Ngoc-Tu Nguyen

On maximizing the lifetime for data aggregation in wireless sensor networks using virtual data aggregation trees

Data gathering is a basic requirement in many applications of wireless sensor networks (WSNs). Because the energy of sensors is limited, the data-gathering mechanism must be carefully designed to save the energy consumption of sensors to prolong the network lifetime. Recently, many researchers have studied gathering data efficiently in WSNs to minimize the total energy consumption when a fixed number of data are allowed to be aggregated into one packet. However, when the total energy consumption is minimized, the energy consumption of sensors for data gathering cannot be guaranteed to be balanced, and thus, the network lifetime cannot be guaranteed to be maximized. This motivates us to study the problem of scheduling virtual data aggregation trees to maximize the network lifetime when a fixed number of data are allowed to be aggregated into one packet, termed the Maximum Lifetime Data Aggregation Tree Scheduling (MLDATS) problem. The MLDATS problem is shown to be NP-complete in the paper. In addition, a local-tree-reconstruction-based scheduling algorithm (LTRBSA) is proposed for the MLDATS problem. We use simulations to evaluate and demonstrate the performance of the LTRBSA when the sink has 2-hop, 3-hop, and all information in the networks. Simulation results show that the LTRBSA of using sinks 3-hop information provides comparable performances to that of using all information in the networks, and outperforms other methods proposed in the simulation.

A Maximum-Weight-Independent-Set-Based Algorithm for Reader-Coverage Collision Avoidance Arrangement in RFID Networks

Radio frequency identification (RFID) systems have been widely developed and applied in identification applications. In RFID systems, a tag can be read by a reader when the tag is within the readers interrogation range. Reader deployment has received a great deal of attention for providing a certain service quality. Many studies have addressed deploying/activating readers such that all the tags in a field can be read. However, in a practical environment, tags cannot be read due to collisions. In addition, the number of tags read by a reader is often limited due to the constraints of processing time and link layer protocols. This motivated us to study the problem of activating readers and adjusting their interrogation ranges to cover maximum tags without collisions subject to the limited number of tags read by a reader, termed the reader-coverage collision avoidance arrangement (RCCAA) problem. In this paper, the RCCAA problem is shown to be NP-complete. In addition, an approximation algorithm, termed the maximum-weight-independent-set-based algorithm (MWISBA), is proposed for the RCCAA problem. The simulation results show that the MWISBA provides good performance for the RCCAA problem.

Network Under Limited Mobile Devices: A New Technique for Mobile Charging Scheduling With Multiple Sinks

Recently, many studies have investigated scheduling mobile devices to recharge and collect data from sensors in wireless rechargeable sensor networks (WRSNs) such that the network lifetime is prolonged. In reality, because mobile devices are more powerful and expensive than sensors, the cost of the mobile devices often consumes a high portion of the budget. Due to a limited budget, the number of mobile devices is often limited. Some sensors in WRSNs may not be operated without time limits due to the limited number of mobile devices. Therefore, sensors in a sensing field must be weighted by their importance, that is, the more important an area covered by a sensor, the higher the weight of the sensor. Therefore, in this paper, the problem of scheduling limited mobile devices for energy replenishment and data collection in WRSNs with multiple sinks such that the total weight of the recharged sensors that can be operated without time limits is maximized, termed the periodic energy replenishment and data collection with limited mobile devices (PERDCLMD) problem, is studied. In addition, the greedy scheduling algorithm (GSA) is proposed for the PERDCLMD problem accordingly. Simulation results show that the GSA provides a good performance in terms of the total weight of the recharged sensors.

An efficient algorithm of constructing virtual backbone scheduling for maximizing the lifetime of dual-radio wireless sensor networks

Wireless sensor networks have often been used to monitor environmental conditions, such as temperature, sound, and pressure. Because the sensors are expected to work on batteries for a long time without charging their batteries, the major challenge in the design of wireless sensor networks is to enhance the network lifetime. Recently, many researchers have studied the problem of constructing virtual backbones, which are backbones used for different time periods, to prolong the network lifetime. In this paper, we study the problem of constructing virtual backbones in dual-radio wireless sensor networks to maximize the network lifetime, called the Maximum Lifetime Backbone Scheduling for Dual-Radio Wireless Sensor Network problem, where each sensor is equipped with two radio interfaces. The problem is shown to be NP-complete here. In addition, rather than proposing a centralized algorithm, a distributed algorithm, called a Dominating-Set-Based Algorithm (DSBA), is proposed for a wide range of wireless sensor networks to find a backbone when a new one is required. Simulation results show that the proposed algorithm outperforms some existing algorithms.

