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

Per-Flow Radio Resource Management to Mitigate Interference in Dense IEEE 802.11 Wireless LANs

Current interference management solutions for dense IEEE 802.11 Wireless Local Area Networks (WLANs) rely on locally measuring the cumulative interference at the Acess Point (AP) in charge of adjusting the spectrum resources to its clients. These solutions often result in coarse-grained spectrum allocation that often leaves many wireless users unsatisfied and increases the spectrum congestion problem instead of easing it. In this paper we present a centralised interference management algorithm that treats the network-wide interference impact of each channel individually and allows the controller to adjust the radio resource of each AP while it is utilised. This coordinated allocation takes into account the Quality of Service (QoS) requirements of downlink flows while minimising its effect on neighbouring APs. Therefore, this paper proposes a novel approach for quantifying the interference impact of each employed channel and jointly addressing the user-side quality requirements and the network-side interference management. The algorithm is tailored for operator-agnostic Software-Defined Networking (SDN)-based Radio Resource Management (RRM) in dense Wireless Fidelity (Wi-Fi) networks and adopts a fine-grained per-flow approach. Simulation results show that our algorithm outperforms existing solutions in terms of reducing the overall interference, increasing the capacity of the wireless channel and improving the users’ satisfaction

Spectrum and power optimization for wireless multiple access networks.

Emerging high-density wireless networks in urban area and enterprises offer great potential to accommodate the anticipated explosion of demand for wireless data services. To make it successful, it is critical to ensure the efficient utilisation of limited radio resources while satisfying predefined quality of service. The objective of this dissertation is to investigate the spectrum and power optimisation problem for densely deployed access points (APs) and demonstrate the potential to improve network performance in terms of throughput and interference. Searching the optimal channel assignment with minimum interference is known as an AfV-haxd problem. The increased density of APs in contrary to the limited usable frequencies has aggravated the difficulty of the problem. We adopt heuristic based algorithms to tackle both centralised and distributed dynamic channel allo cation (DCA) problem. Based on a comparison between Genetic Algorithm and Simulated Annealing, a hybrid form that combines the two algorithms achieves good trade-off between fast convergence speed and near optimality in centralised scenario. For distributed DCA, a Simulated Annealing based algorithm demon strates its superiority in terms of good scalability and close approximation to the exact optimal solution with low algorithm complexity. The high complexity of interactions between transmit power control (TPC) and DCA renders analytical solutions to the joint optimisation problems intractable. A detailed convergence analysis revealed that optimal channel assignment can strengthen the stability condition of TPC. Three distributed algorithms are pro posed to interactively perform the DCA and TPC in a real time and open ended manner, with the ability to appropriately adjust power and channel configurations according to the network dynamics. A real network with practical measurements is employed to quantify and verify the theoretical throughput gain of their inte gration. It shows that the integrated design leads to a substantial throughput improvement and power saving compared with conventional fixed-power random channel allocation system

Improving the Performance of Wireless LANs

This book quantifies the key factors of WLAN performance and describes methods for improvement. It provides theoretical background and empirical results for the optimum planning and deployment of indoor WLAN systems, explaining the fundamentals while supplying guidelines for design, modeling, and performance evaluation. It discusses environmental effects on WLAN systems, protocol redesign for routing and MAC, and traffic distribution; examines emerging and future network technologies; and includes radio propagation and site measurements, simulations for various network design scenarios, numerous illustrations, practical examples, and learning aids

MAC/PHY Co-Design of CSMA Wireless Networks Using Software Radios.

In the past decade, CSMA-based protocols have spawned numerous network standards (e.g., the WiFi family), and played a key role in improving the ubiquity of wireless networks. However, the rapid evolution of CSMA brings unprecedented challenges, especially the coexistence of different network architectures and communications devices. Meanwhile, many intrinsic limitations of CSMA have been the main obstacle to the performance of its derivatives, such as ZigBee, WiFi, and mesh networks. Most of these problems are observed to root in the abstract interface of the CSMA MAC and PHY layers --- the MAC simply abstracts the advancement of PHY technologies as a change of data rate. Hence, the benefits of new PHY technologies are either not fully exploited, or they even may harm the performance of existing network protocols due to poor interoperability. In this dissertation, we show that a joint design of the MAC/PHY layers can achieve a substantially higher level of capacity, interoperability and energy efficiency than the weakly coupled MAC/PHY design in the current CSMA wireless networks. In the proposed MAC/PHY co-design, the PHY layer exposes more states and capabilities to the MAC, and the MAC performs intelligent adaptation to and control over the PHY layer. We leverage the reconfigurability of software radios to design smart signal processing algorithms that meet the challenge of making PHY capabilities usable by the MAC layer. With the approach of MAC/PHY co-design, we have revisited the primitive operations of CSMA (collision avoidance, carrier signaling, carrier sensing, spectrum access and transmitter cooperation), and overcome its limitations in relay and broadcast applications, coexistence of heterogeneous networks, energy efficiency, coexistence of different spectrum widths, and scalability for MIMO networks. We have validated the feasibility and performance of our design using extensive analysis, simulation and testbed implementation.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/95944/1/xyzhang_1.pd

