Performance analysis of a threshold-based dynamic TXOP scheme for intra-AC QoS in wireless LANs

PublishedJournal ArticleThis is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.The IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol has been proposed for provisioning of differentiated Quality-of-Service (QoS) between various Access Categories (ACs), i.e., inter-AC QoS, in Wireless Local Area Networks (WLANs). However, the EDCA lacks the support of the intra-AC QoS provisioning, which is indispensable in practical WLANs since the network loads are always asymmetric between traffic flows of ACs with the same priority. To address the intra-AC QoS issue, this paper proposes a Threshold-Based Dynamic Transmission Opportunity (TBD-TXOP) scheme which sets the TXOP limits adaptive to the current status of the transmission queue based on the pre-setting threshold. An analytical model is further developed to evaluate the QoS performance of this scheme in terms of throughput, end-to-end delay, and frame loss probability. NS-2 simulation experiments validate the accuracy of the proposed analytical model. The performance results demonstrate the efficacy of TBD-TXOP for the intra-AC QoS differentiation. © 2013 Elsevier B.V. All rights reserved

Analysis and improvement of medium access control protocols in wireless networks. Performance modelling and Quality-of-Service enhancement of IEEE 802.11e MAC in wireless local area networks under heterogeneous multimedia traffic.

In order to efficiently utilize the scarce wireless resource as well as keep up with the ever-increasing demand for Quality-of-Service (QoS) of multimedia applications, wireless networks are undergoing rapid development and dramatic changes in the underlying technologies and protocols. The Medium Access Control (MAC) protocol, which coordinates the channel access and data transmission of wireless stations, plays a pivotal role in wireless networks. Performance modelling and analysis has been and continues to be of great theoretical and practical importance in the design and development of wireless networks. This research is devoted to developing efficient and cost-effective analytical tools for the performance analysis and enhancement of MAC protocols in Wireless Local Area Networks (WLANs) under heterogeneous multimedia traffic. To support the MAC-layer QoS in WLANs, the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol has proposed three QoS differentiation schemes in terms of Arbitrary Inter-Frame Space (AIFS), Contention Window (CW), and Transmission Opportunity (TXOP). This research starts with the development of new analytical models for the TXOP scheme specified in the EDCA protocol under Poisson traffic. A dynamic TXOP scheme is then proposed to adjust the TXOP limits according to the status of the transmission queue. Theoretical analysis and simulation experiments show that the proposed dynamic scheme largely improves the performance of TXOP. To evaluate the TXOP scheme in the presence of ii heterogeneous traffic, a versatile analytical model is developed to capture the traffic heterogeneity and model the features of burst transmission. The performance results highlight the importance of taking into account the heterogeneous traffic for the accurate evaluation of the TXOP scheme in wireless multimedia networks. To obtain a thorough and deep understanding of the performance attributes of the EDCA protocol, a comprehensive analytical model is then proposed to accommodate the integration of the three QoS schemes of EDCA in terms of AIFS, CW, and TXOP under Poisson traffic. The performance results show that the TXOP scheme can not only support service differentiation but also improve the network performance, whereas the AIFS and CW schemes provide QoS differentiation only. Moreover, the results demonstrate that the MAC buffer size has considerable impact on the QoS performance of EDCA under Poisson traffic. To investigate the performance of EDCA in wireless multimedia networks, an analytical model is further developed for EDCA under heterogeneous traffic. The performance results demonstrate the significant effects of heterogeneous traffic on the total delay and frame losses of EDCA with different buffer sizes. Finally, an efficient admission control scheme is presented for the IEEE 802.11e WLANs based on analytical modelling and a game-theoretical approach. The admission control scheme can maintain the system operation at an optimal point where the utility of the Access Point (AP) is maximized with the QoS constraints of various users

Distributed Medium Access Control for QoS Support in Wireless Networks

With the rapid growth of multimedia applications and the advances of wireless communication technologies, quality-of-service (QoS) provisioning for multimedia services in heterogeneous wireless networks has been an important issue and drawn much attention from both academia and industry. Due to the hostile transmission environment and limited radio resources, QoS provisioning in wireless networks is much more complex and difficult than in its wired counterpart. Moreover, due to the lack of central controller in the networks, distributed network control is required, adding complexity to QoS provisioning. In this thesis, medium access control (MAC) with QoS provisioning is investigated for both single- and multi-hop wireless networks including wireless local area networks (WLANs), wireless ad hoc networks, and wireless mesh networks. Originally designed for high-rate data traffic, a WLAN has limited capability to support delay-sensitive voice traffic, and the service for voice traffic may be impacted by data traffic load, resulting in delay violation or large delay variance. Aiming at addressing these limitations, we propose an efficient MAC scheme and a call admission control algorithm to provide guaranteed QoS for voice traffic and, at the same time, increase the voice capacity significantly compared with the current WLAN standard. In addition to supporting voice traffic, providing better services for data traffic in WLANs is another focus of our research. In the current WLANs, all the data traffic receives the same best-effort service, and it is difficult to provide further service differentiation for data traffic based on some specific requirements of customers or network service providers. In order to address this problem, we propose a novel token-based scheduling scheme, which provides great flexibility and facility to the network service provider for service class management. As a WLAN has small coverage and cannot meet the growing demand for wireless service requiring communications ``at anywhere and at anytime", a large scale multi-hop wireless network (e.g., wireless ad hoc networks and wireless mesh networks) becomes a necessity. Due to the location-dependent contentions, a number of problems (e.g., hidden/exposed terminal problem, unfairness, and priority reversal problem) appear in a multi-hop wireless environment, posing more challenges for QoS provisioning. To address these challenges, we propose a novel busy-tone based distributed MAC scheme for wireless ad hoc networks, and a collision-free MAC scheme for wireless mesh networks, respectively, taking the different network characteristics into consideration. The proposed schemes enhance the QoS provisioning capability to real-time traffic and, at the same time, significantly improve the system throughput and fairness performance for data traffic, as compared with the most popular IEEE 802.11 MAC scheme

