Evaluation of physical carrier sense based spanner construction and maintenance as well as broadcast and convergecast in ad hoc networks

While the use of physical carrier sensing for medium access control in ad hoc wireless networks is well established, exploiting physical carrier sensing directly for network layer functions is largely unexplored. We conduct extensive simulation evaluations of recently proposed algorithms that directly exploit physical carrier sensing for backbone network (spanner) construction, broadcast, and convergecast in wireless ad hoc networks. Our algorithms accommodate interference ranges larger than transmission ranges, explicitly incorporate the medium access control and packet collisions, and do not require any prior knowledge of the network. For spanner construction, our algorithms include three self-stabilizing phases that establish leader nodes able to reach all nodes in one hop, assign the leaders non-interfering transmission rounds, and connect the leaders through gateway nodes. We evaluate the backbone construction and maintenance as well as broadcast and convergecast through simulations. We find that over 75% of the control messages for backbone network construction are received from physical carrier sensing. While the number of backbone nodes is relatively large, the backbone is very robust, quickly self-stabilizing, and only a fraction of the backbone nodes are used for broadcast.     

一种基于区域划分的虚拟网映射新算法

目前多数启发式虚拟网映射算法是通过在限制性约束条件上构建映射优化目标函数,从而求得虚拟网映射次优解,存在映射匹配方程求解复杂、计算开销大、缺乏具体路径选择方法等问题.该文基于负载平衡路由和小区分结构的思想设计一种虚拟网映射算法VLB-VNE(Valiant Load-Balancing-Virtual Network ...     

Tree-Based Data Broadcast in IEEE 802.15.4 and ZigBee Networks

This paper studies efficient and simple data broadcast in IEEE 802.15.4-based ad hoc networks (e.g., ZigBee). Since finding the minimum number of rebroadcast nodes in general ad hoc networks is NP-hard, current broadcast protocols either employ heuristic algorithms or assume extra knowledge such as position or two-hop neighbor table. However, the ZigBee network is characterized as low data rate and low cost. It cannot provide position or two-hop neighbor information, but it still requires an efficient broadcast algorithm that can reduce the number of rebroadcast nodes with limited computation complexity and storage space. To this end, this paper proposes self-pruning and forward node selection algorithms that exploit the hierarchical address space in ZigBee networks. Only one-hop neighbor information is needed; a partial list of two-hop neighbors is derived without exchanging messages between neighboring nodes. The ZigBee forward node selection algorithm finds the minimum rebroadcast nodes set with polynomial computation time and memory space. Using the proposed localized algorithms, it is proven that the entire network is covered. Simulations are conducted to evaluate the performance improvement in terms of the number of rebroadcast nodes, number of duplicated receivings, coverage time, and communication overhead     

Connected Dominating Sets in Wireless Networks with Different Transmission Ranges

Since there is no fixed infrastructure or centralized management in wireless ad hoc networks, a Connected Dominating Set (CDS) has been proposed to serve as a virtual backbone. The CDS of a graph representing a network has a significant impact on the efficient design of routing protocols in wireless networks. This problem has been studied extensively in Unit Disk Graphs (UDG), in which all nodes have the same transmission ranges. However, in practice, the transmission ranges of all nodes are not necessarily equal. In this paper, we model a network as a disk graph and introduce the CDS problem in disk graphs. We present two efficient approximation algorithms to obtain a minimum CDS. The performance ratio of these algorithms is constant if the ratio of the maximum transmission range over the minimum transmission range in the network is bounded. These algorithms can be implemented as distributed algorithms. Furthermore, we show a size relationship between a maximal independent set and a CDS as well as a bound of the maximum number of independent neighbors of a node in disk graphs. The theoretical analysis and simulation results are also presented to verify our approaches.     

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.     

Computational intelligence based localization of moving target nodes using single anchor node in wireless sensor networks

Wireless Sensor Networks (WSNs) have tremendous ability to interact and collect data from the physical world. The main challenges for WSNs regarding performance are data computation, prolong lifetime, routing, task scheduling, security, deployment and localization. In recent years, many Computational Intelligence (CI) based solutions for above mentioned challenges have been proposed to accomplish the desired level of performance in WSNs. Application of CI provides independent and robust solutions to ascertain accurate node position (2D/3D) with minimum hardware requirement (position finding device, i.e., GPS enabled device). The localization of static target nodes can be determined more accurately. However, in the case of moving target nodes, accurate position of each node in network is a challenging problem. In this paper, a novel concept of projecting virtual anchor nodes for localizing the moving target node is proposed using applications of Particle Swarm Intelligence, H-Best Particle Swarm Optimization, Biogeography Based Optimization and Firefly Algorithm separately. The proposed algorithms are implemented for range-based, distributed, non-collaborative and isotropic WSNs. Only single anchor node is used as a reference node to localize the moving target node in the network. Once a moving target node comes under the range of a anchor node, six virtual anchor nodes with same range are projected in a circle around the anchor node and two virtual anchor nodes (minimum three anchor nodes are required for 2D position) in surrounding (anchor and respective moving target node) are selected to find the 2D position. The performance based results on experimental mobile sensor network data demonstrate the effectiveness of the proposed algorithms by comparing the performance in terms of the number of nodes localized, localization accuracy and scalability. In proposed algorithms, problem of Line of Sight is minimized due to projection of virtual anchor nodes.     

