Trajectory-Aware Rate Adaptation for Flying Networks

Despite the trend towards ubiquitous wireless connectivity, there are scenarios where the communications infrastructure is damaged and wireless coverage is insufficient or does not exist, such as in natural disasters and temporary crowded events. Flying networks, composed of Unmanned Aerial Vehicles (UAV), have emerged as a flexible and cost-effective solution to provide on-demand wireless connectivity in these scenarios. UAVs have the capability to operate virtually everywhere, and the growing payload capacity makes them suitable platforms to carry wireless communications hardware. The state of the art in the field of flying networks is mainly focused on the optimal positioning of the flying nodes, while the wireless link parameters are configured with default values. On the other hand, current link adaptation algorithms are mainly targeting fixed or low mobility scenarios. We propose a novel rate adaptation approach for flying networks, named Trajectory Aware Rate Adaptation (TARA), which leverages the knowledge of flying nodes' movement to predict future channel conditions and perform rate adaptation accordingly. Simulation results of 100 different trajectories show that our solution increases throughput by up to 53% and achieves an average improvement of 14%, when compared with conventional rate adaptation algorithms such as Minstrel-HT

Holistic and efficient link adaptation for 802.11x wireless LANs

Wireless LANs (WLANs), based on the IEEE 802.11 standard, have become the standard means for indoor wireless connectivity. At the same time, the rising number of smart mobile devices, broadband access speeds, and bandwidth hungry applications (e.g., high definition video streaming) have led to an increase not only of usage but also of demand for higher data-rates. This demand for higher rates is being met with newer IEEE 802.11 standards (e.g., 802.11n/ac) that introduce new features and also increase the different possible settings for each feature. Inherent channel variations and the possible interference conditions when operating in unlicensed spectrum necessitate adaptation of the various medium access control (MAC) and physical (PHY) layer features to ensure high performance. Selecting the values of those features to optimise a criterion such as throughput is the link adaptation problem. Link adaptation, the focus of this thesis, can play a key role in improving the performance of 802.11 WLANs. Increasing number of features and feature setting combinations with newer 802.11 standards is not only making link adaptation even more important but also more challenging. The contributions made in this thesis significantly advance the state of the art on link adaptation for 802.11 WLANs along three dimensions. First, we show that not knowing the exact cause of loss is not an impediment to effective link adaptation. Nevertheless, actions taken in response to losses are more crucial and they ought to be holistic and not solely dependent on the exact cause of loss. Second, we make significant methodological contributions for analysing the impact of multiple parameters on a given criterion, based on comprehensive experimental measurements. The application of this methodology on 802.11n measurements, examining the interaction of the protocols various parameters on performance under varying conditions, has lead to several valuable findings on how to perform efficient link adaptation in a complex WLAN scenario like 802.11n and future 802.11 standards. Adaptation should be holistic, based on the channel quality instead of the interference scenario, and independent of loss differentiation. Based on these insights, lastly and most importantly, we propose two novel holistic link adaptation schemes for legacy 802.11a/b/g and 802.11n WLANs, termed Themis and SampleLite, respectively. Both Themis and SampleLite take a hybrid approach relying on easily accessed channel quality information at the sender side to perform holistic adaptation. The hypothesis that adaptation should be holistic is validated by our results, with both Themis and SampleLite outperforming the current state of the art

Reducing Latency in Internet Access Links with Mechanisms in Endpoints and within the Network

Excessive and unpredictable end-to-end latency is a major problem for today’s Internet performance, affecting a range of applications from real-time multimedia to web traffic. This is mainly attributed to the interaction between the TCP congestion control mechanism and the unmanaged large buffers deployed across the Internet. This dissertation investigates transport and link layer solutions to solve the Internet’s latency problem on the access links. These solutions operate on the sender side, within the network or use signaling between the sender and the network based on Explicit Congestion Notification (ECN). By changing the sender’s reaction to ECN, a method proposed in this dissertation reduces latency without harming link utilization. Real-life experiments and simulations show that this goal is achieved while maintaining backward compatibility and being gradually deployable on the Internet. This mechanism’s fairness to legacy traffic is further improved by a novel use of ECN within the network

De l'évaluation des performances Wi-Fi à la mobilité contrôlée pour les réseaux de drones

