International Journal of Ad Hoc and Ubiquitous Computing (30 papers in press)

• Path Diminution in Node-Disjoint Multipath Routing for Mobile Ad hoc Networks is Unavoidable with Single Route Discovery
  by Ash Mohammad Abbas 
  Abstract: In an ad hoc network, identification of all node-disjoint paths between a given pair of nodes is a challenging task. The phenomena that a protocol is not able to identify all node-disjoint paths that exist between a given pair of nodes is called path diminution. In this paper, we discuss that path diminution is unavoidable when a protocol discovers multiple node-disjoint paths in a single route discovery. We discuss schemes to mitigate path diminution. However, no such scheme is guaranteed to discover all node-disjoint paths that exist between a given pair of nodes. We have proved that one cannot devise an efficient algorithm that is guaranteed to compute all node-disjoint paths between a given pair of nodes in a single route discovery.
  Keywords: Routing, ad hoc networks, path diminution, node-disjoint multipath routing, single route discovery.
   
• Performance Analysis of Four Routing Protocols in Sensor Networks
  by Abdelghani Bellaachia, Nilkamal Weerasinghe 
  Abstract: The efficiency of sensor networks strongly depends on the routing protocol used. In this paper, we analyze four different types of routing protocols: LEACH, PEGASIS, HIT-M, and DIRECT. DIRECT routing protocol is one where all the sensing nodes directly send its information to the base station. LEACH sends data directly to the cluster head and the cluster head is in charge of sending them to the base station. PEGASIS is similar to LEACH but the nodes transmit through other nodes that are closer to the base station, rather than directly transmitting to the cluster head like LEACH does. HIT-M is hybrid of LEACH and PEGASIS, using the chain like structure used in PEGASIS to reduce energy costs and using TDMA (Time Division Multiple Access) computed on each individual node to increase parallelism of data transfer. Sensor networks were simulated using TOSSIM simulator. Several experiments were conducted to analyze the performance of these protocols including the power consumption and overall network performance. The experimental results show that HIT-M outperforms all other protocols while PEGASIS has better performance than LEACH and DIRECT. LEACH and DIRECT have similar performance. This paper also shows the power consumption for all protocols. On the average, DIRECT has the worst power consumption.
  Keywords: Sendor Networks, Routing Protocols, LEACH, PEGASIS, HIT-M, and DIRECT
   
• Prioritized Predicted Region based Cache Replacement Policy for Location Dependent Data in Mobile Environment
  by AJEY KUMAR, Anil K. Sarje, Manoj Misra 
  Abstract: Mobile computing as compared to traditional computing paradigms enables clients to have unrestricted mobility while maintaining network connections. Data management in this paradigm poses new challenging problems to the data base community. Location Dependent Information Services (LDIS) is an emergent application in this area where information provided to users depends on their current locations. Caching frequently accessed data items on the mobile client is an effective technique to improve the system performance in mobile environment. Due to cache size limitations, the choice of cache replacement technique to find a suitable subset of items for eviction from cache becomes important. In this paper, we propose a new cache replacement policy for location dependent data in mobile environment. The proposed policy uses a predicted region based cost function to select an item for eviction from cache. The policy selects the predicted region based on client’s movement and uses it to calculate the data distance of an item. This makes the policy adaptive to client’s movement pattern unlike earlier policies that consider the directional/non-directional data distance only. We call our policy the Prioritized Predicted Region based Cache Replacement Policy (PPRRP). Simulation results show that the proposed policy significantly improves the system performance in comparison to previous schemes in terms of cache hit ratio.
  Keywords: Cache replacement, location dependent data, mobile computing, valid scope, location dependent information services
   