一种碎片感知的安全虚拟网络重构方法

针对现有的虚拟网络重构算法对物理网络中产生的碎片资源考虑不够周到,导致其对在线虚拟网络映射算法的性能改善不够显著的问题,该文定义了一种网络资源碎片度度量方法,并提出一种碎片感知的安全虚拟网络重构算法。该算法通过周期性考虑物理网络中节点的碎片度,选择出待迁移虚拟节点集合;通过综合考虑物理网络的碎片度减小量和虚拟网络的映射开销减少量,选择出最佳的虚拟节点迁移方案。仿真结果表明,该算法的请求接受率和收益开销比均优于当前的重构算法,特别是在收益开销比方面的优势更加明显。     

基于双变量泊松点过程的无线Ad Hoc网络的保密广播传输容量分析

本论文利用双变量泊松点过程对无线ad hoc广播网络和非法窃听网络共存的网络场景进行建模,运用随机几何工具,研究了无线ad hoc网络的保密广播传输容量,其定义为未发生窃听中断的广播发送节点密度、广播发送节点的相邻接收节点数量的平均值与保密速率的乘积.针对一般衰落和瑞利衰落信道条件,论文推导了造成保密中断的相邻窃听节点数量的平均值和保密广播传输容量的表达式.分析结果表明,与不存在相关性的网络场景相比,广播网络和窃听网络间的相关性会带来的保密广播传输容量的损失.     

分布式环境中基于协商的虚拟网映射算法

网络虚拟化技术可以在共享的底层物理网络上为用户同时提供多种可定制的服务网络。目前的虚拟网映射算法比较依赖于集中式的管理节点,使其在可靠性和适用范围等方面存在诸多问题。为此,提出了一种分布式环境下的虚拟网映射算法,该算法通过多个节点之间的相互协商来完成虚拟网的映射,并且在降低通信开销和缩短虚拟链路的路径长度方面进行了相应改进。实验结果表明,该算法与同类型算法相比,在资源利用率和通信开销方面具有一定的优越性。     

D2F: A Routing Protocol for Distributed Data Fusion in Wireless Sensor Networks

Data fusion can be distributed into network and executed on network nodes, to reduce data from redundant sensor nodes, to fuse the information from complementary sensor nodes and to get the complete view from cooperative nodes. Consequently only the inference of interest is sent to end user. This distributed data fusion can significantly reduce the data transmission cost and there is no need for a powerful centralized node to process the collected information. However, to achieve the advantages of distributed data fusion and better utilization of network resources, each fusion function needs to be performed at particular network node for minimizing energy cost of data fusion application, both data transmission cost and computation cost. In this paper, distributed data fusion routing (D2F) is proposed, which is designed for deploying distributed data fusion application in wireless sensor networks. D2F can find the optimal route path and fusion placements for a given data fusion tree, which obtains the optimal energy consumption for in-network data fusion. D2F can also handle different link failures and maintain the optimality of energy cost of data fusion by adapting to the dynamic change of network.     

Cost Based Data Dissemination in Satellite Networks

We consider the problem of data dissemination in a broadcast network. In contrast to previously studied models, broadcasting is among peers, rather than client server. Such a model represents, for example, satellite communication among widely distributed nodes, sensor networks, and mobile ad hoc networks. We introduce a cost model for data dissemination in peer to peer broadcast networks. The model quantifies the tradeoff between the inconsistency of the data, and its transmission cost; the transmission cost may be given in terms of dollars, energy, or bandwidth. Using the model we first determine the parameters for which eager (i.e. consistent) replication has a lower cost than lazy (i.e. inconsistent) replication. Then we introduce a lazy broadcast policy and compare it with several naive or traditional approaches to solving the problem.     

