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IEEE 802.11 Rate Adaptation: A Practical Approach
"... Today, three di#erent physical (PHY) layers for the IEEE 802.11 WLAN are available (802.11a/b/g); they all provide multi-rate capabilities. To achieve high performance under varying conditions, these devices need to adapt their transmission rate dynamically. While this rate adaptation algorithm is a ..."
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Cited by 146 (2 self)
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Today, three di#erent physical (PHY) layers for the IEEE 802.11 WLAN are available (802.11a/b/g); they all provide multi-rate capabilities. To achieve high performance under varying conditions, these devices need to adapt their transmission rate dynamically. While this rate adaptation algorithm is a critical component of their performance, only very few algorithms such as Auto Rate Fallback (ARF) or Receiver Based Auto Rate (RBAR) have been published and the implementation challenges associated with these mechanisms have never been publicly discussed. In this paper, we first present the important characteristics of the 802.11 systems that must be taken into account when such algorithms are designed. Specifically, we emphasize the contrast between low latency and high latency systems, and we give examples of actual chipsets that fall in either of the different categories. We propose an Adaptive ARF (AARF) algorithm for low latency systems that improves upon ARF to provide both short-term and long-term adaptation. The new algorithm has very low complexity while obtaining a performance similar to RBAR, which requires incompatible changes to the 802.11 MAC and PHY protocol. Finally, we present a new rate adaptation algorithm designed for high latency systems that has been implemented and evaluated on an AR5212-based device. Experimentation results show a clear performance improvement over the algorithm previously implemented in the AR5212 driver we used.
Self-Management in Chaotic Wireless Deployments
- In ACM MobiCom
, 2005
"... ABSTRACT Over the past few years, wireless networking technologies have made vast forays into our daily lives. Today, one can find 802.11 hardware and other personal wireless technology employed at homes, shopping malls, coffee shops and airports. Present-day wireless network deployments bear two im ..."
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Cited by 137 (9 self)
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ABSTRACT Over the past few years, wireless networking technologies have made vast forays into our daily lives. Today, one can find 802.11 hardware and other personal wireless technology employed at homes, shopping malls, coffee shops and airports. Present-day wireless network deployments bear two important properties: they are unplanned, with most access points (APs) deployed by users in a spontaneous manner, resulting in highly variable AP densities; and they are unmanaged, since manually configuring and managing a wireless network is very complicated. We refer to such wireless deployments as being chaotic.
Energy-Aware Traffic Shaping for Wireless Real-Time Applications
- In Proceedings of the 10th Real-Time and Embedded Technology and Applications Symposium (RTAS
, 2004
"... Sleep modes of wireless network cards are used to switch these cards into low-power state when idle, but large timeout periods and frequent wake-ups can reduce the utility of this approach. Modern processors offer the ability to switch CPU voltages or clock frequencies and therefore reduce CPU energ ..."
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Cited by 28 (7 self)
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Sleep modes of wireless network cards are used to switch these cards into low-power state when idle, but large timeout periods and frequent wake-ups can reduce the utility of this approach. Modern processors offer the ability to switch CPU voltages or clock frequencies and therefore reduce CPU energy consumption, however, that can reduce the sleep durations of a network device, adversely affecting the achievable energy savings. This paper describes an approach in which multiple resource managers cooperate to reduce a mobile device's energy consumption. This systemlevel approach is based on the integrated management of a real-time CPU scheduler, the frequency scaling capabilities of a modern processor, a QoS packet scheduler, and the low-power sleep mode of a wireless network card.
Smart power-saving mode for IEEE 802.11 wireless LANs
- In 24th Annual Joint Conference of the IEEE Computer and Communications Societies
, 2005
"... in the current IEEE 802.11 implementations could not provide any delag-performance guarantee because of their fixed wakeup intervals. In this paper, we propose a smart PSM (SPSM) scheme, which directs a wireless station to sleeplwake up according to an “optimal ” sequence, such that the desired dela ..."
