An energy-efficient MAC protocol with downlink traffic scheduling strategy in IEEE 802.11 infrastructure WLANs

To support mobility, mobile devices are powered by batteries with limited energy. Thus, the good design of energy efficiency becomes one of the most important issues in wireless networks. A well-designed energy-efficient MAC protocols can be realized with both minimum energy consumption as well as maximum data throughput and can be easily implemented in products with de facto standards. Based on IEEE 802.11 infrastructure WLANs, we propose an energy-efficient MAC protocol which employs a novel approach to schedule those to-be-transmitted frames for saving energy by reducing the total waiting time and the collisions of the frames. Fault tolerance issues are also considered in the proposed protocol because frames are transmitted in fading interference wireless environment. Through analyses and simulations, we demonstrate that our protocol presents a better performance than IEEE 802.11 and other protocols not only in energy efficiency but also in aggregate throughput and frame transmission delay.     

IEEE 802.11无线局域网标准研究*

介绍了IEEE 802.11全系列标准,研究了IEEE 802.11系列各标准的发展轨迹和相互关系,建立了该系列标准的层次模型。研究并分析了IEEE 802.11、IEEE 802.11a、IEEE 802.11b、IEEE 802.11g和IEEE 802.11n这几种常见标准,并对相应物理层和媒质访问控制层的关键技术作了重点分析。     

IEEE 802.11无线局域网中分布式协调功能的改进

结合无线局域网和TCP的特点提出了一种改进算法,当AP向无线节点发数据包时,无线节点用一个小的数据包(如:TCP层的ACK等)来代替CTS,这样可以避免无线节点单独发送小数据包,从而提高无线信道的利用率和无线网络的吞吐率。从试验结果可以看出,改进后的DCF协议不仅提高了信道的利用率和无线局域网的性能,而且更好的维护了无线节点间的公平性。     

An energy efficient security protocol for IEEE 802.11 WLANs

Security protocols in wired and wireless networks make use of computationally intensive cryptographic primitives and several message exchanges for authenticated key exchange at the session level and data confidentiality and integrity at the packet level. Moreover, changes in connectivity require mobile stations to repeatedly authenticate themselves, thereby expending more energy. In this paper, we propose an energy efficient security protocol for wireless local area networks (WLANs) that employs (a) different cryptographic primitives based on their suitability in terms of energy consumption and security level, (b) different levels of security and types of security services depending on the type of packet in 802.11 WLANs, and (c) a light-weight hashed key chain to reduce the number of expensive authentication transactions due to connectivity losses. We use packet traces from three different networks to compare the performance of the energy efficient security protocol with that of the standard 802.11 WLAN security protocol and show significant reduction in energy consumption.     

下一代WLAN分组目标唤醒时间调度改进方案

密集WLAN(Wireless Local Area Network,无线局域网)中,大规模站点同时接入信道引起激烈竞争,从而导致网络性能急剧下滑.IEEE工作组着手研发下一代WLAN标准IEEE 802.11ax,该标准结合基于正交频分复用多址技术提出了上行多用户随机接入和广播目标唤醒时间(Target Wake T...     

On the end-to-end flow allocation and channel assignment in multi-channel multi-radio wireless mesh networks with partially overlapped channels

The performance of wireless mesh networks (WMNs) can be improved significantly with the increase in number of channels and radios. Despite the availability of multiple channels in several of the current wireless standards, only a small fraction of them are non-overlapping and many channels are partially overlapped. In this paper, we formulate the joint channel assignment and flow allocation problem for multi-channel multi-radio WMNs as a Mixed Integer Linear Program (MILP). Unlike most of the previous studies, we consider the case when both non-overlapped and partially overlapped channels are being used. We consider an objective of maximizing aggregate end-to-end throughput and minimizing queueing delay in the network, instead of the sum of link capacities, since the traffic characteristics of a multi-hop WMN are quite different from a single hop wireless network. Our static channel assignment algorithm incorporates network traffic information, i.e., it is load aware. Our formulation takes into consideration several important network parameters such as the transmission power of each node, path loss information, the signal to interference plus noise ratio at a node, and the frequency response of the filters used in the transmitter and receiver. We show by simulations that our MILP formulation makes efficient use of the spectrum, by providing superior channel assignments and flow allocations with the addition of partially overlapped channels, without the use of any additional spectrum. We also justify the need to consider alternative objective functions such as, minimizing average queueing in the network. We also propose a polynomially bounded heuristic algorithm to scale the proposed algorithm to bigger network topologies.     

