IEEE 802.11 parameters adaptation for Performance enhancement in high density Wireless networks

Tribunal : Ramón Agüero, Álvaro Martín, Federico LarrocaNowadays, it is common to find wireless networks that are based on the IEEE 802.11 standard deployed in an unplanned and unmanaged manner. Moreover, because of the low hardware cost and, trying to obtain optimal coverage and performance, a large number of devices are usually installed in reduced spaces generating high-density deployments. This kind of networks experiment a myriad of problems (e.g., interference, medium access control, etc.) related with the shared nature of the transmission medium. In recent years, different physical-layer- and link-layer-adaptation mechanisms have been proposed to palliate those problems, however, their feedback-loop-based behaviour in a highly complex RF medium makes their performance hard to assess. In this work, we study the problems of high-density networks, experimentally evaluate some existing solutions and propose a new adaptation mechanism, PRCS, that tackles some common weakness of those solutions. PRCS control the transmit power, the data rate, and the carrier sense threshold of APs of a wireless network so as to mitigate the effects of interference in high-density deployments without causing unfairness between links. In simulation-based experiments, PRCS outperforms similar existing mechanisms in various scenarios and in a particular scenario, where most mechanisms fail, duplicates global network throughput.En la actualidad, es muy común encontrar redes inalámbricas basadas en el estándar IEEE 802.11 desplegadas de manera no planificada ni gestionada. Además, debido al bajo costo de los dispositivos y con la intención de obtener una cobertura y rendimiento óptimos, un gran número de dispositivos son instalados en espacios reducidos, generado despliegues de alta densidad. Este tipo de redes experimentan una gran variedad de problemas (por ej., interferencia, control de acceso al medio, etc.) relacionados con el hecho de que utilizan un medio de transmisión compartido. En los últimos años, diferentes mecanismos de adaptación de parámetros de la capa física y de enlace han sido propuestos con el objetivo de mitigar estos problemas. Estas soluciones adaptan parámetros tales como la potencia de transmisión o la tasa de transmisión. En este trabajo, estudiamos los problemas de las redes inalámbricas de alta densidad, evaluamos mediante experimentos algunas de las soluciones existentes y proponemos un nuevo mecanismo de adaptación, PRCS, que aborda algunas de las debilidades de estas soluciones. PRCS controla la potencia de transmisión, la tasa de transmisión y el umbral del mecanismo de sensado de portadora de los puntos de acceso de una red inalámbrica. El objetivo de este mecanismo es mitigar los efectos de la interferencia en despliegues de alta densidad sin causar asimetrías entre los enlaces. En experimentos basados en simulaciones, mostramos que PRCS supera a los mecanismos existentes en varios escenarios y, en un escenario en particular donde la mayoría de los mecanismos fallan, duplica el rendimiento global de la red

A software framework for alleviating the effects of MAC-aware jamming attacks in wireless access networks

The IEEE 802.11 protocol inherently provides the same long-term throughput to all the clients associated with a given access point (AP). In this paper, we first identify a clever, low-power jamming attack that can take advantage of this behavioral trait: the placement of a lowpower jammer in a way that it affects a single legitimate client can cause starvation to all the other clients. In other words, the total throughput provided by the corresponding AP is drastically degraded. To fight against this attack, we design FIJI, a cross-layer anti-jamming system that detects such intelligent jammers and mitigates their impact on network performance. FIJI looks for anomalies in the AP load distribution to efficiently perform jammer detection. It then makes decisions with regards to optimally shaping the traffic such that: (a) the clients that are not explicitly jammed are shielded from experiencing starvation and, (b) the jammed clients receive the maximum possible throughput under the given conditions. We implement FIJI in real hardware; we evaluate its efficacy through experiments on two wireless testbeds, under different traffic scenarios, network densities and jammer locations. We perform experiments both indoors and outdoors, and we consider both WLAN and mesh deployments. Our measurements suggest that FIJI detects such jammers in realtime and alleviates their impact by allocating the available bandwidth in a fair and efficient way. © Springer Science+Business Media