Asymptotic analysis of multistage cooperative broadcast in wireless networks

Cooperative broadcast aims to deliver a source message to a locally connected network by means of collaborating nodes. In traditional architectures, node cooperation has been at the network layer. Recently, physical layer cooperative schemes have been shown to offer several advantages over the network layer approaches. This form of cooperation employs distributed transmission resources at the physical layer as a single radio with spatial diversity. In decentralized cooperation schemes, collaborating nodes make transmission decisions based on the quality of the received signal, which is the only parameter available locally. In this case, critical parameters that influence the broadcast performance include the source/relay transmission powers and the decoding threshold (the minimum signal-to-noise ratio (SNR) required to decode a transmission). We study the effect of these parameters on the number of nodes reached by cooperative broadcast. In particular, we show that there exists a phase transition in the network behavior: if the decoding threshold is below a critical value, the message is delivered to the whole network. Otherwise, only a fraction of the nodes is reached, which is proportional to the source transmit power. Our approach is based on the idea of continuum approximation, which yields closed-form expressions that are accurate when the network density is high.     

R-Code: Network coding-based reliable broadcast in wireless mesh networks

Broadcast is an important communication primitive in wireless mesh networks (WMNs). Applications like network-wide software updates require reliable broadcast to ensure that every node in the network receives the information completely and correctly. With underlying unreliable wireless links, a key challenge in implementing reliable broadcast in WMNs is to achieve 100% information reception rate at every node with high communication efficiency and low latency. Recently, network coding has emerged as a promising coding scheme in terms of communication efficiency especially for one to many communication patterns. In this paper, we put forward R-Code, a network coding-based reliable broadcast protocol. We introduce a guardian–ward relationship between neighboring nodes that effectively distributes the responsibility of reliable information delivery – from the global responsibility of the source to the localized responsibilities of guardians to their corresponding wards. We use a link quality-based minimum spanning tree as a backbone to guide the selection of guardians adaptively and the transmission of coded packets accordingly. Opportunistic overhearing is also utilized to improve the performance of the protocol. Extensive simulation results show that R-Code achieves 100% packet delivery ratio (PDR), while enjoying significantly less transmission overhead and shorter broadcast latency, compared with a state-of-the-art reliable broadcast protocol, AdapCode.     

Joint multi-cost routing and power control in wireless ad hoc networks

In this work we study the combination of multi-cost routing and adjustable transmission power in wireless ad hoc networks, so as to obtain dynamic energy- and interference-efficient routes to optimize network performance. In multi-cost routing, a vector of cost parameters is assigned to each network link, from which the cost vectors of candidate paths are calculated. Only at the end these parameters are combined in various optimization functions, corresponding to different routing algorithms, for selecting the optimal path. The multi-cost routing problem is a generalization of the multi-constrained problem, where no constraints exist, and is also significantly more powerful than single-cost routing. Since energy is an important limitation of wireless communications, the cost parameters considered are the number of hops, the interference caused, the residual energy and the transmission power of the nodes on the path; other parameters could also be included, as desired. We assume that nodes can use power control to adjust their transmission power to the desired level. The experiments conducted show that the combination of multi-cost routing and adjustable transmission power can lead to reduced interference and energy consumption, improving network performance and lifetime.     

Distributed algorithms for lifetime maximization in sensor networks via Min–Max spanning subgraphs

We consider the problem of static transmission-power assignment for lifetime maximization of a wireless sensor network with stationary nodes operating in a data-gathering scenario. Using a graph-theoretic approach, we propose two distributed algorithms, MLS and BSpan, that construct spanning trees with minimum maximum (minmax) edge cost. MLS is based on computation of minmax-cost paths from a reference node, while BSpan performs a binary search over the range of power levels and exploits the wireless broadcast advantage. We also present a simple distributed method for pruning a graph to its Relative Neighborhood Graph, which reduces the worst-case message complexity of MLS under natural assumptions on the path-loss. In our network simulations both MLS and BSpan significantly outperform the recently proposed Distributed Min–Max Tree algorithm in terms of number of messages required.     

Benefit-Based Data Caching in Ad Hoc Networks

Data caching can significantly improve the efficiency of information access in a wireless ad hoc network by reducing the access latency and bandwidth usage. However, designing efficient distributed caching algorithms is nontrivial when network nodes have limited memory. In this article, we consider the cache placement problem of minimizing total data access cost in ad hoc networks with multiple data items and nodes with limited memory capacity. The above optimization problem is known to be NP-hard. Defining benefit as the reduction in total access cost, we present a polynomial-time centralized approximation algorithm that provably delivers a solution whose benefit is at least 1/4 (1/2 for uniform-size data items) of the optimal benefit. The approximation algorithm is amenable to localized distributed implementation, which is shown via simulations to perform close to the approximation algorithm. Our distributed algorithm naturally extends to networks with mobile nodes. We simulate our distributed algorithm using a network simulator (ns2) and demonstrate that it significantly outperforms another existing caching technique (by Yin and Cao [33]) in all important performance metrics. The performance differential is particularly large in more challenging scenarios such as higher access frequency and smaller memory.     

