Analysis of the impact of background traffic on the performance of 802.11 power saving mechanism

In our previous work [5, 6], we have identified the issue that the performance of 802.11 power saving mechanism degrades significantly with the presence of background traffic. In this letter, we propose a simple model to theoretically analyze the impact of background streams on the power performance of an individual mobile station in power saving mode (PSM). By reasonable assumptions on medium access details, we develop a set of mathematical formulas which gives the ratio of prolonged data retrieval time under condition of background traffic within a beacon period. Simulation results demonstrate the validity of the proposed model for analysis of 802.11 PSM.     

Energy Efficient Schedulers in Wireless Networks: Design and Optimization

Minimizing energy consumption is crucial for portable wireless stations because they operate on a limited battery supply. For example, the IEEE 802.11 standard includes a mechanism called power-saving mode (PSM), which allows a network interface on a mobile station to enter a sleep state whenever possible to reduce its energy consumption. We consider a generic wireless system composed of an access point (AP) and several stations that offer a PSM to its users. Our PSM is AP-centric (i.e., gives control to the AP) to save more energy. We formulate a downlink scheduling optimization problem aimed at saving energy and propose two heuristic scheduling policies to solve it. One of these policies is non-work-conserving, and it offers an interesting tradeoff between energy consumption and user performance. We also study and show how the length of the Beacon Period (BP) has a significant impact on the energy and the delay performance of wireless stations. For each of our two scheduling policies, we derive simple approximate formulas for the length of the BP that minimizes the energy consumption and for the relationship between the delay performance and the length of the BP. Assuming the maximum allowable average packet delay is given by the users as a QoS requirement, we illustrate how to dimension the length of the BP for the two schedulers we have proposed and show that we can achieve significant energy savings while meeting the delay constraint with the non-work conserving one in many cases. Extensive simulations show that a fine-tuning of the length of the BP as well as well-designed scheduling disciplines is essential to saving energy in wireless stations.     

Towards providing optimal energy‐efficiency and throughput for IEEE 802.11 WLANs

IEEE 802.11 wireless network standard has become one of the most used wireless networking technologies for smart devices as it offers mobility support and low cost deployment. However, these devices deeply rely on the energy provided by their batteries, which results in limited running time. IEEE 802.11 network standard provides stations with carrier sense multiple access with collision avoidance for the medium access. Yet it results in stations to consume an important amount of power. Therefore, minimizing WiFi‐based energy consumption in smart devices has been received substantial attention in both academia and industry. Accordingly, this paper * proposes a novel beacon‐based energy‐efficient collision‐free medium access control protocol for any type of IEEE 802.11 stations, regardless of being stationary or mobile, or having different amount of traffic flow, transmission rates, or traffic types. The proposed scheme is valid for all types of low or wide bandwidth, single or multiuser multiple‐input multiple‐output WLAN channels, such as IEEE 802.11a\b\g\n\ac. In the proposed scheme, energy saving is achieved, enabling stations to transmit on the right time and maintaining stations in the doze state during a predetermined sleep_time interval after each successful frame transmission, by making use of modified control and management frames of the standard IEEE 802.11 protocol. The proposed scheme reduces the probability of collisions and may allow stations to enter the collision‐free state, regardless of the number of stations on the channel and their traffic types. Widespread simulations have been executed to validate the efficiency of the proposed method. The results demonstrate that the proposed method significantly increases overall throughput and reduces power consumption of stations over IEEE 802.11 WLANs.     

基于IEEE802.11协议的WLAN节省能耗的策略

在WLAN中移动终端设备的电池寿命是一个关键问题.文章概述了基于IEEE802.11协议的WLAN节省能耗的策略,并通过对IEEE802.11MAC协议层节能机制的分析提出一种改进的轮询方案.该方案能克服IEEE802.11在PSM工作模式下,当无线网络流量负载较重时不能显著降低能耗的缺点.     

Analytical framework for power saving evaluation in two-tier heterogeneous mobile networks

Reducing the power consumption of base stations in mobile networks is an important issue. We investigate the power saving evaluation in two-tier heterogeneous mobile networks which consist of femtocells overlaid by macrocells. In the heterogeneous mobile networks, base stations without traffic load are allowed to enter the sleep mode to save power. The power saving probability that a base station enters the sleep mode and the average total power consumption of this network are complex joint-effects of various factors. Successful modelling of these complex joint-effects is critical to mobile network operators when they pursue the design of green mobile networks. In this paper we propose an analytical framework to facilitate systematic analysis. Based on the proposed analytical framework, we investigate the power saving probabilities and the average total power consumption in terms of several parameters, including the new traffic arrival rate per user, the maximum transmission power of a femtocell, the number of femtocells within a macrocell, and the number of users in the network. Numerical results show that the proposed analytical framework provides a useful and efficient method to facilitate systematic analysis and design of green mobile networks. Simulation results validate the accuracy of the proposed analytical framework.     