고밀도 무선랜 동시 전송 향상 기법

학위논문 (박사)-- 서울대학교 대학원 공과대학 전기·컴퓨터공학부, 2017. 8. 최성현.무선 통신에 대한 수요가 증가함에 따라, Wi-Fi로 흔히 알려진 IEEE 802.11 표준 기반 무선랜(WLAN, Wireless Local Area Network)은 어디에서나 찾아볼 수 있는 기술로 거듭났다. 이로 인해 무선랜의 고밀화, 즉 공간적으로 인접한 많은 AP(Access Point)와 STA(station)들이 동일한 주파수 채널을 사용하며 이로 인해 한 단말이 얻을 수 있는 성능이 제한되는 현상이 두드러지고 있다. 따라서 이러한 고밀도 무선랜 환경에서는 단일 전송에 대한 스펙트럼 효율 뿐만 아니라 주파수 자원의 공간 재사용(spatial reuse)의 중요성 또한 강조된다. 즉, 특정 공간 내에서 얼마나 많은 동시 전송이 가능한지가 중요한 이슈로 자리매김하고 있다. 본 학위논문에서는 고밀도 무선랜 환경에서 더 많은 동시 전송을 성공시키기 위하여 다음과 같은 세 가지 전략을 고려한다. (i) 매체접근제어(MAC, Medium Access Control) 계층의 ACK(Acknowledgment) 및 CTS(Clear-To-Send) 프레임에 대한 송신 전력 제어, (ii) 반송파 감지 임계값(CST, Carrier-Sense Threshold) 적응, (iii) 동시 송신 및 수신 (STR, Simultaneous Transmit and Receiver), 즉 동일대역 전이중 통신(in-band full duplex). 첫번째로, 본 학위 논문에서는 데이터 프레임에 의한 동일 채널 간섭(CCI, Co-Channel Interference)보다 덜 조명되어 왔던 MAC ACK 프레임에 의해 발생하는 CCI에 주목한다. 확률적 기하 분석(stochastic geometry analysis)을 기반으로 ACK 프레임의 송신 전력 조절의 필요성을 확인하였으며, 이를 바탕으로 동적 ACK 프레임 송신 전력 제어 알고리즘인 Quiet ACK(QACK)을 제안한다. QACK은 데이터 프레임 수신 중 수행되는 CCI 검출 및 CCI 전력 추정 기법과 ACK 프레임 전송 통계를 활용하여 세밀하고 신속하게 ACK 프레임의 송신 전력을 조절한다. 더불어, QACK을 바탕으로 CTS 프레임 송신 전력을 조절하여 더 많은 동시 전송이 시도될 수 있게 하는 Quiet CTS(QCTS)라는 알고리즘 또한 제안한다. QACK의 실현 가능성과 성능은 SDR(Software-Defined Radio) 기반 프로토타입을 통해 검증하며 기존 방식 대비 약 1.5배 높은 수율을 얻을 수 있음을 확인한다. 보다 일반적인 무선랜 환경에서의 QACK 및 QCTS의 성능은 ns-3를 사용한 다양한 시뮬레이션을 통해 평가한다. 다음으로, 동시에 더 많은 동시 전송이 시도될 수 있도록 간섭원(interferer node)과 목적 노드(destination node)에 따라 CST를 제어하는 ​​CST 적응 방법, FACT(Fine-grained Adaptation of Carrier-sense Threshold)를 제안한다. 제안하는 방법은 무선랜 표준에서 이미 정의되어 있는 기능을 사용하므로 상용 무선랜 기기에서 쉽게 구현할 수 있다. 또한 FACT 및 다른 CST 적응 기법과 함께 동작할 수 있는 CCA(Clear Channel Assessment) 오버헤드 감소 기법을 제안하며, 제안한 기법들의 성능을 ns-3 시뮬레이션을 통해 비교평가한다. 시뮬레이션 결과를 통해 제안한 방법이 기존 방법에 비해 네트워크 전체 수율을 큰 폭으로 향상시킬 수 있음을 확인한다. 마지막으로, 무선랜에서 STR을 가능하게하는 새로운 MAC 프로토콜, 즉 MASTaR(MAC Protocol for Access points in Simultaneous Transmit and Receive mode)를 기존 무선랜 표준을 준수하는 방법으로 제안한다. 또한 MASTaR 동작을 위해 필요한 물리계층에서 디지털 자가 간섭 상쇄(SIC, Self-Interference Cancellation) 전략을 제안하며 그 실현 가능성과 성능을 3차원 광선 추적(3D-ray tracing) 기반 시뮬레이션을 통해 다양한 측면에서 평가한다. 시뮬레이션 결과는 현재 무선랜 MAC 프로토콜보다 최대 2.58배 높은 수율이 MASTaR를 통해 얻어질 수 있음을 보인다. 요약하면, 본 학위논문에서는 ACK 및 CTS 프레임의 송신 전력 제어 알고리즘과 CST 적응 및 STR을 위한 프로토콜을 제안한다. 제안한 알고리즘 및 프로토콜의 실현 가능성과 성능은 수치 해석, 3차원 광선 추적, ns-3 기반 시스템 수준(system-level) 시뮬레이션, SDR 기반 프로토타입 등 다양한 방법론을 통해 입증한다.With increasing demand for wireless connectivity, IEEE 802.11 wireless local area network (WLAN), a.k.a. Wi-Fi, has become ubiquitous and continues to grow in number. This leads to the high density of WLAN, where many access points (APs) and client stations (STAs) operate on the same frequency channel. In a densely deployed WLAN, greater emphasis is placed on the importance of spatial reuse as