Liusheng Huang

Community-Aware Opportunistic Routing in Mobile Social Networks

Mobile social networks (MSNs) are a kind of delay tolerant network that consists of lots of mobile nodes with social characteristics. Recently, many social-aware algorithms have been proposed to address routing problems in MSNs. However, these algorithms tend to forward messages to the nodes with locally optimal social characteristics, and thus cannot achieve the optimal performance. In this paper, we propose a distributed optimal Community-Aware Opportunistic Routing (CAOR) algorithm. Our main contributions are that we propose a home-aware community model, whereby we turn an MSN into a network that only includes community homes. We prove that, in the network of community homes, we can still compute the minimum expected delivery delays of nodes through a reverse Dijkstra algorithm and achieve the optimal opportunistic routing performance. Since the number of communities is far less than the number of nodes in magnitude, the computational cost and maintenance cost of contact information are greatly reduced. We demonstrate how our algorithm significantly outperforms the previous ones through extensive simulations, based on a real MSN trace and a synthetic MSN trace.

FACTS: A Framework for Fault-Tolerant Composition of Transactional Web Services

Along with the standardization of Web services composition language and the widespread acceptance of composition technologies, Web services composition is becoming an efficient and cost-effective way to develop modern business applications. As Web services are inherently unreliable, how to deliver reliable Web services composition over unreliable Web services is a significant and challenging problem. In this paper, we propose FACTS, a framework for fault-tolerant composition of transactional Web services. We identify a set of high-level exception handling strategies and a new taxonomy of transactional Web services to devise a fault-tolerant mechanism that combines exception handling and transaction techniques. We also devise a specification module and a verification module to assist service designers to construct fault-handling logic conveniently and correctly. Furthermore, we design an implementation module to automatically implement fault-handling logic in WS-BPEL. A case study demonstrates the viability of our framework and experimental results show that FACTS can improve fault tolerance of composite services with acceptable overheads.

Accurate time synchronization for wireless sensor networks

Time synchronization is a critical topic in wireless sensor networks for its wide applications, such as data fusion, TDMA scheduling and cooperated sleeping, etc. In this paper, we present an accurate time synchronization (ATS) algorithm using linear least square for sensor networks. Unlike the previous protocols, all nodes aren’t synchronized to some reference nodes or sink node, but to a virtual clock. Moreover, each pair of the nodes are synchronized each other. The main advantage of ATS is simple and accurate. The variance of the synchronized drift error is no more than Ds*δ / 2β2, where Ds is the depth of the network, δ is the maximal variance of the link delay and β is the sampling interval. The experiments show the high precision compared with the previous algorithms.

Homing spread: Community home-based multi-copy routing in mobile social networks

A mobile social network (MSN) is a special delay tolerant network (DTN) composed of mobile nodes with social characteristics. Mobile nodes in MSNs generally visit community homes frequently, while other locations are visited less frequently. We propose a novel zero-knowledge MSN routing algorithm, homing spread (HS). The community homes have a higher priority to spread messages into the network. Theoretical analysis shows that the proposed algorithm can spread a given number of message copies in an optimal way when the inter-meeting times between any two nodes and between a node and a community home follow exponential distributions. We also calculate the expected delivery delay of HS. In addition, extensive simulations are conducted. Results show that community homes are important factors in efficient message spreading. By using homes to spread messages faster, HS achieves a better performance than existing zero-knowledge MSN routing algorithms, including Epidemic, with a given number of copies, and Spray&Wait.

Centralized Scheduling and Channel Assignment in Multi-Channel Single-Transceiver WiMax Mesh Network

The IEEE 802.16a standard defines WiMax mesh network, using the base station (BS) as a coordinator for the centralized scheduling. This paper proposes a centralized scheduling algorithm for WiMax mesh networks. In our scheme, each node has one transceiver and can be tuned between multiple channels, intending to eliminate the secondary interference for reducing the length of scheduling. We first study the problem when sufficient channels are supported, then extend our solution to the case with insufficient number of channels. Both the scheduling algorithm and the channel assignment strategies are included. The simulation results show that the multi-channel single-transceiver MAC can reduce the length of scheduling substantially as compared with the single channel system, and double channel may provide a performance similar to the multiple channels.