An energy‐saving‐centric downlink scheduling scheme for WiMAX networks

This study proposes an energy‐saving‐centric downlink scheduling scheme to support efficient power utilization and to satisfy the QoS requirements. The base station considers the queue lengths of mobile stations with real‐time and non‐real‐time connections and considers their QoS requirements to determine the sleeping parameters when the mobile stations issue sleep requests. The proposed scheme appropriately reschedules the sleep‐requesting mobile station to transmit its queued packets for optimal power‐saving efficiency. The QoS requirement is considered as the constraint during traffic rescheduling. The treatment of real‐time connections generally requires a trade‐off of the delay requirement and the longer sleep window, and the non‐real‐time connections must concern the packet drop and minimum data rates when performing the energy‐centric scheduling. Two rescheduling algorithms, that is, whole and partial reschedules, are proposed and analyzed in this paper. The whole‐reschedule scheme provides improved energy‐saving performance at the cost of tolerable longer delay and computing complexity when compared with the partial‐reschedule scheme. Our simulation results indicated that both schemes not only guarantee the desired QoS but also achieve superior energy‐saving efficiency to that of traditional scheduling. Copyright © 2012 John Wiley & Sons, Ltd.     

Autonomous and adaptive beaconing strategy for multi‐interfaced wireless mobile nodes

Ad hoc wireless communications rely on beaconing to manage and maintain several network operations and to share relevant network parameters among network nodes. Beacon frames are sent at the start of each beacon interval. The frequency of beaconing depends on whether beacon intervals are fixed size or may be adapted and regulated according to the perceived network and workload conditions. On the other hand, current mobile nodes usually embed several heterogeneous wireless interfaces that urge the design of an adaptive beaconing strategy. In this paper, we propose an autonomous and adaptive beaconing strategy for multi‐interfaced mobile wireless nodes that is capable of regulating the beacon interval size dynamically according to the perceived network conditions. The proposed strategy is based on a joint dynamic estimation of both the announcement traffic indication message (ATIM) window and the beyond‐ATIM window sizes for each beacon interval. Extensive simulations were conducted using OMNeT++ to ascertain the improvements achieved by autonomously regulating the entire beacon interval to take into account the network and workload conditions. Obtained results showed that the two proposed approaches improve significantly the efficiency of the network in terms of throughput, end‐to‐end delay, and power consumption. The proposed fixed beacon interval (fixed‐BI) approach stands as an enhanced version of the power‐saving multi‐channel MAC protocol (PSM‐MMAC). The proposed variable beacon interval (variable‐BI) approach, which regulates dynamically both of the ATIM and the beyond‐ATIM windows, outperforms both the fixed‐BI and the PSM‐MMAC. In particular, under nominal traffic loads, the end‐to‐end delay of the variable‐BI is much lower than those provided by the fixed‐BI and PSM‐MMAC. Copyright © 2015 John Wiley & Sons, Ltd.     

A MAC Protocol for Bursty Traffic Ad-Hoc Wireless LANs with Energy Efficiency

A Self-Adaptive Low Power MAC protocol with carrier sensing for ad-hoc Wireless LANs (WLANs), which is capable of operating efficiently under bursty traffic is proposed in this letter. The protocol utilizes a Learning Automaton structure at each station of the WLAN. Each such structure uses the network feedback to select the mobile station that will transmit. A low-power mode is implemented in order to significantly reduce the energy consumption of the protocol. Simulation results reveal that the low power mode of the proposed protocol reduces the average energy consumption at the mobile stations by as much as 70%.     

IEEE 802.16e/m energy‐efficient sleep‐mode operation with delay limitation in multibroadcast services

Mobile Worldwide Interoperability for Microwave Access networks usually provide flexible sleep‐mode operations that allow mobile stations to conserve energy during sleep or active mode. For example, the IEEE 802.16e/m standard presents three power‐saving classes that can be associated with different types of network connections to decrease the power consumption of mobile stations. However, previous studies failed to fully use the sleep‐mode features to save energy of a mobile station while simultaneously maintaining unicast and multicast/broadcast connections. This study proposes an energy‐efficient packet scheduling algorithm for both multicast and broadcast services that does not violate the QoS requirements of real‐time connections. The proposed activity aggregation selection mechanism approach can minimize total power consumption of mobile stations in one cell and simultaneously satisfy the QoS of real‐time connections. This method improves energy efficiency for IEEE 802.16e/m and the activity aggregation selection mechanism approach can optimize sleeping mode features to save the energy of mobile stations with overlapping connection packets The simulations in this study verified the proposed approach.Copyright © 2012 John Wiley & Sons, Ltd.     