Mobility in telecommunication networks is often seen as a hassle that needs to be dealt with: a mobile wireless device has to adapt is trans-mission parameters in order to remain connected to its counterpart(s),as the channel evolves with the device’s movements. Drones, which are unmanned aerial vehicles in the context of this thesis, are no exception.Because of their freedom of movement, their three-dimensional mobility in numerous and varied environments, their limited payload and their energy constraints, and because of the wide range of their real-world applications, drones represent new exciting study objects whose mobility is a challenge. Yet, mobility can also be a chance for drone networks,especially when we can control it. In this thesis, we explore how con-trolled mobility can be used to increase the performance of a drone network, with a focus on IEEE 802.11 networks and small multi-rotor drones. We first describe how mobility is dealt with in 802.11 networks,that is to say using rate adaptation mechanisms, and reverse engineer the rate adaptation algorithm used in the Wi-Fi chipset of the Intel Aero Drone. The study of this rate adaptation algorithm, both experimental and through simulation, through its implementation in the network simulator NS-3, allows its comparison against other well-known algorithms.This highlights how big the impact of such algorithms are for drone networks, with regard to their mobility, and how different the resulting behaviors of each node can be. Therefore, a controlled mobility solution aiming to improve network performances cannot assume much about the behavior of the rate adaptation algorithms. In addition to that, drone applications are diverse, and imposing mobility constraints without crippling a complete pan of these applications is difficult. We therefore propose a controlled mobility solution which leverages the antenna radiation pattern of the drones. This algorithm is evaluated thanks to a customized simulation framework for antenna and drone simulation,based on NS-3. This solution, which works with any rate adaptation algorithm, is distributed, and do not require a global coordination that would be costly. It also does not require a full and complete control of the drone mobility as existing controlled mobility solutions require, which makes this solution compatible with various applications.La mobilité dans les réseaux de télécommunications est souvent considérée comme un problème qu'il faut résoudre : un appareil mobile sans fil doit adapter ses paramètres de transmission afin de rester connecté à son ou ses homologues, car le canal évolue avec les mouvements de l'appareil. Les drones, qui sont des véhicules aériens sans pilote, ne font pas exception. En raison de leur grande liberté de mouvements, de leur mobilité tridimensionnelle, et ce dans des environnements aussi nombreux que variés, de leur charge utile limitée et de leurs contraintes énergétiques, et en raison du large éventail de leurs applications dans le monde réel, les drones représentent de nouveaux objets d'étude passionnants dont la mobilité est un défi. Pourtant, la mobilité peut aussi être une chance pour les réseaux de drones, surtout lorsque nous pouvons la contrôler. Dans cette thèse, nous explorons comment la mobilité contrôlée peut être utilisée pour augmenter les performances d'un réseau de drones, en mettant l'accent sur les réseaux IEEE 802.11 et les petits drones multi-rotor. Nous décrivons d'abord comment la mobilité est traitée dans les réseaux 802.11, c'est-à-dire en utilisant des mécanismes d'adaptation de débit, puis nous effectuons l'ingénierie inverse de l'algorithme d'adaptation de débit utilisé dans le chipset Wi-Fi du drone Intel Aero. L'étude de cet algorithme d'adaptation de débit, de manière à la fois expérimentale et par simulation, grâce à son implémentation dans le simulateur de réseau NS-3, permet de le comparer à d'autres algorithmes bien connus. Cette étude met en évidence l'importance de ces algorithmes pour les réseaux de drones, en lien avec leur mobilité, et la différence de comportement de chaque nœud en résultant. Par conséquent, une solution de mobilité contrôlée visant à améliorer les performances des réseaux ne peut pas supposer beaucoup du comportement des algorithmes d'adaptation de débits. En outre, les applications des réseaux de drones sont diverses, et il est difficile d'imposer des contraintes de mobilité sans devenir incompatible avec un pan complet d'applications. Nous proposons donc une solution de mobilité contrôlée qui exploite le diagramme de rayonnement de l'antenne des drones. Cet algorithme est évalué grâce à outil de simulation développé pour l'occasion, permettant la simulation d'antennes et de drones, basé sur NS-3. Cette solution, qui fonctionne avec n'importe quel algorithme d'adaptation de débit, est distribuée, et ne nécessite aucune coordination globale ou communication spécifique qui pourrait s'avérer coûteuses. Elle ne nécessite pas non plus un contrôle complet de la mobilité du drone comme le requièrent les solutions de mobilité contrôlée existantes, ce qui rend cette solution compatible avec diverses applications

