Yung-Liang Lai

Mobile robot coordination and navigation with directional antennas in positionless wireless sensor networks

In this paper, we propose a suite of three schemes for mobile robot coordination and navigation in positionless wireless sensor networks with the help of directional antennas. When a specific node, called waiting-for-rescue (WFR) node, detects the occurrence of an event, it broadcasts an event notification packet to the entire network for asking a mobile robot to come to help. In many existent schemes, the broadcast is achieved by the flooding scheme and thus incurs redundant forwarding packets. We propose an energy efficient broadcast scheme called farthest node forwarding (FNF), which utilizes received signal strength for a node to determine the backoff time to forward the broadcast packet. Thus, farther nodes have shorter backoff times and higher probabilities to forwarding. As we will show, this can reduce a lot of redundant forwarding packets to save energy, while achieving high reachability. The FNF scheme can also help construct a navigation tree which is rooted at the WFR node and contains only packet forwarding nodes. Under the consideration of multiple WFR nodes and multiple mobile robots, we also develop energy- and time-efficient mobile robot coordination and navigation schemes based on the navigation tree for the mobile robot equipped with a directional antenna. The effectiveness of the proposed schemes is verified in simulations by the ns-2 simulator.

Broadcasting with Optimized Transmission Efficiency in Wireless Networks

One of the fundamental operations in the wireless network is broadcasting, which is widely used to disseminate information throughout the network. Flooding is a simple method to realize broadcasting. However, flooding will incur a large number of redundant retransmissions, leading to low transmission efficiency. In this paper, we propose an optimized broadcast protocol (OBP) to improve the transmission efficiency. In OBP, each node calculates the retransmission locations based on a hexagon ring pattern in order to minimize the number of retransmissions. Only the nodes nearest to the calculated locations need to retransmit the packet. As shown by analysis, the transmission efficiency bound of OBP is 0.55, which approximates the theoretical optimal bound 0.61 by a ratio of 90%. We also compare OBP with a related protocol called OFP in terms of transmission efficiency and reachability.

Optimal Multipath Planning for Intrusion Detection in Smart Homes Using Wireless Sensor and Actor Networks

Intrusion detection is one of the most important services in a smart home, which requires to monitor intrusion events and to react against them. A Wireless Sensor and Actor Network (WSAN) has a set of sensor nodes for monitoring events and a set of high capability nodes, called actor nodes, for reacting to the events. It can provide an infrastructure for building the intrusion detection system in a smart home. We need to jointly consider fault-tolerance and timeliness issues because sensor nodes are likely to be influenced by failures (e.g., dead battery) and need to deliver packets in real time over wireless links vulnerable to interference caused by walls, floors or furniture. In this paper, we propose Optimal Multipath Planning (or OMP), which is based on Edmonds-Karp maximum flow algorithm and Goldberg and Tarjan minimum cost flow algorithm, for WSANs to set up paths to deliver intrusion event notification from event sources to actors in a smart home. The planning is optimal in the sense that it sets up the maximum number of node-disjoint paths of links with the minimized expected transmission count (ETX). We also evaluate OMP’s performance by simulations and compare it with the minimum cost planning using Dijkstra algorithm to show its advantages.

Optimising sink-connected barrier coverage in wireless sensor networks

This paper proposes an algorithm, named the optimal node selection algorithm ONSA, to solve the sink-connected barrier coverage optimisation problem, which is concerned with how to select randomly deployed sensor nodes of a wireless sensor network WSN to reach two optimisation goals: 1 to maximise the degree of barrier coverage with the minimum number of detecting nodes; 2 to make the detecting nodes sink-connected with the minimum number of forwarding nodes. The detecting nodes are those for detecting intruders crossing a belt-shaped area of interest. On detecting intruders, they send intruding event notifications to one of the sink nodes with the help of the forwarding nodes to relay the notifications. We prove the optimality of ONSA, analyse its time complexity, perform simulations for it, and compare the simulation results with those of a related algorithm to show ONSAs advantages.

A Decreasing k-means algorithm for the Disk Covering Tour Problem in wireless sensor networks

This paper studies a Disk Covering Tour Problem (DCTP) for reducing the energy consumption of a mobile robots movement to provide services for sensor nodes in a wireless sensor network (WSN). Given a set of locations of sensor nodes and a starting location of mobile robot, the DCTP is to find a minimum cost tour of a sequence of tour stops for the mobile robot to serve sensor nodes by keeping every sensor node within a specified distance of a tour stop. We propose an algorithm, called Decreasing k-means (Dk-means), to find an approximate solution to the DCTP. The idea is to select a minimum number of disks or circles of a fixed radius to cover all sensor nodes, and then to find a minimum cost tour passing all disk centers. The simulation results show the proposed algorithm outperforms the related CSP (Covering Salesman Problem) algorithm and the QiF algorithm.