Constrained node-weighted Steiner tree based algorithms for constructing a wireless sensor network to cover maximum weighted critical square grids

Deploying minimum sensors to construct a wireless sensor network such that critical areas in a sensing field can be fully covered has received much attention recently. In previous studies, a sensing field is divided into square grids, and the sensors can be deployed only in the center of the grids. However, in reality, it is more practical to deploy sensors in any position in a sensing field. Moreover, the number of sensors may be limited due to a limited budget. This motivates us to study the problem of using limited sensors to construct a wireless sensor network such that the total weight of the covered critical square grids is maximized, termed the weighted-critical-square-grid coverage problem, where the critical grids are weighted by their importance. A reduction, which transforms our problem into a graph problem, termed the constrained node-weighted Steiner tree problem, is proposed and used to solve our problem. In addition, three heuristics, including the greedy algorithm (GA), the group-based algorithm (GBA), and the profit-based algorithm (PBA), are proposed for the constrained node-weighted Steiner tree problem. Simulation results show that the proposed reduction with the PBA provides better performance than the others.

A dynamic-range-based algorithm for reader-tag collision avoidance deployment in RFID networks

Recently, the problem of scheduling readers to read maximum tags such that readers and tags can be avoided collision within a given multiple interrogation ranges of reader has received a great deal of attention in Radio frequency identification (RFID) systems. Many methods have been proposed for the RFID systems such that readers can read maximum tags. However, most of previous works often require lots of readers or exist reader-tag collisions. In this paper, we propose a new algorithm, called the Dynamic-Range-based algorithm (DRBA), to maximize the number of read tags and avoid collisions within the multiple interrogation ranges of readers. Simulation results show that the DRBA has better performance than other existing methods.

A Virtual Backbone Construction Heuristic for Maximizing the Lifetime of Dual-Radio Wireless Sensor Networks

Recently, the major challenge in the design of wireless sensor networks is to enhance the network lifetime. Many researchers have studied the problem of constructing virtual backbones, which are the backbones used for different time periods, in order to prolong the network lifetime. In this paper, we study the problem of constructing virtual backbones in dual-radio wireless sensor networks to maximize the network lifetime, where each sensor is equipped with two radio interfaces, including small-range and large-range radio. In addition, the backbone nodes can use small-range or large-range radio to maintain the backbone, and the remaining nodes use small-range radio to connect to the backbone to transmit the sensed data. Simulation results show that the proposed method provides good performance.

An Efficient Method for Sweep Coverage with Minimum Mobile Sensor

Recently, sweep coverage, which is the problem of scheduling mobile sensors to periodically visit a certain number of points of interests (POIs) such that the number of mobile sensors is minimized and each of POIs can be visited periodically within a given time period, has received a great deal of attention in the wireless sensor networks. Many methods have been proposed for the sweep coverage to minimize the number of employed mobile sensors. In addition, the sweep coverage is shown to be NP-complete. In this paper, we propose a heuristic, called the perpendicular-distance-based algorithm (PDBA), to minimize the number of employed mobile sensors and the total energy consumed by the mobile sensors. Simulation results show that the PDBA has better performance than other existing methods.

An Efficient Minimum-Latency Collision-Free Scheduling Algorithm for Data Aggregation in Wireless Sensor Networks

Data collection is one of the most important operations in applications of wireless sensor networks (WSNs). In many emerging WSN applications, it is urgent to achieve a guarantee for the latency involved in collecting data. Many researchers have studied collecting data in WSNs with minimum latency but without data collision while assuming that any (or no) data are allowed to be aggregated into one packet. In addition, tree structures are often used for solutions. However, in some cases, a fixed number of data are allowed to be aggregated into one packet. This motivates us to study the problem of minimizing the latency for data aggregation without data collision in WSNs when a fixed number of data are allowed to be aggregated into one packet, termed the minimum-latency collision-avoidance multiple-data-aggregation scheduling (MLCAMDAS) problem. The MLCAMDAS problem is shown to be NP-complete here. In addition, a nontree-based method, termed the independent-set-based collision-avoidance scheduling (ISBCAS) algorithm, is proposed accordingly. The ISBCAS is demonstrated via simulations to have good performance.

Network Under Limited Mobile Sensors: New Techniques for Weighted Target Coverage and Sensor Connectivity

In mobile wireless sensor networks (MWSNs), each sensor has the ability not only to sense and transmit data but also to move to some specific location. Because the movement of sensors consumes much more power than that in sensing and communication, the problem of scheduling mobile sensors to cover all targets and maintain network connectivity such that the total movement distance of mobile sensors is minimized has received a great deal of attention. However, in reality, due to a limited budget or numerous targets, mobile sensors may be not enough to cover all targets or form a connected network. Therefore, targets must be weighted by their importance. The more important a target, the higher the weight of the target. A more general problem for target coverage and network connectivity, termed the Maximum Weighted Target Coverage and Sensor Connectivity with Limited Mobile Sensors (MWTCSCLMS) problem, is studied. In this paper, an approximation algorithm, termed the weighted-maximum-coverage-based algorithm (WMCBA), is proposed for the subproblem of the MWTCSCLMS problem. Based on the WMCBA, the Steiner-tree-based algorithm (STBA) is proposed for the MWTCSCLMS problem. Simulation results demonstrate that the STBA provides better performance than the other methods.