A survey of energy efficient MAC protocols for IEEE 802.11 WLAN

In recent years, IEEE 802.11 wireless local area networks (WLANs) have been widely deployed, and more and more mobile devices have built-in WLAN interfaces. However, WLAN employs the carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol, which consumes a significant portion of the energy resources of a mobile device. Hence, minimizing the energy consumption of the WLAN interface in mobile devices has recently attracted considerable interest in both academia and industry. This article provides a survey and an experimental study of the energy consumption issues and energy-efficient technologies of the MAC protocol in IEEE 802.11 WLAN.     

IEEE 802.11无线局域网OPNET建模与性能测试

讨论了IEEE802．11无线局域网的建模和性能问题。基于对IEEE802．11协议和目前功能最强大的网络仿真工具OPNET软件的研究。首先分析了无线局域网的各种行为,分别对这些行为单独建模后,通过有线状态机将它们集成而形成IEEE802．11协议支持模块。给出了模型输入输出接口的详细说明。并对网络的性能进行了分析比较。     

基于IEEE802.11n的长距离无线链路性能分析

IEEE802.11n-2009在传统802.11协议上添加了帧聚合和块回复功能,实现了MAC层增强,显著提高了网络吞吐量,使其更加适用于长距离无线网络。通过长距离(45km)无线链路信道利用率的理论计算和网络仿真,论证了节点采用帧聚合与块回复功能时的信道利用率明显优于不采用的情况。仿真结果进一步表明,速率越高、聚合帧越大在长距离传输时的吞吐量越高,且距离越远时帧聚合的优势越明显。     

G-PaMeLA: A divide-and-conquer approach for joint channel assignment and routing in multi-radio multi-channel wireless mesh networks

The performance of Multi-Radio Multi-Channel Wireless Mesh Networks (MRMC-WMNs) based on the IEEE 802.11 technology depends significantly on how the channels are assigned to the radios and how traffic is routed between the access points and the gateways. In this paper we propose an algorithmic approach to this problem, for which, as far as we know, no optimal polynomial time solutions have been put forward in the literature. The core of our scheme consists of a sequential divide-and-conquer technique which divides the overall Joint Channel Assignment and Routing (JCAR) problem into a number of local optimization sub-problems that are executed sequentially. We propose a generalized scheme called Generalized Partitioned Mesh network traffic and interference aware channeL Assignment (G-PaMeLA), where the number of sub-problems is equal to the maximum number of hops to the gateway, and a customized version which takes advantage of the knowledge of the topology. In both cases each sub-problem is formulated as an Integer Linear Programming (ILP) optimization problem. An optimal solution for each sub-problem can be found by using a branch-and-cut method. The final solution is obtained after a post-processing phase, which improves network connectivity. The divide-and-conquer technique significantly reduces the execution time and makes our solution feasible for an operational WMN. With the help of a detailed packet level simulation, the G-PaMeLA technique is compared with several state-of-the-art JCAR algorithms. Our results highlight that G-PaMeLA performs much better than the others in terms of packet loss rate, collision probability and fairness among traffic flows.     

