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     

Load balancing for cellular/WLAN integrated networks

The interworking between heterogeneous third-generation cellular networks and wireless local area networks is one promising evolution approach to fourth-generation wireless networks, which can exploit the complementary advantages of the cellular network and WLANs. Resource management for the 4G-oriented cellular/WLAN integrated network is an important open issue that deserves more research efforts. In this article we present a policy framework for resource management in a loosely coupled cellular/WLAN integrated network, where load balancing policies are designed to efficiently utilize the pooled resources of the network. A two-phase control strategy is adopted in the load balancing policies, in which call assignment is used to provide a statistical quality of service guarantee during the admission phase, and dynamic vertical handoff during the traffic service phase is used to minimize the performance variations. Numerical results are presented to demonstrate that the proposed load balancing solution achieves significant performance improvement over two other reference schemes     

The Mathematical Theory of Dynamic Load Balancing in Cellular Networks

While many interesting dynamic load balancing schemes have been proposed for efficient use of limited bandwidth and to increase the capacity of congested or hot spots (or cells) in wireless networks, to date, a comprehensive mathematical framework which encompasses all of these schemes does not exist. In this paper, we provide a unified mathematical framework for dynamic load balancing, which leads to closed-form performance expressions for evaluating the performance of some of the most important dynamic load balancing strategies proposed in the literature. To the best of our knowledge, this is the first generic theoretical framework that can be used to evaluate the performance of many different dynamic load balancing schemes with simple closed-form results. The accuracy of the results predicted by these analytical expressions derived from the theoretical framework is checked by comparing these results with simulation results provided in the literature for well-known schemes.     

异构蜂窝网络中用户关联与基站功率的协同优化

为实现异构蜂窝网络中宏基站和小基站之间的负载均衡,提出了一种基于效用函数最大化模型的用户关联机制和基站功率控制的协同优化方案.通过迭代算法求解该协同优化问题,首先在基站功率固定的情况下求得最佳用户关联策略,然后在所得的用户关联策略基础上通过Zoutendijk可行方向法求得基站最佳功率.通过协同优化获得的用户关联策略和基站功率控制实现了基站之间的负载均衡,通过降低宏基站功率和关闭闲置小基站降低了基站的能耗.仿真实验表明,所提方案和不实施功率控制的用户关联策略相比,实现了宏基站与小基站之间的负载均衡,降低了宏基站对小基站用户的干扰,提升了小基站用户的信号干扰噪声比,用户速率中位值提高了20％.     

基于贝叶斯博弈的WLAN节能机制研究

针对无线局域网（Wireless Local Area Networks,WLAN）中密集部署无线接入点（Access Point,AP）导致的能耗和同频干扰问题,提出了一种基于贝叶斯博弈的节能机制（BaYesian Game based Energy Saving scheme,BYG-ES）.首先,对通用AP设备的能耗进行测量与分析,构建AP发射功率-负载-能耗的关系模型;然后,基于该关系模型及软件定义网络控制器实时收集的网络状态信息,设计基于贝叶斯博弈的能耗优化模型;最后,利用社会选择函数求解能耗优化模型,获得干扰限制下最优的休眠AP集合和发射功率配置规则,完成用户流量卸载和AP发射功率的调整,同时保证AP参与博弈的诚实性.实验结果表明,BYG-ES节能机制能在减小系统能耗的同时提高网络性能.     

A distributed radio channel allocation scheme for WLANs with multiple data rates

For IEEE 802.11 wireless LANs (WLAN) with multiple access points (AP), it is critical to allocate the limited number of radio channels dynamically and efficiently. In this paper, we present a new radio channel allocation (RCA) scheme for WLANs with multiple data rates. First, we propose a new algorithm to dynamically estimate the number of active stations by using the least square estimator (LSE), which is unbiased and has minimum variance. Second, we derive an expression to evaluate the impact of the co-channel stations of an AP on the channel utilization of the AP based on the number of equivalent co-channel stations, which is the difference between the numbers of stations that are sensed by and associated with the AP. Third, we develop a new distributed RCA (DRCA) that considers the changing number of active stations, the impact of co-channel interference (CCI), and different traffic demands for different APs, which have not been considered by the existing RCA schemes. Simulation results have demonstrated that DRCA quickly finds optimal or suboptimal channel assignments and improves overall channel utilization for about 15 ~ 50% for different AP layouts, as compared to the existing schemes.     

