Improving IEEE 802.11 power saving mechanism

This paper presents an optimization of the power saving mechanism in the Distributed Coordination Function (DCF) in an Independent Basic Service Set (IBSS) of the IEEE 802.11 standard. In the power saving mode specified for DCF, time is divided into so-called beacon intervals. At the start of each beacon interval, each node in the power saving mode periodically wakes up for a duration called the ATIM Window. Nodes are required to be synchronized to ensure that all nodes wake up at the same time. During the ATIM window, the nodes exchange control packets to determine whether they need to stay awake for the rest of the beacon interval. The size of the ATIM window has a significant impact on energy saving and throughput achieved by the nodes. This paper proposes an adaptive mechanism to dynamically choose a suitable ATIM window size. We also allow the nodes to stay awake for only a fraction of the beacon interval following the ATIM window. On the other hand, the IEEE 802.11 DCF mode requires nodes to stay awake either for the entire beacon interval following the ATIM window or not at all. Simulation results show that the proposed approach outperforms the IEEE 802.11 power saving mechanism in terms of throughput and the amount of energy consumed. This research is supported in part by National Science Foundation grant 01-25859. Eun-Sun Jung received a Ph.D. degree in Computer Science from Texas A&M University, USA, an M.S. degree in Information Security from University of London, UK, and a B.S degree in Computer Science and Statistics from Dankook University, Seoul, Korea. From 1995 to 1996 she was a member of technical staff in Hanwha Corporation, Seoul, Korea. In 1999, she was employed by Korea Information Security Agency as a research scientist. Since 2005, she has been with Samsung Advanced Institute of Technology, Korea, as a senior researcher. Her research interests include Wireless Networks, Mobile Computing, and Network Security. Nitin Vaidya received the Ph.D. from the University of Massachusetts at Amherst. He is presently an Associate Professor of Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign (UIUC). He has held visiting positions at Microsoft Research, Sun Microsystems and the Indian Institute of Technology-Bombay, as well as a faculty position at the Texas A&M University. His current research is in wireless networking and mobile computing. He co-authored papers that received awards at the ACM MobiCom and Personal Wireless Communications (PWC) conferences. Nitin’s research has been funded by various agencies, including the National Science Foundation, DARPA, Motorola, Microsoft Research and Sun Microsystems. Nitin Vaidya is a recipient of a CAREER award from the National Science Foundation. Nitin has served on the committees of several conferences, including as program co-chair for 2003 ACM MobiCom and General Chair for 2001 ACM MobiHoc. He has served as an editor for several journals, and presently serves as the Editor-in-Chief for the IEEE Transactions on Mobile Computing. He is a senior member of the IEEE and a member of the ACM. For more information, please visit .     

On the impact of IEEE 802.11 MAC on traffic characteristics

IEEE 802.11 medium access control (MAC) is gaining widespread popularity as a layer-2 protocol for wireless local-area networks. While efforts have been made previously to evaluate the performance of various protocols in wireless networks and to evaluate the capacity of wireless networks, very little is understood or known about the traffic characteristics of wireless networks. In this paper, we address this issue and first develop an analytic model to characterize the interarrival time distribution of traffic in wireless networks with fixed base stations or ad hoc networks using the 802.11 MAC. Our analytic model and supporting simulation results show that the 802.11 MAC can induce pacing in the traffic and the resulting interarrival times are best characterized by a multimodal distribution. This is a sharp departure from behavior in wired networks and can significantly alter the second order characteristics of the traffic, which forms the second part of our study. Through simulations, we show that while the traffic patterns at the individual sources are more consistent with long-range dependence and self-similarity, in contrast to wired networks, the aggregate traffic is not self-similar. The aggregate traffic is better classified as a multifractal process and we conjecture that the various peaks of the multimodal interarrival time distribution have a direct contribution to the differing scaling exponents at various timescales.     

Enhancing the performance of TCP over Wi-Fi power saving mechanisms

The Wi-Fi technology is quickly being adopted by new types of devices that pose stringent requirements in terms of energy efficiency. In order to address these requirements the IEEE 802.11 group developed in the recent years several power saving protocols, that are today widely used among devices like smartphones. In this paper we study, by means of analysis and simulation, the effect that these power saving protocols have on the performance/energy trade-off experienced by long lived TCP traffic. Our study unveils that the efficiency of Wi-Fi power saving protocols critically depends on the bottleneck bandwidth experienced by a TCP connection. Based on the obtained insights, we design and evaluate a novel algorithm, BA-TA, which runs in a Wi-Fi station, does not require any modification to existing 802.11 standards, and using only information available at layer two, improves the performance/energy trade off of long lived TCP connections, whilst also exhibiting a notable performance with Web traffic and TCP Streaming.     