Optimal Path Planning for Fault-Tolerant and Energy-Efficient Target Surveillance in Wireless Sensor and Actor Networks

The Wireless Sensor and Actor Network (WSAN) is an extension of the wireless sensor network (WSN). Besides resource-limited sensor nodes, WSANs have resource-rich nodes, called actors, of higher capabilities to perform powerful actions. In this paper, we focus on target surveillance systems built atop WSANs to monitor critical targets. Since sensor nodes are usually equipped with limited energy sources and are likely to be influenced by unpredictable failures occurring in the harsh sensor field, we need to seriously take fault-tolerance and energy-efficiency into consideration. Hence, we develop an optimal path planning (OPP) scheme to construct a maximum number of node-disjoint paths to deliver targets’ event notification with minimum energy consumption. We also evaluate OPP performance by simulations and compare it with a related scheme to show its advantages.

Optimizing Detection Quality and Transmission Quality of Barrier Coverage in Heterogeneous Wireless Sensor Networks

This paper proposes an algorithm, called the Optimized Barrier Coverage Algorithm (OBCA), to optimize the quality of the barrier coverage formed by a wireless sensor network (WSN). OBCA aims at optimizing the barrier coverage quality in terms of the detection degree, the detection quality, and the transmission quality (i.e., the expected transmission time). This paper also proposes a model to formulate the minimum detection probability between two WSN sensors with different sensing ranges. With the model, OBCA can be applied to heterogeneous WSNs whose sensors have various sensing ranges. OBCA’s optimization is proved, and its time complexity is analyzed. The performance of OBCA is simulated and compared with those of two related algorithms.

Silence Coding for RFID Tag Anti-Collision

This paper proposes a tree-based RFID tag anti-collision protocol, called the silence coding query tree (SCQT) protocol, based on a novel coding scheme, namely the silence coding, to speed up tag identification. The proposed protocol can identify multiple tags at a time even at the appearance of tag signal collisions. Simulation results show that the SCQT protocol significantly outperforms other related tree-based protocols in terms of the number of cycles to identify tags.

Wireless Broadcasting with Optimized Transmission Efficiency

Broadcasting is one of the fundamental operations to disseminate information throughout a wireless network. Flooding is a simple method to realize broadcasting. However, flooding will incur a large number of redundant retransmissions, leading to low transmission efficiency, which is the ratio of the effective transmission area to the total transmission area. In this paper, we propose a geometry-based wireless broadcast protocol, called Optimized Broadcast Protocol (OBP), to improve the transmission efficiency. In OBP, each node calculates the retransmission locations based on a hexagon ring pattern in order to minimize the number of retransmissions, and only the nodes nearest to the calculated locations need to retransmit the broadcast packet. As shown by analysis, the transmission efficiency bound of OBP is 0.55, which is about 90% of the theoretical optimal bound 0.61 and is better than that of BPS, the geometry-based broadcast protocol with the highest transmission efficiency 0.41 known so far. Since the transmission efficiency is inversely proportional to the number of required nodes to cover a network area, in a static deployed network, the number of deployed nodes is minimized by OBP. However, in a randomly deployed network or a mobile network, when the node density is not high, the network area of interest may not be fully covered and OBP has worse reachability than BPS for some cases. We thus propose an extension of OBP, called OBPE, to improve the reachability when the node density is not high. We make comparisons for OBP, OBPE and BPS in terms of transmission efficiency, reachability, transmission redundancy, and the number of transmissions, energy consumption to show the advantages of OBP and OBPE.

Optimal Multipath Planning for Neyman-Pearson Detection in Wireless Sensor Networks

Target detection is one of the most important services in wireless sensor networks (WSNs) for making decisions about the presence of specified targets by collecting sensed data from geographically distributed wireless sensors nodes. In this paper, we consider designing target detection systems in WSNs on the basis of the Neyman-Pearson Detector (NPD), a statistical decision making method of which accuracy depends on the amount of data collected within a limited time period. We propose the Optimal Multipath Planning Algorithm (OMPA) based on the maximum flow minimum cost algorithm for WSNs to set up paths to reliably deliver as many as possible data packets from data sources to the sink node. OMPA is optimal in the sense that it sets up the maximum number of node-disjoint paths composed of the links with the minimized expected transmission time (ETT). We also evaluate OMPA¶V decision quality with the help of the Receiver Operating Characteristic (ROC) curves and compare OMPA with the Minimum Cost Path Planning Algorithm (MCPPA) in terms of the detection decision quality and the number of available paths at the presence of node failures.