Performance Evaluation of Wireless Medium Access Control Protocols for Internet of Things

The Internet of Things makes the residents in Smart Cities enjoy a more efficient and high-quality lifestyle by wirelessly interconnecting the physical and visual world. However, the performance of wireless networks is challenged by the ever-growing wireless traffic data, the complexity of the network structures, and various requirements of Quality of Service (QoS), especially on the Internet of Vehicle and wireless sensor networks. Consequently, the IEEE 802.11p and 802.11ah standards were designed to support effective inter-vehicle communications and large-scale sensor networks, respectively. Although their Medium Access Control protocols have attracted much research interest, they have yet to fully consider the influences of channel errors and buffer sizes on the performance evaluation of these Medium Access Control (MAC) protocols. Therefore, this thesis first proposed a new analytical model based on a Markov chain and Queuing analysis to evaluate the performance of IEEE 802.11p under imperfect channels with both saturated and unsaturated traffic. All influential factors of the Enhanced Distributed Channel Access (EDCA) mechanism in IEEE 802.11p are considered, including the backoff counter freezing, Arbitration Inter-Frame Spacing (AIFS) defers, the internal collision, and finite MAC buffer sizes. Furthermore, this proposed model considers more common and actual conditions with the influence of channel errors and finite MAC buffer sizes. The effectiveness and accuracy of the developed model have been validated through extensive ns-3 simulation experiments. Second, this thesis proposes a developed analytical model based on Advanced Queuing Analysis and the Gilbert-Elliot model to analyse the performance of IEEE 802.11p with burst error transmissions. This proposed analytical model simultaneously describes transmission queues for all four Access Categories (AC) queues with the influence of burst errors. Similarly, this presented model can analyse QoS performance, including throughputs and end-to-end delays with the unsaturated or saturated load traffics. Furthermore, this model operates under more actual bursty error channels in vehicular environments. In addition, a series of simulation experiments with a natural urban environment is designed to validate the efficiency and accuracy of the presented model. The simulation results reflect the reliability and effectiveness of the presented model in terms of throughput and end-to-end delays under various channel conditions. Third, this thesis designed and implemented a simulation experiment to analyse the performance of IEEE 802.11ah. These simulation experiments are based on ns-3 and an extension. These simulation experiments' results indicate the Restricted Access Window (RAW) mechanism's influence on the throughputs, end-to-end delays, and packet loss rates. Furthermore, the influences of channel errors and bursty errors are considered in the simulations. The results also show the strong impact of channel errors on the performance of IEEE 802.11ah due to urban environments. Finally, the potential future work based on the proposed models and simulations is analysed in this thesis. The proposed models of IEEE 802.11p can be an excellent fundamental to optimise the QoS due to the precise evaluation of the influence of factors on the performance of IEEE 802.11p. Moreover, it is possible to migrate the analytical models of IEEE 802.11p to evaluate the performance of IEEE 802.11ah

Control-theoretic adaptive mechanisms for performance optimization of IEEE 802.11 WLANs: design, implementation and experimental evaluation

