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Bulk data dissemination is a basic building block for enabling a variety of applications in wireless sensor networks such as software update, network bug fixing, surveillance video distribution, etc. The recent structure based approach looks promising for efficient dissemination since it facilitates transmission and sleep scheduling. However, a number of limitations exist in existing structured protocols. In this paper, we propose a correlated core based solution for efficient bulk data dissemination in wireless sensor networks (called CoCo+). CoCo+ has three salient features. First, CoCo+ is based on an efficient node selection algorithm for constructing the core structure by exploiting link correlation (called Correlated Core). Second, CoCo+ employs a novel consecutive transmission mechanism, which allows out-of-order transmissions and reduces propagation delay. Third, CoCo+ uses a novel lightweight negotiation mechanism that greatly reduces negotiation overhead as compared to the existing structured protocols. We implement CoCo+ with TinyOS/TelosB and conduct both simulation and testbed experiments. Results show that our proposed solution outperforms the state-of-the-art by 52.3 and 49.6% in terms of the number of transmissions and the completion time, respectively.

Wireless charging is an important issue in wireless sensor networks, since it can provide an emerging and effective solution in the absence of other power supplies. The state-of-the-art methods employ a mobile car and a predefined moving path to charge the sensor nodes in the network. Previous studies only consider a factor of the network (i.e., residual energy of sensor node) as a constraint to design the wireless charging strategy. However, other factors, such as the travelled distance of the mobile car, can also affect the effectiveness of wireless charging strategy. In this work, we study wireless charging strategy based on the analysis of a combination of two factors, including the residual energy of sensor nodes and the travelled distance of the charging car. Firstly, we theoretically analyze the limited size of the sensor network to match the capability of a charging car. Then, the networked factors are selected as the weights of traveling salesman problem (TSP) to design the moving path of the charging car. Thirdly, the charging time of each sensor node is computed based on the linear programming problem for the charging car. Finally, a charging period for the network is studied. The experimental results show that the proposed approach can significantly maximize the lifetime of the wireless sensor network.

Previous packet length optimizations for sensor networks often employ a fixed optimal length scheme, while in this study we present DPLC, a Dynamic Packet Length Control scheme. To make DPLC more efficient in terms of channel utilization, we incorporate a lightweight and accurate link estimation method. We further provide two easy-to-use services, i.e., small message aggregation and large message fragmentation, to facilitate upper-layer application programming. The implementation of DPLC based on TinyOS 2.1 is lightweight, with respect to computation, memory, and header overhead. Our experiments using a real indoor testbed running CTP show that DPLC achieves the best performance compared with previous works.

Network passive monitoring is an important method in debugging and analyzing wireless sensor networks. The passive monitoring method for wireless sensor networks (WSN) has the following problems: monitoring traces are incomplete and contain only limited information because some packets may be misheard; how to infer implicit information about network protocol behavior and how to detect network events from incomplete traces are challenging issues in passive monitoring system. To resolve the above issues, we propose the use of time tuning in trace merging and a finite state machine for inferring missing packets, implicit information and network event detection. (1) In order to enhance the integrity of traces, we propose clock-adjusting strategies including clock fine-tuning and clock self-adjustment to solve clock drifting in trace merging. (2) For inference of missing packets and implicit information, we devise and implement a finite state machine to infer missing packets and packet receiving state for multi-hop network protocols. (3) For network event detection, we propose an XML-based description of event rule and network event visualization methods. These methods are implemented in PMSW (passive monitoring system for WSN). We verify the accuracy of merging and inference modules with monitoring traces in the Collect Tree Protocol sensor network. Experiments show that the finite state machine can infer 40-60% of missing packets and more than 90% of the receiving state of data packets, when the trace has more than 50% of the data packets captured in the network.

In order to improve the accuracy of cell selection in heterogeneous cellular systems, this paper proposes a fuzzy multiple-objective decision-based cell selection (FMDCS) strategy. Since heterogeneous cellular systems have different access technologies and multiple traffic classes, the strategy adopts cell type, data rate, coverage, transmission delay, and call arrival rate as evaluation indices, and uses different weight vectors according to the traffic classes of the mobile host. Then, a fuzzy multipleobjective decision algorithm is applied to select the optimal cell from all candidates. This paper also gives an instance analysis and simulation. The instance analysis shows FMDCS makes different selections for different traffic classes. Simulation results of the after-handoff quality-ofservice (QoS) show the selected cell can provide MH optimal service.

