11 research outputs found
Robust transmit beamforming design using outage probability specification
Transmit beamforming (precoding) is a powerful technique for enhancing the channel capacity
and reliability of multiple-input and multiple-output (MIMO) wireless systems. The optimum
exploitation of the benefits provided by MIMO systems can be achieved when a perfect channel
state information at transmitter (CSIT) is available. In practices, however, the channel knowledge
is generally imperfect at transmitter because of the inevitable errors induced by finite
feedback channel capacity, quantization and other physical constraints. Such errors degrade the
system performance severely. Hence, robustness has become a crucial issue.
Current robust designs address the channel imperfections with the worst-case and stochastic approaches.
In worst-case analysis, the channel uncertainties are considered as deterministic and
norm-bounded, and the resulting design is a conservative optimization that guarantees a certain
quality of service (QoS) for every allowable perturbation. The latter approach focuses on the
average performance under the assumption of channel statistics, such as mean and covariance.
The system performance could break down when persistent extreme errors occur. Thus, an
outage probability-based approach is developed by keeping a low probability that channel condition
falls below an acceptable level. Compared to the aforementioned methods, this approach
can optimize the average performance as well as consider the extreme scenarios proportionally.
This thesis implements the outage-probability specification into transmit beamforming design
for three scenarios: the single-user MIMO system and the corresponding adaptive modulation
scheme as well as the multi-user MIMO system. In a single-user MIMO system, the transmit
beamformer provides the maximum average received SNR and ensures the robustness to the
CSIT errors by introducing probabilistic constraint on the instantaneous SNR. Beside the robustness
against channel imperfections, the outage probability-based approach also provides a
tight BER bound for adaptive modulation scheme, so that the maximum transmission rate can
be achieved by taking advantage of transmit beamforming. Moreover, in multi-user MIMO
(MU-MIMO) systems, the leakage power is accounted by probability measurement. The resulting
transmit beamformer is designed based on signal-to-leakage-plus-noise ratio (SLNR)
criteria, which maximizes the average received SNR and guarantees the least leakage energy
from the desired user. In such a setting, an outstanding BER performance can be achieved as
well as high reliability of signal-to-interference-plus-noise ratio (SINR).
Given the superior overall performances and significantly improved robustness, the probabilistic
approach provides an attractive alternative to existing robust techniques under imperfect
channel information at transmitter
Design and Analysis of Medium Access Control Protocols for Broadband Wireless Networks
The next-generation wireless networks are expected to integrate diverse network architectures and various wireless access technologies to provide a robust solution for ubiquitous broadband wireless access, such as wireless local area networks (WLANs), Ultra-Wideband (UWB), and millimeter-wave (mmWave) based wireless personal area networks (WPANs), etc. To enhance the spectral efficiency and link reliability, smart antenna systems have been proposed as a promising candidate for future broadband access networks. To effectively exploit the increased capabilities of the emerging wireless networks, the different network characteristics and the underlying physical layer features need to be considered in the medium access control (MAC) design, which plays a critical role in providing efficient and fair resource sharing among multiple users.
In this thesis, we comprehensively investigate the MAC design in both single- and multi-hop broadband wireless networks, with and without infrastructure support. We first develop mathematical models to identify the performance bottlenecks and constraints in the design and operation of existing MAC. We then use a cross-layer approach to mitigate the identified bottleneck problems. Finally, by evaluating the performance of the proposed protocols with analytical models and extensive simulations, we determine the optimal protocol parameters to maximize the network performance.
In specific, a generic analytical framework is developed for capacity study of an IEEE 802.11 WLAN in support of non-persistent asymmetric traffic flows. The analysis can be applied for effective admission control to guarantee the quality of service (QoS) performance of multimedia applications. As the access point (AP) becomes the bottleneck in an infrastructure based WLAN, we explore the multiple-input multiple-output (MIMO) capability in the future IEEE 802.11n WLANs and propose a MIMO-aware multi-user (MU) MAC. By exploiting the multi-user degree of freedom in a MIMO system to allow the AP to communicate with multiple users in the downlink simultaneously, the proposed MU MAC can minimize the AP-bottleneck effect and significantly improve the network capacity. Other enhanced MAC mechanisms, e.g., frame aggregation and bidirectional transmissions, are also studied.
