Analytical characterization of inband and outband D2D Communications for network access

Mención Internacional en el título de doctorCooperative short-range communication schemes provide powerful tools to solve interference and resource shortage problems in wireless access networks. With such schemes, a mobile node with excellent cellular connectivity can momentarily accept to relay traffic for its neighbors experiencing poor radio conditions and use Device-to-Device (D2D) communications to accomplish the task. This thesis provides a novel and comprehensive analytical framework that allows evaluating the effects of D2D communications in access networks in terms of spectrum and energy efficiency. The analysis covers the cases in which D2D communications use the same bandwidth of legacy cellular users (in-band D2D) or a different one (out-band D2D) and leverages on the characterization of underlying queueing systems and protocols to capture the complex intertwining of short-range and legacy WiFi and cellular communications. The analysis also unveils how D2D affects the use and scope of other optimization techniques used for, e.g., interference coordination and fairness in resource distribution. Indeed, characterizing the performance of D2D-enabled wireless access networks plays an essential role in the optimization of system operation and, as a consequence, permits to assess the general applicability of D2D solutions. With such characterization, we were able to design several mechanisms that improve system capabilities. Specifically, we propose bandwidth resource management techniques for controlling interference when cellular users and D2D pairs share the same spectrum, we design advanced and energy-aware access selection mechanisms, we show how to adopt D2D communications in conjunction with interference coordination schemes to achieve high and fair throughputs, and we discuss on end-to-end fairness—beyond the use of access network resources—when D2D communications is adopted in C-RAN. The results reported in this thesis show that identifying performance bottlenecks is key to properly control network operation, and, interestingly, bottlenecks may not be represented just by wireless resources when end-to-end fairness is of concern.Programa Oficial de Doctorado en Ingeniería TelemáticaPresidente: Marco Ajmone Marsan.- Secretario: Miquel Payaró Llisterri.- Vocal: Omer Gurewit

Enabling Techniques Design for QoS Provision in Wireless Communications

Guaranteeing Quality of Service (QoS) has become a recognized feature in the design of wireless communications. In this thesis, the problem of QoS provision is addressed from different prospectives in several modern communication systems. In the first part of the thesis, a wireless communication system with the base station (BS) associated by multiple subscribers (SS) is considered, where different subscribers require different QoS. Using the cross-layer approach, the conventional single queue finite state Markov chain system model is extended to multiple queues\u27 scenario by combining the MAC layer queue status with the physical layer channel states, modeled by finite state Markov channel (FSMC). To provide the diverse QoS to different subscribers, a priority-based rate allocation (PRA) algorithm is proposed to allocate the physical layer transmission rate to the multiple medium access control (MAC) layer queues, where different queues are assigned with different priorities, leading to their different QoS performance and thus, the diverse QoS are guaranteed. Then, the subcarrier allocation in multi-user OFDM (MU-OFDM) systems is stuied, constrained by the MAC layer diverse QoS requirements. A two-step cross-layer dynamic subcarrier allocation algorithm is proposed where the MAC layer queue status is firstly modeled by a finite state Markov chain, using which MAC layer diverse QoS constraints are transformed to the corresponding minimum physical layer data rate of each user. Then, with the purpose of maximizing the system capacity, the physical layer OFDM subcarriers are allocated to the multiple users to satisfy their minimum data rate requirements, which is derived by the MAC layer queue status model. Finally, the problem of channel assignment in IEEE 802.11 wireless local area networks (WLAN) is investigated, oriented by users\u27 QoS requirements. The number of users in the IEEE 802.11 channels is first determined through the number of different channel impulse responses (CIR) estimated at physical layer. This information is involved thereafter in the proposed channel assignment algorithm, which aims at maximum system throughput, where we explore the partially overlapped IEEE 802.11 channels to provide additional frequency resources. Moreover, the users\u27 QoS requirements are set to trigger the channel assignment process, such that the system can constantly maintain the required QoS

On the Behavior of the Distributed Coordination Function of IEEE 802.11 with Multirate Capability under General Transmission Conditions

The aim of this paper is threefold. First, it presents a multi-dimensional Markovian state transition model characterizing the behavior of the IEEE 802.11 protocol at the Medium Access Control layer which accounts for packet transmission failures due to channel errors modeling both saturated and non-saturated traffic conditions. Second, it provides a throughput analysis of the IEEE 802.11 protocol at the data link layer in both saturated and non-saturated traffic conditions taking into account the impact of both the physical propagation channel and multirate transmission in Rayleigh fading environment. The general traffic model assumed is M/M/1/K. Finally, it shows that the behavior of the throughput in non-saturated traffic conditions is a linear combination of two system parameters; the payload size and the packet rates, $\lambda^{(s)}$, of each contending station. The validity interval of the proposed model is also derived. Simulation results closely match the theoretical derivations, confirming the effectiveness of the proposed models.Comment: Submitted to IEEE Transactions on Wireless Communications, October 21, 200