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Cited by 21 (0 self)
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in the current IEEE 802.11 implementations could not provide any delag-performance guarantee because of their fixed wakeup intervals. In this paper, we propose a smart PSM (SPSM) scheme, which directs a wireless station to sleeplwake up according to an “optimal ” sequence, such that the desired delay performance is guaranteed with minimum energy consumption. Instead of constructing the sequence directlF, SPSM takes a unique two-step approach. First, it translates an arbitrary user-desired delay performance into a generic penalty function. Second, it provides a generic algorithm that takes the penalty function as the input and produces the optimal station action sequence automati-cally. This way, the potentiallycomplicated energy-consumption. minimization problem subject to delay-performance constraints is simplified and solved systematically. Our simulation results show that, with a two-stair penalty function, SPSM achieves delay performance similar to the BSD (Bounded SlowDown) protocol under various scenarios, but always with less energy consumption, thanks to its capability to adapt to changes in the response-time distribution. Moreover, because of SPSM’s twc-step design feature, it is more flexible than BSD in the sense of being able to meet arbitrary user-desired delay requirement, e.g., providing soft delaybound guarantees with power penalty functions. I.
Interference analysis and transmit power control
- in IEEE 802.11a/h wireless LANs,” Iowa State Univ
, 2007
"... Abstract—Reducing the energy consumption by wireless com-munication devices is perhaps the most important issue in the widely deployed and dramatically growing IEEE 802.11 WLANs (wireless local area networks). TPC (transmit power control) has been recognized as one of the effective ways to achieve t ..."
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Cited by 21 (0 self)
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Abstract—Reducing the energy consumption by wireless com-munication devices is perhaps the most important issue in the widely deployed and dramatically growing IEEE 802.11 WLANs (wireless local area networks). TPC (transmit power control) has been recognized as one of the effective ways to achieve this goal. In this paper, we study the emerging 802.11a/h systems that provide a structured means to support intelligent TPC. Based on a rigorous analysis of the relationship among different radio ranges and TPC’s effects on the interference, we present an optimal low-energy transmission strategy, called MiSer, which is deployed in the format of RTS-CTS(strong)-Data(MiSer)-Ack. The key idea of MiSer is to combine TPC with PHY (physical layer) rate adaptation and compute offline an optimal rate–power com-bination table, then at runtime, a wireless station determines the most energy-efficient transmission strategy for each data frame transmission by a simple table lookup. Simulation results show MiSer’s clear superiority to other two-way or four-way frame exchange mechanisms in terms of energy conservation. Index Terms—IEEE 802.11a/h, interference analysis, MiSer, PHY rate adaptation, TPC, transmit power control.
Modeling Energy Consumption in Single-Hop IEEE 802.11 Ad Hoc Networks
- In Thirteenth International Conference on Computer Communications and Networks (ICCCN’04
, 2004
"... This paper presents an analytical model to predict energy consumption in saturated IEEE 802.11 single-hop ad hoc networks under ideal channel conditions. The model we introduce takes into account the different operational modes of the IEEE 802.11 DCF MAC, and is validated against packetlevel simulat ..."
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Cited by 20 (2 self)
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This paper presents an analytical model to predict energy consumption in saturated IEEE 802.11 single-hop ad hoc networks under ideal channel conditions. The model we introduce takes into account the different operational modes of the IEEE 802.11 DCF MAC, and is validated against packetlevel simulations. In contrast to previous works that attempted to characterize the energy consumption of IEEE 802.11 cards in isolated, contention-free channels (i.e., single sender/receiver pair), this paper investigates the extreme opposite case, i.e., when nodes need to contend for channel access under saturation conditions. In such scenarios, our main findings include: (1) contrary to what most previous results indicate, the radio's transmit mode has marginal impact on overall energy consumption, while other modes (receive, idle, etc.) are responsible for most of the energy consumed; (2) the energy cost to transmit useful data increases almost linearly with the network size; and (3) transmitting large payloads is more energy efficient under saturation conditions.
Energy-Aware Media Transcoding in Wireless Systems
- In Proc. of the Second IEEE Intl. Conference on Pervasive Computing and Communications (PerCom
, 2004
"... In distributed systems, transcoding techniques have been used to customize multimedia objects, utilizing trade-offs between the quality and sizes of these objects to provide differentiated services to clients. Our research uses transcoding techniques in wireless systems to customize video streams to ..."
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Cited by 16 (6 self)
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In distributed systems, transcoding techniques have been used to customize multimedia objects, utilizing trade-offs between the quality and sizes of these objects to provide differentiated services to clients. Our research uses transcoding techniques in wireless systems to customize video streams to the requirements of users, while minimizing the energy costs. We introduce an approach to dynamically determine which transcoders to execute and where to execute them (e.g., client or server). The goal is to select appropriate transcoders (a) to provide clients with the quality of service they desire while (b) minimizing the energy consumption of the end-hosts in accordance with application-specific global energy management directives. This paper investigates sample transcoder functions for video streaming on handheld devices and introduces a mechanism for selecting the most appropriate transcoders and transcoder parameters.
