Greedy construction of load‐balanced virtual backbones in wireless sensor networks

Inspired by the backbone concept in wired networks, a virtual backbone is expected to bring substantial benefits to routing in wireless sensor networks (WSNs). A connected dominating set (CDS) is used as a virtual backbone for efficient routing and broadcasting in WSNs. Most existing works focus on constructing a minimum CDS, a k‐connect m‐dominating CDS, a minimum routing cost CDS, or a bounded‐diameter CDS. However, the load‐balance factor is not considered for CDSs in WSNs. In this paper, a greedy‐based approximation algorithm is proposed to construct load‐balanced CDS in a WSN. More importantly, we propose a new problem: the Load‐balanced Allocate Dominatee problem. Consequently, we propose an optimal centralized algorithm and an efficient probability‐based distributed algorithm to solve the Load‐balanced Allocate Dominatee problem. For a given CDS, the upper and lower bounds of the performance ratio of the distributed algorithm are analyzed in the paper. Through extensive simulations, we demonstrate that our proposed methods extend network lifetime by up to 80% compared with the most recently published CDS construction algorithm. Copyright © 2012 John Wiley & Sons, Ltd.     

时延和能耗均衡的强连通支配集构造算法

针对无线传感器网络中链路的非对称性,提出时延约束的强连通支配树(SDTT,strongly connected dominating tree with bounded transmission delay)问题,给出在有向图上构建传输时延和能量消耗均衡的强连通支配集的强连通支配树(SCDT,distributed strongly connected dominating tree)算法。首先在单位圆图(UDG)模型的基础上构建极大独立集(MIS),然后在具有双向权值的有向图上基于最小支撑树和最短路径树实现分布式SCDT算法,同时满足时延和能耗均衡的约束条件要求。理论算例分析和仿真结果表明提出的算法能有效地解决SDTT问题,构造联合约束的强连通支配集,形成时延和能耗均衡的虚拟骨干。     

Construction and maintenance of virtual backbone in wireless networks

In ad hoc wireless networks, there is no predefined infrastructure and nodes communicate with each other via peer communications. In order to make routing efficient in such networks the connected dominating set (CDS) can act as virtual backbone for the network. A smaller virtual backbone suffers less from the interference problem and incurs less maintenance overhead. Computing minimum CDS backbone is proven to be NP-Hard, it is therefore desirable to use efficient heuristic algorithms to find a virtual backbone of small size. Diameter and average backbone path length (ABPL) are other major criteria for evaluation of the backbone produced by an algorithm. In this paper, after giving a brief survey of classical CDS algorithms, two new centralized algorithms are described for the construction of the virtual backbone and their performance has been compared with five recent algorithms (two centralized and three distributed) along the parameters: size, diameter, and ABPL. The new algorithms perform better on most of the criteria. The re-construction of entire CDS upon movement or failure of a few nodes is very costly in terms of processing power, battery utilization, bandwidth utilization etc., as compared to maintaining the CDS for the affected nodes, since the re-construction of the CDS is to be performed for the whole network while maintenance involves the affected nodes and their neighbours only. A new distributed algorithm is described that maintains the virtual backbone on movement or failure of a single node. The overhead of CDS maintenance with this algorithm compares very favourably against that of re-construction.     

Zone-based virtual backbone formation in wireless ad hoc networks

Efficient protocol for clustering and backbone formation is one of the most important issues in wireless ad hoc networks. Connected dominating set (CDS) formation is a promising approach for constructing virtual backbone. However, finding the minimum CDS in an arbitrary graph is a NP-Hard problem. In this paper, we present a novel zone-based distributed algorithm for CDS formation in wireless ad hoc networks. In this Zone algorithm, we combine the zone and level concepts to sparsify the CDS constructed by previous well-known approaches. Therefore, this proposed algorithm can significantly reduce the CDS size. Particularly, we partition the wireless network into different zones, construct a dominating tree for each zone and connect adjacent zones by inserting additional connectors into the final CDS (at the zone borders). Our comprehensive simulation study using a custom simulator shows that this zone-based algorithm is more effective than previous approaches. The number of nodes in the CDS formed by this Zone algorithm is up to around 66% less than that constructed by others. Moreover, we also compare the performance of Zone algorithm with some recently proposed CDS formation protocols in ns2 simulator.     

