Asignación Distribuida Coordinada de Canales para WLANs con Acceso Oportunista

Las WLANs cuentan con una cantidad limitada de canales de frecuencia (espectro radio eléctrico), donde la saturación de estos canales en áreas densamente pobladas se torna un problema inevitable, y es imperativo encontrar nuevos procesos que permitan una eficiente administración de este recurso para mantener una buena calidad de funcionamiento (operación). En este artículo se presenta un algoritmo, basado en la técnica probabilística “Simulated Annealing”, para la asignación de canales de manera distribuida coordinada para redes WLAN, mediante la construcción de árboles de expansión mínima. Se realiza un proceso de asignación de costos y un análisis de niveles de interferencia, el mismo que se ejecuta para cada punto de acceso (AP) del escenario. El objetivo de este trabajo es conseguir una asignación eficiente de canales para cada AP, sea en la banda ISM, o de manera oportunista en una banda licenciada, que permita minimizar los niveles de interferencia de cada AP.WLANs have a limited number of frequency channels (radio spectrum), where the saturation of these channels in densely populated areas becomes an inevitable problem, and it is imperative to find new processes that enable efficient management of this resource to maintain good performance (operation). In this article is presented an algorithm, based on probabilistic technique 'Simulated Annealing', for channel assignment in a distributed coordinated manner for WLAN networks, by building Minimum Spanning Trees. A process of cost allocation and an analysis of interference levels is performed, the same as it is executed for each access point (AP) of the stage. The objective of this work is to achieve efficient allocation of channels for each AP, either in the ISM band, or opportunistically in a licensed band, which minimizes interference levels for each AP

Gestión de Carga en Sistemas con Multi-acceso Inalámbricos

Actualmente los sistemas de comunicaciones inalámbricos disponen de una cantidad limitada de recursos radio (e.g. ancho de banda, potencia de transmisión, etc.), en este sentido, se vuelve importante definir mecanismos que permitan utilizar estos recursos de una manera eficiente para mantener la calidad en el funcionamiento del sistema. Dado lo antes expuesto, en el presente artículo se presenta un mecanismo de gestión de carga, empleando la técnica probabilística simulated annealing (SA), este mecanismo se basa de la solución provista por un análisis de niveles de señales recibidas y la asignación de costos en base a las diferentes tecnologías de estudio que se realizan para cada uno de los múltiples accesos inalámbricos que dispone un dispositivo móvil. El presente trabajo se enfoca en el desarrollo de un algoritmo de balanceo de carga que permita a los sistemas gestionar sus múltiples accesos con el fin de mantener tasas de transmisión elevadas y ofrecer una buena calidad de servicio pese a limitaciones de ancho de banda y condiciones adversas de propagación que caracterizan al canal de radio. En resumen, el objetivo principal de éste trabajo es obtener un acceso o conjunto de accesos operativos con un nivel de carga balanceada, que permita minimizar el costo total de operatividad del sistema sujeto a mantener la capacidad de canal por encima de cierto umbral.Currently, wireless communication systems have a limited amount of radio resources (e.g. bandwidth, transmission power, etc.), in this order, it is important to define mechanisms to use these resources efficiently to maintain quality in the operation of system. Given the above, in this paper a mechanism for load management is presented using the probabilistic technique simulated annealing (SA), this mechanism is based on the solution provided by an analysis of levels of received signals and assigning costs based on different technologies study that are performed for each of multiple wireless access available to a mobile device. This work focuses on the development of a load balancing algorithm that allows managing your multiple access systems in order to maintain high data rates and provide a good quality of service despite bandwidth limitations and adverse conditions characterizing the propagation channel radio. In summary, the main objective of this work is to obtain a set of operational access or access to a level of load balancing, which minimizes the total cost of operation of the system subject to maintaining the channel capacity above a certain threshold