On the power efficiency of cooperative broadcast in dense wireless networks

A fundamental problem in large scale wireless networks is the energy efficient broadcast of source messages to the whole network. The energy consumption increases as the network size grows, and the optimization of broadcast efficiency becomes more important. In this paper, we study the optimal power allocation problem for cooperative broadcast in dense large-scale networks. In the considered cooperation protocol, a single source initiates the transmission and the rest of the nodes retransmit the source message if they have decoded it reliably. Each node is allocated an-orthogonal channel and the nodes improve their receive signal-to-noise ratio (SNR), hence the energy efficiency, by maximal-ratio combining the receptions of the same packet from different transmitters. We assume that the decoding of the source message is correct as long as the receive SNR exceeds a predetermined threshold. Under the optimal cooperative broadcasting, the transmission order (i.e., the schedule) and the transmission powers of the source and the relays are designed so that every node receives the source message reliably and the total power consumption is minimized. In general, finding the best scheduling in cooperative broadcast is known to be an NP-complete problem. In this paper, we show that the optimal scheduling problem can be solved for dense networks, which we approximate as a continuum of nodes. Under the continuum model, we derive the optimal scheduling and the optimal power density. Furthermore, we propose low-complexity, distributed and power efficient broadcasting schemes and compare their power consumptions with those-of-a traditional noncooperative multihop transmission     

Distributed Topology Construction in ZigBee Wireless Networks

Topology control is one of the important techniques in wireless multi-hop networks to preserve connectivity and extend the network lifetime. This is more significant in ZigBee, since the address assignment scheme is tightly coupled with topology construction. For example, there can be orphan nodes that cannot receive the network address and isolated from the network due to predefined network configurations. In this paper, we propose a distributed topology construction algorithm that controls the association time of each node in order to solve the orphan node problem in ZigBee as well as construct an efficient routing tree topology. The main idea of the distributed topology construction algorithm is to construct primary backbone nodes by propagating the invitation packets and controlling the association time based on the link quality. Since the dynamically selected primary nodes are spread throughout the network, they can provide backbone to accept the association requests from the remaining secondary nodes which are majority in a network. In the performance evaluation, we show that the proposed topology construction algorithm effectively solves the orphan node problem regardless of network density as well as provides efficient tree routing cost comparable to the approximation algorithm for degree constrained minimum routing cost tree (DC-MRCT) problem.     

Efficient broadcast for wireless ad hoc networks with a realistic physical layer

In this paper, we investigate the low coverage problem of efficient broadcast protocols in wireless ad hoc networks with realistic physical layer models. To minimize energy consumption, efficient protocols aim to select small set of forward nodes and minimum transmission radii. In ideal physical layer model, nodes within forward nodes’ transmission ranges can definitely receive packets; therefore energy efficient protocols can guarantee full coverage for broadcasting. However, in networks with a realistic physical layer, nodes can only receive packets with probability. We present an analytical model to show that the transmission radii used for nodes can be used to establish a tradeoff between minimizing energy consumption and ensuring network coverage. We then propose a mechanism called redundant radius, which involves using two transmission radii, to form a buffer zone that guarantees the availability of logical links in the physical network, one for broadcast tree calculation and the other for actual data transmission. With this mechanism, we extend well-known centralized protocols, BIP and DBIP, and corresponding localized protocols, LBIP and LDBIP. The effectiveness of the proposed scheme in improving network coverage is validated analytically and by simulation.     

Efficient broadcasting with guaranteed coverage in mobile ad hoc networks

We study an efficient broadcast scheme in mobile ad hoc networks (MANETs). The objective is to determine a small set of forward nodes to ensure full coverage. We first study several methods that guarantee coverage when the local view of each node on its neighborhood information is updated in a timely manner. Then we consider a general case where nodes move even during the broadcast process, making it impractical to maintain up-to-date and consistent local views. A formal framework is used to model inaccurate local views in MANETs, where full coverage is guaranteed if three sufficient conditions, connectivity, link availability, and consistency, are met. Three solutions are proposed to satisfy those conditions. First, we give a minimal transmission range that maintains the connectivity of the virtual network constructed from local views. Then, we use two transmission ranges, one for neighborhood information collection and the other for actual data transmission, to form a buffer zone that guarantees the availability of logical links in the physical network. Finally, we propose a mechanism called aggregated local view to ensure consistent local views. By these, we extend Wu and Dai's coverage condition for broadcasting in a network with mobile nodes. The effectiveness of the proposed scheme is confirmed via both performance analysis and simulation study.