well as spectral efficiency. In other words, it is of particular importance how many simultaneous transmissions are possible in a given area. In this dissertation, we consider the following three strategies to increase the number of successful simultaneous transmissions: (i) Transmit power control for medium access control (MAC) acknowledgment (ACK) and clear-to-send (CTS) frames, (ii) carrier sense threshold (CST) adaptation, and (iii) simultaneous transmit and receive (STR), i.e., in-band full-duplex communication. First, this dissertation sheds light on the co-channel interference (CCI) caused by 802.11 MAC ACK frames, which has been less studied than the CCI caused by data frames. Based on stochastic geometry analysis, we propose Quiet ACK (QACK), a dynamic transmit power control algorithm for ACK frames. Fine-grained transmit power adjustment is enabled by CCI detection and CCI power estimation in the middle of a data frame reception. A power control algorithm for clear-to-send (CTS) frame transmission, namely Quiet CTS (QCTS) is also proposed based on QACK. Our prototype using software-defined radio shows the feasibility and performance gain of QACK, i.e., 1.5X higher throughput than the legacy 802.11 WLAN. The performance of QACK and QCTS is further evaluated in more general WLAN environments via extensive simulations using ns-3. Second, a fine-grained CST adaptation method, which controls CST depending on both interferer and destination nodes, is proposed to improve spatial reuse in WLAN. The proposed method utilizes pre-defined functions in the WLAN standard, thus making itself easily implementable in commercial WLAN devices. Supplementary clear channel assessment (CCA) method is also proposed to further enhance network performance by reducing CCA overhead. The performance of the proposed methods is comparatively evaluated via ns-3 simulation. Simulation results show that the proposed methods significantly improve network throughput compared with the legacy method. Finally, a novel MAC protocol that enables STR in 802.11 WLAN, namely MASTaR, is proposed based on standard-compliant methods. Also, a digital self-interference cancellation (SIC) strategy is proposed to support the operation of MASTaR. The feasibility and the performance of MASTaR are extensively evaluated via 3D ray tracing-based simulation. The simulation results demonstrate that significant performance enhancement,e.g., up to 2.58X higher throughput than the current 802.11 MAC protocol, can be achieved by an STR-capable access point. In summary, we propose an algorithm for ACK and CTS transmission power control and two protocols each for CST adaptation and STR which enhance the efficiency of WLAN by enriching simultaneous transmission. The