Limitations of experimental channel characterisation [Elektronische Ressource] / Markus Landmann

Dipl.-Ing. Markus Landmann

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• Publié par: technische_universitat_ilmenau
• Publié le: 01 janvier 2008
• Nombre de lectures: 97
• Langue: English
• Poids de l'ouvrage: 15 Mo

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TECHNISCHE UNIVERSITÄT ILMENAU
Fakult¨at fu¨r Elektrotechnik und Informationstechnik
der Technischen Universitat Ilmenau¨
Limitations of Experimental
Channel Characterisation
Markus Landmann
Dissertation zur Erlangung des
akademischen Grades Doktor-Ingenieur (Dr.-Ing)
Anfertigung im: Fachgebiet Elektronische Messtechnik
Institut fu¨r Informationstechnik
Fakultat fur Elektrotechnik und Informationstechnik¨ ¨
Gutachter: Univ.-Prof. Dr.-Ing. habil. Reiner S. Thoma¨
Univ.-Prof. Dr. rer. nat. habil. Matthias Hein
o.Univ.-Prof. Jun-ichi Takada
Vorgelegt am: 11.12.07
Verteidigt am: 28.03.08
urn:nbn:de:gbv:ilm1-2008000090ABSTRACT
This thesis deals with Experimental Channel Characterisation and its performance limits in real
propagation environments. This includes recording of the multidimensional wideband channel
matrix by using a Multiple-Input Multiple-Output (MIMO) channel sounder and antenna arrays
at both sides of the link. High-resolution parameter estimation is finally applied to characterise
the channel in terms of Direction of Departure (DoD), Direction of Arrival (DoA), Time Delay
of Arrival (TDoA), and complex polarimetric path weights. The quality of these estimates in
“real world”scenarios is degraded by several impairments of the practical antenna arrays and the
measurement system used. The resulting estimation quality limits are investigated in detail by
simulations and measurements. The entire processing chain is analysed in terms of possible error
sources. To this end, measurement system impairments, antenna array calibration errors as well
as limitations of the radio channel model applied by the high-resolution parameter estimation pro-
cedure are investigated. Moreover, consequences of using these results to deduce and parameterise
geometry based channel models are demonstrated.
Propagation measurements give us an antenna dependent description of the radio channel. For the
antenna independent characterisation of the radio channel, high-resolution parameter estimation
algorithms are applied to determine the DoD and DoA of the specular paths at the transmit and
receive side respectively. The gradient based Maximum Likelihood (ML) parameter estimation
framework RIMAX, which is reviewed in this thesis uses a data model that describes the radio
channel and the measurement system including the antenna arrays. Contrary to other ML pa-
rameter estimation algorithms, the model of the radio channel comprises two parts: specular like
reflections anddistributeddiffusescattering. For themodelofthemeasurementsystem,an efficient
and accurate description of the measured polarimetric antennaarray radiation patterns is required.
The proposed analytic description of antenna array radiation patterns, which is called Effective
Aperture Distribution Function (EADF), is essentially a two dimensional (2D) Fourier transfor-
mation of the periodic radiation patterns. As opposed to other models, radiation patterns and its
derivativescanbeeasilycalculated analyticallyfromtheEADFwithlowcomputationalburdenand
high accuracy. A full polarimetric 2D array calibration procedure for the accurate measurement
of the radiation patterns of antenna arrays is proposed. This procedure contains the calibration of
the entire measurement setup including the MIMO channel sounder, the dual polarised reference
horn antenna, and all devices in the Radio Frequency signal path.In this context, a new gradient
based ML estimation algorithm is proposed to correct the measured radiation patterns for a phase
offset, which occurs during the calibration measurement.
A powerful framework for the performance evaluation of practical antenna arrays in terms of an-
gular resolution limits in the presence of additive independent and identically distributed (i.i.d.)
Gaussianmeasurementnoiseispresented. ItisbasedontheEADFsofmeasuredradiationpatterns,
which allow us to calculate the Cram´er-Rao Lower Bounds of the angular parameters of the spec-
ular like reflections. The benefits of using the EADF to describe the radiation patterns including
all“imperfections”of the measured antenna array is herebyexploited. The proposed antenna array
performance evaluation framework is verified based on measurements in an anechoic chamber.
Thederivedmodelofthemeasurementsystemincludingtheantennaarrayscanonlybedetermined
within certain accuracy. A mismatch between the real measurement system and its model usediv