Improved Multilevel Hysteresis Current Regulation and Capacitor Voltage Balancing Schemes for Flying Capacitor Multilevel Inverter

This paper focuses on the development of multilevel hysteresis current regulation strategies. Two such strategies have been discussed and some modifications in their control tasks have been proposed to achieve more reliable and improved performance. In general, the multiband concept has been used while making the proposals. The hysteresis band size considerations have also been presented by taking into account the desired and existing system conditions. The proposed modulation schemes have been applied to a five-level flying-capacitor inverter, whose operation under hysteresis current control mode is much less established. A new method of flying-capacitor voltage balancing is proposed which ensures balanced flying-capacitor voltages and, at the same time, maintains the desired current profile. It uses a time-based approach for controlling the capacitor voltages and achieves appreciable voltage spectrum under wide range of load power factor conditions. The performance of the proposed strategies is confirmed through both simulation and experimental investigations.     

Domain load balancing routing for multi-gateway wireless mesh networks

As Wireless Mesh Networks (WMNs) are typically used for Internet access, most traffic is routed through the gateways which connect WMN to the wired network. As a result, the gateways tend to get congested and balancing of the traffic load of gateways is critical. In this paper, we consider applications that require continuous provision of a certain bandwidth to a server located at the wired network. If a path that satisfies the bandwidth request cannot be found, the request will be rejected, so that load imbalance will result underutilization of the network capacity. We present a novel load balancing routing algorithm for maximizing the network utilization (i.e., accommodating service requests as many as possible) for multi-gateway WMNs. In the proposed scheme, a WMN is divided into domains. Each domain is served by one gateway, so that all traffic of a domain is served by the corresponding gateway. Our scheme determines routing to balance the traffic load among domains, and then performs load balancing routing within each domain. Simulation results show that in square grid topologies, our intra-domain routing achieves near optimal performance with about 70% less overhead than the existing schemes. Our inter-domain load balancing scheme outperforms the existing heuristics by up to 25% while achieving about 80% performance of the optimal solution.     

WLAN中基于OpenFlow的无缝切换机制设计与实现

在传统的WLAN网络中,因为用户使用的移动终端（Station,STA）具有移动性,STA会出现离开当前网络接入点（Access Point,AP）的覆盖范围进入另一AP覆盖范围的情况,此时STA需要在AP间进行切换.传统WLAN中这样的AP间切换会产生网络延迟突然增大、吞吐量损失、以及掉线等服务质量下降的问题.本文提出并实现了一种基于AP虚拟化和OpenFlow技术的解决方案,通过搭建基于OpenFlow的交换网络对STA的流量进行细粒度的控制从而完成STA在不同AP间的无缝切换.经过实际网络环境测试,本方案具有5ms左右的切换延时、在AP切换时只会造成1秒左右的瞬时吞吐量减少和16ms左右的网络延时.相较于其他方案,本方案由于不需要再次进行认证和重新路由,因而具有更好的无缝切换性能.     

Load-balancing routing in multichannel hybrid wireless networks with single network interface

A hybrid wireless network is an extension of an infrastructure network, where a mobile host may connect to an access point (AP) using multihop wireless routes, via other mobile hosts. The APs are configured to operate on one of multiple available channels. Mobile hosts and wireless routers can select its operating channel dynamically through channel switching. In this environment, a routing protocol that finds routes to balance load among channels while maintaining connectivity was proposed. The protocol works with nodes equipped with a single network interface, which distinguishes the work with other multichannel routing protocols that require multiple interfaces per node. The protocol discovers multiple routes to multiple APs, possibly operating on different channels. Based on a traffic load information, each node selects the "best" route to an AP and synchronizes its channel with the AP. With this behavior, the channel load is balanced, removing hot spots and improving channel utilization. The protocol assures every node has at least one route to an AP, where all intermediate nodes are operating on the same channel. The simulation results show that the proposed protocol successfully adapts to changing traffic conditions and improves performance over a single-channel protocol and a multichannel protocol with no load balancing.     

Threshold-Based Load Balancing for Multiple Home Agents in Mobile IP Networks

Mobile IP is an extension of the IP protocol, designed to provide seamless connectivity to mobile nodes roaming over the Internet. Under certain conditions of traffic, such as in Mobile IP networks supporting multimedia applications, overhead can cause significant delays at the mobility agents, i.e. foreign and home agents. Some multiple home agents protocol extensions have been proposed to avoid potential bottlenecks in single home agents configurations. Due to the highly unpredictable nature of the IP data traffic, efficient load balancing applied in such schemes is crucial to the overall performance improvement. In this paper, we propose a novel threshold-based dynamic load balancing policy that uses a realistic data-sharing model operational at each home agent. A discrete event computer simulator is developed to study the system performance with the proposed load balancing policy. We also introduce two new policy tuning parameters, the number of information queue slices and the retry latency, by which we control the load balancing benefit. Due to the relatively large number of simulation parameters, results are presented for typical configuration scenarios. In general, in all the results obtained, our threshold-based load balancing policy provides a significant performance improvement. The proposed architecture efficiently uses parallel processing for handling the overhead generated by the load balancing, which results in minimal performance degradation.     