Furthermore, different from a narrowband system where simultaneous transmissions by nearby neighbors collide with each other, wideband system can support multiple concurrent transmissions if the multi-user interference can be properly managed. Taking advantage of the salient features of UWB and mmWave communications, we propose an exclusive region (ER) based MAC protocol to exploit the spatial multiplexing gain of centralized UWB and mmWave based wireless networks. Moreover, instead of studying the asymptotic capacity bounds of arbitrary networks which may be too loose to be useful in realistic networks, we derive the expected capacity or transport capacity of UWB and mmWave based networks with random topology. The analysis reveals the main factors affecting the network (transport) capacity, and how to determine the best protocol parameters to maximize the network capacity. In addition, due to limited transmission range, multi-hop relay is necessary to extend the communication coverage of UWB networks. A simple, scalable, and distributed UWB MAC protocol is crucial for efficiently utilizing the large bandwidth of UWB channels and enabling numerous new applications cost-effectively. To address this issue, we further design a distributed asynchronous ER based MAC for multi-hop UWB networks and derive the optimal ER size towards the maximum network throughput. The proposed MAC can significantly improve both network throughput and fairness performance, while the throughput and fairness are usually treated as a tradeoff in other MAC protocols
Energy-aware resource allocation in next generation wireless networks : application in large-scale MIMO Systems
In this thesis, we investigate the resource allocation problem for wireless networks that incorporate large-scale multiple-input multiple-output (MIMO) systems. These systems are considered as key technologies for future 5G wireless networks and are based on using few hundreds of antennas simultaneously to serve tens of users in the same time-frequency resource. The gains obtained by large-scale MIMO systems cannot be fully exploited without adequate resource allocation strategies. Hence, the aim of this thesis is to develop energy-aware resource allocation solutions for large-scale MIMO systems that take into consideration network power cost.
Firstly, this thesis investigates the downlink of a base station equipped with large-scale MIMO system while taking into account a non-negligible transmit circuit power consumption. This consumption involves that activating all RF chains does not always necessarily achieve the maximum sum-rate. Thus, we derive the optimal number of activated RF chains. In addition, efficient antenna selection, user scheduling and power allocation algorithms in term of instantaneous sum-rate are proposed and compared. Also, fairness is investigated by considering equal receive power among users.
Secondly, this thesis investigates a large-scale MIMO system that incorporates energy harvesting that is a promising key technology for greening future wireless networks since it reduces network operation costs and carbon footprints. Hence, we consider distributed large-scale MIMO systems made up of a set of remote radio heads (RRHs), each of which is powered by both an independent energy harvesting source and the grid. The grid energy source allows to compensate for the randomness and intermittency of the harvested energy. Optimal on-line and off-line energy management strategies are developed. In addition, on-line energy management algorithm based on energy prediction is devised. The feasibility problem is addressed by proposing an efficient link removal algorithm and for better energy efficiency, RRH on/off operation is investigated.
Thirdly, wireless backhauling was proposed as an alternative solution that enable low-cost connection between the small base stations and the macro base station in heterogeneous networks (HetNets). The coexistence of massive MIMO, HetNets and wireless backhauling is a promising research direction since massive MIMO is a suitable solution to enable wireless backhauling. Thus, we propose a new transmission technique that is able to efficiently manage the interference in heterogeneous networks with massive MIMO wireless backhaul. The optimal time splitting parameter and the allocated transmit power are derived. The proposed transmission technique is shown to be more efficient in terms of transmit power consumption than the conventional reverse time division duplex with bandwidth splitting.
