Cell Breathing in Wireless LANs: Algorithms and Evaluation

Wireless LAN administrators often have to deal with the problem of sporadic client congestion in popular locations within the network. Existing approaches that relieve congestion by balancing the traffic load are encumbered by the modifications that are required to both access points and clients. We propose cell breathing, a well-known concept in cellular telephony, as a load balancing mechanism to handle client congestion in a wireless LAN. We develop power management algorithms for controlling the coverage of access points to handle dynamic changes in client workloads. We further incorporate hand-off costs and manufacturer specified power level constraints into our algorithms. Our approach does not require modification to clients or to the standard. It only changes the transmission power of beacon packets and does not change the transmission power of data packets to avoid the interactions with auto-rating. We analyze the worst-case bounds of the algorithms and show that they are either optimal or close to optimal. In addition, we evaluate our algorithms empirically using synthetic and real wireless LAN traces. Our results show that cell breathing significantly outperforms the commonly used fixed power scheme and performs at par with sophisticated load balancing schemes that require changes to both the client and access points     

An Overlay Smart Spaces System for Load Balancing in Wireless LANs

An overlay smart spaces system, called MITOS, is proposed for managing the use of the resources in wireless local area networks (WLAN). MITOS monitors the traffic load distribution in the different WLAN segments, as well as the location of each user, and when necessary, suggests to specific users to change their location in order to improve their quality of service. Enhancements to the basic MITOS architecture are introduced to intelligently manage local congestion, and maintain an almost uniform load level across the network. The approach used for load balancing is based on game theoretic mechanisms, such as the solutions to the Santa Fe Bar Problem. Simulation results are provided showing the efficiency of the proposed system. The research of the author for his PhD studies is supported by the Alexander S. Onassis Foundation Scholarship Programme. George Alyfantis received his B.Sc. degree in Informatics and Telecommunications from the Department of Informatics and Telecommunications, University of Athens, Athens Greece, in 2002. He received his M.Sc. degree in Communication and Network Systems from the same Department, in 2003. Since 2001, he is a member of the Communication Networks Laboratory (CNL) of the University of Athens. Currently, he is working towards his Ph.D. thesis. His research interests include pervasive/mobile computing, middleware for wireless sensor networks, web caching performance and game theory. He is the author of 5 papers in the aforementioned areas. In the course of his studies he received numerous distinctions like the Alexandros Onassis Foundation Scholarship for his Ph.D. studies, the best student award of the Department of Informatics and Telecommunications for graduating first in his B.Sc./M.Sc. class and the best M.Sc. thesis Ericsson Award of Excellence in Telecommunications 2004. Stathes Hadjiefthymiades received his B.Sc. (honors) in Informatics from the Department of Informatics at the University of Athens, Greece, in 1993 and his M.Sc. (honors) in Informatics (Advanced information systems) from the same department in 1996. In 1999 he received his Ph.D. from the University of Athens (Department of Informatics and Telecommunications). In 2002 he received a joint engineering-economics M.Sc. degree from the National Technical University of Athens. In 1992 he joined the Greek consulting firm Advanced Services Group, Ltd., where he was involved in the analysis and specification of information systems and the design-implementation of telematic applications. In 1995 he became a member of the Communication Networks Laboratory (UoA-CNL) of the University of Athens. During the period September 2001–July 2002, he served as a visiting assistant professor at the University of Aegean, Department of Information and Communication Systems Engineering. On the summer of 2002 he joined the faculty of the Hellenic Open University (Department of Informatics), Patras, Greece, as an assistant professor. Since December 2003, he is in the faculty of the Department of Informatics and Telecommunications, University of Athens, where he is presently an assistant professor. He is coordinating the Pervasive Computing Research Group of the Dept. of Informatics and Telecommunications at the University of Athens. He has participated in numerous projects realized in the context of EU programs (ACTS, ORA, TAP, and IST), EURESCOM projects, as well as national initiatives. His research interests are in the areas of web engineering, wireless/mobile computing, and networked multimedia applications. He is the author of over 80 publications in the above areas. Lazaros Merakos received the Diploma in electrical and mechanical engineering from the National Technical University of Athens, Athens, Greece, in 1978, and the M.S. and Ph.D. degrees in electrical engineering from the State University of New York, Buffalo, in 1981 and 1984, respectively. From 1983 to 1986, he was in the faculty of the Electrical Engineering and Computer Science Department University of Connecticut, Storrs. From 1986 to 1994 he was in the faculty of the Electrical and Computer Engineering Department, Northeastern University, Boston, MA. During the period 1993–1994, he served as director of the Communications and Digital Processing Research Center, Northeastern University. During the summers of 1990 and 1991, he was a visiting scientist at the IBM T. J. Watson Research Center, Yorktown Heights, NY. In 1994, he joined the faculty of the University of Athens, Athens, Greece, where he is presently a professor in the Department of Informatics and Telecommunications, and director of the Communication Networks Laboratory (UoA-CNL) and the Networks Operations and Management Center. Since 1995, he is leading the research activities of UoA-CNL in the area of mobile communications, in the framework of the Advanced Communication Technologies and Services (ACTS) and Information Society Technologies (IST) programs funded by the European Union (projects RAINBOW, Magic WAND, WINE, MOBIVAS, POLOS, ANWIRE, E2R, LIAISON). His research interests are in the design and performance analysis of communication networks, and wireless/mobile communication systems and services. He has authored more than 190 papers in the above areas. Dr. Merakos is chairman of the board of the Greek Universities Network, the Greek Schools Network, and member of the board of the Greek Research Network. In 1994, he received the Guanella Award for the best paper presented at the International Zurich Seminar on Mobile Communications.     

