Wireless video multicast over IEEE 802.11 WLANs is a viable approach to bridging the gap between limited wireless resources and the ever-increasing mobile video traffic demand. However, existing wireless multicast mechanisms have several limitations, such as low spectral efficiency, high feedback overhead, and lack of consideration of the frame aggregation feature of current WLANs. In this paper, we propose FlexVi, a flexible wireless multicast solution for efficient video streaming over WLANs. Considering the frame aggregation of the current WLANs, FlexVi allows an access point to dynamically adjust the data rate on the basis of three factors: available wireless bandwidth, heterogeneity of the channel qualities among the clients, and the priorities among the video frames in terms of video quality. In addition, by harnessing the orthogonality of the subcarriers in the orthogonal frequency division multiplexing, FlexVi enables multiple clients to deliver their feedback to an access point simultaneously without collision, which results in very low feedback overhead. We verified the feasibility of FlexVi through experiments on a software defined radio platform. We also conducted an extensive simulation study and found that FlexVi outperforms the latest wireless multicast mechanisms.

Power saving mode mechanism in IEEE 802.11 is designed for reducing power consumption by switching WiFi interface of mobile device between active-state and sleep-state alternately. Since the power consumption in active-state is significantly higher than that in sleep-state, switching between both states should be done carefully; e.g., low priority packets such as delay tolerant packet should not trigger switching to active-state for increasing power saving effect. Delay tolerant traffic, however, also equally affects behaviors of the mechanism since the mechanism is operated within the MAC layer. To overcome this issue, we propose Scrooge which separates delay tolerant traffic from delay sensitive traffic to prevent delay tolerant traffic from impacting on behavior of power saving mechanism. Thus, delay tolerant packets never affect the behavior of power saving mode mechanism. Our prototype implementation improves power saving performance by up to 95% without significant transmission delay under common applications' traffic patterns.

A wireless distribution system (WDS)-based wireless local area network (WLAN) is composed of a base access point (AP) which is connected to wired line and one or more linked APs which are connected to the base AP or other linked APs via wireless links. Usually, WLAN stations try to associate with an AP from which the stations receive the strongest signal strength. However, in WDS-based WLANs, the base AP may provide higher throughput than linked APs although the signal strength of base AP is weaker than those of linked APs. In this paper, we propose a new medium access scheme in which each station uses an AP that can provide the highest throughput to improve the capacity of WDS-based WLANs. To implement the proposed scheme, no modification is required to stations, while some modifications are required to APs. Our experiment and simulation results show that the proposed scheme achieves improved throughput performance over existing schemes.