6 research outputs found
Multipair Massive MIMO Relaying Systems with One-Bit ADCs and DACs
This paper considers a multipair amplify-and-forward massive MIMO relaying
system with one-bit ADCs and one-bit DACs at the relay. The channel state
information is estimated via pilot training, and then utilized by the relay to
perform simple maximum-ratio combining/maximum-ratio transmission processing.
Leveraging on the Bussgang decomposition, an exact achievable rate is derived
for the system with correlated quantization noise. Based on this, a closed-form
asymptotic approximation for the achievable rate is presented, thereby enabling
efficient evaluation of the impact of key parameters on the system performance.
Furthermore, power scaling laws are characterized to study the potential energy
efficiency associated with deploying massive one-bit antenna arrays at the
relay. In addition, a power allocation strategy is designed to compensate for
the rate degradation caused by the coarse quantization. Our results suggest
that the quality of the channel estimates depends on the specific orthogonal
pilot sequences that are used, contrary to unquantized systems where any set of
orthogonal pilot sequences gives the same result. Moreover, the sum rate gap
between the double-quantized relay system and an ideal non-quantized system is
a moderate factor of in the low power regime.Comment: 14 pages, 10 figures, submitted to IEEE Trans. Signal Processin
Full-duplex MU-MIMO systems under the effects of non-ideal transceivers: performance analysis and power allocation optimization
Modern Technologies, particularly connectivity, increasingly support many facets of everyday life. The next generation of wireless communication systems aims to provide new
advanced services and support new demands. These services are required to serve a massive number of devices and achieve higher spectral and energy efficiency, ultra-low latency,
and reliable communication. The research community around the globe is still working on
finding novel technologies to meet these requirements. Full duplex (FD) communications
have been recognized as one of the promising wireless transmission candidates and gamechangers for the future of wireless communication and networking technologies, thanks to
their ability to greatly improve spectral efficiency (SE) and dramatically enhance energy
efficiency (EE). In this thesis, first, the influence of hardware impairment (HWI) on singleinput single-output (SISO) FD access point (AP) is studied. More precisely, the SE and
EE when the systemâs terminals have impaired transceivers are analyzed. Optimization
problem for EE maximization is formulated to fulfill quality of service (QoS) and power
budget constraints. An algorithm to solve the optimization problem by using the fractional
programming theory and KarushâKuhnâTucker (KKT) conditions technique is proposed. [...
Advanced Signal Processing Techniques for Two-Way Relaying Networks and Full-Duplex Communication Systems
ï»żSehr hohe Datenraten und stĂ€ndig verfĂŒgbare Netzabdeckung in
zukĂŒnftigen drahtlosen Netzwerken erfordern neue Algorithmen auf der
physischen Schicht. Die Nutzung von Relais stellt ein vielversprechendes
Verfahren dar, da die Netzabdeckung gesteigert werden kann. ZusÀtzlich
steht hierdurch im Vergleich zu Kupfer- oder Glasfaserleitungen eine
preiswerte Lösung zur Anbindung an die Netzinfrastruktur zur VerfĂŒgung.
