Jonghoe Koo

Video multicast over WLANs: Power saving and reliability perspectives

Video streaming service via multicast is one promising technology for multimedia services over wireless local area networks. Given that many portable devices are battery-powered while video quality relies on the reliable delivery of video traffic, video multicast frames need to be reliably delivered to power-saving stations. In this article, we study video multicast from the power saving and reliability perspectives. The IEEE 802.11 standard allows multicast receivers to enable power management while receiving multicast frames. However, from measurements with several commercial WLAN devices, we observe that many devices are not standards- compliant, thus severely degrading video multicast performance when multicast receivers are in the power saving mode. We identify various standards-non-compliant malfunctions of both access points and stations, and then categorize these malfunctions. Meanwhile, the legacy 802.11 standard is known to support only unreliable multicast service due to the lack of retransmissions. We present various reliable multicast schemes including application layer forward error correction and reliable multicast protocols defined in the emerging IEEE 802.11v and 802.11aa, and comparatively evaluate them via simulations.

Reliable Video Multicast over Wi-Fi Networks with Coordinated Multiple APs

Forward Error Correction (FEC) can be exploited to realize reliable video multicast over Wi-Fi with high video quality. We propose reliable video multicast over Wi-Fi networks with coordinated multiple Access Points (APs) to enhance video quality. By coordinating multiple APs, each AP can transmit entirely or partially different FEC-encoded packets so that a multicast receiver can benefit from both spatial and time diversities. The proposed schemes can enlarge the satisfactory video multicast region by exploiting the AP diversity, thus serving more multicast receivers located at cell edge with satisfactory video quality. We propose a resource-allocation algorithm for FEC-code rate adaptation, utilizing the limited wireless resource more efficiently while enhancing video quality. We also introduce the method for estimating the video packet delivery ratio after FEC decoding. The effectiveness of the proposed schemes is comparatively evaluated via extensive simulation and experimentation. The proposed schemes are observed to enhance the ratio of satisfied users by up to 37.1% compared to the conventional single AP multicast scheme.

Empirical analysis of video multicast over WiFi

Video multicast service is becoming one of the most important applications over WiFi, due to the increasing popularity of WiFi for multimedia communication. On the one hand, energy efficient operation is required to WiFi technology due to the limited battery power of most WiFi-equipped devices. In this paper, we empirically study the video multicast operation, especially, along with power management operation in two aspects: (1) whether commercial WiFi devices correctly operate as defined in IEEE 802.11 standard and (2) what problem the standard-compliant operation can induce. From our experimental results, we first figure out that some of commercial WiFi devices do not follow the standard with respect to the power saving operation, and this noncompliance worsens interoperability. We also find that the standard-compliant operation may cause significant delay of voice over IP (VoIP) traffic, when video multicast coexists with VoIP. Through this experimental study, we provide the guidelines for energy-efficient video multicast service.

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Link Adaptation for High-Quality Uncompressed Video Streaming in 60-GHz Wireless Networks

), and expected file transfer completion time (performance) simultaneously, and is motivated by the growing sensitivity of todays smartphone users to these attributes. Each time the individual attributes are calculated and updated, E

PIMM: Packet Interval-Based Power Modeling of Multiple Network Interface-Activated Smartphones

PA selects one of the three modes that minimizes the overall cost: (i) activation of both LTE and WiFi interfaces for parallel data transfer; (ii) LTE interface activation only; or (iii) WiFi interface activation only. The primary benefit of the E

BattTracker: Enabling energy awareness for smartphone using Li-ion battery characteristics

PA is that it enables the smartphone to always operate in the “best” mode without the need for users manual control; the energy saving mode if the remaining battery energy is becoming nearly depleted; the cost-saving mode if the remaining data quota is almost running out; or, the maximum throughput mode if remaining data quota and battery life are both sufficient. Our multi-attribute cost model also takes into account the overheads (delays and energy consumption) associated with network interface turn-on/off and switching, as they impact the estimations of both performance (transfer time) and energy (battery life) attributes. Simulation results show that E

EQ-Video: Energy and Quota-Aware Video Playback Time Maximization for Smartphones

PA indeed chooses the “best” operational mode by maintaining dynamic balance among transfer time, energy consumption, and service charge.