Fairness and Load Balancing in Wireless LANs Using Association Control

The traffic load of wireless LANs is often unevenly distributed among the access points (APs), which results in unfair bandwidth allocation among users. We argue that the load imbalance and consequent unfair bandwidth allocation can be greatly reduced by intelligent association control. In this paper, we present an efficient solution to determine the user-AP associations for max-min fair bandwidth allocation. We show the strong correlation between fairness and load balancing, which enables us to use load balancing techniques for obtaining optimal max-min fair bandwidth allocation. As this problem is NP-hard, we devise algorithms that achieve constant-factor approximation. In our algorithms, we first compute a fractional association solution, in which users can be associated with multiple APs simultaneously. This solution guarantees the fairest bandwidth allocation in terms of max-min fairness. Then, by utilizing a rounding method, we obtain the integral solution from the fractional solution. We also consider time fairness and present a polynomial-time algorithm for optimal integral solution. We further extend our schemes for the on-line case where users may join and leave dynamically. Our simulations demonstrate that the proposed algorithms achieve close to optimal load balancing (i.e., max-min fairness) and they outperform commonly used heuristics.     

Cell Selection for Load Balancing in Heterogeneous Networks

The vision of advanced long-term evolution (LTE-A) project is set to ultimate increase of network capacity in heterogeneous networks (HetNets). In HetNets with small cell configuration, a considerable majority of user devices is eventually connected to the macrocell base station (MBS), while small base stations (BSs), such as femtocell access points (FAPs), are still without any user. This results in unbalanced load and reduces the data rate of macrocell user equipment (MUE). In this paper, a method is proposed for load balancing among FAPs, while desired throughput is achieved. The proposed method uses the estimated received signal strength from different BSs and adjusted pilot signals. Under the critical signal to interference plus noise ratio (SINR) condition, a list of candidate FAPs is prepared. The updated candidate list henceforth does not include the least visited FAPs, which in turn leads to lower unnecessary handoffs. Once the BS with the highest number of free RBs and the highest pilot signal power is selected, FAP allocates the RBs with higher SINRs (qualified RBs) to user. In the case of FAP unavailability, the algorithm compels users to connect to the MBS with adequate qualified RBs. The performance of the proposed method was evaluated under a variety of FAPs density, and the number and velocity of users in terms of throughput and Jain’s fairness index. The results evidence affordable improvements in the throughput and Jain’s index in comparison with other methods.     