• A Weighted Checkpointing Protocol for Mobile Distributed Systems
  by Lalit Kumar Awasthi, Manoj Misra, Ramesh C Joshi 
  Abstract: Here, we propose a weighted checkpointing approach for Mobile Distributed Computing Systems (MDCSs) that significantly reduces checkpointing overheads on mobile nodes. Checkpointing protocols proposed so far in the literature for MDCSs are either coordinated, log based or quasi-synchronous. Coordinated checkpointing requires extra synchronization messages and may block the underlying computation. In quasi-synchronous approach, processes have limited autonomy in checkpointing but all nodes need not checkpoint concurrently as is the case with coordinated checkpointing. Also, only limited messages are logged as compared to log-based checkpointing protocols. Quasi-synchronous checkpointing protocols guarantee a consistent global state but the checkpointing frequency is governed by the message arrival pattern at various nodes and thus results in dynamic checkpointing overheads that cannot be anticipated and may be very high. To minimize these dynamic overheads, we propose a protocol that is hybrid of quasi-synchronous and message-logging approaches and uses concept of weighted checkpoints. We also propose recovery protocol for weighted checkpointing protocol. The weighted quasi-synchronous approach proposed by us requires no synchronization messages, reduces the checkpointing overheads at mobile nodes but requires logging for mobile nodes. Simulation results show that the new approach is better than quasi-synchronous approach.
  Keywords: Mobile Computing; Checkpointing; Fault Tolerance; Coordinated Checkpointing; Domino-effect;Global state, Consistent Global State, snapshot, independent checkpointing, quasi-synchronous checkpointing
   
• Key Establishment for Layered Group-based Wireless Sensor Networks
  by Xueping Li, Dengfeng Yang, Rapinder Sawhney 
  Abstract: Establishing pairwise keys for sensors is crucial to secure communications in wireless sensor networks. It is one of the most challenging security issues because sensors have limited communication, computation, and memory capabilities. Several key pre-distribution schemes have been proposed to establish pairwise keys for this purpose in wireless sensor network, but they are not scalable and suffer from a dramatic degradation of security when the number of compromised sensor exceeds a threshold. In this paper, we propose a Layered Group-based Key Establishment scheme (LGKE), in which a logic top layer ensures the scalability through an Exclusion Basic System (EBS) technique while a logic low layer adopts a group-based key preload scheme to ensure the security. The security analysis and quantitative evaluation show the superiority of LGKE with regard to scalability, resilience, robustness and communication overhead.
  Keywords: Wireless Sensor Networks, Security, Key Establishment, Scalability, Group-based Deployment
   
• COMMUNICATION IN WIRELESS SENSOR NETWORKS (WSNs)
  by Alejandro Quintero, Paul Stoina 
  Abstract: Wireless sensor and actor applications need data that arrive in time and which are necessary for actors to conduct their activity within a valid time frame. This demand is fulfilled by a real-time communication for applications that use WSN technologies. The protocols, TCP and UDP, were not designed for real-time communication, neither for wireless networks. The proposed protocol, Bonaventura, can manage data unit delays by considering time and space evaluations. This transport protocol contains an entity in every node along the path of the data units. The scheduling mechanism of the protocol determines the data unit priority, which establishes the transmission order of the data units in a node. The traffic shaping mechanism limits data unit arrival rates in order to keep the network congestion-free. These two mechanisms help the data units meet their deadline. The protocol designed in this study is compared with the UDP protocol, using mathematical models in MATLAB. Both protocols are compared for the data units travel times and for the timelyput, that is the throughput of data units which arrive in time and which can be used by the application. This novel protocol achieves better results, for over 18% of timelyput, for a 500-sensor and 3-sink-network deployed on a 1000m2 surface, using different transmission rate values
  Keywords: real-time communication, transport protocol, wireless sensor networks, travel time, deadline
   
• Agenda Driven Mobility Modeling
  by Qunwei Zheng, Xiaoyan Hong, Jun Liu, Wan Huang, David Cordes 
  Abstract: Mobility modeling is an essential component of wireless and mobile networking research. It assists planning, developing and evaluating protocols and mobile systems. A simulated mobile world provides flexibility for constructing scenarios that closely resemble the real world. Our proposed mobility model emphasizes humans' social roles when making movement decisions. Our model, the Agenda Driven Mobility Model, takes into consideration a person's social activities in the form of agenda (when, where and what) for motion generation. The paper uses a constructive approach to define functional components of the Agenda Driven Mobility Model for building specific real world scenarios and generating motion steps. A variety of real data sources can be used to populate these components. In this sense, the model provides a framework for translating social agendas into a mobile world. In the paper, we utilize National Household Travel Survey (NHTS) information from the U.S. Department of Transportation to obtain activity and dwell time distributions. As an example, we simulate a mobile ad hoc network in an urban scenario, analyzing the geographic features of the network topology generated by the model and the impact of the model on routing performance. Our simulation results suggest that social roles and agenda activities tend to cause geographic concentrations, significantly impacting network performance. We conclude that the incorporation of social agendas into mobility modeling produces a performance evaluation that better reflects real world scenarios.
  Keywords: agenda driven mobility model, mobility model, mobile ad hoc networks, simulation
   
