Chao-Tsun Chang

Obstacle-Resistant Deployment Algorithms for Wireless Sensor Networks

Node deployment is an important issue in wireless sensor networks (WSNs). Sensor nodes should be efficiently deployed in a predetermined region in a low-cost and high-coverage-quality manner. Random deployment is the simplest way to deploy sensor nodes but may cause unbalanced deployment and, therefore, increase hardware costs and create coverage holes. This paper presents the efficient obstacle-resistant robot deployment (ORRD) algorithm, which involves the design of a node placement policy, a serpentine movement policy, obstacle-handling rules, and boundary rules. By applying the proposed ORRD, the robot rapidly deploys a near-minimal number of sensor nodes to achieve full sensing coverage, even though there exist unpredicted obstacles with regular or irregular shapes. Performance results reveal that ORRD outperforms the existing robot deployment mechanism in terms of power conservation and obstacle resistance and, therefore, achieves better deployment performance.

A Novel Relay Placement Mechanism for Capacity Enhancement in IEEE 802.16j WiMAX Networks

The IEEE 802.16j draft proposes a multi-hop relay network architecture that introduces the new network element of relay station aimed at increasing the network throughput or coverage. The deployment of the relay stations is one of the most important issues that determines the network throughput. Given a base station, k relay stations, and a deployed region that can be fully covered by the BS, this paper proposes a relay deployment mechanism that determines the deployed locations of RSs so that the bandwidth requirement of MSs can be satisfied while the network throughput can be significantly improved. Experimental study reveals that the proposed mechanism can efficiently determine the locations for relay deployment and improve the network throughput.

The k-barrier coverage mechanism in Wireless Visual Sensor Networks

Wireless Visual Sensor Networks (WVSNs) consist of a set of camera sensor nodes each of which equips with a camera and is capable of communicating with the other camera sensors within a specific distance range. As an extension of wireless sensor networks (WSNs), the WVSNs can provide richer information such as image and picture during executing targets monitoring and tracking tasks. Since the sensing area of each camera sensor is fan-shaped, existing barrier-coverage algorithms developed for WSNs cannot be applied to the WVSNs. This paper is considering to address the k-barrier coverage problems in WVSNs and to propose a barrier-coverage approach aiming at finding a maximal number of distinct defense curves with each of which consists of as few camera sensors as possible but still guarantees k-barrier coverage. Compared with the related work, experimental study reveals that the proposed k-barrier coverage mechanism constructs more defense curves than the k-barrier coverage and the number of camera sensors participating in each defense curve is smaller.

Active Route-Guiding Protocols for Resisting Obstacles in Wireless Sensor Networks

In wireless sensor networks, a geographic region without the functionality of sensing and communication can generally be treated as an obstacle, which significantly impacts the performance of existing location-based routing. An obstacle can dynamically be formed due to unbalanced deployment, sensor failure, or power exhaustion, animus interference, or physical obstacles such as mountains or buildings. This paper proposes novel algorithms that enable the existing location-based routing protocols that resist obstacles. Applying the proposed active route-guiding protocol for single obstacles (S-RGP), border nodes that surround the obstacles will actively establish a forbidden region for concave obstacles and make the obstacle information transparent. Then, packets will be guided to overcome the obstacle and move along the shorter path from the encountered border node to the sink node. In addition, the proposed active route-guiding protocol for multiple obstacles (M-RGP) takes multiple obstacles into consideration and integrates their information to help the packets overcome multiple obstacles. Simulation results show that the proposed S-RGP and M-RGP create low overhead and significantly reduce the average route length, and, therefore, improve the energy consumption and end-to-end delay for a wireless sensor network with obstacles.

Throughput-Enhanced Relay Placement Mechanism in WiMAX 802.16j Multihop Relay Networks

The IEEE 802.16j standard proposes a multihop relay network architecture that introduces relay stations aiming at increasing the network throughput or coverage. The deployment of the relay stations is one of the most important issues that determine the network throughput. In literature, some deployment strategies have been proposed. However, none of them follows the frame structure designed in IEEE 802.16j standard. Furthermore, they did not consider the fact that the bandwidth constraints of a base station, relay stations, and mobile stations (MSs) are highly related to the locations of relays. Given a base station, k relay stations, and a region that can be fully covered by the base station, this paper proposes a relay deployment mechanism aiming to determine the best deployed locations for relays so that the bandwidth requirement of MSs can be satisfied while the network throughput can be significantly improved. Performance study reveals that the proposed relay deployment mechanism can improve the network throughput as compared with the existing approaches.