无线局域网的速率自适应算法设计与仿真分析

目前的IEEE802.11在物理层提供了不同的传输速率,因此根据不同的信道条件可以选择一个合适的传输速率,以使系统吞吐量达到最大。在WLANs中,当有多个用户向同一个接入点传输数据时,碰撞就会产生。Collision-Aware Rate Adaptation（CARA）算法能够有选择地启用Request-To-Send/Clear-To-Send（RTS/CTS）识别出这种碰撞,很大程度上避免了由于碰撞引起的吞吐量下降。但随着碰撞的增加,CARA吞吐量还是有明显下降。为了提高吞吐量,提出了一种新的速率自适应算法Adaptive Avoid Collision Rate Adaptation（Adaptive-ACRA）,该算法根据信道条件不同改变门限值,有效地提高了大量碰撞存在情况下的吞吐量。最后,通过大量NS2仿真证明了新算法提高系统吞吐量的有效性。     

Performance modeling of IEEE 802.11 wireless LANs with stochastic Petri nets

In 1997, IEEE standardized the physical layers and the medium access for wireless local area networks. This paper presents a performance study of the distributed coordination function, the fundamental contention-based access mechanism. Most performance studies adopt unchecked simplifying assumptions or do not reveal all details of the simulation model. We develop a stochastic Petri net model, which captures all relevant system aspects in a concise way. Simulation allows to quantify the influence of many mandatory features of the standard on performance, especially the backoff procedure, extended interframe spaces, and the timing synchronization function. We identify conditions when simplifying assumptions commonly used in analytical modeling are justified. Applying these conditions, we derive a more compact and analytically tractable model from the detailed model.     

An efficient quality-of-service MAC protocol for infrastructure WLANs

In this paper, we propose a new efficient MAC protocol, named quality-of-service MAC (QMAC), which is an integrated solution for providing QoS guarantees to real-time multimedia applications in infrastructure WLANs. In addition, QMAC has the following attractive features: (i) its reservation scheme ensures that real-time stations enter the polling list in bounded time, (ii) it supports multiple priority levels and guarantees that high-priority stations always join the polling list earlier than low-priority stations, (iii) it employs the distributed pre-check technique such that the access point can admit as many newly flows as possible, while not violating admitted flows' guarantees, (iv) its dynamic bandwidth allocation scheme provides real-time traffic transmission with per-flow probabilistic bandwidth assurances, and (v) it uses a multipoll frame to poll all stations on the polling list at a time, therefore, the bandwidth can be utilized more efficient. Through simulations, we demonstrate the advantage of our QMAC.     

Adaptive channel assignment scheme for wireless networks

In this paper, an adaptive channel assignment scheme is proposed to ensure the quality of services for the wireless networks. The proposed scheme divides the channels into two categories, the guard channels and the shared channels. The number of guard channels is estimated by the Markovian model in order to keep the handoff calls higher priority. The remaining channels, called shared channels, can be used by both new calls and handoff calls. The proposed scheme based on incoming rates of handoff and new calls allocates channels for guard and shared channels. In addition, this approach is able to provide quality of service guarantee in terms of handoff dropping rate. From the simulation, the proposed scheme significantly improves the dropping rate and the blocking rate in comparison with the existing methods.     

基于IEEE802.11n的无线网络及其在校园网的应用研究

该文对IEEE802.11n的标准及其核心技术进行了介绍,并就基于它的无线设备组建的校园网进行了分析,对它在校园网中的应用进行了研究。     

A comparison of deterministic and probabilistic methods for indoor localization

Received signal strength indication fingerprinting (RSSIF) is an indoor localization technique that exploits the prevalence of wireless local area networks (WLANs). Past research into RSSIF systems has seen the development of a number of algorithmic methods that provide effective indoor positioning. A key limitation, however, is that the performance of these methods is heavily dependent on practical implementation parameters and the nature of the test-bed environment. As a result, past research has tend to only compare algorithms of the same paradigm using a specific test-bed, and thus making it difficult to judge and compare their performance objectively. There is, therefore, a critical need for a study that addresses this gap in the literature. To this end, this paper compares a range of RSSIF methods, drawn from both probabilistic and deterministic paradigms, on a common test-bed. We evaluate their localization efficiency and accuracy, and also propose a number of improvements and modifications. In particular, we report on the impact of dense and transient access points (APs) - two problems that stem from the popularity of WLANs. Our results show methods that average the distance to the k nearest neighbors in signal space perform well with reduced dimensions. Moreover, we show the benefits of using the standard deviation of RSSI values to exclude transient APs. Other than that, we outline a shortcoming of the Bayesian algorithm in uncontrolled environments with highly variable APs and RSSI values, and propose an extension that uses a mode filter to restore its accuracy with increasing samples.     