Performance Analysis of Wireless Sensor Networks With Mobile Sinks

In wireless sensor networks (WSNs), one major challenge is how to prolong the network lifetime while maintaining a certain data collection rate for resource-limited static sensors. To achieve this goal, many mobility-assisted data collection (MADC) schemes have been proposed in the literature. However, there is a lack of systematic analysis on the behaviors of the MADC models in terms of both throughput capacity, which is defined as the maximal data collection rate, and lifetime, which will be associated with a specific data collection rate. In this paper, we address this issue in a large-scale WSN with mobile sinks from a theoretical perspective, which has not yet been studied. In particular, we first propose a general MADC model that includes many important parameters such as the number of mobile sinks, the velocity of a mobile sink, and the traveling path of a mobile node. We then develop a comprehensive theoretical approach to obtain the achievable throughput capacity and lifetime. By applying the proposed approach, we investigate the behaviors of WSNs with one or more mobile sinks. Our analysis not only shows how a WSN with mobile sinks can outperform a static WSN but also provides insights on how we can adjust the MADC parameters to improve the data collection rate and to maximize the lifetime. Finally, our analysis is validated through extensive simulations.

A Declarative Approach to Enhancing the Reliability of BPEL Processes

Currently, BPEL is the de-facto standard for the Web service composition. Because Web services are autonomous and loosely coupled, BPEL processes are susceptible to a wide variety of faults. However, BPEL only provides limited constructs for handling faults, which makes fault handling a time-consuming and error-prone task. In this paper, we propose a declarative approach to enhancing the reliability of BPEL processes. Our solution specifies fault handling logic through a set of event- condition-action (ECA) rules which build on an extensible set of fault-tolerant patterns. These ECA rules are integrated with normal business logic before deployment to generate a fault-tolerant BPEL process. We also develop a GUI tool to assist designers to specify ECA rules. Experiments show our approach is feasible.

Passive interference measurement in Wireless Sensor Networks

Interference modeling is crucial for the performance of numerous WSN protocols such as congestion control, link/channel scheduling, and reliable routing. In particular, understanding and mitigating interference becomes increasingly important for Wireless Sensor Networks (WSNs) as they are being deployed for many data-intensive applications such as structural health monitoring. However, previous works have widely adopted simplistic interference models that fail to capture the wireless realities such as probabilistic packet reception performance. Recent studies suggested that the physical interference model (i.e., PRR-SINR model) is significantly more accurate than existing interference models. However, existing approaches to physical interference modeling exclusively rely on the use of active measurement packets, which imposes prohibitively high overhead to bandwidth-limited WSNs. In this paper, we propose the passive interference measurement (PIM) approach to tackle the complexity of accurate physical interference characterization. PIM exploits the spatiotemporal diversity of data traffic for radio performance profiling and only needs to gather a small amount of statistics about the network. We evaluate the efficiency of PIM through extensive experiments on both a 13-node and a 40-node testbeds of TelosB motes. Our results show that PIM can achieve high accuracy of PRR-SINR modeling with significantly lower overhead compared with the active measurement approach.

Multi-party quantum state sharing of an arbitrary two-qubit state with Bell states

We present a new scheme for sharing an arbitrary two-qubit quantum state with n agents. In our scheme, the sender Alice first shares n Einsein-Podolsky-Rosen (EPR) pairs in Bell states with n agents. After setting up the secure quantum channel, Alice first applies (n − 2) Controlled-Not (CNOT) gate operations, and then performs two Bell-state measurements and (n − 2) single-particle measurements (n >2). In addition, all controllers only hold one particle in their hands, respectively, and thus they only need to perform a single-particle measurement on the respective particle with the basis