Cross-Layer Techniques for Efficient Medium Access in Wi-Fi Networks

IEEE 802.11 (Wi-Fi) wireless networks share the wireless medium using a Carrier Sense Multiple Access (CSMA) Medium Access Control (MAC) protocol. The MAC protocol is a central determiner of Wi-Fi networks’ efficiency–the fraction of the capacity available in the physical layer that Wi-Fi-equipped hosts can use in practice. The MAC protocol’s design is intended to allow senders to share the wireless medium fairly while still allowing high utilisation. This thesis develops techniques that allow Wi-Fi senders to send more data using fewer medium acquisitions, reducing the overhead of idle periods, and thus improving end-to-end goodput. Our techniques address the problems we identify with Wi-Fi’s status quo. Today’s commodity Linux Wi-Fi/IP software stack and Wi-Fi cards waste medium acquisitions as they fail to queue enough packets that would allow for effective sending of multiple frames per wireless medium acquisition. In addition, for bi-directional protocols such as TCP, TCP data and TCP ACKs contend for the wireless channel, wasting medium acquisitions (and thus capacity). Finally, the probing mechanism used for bit-rate adaptation in Wi-Fi networks increases channel acquisition overhead. We describe the design and implementation of Aggregate Aware Queueing (AAQ), a fair queueing discipline, that coordinates scheduling of frame transmission with the aggregation layer in the Wi-Fi stack, allowing more frames per channel acquisition. Furthermore, we describe Hierarchical Acknowledgments (HACK) and Transmission Control Protocol Acknowledgment Optimisation (TAO), techniques that reduce channel acquisitions for TCP flows, further improving goodput. Finally, we design and implement Aggregate Aware Rate Control (AARC), a bit-rate adaptation algorithm that reduces channel acquisition overheads incurred by the probing mechanism common in today’s commodity Wi-Fi systems. We implement our techniques on real Wi-Fi hardware to demonstrate their practicality, and measure their performance on real testbeds, using off-the-shelf commodity Wi-Fi hardware where possible, and software-defined radio hardware for those techniques that require modification of the Wi-Fi implementation unachievable on commodity hardware. The techniques described in this thesis offer up to 2x aggregate goodput improvement compared to the stock Linux Wi-Fi stack

MAP/PH/1 systems with group service: performance analysis under different admission strategies

2015 - 2016Recent advances in wireless communication networks led to possibility of multi-rate transmission of information. The queueing theory represents a valid tool to study how the performances of such communication systems can be improved, and to give proper solutions. Modeling a multi-rate transmission system, in terms of queueing theory, means that a particular discipline has to be considered: a group of requests from users can be processed simultaneously in parallel and processing of the whole group is supposed finished if processing of all individual requests belonging to this group is over. In order to model this typology of telecommunication systems, some particular assumption can be made on arrivals, which occur by a Markovian arrival process, and on service time and length of admission period, which are regulated by phase type distributions. Thus, in this thesis MAP/PH/1 queueing systems have been considered, with and without retrial to take into account all possible behaviours of the customers. The main goal of the research activity presented in this work is to introduce novel admission strategies for the described systems, in order to give a major contribute to the current performance analysys, in particular as regard the choice of the optimal length of admission period and optimal size of the groups. Dynamics of such systems are described by multidimensional Markov chains. Ergodicity condition for these Markov chains have been derived, stationary probability distribution of the states have been computed, formulas for the main performance measures of the system have been attained. Essential advantages of the proposed customer’s service disciplines have been numerically illustrated. [edited by author]I recenti progressi ottenuti per le reti di comunicazione wireless, permettono la trasmissione multi-frequenza delle informazioni. La teoria delle code rappresenta un valido strumento per studiare come le performance di tali sistemi di comunicazione possano essere migliorate, e individuare opportune soluzioni. In termini di teoria delle code, modellare un sistema di trasmissione multi-frequenza significa considerare una determinata disciplina: un gruppo di richieste da parte di utenti possono essere processate simultaneamente in parallelo, e il processo dell’intero gruppo risulta completato se tutte le richieste appartenenti a tale gruppo sono espletate. Al fine di modellare tale tipologia di sistemi di telecomunicazione, si possono definire particolari assunzioni sugli arrivi, determinati da processi di arrivo Markoviani, e sul tempo di servizio e lunghezza del periodo di ammissione, regolati da distribuzioni di tipo a fasi. Pertanto, in tale lavoro di tesi sono stati considerati sistemi a coda di tipo MAP/PH/1, con e senza retrial per considerare tutti i possibili comportamenti degli utenti. Il principale obiettivo dell’attivita` di ricerca presentata in tale lavoro `e introdurre nuove strategie di ammissione per i sistemi descritti, al fine di fornire un maggior contributo alle attuali analisi sulle performance, in particolare relativamente alla scelta della lunghezza ottimale del periodo di ammissione e la dimensione ottimale dei gruppi. Le dinamiche di tali sistemi sono descritte da catene di Markov multidimensionali. `E stata ricavata la condizione di ergodicit`a per tali catene di Markov, `e stata calcolata la distribuzione delle probabilita` stazionarie degli stati, e sono state ottenute le formule per le misure dei principali parametri prestazionali del sistema. I principali vantaggi delle discipline di servizio proposte sono state illustrate numericamente. [a cura dell'autore]XXIX n.s

