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Baseband compensation principles for defects in quadrature signal conversion and processingVan Rooyen, Gert-Jan 04 1900 (has links)
Thesis (PhD)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: Keywords: software-defined radio, SDR, quadrature mixing, quadrature modulation, quadrature
demodulation, digital compensation, software radio, direct-digital synthesis, DDS.
An often-stated goal of software-defined transceiver systems is to perform digital signal conversion
as close to the antenna as possible by using high-rate converters. In this dissertation,
alternative design principles are proposed, and it is shown that the signal processing techniques
based on these principles improve on the prior system's accuracy, while maintaining
system flexibility.
Firstly, it is proposed that digital compensation can be used to reverse the effects of
hardware inaccuracies in the RF front-end of a software-defined radio. Novel compensation
techniques are introduced that suppress the signal artefacts introduced by typical frontend
hardware. The extent to which such artefacts may be suppressed, is only limited by the
accuracy by which they may be measured and digitally represented. A general compensation
principle is laid down, which formalises the conditions under which optimal compensation
may be achieved.
Secondly, it is proposed that, in the design of such RF front-ends, a clear distinction
should be drawn between signal processing complexity and frequency translation. It is
demonstrated that conventional SDR systems often neglect this principle. As an alternative,
quadrature mixing is shown to provide a clear separation between the frequency translation
and signal processing problems. However, effective use of quadrature mixing as design approach
necessitates the use of accurate compensation techniques to circumvent the hardware
inaccuracies typically found in such mixers.
Quadrature mixers are proposed as general-purpose front-ends for software-defined radios,
and quadrature modulation and demodulation techniques are presented as alternatives
to existing schemes. The inherent hardware inaccuracies are analysed and simulated, and
appropriate compensation techniques are derived and tested. Finally, the theory is verified
with a prototype system. / AFRIKAANSE OPSOMMING: Sleutelwoorde: sagteware-gedefinieerde radio, SDR, haaksfasige menging, haaksfasige modulasie,
haaksfasige demodulasie, digitale kompensasie, sagteware-radio, direk-digitale sintese,
DDS.
'n Gewilde stelling is dat digitale seinomsetting in sagteware-gedefinieerde kommunikasiestelsels
so na as moontlik aan die antenna moet geskied deur gebruik te maak van hoëspoed
omsetters. Hierdie verhandeling stel alternatiewe ontwerpsbeginsels voor, en toon
aan dat hierdie beginsels die eersgenoemde stelsel se akkuraatheid verbeter, terwyl stelselbuigsaamheid
gehandhaaf word.
Dit word eerstens voorgestel dat digitale kompensasie gebruik word om die effekte van
hardeware-onakkuraathede in die RF-koppelvlak van sagteware-gedefinieerde radio's om te
keer. Nuwe kompensasietegnieke, wat seinartefakte weens koppelvlak-onakkuraathede kan
onderdruk, word aangebied. Die mate waartoe hierdie artefakte onderdruk kan word, word
slegs beperk deur die akkuraatheid waarmee dit gemeet en digitaal voorgestel kan word. 'n
Algemene kompensasiebeginsel word neergelê waarin die voorwaardes vir optimale kompensasie
vasgelê word.
Tweedens word voorgestel dat 'n duidelike onderskeid getref word tussen seinverwerkingskompleksiteit
en seinverskuiwing in RF-koppelvlakke. Daar word getoon dat konvensionele
SDR-stelsels dikwels nie hierdie beginsel handhaaf nie. 'n Alternatief, naamlik haaksfasige
menging, word voorgehou as 'n tegniek wat duidelik onderskei tussen seinverskuiwing en
seinverwerking. Akkurate kompensasietegnieke is egter nodig om effektief van sulke mengers
gebruik te maak.
Haaksfasige mengers word voorgestel as veeldoelige koppelvlakke vir sagteware-gedefinieerde
radio's, en haaksfasige modulasie- en demodulasietegnieke word voorgestel as plaasvervangers
vir bestaande tegnieke. Die inherente hardeware-onakkuraathede word geanaliseer
en gesimuleer, en geskikte kompensasietegnieke word afgelei en getoets. Laastens word die
teoretiese resultate met 'n praktiese prototipe bevestig.
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Modelling, estimation and compensation of imbalances in quadrature transceiversDe Witt, Josias Jacobus 03 1900 (has links)
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.
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