• Equal-Gain Combination for Adaptive Distributed Classification in Wireless Sensor Networks
  by Hung-Ta Pai, Jing-Tian Sung 
  Abstract: A fault-tolerant classification system in wireless sensor networks combining distributed detection with error-correcting codes have recently been proposed. A codeword is designed for each hypothesis. Each sensor makes a local decision based on the codeword and its observation result. The local decision is then transmitted to a fusion center to make a final decision. An adaptive redetection algorithm and an adaptive retransmission scheme were later developed to reduce the misclassification probability of the system when the observation is highly noisy, and the transmission channel between the sensor and the fusion center is deeply faded, respectively. The observation result at the sensor and the received data at the fusion center are discarded if they are not reliable in the adaptive method. However, they still have useful information about the hypothesis and should be utilized. This work applies Equal-Gain Combination (EGC) techniques to utilize the unreliable data. Little extra complexity is needed. Simulation results show that the new adaptive method with EGC outperforms the original one.
  Keywords: equal-gain combination; wireless sensor networks; adaptivedistributed detection; fading channels; fault-tolerant.
   
• A Network-based Global Mobility Management Architecture
  by Huachun Zhou, Hongbin Luo, Hongke Zhang, Chi-Hsiang Lo, Han-Chieh Chao 
  Abstract: This paper specifies a network-based global mobility management architecture, named NetGMM. NetGMM supports network-based mobility management and non-Mobile IP mobile environment. There are two design considerations. The first is that a future mobile network requires network-based mobility management shifting the mobility management function from mobile nodes to access network nodes. The second is that future mobile networks will support IP multi-services, introducing a separation between network address and identity of a mobile node entity allow heterogeneous networks to work together without loss of functionality.
  Keywords: mobility, network-based, host identity, handoff
   
• An Analytical Review for Multipath Routing in Mobile Ad Hoc Networks
  by Ammar Zahary, Aladdin Ayesh 
  Abstract: Multipath routing is a new extension to many traditional routing protocols in MANETs which is addressed recently in so many approaches. Multipath routing protocols are considered more reliable and robust than single path due to easy recovery from a route failure. In multipath routing, route availability is enhanced and consequently frequent re-establishing of route discovery process is minimized. In other words, using multipath routing in MANETs can save energy, reduce frequent routing update, enhance data transmission rates, and increase wireless network bandwidth. This paper introduces an analytical review for multipath routing in MANETs covering its applications, classification, and design issues. A simulation-based analytical evaluation is presented in this review using NS2 for AODV and its multipath extensions namely, AOMDV and MRAODV against two traditional multipath routing protocols namely, DSR and TORA. Simulation results show that traditional multipath protocols outperform the single path version of AODV in terms of packet delivery fraction, routing packets overhead, and throughput while AODV is the best in term of average end-to-end delay. It is also shown that both AOMDV and MRAODV have better average performance compared to the traditional multipath protocols in terms of all performance metrics except routing packets overhead which is still better in the traditional protocol TORA. Regarding average end-to-end delay, AOMDV outperforms AODV while the performance of MRAODV is reduced compared to AOMDV performance.
  Keywords: single path routing; multipath extensions; multipath classification; route availability; fault tolerance; load balancing.
   
• Anonymous Addressing Servers: a Solution of Failures in Wireless Mobile Location Service
  by Mohammed Alchaita, Omar Alani 
  Abstract: Many proposed routing protocols for mobile ad hoc networks rely on geographical information for forwarding packets to the final destinations. These protocols are known as location-based routing algorithms. A location service protocol is combined with and used by these algorithms to provide the source node with the location information for the required destination node. In this paper a new Adaptive Centralised Location Service (ACLS) routing protocol is presented, which tracks mobile node locations and recover the side effects of nodes mobility. In ACLS, some nodes consider themselves as servers serve other nodes according to their location and status in the network. Other nodes send their position information to these servers. This transmission is achieved by only knowing the expected location of the servers without knowing the actual identities of these servers. This is called “anonymous addressing” because the receivers decide on their own, whether they are the intended destination. Results indicate very good and remarkable performance of the ACLS in terms of scalability with the number of nodes, speed and location update success rate.
  Keywords: Ad hoc networks, MANET, Location service, Routing, Mobile node, Mobile server
   