Queueing Networks for Vertical Handover

PhDIt is widely expected that next-generation wireless communication systems will be heterogeneous, integrating a wide variety of wireless access networks. Of particular interest recently is a mix of cellular networks (GSM/GPRS and WCDMA) and wireless local area networks (WLANs) to provide complementary features in terms of coverage, capacity and mobility support. If cellular/ WLAN interworking is to be the basis for a heterogeneous network then the analysis of complex handover traffic rates in the system (especially vertical handover) is one of the most essential issues to be considered. This thesis describes the application of queueing-network theory to the modelling of this heterogeneous wireless overlay system. A network of queues (or queueing network) is a powerful mathematical tool in the performance evaluation of many large-scale engineering systems. It has been used in the modelling of hierarchically structured cellular wireless networks with much success, including queueing network modelling in the study of cellular/ WLAN interworking systems. In the process of queueing network modelling, obtaining the network topology of a system is usually the first step in the construction of a good model, but this topology analysis has never before been used in the handover traffic study in heterogeneous overlay wireless networks. In this thesis, a new topology scheme to facilitate the analysis of handover traffic is proposed. The structural similarity between hierarchical cellular structure and heterogeneous wireless overlay networks is also compared. By replacing the microcells with WLANs in a hierarchical structure, the interworking system is modelled as an open network of Erlang loss systems and with the new topology, the performance measures of blocking probabilities and dropping probabilities can be determined. Both homogeneous and non-homogeneous traffic have been considered, circuit switched and packet-switched. Example scenarios have been used to validate the models, the numerical results showing clear agreement with the known validation scenarios

Recent Advances in Wireless Communications and Networks

This book focuses on the current hottest issues from the lowest layers to the upper layers of wireless communication networks and provides "real-time" research progress on these issues. The authors have made every effort to systematically organize the information on these topics to make it easily accessible to readers of any level. This book also maintains the balance between current research results and their theoretical support. In this book, a variety of novel techniques in wireless communications and networks are investigated. The authors attempt to present these topics in detail. Insightful and reader-friendly descriptions are presented to nourish readers of any level, from practicing and knowledgeable communication engineers to beginning or professional researchers. All interested readers can easily find noteworthy materials in much greater detail than in previous publications and in the references cited in these chapters

Towards next generation WLANs: exploiting coordination and cooperation

Wireless Local Area Networks (WLANs) operating in the industrial, scientific and medical (ISM) radio bands have gained great popularity and increasing usage over the past few years. The corresponding MAC/PHY specification, the IEEE 802.11 standard, has also evolved to adapt to such development. However, as the number of WLAN mobile users increases, and as their needs evolve in the face of new applications, there is an ongoing need for the further evolution of the IEEE 802.11 standard. In this thesis we propose several MAC/PHY layer protocols and schemes that will provide more system throughput, lower packet delivery delay and lessen the power consumption of mobile devices. Our work investigates three approaches that lead to improved WLAN performance: 1) cross-layer design of the PHY and MAC layers for larger system throughput, 2) exploring the use of implicit coordination among clients to increase the efficiency of random media access, and 3) improved packets dispatching by the access points (APs) to preserve the battery of mobile devices. Each proposed solution is supported by theoretical proofs and extensively studied by simulations or experiments on testbeds