The demand for end-to-end Quality of Service (QoS) in Wireless Local Area Networks (WLANs) is becoming ever more important due to the trend towards converged communication networks. The recently accepted QoS mechanism in WLAN; the IEEE 802.11e has limitations in providing fairness to different types of traffic. We propose Dynamic Weighted Fair Scheduling Scheme (DWFSS) to improve fairness in WLANs by enhancing the IEEE 802.11e. The DWFSS allocates bandwidth to four different classes of traffic. These classes are assigned weights which are dynamically changed. The service interval in IEEE 802.11e is divided into two intervals i.e., High Priority Polling Interval (HPPI) and Low Priority Polling Interval (LPPI). The high priority traffic is polled during HPPI and low priority traffic is polled during LPPI. The performance of DWFSS is evaluated on NCTUns simulator using multiple types of traffic and compared with the standard scheduler. The simulation results showed that DWFSS improved fairness when compared to IEEE 802.11e standard scheduler. DWFSS increased average throughput by 13.48% and reduced average jitter by 16.21% while maintaining an acceptable level of end-to-end delay.

Improving qos in wlan using dynamic weighted fair scheduling

This PhD study aims to investigate techniques for efficient usage of spectrum for next generation mobile communication networks. The Long Term Evolution (LTE) and LTEAdvanced (LTE-A) systems are taken as case studies. The LTE is under development within 3rd Generation Partnership Project (3GPP) and heading towards its final phase of standardization. The LTE aims for reduced latency, higher user data rates, improved system capacity and coverage, and reduced cost for the operators. Currently the International Telecommunications Union (ITU) is working on specifying the system requirements towards next generation mobile communication systems called International Mobile Telecommunications-Advanced (IMT-A). The 3GPP aims to further evolve LTE towards LTE-A in order to meet or exceed the IMT-A requirements as well as its own requirements for advancing LTE for long term competitiveness. The first half of the PhD study is mainly concerned with LTE, with the main focus on higher order sectorization and inter-cell interference avoidance to improve system capacity and coverage. Typically three antennas are considered rendering 3 sector site deployments for LTE. A migration to 6 sector site deployment has been investigated. A mixed network topology composed of a combination of 3 and 6 sectors site deployment is also proposed. The mixed network topology is found to provide significantly high performance gains in terms of cell throughput and user outage throughput performance, and therefore recommended as a potential solution to meet high traffic demands in localized areas such as hot spots. LTE uses Orthogonal Frequency Division Multiple Access (OFDMA) in the downlink with universal frequency reuse. Due to the characteristics of OFDMA, the intra-cell interference is ideally avoided , but the environment still remains interference limited due to the presence of inter-cell interference. Our focus in this study is on development of schemes for inter-cell interference avoidance under fractional load conditions. The fractional load conditions arise when all the resources are not required to be used due to lack of traffic in the cell. We propose several autonomous inter-cell interference avoidance schemes, which do not require inter-cell signaling and provide significant improvements in cell throughput and user outage throughput performance. The second half of the study is concerned with LTE-A, which aims to provide peak data rates in the order of 1 Gbps in downlink and 500 Mbps in uplink for the nomadic local area/indoor deployment scenarios. Such high data rates may require high spectral efficiency and a wide bandwidth spectrum allocation in the order of 100 MHz. Such high bandwidth allocation may require sharing of spectrum among operators in a flexible manner. Currently, Home e-nodeB (HeNB) is emerging as a potential solution to provide high data rate high quality indoor coverage. Potentially large scale uncoordinated deployment of HeNBs, sharing over the same

Techniques for Efficient Spectrum Usage for Next Generation Mobile Communication Networks. An LTE and LTE-A Case Study

We model wireless local area network channel utilization over a finite interval through a finite time-horizon Markov (FTHM) model. By accurately capturing time-varying utilization, the FTHM model allows for generally distributed transmission-opportunity (TXOP) duration, which most existing models do not account for. An absorbing state is introduced to limit the lifetime of the counting process, resulting in a non-ergodic Markov chain that is solved via transient analysis. The model predictions for time-varying utilization are validated by simulation with errors of no more than 0.1% after eight beacon intervals. Moreover, we show that the FTHM model prediction error is below 4% for Poisson distributed and uniformly distributed TXOP durations.

Finite time-horizon Markov model for IEEE 802.11e

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A Testbed About Priority-Based Dynamic Connection Profiles in QoS Wireless Multimedia Networks

Hoy en dia existen varias tecnologias que coexisten en una misma zona formando un sistema heterogeneo. Ademas, este hecho se espera que se vuelva mas acentuado con todas las nuevas tecnologias que se estan estandarizando actualmente. Hasta ahora, generalmente son los usuarios los que eligen la tecnologia a la que se van a conectar, ya sea configurando sus terminales o usando terminales distintos. Sin embargo, esta solucion es incapaz de aprovechar al maximo todos los recursos. Para ello es necesario un nuevo conjunto de estrategias. Estas estrategias deben gestionar los recursos radioelectricos conjuntamente y asegurar la satisfaccion de la calidad de servicio de los usuarios. Siguiendo esta idea, esta Tesis propone dos nuevos algoritmos. El primero es un algoritmo de asignacion dinamica de recusos conjunto (JDRA) capaz de asignar recursos a usuarios y de distribuir usuarios entre tecnologias al mismo tiempo. El algoritmo esta formulado en terminos de un problema de optimizacion multi-objetivo que se resuelve usando redes neuronales de Hopfield (HNNs). Las HNNs son interesantes ya que se supone que pueden alcanzar soluciones sub-optimas en cortos periodos de tiempo. Sin embargo, implementaciones reales de las HNNs en ordenadores pierden esta rapida respuesta. Por ello, en esta Tesis se analizan las causas y se estudian posibles mejoras. El segundo algoritmo es un algoritmo de control de admision conjunto (JCAC) que admite y rechaza usuarios teniendo en cuenta todas las tecnologias al mismo tiempo. La principal diferencia con otros algorimos propuestos es que estos ultimos toman las dicisiones de admision en cada tecnologia por separado. Por ello, se necesita de algun mecanismo para seleccionar la tecnologia a la que los usuarios se van a conectar. Por el contrario, la tecnica propuesta en esta Tesis es capaz de tomar decisiones en todo el sistema heterogeneo. Por lo tanto, los usuarios no se enlazan con ninguna tecnologia antes de ser admitidos.

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Common Radio Resource Management Strategies for Quality of Service Support in Heterogeneous Wireless Networks

The appearance of the 802.11e standard made the 802.11 wireless local area networks (WLANs) capable of providing different levels of quality of service (QoS). This standard defines two new channel access mechanisms (CAMs), namely the enhanced distributed channel access (EDCA) and the HCF controlled channel access (HCCA). The introduction of two CAMs increases the complexity of traffic management, since now not only the available resources have to be distributed, but also the optimal CAM for each data flow has to be selected. However, the best CAM selection algorithm is still not clear. This paper presents and analyses different CAM selection policies in order to derive the best-suited strategy in terms of system performance. From this study, an optimal policy, based on traffic type and direction (uplink or downlink), is proposed. The best user QoS satisfaction shown in the results confirms the good performance of this new selection policy.

D. Gozalvez

Papers

Policy-based channel access mechanism selection for QoS provision in IEEE 802.11e