• Analysis of Multiple Attempt Multipath Routing for Mobile Ad hoc Networks
  by Ash Mohammad Abbas 
  Abstract: Devising a protocol that guarantees the identification of a maximal set of node-disjoint paths between a given source and a destination, and incurs a low overhead, is a challenging task in case of a mobile ad hoc network. In this paper, we analyze a routing protocol that identifies a maximal set of node-disjoint paths between a given source and a destination in multiple attempts using an approach that is hybrid of a single-go routing protocol and an incremental protocol. We prove that doing so preserves the guarantee inherited from the incremental protocol to discover a maximal set of node-disjoint paths. In our analysis, we focus on the computational and communication overheads incurred in identifying node-disjoint paths and the time after which all routes identified are expected to fail.
  Keywords: Ad hoc networks; multipath routing; multiple attempts; node-disjoint; incremental approach; single-go protocols; route failure time; overheads.
   
• Towards A Routing Framework in Ad Hoc Space Networks
  by Chao Chen, Zesheng Chen 
  Abstract: The unique characteristics of space networks lead to different research approaches from those in terrestrial networks. In this paper, a routing framework called Space Gateway Routing (SGR) is proposed for routing through different autonomous regions (ARs) in ad hoc space networks. SGR has two integral parts: External SGR (ESGR) and Interior SGR (ISGR). ESGR addresses the delivery of different traffic types through ARs. Inside ESGR, the Location-Predicted Directional Broadcast (LPDB) is proposed for fast delivery of remote control messages and automatic data delivery. The Receiver-Initiated On-demand Routing (RIOR) is proposed for controlled data delivery, where the route discovery is initiated on-demand by the receiver, and routing tables are maintained in soft state at intermediate nodes. ISGR exchanges inter-AR routing information among border routers within an AR and schedules inter-AR message transmission. The Longest Queues (LQ) policy is proposed for contact allocation for AR border routers, and the Minimum Waiting (MW) policy is introduced for scheduling inter-region messages through an AR. Simulation results show that LPDB and RIOR are efficient both in message delivery and power consumption, and a combination of proposed LQ and MW policies achieves good delay and throughput performances.
  Keywords: routing; ad hoc networks; space communication networks
   
• Context-Aware Cluster-based Hierarchical Protocol for Wireless Sensor Networks
  by Md Enamul Haque, Noriko Matsumoto, Norihiko Yoshida 
  Abstract: Wireless Sensor Network (WSN) has been a key research topic for its numerous, multi dimensional applications. Most of such applications require accurate information collecting as well as uninterrupted, prolonged service life. Among the constituting elements of WSN, employing an efficient routing protocol plays a significant role in attaining such service requirements. In this paper, an energy efficient routing protocol, CACH (Context Aware Clustering Hierarchy) has been proposed where cluster formation is entirely based on the context of the environment. Moreover, an efficient technique has been utilized to avoid similar data traffic across the network. Again, cluster head role has been equally distributed among the nodes during the total service life. The performance in the simulation shows substantial amount of energy saving which ensures prolonged service life.
  Keywords: wireless sensor networks; hierarchical routing protocol; context awareness
   
• Energy-Efficient Routing in Wireless Sensor Networks for Delay Sensitive Applications
  by Pavan Pothuri, Divya Ranganathan, Venkatesh Sarangan, Sridhar Radhakrishnan 
  Abstract: Advances in wireless technologies along with sophistications in embedded computing systems have led to the emergence of un-attended Wireless Sensor Networks (WSNs). Not withstanding the limited energy reserves in the sensor nodes, WSNs have enabled a plethora of new services and applications. While several routing protocols have been proposed to address the energy limitations of the sensors, these protocols tend to increase the end-to-end delay involved in data transmission to the control center. This leads to the Delay-Constrained, Energy-Efficient Routing Problem (DCEERP) in several WSN applications. This paper presents a methodology for solving the aforesaid problem using topology control in a network of sensor nodes that employ contention based channel access mechanisms. A distinguishing aspect of the proposed solution is that it takes in to account the access delays caused by the underlying MAC layer. We propose a logical network architecture and a routing framework that enable us to identify the nodes that interfere with a sensor node’s transmission, thereby allowing us to estimate the access delays caused by the MAC protocols using existing analytical models. This in turn permits us to discover energy-efficient paths that satisfy the delay constraint on the sensory data. Results from our study show that the proposed framework achieves a good balance between latency introduced in the transfer and energy consumption when compared with conventional solutions.
  Keywords: wireless sensor networks; delay sensitive routing; energy efficiency; topology control; access delay modeling.
   