feasibility and the performance of the algorithm and protocols are demonstrated via various methodologies including numerical analysis, 3D ray-tracing, ns-3 based system-level simulation, and prototype using a software-defined radio.1 Introduction 1 1.1 Motivation 1 1.2 Overview of Existing Approaches 3 1.2.1 Transmit power control for CCI reduction 3 1.2.2 CST adaptation for better spatial reuse 3 1.2.3 MAC protocol for STR in WLAN 4 1.3 Main Contributions 7 1.3.1 Quiet ACK: ACK Transmit Power Control 7 1.3.2 FACT: CST adaptation scheme 8 1.3.3 MASTaR: MAC protocol for STR in WLAN 8 1.4 Organization of the Dissertation 9 2 Quiet ACK: ACK Transmit Power Control in IEEE 802.11 WLANs 10 2.1 Introduction 10 2.2 Numerical Analysis 12 2.2.1 System Model 13 2.2.2 AISR Expansion by ACK Power Control 18 2.2.3 Optimization of ACK Outage Tolerance 19 2.3 QACK: Proposed ACK power Control 21 2.3.1 CCI Detection and CCI Power Estimation 22 2.3.2 Link Margin Estimation 26 2.3.3 ACK Power Adjustment 29 2.3.4 Conditional QACK Enabling/Disabling 30 2.4 Prototyping-Based Feasibility Evaluation 30 2.4.1 Feasibility of CCI Detection and CCI Power Estimation 30 2.4.2 Throughput Enhancement by QACK 33 2.5 Simulation-based Performance Evaluation 34 2.5.1 Two BSS Topology 35 2.5.2 Multiple BSS Environment 38 2.5.3 Coexistence with Legacy Devices 41 2.6 Quiet CTS: Proposed CTS Power Control 41 2.6.1 Problem Statement 41 2.6.2 CTS Power Control 42 2.6.3 Relationship with Quiet ACK 44 2.6.4 Simulation Results 45 2.7 Summary 48 3 FACT: Fine-Grained Adaptation of Carrier Sense Threshold in IEEE 802.11 WLANs 49 3.1 Introduction 49 3.2 Preliminaries 50 3.2.1 IEEE 802.11h Transmit Power Control (TPC) 50 3.2.2 IEEE 802.11ah Basic Service Set (BSS) Color 52 3.3 FACT: Proposed CST Adaptation Scheme 52 3.3.1 Basic Principle 53 3.3.2 Challenges and Solutions 54 3.3.3 Specification 54 3.3.4 Transmit Power Adjustment 56 3.3.5 Conditional Update of CST 57 3.4 Blind CCA and Backoff Compensation 57 3.4.1 Blind CCA 58 3.4.2 Backoff Compensation 59 3.5 Performance Evaluation 59 3.6 Summary 63 4 MASTaR: MAC Protocol for Access Points in Simultaneous Transmit and Receive Mode 64 4.1 Introduction 64 4.2 Preliminaries 68 4.2.1 Explicit Block ACK 68 4.2.2 Capture Effect 69 4.3 MASTaR: Proposed MAC Protocol 70 4.3.1 PTX Identification 70 4.3.2 Initial Training 73 4.3.3 Link Map Management 73 4.3.4 Secondary Transmission 74 4.4 Feasibility Study 76 4.4.1 Analog SIC and Channel Modeling 76 4.4.2 Digital SIC for WLAN 79 4.5 Performance Evaluation 83 4.5.1 Simulation with UDP Data Traffic 87 4.5.2 Simulation with Voice and Data Traffic 100 4.6 Summary 102 5 Concluding Remarks 103 5.1 Research Contributions 103 5.2 Future Work 104 Abstract (In Korean) 110Docto