Robust and Interference-Resilient MAC/PHY Layer Strategies for WLANs

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·컴퓨터공학부, 2018. 2. 최성현.Thanks to the explosive growth of mobile devices such as smartphones and tablet PCs, IEEE 802.11 wireless local area network (WLAN), often referred to as WiFi, has become one of the most successful wireless access technologies, supporting ever increasing demand for high data rates at relatively low cost. Encouraged by this remarkable success, the state-of-the-art IEEE 802.11 WLAN provides a physical layer (PHY) data rate of Gb/s to a single user in the 5 GHz unlicensed band, by enabling multi-input and multi-output (MIMO) technology, which utilizes multiple antennas at both transmitter and receiver, and channel bonding which aggregates multiple 20 MHz channels up to 160 MHz bandwidth. Furthermore, as a key feature to enhance medium access control (MAC) efficiency, IEEE 802.11 standard defines frame aggregation called aggregate MAC protocol data unit (A-MPDU), which amortizes PHY protocol overhead over multiple frames by packing several MPDUs into a single frame. In this dissertation, we propose the following three strategies to enhance throughput performance in practice: (1) Mobility-aware PHY rate and A-MPDU length control, (2) Receiver-driven operating channel width adaptation, and (3) Receive architecture for eliminating time-domain interference not overlapping with the desired signal in frequency-domain. Firstly, a significant growth of mobile data traffic volume, primarily generated by portable devices, has led to a change of WLAN communication environmentsthe wireless channel condition in WLAN system is no longer quasi-stationary over the duration of a single frame reception. Especially, frame aggregation, i.e., A-MPDU, which lengthens frame duration significantly, causes the channel state information (CSI) obtained at the preamble can be no longer valid for successfully decoding the latter part of A-MPDUs, when the channel condition substantially changes during the A-MPDU reception. To cope with this problem, we analyze the wireless channel dynamics considering mobility through extensive measurements, and we then build a model which represents the impact of mobility with a noise vector in the I-Q plane, to investigate how the mobility affects the A-MPDU reception performance. Based on our analysis, we develop STRALE, a standard-compliant and mobility-aware PHY rate and A-MPDU length adaptation scheme with ease of implementation. Through extensive simulations with 802.11ac using ns-3 and prototype implementation with commercial 802.11n devices, we demonstrate that STRALE achieves up to 2.9 higher throughput, compared to a fixed duration setting according to IEEE 802.11 standard. STRALE simply requires to update device driver only at one end of the wireless link (i.e., transmitter), thus allowing it to be applicable to any kind of platforms. Second, IEEE 802.11ac supports bandwidth of 20, 40, and 80 MHz as a mandatory feature, and optionally supports 160 MHz bandwidth. To transmit and receive packets using such wide bandwidth, the 802.11ac devices need to increase the size of fast Fourier transform (FFT), equivalently, the baseband bandwidth, referred to as operating channel width (OCW). However, our experiment results reveal various situations where bandwidth adaptation without changing the receivers OCW, leads to poor reception performance due surprisingly to time-domain interference not overlapping with the incoming desired signal in frequency domain. To cope with this problem, we develop RECONN, a standard-compliant and receiver-driven OCW adaptation scheme with ease of implementation. Our prototype implementation in commercial 802.11ac devices shows that RECONN achieves up to 1.85x higher throughput by completely eliminating time-domain interference. To our best knowledge, this is the first