• Lifetime Maximization Algorithm in Wireless Sensor Network
  by Ouadoudi Zytoune, Youssef Fakhri, Driss Aboutajdine 
  Abstract: In a Wireless Sensor Network (WSN), nodes are battery powered, therefore, they are energy constrained. Network lifetime is one of the most important characteristics of performance for wireless sensor networks. A number of routing schemes, energy efficient and energy-aware, have been proposed to maximize the network lifetime. These schemes typically try to find the minimum energy path to optimize energy usage at a node. In this paper, considering the lifetime maximization problem, we propose routing protocols that take into account the battery residual energy in sensor nodes and the required energy for transmission along the path toward the sink. For each transmission round, only the nodes which have their remaining energies greater than a threshold can participate as relays for other nodes data packets in addition to sense the environment. This choice allows the distribution of energy load among the whole network nodes, thus extends network lifetime. Simulation results show that the network lifetimes increases up to 50% until the first node die and up to 114% until the last node die compared to schemes like MLER protocol. Nodes also burn energy in a more equitable way across the network ensuring a more graceful degradation of service with time.
  Keywords: Wireless Sensors Networks; Routing algorithms; Energy balancing; Energy efficiency; Lifetime maximization.
   
• A distributed token based h-out of-k mutual exclusion protocol for mobile ad hoc networks
  by Benchaïba Mahfoud, Ahmed Nacer Mohamed 
  Abstract: In this paper, we describe a new distributed token based h-out of-k mutual exclusion protocol for mobile ad hoc networks. This protocol does neither use the routing layer nor a logical structure and agrees requests based on their distances to the token, their ages, and the resources number. A request is sent within a dynamical radius computed so to reach a part of the nodes (typically 25%) for which a request is present in the local queue. Simulation results show that the radius tends to 1.2 hops for medium and high request charges. The protocol deals with many characteristics of mobile ad hoc networks: Nodes’ movements, creation of links, partition and merge of the network, links’ failures, nodes’ failures and token and resources loss. The protocol manages one token with k resources in each partition and generates them in case of loss. In general, the simulation provides satisfactory results. The number of messages of all measurements is rather low especially for medium and heavy loads. The mobility has little effect on the protocol’s performances especially for medium and heavy loads.
  Keywords: mobile ad hoc network, h-out of-k mutual exclusion, critical section, token, resource allocation
   
• A Market-based Mechanism for Integration of Mobile Devices into Mobile Grids
  by Li ChunLin 
  Abstract: In mobile grid, energy resources distribution and computation workloads are not balanced within mobile devices. Some mobile devices have spare energy; some mobile devices are energy exhausted. In this paper, we present a market-based mechanism for efficient integration of mobile devices into mobile grids to optimize the system performance. All mobile devices in mobile grid can be classified different roles, such as buyers (consumers) and sellers (providers). By market-based cooperation among devices, an energy saving scheme is proposed for mobile gird. The paper is targeted to solve energy allocation of mobile device by using utility-based scheme. The system utility of mobile grid is maximized when the equilibrium prices are obtained through the device market optimization. A market-based algorithm for integration of mobile devices into mobile grid is proposed. In order to test the performance of the algorithm, simulation is conducted by comparing with other power-aware scheduling in mobile Grids.
  Keywords: mobile device; mobile grid; market-based mechanism
   
• Rigidity Guided Localization for Mobile Robotic Sensor Networks
  by Changhua Wu, Weihua Sheng, Ying Zhang, Saroja Kanchi 
  Abstract: The accurate localization of sensor nodes in a mobile robotic sensor network is important in many surveillance applications. Based on our previous work in mobility assisted sensor localization, this paper introduces a rigidity-guided localization approach for mobile robotic sensor networks, using motion trajectories from robot odometry. The rigidity test of a network is based on a pebble game algorithm, that decides whether the network is uniquely localizable or not. If its local network is not uniquely localizable, the mobile node moves around its original position to collect at least two extra ranging data with each of its neighbors while recording its trajectory using odometer. We prove that the extra data with robot trajectory will make the local network uniquely localizable. The local maps of all the nodes are then merged into a globally consistent map. We evaluate the effectiveness of the proposed approach using two examples of low-degree networks and four types of topologically different networks. Additional evaluation on the number of moving nodes in already uniquely realizable networks is also done.
  Keywords: localization;robot;rigidity; mobile sensor network
   