An adaptive dual-threshold power saving mechanism in WiMAX

In the energy saving mechanism with random delay in broadband wireless network, an adaptive algorithm based on the dual-threshold and dynamic scheduling model is presented. First, to solve the demand assignment problem of bandwidth allocation and improve the system overall performance in broadband wireless network, using dynamic scheduling method and best-effort and non-real-time polling service traffic are analyzed. Then, an adaptive dual-threshold PSM for WiMAX is proposed, which not only tunes the tradeoff to satisfy various QoS requirements, but also makes adaptive adjustment based on traffic. Finally, Simulation results show that the mechanism has superior performance in comparison with the ideal assumption of Poisson arriving.     

The influence of background power on the performance of an ideal bolometer

The effects of radiant power loading on the performance of an ideal bolometer are analysed. The operation of the bolometer is characterized in terms of dimensionless parameters which correspond to the temperature sensitivity of the thermometric material, the electrical bias point and the amount of optical power loading. Expressions are derived for the zero frequency NEP and responsivity. Examples are given for the case of a bolometer cooled to 100 mK and used for ground-based astronomical photometry at submillimetre wavelengths.     

基于主导节点竞争机制的802.11n协议性能分析

针对现有IEEE802.11n协议中存在的节点间竞争信道时冲突概率较大和系统吞吐量受限的问题,提出一种新的基于主导节点竞争的MAC信道接入机制.该方法根据节点的地理位置将所有节点分成若干个独立的区域组,每个组设一个主导节点,由主导节点竞争信道;当主导节点竞争到信道后,组中其他成员节点在主导节点发送完数据之后,根据主导节点发送的轮询帧中的调度信息轮流发送数据.理论分析和仿真结果表明,与传统分布式协调功能DCF信道接入机制相比,文中方法能提高系统的整体性能,减小站点之间竞争信道时的碰撞概率,在节点数量较多时系统的整体性能更优.     

A performance study for the multicast collision prevention mechanism for IEEE 802.11

In IEEE 802.11 networks a data packet is delivered simultaneously to multiple receivers through the multicast paradigm. The standard defines a simple mechanism that does not implement any error-recovery mechanism, thus, the reliability of the service provided to the multicast users is penalized. This issue is more important as the number of collisions increases due to a large number of active stations and/or a high load network. In this paper we carry out a detailed optimization study of the multicast collision prevention (MCP) mechanism, a highly-efficient multicast collision avoidance mechanism for IEEE 802.11 previously introduced by the authors. Besides a more in deep explanation of MCP, this study includes a comparative performance evaluation of the optimized MCP with the IEEE 802.11 standard. Results shown that, through this optimization, the number of collisions in MCP can be made negligible for any network load.     

CMOS RFIC开关浅析简洁而廉价,最新的2.5GHz CMOS开关向GaAs开关提出了挑战

CMOS开关已经引起了从事RF设计的工程师们的关注,其中的原因是多方面的。首先,CMOS开关价格低廉,同时其结构简洁并且没有双电压控制的问题,不像其他技术那样需要复杂的外部电路。     

Delay analysis for sleep-based power saving mechanisms with downlink and uplink traffic

In wireless networks, sleep-based power saving mechanisms can reduce the energy consumption at the expense of additional packet delay. This paper proposes a queueing model to analyze the packet queueing delay. Compared with the existing models which consider downlink traffic only, both downlink and uplink traffic are considered in the analysis.     

EPON中一种新型的ONU休眠节能机制研究

为实现以太网无源光网络(EPON)的能源节省,提出了一种新型的基于双向业务流量的光网络单元休眠节能的控制机制。该机制通过扩展多点控制协议,并根据业务汇聚到缓存的容量来进行ONU休眠节能的时隙安排。仿真结果表明,该机制在实现绿色节能的同时可有效保证EPON网络的性能。     

IEEE 802.11 protocol: design and performance evaluation of anadaptive backoff mechanism

In WLANs, the medium access control (MAC) protocol is the main element that determines the efficiency of sharing the limited communication bandwidth of the wireless channel. The fraction of channel bandwidth used by successfully transmitted messages gives a good indication of the protocol efficiency, and its maximum value is referred to as protocol capacity. In a previous paper we have derived the theoretical limit of the IEEE 802.11 MAC protocol capacity. In addition, we showed that if a station has an exact knowledge of the network status, it is possible to tune its backoff algorithm to achieve a protocol capacity very close to its theoretical bound. Unfortunately, in a real case, a station does not have an exact knowledge of the network and load configurations (i.e., number of active stations and length of the message transmitted on the channel) but it can only estimate it. In this work we analytically study the performance of the IEEE 802.11 protocol with a dynamically tuned backoff based on the estimation of the network status. Results obtained indicate that under stationary traffic and network configurations (i.e., constant average message length and fixed number of active stations), the capacity of the enhanced protocol approaches the theoretical limits in all the configurations analyzed. In addition, by exploiting the analytical model, we investigate the protocol performance in transient conditions (i.e., when the number of active stations sharply changes)     

