Kuei-Ping Shih

A TDMA-based bandwidth reservation protocol for QoS routing in a wireless mobile ad hoc network

This paper considers the bandwidth reservation problem in a mobile ad hoc network (MANET) to support QoS (quality-of-service) routing. We approach this problem by assuming a common channel shared by all hosts under a TDMA (time division multiple access) channel model. Existing solutions have addressed this problem by assuming a stronger multi-antenna model, where the bandwidth of a link is independent of the transmitting/receiving activities of its neighboring links, or a less strong CDMA-over-TDMA channel model, where the use of a time slot on a link is only dependent on the status of its one-hop neighboring links. While more practical and less costly, using a TDMA model needs to face the challenge of radio interference problems. In this paper, we propose a new protocol that can reserve routes by addressing both the hidden-terminal and exposed-terminal problems. The protocol can conduct accurate bandwidth calculation while performing route discovery. Simulation results are presented to verify how this new protocol performs.

CAPC: a collision avoidance power control MAC protocol for wireless ad hoc networks

The letter identifies a power control induced hidden terminal problem, named POINT problem, and proposes a collision avoidance power control (CAPC) MAC protocol to solve the POINT problem for wireless ad hoc networks. CAPC takes the interference range into consideration and uses the appropriate power to exchange Data/ACK, instead of the exact power in order to resist the interference of other stations. Simulation results verify that CAPC can effectively prevent the POINT problem.

A Distributed Active Sensor Selection Scheme for Wireless Sensor Networks

The paper proposes a distributed active sensor selection scheme, named DASS, for WSNs, under the requirement of complete coverage of a sensing field. By means of Voronoi diagram, the sensor can find appropriate sensors to work together for the sensing tasks. DASS can find as few number of sensors as possible to be in charge of the sensing task. Simulation results show that DASS can efficiently select few sensors to cover the whole sensing field. Furthermore, the network lifetime can be protracted significantly in comparison with the state-of-the-art schemes.

Distributed direction-based localization in wireless sensor networks

Location awareness is an attractive research issue in the wireless sensor network (WSN). However, precise location information may be unavailable due to the constraint in energy, computation, or terrain. Additionally, several applications can tolerate the diverse level of inaccuracy in such geographic information. Thus, this paper presents a direction-based localization scheme, DLS, whose main goal is for each sensor to determine its direction rather than its absolute position. The direction we are concerned with is the one relative to the sink. Motivated by the proposed spatial locality property, DLS considers multiple messages received for a sensor to determine its direction. Furthermore, a novel scheme, anchor deployment strategy, is also proposed for the improvement of the estimated correctness in direction of the sensor within the communication range of the sink. With the aid of the virtual dual direction coordinate (VDDC) system, DLS is able to efficiently and precisely position sensors around the axes. We evaluate DLS via simulations in terms of various numbers of sensors and communication ranges for the scenarios with different numbers of directions. The average correct rates in DLS reach approximately 94%, 86%, and 81% for the networks with 4, 8, and 16 directions, respectively. DLS achieves outstanding performance for the high density networks as well. In addition, DLS also works well regardless of the sink placement. Overall, simulation results validate the practicality of DLS, and show that DLS can effectively achieve direction estimation.

CollECT: Collaborative event detection and tracking in wireless heterogeneous sensor networks

Tracking is an important application in wireless sensor networks (WSNs), especially for the urgent event of interest. Recent research has paid much attention to the WSN wherein all sensor nodes are identical in sensing units, but the utilization of different types of sensor nodes has not been widely explored. In the paper, we propose a fully distributed protocol, CollECT, to event detection and tracking in wireless heterogeneous sensor networks (WHSNs), which consists of various types of sensor nodes with different sensing units. The main idea of CollECT is collaboration, by which the same type of sensor nodes construct the attribute region, represented by a convex polygon, whereas the different types of sensor nodes determine whether the event occurs. In CollECT, three procedures, vicinity triangulation, event determination, and border sensor node selection, are proposed to construct the attribute region, to determine the occurrence of the event, and to select border sensor nodes to stand for the event boundary, respectively. Simulation results validate the performance of CollECT in terms of accuracy of event tracking and fitness of the border sensor nodes selected. Approximately 87% sensor nodes within the event region can be correctly identified on average. Additionally, the border sensor nodes selected by CollECT are beneficial to efficiently stand for the event boundary.