• Quality of Service in Mobile Ad hoc Networks: A Survey
  by Ash Mohammad Abbas 
  Abstract: To support multimedia applications, it is desirable that an ad hoc network has a provision of quality of service (QoS). However, the provision of QoS in a mobile ad hoc network is a challenging task. In this paper, we present a review of the current research related to the provision of QoS in an ad hoc environment. We examine issues and challenges involved in providing QoS in an ad hoc network. We discuss methods of QoS provisioning at different levels including those at the levels of routing, medium access control, and cross layer. Also, we discuss schemes for admission control and scheduling that are proposed in the literature for the provision of QoS. We compare salient features of various solutions and approaches and point out directions for future work.
  Keywords: Ad hoc networks; quality of service; methodologies; admission control; scheduling; fairness.
   
• Maximum Lifetime Broadcasting in Cooperative Multi-hop Wireless Ad Hoc Networks
  by Tamaghna Acharya, Samiran Chattopadhyay, Rajarshi Roy 
  Abstract: We investigate the scope of using cooperative routing for maximizing network lifetime for a given broadcast connection in an energy-constrained multi-hop static wireless ad-hoc network. We assume that each node in the network uses single omni-directional antenna. Most broadcast/multicast routing algorithms for maximum network lifetime have formulated it as a min-max tree problem. But, our formulation of the problem reflects node-based nature of wireless networks. We consider three different transmission techniques at the physical layer (i) point-to-point, (ii) point-to-multipoint (i.e. multicast) and (iii) multipoint-to-point (i.e. cooperative transmission). We propose a polynomial time greedy algorithm for constructing a broadcast tree for maximum network lifetime. In fact, a modified version of our algorithm runs in O(n*n*n) time. Simulation results show that our algorithm outperforms the global optimal solution that achieves maximum network lifetime without using cooperative transmission. Our algorithm also performs competitively with existing algorithms in terms of minimizing total broadcast power.
  Keywords: Wireless Ad hoc Networks; Maximum Lifetime Broadcast; Cooperative Transmission, Minimizing Broadcast Power, Complexity Analysis, Performance Evaluation, Greedy Algorithm, Broadcast Tree, Omni-directional Antenna, Polynomial time Algorithm.
   
• Design and Implementation of a Navigation System for Autonomous Mobile Robots
  by Jang-Ping Sheu, Chia-Chi Chang, Kai-Wen Lo, Chi-Wen Deng 
  Abstract: In this paper, a navigation system for autonomous mobile robots is proposed. Our navigation system is a hybrid of behavior-based and model-based navigation systems. In our system, a behavior-based subsystem is in charge of low-level reactive actions, and a model-based subsystem is responsible for high-level planned actions. If there are obstacles in the way, the navigation system will use our obstacle avoidance algorithm to navigate around these obstacles and keep the robot moving toward the destination. Based on our experimental results, our navigation system can navigate the robot to the destination effectively.
  Keywords: Hybrid architecture, localization, navigation system, obstacle avoidance, wireless sensor networks
   
• Multi-Frame Beacon Management for Constructing Interference-Avoided LR-WPAN
  by Kwang-il Hwang, Jong Hyuk Park 
  Abstract: Advances in wireless technologies have accelerated prevalent deployment of various wireless systems. Meanwhile, the wireless coexistence problem is also arising as one of the most challenging issues. Specifically, in spite of tremendous popularity in a variety of application fields, it is shown that the IEEE802.15.4 LR-WPAN, which has limited resources, is more vulnerable to effects of several interferences operating on the same frequency bands. In this paper, we propose multi-frame beacon management (MBM) MAC protocol for constructing interference-avoided LR-WPAN. By maintaining multi-frames on different channels dynamically, a coordinator and devices can cope well with several interference environments, during the steady state as well as association stage. In addition, in no interfered environment, each device can maintain very low duty cycle as in the standard. The experimental results show that the MBM-MAC can improve interference avoidance ability without deterioration of energy consumption and delay.
  Keywords: Beacon Collision, Coexistence, LR-WPAN, Multi-Channel, Wireless Sensor Networks.
   