Traditionelle Einwege-Relais-Techniken (One-Way Relaying [OWR]) nutzen
Halbduplex-Verfahren (HD-Verfahren), welche das Ăbertragungssystem
ausbremst und zu spektralen Verlusten fĂŒhrt. Einerseits erlauben es
Zweiwege-Relais-Techniken (Two-Way Relaying [TWR]), simultan sowohl an das
Relais zu senden als auch von diesem zu empfangen, wodurch im Vergleich zu
OWR das Spektrum effizienter genutzt wird. Aus diesem Grunde untersuchen
wir Zweiwege-Relais und im Speziellen TWR-Systeme fĂŒr den
Mehrpaar-/Mehrnutzer-Betrieb unter Nutzung von Amplify-and-forward-Relais
(AF-Relais). Derartige Szenarien leiden unter Interferenzen zwischen Paaren
bzw. zwischen Nutzern. Um diesen Interferenzen Herr zu werden, werden
hochentwickelte Signalverarbeitungsalgorithmen â oder in anderen Worten
rÀumliche Mehrfachzugriffsverfahren (Spatial Division Multiple Access
[SDMA]) â benötigt. Andererseits kann der spektrale Verlust durch den
HD-Betrieb auch kompensiert werden, wenn das Relais im Vollduplexbetrieb
arbeitet. Nichtsdestotrotz ist ein FD-GerÀt in der Praxis aufgrund starker
interner Selbstinterferenz (SI) und begrenztem Dynamikumfang des
Tranceivers schwer zu realisieren. Aus diesem Grunde sollten
fortschrittliche Verfahren zur SI-ĂnterdrĂŒckung entwickelt werden. Diese
Dissertation trÀgt diesen beiden Zielen Rechnung, indem optimale und/oder
effiziente algebraische Lösungen entwickelt werden, welche verschiedenen
Nutzenfunktionen, wie Summenrate und minimale Sendeleistung, maximieren.Im
ersten Teil studieren wir zunÀchst Mehrpaar-TWR-Netzwerke mit einem
einzelnen Mehrantennen-AF-Relais. Dieser Anwendungsfall kann auch so
betrachtet werden, dass sich mehrere verschiedene Dienstoperatoren Relais
und Spektrum teilen, wobei verschiedene Nutzerpaare zu verschiedenen
Dienstoperatoren gehören. Aktuelle AnsÀtzen zielen auf
InterferenzunterdrĂŒckung ab. Wir schlagen ein auf Projektion basiertes
Verfahren zur Trennung mehrerer Dienstoperatoren (projection based
separation of multiple operators [ProBaSeMO]) vor. ProBaSeMO ist leicht
anpassbar fĂŒr den Fall, dass jeder Nutzer mehrere Antennen besitzt oder
unterschiedliche Systemdesignkriterien angewendet werden mĂŒssen. Als
BewertungsmaĂstab fĂŒr ProBaSeMO entwickeln wir optimale Algorithmen zur
Maximierung der Summenrate, zur Minimierung der Sendeleistung am Relais
oder zur Maximierung des minimalen
Signal-zu-Interferenz-und-Rausch-VerhÀltnisses (Signal to Interference and
Noise Ratio [SINR]) am Nutzer. Zur Maximierung der Summenrate wurden
spezifische gradientenbasierte Methoden entwickelt, die unabhÀngig davon
sind, ob ein Nutzer mit einer oder mehr Antennen ausgestattet ist. Um im
Falle eines âWorst-Caseâ immer noch eine polynomielle Laufzeit zu
garantieren, entwickelten wir einen Algorithmus mit polynomieller Laufzeit.
Dieser ist inspiriert von der âPolynomial Time Difference of Convex
Functionsâ-Methode (POTDC-Methode). BezĂŒglich der Summenrate des Systems
untersuchen wir zuletzt, welche Bedingungen erfĂŒllt sein mĂŒssen, um einen
Gewinn durch gemeinsames Nutzen zu erhalten. Hiernach untersuchen wir die
Maximierung der Summenrate eines Mehrpaar-TWR-Netzwerkes mit mehreren
Einantennen-AF-Relais und Einantennen-Nutzern. Das daraus resultierende
Problem der Summenraten-Maximierung, gebunden an eine bestimmte
Gesamtsendeleistung aller Relais im Netzwerk, ist Àhnlich dem des
vorangegangenen Szenarios. Dementsprechend kann eine optimale Lösung fĂŒr
das eine Szenario auch fĂŒr das jeweils andere Szenario genutzt werden.
Weiterhin werden basierend auf dem Polynomialzeitalgorithmus global
optimale Lösungen entwickelt. Diese Lösungen sind entweder an eine
maximale Gesamtsendeleistung aller Relais oder an eine maximale
Sendeleistung jedes einzelnen Relais gebunden. ZusÀtzlich entwickeln wir
suboptimale Lösungen, die effizient in ihrer Laufzeit sind und eine
Approximation der optimalen Lösung darstellen. Hiernach verlegen wir unser
Augenmerk auf ein Mehrpaar-TWR-Netzwerk mit mehreren Mehrantennen-AF-Relais
und mehreren Repeatern. Solch ein Szenario ist allgemeiner, da die
vorherigen beiden Szenarien als spezielle Realisierungen dieses Szenarios
aufgefasst werden können. Das Interferenz-Management in diesem Szenario
ist herausfordernder aufgrund der vorhandenen Repeater.