自组织无线网络中的移动负载均衡技术

文章认为基于人工进行的网络优化方法难以适应未来网络发展需要,为此LTE系统引入了自组织网络技术。自组织网络技术涉及网络部署、运行的各个环节,其中移动负载均衡技术是自组织网络技术的一个关键技术。移动负载均衡技术通过用户在不同小区之间的切换实现负载的转移,从而实现负载的均衡分布,提高网络性能。针对很多移动负载均衡算法没有考虑用户的服务质量(QoS)要求,文章介绍了一种保证QoS要求的移动负载均衡算法。     

3patial Load Balancing in Nide-Area Wireless Networks

Load balancing is typically used in the frequency domain of cellular wireless networks to balance paging, access, and traffic load across the available bandwidth. In this paper, we extend load balancing into the spatial domain, and we develop two approaches-network load balancing and single-carrier multilink-for spatial load balancing. Although these techniques are mostly applied to cellular wireless networks and Wi-Fi networks, we show how they can be applied to EV-DO, a 3G cellular data network. When a device has more than one candidate server, these techniques can be used to determine the quality of the channel between a server and the device and to determine the load on each server. The proposed techniques leverage the advantages of existing EV-DO network architecture and are fully backward compatible. Network operators can substantially increase network capacity and improve user experience by using these techniques. Combining load balancing in the frequency and spatial domains improves connectivity within a network and allows resources to be optimally allocated according to the p-fair criterion. Combined load balancing further improves performance.     

WMN中一种基于干扰感知的负载均衡路由协议

无线信道干扰和负载分布的不均衡严重影响无线Mesh网络吞吐量、端到端延时和资源利用率。在已有基于信噪比和邻居节点个数的干扰模型基础上,进一步研究了无线Mesh网络的链路干扰。在综合考虑了无线Mesh网络流间干扰和和流内干扰的基础上,提出路由判据PIL（Path Interfer-ence Level）。在此基础上,提出一种新的基于干扰感知的负载均衡路由协议IA-DSR（Interference-Aware DSR）。IA-DSR考虑无线网络拥塞并选择受到干扰最小的路径。仿真结果表明,在不显著增加开销的情况下,IA-DSR可以有效地提高网络的整体吞吐量,降低网络端到端时延和丢包率。     

东山再起的无线局域网(WLAN)

1 引言 无线局域网（WLAN）本身并不是新概念、新技术,它已存在10多年了。顾名思义,WLAN是用无线通信技术构建的局域网,虽不采用缆线,但也能提供传统有线局域网的所有功能。与有线局域网相比,WLAN具有一定移动性、灵活性高、建网迅速、管理方便、网络造价低、扩展能力强,但WLAN的网络产品较贵、硬件初始投资比有线局域网高、传输速率较低。WLAN还有一个好处是它使用不需许可证的2.4GHz频段,其运营者不用花钱申请频谱许可证,随时可以建网使用。     

QoS Routing for Mesh-Based Wireless LANs

Wireless LANs with their increased data rate become an attractive technology for connecting mobile users to the Internet. Efficient deployment of wireless LANs will require the ability to extend the wireless LANs coverage without the need to deploy a very large number of access points. Mesh-based wireless LANs are an attractive solution to this problem. These networks extend wireless LAN coverage by using each node in the network as a router, resulting in a multihop topology. In this paper we introduce a novel routing algorithm, wireless mesh routing (WMR), that provides quality-of-service (QoS) support and accounts for the characteristics of both infrastructure-based wireless LANs and ad hoc networks. The algorithm is validated using the OPNET modeler. The simulation results show that the mesh network using WMR protocol can provide QoS support and react dynamically to the network status changes with low control overheads. Using the proposed software architecture the proposed routing protocol can be implemented with any MAC protocol, resulting in easy implementation in existing wireless nodes.     