work to discover the time-domain interference problem, and to develop OCW adaptation scheme in 802.11ac system. Finally, based on the observation that time-domain interference causes 1) packet detection and synchronization failure, 2) undesirable receive locking problem, and 3) automatic gain control (AGC) failure, we propose a receive architecture called REACTER to eliminate the impact of time-domain interference: REACTER digitally extracts the desired preamble signal not affected by time-domain interference, and provides interference-resilient A-MPDU reception performance by real-time AGC level adaptation during A-MPDU reception. The proposed receive architecture extensively evaluated via IT++ based link-level simulator, and the simulation results show that REACTER significantly improves the frame reception performance by completely eliminates the impact of time-domain interference. In summary, we identify the two existing problems through the extensive measurement and simulations, and we then propose compelling algorithms to improve the throughput performance. We demonstrate the feasibility of our approaches by implementing prototypes in off-the-shelf commercial 802.11n/ac devices, showing that our proposed algorithms fully comply with the 802.11 MAC and requires no PHY modification such that it can be applicable to the existing hardware platform by simply updating the device driver only at one end of the wireless link. Furthermore, we present a novel receive architecture which shows the ability to fundamentally enhance the performance of wide bandwidth operation with very low cost and complexity.1 Introduction 1 1.1 Motivation 1 1.2 Overview of Existing Approach 3 1.2.1 A-MPDU Length Adaptation 3 1.2.2 Wide Bandwidth Operation in IEEE 802.11ac WLANs 4 1.2.3 Receive Architecture for WLAN Devices 5 1.3 Main Contributions 6 1.3.1 Mobility-Aware PHY Rate and A-MPDU Length Adaptation 6 1.3.2 Receiver-Driven Operating Channel Width Adaptation 7 1.3.3 Rx Architecture for Eliminating Time-Domain Interference 7 1.4 Organization of the Dissertation 8 2 STRALE: Mobility-Aware PHY Rate and A-MPDU Length Adaptation in IEEE 802.11 WLANs 10 2.1 Introduction 10 2.2 Preliminaries . 12 2.2.1 Channel Estimation and Compensation 12 2.2.2 Frame Aggregation 14 2.2.3 Modulation and Coding Schemes 15 2.2.4 MIMO, SM, STBC and channel bonding 15 2.3 Case Study 16 2.3.1 Experimental Setting 16 2.3.2 Temporal Selectivity 17 2.3.3 Impact of Mobility 18 2.3.4 Impact of MCSs 21 2.3.5 IEEE 802.11n/ac Features 22 2.3.6 Rate Adaptation: Minstrel 23 2.4 Caudal Noise Model 25 2.4.1 Caudal Noise Modeling for n x n MIMO Channel 26 2.4.2 Impact of Caudal Noise 28 2.5 STRALE: Proposed Algorithm 30 2.5.1 Possible Solutions for Caudal Loss Problem 31 2.5.2 Operation of STRALE 32 2.6 Performance Evaluation 37 2.6.1 Methodology 37 2.6.2 Simulation Results 39 2.6.3 Prototype Implementation 44 2.7 Summary 46 3 RECONN: Receiver-Driven Operating Channel Width Adaptation in IEEE 802.11ac WLANs 48 3.1 Introduction 48 3.2 Preliminaries 51 3.2.1 Packet Detection and Initial Synchronization 51 3.2.2 Wide Bandwidth Operation 52 3.3 Cast Study 53 3.3.1 Motivation 55 3.3.2 Packet Detection and Synchronization Failure 57 3.3.3 Receive Locking to Interference Signal 59 3.3.4 AGC Failure 61 3.4 RECONN: Proposed Algorithm 64 3.4.1 Possible Solutions 64 3.4.2 RECONN 67 3.5 Performance Evaluation 70 3.5.1 One-to-One Scenario 72 3.5.2 Multi-station Scenario 74 3.6 Summary 75 4 REACTER: Receive Architecture for Eliminating Time-Domain Interference 76 4.1 Introduction 76 4.2 Preliminaries 78 4.2.1 Packet Detection and Synchronization 78 4.2.2 Automatic Gain Control in IEEE 802.11 WLAN 80 4.3 REACTER: Proposed Architecture 80 4.3.1 Simulation Methodology 80 4.3.2 Digital Low Pass Filter (DLPF) 82 4.3.3 Real-Time AGC 89 4.3.4 Structure of REACTER 96 4.4 Performance Evaluation 100 4.5 Summary 101Docto