Interferenzneutralisierung (IN) stellt eine Lösung dar, um diese Art
Interferenz zu handhaben. Im Zuge dessen werden notwendige und ausreichende
Bedingungen zur Aufhebung der Interferenz hergeleitet. Weiterhin wird ein
Framework entwickelt, dass verschiedene Systemnutzenfunktionen optimiert,
wobei IN im jeweiligen Netzwerk vorhanden sein kann oder auch nicht. Dies
ist unabhÀngig davon, ob die Relais einer maximalen Gesamtsendeleistung
oder einer individuellen maximalen Sendeleistung unterliegen. Letztendlich
entwickeln wir ein Ăbertragungsverfahren sowie ein Vorkodier- und
Dekodierverfahren fĂŒr Basisstationen (BS) in einem TWR-assistierten
Mehrbenutzer-MIMO-Downlink-Kanal. Im Vergleich mit dem
Mehrpaar-TWR-Netzwerk leidet dieses Szenario unter Interferenzen zwischen
den KanÀlen. Wir entwickeln drei suboptimale Algorithmen, welche auf
Kanalinversion basieren. ProBaSeMO und âZero-Forcing Dirty Paper
Codingâ (ZFDPC), welche eine geringe ZeitkomplexitĂ€t aufweisen, schaffen
eine Balance zwischen LeistungsfÀhigkeit und KomplexitÀt. ZusÀtzlich
gibt es jeweils nur geringe EinbrĂŒche in stark beanspruchten
Kommunikationssystemen.Im zweiten Teil untersuchen wir Techniken zur
SI-UnterdrĂŒckung, um den FD-Gewinn in einem Punkt-zu-Punkt-System
auszunutzen. ZunĂ€chst entwickeln wir ein Ăbertragungsverfahren, dass auf
SI RĂŒcksicht nimmt und die SI-UnterdrĂŒckung gegen den Multiplexgewinn
abwÀgt. Die besten Ergebnisse werden durch die perfekte Kenntnis des
Kanals erzielt, was praktisch nicht genau der Fall ist. Aus diesem Grund
werden Ăbertragungstechniken fĂŒr den âWorst Caseâ entwickelt, die den
KanalschÀtzfehlern Rechnung tragen. Diese Fehler werden deterministisch
modelliert und durch Ellipsoide beschrÀnkt. In praktischen Szenarien ist
der HF-Schaltkreise nicht perfekt. Dies hat Einfluss auf die Verfahren zur
SI-UnterdrĂŒckung und fĂŒhrt zu einer Restselbstinterferenz. Wir entwickeln
effiziente Ăbertragungstechniken mittels Beamforming, welche auf dem
Signal-zu-Verlust-und-Rausch-VerhÀltnis (signal to leakage plus noise
ratio [SLNR]) aufbauen, um Unvollkommenheiten der HF-Schaltkreise
auszugleichen. ZusÀtzlich können alle Designkonzepte auf FD-OWR-Systeme
erweitert werden.To enable ultra-high data rate and ubiquitous coverage in future wireless
networks, new physical layer techniques are desired. Relaying is a
promising technique for future wireless networks since it can boost the
coverage and can provide low cost wireless backhauling solutions, as
compared to traditional wired backhauling solutions via fiber and copper.