Planning and realization of a WiFi 6 network to replace wired connections in an enterprise environment

WiFi (Wireless Fidelity) is a popular wireless LAN technology. It provides broadband wireless connectivity to all the users in the unlicensed 2.4 GHz and 5 GHz frequency bands. Given the fact that the WiFi technology is much easier and cost-efficient to deploy, it is rapidly gaining acceptance as an alternative to a wired local area network. Nowadays the Wireless access to data is a necessity for everyone in the daily life. Considering the last 30 years, the unlimited access to information has transformed entire industries, fueling growth, productivity and profits.The WiFi technology, which is governed by the IEEE 802.11 standards body, has played a key role in this transformation. In fact, thanks to WiFi, users can benefit of low cost access to high data rate wireless connectivity. The first version of the IEEE 802.11 protocol was released in 1997. IEEE 802.11 has been improved with different versions in order to enhance the throughput and support new technologies. WiFi networks are now experiencing the bandwidth-demanding media content as well as multiple WiFi devices for each user. As a consequence of this, WiFi 6, which is based on the IEEE 802.11ax standard, is focused on improving the efficiency of the radio link. However, there is a relatively modest increase in peak data rate too. In this thesis we have planned and realized a WiFi 6 network to replace wired connections in an enterprise environment. To do this the optimal access point placement problem has been taken into account, resulting in an improvement of the coverage. Subsequently, after the configuration from the controller, the performance of the new network has been tested in order to study if WiFi 6 can be used instead of wired connections.WiFi (Wireless Fidelity) is a popular wireless LAN technology. It provides broadband wireless connectivity to all the users in the unlicensed 2.4 GHz and 5 GHz frequency bands. Given the fact that the WiFi technology is much easier and cost-efficient to deploy, it is rapidly gaining acceptance as an alternative to a wired local area network. Nowadays the Wireless access to data is a necessity for everyone in the daily life. Considering the last 30 years, the unlimited access to information has transformed entire industries, fueling growth, productivity and profits.The WiFi technology, which is governed by the IEEE 802.11 standards body, has played a key role in this transformation. In fact, thanks to WiFi, users can benefit of low cost access to high data rate wireless connectivity. The first version of the IEEE 802.11 protocol was released in 1997. IEEE 802.11 has been improved with different versions in order to enhance the throughput and support new technologies. WiFi networks are now experiencing the bandwidth-demanding media content as well as multiple WiFi devices for each user. As a consequence of this, WiFi 6, which is based on the IEEE 802.11ax standard, is focused on improving the efficiency of the radio link. However, there is a relatively modest increase in peak data rate too. In this thesis we have planned and realized a WiFi 6 network to replace wired connections in an enterprise environment. To do this the optimal access point placement problem has been taken into account, resulting in an improvement of the coverage. Subsequently, after the configuration from the controller, the performance of the new network has been tested in order to study if WiFi 6 can be used instead of wired connections

Load-Aware Traffic Control in Software-Defined Enterprise Wireless Local Area Networks

With the growing popularity of Bring Your Own Device (BYOD), modern enterprise Wireless Local Area Networks (WLANs) deployments always consist of multiple Access Points (APs) to meet the fast-increasing demand for wireless access. In order to avoid network congestion which leads to issues such as suboptimal Quality of Service (QoS) and degraded user Quality of Experience (QoE), intelligent network traffic control is needed. Software Defined Networking (SDN) is an emerging architecture and intensively discussed as one of the most promising technologies to simplify network management and service development. In the SDN architecture, network management is directly programmable because it is decoupled from forwarding layer. Leveraging SDN to the existing enterprise WLANs framework, network services can be flexibly implemented to support intelligent network traffic control. This thesis studies the architecture of software-defined enterprise WLANs and how to improve network traffic control from a client-side and an AP-side perspective. By extending an existing software-defined enterprise WLANs framework, two adaptive algorithms are proposed to provide client-based mobility management and load balancing. Custom protocol messages and AP load metric are introduced to enable the proposed adaptive algorithms. Moreover, a software-defined enterprise WLAN system is designed and implemented on a testbed. A load-aware automatic channel switching algorithm and a QoS-aware bandwidth control algorithm are proposed to achieve AP-based network traffic control. Experimental results from the testbed show that the designed system and algorithms significantly improve the performance of traffic control in enterprise WLANs in terms of network throughput, packet loss rate, transmission delay and jitter