Busy tone contention protocol: a new high‐throughput and energy‐efficient wireless local area network medium access control protocol using busy tone

Design of an efficient wireless medium access control (MAC) protocol is a challenging task due to the time‐varying characteristics of wireless communication channel and different delay requirements in diverse applications. To support variable number of active stations and varying network load conditions, random access MAC protocols are employed. Existing wireless local area network (WLAN) protocol (IEEE 802.11) is found to be inefficient at high data rates because of the overhead associated with the contention resolution mechanism employed. The new amendments of IEEE 802.11 that support multimedia traffic (IEEE 802.11e) are at the expense of reduced data traffic network efficiency. In this paper, we propose a random access MAC protocol called busy tone contention protocol (BTCP) that uses out‐of‐band signals for contention resolution in WLANs. A few variants of this protocol are also proposed to meet the challenges in WLAN environments and application requirements. The proposed BTCP isolate multimedia traffics from background data transmissions and gives high throughput irrespective of the number of contending stations in the network. As a result, in BTCP, admission control of multimedia flows becomes simple and well defined. Studies of the protocol, both analytically and through simulations under various network conditions, have shown to give better performance in comparison with the IEEE 802.11 distributed coordination function. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance of Energy-Efficient Cooperative MAC Protocol with Power Backoff in MANETs

This paper presents an energy-efficient cooperative MAC (EECO-MAC) protocol using power control in mobile ad hoc networks. Cooperative communications improve network performance by taking full advantage of the broadcast nature of wireless channels. The power control technique improves the network lifetime by adjusting the transmission power dynamically. We propose the best partnership selection algorithm, which takes energy consumption into consideration for selection of the optimal cooperative helper to join in the transmission. Through exchanging control packets, the optimal transmission power is allocated for senders to transmit data packets to receivers. In order to enhance energy saving, space–time backoff and time–space backoff algorithms are proposed. Simulation results show that EECO-MAC consumes less energy and prolongs the network lifetime compared to IEEE 802.11 DCF and CoopMAC at the cost of delay. Performance improvement offered by our proposed protocol is apparent in congested networks where nodes have low and limited energy.     

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.     

An outband paging protocol for energy-efficient mobile communications

A new protocol is proposed for reducing the power consumption of battery-powered terminals in a mobile computing environment. We exploit the fact that, in a mobile data network, mobile terminals do not continuously receive data and therefore they need not continuously operate their receivers. Nevertheless, they need to check their traffic condition periodically, that is, whether there are pending data for them or not. The proposed energy-efficient protocol is based on a paging procedure wherein a dedicated channel is used to alert (page) terminals with pending traffic. Each terminal may check its traffic condition whenever it decides to by monitoring the paging channel. The protocol is evaluated through an approximated theoretical model and through computer simulation. We focus on deriving approximate formulas for the mean message delay, the message delay variance and the power consumption. It is shown that the proposed protocol can achieve considerable power saving at a cost of increased message delivery delay.     

IIPP: integrated IP paging protocol with a power save mechanism

The advent of advanced mobile/wireless systems has been facilitating the battery‐powered mobile computing devices (nodes) to remain always connected to the internet. However, until now, the power‐drain rate of mobile nodes is very high in comparison with the available power of portable batteries. To reduce the energy consumption of mobile nodes, we present an integrated IP paging protocol (IIPP) by integrating the IP‐layer paging protocol based on Mobile IPv4 regional registration (MIPRR) with a power save mechanism. IIPP reduces the frequency of signaling messages between mobile nodes and networks. When not sending or receiving data for a certain time, mobile nodes enter power save mode (PSM), and consume very low power. We formulate analytical models and carry out simulations to evaluate the proposed IIPP. The results show that, compared to MIPRR, IIPP significantly reduces the average power consumption of the mobile node and signaling overheads in the network. Copyright © 2006 John Wiley & Sons, Ltd.     