In multi-hop wireless ad-hoc networks, packet delivery delay is one of the most important performance metrics. While a lot of research efforts have been spent on measuring and optimizing the end-to-end delay performance, there usually lack accurate and lightweight methods for decomposing the end-to-end delay into the per-hop delay for each packet. Knowledge on the per-hop per-packet delay can greatly improve the network visibility and facilitate network measurement and management. In this paper, we propose Domo, a passive, lightweight and accurate delay tomography approach to decomposing the packet end-to-end delay into each hop. The basic idea is to formulate the problem into a set of optimization problems by carefully considering the constraints among various timing quantities. At the network side, Domo attaches a small overhead to each packet for constructing constraints of the optimization problems. At the PC side, Domo employs semi-definite relaxation and several other methods to efficiently solve the optimization problems. We implement Domo and evaluate its performance extensively using large-scale simulations. Results show that Domo significantly outperforms two existing methods, nearly tripling the accuracy of the state-of-the-art.

Bulk data dissemination is a basic building block for enabling software update and reprogramming in wireless sensor networks. The recent structure based approach looks promising for efficient dissemination since it facilitates transmission and sleep scheduling. However, a number of limitations exist in existing structured protocols. In this paper, we propose a correlated core based solution for efficient bulk data dissemination in wireless sensor networks. We propose an efficient backbone node selection algorithm to construct the core structure by exploiting link correlation. We also design a novel negotiation mechanism which greatly reduces the control message overhead as compared to the existing structured protocols. We conduct both simulation and testbed experiments, and the results show that our proposed solution outperforms the state-of-the-art in terms of both the number of transmissions and the completion time.

Reprogramming over the air is important for maintaining a wireless sensor network. Traditional reprogramming approaches assume always-on link layers. Given the energy limitation of sensor nodes, always-on link layers are often not desired for most sensor network applications. In this paper, we propose ROLP, a novel reprogramming protocol built on a widely used low power link layer in wireless sensor networks. ROLP employs an efficient control packets self-suppression scheme for reliable data transmission. ROLP also employs an adaptively falling asleep scheme based on the neighbor information to reduce the energy consumption. We implement ROLP based on TinyOS and evaluate its performance in two different indoor networks. Compared with the standard reprogramming protocol in TinyOS, ROLP is able to reduce the radio-on time by 57.6% and 39.0% in the two networks. Since radio operations cost most of the energy, these reductions save significant amount of energy and prolong the lifetime of a wireless sensor network.

With the widespread development of RFID technology, security and privacy issues become more prominent in RFID applications. In this paper, a new one- way hash function based mutual authentication protocol is proposed to address such security and privacy problems. Particularly, access list and pseudorandom flags are adopted for quick search, to ensure good efficiency and scalability. The proposed protocol is analyzed according to three aspects: logic, security and performance. Concretely, GNY logic formal method is used to verify the design correctness of the protocol, the attack model is used to analyze the security, and the performance is evaluated from communication overload, storage, and computation requirement. The analysis results show that the protocol has no obvious design flaws, can resist major attacks, and improves the system reliability and effectiveness. The proposed protocol can be easily scalable for lightweight RFID systems.

Nodes of wireless sensor networks (WSN) may fail easily due to the lack of energy or disaster scenarios. Such failures can severely reduce the persistence and collection efficiency of sensed data. Network coding technology can be employed to enhance the data persistence of wireless sensor network, but it may cause serious "cliff effect" in decoding process. In this paper, the influence of prioritized coding degree distribution strategy on cliff effect is observed, and a distributed storage algorithm PLTD-Alpha is proposed. With PLTD-Alpha, the data in sensor network nodes present a trend that their degree distribution increase along with the degree level predefined, and the persistent data packets can be submitted to the sink node according to its degree in order. Experiment results show that PLTD-Alpha can greatly improve the data collection and decoding efficiency of sensor network while data persistence is not notably affected.

Wireless sensor network (WSN) is a typical distributed storage system, and network coding technology is developed to enhance the data persistence of WSN. However, the traditional distributed coding strategy may cause serious "cliff effect" in the decoding process, that is to say, few source data can be recovered before sufficient encoded packets are received. Moreover, nodes may fail due to the lack of energy or the influence of the switching of external environment, such as a disaster scenario. Such failures may concentrate in a small region or distribute in the whole deployment area which can severely reduced the decoding efficiency of the persistent data in WSN. In this paper, we propose the PLTCDS (prioritized LT codes based distributed storage) algorithm to improve the data decoding efficiency when the data persistence is assured. The main idea of PLTCDS is that the predefined node broadcasts a beacon to stimulate the nodes to form the network with degree distribution priority. To ensure the effectiveness of storage nodes, PLTCDS introduces a class of cumulative counter scheme to avoid empty storage. Also we discuss about the idea of another type of PLTCDS. Experimental results show that PLTCDS algorithm can enhance the network data collection performance and reduce the influence of "cliff effect".

