Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The use of the quadrature mixing topology has been severely limited in the past due to
its sensitivity towards mismatches between its signal paths. In recent years, researchers
have suggested that digital techniques can be used to compensate for the impairments in
the analogue quadrature mixing front-end. Most authors, however, focus on the modelling
and compensation of frequency-independent imbalances, reasoning that this approach is
sufficient for narrow band signal operation. This common assumption is, however, becoming
increasing less applicable as the use of wider bandwidth signals and multi-channel systems
becomes more prevalent.
In this dissertation, baseband equivalent distortion models are derived, which model
frequency-independent, as well as frequency-dependent contributions towards the imbalances
of the front-end. Both lowpass and bandpass imbalances are modelled, which extends current
modelling approaches found in literature. The resulting baseband models are shown to be
capable of explaining the imbalance characteristics observed in practical quadrature mixing
front ends, where existing models fail to do so.
The developed imbalance models is then used to develop novel frequency-dependent imbalance
extraction and compensation techniques, which directly extract the exact quadrature
imbalances of the front end, using simple test tones. The imbalance extraction and compensation
procedures are implemented in the digital baseband domain of the transceiver and
do not require high computational complexity. The performance of these techniques are
subsequently verified through simulations and a practical hardware implementation, yielding
significant improvement in the image rejection capabilities of the quadrature mixing
transceiver.
Finally, a novel, blind imbalance compensation technique is developed. This technique
is aimed at extracting frequency-independent I/Q imbalances in systems employing digital
modulation schemes. No test tones are employed and the imbalances of the modulator and
demodulator are extracted from the second order statistics of the received signal. Simulations
are presented to investigate the performance of these techniques under various operating
conditions. / AFRIKAANSE OPSOMMING: Die gebruik van die haaksfasige mengtopologie word geweldig beperk deur die sensitiwiteit
vir wanbalanse wat mag bestaan tussen die twee analoog seinpaaie. In die afgelope paar
jaar het navorsers digitale metodes begin voorstel om te kompenseer vir hierdie wanbalanse
in die analooggebied. Meeste navorsers fokus egter op frekwensie-onafhanklike wanbalanse.
Hulle staaf hierdie aanslag deur te redineer dat dit ’n aanvaarbare aaname is vir ’n nouband
stelsel. Hierdie algemene aanvaarding is egter besig om minder akkuraat te raak, namate
wyeband- en multikanaalstelses aan die orde van die dag raak.
In hierdie tesis word basisband-ekwiwalente wanbelansmodelle afgelei wat poog om die
effek van frekwensie-afhanklike en -onafhanklike wanbalanse akkuraat voor te stel. Beide
laagdeurlaat- en banddeurlaatwanbalanse word gemodelleer, wat ‘n uitbreiding is op die
huididge modellerings benaderings wat in literatuur gevind word. Dit word aangetoon dat
die modelle van hierdie tesis daarin slaag om die karakteristieke van ’n werklike haaksfasige
mengstelsel akkuraat te vervat – iets waarin huidige modelle in die literatuur nie slaag nie.
Die basisband-ekwiwalente modelle word dan gebruik om nuwe digitale kompensasie
metodes te ontwikkel, wat daarin slaag om die frekwensie-afhanklike wanbalanse van die
haaksfasige mengstelsel af te skat, en daarvoor te kompenseer in die digitale deel van die
stelsel. Hierdie kompensasiemetodes gebruik eenvoudige toetsseine om die wanbalanse af te
skat. Die werksverrigting van hiedie kompensasiemetodes word dan ondersoek deur middel
van simulasies en ’n praktiese hardeware-implementasie. Die resultate wys daarop dat hierdie
metodes daarin slaag om ’n aansienlike verbetering in die beeldonderdrukkingsvermo¨ens van
die haaksfasige mengers te weeg te bring.
Laastens word daar ook ’n blinde kompensasiemetode ontwikkel, wat gemik is op frekwensie-
onafhanklike wanbalanse in digital-modulasie-skama stelsels. Vir hierdie metodes
is geen toetsseine nodig om die wanbalanse af te skat nie, en word dit gedoen vanuit die
tweede-orde statistiek van die ontvangde sein. Die werksverrigting van hierdie tegnieke word
verder bevestig deur middel van simulasies.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6808 |
| Date | 03 1900 |
| Creators | De Witt, Josias Jacobus |
| Contributors | Van Rooyen, G-J., University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 216 p. : ill. |
| Rights | University of Stellenbosch |
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