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.

A wide bandwidth through the channel bonding of IEEE 802.11ac significantly increases the capacity of wireless transmissions. However, multicast traffic is simply transmitted using a narrow 20 MHz bandwidth because the access point (AP) is agnostic to the supportable bandwidth information of clients in a multicast group. This paper proposes WiderCast which enables channel bonding for multicast in IEEE 802.11ac WLANs. In WiderCast, the AP scales the bandwidth for multicast transmissions according to the supportable bandwidths of multicast clients. To enable bandwidth negotiation between the AP and clients without high control overhead, WiderCast employs a novel bandwidth signaling scheme, in which multicast clients can simultaneously deliver their supportable bandwidth information to the AP without collision. We verified the feasibility of WiderCast with a prototype on software-defined radio. We also conducted an extensive simulation study demonstrating that WiderCast achieves higher throughput and improved video quality than traditional wireless multicast. To the best of our knowledge, this is the first work to take into account channel bonding for wireless multicast in WLANs.

Breathing pattern and heart rate can be major indicators of a person's physical condition, and an easy way to measure the vital signs can be useful in health monitoring. In this paper, we propose a new method for identifying the changes in breathing and heart rate pattern of a person using commercial WiFi devices. The amplitude of signal waves can represent the periodic up-and-down chest movements caused by breathing and heartbeat, and prominent changes of the signal pattern can be detected by using the Dynamic Time Warping algorithm. We verified the feasibility of the proposed method in real testbeds and evaluated the method through various experiments with 10 participants. The proposed method achieves 94% accuracy in identifying a subjects physical status. This low-cost method will be useful for monitoring our health in everyday life.

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.