Measurement and Optimization of LTE Performance

4G Long Term Evolution (LTE) mobile system is the fourth generation communication system adopted worldwide to provide high-speed data connections and high-quality voice calls. Given the recent deployment by mobile service providers, unlike GSM and UMTS, LTE can be still considered to be in its early stages and therefore many topics still raise great interest among the international scientific research community: network performance assessment, network optimization, selective scheduling, interference management and coexistence with other communication systems in the unlicensed band, methods to evaluate human exposure to electromagnetic radiation are, as a matter of fact, still open issues. In this work techniques adopted to increase LTE radio performances are investigated. One of the most wide-spread solutions proposed by the standard is to implement MIMO techniques and within a few years, to overcome the scarcity of spectrum, LTE network operators will offload data traffic by accessing the unlicensed 5 GHz frequency. Our Research deals with an evaluation of 3GPP standard in a real test best scenario to evaluate network behavior and performance

Tiheiden Wi-Fi verkkojen optimointi Markov-ketjumallien ja simuloidun jäähdytyksen avulla

Currently, the demand for wireless communication capacity is rising rapidly due to challenging applications such as video streaming and the emerging Internet of things. In meeting these ambitious requirements, the most important factor is predicted to be network densification, which refers to increasing the geographical density of simultaneously communicating devices. A natural choice for implementing dense networks is the wireless local area network technology Wi-Fi, characterized by being cheap and easy to deploy. Network density aggravates the harmful effects of interference and causes scarcity of free transmission bandwidth. To counter this, dense networks need radio resource management algorithms. This thesis presents a Wi-Fi radio resource management algorithm, which jointly optimizes access point channels, user association and transmission power. It estimates future throughput using a continuous time Markov chain based model, and finds solutions maximizing this estimate via a discrete search metaheuristic called simulated annealing. The algorithm is validated through a wide range of simulations where for instance network density is varied. The algorithm is found to be highly versatile, yielding good performance in all scenarios. Moreover, the general design approach places few restrictions on further algorithm improvement and extension. Markov chain modeling, although accurate in an idealized setting, turns out to be inaccurate with real-world Wi-Fi, with a simpler model offering similar accuracy but lighter computational load.Nykyisin vaatimukset langattoman tiedonsiirron kapasiteetille ovat voimakkaassa kasvussa johtuen haastavista sovelluksista kuten videon suoratoistosta ja tulossa olevasta esineiden Internetistä. Näiden vaatimusten täyttämiseksi tärkein keino on langattomien tiedonsiirtoverkkojen tihentäminen, mikä tarkoittaa yht’aikaa samalla maantieteellisellä alueella kommunikoivien laitteiden määrän kasvattamista. Luonnollinen valinta tiheiden verkkojen toteuttamiseen on langattomien lähiverkkojen teknologia Wi-Fi, jonka etuja ovat edullisuus ja asennuksen helppous. Langattoman verkon tiheys lisää haitallista interferenssiä ja aikaansaa pulaa vapaista lähetystaajuuksista. Näiden ongelmien ratkaisemiseksi tarvitaan radioresurssien hallinta-algoritmeja. Tässä työssä suunnitellaan Wi-Fiä varten radioresurssien hallinta-algoritmi, joka optimoi samanaikaisesti tukiasemien kanavia, käyttäjien allokaatiota tukiasemille sekä lähetystehoja. Se estimoi tulevia tiedonsiirtonopeuksia jatkuvan ajan Markov-ketjuihin pohjautuvan mallin avulla ja löytää tämän estimaatin maksimoivia ratkaisuja hyödyntämällä diskreettiä hakumenetelmää nimeltä simuloitu jäähdytys. Algoritmi validoidaan käyttäen monipuolista joukkoa simulaatioita, jossa vaihtelee esimerkiksi verkon tiheys. Algoritmi osoittautuu erittäin monipuoliseksi, sillä sen suorituskyky on hyvä kaikissa simulaatioskenaarioissa. Käytetyn lähestymistavan etuna on myös se, että se asettaa varsin vähän rajoituksia algoritmin jatkokehitykselle. Markov-ketjumallit osoittautuvat todellisen Wi-Fin tapauksessa epätarkoiksi, vaikka ne idealisoidussa ympäristössä ovatkin tarkkoja. Käy ilmi, että yksinkertaisemmalla mallilla saadaan vastaava tarkkuus, mutta laskentatehoa tarvitaan vähemmän