A practical framework for 802.11 MIMO rate adaptation

The emergence of MIMO antennas and channel bonding in 802.11n wireless networks has resulted in a huge leap in capacity compared with legacy 802.11 systems. This leap, however, adds complexity to optimizing transmission. Not only does the appropriate data rate need to be selected, but also the MIMO transmission technique (e.g., Spatial Diversity or Spatial Multiplexing), the number of streams, and the channel width. Incorporating these features into a rate adaptation (RA) solution requires a new set of rules to accurately evaluate channel conditions and select the appropriate transmission setting with minimal overhead. To address these challenges, our contributions in this work are two-fold. First, we propose a practical link metric that accurately captures channel conditions in MIMO 802.11n environments, and we call this metric diffSNR. Using diffSNR captured from real testbed environments, we build performance models that accuractely predict link quality in 95.5% of test cases. Practicality and deployability are guaranteed with diffSNR as it can be measured on all off-the-shelf MIMO WiFi chipsets. Second, we propose ARAMIS (Agile Rate Adaptation for MIMO Systems), a standard-compliant, closed-loop RA solution that jointly adapts rate and bandwidth, and we utilize the diffSNR-based 802.11n performance models within ARAMIS’s framework. ARAMIS adapts transmission rates on a per-packet basis; we believe it is the first closed-loop, 802.11 RA algorithm that simultaneously adapts rate and channel width. We have implemented ARAMIS with diffSNR on Atheros-based devices and deployed it on our 15-node testbed. Our experiments show that ARAMIS accurately adapts to a wide variety of channel conditions with negligible overhead. Furthermore, ARAMIS outperforms existing RA algorithms in 802.11n environments with up to a 10-fold increase in throughput.     

Throughput analysis of IEEE 802.11 multirate WLANs with collision aware rate adaptation algorithm

This paper presents a mathematical model that analyzes the throughput of the IEEE 802.11b distributed coordination function (DCF) with the collision aware rate adaptation (CARA) algorithm. IEEE 802.11 WLANs provide multiple transmission rates to improve system throughput by adapting the transmission rate to the current channel conditions. The system throughput is determined by some stations using low transmission rates due to bad channel conditions. CARA algorithm does not disturb the existing IEEE 802.11b formats and it can be easily incorporated into the commercial wireless local area networks (WLAN) devices. Finally, we verify our findings with simulation.     

A weight-aware channel assignment algorithm for mobile multicast in wireless mesh networks

Wireless mesh networks (WMNs) are one of key technologies for next generation wireless networks. In this paper, we propose a heuristic channel assignment algorithm with weight awareness to support mobile multicast in WMNs. To enhance network throughput, our algorithm is based on the path forwarding weight to perform channel assignment. In addition to non-overlapping channels, partially-overlapping channels are also used in channel assignment. To fully exploit all available channels in channel assignment, we devise a new channel selection metric to consider the channel separation and the distance between nodes. In mobile multicast, the multicast tree structure cannot be fixed due to receiver (multicast member) mobility. The change of the multicast tree structure will result in channel re-assignment. The proposed algorithm is based on a critical-event driven manner to reduce the times of channel re-assignment as much as possible. Finally, we perform simulation experiments to show the effectiveness of the proposed channel assignment algorithm.     

一种802.11e EDCA机制的优化算法

IEEE 802.11e增强型分布式信道访问机制对高优先级业务服务质量的保证,是通过牺牲低优先级业务服务质量来实现的.为避免这种信道资源分配不公平的现象,提出一种优化算法.将信道中部分时隙合并起来构成合并时隙,高优先级和低优先级业务在合并时隙中被先后发送,而单个时隙通常只发送低优先级业务.仿真结果表明,该算法可以提高业务的吞吐量,当站点数目增多时,高优先级业务和低优先级业务的吞吐量均表现稳定,可达到各种业务公平利用信道资源的目的.