Gestión de Carga en Sistemas de multi-acceso inalámbrico

Actualmente los sistemas de comunicaciones inalámbricos disponen de una cantidad limitada de recursos radio (e.g. ancho de banda, potencia de transmisión, etc.), en este sentido, se vuelve importante definir mecanismos que permitan utilizar estos recursos de una manera eficiente para mantener la calidad en el funcionamiento del sistema. Dado lo antes expuesto, en el presente artículo se presenta un mecanismo de gestión de carga, empleando la técnica probabilística simulated annealing(SA), este mecanismo se basa de la solución provista por un análisis de niveles de señales recibidas y la asignación de costos en base a las diferentes tecnologías de estudio que se realizan para cada uno de los múltiples accesos inalámbricos que dispone un dispositivo móvil. El presente trabajo se enfoca en el desarrollo de un algoritmo de balanceo de carga que permita a los sistemas gestionar sus múltiples accesos con el fin de mantener tasas de transmisión elevadas y ofrecer una buena calidad de servicio pese a limitaciones de ancho de banda y condiciones adversas de propagación que caracterizan al canal de radio. En resumen, el objetivo principal de éste trabajo es obtener un acceso o conjunto de accesos operativos con un nivel de carga balanceada, que permita minimizar el costo total de operatividad del sistema sujeto a mantener la capacidad de canal por encima de cierto umbral.Currently, wireless communication systems have a limited amount of radio resources (e.g. bandwidth, transmission power, etc.), in this order, it is important to define mechanisms to use these resources efficiently to maintain quality in the operation of system. Given the above, in this paper a mechanism for load management is presented using the probabilistic technique simulated annealing (SA), this mechanism is based on the solution provided by an analysis of levels of received signals and assigning costs based on different technologies study that are performed for each of multiple wireless access available to a mobile device. This work focuses on the development of a load balancing algorithm that allows managing your multiple access systems in order to maintain high data rates and provide a good quality of service despite bandwidth limitations and adverse conditions characterizing the propagation channel radio. In summary, the main objective of this work is to obtain a set of operational access or access to a level of load balancing, which minimizes the total cost of operation of the system subject to maintaining the channel capacity above a certain threshold

Novel Approaches for the Performance Enhancement of Cognitive Radio Networks

This research is dedicated to the study of the challenges faced by Cognitive Radio (CR) networks, which include self-coexistence of the networks in the spectral environment, security and performance threats from malicious entities, and fairness in spectrum contention and utilization. We propose novel channel acquisition schemes that allow decentralized CR networks to have multiple channel access with minimal spectrum contentions. The multiple channel acquisition schemes facilitate fast spectrum access especially in cases where networks cannot communicate with each other. These schemes enable CR networks to self-organize and adapt to the dynamically changing spectral environment. We also present a self-coexistence mechanism that allows CR networks to coexist via the implementation of a risk-motivated channel selection based deference structure (DS). By forming DS coalitions, CR networks are able to have better access to preferred channels and can defer transmission to one another, thereby mitigating spectrum conflicts. CR networks are also known to be susceptible to Sybil threats from smart malicious radios with either monopolistic or disruptive intentions. We formulate novel threat and defense mechanisms to combat Sybil threats and minimize their impact on the performance of CR networks. A dynamic reputation system is proposed that considerably minimizes the effectiveness of intelligent Sybil attacks and improves the accuracy of spectrum-based decision-making processes. Finally, we present a distributed and cheat-proof spectrum contention protocol as an enhancement of the adaptive On-Demand Spectrum Contention (ODSC) protocol. The Modified On-Demand Spectrum Contention (MODSC) protocol enhances fairness and efficiency of spectrum access. We also show that there is substantial improvement in spectrum utilization with the incorporation of channel reuse into the MODSC protocol

Distributed channel assignment algorithm based on simulated annealing for uncoordinated OSA-enabled WLANs

A promising approach to alleviate ISM band congestion problems in highly dense WLAN scenarios consists of exploiting opportunistic spectrum access (OSA) to underutilized bands under a primary-secondary model. This paper develops a distributed channel assignment algorithm valid for uncoordinated WLAN deployments where access points do not follow any specific planning and they could belong to different administrative domains. Unlike existing channel assignment schemes proposed for legacy WLANs, channel assignment mechanisms for OSA-enabled WLAN should address two distinguishing issues: channel prioritization and spectrum heterogeneity. Over such a basis, this paper develops and assesses the performance of a distributed channel assignment algorithm that is able to exploit both channel prioritization and spectrum heterogeneity concepts. In particular, the algorithm is based on a distributed adaptation of the simulated annealing metaheuristic algorithm commonly used in global optimization problems.Peer ReviewedPostprint (published version

Distributed channel assignment algorithm based on simulated annealing for uncoordinated OSA-enabled WLANs