无线传感器网络中一种能量均衡的基于连通支配集的数据收集算法

采用连通支配集来构建虚拟骨干可以减轻无线传感器网络的广播风暴问题.目前已有大量工作通过构造最小连通支配集形成网络虚拟骨干来进行高效数据收集.然而,最小连通支配集并不能有效均衡节点的能量耗费,导致网络生命周期较短.提出了一种能量均衡的基于连通支配集的分布式算法EBCDS来进行数据收集,通过选择能量水平和度均比较大的节点组成连通支配集,支配集中的节点组成一个规模不大但具有较高能量水平的网络骨干.网络中的所有数据沿骨干在较小的寻路空间中转发,能够节省节点能量,使骨干节点不会因为能量不足而过早死亡.理论分析表明,EBCDS能以O(nlogn)的消息复杂度构造连通支配集,仿真实验表明,EBCDS能有效节省节点能耗并延长网络生命周期.     

A new distributed approximation algorithm for constructing minimum connected dominating set in wireless ad hoc networks

In recent years, constructing a virtual backbone by nodes in a connected dominating set (CDS) has been proposed to improve the performance of ad hoc wireless networks. In general, a dominating set satisfies that every vertex in the graph is either in the set or adjacent to a vertex in the set. A CDS is a dominating set that also induces a connected sub‐graph. However, finding the minimum connected dominating set (MCDS) is a well‐known NP‐hard problem in graph theory. Approximation algorithms for MCDS have been proposed in the literature. Most of these algorithms suffer from a poor approximation ratio, and from high time complexity and message complexity. In this paper, we present a new distributed approximation algorithm that constructs a MCDS for wireless ad hoc networks based on a maximal independent set (MIS). Our algorithm, which is fully localized, has a constant approximation ratio, and O(n) time and O(n) message complexity. In this algorithm, each node only requires the knowledge of its one‐hop neighbours and there is only one shortest path connecting two dominators that are at most three hops away. We not only give theoretical performance analysis for our algorithm, but also conduct extensive simulation to compare our algorithm with other algorithms in the literature. Simulation results and theoretical analysis show that our algorithm has better efficiency and performance than others. Copyright © 2005 John Wiley & Sons, Ltd.     

The first constant factor approximation for minimum partial connected dominating set problem in growth-bounded graphs

The idea of virtual backbone has emerged to improve the efficiency of flooding based routing algorithms for wireless networks. The effectiveness of virtual backbone can be improved as its size decreases. The minimum connected dominating set (CDS) problem was used to compute minimum size virtual backbone. However, as this formulation requires the virtual backbone nodes to connect all other nodes, even the size of minimum virtual backbone can be large. This observation leads to consider the minimum partial CDS problem, whose goal is to compute a CDS serving only more than a certain portion of the nodes in a given network. So far, the performance ratio of the best approximation algorithm for the problem is \(O(\ln \varDelta ),\) where \(\varDelta\) is the maximum degree of the input general graph. In this paper, we first assume the input graph is a growth-bounded graph and introduce the first constant factor approximation for the problem. Later, we show that our algorithm is an approximation for the problem in unit disk graph with a much smaller performance ratio, which is of practical interest since unit disk graph is popular to abstract homogeneous wireless networks. Finally, we conduct simulations to evaluate the average performance of our algorithm.     

基于图着色的无线自组网极小连通支配集算法

基于连通支配集算法的虚拟主干网技术对于无线自组网的路由优化、能量保护和资源分配都具有重要的作用。通过引入极大独立集和极小支配集概念,基于图着色思想提出一种新的适合于无线自组网的极小连通支配集算法,从理论上证明了该算法的正确性和高效性,也通过仿真实验分析了该算法在多种情况下的实际性能,仿真结果表明新算法在簇头和主干节点数目方面具有较好的性能,特别在节点密集的网络环境中更加突出。     