Traditional one-way relaying (OWR) techniques suffer from the spectral loss
due to the half-duplex (HD) operation at the relay. On one hand, two-way
relaying (TWR) allows the communication partners to transmit to and/or
receive from the relay simultaneously and thus uses the spectrum more
efficiently than OWR. Therefore, we study two-way relays and more
specifically multi-pair/multi-user TWR systems with amplify-and-forward
(AF) relays. These scenarios suffer from inter-pair or inter-user
interference. To deal with the interference, advanced signal processing
algorithms, in other words, spatial division multiple access (SDMA)
techniques, are desired. On the other hand, if the relay is a full-duplex
(FD) relay, the spectral loss due to a HD operation can also be
compensated. However, in practice, a FD device is hard to realize due to
the strong loop-back self-interference and the limited dynamic range at the
transceiver. Thus, advanced self-interference suppression techniques should
be developed. This thesis contributes to the two goals by developing
optimal and/or efficient algebraic solutions for different scenarios
subject to different utility functions of the system, e.g., sum rate
maximization and transmit power minimization. In the first part of this
thesis, we first study a multi-pair TWR network with a multi-antenna AF
relay. This scenario can be also treated as the sharing of the relay and
the spectrum among multiple operators assuming that different pairs of
users belong to different operators. Existing approaches focus on
interference suppression. We propose a projection based separation of
multiple operators (ProBaSeMO) scheme, which can be easily extended when
each user has multiple antennas or when different system design criteria
are applied. To benchmark the ProBaSeMO scheme, we develop optimal relay
transmit strategies to maximize the system sum rate, minimize the required
transmit power at the relay, or maximize the minimum signal to interference
plus noise ratio (SINR) of the users. Specifically for the sum rate
maximization problem, gradient based methods are developed regardless
whether each user has a single antenna or multiple antennas. To guarantee a
worst-case polynomial time solution, we also develop a polynomial time
algorithm which has been inspired by the polynomial time difference of
convex functions (POTDC) method. Finally, we analyze the conditions for
obtaining the sharing gain in terms of the sum rate. Then we study the sum
rate maximization problem of a multi-pair TWR network with multiple single
antenna AF relays and single antenna users. The resulting sum rate
maximization problem, subject to a total transmit power constraint of the
relays in the network, yields a similar problem structure as in the
previous scenario. Therefore the optimal solution for one scenario can be
used for the other. Moreover, a global optimal solution, which is based on
the polyblock approach, and several suboptimal solutions, which are more
computationally efficient and approximate the optimal solution, are
developed when there is a total transmit power constraint of the relays in
the network or each relay has its own transmit power constraint. We then
shift our focus to a multi-pair TWR network with multiple multi-antenna AF
relays and multiple dumb repeaters. This scenario is more general because
the previous two scenarios can be seen as special realizations of this
scenario. The interference management in this scenario is more challenging
due to the existence of the repeaters. Interference neutralization (IN) is
a solution for dealing with this kind of interference. Thereby, necessary
and sufficient conditions for neutralizing the interference are derived.
Moreover, a general framework to optimize different system utility
functions in this network with or without IN is developed regardless
whether the AF relays in the network have a total transmit power limit or
individual transmit power limits. Finally, we develop the relay transmit
strategy as well as base station (BS) precoding and decoding schemes for a
TWR assisted multi-user MIMO (MU-MIMO) downlink channel. Compared to the
multi-pair TWR network, this scenario suffers from the co-channel
interference. We develop three suboptimal algorithms which are based on
channel inversion, ProBaSeMO and zero-forcing dirty paper coding (ZFDPC),
which has a low computational complexity, provides a balance between the
performance and the complexity, and suffers only a little when the system
is heavily loaded, respectively.In the second part of this thesis, we
investigate self-interference (SI) suppression techniques to exploit the FD
gain for a point-to-point MIMO system. We first develop SI aware transmit
strategies, which provide a balance between the SI suppression and the
multiplexing gain of the system. To get the best performance, perfect
channel state information (CSI) is needed, which is imperfect in practice.
Thus, worst case transmit strategies to combat the imperfect CSI are
developed, where the CSI errors are modeled deterministically and bounded
by ellipsoids. In real word applications, the RF chain is imperfect. This
affects the performance of the SI suppression techniques and thus results
in residual SI. We develop efficient transmit beamforming techniques, which
are based on the signal to leakage plus noise ratio (SLNR) criterion, to
deal with the imperfections in the RF chain. All the proposed design
concepts can be extended to FD OWR systems
Future cellular systems: fundamentals and the role of large antenna arrays
In this thesis, we analyze the performance of three promising technologies being
considered for future fifth generation (5G) and beyond wireless communication systems,
with primary goals to: i) render 10-100 times higher user data rate, ii) serve 10-100
times more users simultaneously, iii) 1000 times more data volume per unit area, iv)
improve energy efficiency on the order of 100 times, and iv) provide higher bandwidths.
Accordingly, we focus on massive multiple-input multiple-output (MIMO) systems and
other future wireless technologies, namely millimeter wave (mmWave) and full-duplex
(FD) systems that are being considered to fulfill the above requirements.
We begin by focusing on fundamental performance limits of massive MIMO systems
under practical constraints such as low complexity processing, array size and limited
physical space. First, we analyze the performance of a massive MIMO base station
(BS) serving spatially distributed multi-antenna users within a fixed coverage area.
