This article proposes a novel energy-efficient multimedia delivery system called EStreamer. First, we study the relationship between buffer size at the client, burst-shaped TCP-based multimedia traffic, and energy consumption of wireless network interfaces in smartphones. Based on the study, we design and implement EStreamer for constant bit rate and rate-adaptive streaming. EStreamer can improve battery lifetime by 3x, 1.5x, and 2x while streaming over Wi-Fi, 3G, and 4G, respectively.
Other approaches identify idle periods at different phases of TCP-based applications, such as in the middle of the data transmission @cite_19 @cite_17 . Another example is choking unchoking the TCP receive window size to make the TCP traffic bursty @cite_6 . In this case, the burst interval is the duration between a choking and unchoking period. Authors in @cite_17 applied this trick for multimedia streaming services such as RealNetwork, Windows Media and YouTube with a burst interval of 200 ms. However, these mechanisms cannot be applied for 3G and 4G, because these solutions are wireless access technology dependent as they force the Wi-Fi interface into sleep state and such an operation on cellular network interfaces would bar the smartphone from basic phone functioning. In contrast, EStreamer is independent of the WNI being used for streaming. Recently, limm2012 proposed GreenTube to save communication energy for YouTube using multiple TCP connections. However, such approaches cannot be successful in reducing energy consumption when the application receives content at the server controlled lower rate @cite_11 .
@cite_19 @cite_11 @cite_6 @cite_17
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Shaping constant bit rate traffic into bursts has been proposed earlier for UDP-based multimedia streaming to save Wi-Fi communication energy of mobile devices. The relationship between the burst size and energy consumption of wireless interfaces is such that the larger is the burst size, the lower is the energy consumption per bit received as long as there is no packet loss. However, the relationship between the burst size and energy in case of TCP traffic has not yet been fully uncovered. In this paper, we develop a power consumption model which describes this relationship in wireless multimedia streaming scenarios. Then, we implement a cross-layer stream delivery system, EStreamer. This system relies on a heuristic derived from the model and on client playback buffer status to determine a burst size and provides as small energy consumption as possible without jeopardizing smooth playback. The heuristic greatly simplifies the deployment of EStreamer compared to most existing solutions by ensuring energy savings regardless of the wireless interface being used. We show that in the best cases using EStreamer reduces energy consumption of a mobile device by 65 , 50-60 and 35 while streaming over Wi-Fi, LTE and 3G respectively. Compared with existing energy-aware applications energy consumption can be reduced by 10-55 further. While the 802.11 power saving mode (PSM) and its enhancements can reduce power consumption by putting the wireless network interface (WNI) into sleep as much as possible, they either require additional infrastructure support, or may degrade the transmission throughput and cause additional transmission delay. These schemes are not suitable for long and bulk data transmissions with strict QoS requirements on wireless devices. With increasingly abundant bandwidth available on the Internet, we have observed that TCP congestion control is often not a constraint of bulk data transmissions as bandwidth throttling is widely used in practice. In this paper, instead of further manipulating the trade-off between the power saving and the incurred delay, we effectively explore the power saving potential by considering the bandwidth throttling on streaming downloading servers. We propose an application-independent protocol, called PSM-throttling. With a quick detection on the TCP flow throughput, a client can identify bandwidth throttling connections with a low cost Since the throttling enables us to reshape the TCP traffic into periodic bursts with the same average throughput as the server transmission rate, the client can accurately predict the arriving time of packets and turn on off the WNI accordingly. PSM-throttling can minimize power consumption on TCP-based bulk traffic by effectively utilizing available Internet bandwidth without degrading the application's performance perceived by the user. Furthermore, PSM-throttling is client-centric, and does not need any additional infrastructure support. Our lab-environment and Internet-based evaluation results show that PSM-throttling can effectively improve energy savings (by up to 75 ) and or the QoS for a broad types of TCP-based applications, including streaming, pseudo streaming, and large file downloading, over existing PSM-like methods. We consider an IEEE 802.11 based wireless LAN where an access point is used to connect a fixed number of users to the Web or to a shared file system. Users alternate between activity periods (corresponding to the download of a file) and idle periods (corresponding to think times). We first consider the interaction of TCP with the IEEE 802.11 MAC protocol, and get approximate expressions for the TCP throughput in the presence of n"c competing persistent connections. This result is then used to develop a queueing model, which provides the mean session delay in the presence of short-lived flows. The analysis also accounts for the TCP delayed ACK option. Comparison with simulation outcomes is provided, validating the model and providing guidelines for network designers. A particular emphasis is devoted to the impact of the TCP's advertised window size; in particular, it is proved that setting it to a small value leads to insensitivity of mean file transfer times to the file size distribution. We consider a frequency-flat fading multihop network with a single active source-destination pair terminals communicating over multiple hops through a set of intermediate relay terminals. We use Shannon-theoretic tools to analyze the tradeoff between energy efficiency and spectral efficiency (known as the power-bandwidth tradeoff) for a simple communication protocol based on time-division decode-and-forward relaying in meaningful asymptotic regimes of signal-to-noise ratio (SNR) under a system-wide power constraint on source and relay transmissions. The impact of multi-hopping and channel fading on the key performance measures of the high and low SNR regimes is investigated to shed new light on the possible enhancements in power bandwidth efficiency and link reliability. In contrast to the common belief that in fading environments communicating over multiple hops suffers significantly in performance due to the worst link limitation, our results indicate that hopping could significantly improve the outage behavior over slow-fading networks and stabilize links against the random channel fluctuations. In particular, we prove that there exists an optimal number of hops that minimizes the end-to-end outage probability and characterize the dependence of this optimal number on the fading statistics and target energy and spectral efficiencies.