Adaptive Backbone Based Cooperative Caching in Mobile Ad hoc Networks

Existing cooperative caching algorithms for mobile ad hoc networks face serious challenges due to message overhead and scalability issues. To solve these issues, we propose an adaptive virtual backbone based cooperative caching that uses a connective dominating set (CDS) to find the desired location of cached data. Message overhead in cooperative caching is mainly due to cache lookup process used for cooperative caching. The idea in this scheme is to reduce the number of nodes involved in cache look up process, by constructing a virtual backbone adaptive to the dynamic topology in mobile ad hoc networks. The proposed algorithm is decentralized and the nodes in the CDS perform data dissemination and discovery. Simulation results show that the message overhead created by the proposed cooperative caching technique is very less compared to other approaches. Moreover, due to the CDS based cache discovery we applied in this work, the proposed cooperative caching has the potential to increase the cache hit ratio and reduce average delay.     

Connected dominating sets in disk graphs with bidirectional links

In this paper, we study the connected dominating set (CDS) problem in disk graphs. The CDS problem has a significant impact on an efficient design of routing protocols in wireless networks. This problem has been studied extensively in unit disk graphs, in which each node has the same transmission range. However, in wireless ad hoc networks, the transmission ranges of all nodes are not necessary equal. In this paper, we introduce the CDS problem in disk graphs and present a constant approximation algorithm which can be implemented as a distributed algorithm.     

Rotation of CDS via Connected Domatic Partition in Ad Hoc Sensor Networks

Wireless ad hoc and sensor networks (WSNs) often require a connected dominating set (CDS) as the underlying virtual backbone for efficient routing. Nodes in a CDS have extra computation and communication load for their role as dominator, subjecting them to an early exhaustion of their battery. A simple mechanism to address this problem is to switch from one CDS to another fresh CDS, rotating the active CDS through a disjoint set of CDSs. This gives rise to the connected domatic partition (CDP) problem, which essentially involves partitioning the nodes V(G) of a graph G into node disjoint CDSs. We have developed a distributed algorithm for constructing the CDP using our maximal independent set (MIS)-based proximity heuristics, which depends only on connectivity information and does not rely on geographic or geometric information. We show that the size of a CDP that is identified by our algorithm is at least lfloor{frac{delta+1}{beta(c+1)}}rfloor-f, where delta is the minimum node degree of G, betaleq 2, cleq 11 is a constant for a unit disk graph (UDG), and the expected value of f is epsilondelta|V|, where epsilon ll 1 is a positive constant, and delta geq 48. Results of varied testing of our algorithm are positive even for a network of a large number of sensor nodes. Our scheme also performs better than other related techniques such as the ID-based scheme.     

Energy‐aware virtual multi‐input‐multi‐output‐based routing for wireless ad hoc networks

Virtual multi‐input‐multi‐output (vMIMO) technology is becoming a promising way to improve the energy efficiency of wireless networks. Previous research always builds up the vMIMO‐based routing on the fixed structure such as clusters, and the MIMO mode is omitted in most cases. So, they cannot fully explore the advantage of vMIMO in routing. In this paper, we study a general routing scheme in which no fixed structure is required, and any communication mode of vMIMO is allowed for sake of the energy efficiency. We define two vMIMO‐based routing problems aiming to energy‐minimization and lifetime‐optimization. The first problem can be solved by our distributed energy‐minimum vMIMO‐based algorithm. The algorithm constructs the virtual cooperative graph, and applies the shortest path method on the virtual cooperative graph to solve this problem. The second problem is non‐deterministic polynomial‐time hard, and we design the distributed lifetime‐oriented vMIMO‐based algorithm, which is based on the modified Bellman‐Ford method. It can reach approximation ratio of four. The simulations show that our algorithms can work well in many situations. For example, distributed lifetime‐oriented vMIMO‐based algorithm can prolong the lifetime about 20.2% in dense topologies compared with the cooperative routing algorithm on average. Copyright © 2015 John Wiley & Sons, Ltd.     