A promising approach to alleviate ISM band congestion problems in highly dense WLAN scenarios consists of exploiting opportunistic spectrum access (OSA) to underutilized bands under a primary-secondary model. This paper develops a distributed channel assignment algorithm valid for uncoordinated WLAN deployments where access points do not follow any specific planning and they could belong to different administrative domains. Unlike existing channel assignment schemes proposed for legacy WLANs, channel assignment mechanisms for OSA-enabled WLAN should address two distinguishing issues: channel prioritization and spectrum heterogeneity. Over such a basis, this paper develops and assesses the performance of a distributed channel assignment algorithm that is able to exploit both channel prioritization and spectrum heterogeneity concepts. In particular, the algorithm is based on a distributed adaptation of the simulated annealing metaheuristic algorithm commonly used in global optimization problems.Peer Reviewe

Efficient Passive Clustering and Gateways selection MANETs

Passive clustering does not employ control packets to collect topological information in ad hoc networks. In our proposal, we avoid making frequent changes in cluster architecture due to repeated election and re-election of cluster heads and gateways. Our primary objective has been to make Passive Clustering more practical by employing optimal number of gateways and reduce the number of rebroadcast packets

Proposal and evaluation of channel assignment algorithms for wireless local area networks with opportunistic spectrum acces capabilities

The growing need for wireless connectivity is pushing the massive adoption and usage of Wireless Local Area Networks (WLANs) based on the IEEE 802.11 standard (Wi-Fi), leading to dense deployments of individual, uncoordinated access points (AP) in highly populated areas. By 2016, over half of the world's Internet traffic is expected to come from WLAN connections, according to the latest Cisco® Visual Networking Index (VNI) Forecast (2011-2016). The proliferation of dense deployments causes high interference levels in the unlicensed bands (i.e. ISM bands) available for WLAN operation, which, ultimately, may result in both an unpredictable degradation in network performance and unfairness among APs. Channel assignment mechanisms are the central tool used nowadays for mitigating the interference problems in the ISM band caused by neighboring APs. However, regardless of the ability of different channel assignment algorithms to improve WLAN performance, the amount of available spectrum in unlicensed bands for WLAN use may still constitute a key limiting factor in high dense deployments. In this context, the exploitation of additional portions of the radio spectrum bands that are assigned to a particular application or service but remain unused or unoccupied at specific locations and times can help to further improve the performance of WLANs networks. This spectrum usage concept is known in the literature as Opportunistic Spectrum Access (OSA), where secondary users are allowed to share the same frequencies used by some primary users whenever these primary services are not disturbed. This thesis work has addressed a novel study for OSA-enabled WLANs in which the possibilities and benefits offered by WLANs using OSA capabilities are discussed and quantified. This thesis provides two main contributions. The first contribution is the development of the formulation and assessment of the spatial availability of a certain spectrum segment within indoor locations in dense urban areas in order for it to be opportunistically reused by WLANs. To this end, the interference conditions between primary and secondary users have been established along with the necessary propagation models accounting for outdoor, indoor and outdoor-to-indoor losses. Considering the service area of a primary system devoted to providing outdoor coverage, the proposed model has been used to compute the percentage of indoor locations where the secondary users can actually reuse the primary frequency band without interfering with the primary system. The second contribution is the proposal, development and evaluation of a set of channel assignment algorithms that allow WLANs to operate on available channels in both unlicensed ISM and OSA-enabled spectrum bands. Unlike the classical schemes for legacy WLANs, the proposed algorithms cope with two distinguishing issues arising in the OSA-enabled WLAN channel assignment problem: channel prioritization and spectrum heterogeneity. To that end, a system model is developed to describe and represent the main components involved in an OSA-enabled WLAN scenario. The model allows setting up a network scenario with primary and secondary systems, determining the list of available primary channels for each WLAN and defining the channel assignment constraints for WLANs. From this basis, the thesis has first formulated the channel assignment problem for OSA-enabled WLANs as a Binary Linear Programming (BLP) problem, which has been optimally solved by means of branch-and bound (BB) algorithms and used as a benchmark. Motivated by the need to have more computationally efficient solutions than that offered by the BB algorithm, a number of centralized and distributed heuristic algorithms have been proposed, encompassing simulated annealing (SA) techniques and the construction of minimum spanning tree (MST) graphs to reduce the level of coupling between neighboring APs. The algorithms have been evaluated under different conditions of AP density and spectrum availability and compared to the optimal solution as well as classical algorithms proposed for legacy WLANs.Postprint (published version