On Barrier Coverage in Wireless Camera Sensor Networks

The paper proposed a distributed algorithm, namely CoBRA (Cone-based Barrier coveRage Algorithm), to achieve barrier coverage in wireless camera sensor networks (WCSNs). To the best understanding, CoBRA is the first algorithm which try to deal with the barrier coverage issue in WCSNs. Based on some observations, the basic concept of CoBRA is that each camera sensor can determine the local possible barrier lines according to the geographical relations with their neighbors. A sink in a WCSN initiates Barrier Request (BREQ) messages to form the possible barrier lines. Afterward, a barrier line is constructed by the Barrier Reply (BREQ) message initiated by another sink. CoBRA mainly includes three phases: Initial Phase, Candidate Selection Phase, and Decision Phase. In the Initial Phase, each camera sensor collects the local information of its neighbors and estimates the possible barrier lines. In the Candidate Selection Phase, a sink initiates the BREQ packets and forwards the BREQ packets to camera sensors. Camera sensors receiving the BREQ then reforward the BREQ packets to its neighbors who are capable of forming a barrier line. All camera sensors receiving the BREQ will forward the BREQ to their neighbors again in the same manner. Finally, in the decision phase, after the BREQ message is transmitted through the whole monitoring area, a BREP message is used by the sink to select a barrier line in a WCSN. The barrier coverage is achieved by finding the barrier line in the monitoring area. Experiment results show that CoBRA can efficiently achieve barrier coverage in WCSNs. Comparing to the ideal results, CoBRA can use fewer nodes to accomplish barrier coverage in random deployment scenarios.

CollECT: Collaborative Event deteCtion and Tracking in Wireless Heterogeneous Sensor Networks

Event detection and tracking are attractive research issues in the wireless sensor network (WSN). The paper proposes a fully distributed protocol, CollECT, to event detection and tracking in a Wireless Heterogeneous Sensor Network (WHSN), composed of many kinds of sensors. In CollECT, three major procedures, vicinity triangulation, event determination, and border sensor selection are used to construct the logical triangle in the vicinity of a sensor, to determine the event, and to select the border sensor to identify the event boundary, respectively. The procedures perform repeatedly to both detect and track events. Simulation results demonstrate that CollECT is promising for event detection and tracking due to satisfactory event accuracy and reasonable fitness of border sensors.

Dynamic bandwidth allocation for QoS routing on TDMA-based mobile ad hoc networks

The paper proposes several dynamic bandwidth allocation strategies for QoS routing on TDMA-based mobile ad hoc networks. Comprehensively, these strategies are called a distributed slots reservation protocol (DSRP). In DSRP, QoS routing only depends on one-hop neighboring information of each mobile host (MH). In addition, slot inhibited policies (SIPs) and slot decision policies (SDPs) are proposed to determine which slots are valid to use and which slots in the valid slots can be used actually, respectively. In SDPs, three heuristic policies, 3BDP, LCFP, and MRFP, are proposed to increase the success rate of a QoS route and alleviate the slot shortage problems. Moreover, a slot adjustment protocol (SAP) is proposed for a conflicting MH to coordinate the slot usage of its neighbors during the route reservation phase in order to accommodate more routes in the network. The slot adjustment algorithm (SAA) invoked in SAP is a branch-and-bound algorithm, which is an optimum algorithm in terms of the number of slots to be adjusted, on the premise that not to break down any existing route. QoS route maintenance and improvement are also provided. By the simulation results, the proposed protocol cannot only increase the success rate in search of a route with bandwidth requirement guaranteed but also raise the throughput and efficiency of the network.

A Physical/Virtual Carrier-Sense-Based Power Control MAC Protocol for Collision Avoidance in Wireless Ad Hoc Networks

A kind of hidden terminal problem, called the POINT problem, which is caused by the expansion of the interference range of the receiver due to the controlled transmission power of the sender, is deemed a notorious problem in wireless ad hoc networks. This paper utilizes physical and virtual carrier-sensing schemes to avoid the POINT problem. We analyze the relationships among the transmission range, the carrier-sensing range, and the interference range in case power control is adopted, and based on the analyzed results, we propose four mechanisms to prevent the POINT problem from occurring in wireless ad hoc networks. This paper further analyzes the superiority of each mechanism under certain situations and proposes an adaptive range-based power control (ARPC) MAC protocol to make use of the advantages of the four mechanisms to avoid the POINT problem from happening. The proposed protocol cannot only prevent collisions caused by the POINT problem, but it can also reduce the energy consumption of STAs. Simulation results also verify the advantages of the proposed protocol.

A grid-based dynamic load balancing approach for data-centric storage in wireless sensor networks

In many data-centric storage techniques, each event corresponds to a hashing location by event type. However, most of them fail to deal with storage memory space due to high percentage of the load is assigned to a relatively small portion of the sensor nodes. Hence, these nodes may fail to deal with the storage of the sensor nodes effectively. To solve the problem, we propose a grid-based dynamic load balancing approach for data-centric storage in sensor networks that relies on two schemes: (1) a cover-up scheme to deal with a problem of a storage node whose memory space is depleted. This scheme can adjust the number of storage nodes dynamically; (2) the multi-threshold levels to achieve load balancing in each grid and all nodes get load balancing. Simulations have shown that our scheme can enhance the quality of data and avoid hotspot of the storage while there are a vast number of the events in a sensor network.