Ultra-reliable low-latency industrial wireless communications: optimization and implementation

Ultra-reliable and low-latency communications (URLLC) are crucial for mission-critical services in fifth-generation (5G) mobile networks. Due to limited time and frequency resources in URLLC, decoding packet error probability (PEP) is unavoidable, which makes meeting the reliability constraint extremely challenging. A key challenge is that current wireless systems use pilot symbols for channel estimation, sharing channel resources with data symbols. In this thesis, I first design unsupervised learning algorithms to estimate a resource allocation policy for independent and identically distributed fading channels, including a model-based algorithm for measurable PEP and a model-free method for discrete PEP observations. Results demonstrate that my methods can significantly enhance resource utilization efficiency, even with a lower signal-to-interference-plus-noise ratio. Furthermore, I focus on temporally correlated channel realizations and propose deep reinforcement learning algorithms to determine the resource allocation policy that can maximize long-term resource utilization efficiency. I formulate the optimization problem as a partial observation Markov decision process and develop a cascaded-action Twin Delayed Deep Deterministic policy (CA-TD3) to address it. I introduce a primal CA-TD3 algorithm and compare it with a primal-dual method. The results indicate that the primal CA-TD3 converges more efficiently than the primal-dual method. Lastly, I aspire to design a hardware platform to implement wireless time-sensitive networking, which is one of the most vital scenarios of URLLC. I select a commercial 802.11-based platform and utilize a time division multiple access (TDMA) mechanism to schedule transmissions through novel real-time quality of service and fine-grained aggregation schemes. Experimental results demonstrate the superiority of my proposed protocol compared to existing TDMA-based 802.11 and legacy 802.11 systems

Design and analysis of LTE and wi-fi schemes for communications of massive machine devices

Existing communication technologies are designed with speciÿc use cases in mind, however, ex-tending these use cases usually throw up interesting challenges. For example, extending the use of existing cellular networks to emerging applications such as Internet of Things (IoT) devices throws up the challenge of handling massive number of devices. In this thesis, we are motivated to investigate existing schemes used in LTE and Wi-Fi for supporting massive machine devices and improve on observed performance gaps by designing new ones that outperform the former. This thesis investigates the existing random access protocol in LTE and proposes three schemes to combat massive device access challenge. The ÿrst is a root index reuse and allocation scheme which uses link budget calculations in extracting a safe distance for preamble reuse under vari-able cell size and also proposes an index allocation algorithm. Secondly, a dynamic subframe optimization scheme that combats the challenge from an optimisation solution perspective. Thirdly, the use of small cells for random access. Simulation and numerical analysis shows performance improvements against existing schemes in terms of throughput, access delay and probability of collision. In some cases, over 20% increase in performance was observed. The proposed schemes provide quicker and more guaranteed opportunities for machine devices to communicate. Also, in Wi-Fi networks, adaptation of the transmission rates to the dynamic channel condi-tions is a major challenge. Two algorithms were proposed to combat this. The ÿrst makes use of contextual information to determine the network state and respond appropriately whilst the second samples candidate transmission modes and uses the e˛ective throughput to make a deci-sion. The proposed algorithms were compared to several existing rate adaptation algorithms by simulations and under various system and channel conÿgurations. They show signiÿcant per-formance improvements, in terms of throughput, thus, conÿrming their suitability for dynamic channel conditions

Quality of Service in Vehicular Ad Hoc Networks: Methodical Evaluation and Enhancements for ITS-G5

After many formative years, the ad hoc wireless communication between vehicles has become a vehicular technology available in mass production cars in 2020. Vehicles form spontaneous Vehicular Ad Hoc Networks (VANETs), which enable communication whenever vehicles are nearby without need for supportive infrastructure. In Europe, this communication is standardised comprehensively as Intelligent Transport Systems in the 5.9 GHz band (ITS-G5). This thesis centres around Quality of Service (QoS) in these VANETs based on ITS-G5 technology. Whilst only a few vehicles communicate, radio resources are plenty, and channel congestion is a minor issue. With progressing deployment, congestion control becomes crucial to preserve QoS by preventing high latencies or foiled information dissemination. The developed VANET simulation model, featuring an elaborated ITS-G5 protocol stack, allows investigation of QoS methodically. It also considers the characteristics of ITS-G5 radios such as the signal attenuation in vehicular environments and the capture effect by receivers. Backed by this simulation model, several enhancements for ITS-G5 are proposed to control congestion reliably and thus ensure QoS for its applications. Modifications at the GeoNetworking (GN) protocol prevent massive packet occurrences in a short time and hence congestion. Glow Forwarding is introduced as GN extension to distribute delay-tolerant information. The revised Decentralized Congestion Control (DCC) cross-layer supports low-latency transmission of event-triggered, periodic and relayed packets. DCC triggers periodic services and manages a shared duty cycle budget dedicated to packet forwarding for this purpose. Evaluation in large-scale networks reveals that this enhanced ITS-G5 system can reliably reduce the information age of periodically sent messages. The forwarding budget virtually eliminates the starvation of multi-hop packets and still avoids congestion caused by excessive forwarding. The presented enhancements thus pave the way to scale up VANETs for wide-spread deployment and future applications