sender- og en modtagerantenne. Der gives den nødvendige og tilstrækkelige betingelse for, at et givet rum-tid apertur minimerer Cramer-Rao begrænsningen på doppler-retnings bestemmelse. Rum-tid aperturet har også indflydelse på hvor nøjagtigt MIMO-kanalkapaciteten kan estimeres når målesystemets fasestøj tages i betragtning. Ved at udnytte kendskab til fasestøjens autokorrelationsfunktion og strukturen af rum-tid aperturet, udledes en forbedret kapacitets estimator.

Dernæst behandles estimering af sprednings egenskaber for udbredelsesveje i et miljø med flervejsudbredelse. effektspektret for en udbredelsesvej modelleres ved hjælp af en entropi-maximerende fordelingsfunktion (pdf). Denne pdf er givet ved det første og andet moment, for hvilke en estimator udledes. Estimatorens anvendelighed illustreres ved brug af måledata. De opnåede spredningsestimater er væsentligt mindre end tidligere publicerede estimater, hvor traditionelle metoder er anvendt. Estimeringsresultaterne indikerer, at signalspredningen for de enkeltvise signalveje kan være overvurderet i standardiserede radiokanalmodeller.

Til slut opstilles en model for overgangen fra separate til diffuse signalkomponenter som kan observeres i målinger af radiokanaler med efterklang. Modellen bygger på en `udbredelsesgraf', hvori punkter repræsenterer objekter i udbredelses miljøet, og kanter representerer bølgeudbredelsen mellem objekter. Der udledes et udtryk for grafens overføringsfunktion, der gælder for signalkomponenter der udbredes via et vilkårligt antal interaktioner. Overføringsfunktionen anvendes til simulering af impulsresponset af stokastisk genererede udbredelsesgrafer. Impulsresponserne udviser den førnævnte overgang fra separate til et diffust signalbidrag.

Originalsprog	Engelsk
Udgivelsessted	Aalborg
Udgave	1
ISBN'er, trykt	978-87-92328-02-1
Status	Udgivet - 2009

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Radiokanalkarakterisering
Radiokanal målesystemer
Radiokanal modellering
Radiokommunikation

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abstract = "This thesis spans over three strongly related topics in wireless communication: channel-sounding, -modeling, and -estimation. Three main problems are addressed: optimization of spatio-temporal apertures for channel sounding; estimation of per-path power spectral densities (psds); and modeling of reverberant channels.We develop a theory for optimization of spatio-temporal apertures used in multiple-input multiple-output (MIMO) channel sounding. Initially, we focus on joint estimation of bi-direction and Doppler frequency from time-division multiplexing (TDM) MIMO measurements. We introduce and analyze a bi-spatio-temporal ambiguity function for spatio-temporal channel sounding. The analysis reveals that by proper design of the spatio-temporal aperture, the maximum estimable Doppler frequency of a TDM-MIMO sounder is as high as that of a traditional single-input single-output sounder. We give the necessary and sufficient conditions for spatio-temporal apertures to minimize the Cramer-Rao lower bound on the joint bi-direction and Doppler frequency estimation. The spatio-temporal aperture also impacts on the accuracy of MIMO-capacity estimation from measurements impaired by colored phase noise. We present an improved capacity estimator, which exploits the second order statistics of the phase noise and the structure of the spatio-temporal aperture.Next we turn to the problem of estimating the per-path psd resolved in directions and delay. We model the per-path psds using entropy maximizing probability density functions (pdfs); the pdfs are defined by their first- and second-order moments. We derive estimators of these parameters and illustrate their applicability on measurement data. The obtained spread estimates are significantly smaller, and the estimated psds are much more concentrated, than corresponding results from literature. These findings indicate that the per-path directional spreads (or cluster spreads) assumed in standard models are set too large.Finally, we propose a model of the specular-to-diffuse transition observed in measurements of reverberant channels. The model relies on a ``propagation graph'' where vertices represent scatterers and edges represent the wave propagation conditions between scatterers. The graph has a recursive structure, which permits modeling of the transfer function of the graph. We derive a closed-form expression of the infinite-bounce impulse response. This expression is used for simulation of the impulse response of randomly generated propagation graphs. The obtained realizations exhibit the well-observed exponential power decay versus delay and specular-to-diffuse transition.",

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AB - This thesis spans over three strongly related topics in wireless communication: channel-sounding, -modeling, and -estimation. Three main problems are addressed: optimization of spatio-temporal apertures for channel sounding; estimation of per-path power spectral densities (psds); and modeling of reverberant channels.We develop a theory for optimization of spatio-temporal apertures used in multiple-input multiple-output (MIMO) channel sounding. Initially, we focus on joint estimation of bi-direction and Doppler frequency from time-division multiplexing (TDM) MIMO measurements. We introduce and analyze a bi-spatio-temporal ambiguity function for spatio-temporal channel sounding. The analysis reveals that by proper design of the spatio-temporal aperture, the maximum estimable Doppler frequency of a TDM-MIMO sounder is as high as that of a traditional single-input single-output sounder. We give the necessary and sufficient conditions for spatio-temporal apertures to minimize the Cramer-Rao lower bound on the joint bi-direction and Doppler frequency estimation. The spatio-temporal aperture also impacts on the accuracy of MIMO-capacity estimation from measurements impaired by colored phase noise. We present an improved capacity estimator, which exploits the second order statistics of the phase noise and the structure of the spatio-temporal aperture.Next we turn to the problem of estimating the per-path psd resolved in directions and delay. We model the per-path psds using entropy maximizing probability density functions (pdfs); the pdfs are defined by their first- and second-order moments. We derive estimators of these parameters and illustrate their applicability on measurement data. The obtained spread estimates are significantly smaller, and the estimated psds are much more concentrated, than corresponding results from literature. These findings indicate that the per-path directional spreads (or cluster spreads) assumed in standard models are set too large.Finally, we propose a model of the specular-to-diffuse transition observed in measurements of reverberant channels. The model relies on a ``propagation graph'' where vertices represent scatterers and edges represent the wave propagation conditions between scatterers. The graph has a recursive structure, which permits modeling of the transfer function of the graph. We derive a closed-form expression of the infinite-bounce impulse response. This expression is used for simulation of the impulse response of randomly generated propagation graphs. The obtained realizations exhibit the well-observed exponential power decay versus delay and specular-to-diffuse transition.

KW - Radiokanalkarakterisering

KW - Radiokanal målesystemer

KW - Radiokanal modellering

KW - Radiokommunikation

KW - Radio channel characterization

KW - Radio channel sounding

KW - Radio channel modelling

KW - Radiocommunications

M3 - PhD thesis

SN - 978-87-92328-02-1

VL - 1

CY - Aalborg

ER -

Contributions in Radio Channel Sounding, Modeling, and Estimation

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