Shuffled Complex Evolution Approach for Load Balancing of Gateways in Wireless Sensor Networks

Wireless Personal Communications - Energy consumption is one of the important factor of Wireless Sensor Networks (WSN). It has much attention in many fields. From recent studies, it is observed...     

Collision Localization for IEEE 802.11 Wireless LANs

In this paper, we examine an algorithm for estimating the location of packet collisions, in the presence of bandlimited multipath channels. We propose an improvement to the collision localization algorithm to further enhance its performance to compensate for the increased impairments of the multipath channel. We then examine the collision localization algorithm in conjunction with two common wireless LAN standards, 802.11b and 802.11a/g. We show that for the 802.11b standard, the collision localization algorithm performs well, even in the presence of a multi-path channel. We also show that the 802.11 a/g standards are compatible with collision localization. However, we will see that the IFFT/FFT operations required to perform OFDM transmission limit the effectiveness of collision localization. We therefore also investigate collision localization in conjunction with block-based single carrier transmission, a comparable technology to OFDM, and offers some advantages when used with collision localization. In addition, we also investigate two applications of collision localization. First, we will show that collision localization in conjunction with Viterbi decoding with erasures can, in many cases, allow for corrupted packets to be completely recovered at the receiver. Second, we will also demonstrate that collision localization can be used to combat narrow-band interference, such as Bluetooth, in 802.11 a/g networks.     

基于等概率路由模型的传感器网络负载均衡研究

无线传感器网络的能耗效率与流量负载分布密切相关。论文从微观角度研究了无线传感器网络的负载均衡问题。基于等概率路由模型,分析了拓扑传输结构对于感知数据流量的分流作用。根据分析结果,提出了多对一传输模式下任意节点负载密度的定义和算法。分析了节点的负载密度与传感器网络生命期的关系,进一步论证了在多对一的多跳传感器网络中不能实现完全的负载均衡,但是通过设计合理的拓扑结构可以实现准负载均衡。仿真结果说明,从微观角度得到的节点负载密度可以准确描述无线传感器网络的流量负载分布,由此得到的准负载均衡条件也能实现绝大多数节点的负载均衡。     

Low-Complexity Symbol Detector for MIMO-OFDM-Based Wireless LANs

In this brief, a low-complexity hardware architecture for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) symbol detectors with two transmit and two receive antennas is proposed. The detectors support two MIMO-OFDM schemes of space-frequency block coded OFDM and space-division multiplexing OFDM in order to achieve higher performance and throughput. However, symbol detection processes for these two schemes have high computational complexity, which is a burden to hardware implementation of MIMO-OFDM symbol detectors. In order to reduce complexity, the proposed symbol detector is designed with shared architecture, where similar functional blocks are merged and share the hardware resources, and results in the reduction of logic gates by 34% over a conventional architecture employing two individual detectors     

Reliable Multicast in Multi-Access Wireless LANs

Multicast is an efficient paradigm for transmitting data from a sender to a group of receivers. In this paper, we focus on multicast in single channel multi-access wireless local area networks (LANs) comprising several small cells. In such a system, a receiver cannot correctly receive a packet if two or more packets are sent to it at the same time, because the packets collide. Therefore, one has to ensure that only one node sends at a time. We look at two important issues. First, we consider the problem of the sender acquiring the multi-access channel for multicast transmission. Second, for reliable multicast in each cell of the wireless LAN, we examine ARQ-based approaches. The second issue is important because the wireless link error rates can be very high.We present a new approach to overcome the problem of feedback collision in single channel multi-access wireless LANs, both for the purpose of acquiring the channel and for reliability. Our approach involves the election of one of the multicast group members (receivers) as a leader or representative for the purpose of sending feedback to the sender. For reliable multicast, on erroneous reception of a packet, the leader does not send an acknowledgment, prompting a retransmission. On erroneous reception of the packet at receivers other than the leader, our protocol allows negative acknowledgments from these receivers to collide with the acknowledgment from the leader, thus destroying the acknowledgment and prompting the sender to retransmit the packet.Using analytical models, we demonstrate that the leader-based protocol exhibits higher throughput in comparison to two other protocols which use traditional delayed feedback-based probabilistic methods. Last, we present a simple scheme for leader election.     