A distributed battery recovery aware topology control algorithm for wireless sensor networks

Battery recovery effect is a phenomenon that the available capacity of a battery could increase if the battery can sleep for a certain period of time since its last discharging. Accordingly, the battery can work for a longer time when it takes some rests between consecutive discharging processes than when it works all the time. However, this effect has not been considered in the design of energy‐efficient topology control algorithms for wireless sensor networks. In this paper, we propose a distributed battery recovery effect aware connected dominating set constructing algorithm (BRE‐CDS) for wireless sensor networks. In BRE‐CDS, each network node periodically decides to join the connected dominating set or not. Nodes that have slept in the preceding round have priority to join the connected dominating set in the current round while nodes that have worked in the preceding round are encouraged to take sleep in the current round for battery recovery. Detailed algorithm design is presented. The computational complexity of BRE‐CDS is deduced to be O(D²), where D is node degree. Simulation results show that BRE‐CDS can significantly prolong the network lifetime as compared with existing work. Copyright © 2016 John Wiley & Sons, Ltd.     

Bit-per-joule performance of power saving ad hoc networks with a mobile backbone

Energy efficient MAC protocols have been developed for wireless sensor and mobile ad hoc networks so that inactive nodes can transition into sleep state to conserve energy. It has been recognized that maintaining a continuously awake connected dominating set (CDS) serves to reduce the route setup latency. Under the mobile backbone network (MBN) architecture introduced by Rubin et al., a mobile backbone (Bnet) is dynamically constructed to provide a topological covering of the network. The MBN employs a hybrid routing algorithm under which flows that travel a distance longer than a threshold are directed along routes across the Bnet. In turn, a limited span network-wide global route discovery process is applied for routing shorter distance flows. In this paper, we introduce and analyze an MBN based power saving protocol (MBN-PS) that employs this hybrid routing scheme. Under the MBN-PS scheme, dynamically elected backbone nodes are kept awake, while inactive non-backbone nodes can reside in sleep state. We analytically show that, when the number of network flows is above a minimal level, the throughput per watt efficiency attained in an ad hoc network under complete backbone coverage is better than that achieved by a corresponding network that does not form a backbone. We present a model for the calculation of the bit-per-joule performance of the network as a function of the distance threshold. We confirm the validity of our analytical approach through simulations. Using our method, a network designer is able to choose the optimal distance threshold to be used by this scheme, based on traffic loading conditions.     

Virtual network construction with K‐shortest path algorithm and optimization problems for robust physical networks

In network virtualization, it has been considered that virtual networks are constructed over a physical network where conventional data transmission services have been utilized. Here, virtual networks have to be constructed while keeping qualities of the conventional services. In this paper, we propose a new virtual network construction in order to construct many virtual networks while keeping the robustness of a physical network by using network resources effectively. The proposed method consists of three processes: K ‐shortest path algorithm and Prim's minimum spanning tree algorithm, path splitting, and path migration. In the proposed method, at first, multiple topologies are designed by using the K ‐shortest path algorithm and the Prim's MST algorithm according to the user's request. After the topology design is completed, an admission control with network robustness of the physical network is performed. Then, if one of the designed topologies can satisfy the construction conditions, a virtual network is constructed and provided with the user. Otherwise, the path splitting and path migration are performed. Here, the path splitting is utilized to design another topology of a virtual network and path migration is used to change the topologies of the virtual networks that have already been constructed. These processes are formulated as optimization problems and those are processed by solving the optimization problems. In numerical examples, we show that our proposed method can construct a higher number of virtual networks while keeping the robustness of a physical network by comparing with the conventional method where only the Kou–Markowsky–Berman algorithm is used. Copyright © 2015 John Wiley & Sons, Ltd.     

Reliable Multi-hop Routing with Cooperative Transmissions in Energy-Constrained Networks

We present a novel approach in characterizing the optimal reliable multi-hop virtual multiple-input single-output (vMISO) routing in ad hoc networks. Under a high node density regime, we determine the optimal cardinality of the cooperation sets at each hop on a path minimizing the total energy cost per transmitted bit. Optimal cooperating set cardinality curves are derived, and they can be used to determine the optimal routing strategy based on the required reliability, transmission power, and path loss coefficient. We design a new greedy geographical routing algorithm suitable for vMISO transmissions, and demonstrate the applicability of our results for more general networks.     