AP-Initiated Reservations for Performance Enhancement in 802.11 MAC

In the infrastructure mode of the IEEE 802.11 Wireless Local Area Networks (WLANs), usually an Access Point (AP) requires more transmission opportunities than mobile stations, since the AP relays all the data traffic among mobile stations. However, the current MAC protocol gives AP the same opportunity with mobile stations for channel accessing, and it may introduce unfairness in the infrastructure mode of WLANs. In this paper, aiming at resolving the unfairness problem and enhancing the network performance, we propose an AP-initiated reservation scheme. Our scheme gives a high priority for AP’s channel accessing and allows AP to transmit multiple frames at once. We develop an analytical model to study the performance of proposed scheme, and also perform extensive simulations. Both the analytical and simulation results show that proposed scheme significantly enhances the performance of 802.11 MAC.     

Load balancing and its performance evaluation for layer 3 and IEEE 802.21 frameworks in PMIPv6‐based wireless networks

Mobile IP (MIP) requires mobile nodes (MNs) to register with the home agents (HAs) whenever the MNs change their point of attachment (PoA: access point (AP) or base station (BS)) in different subnets. Thus, such registrations cause excessive signaling overhead and long service delay. To solve this problem, proxy mobile IPv6 (PMIPv6) has been proposed by the IETF NETLMM working group. In PMIPv6, a new entity called mobile access gateway (MAG) performs the mobility‐related signaling with the local mobility anchor (LMA) on behalf of the MN and establishes a tunnel with the LMA. However, a number of MNs must be associated with an MAG, which means that the MAG can be easily overloaded. Therefore, in this paper, we propose a load balancing mechanism among the MAGs in the PMIPv6 network. The PMIPv6 handover signaling procedure is extended to support the proposed load balancing mechanism. We also discuss using IEEE 802.21 Media Independent Handover (MIH) protocol for load balancing to determine the load status at the candidate PoAs, in addition to the load status at the candidate MAGs. To evaluate the performance, we analyze the average waiting time in the queue at the MAG. Through simulations and numerical analysis, we show that the proposed load balancing mechanism can produce less queueing delay at the MAG and a higher data transmission rate at the PoA than when a load balancing operation is not performed in the PMIPv6 network. Copyright © 2009 John Wiley & Sons, Ltd.     

A distributed implementation of mobility load balancing with power control and cell reselection in 4G network

We consider a self‐organizing network (SON) capability of mobility load balancing in a 4G network, which determines the transmission power level for individual base stations and cell reselection for individual mobile stations such that the network‐wide load is minimized while satisfying the minimum signal‐to‐noise and interference ratio (SINR) requirement of individual users. Both centralized and distributed schemes are proposed. The centralized scheme is based on the greedy algorithm, serving as a performance bound to the distributed scheme. The distributed scheme is to solve the system‐wide optimization problem in the flat network model, i.e. no central control node. Furthermore, it requires relatively low inter‐cell exchange information among neighboring cells over an inter‐cell channel, e.g. X2 interface in the LTE network. The proposed design objective is to minimize the number of mobile users that do not satisfy the specified average throughput, while distributing the user traffic load as uniformly as possible among the neighboring cells. Our simulation results for a uniform user distribution demonstrate that the proposed scheme can achieve up to almost 80% of a load balancing gain that has been achieved by a greedy algorithm in the centralized optimization. Copyright © 2014 John Wiley & Sons, Ltd.     

A low overhead load balancing router for network-on-chip

The design of a router in a network-on-chip (NoC) system has an important impact on some performance criteria. In this paper, we propose a low overhead load balancing router (LOLBR) for 2D mesh NoC to enhance routing performance criteria with low hardware overhead. The proposed LOLBR employs a balance toggle identifier to control the initial routing direction of X or Y for flit injection. The simplified demultiplexers and multiplexers are used to handle output ports allocation and contention, which provide a guarantee of deadlock avoidance. Simulation results show that the proposed LOLBR yields an improvement of routing performance over the reported routing schemes in average packet latency by 26.5%. The layout area and power consumption of the network compared with the reported routing schemes are 15.3% and 11.6% less respectively.     