Energy Consumption Anatomy of 802.11 Devices and its Implication on Modeling and Design
"... A thorough understanding of the power consumption behav-ior of real world wireless devices is of paramount importance to ground energy-efficient protocols and optimizations on re-alistic and accurate energy models. This paper provides an in-depth experimental investigation of the per-frame energy co ..."
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Cited by 16 (2 self)
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A thorough understanding of the power consumption behav-ior of real world wireless devices is of paramount importance to ground energy-efficient protocols and optimizations on re-alistic and accurate energy models. This paper provides an in-depth experimental investigation of the per-frame energy consumption components in 802.11 Wireless LAN devices. To the best of our knowledge, our measurements are the first to unveil that a substantial fraction of energy consump-tion, hereafter descriptively named cross-factor, may be as-cribed to each individual frame while it crosses the proto-col/implementation stack (OS, driver, NIC). Our findings, summarized in a convenient new energy consumption model, contrast traditional models which either neglect or amortize such energy cost component in a fixed baseline cost, and raise the alert that, in some cases, conclusions drawn using traditional energy models may be fallacious.
Symphony: Synchronous Two-phase Rate and Power Control in 802.11 WLANs
, 2008
"... Adaptive transmit power control in 802.11 Wireless LANs (WLANs) on a per-link basis helps increase network capacity and improves battery life of Wifi-enabled mobile devices. However, it faces the following challenges: (1) it can exacerbate receiver-side interference and asymmetric channel access, (2 ..."
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Cited by 15 (2 self)
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Adaptive transmit power control in 802.11 Wireless LANs (WLANs) on a per-link basis helps increase network capacity and improves battery life of Wifi-enabled mobile devices. However, it faces the following challenges: (1) it can exacerbate receiver-side interference and asymmetric channel access, (2) it can incorrectly lead to lowering the data rate of a link, (3) mobility-induced channel variations at short timescales make detecting and avoiding these problems more complex. Despite significant research in rate and power control, state of the art solutions lack comprehensive techniques to address the above problems. In this paper, we design and implement Symphony—a Synchronous Two-phase Rate and Power control system, whose agility in adaptation enables us to systematically address the three problems, while maximizing the benefits of power control on a per-link basis. We implement Symphony in the Linux MadWifi driver, and show that it can be realized on hardware that supports transmit power control with no modifications to the 802.11 MAC, thereby fostering immediate deployability. Our extensive experimental evaluation on a real testbed in an office environment demonstrates that Symphony (1) enables up to 80 % of the clients in 3 different cells to settle at 50 % to 94 % lower transmit power than a percell power control solution, (2) increases network throughput by up to 50 % across realistic deployment scenarios, (3) improves the throughput of asymmetry-affected links by 300%, and (4) opportunistically reduces the transmit power of mobile clients running VOIP calls by up to 97%, while causing minimum impact on voice quality.
PAWP: A Power Aware Web Proxy for Wireless LAN Clients
- IN 6TH IEEE WORKSHOP ON MOBILE COMPUTING SYSTEMS AND APPLICATIONS (WMCSA
, 2004
"... The relative power consumed in the WLAN interface of a mobile device is rising due to significant improvements in the energy efficiency of the other device components. The unpredictability of the incoming WLAN traffic limits the effectiveness of existing power saving techniques. This paper introduce ..."
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Cited by 14 (1 self)
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The relative power consumed in the WLAN interface of a mobile device is rising due to significant improvements in the energy efficiency of the other device components. The unpredictability of the incoming WLAN traffic limits the effectiveness of existing power saving techniques. This paper introduces a Power Aware Web Proxy (PAWP) architecture designed to schedule incoming web traffic into intervals of high and no communication. This traffic pattern allows WLAN interfaces to switch to a low power state after very short idle intervals. PAWP uses a collection of HTTP-level techniques to compensate any negative impact that traffic scheduling may have. PAWP does not require any client or web server modifications. In this paper, we describe our initial experiences with a PAWP implementation for 802.11b WLANs. Our experiments show savings of more than 50 % in the energy consumed by the WLAN interface. Finally, our experiences give us insights into possible browser improvements when power consumption is taken into account.