A Bandwidth Guaranteed Integrated Routing Algorithm in IP over WDM Optical Networks

In this paper, we have developed an integrated online algorithm for dynamic routing of bandwidth guaranteed label switched paths (LSPs) in IP-over-WDM optical networks. Traditionally, routing at an upper layer (e.g., IP layer) is independent of wavelength routing at the optical layer. Wavelength routing at the optical layer sets up a quasi-static logical topology which is then used at the IP layer for IP routing. The coarse-grain wavelength channels and the pre-determined virtual topologies with respect to some a priori assumed traffic distribution are barriers to efficient resource use and inflexible to changing traffic. We take into account the combined knowledge of resource and topology information at both IP and optical layers. With this added knowledge, an integrated routing approach may extract better network efficiencies, be more robust to changing traffic patterns at the IP layer than schemes that either use dynamic routing information at the IP layer or use a static wavelength topology only. LSP set-up requests are represented in terms of a pair of ingress and egress routers as well as its bandwidth requirement, and arrive one-by-one. There is no a priori knowledge regarding the arrivals and characteristics of future LSP set-up requests. Our proposed algorithm considers not only the importance of critical links, but also their relative importance to routing potential future LSP set-up requests by characterizing their normalized bandwidth contribution to routing future LSP requests with bandwidth requirements. Moreover, link residual bandwidth information that captures the link's capability of routing future LSPs is also incorporated into route calculation. Extensive simulation was conducted to study the performance of our proposed algorithm and to compare it with some existing ones, such as the integrated minimum hop routing algorithm and the maximum open capacity routing algorithm. Simulation results show that our proposed algorithm performs better than both routing algorithms in terms of the number of LSP set-up requests rejected and the total available bandwidth between router pairs.     

传感器网络虚拟骨干构造算法及时钟同步应用

通过构造虚拟骨干可以大幅度降低无线传感器网络的广播开销和路由协议的复杂度。本文基于连通支配集．提出了一种虚拟骨干分布式构造算法，其最终尺寸、构造过程中的计算复杂度都优于现有算法。并结合虚拟骨干对Su Ping等学者提出的DMTS时钟同步算法进行了改进，降低其同步通信开销60％左右。     

Network coding over connected dominating set: energy minimal broadcasting in wireless ad hoc networks

Energy efficient broadcast is indispensable for many applications in wireless ad hoc networks. It has been proved that network coding has great potential to improve performance in terms of energy consumption in wireless ad hoc networks. However, the power of network coding depends on the availability of coding opportunities, which in turns depends on how routing paths are established. It is thus beneficial to establish paths in such a way that more coding opportunities are created. By combining network coding and connected dominating set (CDS), we explore energy minimal broadcast protocols in wireless ad hoc networks. The rationale behind this combination is that CDS provides better chances for data flows to intersect, which means more coding opportunities. We design a scheme, named NCDS, that uses network coding over connected dominating set, to reduce energy consumption. Analysis and experimental results show that NCDS outperforms broadcast algorithms that use CDS or network coding alone.     

Efficient routing and wavelength assignment for reconfigurable WDMnetworks

Through the use of configurable wavelength-division-multiplexing (WDM) technology including tunable optical transceivers and frequency selective switches, next-generation WDM networks will allow multiple virtual topologies to be dynamically established on a given physical topology. For N node P port networks, we determine the number of wavelengths required to support all possible virtual topologies (PN lightpaths) on a bidirectional ring physical topology. We show that if shortest path routing is used, approximately N wavelengths are needed to map N lightpaths. We then present novel adaptive lightpath routing and wavelength assignment strategies that reduce the wavelength requirements to [(N/2)] working wavelengths per port for protected networks and [(N/3)] wavelengths in each direction per port for unprotected networks. We show that this reduced wavelength requirement is optimal in the sense that it is the minimum required to support the worst case logical topology. Furthermore, we prove that a significant number of logical topologies require this minimum number of wavelengths. We also develop joint routing and wavelength assignment strategies that not only minimize the number of wavelengths required to implement the worst case logical topologies but also reduce average wavelength requirements. Finally, methods for extending these routing and wavelength assignment results to general two-connected and three-connected physical topologies are presented