The media access control (MAC) layer of the IEEE 802.11 standard specifies a set of parameters that regulate the behavior of the wireless stations when accessing the channel. Although the standard defines a set of recommended values for these parameters, they are statically set and do not take into account the current conditions in the wireless local area network (WLAN) in terms of, e.g., number of contending stations and the traffic they generate, which results in suboptimal performance. In this thesis we propose two novel control theoretic approaches to optimally configure the WLAN parameters based on the dynamically observed network conditions: a Centralized Adaptive Control (CAC) algorithm, whereby the access point (AP) computes the con guration that maximizes performance and signals it to the active stations, and a Distributed Adaptive Control (DAC) algorithm, which is independently employed by each station with the same goal. In contrast to previous proposals, which are mostly based on heuristics, our approaches build upon (i) analytical models of the WLAN performance, used to derive the optimal point of operation of the IEEE 802.11 protocol, and (ii) mathematical foundations from single- and multi-variable control theory, used to design the mechanisms that drive the WLAN to this point of operation. Another key advantage of the proposed algorithms over existing approaches is that they are compliant with the IEEE 802.11 standard and can be implemented with current wireless cards without introducing any modifications into their hardware and/or firmware. We show by means of an exhaustive performance evaluation study that our algorithms maximize the WLAN performance in terms of throughput and delay under a wide set of network conditions, substantially outperforming the standard recommended configuration as well as previous adaptive proposals. Finally, we present our experiences with implementing the proposed adaptive algorithms in a real IEEE 802.11 testbed and discuss the implementation details of the building blocks that comprise these mechanisms. We evaluate their performance by conducting extensive measurements, considering different network conditions in terms of number of nodes, transmission power employed and tra c generated. Based on the obtained results, we provide valuable insights on the performance of the distributed and centralized algorithms and discuss the suitability of these schemes for real deployments. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------El nivel MAC (Media Access Control) del estándar IEEE 802.11 especifica una serie de parámetros que definen el comportamiento de las estaciones inalámbricas cuando acceden al canal. En dicho estándar se define un conjunto de valores recomendados para estos parámetros, si bien estos valores, constantes, no tienen en cuenta las condiciones de la red inalámbrica -en términos de, por ejemplo, número de estaciones o tráfico cursado- por lo que resultan en un rendimiento subóptimo. En esta tesis se proponen dos nuevos algoritmos para configurar de forma óptima estos parámetros partiendo de las condiciones observadas de la red. Dichos algoritmos, construidos sobre la base de la teoría de control, son los siguientes: CAC (Centralized Adaptive Control), que se ejecuta en el punto de acceso, el cual distribuye la configuración a usar al resto de estaciones; y DAC (Distributed Adaptive Control), ejecutado por cada estación de la red inalámbrica de forma independiente. A diferencia de las propuestas anteriores, casi todas ellas basada en heurísticos, los algoritmos se basan en (i) un modelo analítico del rendimiento de la red inalámbrica, necesario para obtener el punto de operación óptimo de la red; y (ii) fundamentos matemáticos de la teoría de control mono y multivariable, aplicados para diseñar el mecanismo que lleva la red a dicho punto de operación. Otra ventaja de los esquemas propuestos frente al trabajo previo es que son compatibles con el estándar IEEE 802.11, y pueden ser implementados sobre las tarjetas existentes sin necesidad de cambiar el hardware o el firmware. Mediante una extensa evaluación de rendimiento bajo diversas condiciones, se comprueba que los algoritmos maximizan las prestaciones de la red tanto en ancho de banda como en retardo, mejorando notablemente los resultados proporcionados por la configuración recomendada en el estándar así como por propuestas dinámicas anteriores. Por último, se presentan las experiencias del prototipado de dichos algoritmos sobre dispositivos IEEE 802.11, discutiendo los detalles de implementación de sus diferentes bloques. Se evalúan las prestaciones de los mismos mediante una extensa serie de experimentos, incluyendo diferentes escenarios en términos del número de nodos, potencia de transmisión usada y tráfico generado. Los resultados obtenidos permiten extraer valiosas conclusiones sobre el rendimiento de los esquemas adaptativos centralizados y distribuidos, así como la viabilidad de su despliegue en escenarios reales

Enhancements and Challenges in IEEE 802.11ah - A Sub-Gigahertz Wi-Fi for IoT Applications

Internet of Things is a concept which brings ubiquitous connectivity to objects that we interact with in the course of our daily activities. With the projected estimates of the number of wireless connected devices reaching massive numbers, it is expected to revolutionize our daily lives significantly. This sort of augmented connectivity will enable new applications in a myriad of domains including smart cities, smart houses, healthcare monitoring, industrial automation and smart metering. These applications entail efficient operation of wireless networks with a large number of energy constrained devices. However, the existing infrastructure for wireless connectivity is not designed to handle such volume of projected growth. Addressing this requirement, the IEEE 802.11ah task group is working on a new amendment of the IEEE 802.11 standard, suitable for high density WLAN networks in the sub 1 GHz band. It is expected to be the prevalent standard in many Internet of Things (IoT) and Machine to Machine (M2M) applications where it will support long-range and energy-efficient communication in dense network environments. Therefore, significant changes in the legacy 802.11 standards have been proposed to improve the network performance in high contention scenarios. In this thesis we evaluate the performance of many of the new features that have been introduced in the new standard including the Restricted Access Window, Sectorization and Subchannel Selective Transmission mechanisms by means of analytical and simulated models. We propose novel Medium Access Control (MAC) layer algorithms which are shown to have improved the throughput and energy efficiency performance in IEEE 802.11ah networks. We consider practical deployment scenarios in our simulations and evaluate the effects of challenges such as dense networks, interference from neighboring cells and duty cycle limitations on the performance metrics. Overall, we find that the advanced new features make 802.11ah standard a true IoT-enabling technology towards seamless integration of massive amount of connected devices in the future. Our research effort supports the notion that IEEE 802.11ah will be a key technology for future IoT and M2M applications especially in long-range and energy efficient deployments