Evaluating voice traffic requirements on IEEE 802.11 ad hoc networks

This paper analyzes voice transmission capacity on IEEE 802.11 ad hoc networks by performing simulations related to delay, jitter, loss rate, and consecutive losses. We evaluate the influence of mobility on the number of sources transmitting voice. Another issue addressed in this paper is the effect of node density on voice transmission. Our simulation model has allowed us to identify the main reasons for voice degradation in ad hoc networks. Results show that voice transmission capacity degrades with mobility and network load, being more sensitive to high mobility due to link failures. The network capacity can easily experience a decrease of up to 60% on the number of voice transmissions on a multi-hop environment. We also show that node density is also relevant when considering voice transmission on multi-hop networks.     

RA-PSM: a rate-aware power saving mechanism in multi-rate wireless LANs

Improving energy efficiency is one of the most important issues in wireless local area networks (WLANs) and a power saving mechanism (PSM) has been proposed in IEEE 802.11 WLANs. However, the conventional PSMs do not consider multi-rate transmissions and thus the waiting time for retrieving buffered frames from the access point can be unnecessarily long and more energy can be consumed. In this paper, we propose a rate-aware power saving mechanism (RA-PSM) in multi-rate WLANs. In RA-PSM, a station sets its contention window size inversely proportional to the transmission rate and thus a station with higher transmission rate can request the buffered frames at the access point with higher priority. As a result, the overall channel waiting time can be reduced and the energy consumption can be saved accordingly. Analytical and simulation results demonstrate that RA-PSM can reduce the average channel waiting time and the energy consumption by up to 77 and 40.3 %, respectively, compared with the conventional IEEE 802.11 PSM.     

电力工程设计中的节能措施探析

电能作为一种清洁可再生能源,有效地改善了我国能源供应紧张的局面。近年来为响应国家节能减排的号召,开始加大电力工程建设,电力工程在设计建造时越发重视节能设计,文章对电力工程设计中的节能措施进行了分析,以期为节约能源降低污染起到一定帮助。     

802.11a/g相对于802.11b的低功耗优势

引言 802.11无线局域网(WLAN)技术正在全球范围内的企业与家庭中得到应用.随着Wi-Fi的实施不断发展,基于其上运行的新型应用数量也不断上升.起初,人们认为Wi-Fi只是家庭与商业网络中以太网以及工业移动计算的简单替代,但过去一年以来已显现了新的趋势.     

基于802.11r漫游性能优化的WLAN建设

采用高级安全策略的无线网络在漫游时要忍受较大的时延,在不牺牲安全性的前提下快速灵活地漫游于无线局域之间成了无线局域网搭建的重中之重。基于IEEE 802.11r协议的快速BSS切换协议,以及对密钥结构和认证过程的较大改动,采用三层漫游技术实现了能够无缝漫游的校园无线网络,经过近1年的运营证明,该文提出的方案切实有效。     

Comprehensive Analysis of the IEEE 802.11

Wireless Local Area Networks (WLANs) have attracted significant research interest over the past few years. The IEEE 802.11 standard is the most mature technology for WLANs and has been widely adopted for wireless networks. This paper outlines a new performance analysis for IEEE 802.11 Distributed Coordinated Function (DCF) using Direct Sequence Spread Spectrum (DSSS) in terms of the channel throughput, packet processing rate, packet loss probability and average packet delay using a perfect channel as well as a slow Rayleigh fading channel. The theoretical results are subsequently compared with the simulation results. It is shown that there is a good match between these two results, which validates the analytical model.Peter P. Pham received the B.E. in computer system engineering (honour) from the University of Adelaide, Australia in December 2000. After graduation, he worked as a software engineer for Motorola for 6 months in Singapore. Since August 2001, he received a President scholarship and started as a Ph.D. candidate at Institute for Telecommunications Research, the University of South Australia. His area of interests are performance analysis and coding techniques for ad hoc networks.     

移动基站电耗评估与节能分析

随着我国信息化建设的不断发展进步,我国移动通信行业不断加速转型升级,积极开展3G、4G网络建设及业务应用来满足市场的需求。日益增长的市场需求催生了电信行业基站的建设,随着基站数量的增加,导致基站电耗使用量也大大增加,同时也给基站的日常维护和管理增加了负担。如何控制基站能耗利用量,减少电信公司成本问题,对电信企业来说是个迫不及待要解决的问题。因此,围绕基站节能与管理的需求,分析讨论基站电耗产生的主要原因,分析基站设备耗电情况,找出了基站内的空调设备是形成基站电耗量使用大的主要原因,文中提出使用智能风控管理,利用控制系统对基站室内外温湿度进行识别、判断,从而来控制空调的起停,已到达节能的目的,从而降低成本,极大提高移动公司竞争力。