In this thesis, we developed efficient resource allocation solutions related to system power for wireless networks that incorporate large-scale MIMO systems under different assumptions and network architectures. The results in this thesis can be expanded by investigating the research problems given at the end of the dissertation
Advanced Signal Processing Techniques for Two-Way Relaying Networks and Full-Duplex Communication Systems
Sehr hohe Datenraten und ständig verfügbare Netzabdeckung in
zukünftigen drahtlosen Netzwerken erfordern neue Algorithmen auf der
physischen Schicht. Die Nutzung von Relais stellt ein vielversprechendes
Verfahren dar, da die Netzabdeckung gesteigert werden kann. Zusätzlich
steht hierdurch im Vergleich zu Kupfer- oder Glasfaserleitungen eine
preiswerte Lösung zur Anbindung an die Netzinfrastruktur zur Verfügung.
Traditionelle Einwege-Relais-Techniken (One-Way Relaying [OWR]) nutzen
Halbduplex-Verfahren (HD-Verfahren), welche das Übertragungssystem
ausbremst und zu spektralen Verlusten führt. 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 für 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 – oder in anderen Worten
räumliche Mehrfachzugriffsverfahren (Spatial Division Multiple Access
[SDMA]) – benötigt. Andererseits kann der spektrale Verlust durch den
HD-Betrieb auch kompensiert werden, wenn das Relais im Vollduplexbetrieb
arbeitet. Nichtsdestotrotz ist ein FD-Gerät in der Praxis aufgrund starker
interner Selbstinterferenz (SI) und begrenztem Dynamikumfang des
Tranceivers schwer zu realisieren. Aus diesem Grunde sollten
fortschrittliche Verfahren zur SI-Ünterdrückung entwickelt werden. Diese
Dissertation trägt 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 zunächst 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 Ansätzen zielen auf
Interferenzunterdrückung ab. Wir schlagen ein auf Projektion basiertes
Verfahren zur Trennung mehrerer Dienstoperatoren (projection based
separation of multiple operators [ProBaSeMO]) vor. ProBaSeMO ist leicht
anpassbar für den Fall, dass jeder Nutzer mehrere Antennen besitzt oder
unterschiedliche Systemdesignkriterien angewendet werden müssen. Als
Bewertungsmaßstab für 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-Verhältnisses (Signal to Interference and
Noise Ratio [SINR]) am Nutzer. Zur Maximierung der Summenrate wurden
spezifische gradientenbasierte Methoden entwickelt, die unabhängig davon
sind, ob ein Nutzer mit einer oder mehr Antennen ausgestattet ist. Um im
Falle eines „Worst-Case“ immer noch eine polynomielle Laufzeit zu
garantieren, entwickelten wir einen Algorithmus mit polynomieller Laufzeit.
Dieser ist inspiriert von der „Polynomial Time Difference of Convex
Functions“-Methode (POTDC-Methode). Bezüglich der Summenrate des Systems
untersuchen wir zuletzt, welche Bedingungen erfüllt sein müssen, 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 ähnlich dem des
vorangegangenen Szenarios. Dementsprechend kann eine optimale Lösung für
das eine Szenario auch für 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. Zusätzlich 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 unabhängig davon, ob die Relais einer maximalen Gesamtsendeleistung
oder einer individuellen maximalen Sendeleistung unterliegen. Letztendlich
entwickeln wir ein Übertragungsverfahren sowie ein Vorkodier- und
Dekodierverfahren für Basisstationen (BS) in einem TWR-assistierten
Mehrbenutzer-MIMO-Downlink-Kanal. Im Vergleich mit dem
Mehrpaar-TWR-Netzwerk leidet dieses Szenario unter Interferenzen zwischen
den Kanälen. Wir entwickeln drei suboptimale Algorithmen, welche auf
Kanalinversion basieren. ProBaSeMO und „Zero-Forcing Dirty Paper
Coding“ (ZFDPC), welche eine geringe Zeitkomplexität aufweisen, schaffen
eine Balance zwischen Leistungsfähigkeit und Komplexität. Zusätzlich
gibt es jeweils nur geringe Einbrüche in stark beanspruchten
Kommunikationssystemen.Im zweiten Teil untersuchen wir Techniken zur
SI-Unterdrückung, um den FD-Gewinn in einem Punkt-zu-Punkt-System
auszunutzen. Zunächst entwickeln wir ein Übertragungsverfahren, dass auf
SI Rücksicht nimmt und die SI-Unterdrückung gegen den Multiplexgewinn
abwägt. Die besten Ergebnisse werden durch die perfekte Kenntnis des
Kanals erzielt, was praktisch nicht genau der Fall ist. Aus diesem Grund