Stochastic geometry is used to characterize the spatially distributed users while large
dimensional random matrix theory is used to achieve deterministic approximations of
the sum rate of the system. We then examine the deployment of a massive MIMO
BS and the resulting energy efficiency (EE) by considering a more realistic set-up of a
rectangular array with increasing antenna elements within a fixed physical space. The
effects of mutual coupling and correlation among the BS antennas are incorporated
by deriving a practical mutual coupling matrix which considers coupling among all
antenna elements within the BS. Accordingly, the optimum number of antennas that
can be deployed for a particular antenna spacing when EE is considered as a design
criteria is derived. Also, it is found that mutual coupling effect reduces the EE of the
massive system by around 40-45% depending on the precoder/receiver used and the
physical space available for antenna deployment.
After establishing the constraints of antenna spacing on massive MIMO systems
for the current microwave spectrum, we shift our focus to mmWave frequencies (more
than 100GHz available bandwidth), where the wavelength is very small and as a result
more antennas can be rigged within a constrained space. Accordingly, we integrate
the massive MIMO technology with mmWave networks. In particular, we analyze the
performance of a mmWave network consisting of spatially distributed BS equipped with
very large uniform circular arrays (UCA) serving spatially distributed users within a
fixed coverage area. The use of UCA is due to its capability of scanning through both
the azimuth as well as elevation dimensions. We show that using such 3D massive
MIMO techniques in mmWave systems yield significant performance gains. Further,
we show the effect of blockages and path loss on mmWave networks. Since blockages are
found to be quite detrimental to mmWave networks, we create alternative propagation
paths with the aid of relays. In particular, we consider the deployment of relays in
outdoor mmWave networks and then derive expressions for the coverage probability
and transmission capacity from sources to a destination for such relay aided mmWave
networks using stochastic geometric tools. Overall, relay aided mmWave transmission
is seen to improve the signal to noise ratio at the destination by around 5-10dB with
respect to specific coverage probabilities.
Finally, due to the fact that the current half duplex (HD) mode transmission only
utilizes half the spectrum at the same time in the same frequency, we consider a multiuser
MIMO cellular system, where a FD BS serves multiple HD users simultaneously.
However, since FD systems are plagued by severe self-interference (SI), we focus on the
design of robust transceivers, which can cancel the residual SI left after antenna and
analog cancellations. In particular, we address the sum mean-squared-errors (MSE)
minimization problem by transforming it into an equivalent semidefinite programming
(SDP) problem. We propose iterative alternating algorithms to design the transceiver
matrices jointly and accordingly show the gains of FD over HD systems. We show that
with proper SI cancellation, it is possible to achieve gains on sum rate of up to 70-80%
over HD systems
Analysis of quantized MRC-MRT precoder for FDD massive MIMO two-way AF relaying
The maturing massive multiple-input multiple-output (MIMO) literature has provided asymptotic limits for the rate and energy efficiency (EE) of maximal ratio combining/maximal ratio transmission (MRC-MRT) relaying on two-way relays (TWR) using the amplify-and-forward (AF) principle. Most of these studies consider time division duplexing, and a fixed number of users. To fill the gap in the literature, we analyze the MRC-MRT precoder performance of a N -antenna AF massive MIMO TWR, which operates in frequency division duplex mode to enable two-way communication between 2M = âN α â single-antenna users, with α â [0, 1), divided equally in two groups of M users. We assume that the relay has realistic imperfect uplink channel state information (CSI), and that quantized downlink CSI is fed back by the users relying on B â„ 1 bits per-user per relay antenna. We prove that for such a system with α â [0, 1), the MRC-MRT precoder asymptotically cancels the multi-user interference (MUI) when the supremum and infimum of large scale fading parameters is strictly non-zero and finite, respectively. Furthermore, its per-user pairwise error probability (PEP) converges to that of an equivalent AWGN channel as both N and the number of users 2M = âN α â tend to infinity, with a relay power scaling of Pr = 2M Er and Er being a constant. N We also derive upper bounds for both the per-user rate and EE. We analytically show that the quantized MRC-MRT precoder requires as few as B = 2 bits to yield a BER, EE, and per-user rate close to the respective unquantized counterparts. Finally, we show that the analysis developed herein to derive a bound on α for MUI cancellation is applicable both to Gaussian as well as to any arbitrary non-Gaussian complex channels