Priority-Oriented Adaptive Control With QoS Guarantee for Wireless LANs.

In today’s wireless networks there is a great need for QoS, because of the time-bounded voice, audio and video traffic. A new QoS enhanced standard is being standardized by the IEEE 802.11e workgroup. It uses a contention free access mechanism called Hybrid Control Channel Access (HCCA) to guarantee QoS. However, HCCA is not efficient for all types of time-bounded traffic. This work proposes an alternative protocol which could be adapted in HCF (Hybrid Coordination Function). The Priority Oriented Adaptive Control with QoS Guarantee (POAC-QG) is a complete centralized channel access mechanism, it is able to guarantee QoS for all types of multimedia network applications, it enhances the parameterized traffic with priorities, and it supports time division access using slots. Furthermore, it instantly negotiates the quality levels of the traffic streams according to their priorities, supporting multiple streams to the best quality it can achieve. POAC-QG compared to HCCA, provides higher channel utilization, adapts better to the characteristics of the different traffic types, differentiates the traffic streams more efficiently using priorities, and generally exhibits superior performance

A fair access mechanism based on TXOP in IEEE 802.11e wireless networks

IEEE 802.11e is an extension of IEEE 802.11 that provides Quality of Service (QoS) for the applications with different service requirements. This standard makes use of several parameters such as contention window; inter frame space time and transmission opportunity to create service differentiation in the network. Transmission opportunity (TXOP), that is the focus point of this paper, is the time interval, during which a station is allowed to transmit packets without any contention. As the fixed amounts of TXOPs are allocated to different stations, unfairness appears in the network. And when users with different data rates exist, IEEE 802.11e WLANs face the lack of fairness in the network. Because the higher data rate stations transfer more data than the lower rate ones. Several mechanisms have been proposed to solve this problem by generating new TXOPs adaptive to the network's traffic condition. In this paper, some proposed mechanisms are evaluated and according to their evaluated strengths and weaknesses, a new mechanism is proposed for TXOP determination in IEEE 802.11e wireless networks. Our new algorithm considers data rate, channel error rate and data packet lengths to calculate adaptive TXOPs for the stations. The simulation results show that the proposed algorithm leads to better fairness and also higher throughput and lower delays in the network.

A Greedy Reclaiming Scheduler for IEEE 802.11e HCCA Real-Time Networks

The IEEE 802.11e standard introduces Quality of Service (QoS) support for wireless local area networks and suggests how to design a tailored HCF Controlled Channel Access (HCCA) scheduler. However the reference scheduling algorithm is suitable to assure service guarantees only for Constant Bit Rate traffic streams, whereas shows its limits for Variable Bit Rate traffic. Despite the numerous alternative schedulers proposed to improve the QoS support for multimedia applications, in the case of VBR traffic satisfactory real-time performance has not been yet achieved. This paper presents a new scheduling algorithm, Unused Time Shifting Scheduler (UTSS). It integrates a mechanism for bandwidth reclaiming into a HCCA real-time scheduler. UTSS assigns the unused portion of each transmission opportunity to the next scheduled traffic stream. Thanks to such feature, traffic variability is absorbed, reducing the waste of resources. The analytical evaluation, corroborated by the simulation results, shows that UTSS is suitable to reduce the delay experienced by VBR traffic streams and to increase the maximum burstiness sustainable by the network

A IEEE 802.11e HCCA Scheduler with a Reclaiming Mechanism for Multimedia Applications

The QoS offered by the IEEE 802.11e reference scheduler is satisfactory in the case of Constant Bit Rate traffic streams, but not yet in the case of Variable Bit Rate traffic streams, whose variations stress its scheduling behavior. Despite the numerous proposed alternative schedulers with QoS, multimedia applications are looking for refined methods suitable to ensure service differentiation and dynamic update of protocol parameters. In this paper a scheduling algorithm,Unused Time Shifting Scheduler(UTSS), is deeply analyzed. It is designed to cooperate with a HCCA centralized real-time scheduler through the integration of a bandwidth reclaiming scheme, suitable to recover nonexhausted transmission time and assign that to the next polled stations. UTSS dynamically computes with anO(1)complexity transmission time providing an instantaneous resource overprovisioning. The theoretical analysis and the simulation results highlight that this injection of resources does not affect the admission control nor the centralized scheduler but is suitable to improve the performance of the centralized scheduler in terms of mean access delay, transmission queues length, bursts of traffic management, and packets drop rate. These positive effects are more relevant for highly variable bit rate traffic