Self management of high density wireless networks

IEEE 802.11 wireless networks are very popular in today’s world. This popularity has been stimulated due to the use of mobile computing devices such as laptops, tablets, and Wi-Fi enabled phones. We can get 802.11 connectivity in schools, squares, parks and other public places. All of these places can have a high concentration of users. Moreover, there are other nonpublic places like lecture halls, hotel ballrooms, and convention centers that are common examples of spaces with high concentration of users in a high-density wireless communications environment. Dense deployments of wireless networks suffer from increased interference and, as a result, bad user experience. The interference caused by the co-channel and adjacent channel interference driven by co-located devices is one of the main issues to address to improve network performance. The limited number of nonoverlapping channels may lead to severe interference scenarios if no appropriated spectrum planning is employed. In this work, we present an in-depth review of research work for the channel allocation strategies. Then, we formalize the channel allocation as a minimization problem of the interference level and we propose three different manners to optimize channel assignment between participating Access Points with the aim to improve network performance. The algorithms that we propose can be classified as local and uncoordinated, coordinated and distributed, and centralized. The local and uncoordinated solution behaves well in our testbed but present oscillatory issues that we tackle with a feedback control technique. Finally, this work presents an evaluation of the strategies, on a testbed and on a simulation environment. In the testbed we demonstrate the practical deployability of the solutions and lead to the conclusion that the local and uncoordinated implementation is worthy to be considered as a good strategy for the channels allocation problem where Access Points works in isolated manner. In the simulation, we test the scalability of both, the coordinated and centralized solution, and we show that they can be deployed in networks with more than thirty Access Points and as a results, we conclude that the centralized implementation is the best strategy to perform optimization decisions for channel allocation in connected networks.Las redes inalámbricas IEEE 802.11 son muy populares en el mundo actual. Esta popularidad ha sido estimulada debido al uso de dispositivos móviles tales como laptops, tablets y teléfonos Wi-Fi compatibles. Se puede tener conectividad 802.11 en escuelas, plazas, parques y otros lugares públicos. Todos estos lugares pueden tener una gran concentración de usuarios. Más aún, hay otros lugares no públicos como las bibliotecas, centros de convenciones, salas de conferencias en hoteles, los cuales también son ejemplo de espacios comunes con una gran concentración de usuarios en entornos de comunicación inalámbrica de alta densidad. Instalaciones de redes cámbricas densas experimentan una interferencia creciente, y como resultado, una mala experiencia de usuario. Las interferencias co-canal y de canal adyacente producidas por dispositivos próximos entre sí, son uno de los principales problemas a abordar para mejorar la performance de la red. El número limitado de canales que no se superponen pueden conducir a escenarios de severa interferencia si no se emplea una planificaci´on apropiada del espectro. En este trabajo, se presenta una revisi´on profunda de los trabajos de investigación para estrategias de asignaci´on de canales. Luego, se formaliza la asignación de canales como un problema de minimización del nivel de interferencia y se proponen tres diferentes maneras para optimizar la asignación de canales entre los Puntos de Acceso participantes con el objetivo de mejorar la performance de la red. Los algoritmos propuestos pueden clasificarse como local y no-coordinado, coordinado y distribuido, y centralizado. La solución local y no- coordinada se comparta de manera aceptable en el prototipo pero presenta problemas de oscilación que se aborda con una técnica de control por retro alimentación. Finalmente, este trabajo presenta una evaluación de las estrategias, en un prototipo y en un entorno de simulación. En el prototipo se demuestra el despliegue práctico de las soluciones y se llega a la conclusi´on que la implementación local y no-coordinada es digna de ser considerada como una buena estrategia para el problema de asignación de canales cuando los Puntos de Acceso trabajan en forma aislada. En la simulación, se prueban la escalabilidad de las soluciones coordinada y centralizada, y se muestra que pueden ser desplegadas en redes con más de treinta Puntos de Acceso y como resultado, se concluye que la implementación centralizada es la mejor estrategia para realizar decisiones de optimizaci´on para la asignaci´on de canales en redes conectadas