In order to protect the privacy and the security of the tag, we propose a mutual authentication protocol for low-cost RFID system. The protocol ensures that the reader (or server) and the tag authenticate each other, provides the privacy and security properties for low-cost RFID system and also has good performance. The protocol resists almost all attacks except cloning attack, and achieves backward secrecy without any assumption and forward secrecy under an assumption. We also show that it requires less storage than other related RFID protocols.

Data collection is the fundamental and important function in wireless sensor networks. Due to the restriction of node power, how to improve the nodei¯s energy efficiency and prolong the network lifetime is an important issue in practical network deployment. In this paper, we propose the RS-LPL ¨C Relative Synchronized Low-Power Listening which uses the relative time synchronization to improve the traditional low power listening scheme, and realize the RS-LPL in Collection Tree Protocol to enhance the network energy efficiency and prolong the network lifetime. The experiment results in a network consisted of Telosb mote shows that RS-LPL is more energy efficiency than traditional low power listening.

Problems of Wireless Sensor Networks (WSN）caused in the laboratory are predictable, and easy to resolve. While in the deployment and management phases, a number of factors in the environment raise more problems that are difficult to predict or simulation than in laboratory condition. To effective manage and monitor those problems, an effective management mechanism is needed, which analysis the problems and enables managers configure the networks and deal with exceptions. Wireless sensor networks are application-related systems, different scenarios the network structure and function are quite different. There is no uniform standard of network infrastructure design and implementation of communication protocols, which leading to the present there is no unified network management standards. In this paper, we developed a wireless sensor network visualization management system based on the ZigBee technique, which has data management, data changes and topology visualizing, offline analysis, and the initial network fault detection functions.

BitTorrent(BT)-like P2P traffic which occupy main network bandwidth affect other normal network applications badly. This paper presents a triggered dynamic mechanism for BT-like P2P bandwidth management. According to the variety of utilization percentage of egress router input/output cache, this mechanism could estimate the potential network congestion and be triggered to control the BT-like P2P bandwidth dynamically. This paper puts forward a new way to control BT-like P2P bandwidth by intercepting the massage packets of BT-like P2P. The experiments results verify that the proposed method for BT-like P2P bandwidth management can manage BT-like P2P bandwidth effectively.

How to meet the QoS of the applications and improve resource utilization is an important problem in virtualized environment. In this paper, we propose a Utility based resource allocation policy with QoS constrained in virtualized environment. Firstly, we build a model reflecting the mapping relation between performance metrics and resource allocation through web server benchmarking experiments. Then, we devise a utility function as objective to optimizing the total utility and achieving a reasonable resource allocation. Finally, based on the model and the requirements of the applications QoS, we present an optimized policy for resource allocation in virtualized system. The simulation results show that the utility-based policy is effective to allocate resource from user perspective while improving the resource utilization.

The reliability of wireless sensor networks is affected by faults that may occur due to various reasons. In ZigBee sensor networks, ZigBee specification presents a self-healing process which relies on its tree topology. When a ZigBee node failed, all of the descendants of the fault node should rejoin the network. Instead, we present an efficient scheme for repair itself after node failure that just one or some of the descendants should rejoin the network. It allows a subnet of fault node rejoin the network with minimum message exchanges and, therefore, saves energy. Simulation results show that most of subnet rejoin the network in the first level of sub-tree, and confirm the efficiency of the proposed scheme.

In Wireless Sensor networks (WSNs), most existing routing protocols do not consider a node mobility problem, because nodes in sensor network are generally assumed to be static.The network may get partitioned, due to the mobility of some nodes will cause other nodes to lose their connection with the network. Network partitioning poses significant challenges to the provisioning of continuous data streaming services in WSNs. In this paper, we propose a routing scheme which supports node Mobility and Energy-Efficient based on Directed Diffusion (MEDD) for WSNs. In MEDD, we design a gradient model which considers energy consumption balance and real-time requirement. Based on this, we mainly propose a mechanism which makes node be able to localize the gradient reconfiguration whenever its movement occurs. It ensures the robustness of network transmission. Simulation results show that our proposed method decreases the network overhead and prolongs the lifetime of network efficiently.

