Resumen de Radio resource and mobility management issues in the framework of wlan 802.11 networks
One of the major challenges of a wireless mobile Internet is the provision of quality of service (QoS) over lP-based wireless access networks. Within the context of this thesis, we have been concentrated on two research areas of QoS in wireless communication: radio resource management in IEEE B02.11 networks and intra-domain seamless mobility.
The first part of the thesis focuses on QoS capabilities and risks in IEEE B02.11 networks. This topic became a huge research area with the change of focus from the best effort based system towards a local area networking solution, centralized around delay sensitive type of applications with quality of service constraint, like voice over IP or streaming multimedia. In this area the developed work includes: analysis of the problem with non-elastic traffic over best effort oriented legacy IEEEB02.11 standard, review of QoS enhancements developed in IEEE B02.11 Task Group "e' (TGe) and innovative strategies for improving WLAN performance.
The assessment of QoS capabilities and risks of the IEEEB02.11 WLAN standard has been done by means of a simulator, developed in OPNET environment and validated through analytical model, which includes the main QoS features of Enhanced Distributed Channel Access mechanism proposed in IEEEB02.11e.
The main findings of the QoS analysis originated the work on three radio resource management (RRM) topics: admission control, efficient resource usage through enhanced transmission opportunity (TXOP) schemes as well as QoS provision in the QoS aware basic service set (QBSS), composed of the legacy non-QoS devices and QoS enabled devices.
The admission control mechanism builds on distributed admission control mechanism (DAC) (initially proposed to IEEEB02.11e but currently not part of the standard). It addresses its issues with the accurate estimation of the used resources and the limitation of use with only non-elastic type of traffic (with constant bandwidth/delay requirements). As oppose to DAC the developed solution does not rely on fix chunks of resources assigned to each EDCA function and, consequently, it can respond faster and adapt to temporary resource usage variations.
The devised TXOP management schemes tackle the optimum TXOP duration issue and usage of TXOP to address asymmetry of uplink and down link traffic. The optimum TXOP duration approach makes use of a distribution of backlogged packets within AP's queues to define the rules for TXOP duration adjustment. Whereas through enhanced TXOP (ETXOP) the changes to EDCA access rules are proposed to give higher priority to access point (AP) to deal with asymmetry of uplink and down link traffic. The simulation study verifies proposed solutions.
The study on coexistence of the legacy non-QoS and QoS enabled devices reveals important dependency of QoS service level and the number and type of coexisting legacy stations. Two mechanisms have been investigated to ensure QoS in this mixed scenario: hierarchical token bucket (HTB) link sharing scheme and MAC level medium reservation mechanism.
In the second part of the thesis approaches the QoS and RRM challenge in WLAN from different angle. Instead of having bottom-up approach the problem has been analysed starting from deployment architecture. The proposed channel blanket deployment has been analysed and compared with the typical cellular deployment methodology, focusing on issues like coverage, capacity, mobility, QoS and energy consumption. After that the global radio resource manager (GRRM) has been developed to manage channel access schedules and enforce access policies to provide seamless mobility and data rate optimization.