An in-band power-saving protocol for mobile data networks

A new alternative is proposed for reducing the power consumption of the portable (battery-powered) units operating in a mobile packet-data network. First, a review of the current power-saving protocols is given. It is shown that the most common means for conserving power is the intermittent operation of the receivers (at the portable units) and a central administration authority that synchronizes the receivers. Some drawbacks of the synchronous operation lead us to the introduction of an asynchronous power-saving protocol, where no central synchronization is necessary and where each terminal may control its power consumption relative to its current needs. According to the proposed power-saving page-and-answer protocol, an acknowledgment paging procedure is preceding every packet transmission in order to alert mobile terminals with pending traffic. Steady-state performance is evaluated with the aid of simulation. The relationship between the achieved power-saving and the mean packet delay degradation is presented. Finally, we express some notable implementation issues and some considerations regarding the employment of this protocol as a supplementary power-saving service in microcellular mobile data networks and wireless local area networks     

Delay-efficient MAC protocol with traffic differentiation and run-time parameter adaptation for energy-constrained wireless sensor networks

This paper presents an asynchronous cascading wake-up MAC protocol for heterogeneous traffic gathering in low-power wireless sensor networks. It jointly considers energy/delay optimization and switches between two modes, according to the traffic type and delay requirements. The first mode is high duty cycle, where energy is traded-off for a reduced latency in presence of realtime traffic (RT). The second mode is low duty cycle, which is used for non-realtime traffic and gives more priority to energy saving. The proposed protocol, DuoMAC, has many features. First, it quietly adjusts the wake-up of a node according to (1) its parent’s wake-up time and, (2) its estimated load. Second, it incorporates a service differentiation through an improved contention window adaptation to meet delay requirements. A comprehensive analysis is provided in the paper to investigate the effectiveness of the proposed protocol in comparison with some state-of-the-art energy-delay efficient duty-cycled MAC protocols, namely DMAC, LL-MAC, and Diff-MAC. The network lifetime and the maximum end-to-end packet latency are adequately modeled, and numerically analyzed. The results show that LL-MAC has the best performance in terms of energy saving, while DuoMAC outperforms all the protocols in terms of delay reduction. To balance the delay/energy objectives, a runtime parameter adaptation mechanism has been integrated to DuoMAC. The mechanism relies on a constrained optimization problem with energy minimization in the objective function, constrained by the delay required for RT. The proposed protocol has been implemented on real motes using MicaZ and TinyOS. Experimental results show that the protocol clearly outperforms LL-MAC in terms of latency reduction, and more importantly, that the runtime parameter adaptation provides additional reduction of the latency while further decreasing the energy cost.     

An adaptive quorum-based energy conserving protocol for IEEE 802.11 ad hoc networks

The lifetime of a mobile ad hoc network (MANET) depends on the durability of the mobile hosts' battery resources. In the IEEE 802.11 Power Saving Mode, a host must wake up at every beacon interval, to check if it should remain awake. Such a scheme fails to adjust a host's sleep duration according to its traffic, thereby reducing its power efficiency. This paper presents new MAC protocols for power saving in a single hop MANET. The essence of these protocols is a quorum-based sleep/wake-up mechanism, which conserves energy by allowing the host to sleep for more than one beacon interval, if few transmissions are involved. The proposed protocols are simple and energy-efficiency. Simulation results showed that our protocols conserved more energy and extended the lifetime of a MANET.     

IP over WDM网络最小功耗模型和休眠机制研究

针对IP over WDM网络,建立了整数线性规划(ILP)最小功耗模型,计算了满足峰值业务需要开启的设备数目;对于低峰业务提出休眠机制,分别利用最小光路数算法与最小跳数算法,在保证连接无阻塞的情况下找出空闲设备,对比峰值业务得到不同算法下的设备使用率,确定IP over WDM网络的节能潜力。结果表明,ILP优化模型的网络功耗最小,最小光路数算法次之;低峰业务下利用休眠机制可以关闭设备的比例占40%～60%;采用最小光路数算法的休眠机制节能效果较优。     

如何利用高层协议栈软件降低终端功耗

在GSM系统中,待机时间是终端性能指标之一,在市场竞争中,越来越显示出其重要性.对于TD-SCDMA系统而言,终端的省电问题也是一个不可回避的问题,不幸的是目前所有的TD-SCDMA系统终端的省电都不尽人意,要么没有考虑,要么处理得不理想.对于TD-SCDMA系统,根据自身的特点终端省电的处理有一定的方便之处,也有一定的难度.本文将讨论怎样利用协议栈提高终端的待机能力,提高省电性能.     

基于AODV的多度量无线路由算法研究

随着移动自组网络的快速发展,对距离矢量按需路由协议(AODV)的服务质量提出了越来越高的要求.为了提升AODV在无线传感器网络通信中的表现,文章提出了一种新型的基于AODV的多度量无线路由协议(MWR-AODV).MWR-AODV综合考虑了对路由协议性能影响重大的最小跳数、剩余能量、能量流失率和网络节点密度这四个因素,并且引入了一种低成本且高效的本地修复策略.通过Network Simulator-2仿真平台对MWR-AODV与标准AODV、DSDV协议的表现进行了仿真分析.结果表明,所提出的MWR-AODV能为无线传感器网络提供更好的通信服务,并且在均衡能量消耗延长网络寿命和平衡网络通信负载方面也有上佳表现.