Throughput enhancement by exploiting spatial reuse opportunities with smart antenna systems in wireless ad hoc networks

Smart antenna (or multi-beam antenna) systems can support simultaneous transmissions (or receptions) of multiple packets in different beams using the same channel. However, network performance is highly dependent on transmission scheduling. This study develops two transmission-scheduling schemes for use with smart antenna systems to improve network throughput and reduce transmission delay. The proposed scheduling mechanisms, which are designed to minimize the average latency and maximize network throughput, exploit the opportunities for parallel transmissions and consider communication restrictions and packet sizes. The performance results indicate that the proposed schemes outperform previous schemes in network throughput and transmission delay.

Maximizing Throughput by Exploiting Spatial Reuse Opportunities with Smart Antenna Systems

Smart antenna (or Multi-beam antenna) systems can support simultaneous transmissions (or receptions) of multiple packets on different beams using the same channel. However, the network performance highly depends on the transmission scheduling. Based on the cluster topology, this paper aims at developing transmission scheduling approaches with smart antenna systems for maximizing the network throughput and minimizing the transmission delays. Initially, a set of parallel groups are constructed with consideration of the constraints for multi-beam smart antenna systems. Then two scheduling approaches, called MaxPTran and DAS, are proposed for scheduling multiple transmissions on different beams. Performance study reveals that the proposed approaches outperform existing work in terms of network throughput and transmission delay.

A compact covering method to exploit embedding capacity for matrix encoding

Recently, a number of covering schemes proposed to exploit embedding capacity in covering images using matrix encoding. When binary secret data include a high frequency of repeated bit-blocks, a preprocessing phase is employed to compress secret data prior to the embedding process regardless of whether the compressed secret data still contain some repeated bit-blocks. This paper proposes two novel compact covering schemes, compact covering scheme (CCS) and intelligent compact covering scheme (ICCS), which directly compress and conceal the repeated bit-blocks of secret data bits into covering images within a single phase. The proposed schemes can exploit the embedding capacity and increase the embedding efficiency by reducing the required encoding operations. In addition, the proposed ICCS scheme can indicate up to which degree of repeated bit-blocks of secret data it can take advantage of in order to improve the embedding capacity. Experimental results demonstrate that the proposed ICCS method can significantly improve the embedding capacity when the ratio of the repeated bit-blocks over the total number of blocks is low. The proposed schemes are feasible for actual data-hiding applications.

TMCP: Two-layer multicast communication protocol for Bluetooth radio networks

Bluetooth is a low power, low cost, and short-range wireless technology developed for Personal Area Networks (PANs). A Bluetooth multicast group is a set of Bluetooth devices that desire for periodically receiving the multicast messages from the same source. For reducing the propagation delay and saving the bandwidth and energy consumptions, a multicast tree which connects all multicast members serves for the delivery of multicast messages. However, a given connected scatternet topology may not be appropriate for constructing an efficient multicast tree and hence causes power consumption and end-to-end delay. This paper develops a two-layer multicast communication protocol (TMCP) using role switching techniques for constructing an efficient multicast tree. The proposed TMCP collects as many as possible the members into the same piconet, reduces the length of multicast paths and assigns each member with a proper role. The constructed multicast tree has several features including as few as possible the non-member devices, the smallest tree level and the minimal propagation delay. Experiment results show that the TMCP offers efficient multicast service with low power consumption and small delay.

SRA: A Sensing Radius Adaptation Mechanism for Maximizing Network Lifetime in WSNs

Coverage is an important issue that has been widely discussed in wireless sensor networks (WSNs). However, it is still a big challenge to achieve both purposes of full coverage and energy balance. This paper considers the area coverage problem for a WSN in which each sensor has a variable sensing radius. To prolong the network lifetime, a weighted Voronoi diagram (WVD) is proposed as a tool for determining the responsible sensing region of each sensor according to the remaining energy in a distributed manner. The proposed mechanism, which is called sensing radius adaptation (SRA), mainly consists of three phases. In the first phase, each sensor and its neighboring nodes cooperatively construct the WVD to identify the responsible monitoring area. In the second phase, each sensor adjusts its sensing radius to reduce the overlapping sensing region such that the purpose of energy conservation can be achieved. In the last phase, the sensor with the least remaining energy further adjusts its sensing radius with its neighbor for to maximize the network lifetime. Performance evaluation and analysis reveal that the proposed SRA mechanism outperforms the existing studies in terms of the network lifetime and the degree of energy balance.