• An Early Warning Scheme for Broadcasting Critical Messages Using VANET
  by Li-Der Chou, Ching-Chiang Ho, Jui-Ming Chen 
  Abstract: Traffic safety improvement is the most critical and promising application of Vehicular Ad-hoc Network (VANET). Using VANET, the information of a sudden vehicle breaking can be broadcasted to neighboring vehicles so that the driver can avoid the accident earlier. Current researches proposed that the best time to start broadcasting is when the breaking deceleration exceeds 4m/s2. However, the researches did not consider the delivery time. Indeed, many proposals have been provided solutions to solve the packet collisions problem and reduce the redundant data during communications, but seldom of them consider the human influence like reaction time of driver and break intensity. In the paper, an Early Warning Scheme for Broadcasting Critical Messages scheme (EWBCM) is proposed to reduce the latency of message transmission. Simulation results show that the EWBCM can reduce the delivery time, the packet loss rate and the receiving failure rate effectively.
  Keywords: VANET; Reaction time of driver; Broadcasting protocol; Critical message
   
• Cross-Layer Mobile Chord P2P Protocol Design For VANET
  by Che-Liang Liu, Chih-Yu Wang, Hung-Yu Wei 
  Abstract: Efficient content distribution is one of the emerging applications in vehicular networks. To provide scalable content distribution in vehicular networks, Chord peer-to-peer overlay could be applied. Most P2P protocols, including Chord, are designed for wired-line network, and might perform poorly in mobile networks. Mobile Chord (MChord) is proposed to enhance the P2P performance over vehicular ad hoc network (VANET). In addition, cross-layer design to improve MChord performance in VANET is also investigated. Extensive NS-2 simulations with vehicular mobility traces are conducted to evaluate the P2P overlay performance in VANET. Mobile Chord and its cross-layer design outperforms the original Chord in various aspects, including application layer forwarding steps, query response ratio, correct query response ratio, and application delay.
  Keywords: peer-to-peer, cross-layer, vehicular ad hoc network
   
• A Distributed Wireless Sensor Network Testbed with Energy Consumption Estimation
  by Jang Ping Sheu, Chia-Chi Chang, Wei-Sheng Yang 
  Abstract: Because the procedures of experiments in wireless sensor networks (WSNs) are cumbersome and network simulators cannot present the real effects of wireless communications such as signal fading and anisotropic propagation, WSN testbeds have become a good solution for performance evaluation of protocols in WSNs. In this paper, we design and implement a WSN testbed with a distributed architecture. Our testbed can deploy WSNs in different locations and connect them through the Internet and gateways. Our testbed allows researchers to submit their experiments and to retrieve the results from the central server. In outdoor applications, energy consumption is an important metric to evaluate the performance of WSN protocols. In the testbed, we also propose a software-based hardware-supported scheme to measure the energy consumption of running sensor nodes. And we compare our energy-consumption estimation with oscilloscope measurements. The results show that the energy consumption measured by our scheme is very close to oscilloscope measurements.
  Keywords: Embedded system; power consumption estimation; wireless sensor networks
   
• Vector Routing Protocols for Delay Tolerant Networks
  by Hyunwoo Kang, Dongkyun Kim 
  Abstract: In delay tolerant networks (DTNs) with frequent network partitioning, routing packets is a challenge, because the successful establishment of an end-to-end path between source and destination nodes is not guaranteed. Typical routing protocols for DTNs depend on data replications over multiple paths for reliable data delivery. Since they invoke a lot of replicated packets, this paper therefore proposes three efficient Vector Routing protocols based on the vector of node movements in order to reduce such replications: Flooding-based Vector Routing (FVR), History-based Vector Routing (HVR) and Location-aware Vector Routing (LVR). In FVR, the vector information is calculated using the nodal location information. With the vector information only, nodes efficiently decide which nodes should take replicated packets as well as the number of packets to replicate for each of selected nodes. In HVR, nodes store and share the vector information of other nodes that they met (i.e. history). With such a history, a node calculates a probability that each of its current neighbor nodes will meet the destination node of packets. Based on the probability, the node decides packet replications. In LVR, global network information such as the destination node's location is used for more efficient routing. Using ns-2 simulation with two different mobility models, namely Random Waypoint and Manhattan mobility models, we verify that Vector Routing protocols perform better than other existing routing protocols in terms of less amount of traffic incurred without loss of packet delivery ratio.
  Keywords: delay tolerant networks; routing; vector; packet replication; rendezvous probability.
   