for parameter estimation always exists. From the analysis of several estimation results of a wide
range of measurements it was found that such a model mismatch partially may cause significant
errors in the estimation results. In this thesis a distinction is made between antenna array related
model mismatch and measurement system related model mismatch. Antenna array related model
mismatch caused by systematic errors depending on the quality of antenna array calibration and
systematic errors due to the usage of incomplete data models (e.g. ignoring polarisation charac-
teristic of the antenna elements) are investigated. The consequence of phase noise and unsuitable
calibrated measurement systems are presented in the context of model mismatch related to the
measurement system. It is shown that the use of an inaccurate model of the measurement system
inherently will result in biased and/or artificially spread angular estimates of the parameters of
the specular reflections. Methods are proposed to correct/avoid model mismatch and to reduce
the consequence of inaccurate/simplified models, whereas it is emphasised that some errors are
unavoidable.
The consequences of all unavoidable errors on Experimental Channel Characterisation in complex
propagation environments are investigated in the last part of this work. It is clearly shown un-
der which circumstances the estimated specular reflections and distributed diffuse scattering are
reliable and relevant. The investigations are based on realistic simulations of the radio channel
(ray-tracing) and macro-cell propagation measurements. This synthesis of ray-tracing simulations
and measurements guarantees the correctness and reliability of the accomplished results.
Thecontributionsofthisthesisareofinterestforresearchersdealingwithhigh-resolution parameter
estimation and channel modelling and can be summarised as follows:
• the efficient and accurate radiation pattern modelling of antenna arrays,
• the powerful performance evaluation framework for practical antenna arrays,
• the exposure of consequence of modelling errors on parameter estimation,
• and the demonstration of overall limitations of Experimental Channel Characterisation.KURZFASSUNG
In dieser Dissertation wird die Experimentelle Kanalcharakterisierung und deren Grenzen in rea-
len Ausbreitungsumgebungenuntersucht.Dies beinhaltet die Aufzeichnungder mehrdimensionalen
breitbandigen Kanalmatrix mit einem Multiple-Input Multiple-Output (MIMO) Channel-Sounder
unter Verwendung von Antennenarrays auf der Sende- und Empfangsseite. Um den Funkkanal
mit Hilfe der Parameter Sendewinkel (DoD), Empfangswinkel (DoA), Laufzeit (TDoA) und den
komplexen polarimetrischen Pfadgewichten zu charakterisieren, werden hochauflosende Parame-¨
terscha¨tzverfahren verwendet. Die Genauigkeit dieser Parameterscha¨tzergebnisse in realen“ Mess-
”
umgebungen wird durch eine Vielzahl von Fehlerquellen begrenzt. Diese Genauigkeitsgrenzen der
Parametersch¨atzung werden anhand zahlreicher Simulationen und Messungen analysiert. Fehler-
quellen im gesamten Verarbeitungsablauf werden untersucht. Dazu gehoren die Einschrankungen¨ ¨
durchdasMesssystem,systematischeFehler beiderKalibrierungpraktischer Antennenarrayssowie
Unzula¨nglichkeitendesFunkkanalmodellsdeshochauflo¨senden Parametersch¨atzers.Daru¨berhinaus
werden die Auswirkungen der Parametrierung bzw. Ableitung geometrisch basierter Kanalmodelle
auf der Grundlage von Parameterscha¨tzergebnissen mit begrenzter Genauigkeit aufgezeigt.
Mit Messungen in typischen Ausbreitungsumgebungen kann der Funkkanal immer nur in Abha¨n-
gigkeit der Messantennen beschrieben werden. Als Ziel wird jedoch eine antennenunabhangige Be-¨
schreibungdes Funkkanals angestrebt. Daher ist es notwendig, die Sende- und Empfangswinkelder
spekularen Ausbreitungspfade mittels hochauflosender Parameterschatzverfahren zu bestimmen.¨ ¨
Der gradientenbasierte Maximum Likelihood (ML) Parametersch¨atzer RIMAX, auf dem diese Ar-
beit aufbaut, verwendet ein Datenmodell, das den Funkkanal und das Messsystem inklusive der
Antennenarraysbeschreibt.ImGegensatzzuanderenML-ParameterschatzernwirdeinFunkanalm-¨
odell angewendet, welches spekulare Reflektionen und verteilte diffuse Streuungen beru¨cksichtigt.
Fur die Modellierung des Messsystems wird ein effizientes und exaktes Modell der gemessenen¨
polarimetrischen Richtcharakteristika beno¨tigt. Das hier vorgeschlagene Modell, die so genann-
te Effective Aperture Distribution Function (EADF), beschreibt die Antennenrichtcharakteristika
analytisch und basiert im Wesentlichen auf der zweidimensionalen (2D) Fouriertransformation der
periodischen Richtcharakteristika. Im Gegensatz zu anderen Verfahren konnen auf der Grundlage¨
der EADF die Antennencharakteristika und ihre Ableitungen mit geringem Aufwand und hoher
Genauigkeit berechnet werden. Fur eine exakte Messung der Richtchara