werden Übertragungstechniken für den „Worst Case“ entwickelt, die den
Kanalschätzfehlern Rechnung tragen. Diese Fehler werden deterministisch
modelliert und durch Ellipsoide beschränkt. In praktischen Szenarien ist
der HF-Schaltkreise nicht perfekt. Dies hat Einfluss auf die Verfahren zur
SI-Unterdrückung und führt zu einer Restselbstinterferenz. Wir entwickeln
effiziente Übertragungstechniken mittels Beamforming, welche auf dem
Signal-zu-Verlust-und-Rausch-Verhältnis (signal to leakage plus noise
ratio [SLNR]) aufbauen, um Unvollkommenheiten der HF-Schaltkreise
auszugleichen. Zusätzlich 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
Alocação de recursos para sistemas móveis multi-utilizador e multi-antena
Doutoramento em Engenharia ElectrotécnicaThe thesis addresses the sum rate or spectral e ciency maximization problem
in cellular systems with two main components, multiple antennas and
multiple users. In order to solve such a problem, several resource allocation
techniques are studied and developed for di erent cellular scenarios. The
antennas at the transmitters are arranged in several con gurations, i.e.,
co-located or distributed and for such arrangements di erent levels of coordination
and cooperation between transmitters are investigated. Accounting
for more receiver antennas than transmitter antennas implies that system
optimization must select the best transmitter-receiver match (combinatorial
problem) which can be solved with di erent degrees of cooperation between
transmitters. The system models studied can be classi ed either as interference
limited or as power limited systems.
In interference limited systems the resource allocation is carried out independently
by each transmitter which yield power leakage to unintended
receivers. For this kind of systems, the access network using distributed
antenna architectures is examined. The properties of distributed antenna
in cellular systems as well as the gains they provide in terms of frequency
reuse and throughput are assessed. Accounting for multiple user scenarios,
several techniques and algorithms for transmitter-receiver assignment,
power allocation, and rate allocation are developed in order to maximize
the spectral e ciency.
In power limited systems the transmitters jointly allocate resources among
transmit and receive antennas. The transmitters are equipped with multiple
antennas and signal processing is implemented in order to suppress inter-user
interference. Single-cell and multi-cell systems are studied and the problem
of sum rate maximization is tackled by decoupling the user selection and
the resource allocation (power and precoding) processes. The user selection
is a function of the type of precoding technique that is implemented
and the level of information that can be processed at the transmitter. The
developed user selection algorithms exploit information provided by novel
channel metrics which establish the spatial compatibility between users.
Each metric provides a di erent trade-o between the accuracy to identify
compatible users, and the complexity required to compute it. Numerical
simulations are used to assess the performance of the proposed user selection
techniques (metrics and algorithms) whose performance are compared
to state-of-the-art techniques.Esta tese descreve o problema da maximização da taxa de transmissão ou
e ciência espectral em sistemas moveis tomando em atenção duas características fundamentais destes, o número de antenas e utilizadores.
A fim de resolver este tipo de problema, várias técnicas de alocação de recursos
foram estudadas e propostas para diferentes cenários. As antenas nos transmissores
estão organizadas em diferentes configurações, podendo ser localizadas
ou distribuídas e para estes esquemas, diferentes níveis de cooperação
e coordenação entre transmissores foram investigados. Assumindo mais antenas
receptoras do que antenas transmissoras, implica que a otimização do
sistema seleccione as melhores combinações de transmissor-receptor (problema
combinatório), o que pode ser concretizado usando diferentes graus
de cooperação entre transmissores. Os modelos de sistemas estudados, podem
ser classificados como sistemas limitados por interferência ou sistemas
limitados por potência.