• RARS: A Resource-Aware Replica Selection and co-allocation scheme for Mobile Grid
  by Yue-Shan Chang, Guo-Jie Zou 
  Abstract: With the advance of grid technologies and mobile computing, mobile grid becomes an increasingly important research topic. In the grid community, data grid usually plays an important role in data-intensive applications. Mobile data grid research hence obtains more attention in recent years. As well known, mobile device has with some inherent characteristics, such as limited energy, intermittent connection, and lower bandwidth. Accessing data (file) from mobile data grid nodes needs to take these issues into account. Existing replicas scheduling algorithms proposed for wired networks did not consider these issues. The paper designs a mobile data grid architecture based on agent technology, and based on which, a Resource-Aware Replica Scheduling co-allocation algorithm named RARS is proposed on mobile data grid environment. Mobile clients can access replicas of desired data (file) from those, in parallel, mobile grid nodes that are with superior in a variety of device’s resource, such as remaining energy, bandwidth, and connection stability of node, in an effective, efficient, and reliable way. We also adopt deadline-of-service scheme to enhance the service reliability of whole system while service exceeds deadline. The simulations we made show the RARS are excellent in transmission time and survival rate of mobile node than other approaches.
  Keywords: Mobile Grid; Data Grid; Replica Scheduling Algorithm; Mobile Computing;
   
• A Cell-based Sensor Deployment Strategy with Improved Coverage for Mobility-Assisted Hybrid Wireless Sensor Networks
  by Tien-Wen Sung, Chu-Sing Yang 
  Abstract: Wireless sensor networks are gradually becoming a practical and feasible method of collecting diverse data for environmental surveillance and target tracking applications over large areas. The deployment of wireless sensor devices is one of the most fundamental and important issues in wireless sensor network applications, and coverage is a chief consideration in deployment requirements. Utilizing a mobility-assisted hybrid wireless sensor network which consists of both static and mobile sensor devices may offer better coverage than a stationary sensor network consisting of merely static sensor devices. This paper proposes a hexagonal cell-based sensor deployment strategy that adopts a mobility-assisted hybrid wireless sensor network. Calculation of coverage hole size, the corresponding hole-healing process, and discovery of nearly redundant sensors are based on the hexagonal cells into which the sensing field is virtually divided. Simulations show that the proposed algorithm based on a hexagonal cell-based deployment strategy achieves significantly improved field coverage, and indicates both the number and influence of nearly redundant sensors in the wireless sensor network.
  Keywords: Hybrid Wireless Sensor Networks; Sensor Deployment; Mobile Sensors; Hexagonal Cells
   
• Secure Traffic Data Propagation in Vehicular Ad Hoc Networks
  by Baber Aslam, Soyoung Park, Cliff Zou, Damla Turgut 
  Abstract: A vehicular ad hoc network (VANET) allows vehicles to share traffic information and to alert each other of emergency events. To achieve this goal, a security mechanism must be designed to guarantee that no malicious vehicles can intercept, manipulate, or modify the traffic information without being detected. In this paper, we present two novel approaches to provide reliable traffic information propagation in a VANET: "two-directional data verification", and "time-based data verification". The two-directional data verification approach uses vehicles in both driving directions of a two-way road as two separated media channels. A traffic message will be transmitted through both channels. A recipient vehicle verifies the message integrity by checking if data received from both channels are matched. This approach exploits the fact that it is difficult and costly to have two collaborative vehicles on both driving directions in the same region. In addition, we provide mathematical analysis of the data propagation connectivity and also the robustness against denial-of-service attacks, which match quite well with our simulation results. The time-based data verification approach uses vehicles in the opposite driving direction to propagate a traffic message by issuing the message to those vehicles twice with certain time delay. It relies on the time delay between these two messages and the mobility of vehicles to cause two separated groups of vehicles on the opposite direction carrying and propagating the message. Compared with the popular public-key based security systems, the proposed approaches are much simpler and cheaper to implement, especially during the initial transition stage when a mature VANET network infrastructure does not exist.
  Keywords: Vehicular ad hoc network; initial deployment stage; secure data propagation