This paper assesses application-level QoS and Quality of Experience (QoE) in the case where audio and video streams are transferred with the enhanced distributed channel access (EDCA) of the IEEE 802.11e MAC. In EDCA, a station can transmit multiple MAC frames during a transmission opportunity (TXOP); this is referred to as TXOP-bursting. By simulation, we first compare application-level QoS with the TXOP-bursting scheme and that without the scheme for various distances between access point (AP) and stations. In this paper, we suppose that the bit error rate (BER) becomes larger as the distance increases. Numerical results show that TXOP-bursting can improve many metrics of video quality such as average media unit (MU) delay, MU loss ratio, and media synchronization quality, particularly when the AP sends audio and video streams to stations in the downlink direction. We then examine the effect of TXOPLimit on the video quality. Simulation results show that the video quality can be degraded if the value of TXOPLimit is too small. Furthermore, we assess QoE by the method of successive categories, which is a psychometric method. Numerical results show that TXOP-bursting can also improve the QoE. We also perform QoS mapping between application-level and user-level with principal component analysis and multiple regression analysis.

Recent rapid development of high-speed wireless access technologies has created mixed WLAN (Wireless LAN) environments where QoS capable APs coexist with legacy APs. To provide QoS guarantee in this mixed WLAN environment, this paper proposes a new AP selection algorithm. The proposed algorithm assigns an STA (Station) to an AP in the overall WLAN service area. Simulation results show improvement in the VoIP performance in terms of an eMOS (estimated Mean Opinion Score) value and the FTP throughput compared to conventional algorithms.

The IEEE802.11e is a standard developed by a Task Group E of the IEEE802.11 working group and defines a MAC protocol, which provides EDCA (enhanced distributed channel access) and HCCA (HCF controlled channel access) to support differentiation service over WLAN (wireless LAN). In IEEE802.11e WLAN, real-time application such as VoIP (Voice over IP) can have more chances to access the WM (wireless medium) than non real-time application. In addition to QoS support in WLAN, power consumption is a critical issue when WLAN is used in handheld devices. For power saving in the use of real-time applications like VoIP under EDCA, U-APSD (Unscheduled Automatic Power Save Delivery) was proposed in [2] and [4]. In fact, it can save power consumption and works well when it is used for bi-directional voice connections generated at constant bit rate. However, when it is used for real-time applications like ON-OFF traffic, buffering delay at AP (access point) increases. To reduce the buffering delay, this paper proposes two mechanisms. Simulation results show that they can alleviate buffering delay generated at AP.

In wireless local area networks (WLANs), the necessity of quality-of-service (QoS) control for uplink flows is increasing because interactive applications are becoming more popular. Fairness between flows transmitted by stations with different physical transmission rates must be ensured in QoS control for link-adaptive WLANs, which are widely used nowadays. We propose a novel distributed access scheme called QC-DCA to satisfy these requirements. QC-DCA adaptively controls the parameters of carrier sense multiple access with collision avoidance (CSMA/CA). QC-DCA has two QoS control functions: guarantee and classification. QC-DCA guarantees target throughputs and packet delays by quickly adjusting CSMA/CA parameters. In QoS classification, the difference of throughputs and packet delays between different QoS classes is maintained. These two functions allow QC-DCA to suppress the unfairness caused by differences of transmission rates in the physical layer. We evaluated the throughput and delay performances of our scheme using computer simulations. The results show the viability of our scheme.