Cell Planning in WCDMA Networks for Service Specific Coverage and Load Balancing

Third-generation (3G) Wideband Code Division Multiple Access network is an evolutionary network which supports services from circuit-based voice service to high and low rate packet-based data services. Unlike the voice oriented second-generation service, the 3G network is enhanced to support services with different data rate, different asymmetry, and different coverage. We thus need to investigate the coverage of multiple services and the capacity of a cell in cell planning for the advanced network. Service specific uplink coverage and downlink capacity with load balancing are considered in our cell planning. The problem is formulated as a linear integer programming optimization model. An efficient tabu search heuristic is developed to solve the NP-hard problem. Very promising computational results are demonstrated, where the solution gap from the optimal to the lower bound by CPLEX is within 0.9% in problems to cover all service traffic in the system. It is demonstrated that higher load factor effectively reduces cell sites for multiple service classes. Load balancing among cells is also demonstrated with different coverage ratio.     

Out-of-Band Signaling Scheme for High Speed Wireless LANs

In recent years, the physical layer data rate provided by 802.11 Wireless LANs has dramatically increased thanks to significant advances in the modulation and coding techniques employed. However, previous studies show that the 802.11 MAC operation, namely the distributed coordination function (DCF), represents a limiting factor: the throughput efficiency drops as the channel bit rate increases, and a throughput upper limit does indeed exist when the channel bit rate goes to infinite high. These findings indicate that the performance of the DCF protocol will not be efficiently improved by merely increasing the channel bit rate. This paper shows that the DCF performance may significantly benefit from the adoption of two separate physical carriers: one devised to manage the channel access contention, and another devised to deliver information data. We propose a scheme, referred to as out-of-band signaling (OBS), designed to reuse (and remain backward compatible with) the existing 802.11 medium access control (MAC) specification. Performance evaluation of OBS is carried out through analytical techniques validated via extensive simulation, for both saturation and statistical traffic conditions. Numerical results show that OBS improves the throughput/delay performance, and provides better bandwidth usage compared with the in-band signaling technique employed by DCF.     

Energy-Efficient Load Balancing Strategy for Wireless Sensor Networks using Quasi-oppositional based Jaya Optimization

Wireless Personal Communications - The area of wireless sensor networks (WSNs) has gained significant attention from researchers due to its expansive range of applications, such as industrial...     

CoopMAC: A Cooperative MAC for Wireless LANs

Due to the broadcast nature of wireless signals, a wireless transmission intended for a particular destination station can be overheard by other neighboring stations. A focus of recent research activities in cooperative communications is to achieve spatial diversity gains by requiring these neighboring stations to retransmit the overheard information to the final destination. In this paper we demonstrate that such cooperation among stations in a wireless LAN (WLAN) can achieve both higher throughput and lower interference. We present the design for a medium access control protocol called CoopMAC, in which high data rate stations assist low data rate stations in their transmission by forwarding their traffic. In our proposed protocol, using the overheard transmissions, each low data rate node maintains a table, called a CoopTable, of potential helper nodes that can assist in its transmissions. During transmission, each low data rate node selects either direct transmission or transmission through a helper node in order to minimize the total transmission time. Using analysis, simulation and testbed experimentation, we quantify the increase in the total network throughput, and the reduction in delay, if such cooperative transmissions are utilized. The CoopMAC protocol is simple and backward compatible with the legacy 802.11 system. In this paper, we also demonstrate a reduction in the signal-to-interference ratio in a dense deployment of 802.11 access points, which in some cases is a more important consequence of cooperation