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.

The playout delay for voice over IP applications is adjusted on every talkspurt. The parameter β that controls the delay/packet loss ratio is usually fixed, based on high jitter conditions. In this letter, a β-adaptive playout algorithm is presented, where the β is adjusted. The buffering delays and lateness rates are compared against the existing algorithm with the fixed β. We show that the β-adaptive system improves the lateness loss performance, especially for low jitter conditions, while maintaining almost identical buffering delay/lateness loss performance when jitter is high.

Adaptive Battery Conservation Management (ABCM), an effective form of power conservation for mobile terminals in an always-connected environment, was proposed and evaluated in a previous published work. The ABCM method employs three states: active, dormant, and the Battery Saving Mode (BSM). The BSM is defined as a battery-saving state; in the BSM, the mobile terminal saves power by intermittently receiving paging notifications via a paging channel between the packet bursts of a session. Two control parameters, the sleep-timer and paging interval, are set up according to packet class and are the keys to the performance of a system with this method. In real-time communications, a long sleep-timer and short paging interval are selected to minimize buffering delay. In non-real-time communications, on the other hand, a short sleep-timer and long paging interval are chosen to reduce power consumption by the mobile terminal. Our previous evaluation showed that the method is effective as a means for power conservation in non-real-time communications. In real-time communications, on the other hand, the ABCM method provides shorter buffering delays and the same battery-conservation performance as the conventional method. To further improve the ABCM method's performance, we now propose an enhanced ABCM method that employs multiple BSM sub-modes, each of which has a different paging interval. As dormant periods become longer, the mobile terminal makes transition to successive sub-modes, each of which has a longer interval than the previous one. In this paper, we evaluate the battery conservation effect of the ABCM method through theoretical analysis and computer simulation. Numerical evaluation indicates that the ABCM method will be suitable for the broadband multimedia packet-radio systems of the future.