Em sistemas limitados por interferência a alocação de recursos e feita independentemente
para cada transmissor o que resulta em perda de energia
para os receptores não tomados em consideração. Para este tipo de sistemas,
e considerado o caso em que a rede de acesso e constituída por antenas
distribuídas. Os ganhos obtidos devido ao uso de antenas distribuídas,
quer em termos do planeamento de frequências quer da maximização da taxa
de transmissão são considerados. Assumindo esquemas multi-utilizador,
várias técnicas e algoritmos de transmissão-recepção, alocação de potência
e de taxa de transmissão foram desenvolvidos para maximizar a e ciência
espectral.
Para sistemas limitados em potência os transmissores alocam os recursos
quer de antenas de transmissão quer de recepção conjuntamente. Os transmissores
estão equipados com várias antenas e o processamento de sinal e
implementado de modo a eliminar a interferência entre utilizadores. Sistemas
de célula única e de múltiplas células foram estudados. Para estes foi
considerado o problema da maximização de taxa de transmissão o qual foi
resolvido heuristicamente, através do desacoplamento do problema em duas
partes, uma onde se efectua a seleção de utilizadores e outra onde se considera
a alocação de recursos. A seleção de utilizadores e feita em função do
tipo de técnicas de pré-codificação implementadas e do nível de informação
que o transmissor possui. Os algoritmos de seleção de utilizadores desenvolvidos
verificam a compatibilidade espacial entre utilizadores, usando para
tal métricas propostas. Cada uma das métricas oferece um trade-off diferente
entre a precisão para identificar um utilizador compatível e a complexidade
necessária para a implementar. Foram usadas simulações numéricas
para avaliar a performance das técnicas de seleção de utilizadores propostas
(métricas e algoritmos), performance que foi comparada com as técnicas
mais inovadoras
Industrial Wireless Sensor Networks
Wireless sensor networks are penetrating our daily lives, and they are starting to be deployed even in an industrial environment. The research on such industrial wireless sensor networks (IWSNs) considers more stringent requirements of robustness, reliability, and timeliness in each network layer. This Special Issue presents the recent research result on industrial wireless sensor networks. Each paper in this Special Issue has unique contributions in the advancements of industrial wireless sensor network research and we expect each paper to promote the relevant research and the deployment of IWSNs
Modelling, Dimensioning and Optimization of 5G Communication Networks, Resources and Services
This reprint aims to collect state-of-the-art research contributions that address challenges in the emerging 5G networks design, dimensioning and optimization. Designing, dimensioning and optimization of communication networks resources and services have been an inseparable part of telecom network development. The latter must convey a large volume of traffic, providing service to traffic streams with highly differentiated requirements in terms of bit-rate and service time, required quality of service and quality of experience parameters. Such a communication infrastructure presents many important challenges, such as the study of necessary multi-layer cooperation, new protocols, performance evaluation of different network parts, low layer network design, network management and security issues, and new technologies in general, which will be discussed in this book
A throughput fair SLNR scheduling algorithm for hybrid Fi-Wi indoor downlink MU-MIMO
Indoor downlink communication contributes to a large part of the data traffic generated in today’s world. Enormous high data rate supporting devices are entering todays market. They demand for high rate wireless indoor coverage for their uninterrupted service. The main challenge lies in working with the existing wireless technologies while providing a future proof centralized optical fiber indoor backhaul for efficient indoor coverage. Fiber to the room paradigm is gaining a lot of attention in this regard. For supporting high data rates indoor, multiuser MIMO (MU-MIMO) is definitely a prominent choice. While quality of service serves as the most attractive feature that should be ensured among the mobile terminals (MTs). In this work we propose a throughput fair successive signal to leakage and noise ratio (SLNR) precoding algorithm for such a fiberwireless (Fi-Wi) MU-MIMO indoor. The network capacity and individual MT data rate for our proposed scheme are compared against the greedy SLNR scheme and a random selection based SLNR precoding scheme. The Jains fairness index value for our scheme is shown to achieve maximal fairness