ZigBee is a well accepted industrial standard for wireless sensor networks based on IEEE 802.15.4. Since aiming for the application of low data rate, low price and low power consumption, ZigBee networks have the limited resources such as computation complexity and storage space. So it is especially important to design an efficient and effective routing protocol to save the consuming energy and extend the lifetime for ZigBee networks. In this paper, we survey two kinds of routing methods of the existing ZigBee routing protocol, and then propose two improved algorithms respectively. Simulation results show that the proposed routing version is a more efficient routing protocol, which can reduce routing overhead and routing discovery delay.

In wireless sensor network (WSN), sensor node is limited in energy, thus energy efficiency is an important concern in routing protocol design. And some applications in sensor networks have the requirement of timely delivery, real-time also become needed for routing. Directed diffusion (DD) is a data centric dissemination protocol for sensor networks, but DD cannot support time-sensitive traffic nor perform balance of energy consumption to increase network lifetime. To solve this issue, we design a new kind of gradient mechanism, which considers residual energy of node and the number of hops from the sink to an intermediate node synchronously. It can find a best-effort optimal path in sensor networks for data transfer. Simulation results show that our proposed method achieves more globally energy balancing and lower delay for data transfer than originally DD. It prolongs the lifetime of network efficiently.

Clustering routing protocols have prominent advantages over flat routing protocols in terms of scalability, which is very useful for wireless mesh network with dense nodes distribution. However, clustering schemes will add large extra overhead in order to select cluster-heads and collect neighbor nodes information during the phase of cluster construction. At present, there exist a lot of excellent clustering schemes, and in this paper, we propose different classification criteria according to clustering charateristics. Then, we present a comprehensive review of several representatives, and especially focus on cluster formation mechanism. At last, we sum up with three typical problems we have to seriously consider when analyzing or design a clustering routing protocol.

Different from traditional networks, wireless sensor networks (WSNs) are highly dependent on specific applications and are severely constrained by energy, storage capacity and computing power. To prolong the lifetime of the whole networks, energy awareness is an essential consideration when we design or analyze routing protocols. In this paper, we present a review of recent routing protocols in WSNs and classify them into three categories based on the network structure in WSNs. Then we describe the existing routing protocols and discuss their advantages and disadvantages of each routing algorithm. Finally we conclude this paper with open research issues and challenges.

Dynamic address assignment is a desirable feature for deploying wireless sensor network. Typically, a distributed address assignment mechanism is accomplished by ZigBee alliance, whereas, sensors join a network is unpredictable, it may engender uneven node density, so it is possible that one node exhausts its list of addresses while another node has addresses go unused. Therefore, a preemptive approach is needed for ZigBee addressing mechanism. This paper presents a preemptive distributed address assignment to provide a preemptive scheme for ZigBee addressing mechanism. In addition, we give an autorouting algorithm. Simulation results show that nodes can acquire an address even in high node density area, and the scheme increases the total number of nodes in a sensor network.

Recently, peer-to-peer approach has emerged as an effective solution for live streaming services. However, some channels may not provide good streaming services due to their less audience, and some peers may receive bad services owning to their relatively narrower bandwidth. To address these issues, we introduce a peer-to-peer inter-channel assisting scheme for live streaming services. In the scheme, the social network theory is employed to construct the inter-channel overlay network. The scope of cooperation is scaled from intrachannel to inter-channel through active assistance and passive assistance. Besides, the relationship in social network works as the incentive mechanism to stimulate the assisting behaviors among peers. Simulations demonstrate that our scheme can promote the cooperation effectively and consequently improve the streaming qualities significantly.

The wireless overlay network will play an important role in future mobile communications and Internet access. It will be an IP-based network, which includes various wireless access methods and provides all kinds of services such as voice, data and multimedia. Handoff is a critical issue of the wireless overlay network, because it can guarantee seamless roaming among different networks. Based on a WLAN-GPRS wireless overlay network model, and considering channel characteristics, service types and factors influencing the handoff process, a novel inter-system handoff scheme is proposed and relative decision benchmarks are discussed. Simulations on the key parameters, such as throughput, packet loss and handoff delay, prove that the proposed handoff scheme can provide powerful support for seamless handoff and continuous communication.