Gossip-Based Load Balance Strategy in Big Data Systems with Hierarchical Processors

In big data systems, data are assigned to different processors by the system manager, which has a large amount of work to perform, such as achieving load balances and allocating data to the system processors in a centralized way. To alleviate its load, we claim that load balancing can be conducted in a decentralized way, and thus, the system manager need not be in charge of this task anymore. Two decentralized approaches are proposed for load balancing schemes, namely, a utilization scheme based on a load balance algorithm (UBLB) and a number of layers scheme based on a load balance algorithm (NLBLB). In the UBLB scheme, considering the hierarchy of the processor’s processing abilities, a gossip-based algorithm is proposed to achieve load balance using the jobs’ utilizations as load balance indicators in addition to the number of jobs. The reason for this action is that the processor’s process abilities are different from one another. Thus, the utilization indicator is more reasonable. In the NLBLB scheme, the processors are classified into different layers according to their processing abilities. In each layer, a sub-load balance is conducted, which means that the UBLB is achieved in a sub-region. The efficiencies of the two proposed schemes are validated by simulation, which proves their positive effect.     

Collision-aware design of rate adaptation for multi-rate 802.11 WLANs

One of the key challenges in designing a rate adaptation scheme for IEEE 802.11 wireless LANs (WLANs) is to differentiate bit errors from link-layer collisions. Many recent rate adaptation schemes adopt the RTS/CTS mechanism to prevent collision losses from triggering unnecessary rate decrease. However, the RTS/CTS handshake incurs significant overhead and is rarely activated in today's infrastructure WLANs. In this paper we propose a new rate adaptation scheme that mitigates the collision effect on the operation of rate adaptation. In contrast to previous approaches adopting fixed rate-increasing and decreasing thresholds, our scheme varies threshold values based on the measured network status. Using the "retry" information in 802.11 MAC headers as feedback, we enable the transmitter to gauge current network state. The proposed rate adaptation scheme does not require additional probing overhead incurred by RTS/CTS exchanges and can be easily deployed without changes in firmware. We demonstrate the effectiveness of our solution by comparing with existing approaches through extensive simulations.     

Distributed resource allocation for DS-CDMA-based multimedia ad hocwireless LANs

Power control in direct sequence code division multiple access (DS-CDMA) systems and power/rate allocation in multirate DS-CDMA based networks is an open and interesting research area which has attracted much attention. However, with a few exceptions, most researchers have emphasized centralized resource allocation algorithms for cellular systems where the base station keeps track of the requirements of the various users and is thus responsible for the management of network resources. Ad hoc wireless local area networks (WLANs), on the other hand, are generally configured as peer-to-peer networks with no centralized hub or controller. Thus resource allocation has to be conducted in a distributed fashion. We address the issue of distributed resource management for multirate DS-CDMA based multimedia WLANs by (1) presenting a distributed resource allocation protocol, known as distributed resource negotiation protocol (DRNP) that builds on the RTS/CTS bandwidth reservation mechanism provided by IEEE 802.111, and provides quality of service (QoS) guarantees through distributed control of resources in DS-CDMA based multimedia WLANs and (2) investigating the performance of various resource allocation schemes within the context of DRNP, in terms of network wide metrics such as overall throughput and blocking rates     

Resources-aware trusted node selection for content distribution in mobile ad hoc networks

We propose a novel trust and probabilistic node selection mechanism for content distribution in mobile ad hoc networks. Due to the open nature of such networks which as a rule do not have strict node membership control, the selection of trustworthy nodes is an important challenge, especially as the resources (e.g., battery, bandwidth) of the mobile devices are limited and should not be wasted on erroneous or malicious content. Our proposal, in addition to considering the trustworthiness of nodes, ensures that the traffic load is equally shared amongst the population of nodes, thus further conserving mobile node resources. We analyse the proposed mechanisms and evaluate it against selected previously proposed trust schemes which, in the majority, favour the selection of the most trustworthy node. We demonstrate the benefits of our proposal which provides load balancing and prevents overuse of a single node’s resources, while still providing a good performance in regards to accurately choosing trustworthy nodes to provide the required content.     

Effectiveness of Explicit Stations Grouping in Crowded Wireless LANs

In this letter, we evaluate the effectiveness of a multi-stage contention scheme for wireless local area networks (WLANs) medium access control (MAC). Multi-stage contention schemes basically divide the stations into smaller groups to resolve the contention more efficiently. Previous researchers have proposed virtual grouping schemes for WLANs MAC. Here we quantitatively analyze what can be achieved with a simple grouping scheme, i.e. through multi-stage contention. Our analysis shows that the multi-stage scheme is efficient in resolving contention, making it a good alternative to the commonly used exponential backoff mechanism.