Thang Le Duc

Level-based approach for minimum-transmission broadcast in duty-cycled wireless sensor networks

Broadcast is a fundamental activity in wireless sensor networks (WSNs) and many problems related to broadcast have been formulated and investigated in the literature. Among them, the minimum-transmission broadcast (MTB) problem, which aims to reduce broadcast redundancy, has been well studied in conventional wireless ad hoc networks, where network nodes are assumed to be active all the time. In this paper, we study the MTB problem in duty-cycled WSNs where sensor nodes operate under active/dormant cycle and propose a novel scheme to solve it efficiently. The proposed Level-Based Approximation Scheme first identifies the forwarding nodes and their corresponding receivers for all time slots; then constructs a broadcast backbone by connecting these forwarding nodes to the broadcast source. The backbone construction is accomplished by a two-stage traversal on all the forwarding nodes, which successfully exploits transmissions of each forwarding node to its receivers. We have also conducted extensive simulations to evaluate the performance of our proposed scheme. Simulation results indicate that our scheme significantly outperforms existing ones. The algorithm of finding covering nodes helps to reduce a number of transmissions.The concept of duty-transmission highlights the advantage of our scheme.Level-based traversal on covering nodes reduces a number of transmissions and the time complexity.Examining the impact of network density and duty cycle shows the advantage of our scheme.The trade-off between number of broadcast transmissions and broadcast delay is also disclosed.

LABS: Latency aware broadcast scheduling in uncoordinated Duty-Cycled Wireless Sensor Networks

Abstract Broadcast is a fundamental operation in Wireless Sensor Networks (WSNs) and plays an important role in a communication protocol design. In duty-cycled scenarios, a sensor node can receive a message only in its active time slot, which makes it more difficult to design collision-free scheduling for broadcast operations. Recent studies in this area have focused on minimizing broadcast latency and guaranteeing that all nodes receive a broadcast message. This paper investigates the problem of Minimum Latency Broadcast Scheduling in Duty-Cycled (MLBSDC) WSNs. By using special geometric properties of independent sets of a broadcast tree, we reduce the number of transmissions, consequently reducing the possibility of collision. Allowing multiple transmissions in one working period, our proposed Latency Aware Broadcast Scheduling (LABS) scheme provides a latency-efficient broadcast schedule. Theoretical analysis proves that the scheme has the same approximation ratio and complexity as the previous best algorithm for the MLBSDC problem. Moreover, simulation shows that the new scheme achieves up to 34%, 37%, and 21% performance improvement over previous schemes, in terms of latency, number of transmissions, and energy consumption, respectively.

Collision-tolerant broadcast scheduling in duty-cycled wireless sensor networks

The minimum-latency broadcast problem in duty-cycled wireless sensor networks has received significant attention over the last few years. A common approach for the problem is to assign collision-free transmitting times to forwarding nodes for disseminating a message from one source node to all other nodes according to their given duty-cycle schedules and transmission ranges. However, preventing collision for all transmissions may increase latency in the broadcast schedules. This paper proposes a novel strategy of Collision-Tolerant Scheduling (CTS) that offers an opportunity to reduce broadcast latency by allowing collisions at non-critical nodes to speed up the broadcast process for critical ones. The completion of broadcast scheduling, i.e. all nodes receive a broadcast message, is ensured by additionally transmitting the message to non-critical nodes experiencing collision. We employ the scheduling strategy in two proposed broadcast schemes: Degree-based CTS (DCTS) and MIS-based CTS (MCTS), which select forwarding nodes based on the node degree and maximal independent set information, respectively. The results of both theoretical analysis and simulation reveal the remarkable advantages of CTS in minimizing broadcast latency in duty-cycled WSNs. DCTS and MCTS guarantee approximation ratios of (1)T and 12T in terms of broadcast latency, where and T denote the maximum node degree and the number of time slots in a working period, respectively. The two schemes reduce to at least 94 percent of the broadcast latency compared with existing schemes, while slightly increasing the number of transmissions due to the additional transmissions. Thanks to the latency reduction, the proposed schemes require 93 percent less energy than existing ones. A novel scheduling strategy for broadcast latency minimization in duty-cycled WSNs.Allowing collisions at non-critical nodes to speed up the broadcast process.The completion of broadcast scheduling is ensured by additional transmissions.Achieving significant improvement in both theoretical and simulation results.

Towards broadcast redundancy minimization in duty-cycled wireless sensor networks

Summary Broadcast is an essential operation in wireless sensor networks. Because of the necessity of energy conservation, minimizing the number of transmissions is always a challenging issue in broadcasting scheme design. This paper studies the minimum-transmission broadcast problem in duty-cycled wireless sensor networks where each sensor operates under active/dormant cycles. To address the problem, our proposed scheme, Broadcast Redundancy Minimization Scheduling (BRMS), finds a set of forwarding nodes, which minimizes the number of broadcast transmissions. Then, it constructs a forest of sub-trees based on the relationship between each forwarding node and its corresponding receivers. A broadcast tree is constructed ultimately by connecting all sub-trees with a minimum number of connectors. Theoretical analysis shows that BRMS obtains a lower approximation ratio as well as time complexity compared with existing schemes. A set of extensive simulations is conducted to evaluate the performance of BRMS. The results reveal that BRMS outperforms others and its solution is close to the lower bound of the problem in terms of the total number of transmissions. Copyright

On minimizing the broadcast redundancy in duty-cycled wireless sensor networks

Broadcast is a fundamental activity in wireless sensor networks (WSNs) and many problems related to broadcast thus have been formulated and investigated in the literature. Among them, the minimum-transmission broadcast (MTB) problem, which aims to reduce the broadcast redundancy, has been well studied in conventional wireless ad hoc networks, where network nodes are assumed to be active all the time. In this paper, we study MTB problem in duty-cycled WSNs (MTB-DC problem) where sensor nodes operate under active/dormant cycles; then propose a novel scheme to solve it. The proposed Level-Based Approximation Scheme (LBAS) first identifies the minimum sets of forwarding nodes for all time slots. Then the broadcast backbone is constructed efficiently through a two-stage traversal which completely exploits duty transmission of forwarding nodes when connecting them to the broadcast source. We have also conducted extensive simulations to evaluate the performance of our proposed scheme. The results indicate that our scheme outperforms existing ones significantly.

A Distributed Scheme for Broadcast Scheduling in Duty-cycled Wireless Sensor Networks

The paper investigates the minimum-transmission broadcast problem in duty-cycled wireless sensor networks in which each sensor node alternates between active and sleeping modes during its lifetime for energy saving. We propose a scheme, Distributed Broadcast Scheduling (DiBS), to construct a broadcast backbone together with a broadcast schedule for each backbone node such that a broadcast message is disseminated to all other nodes in the network with a minimum number of transmissions. The minimization of the total number of transmissions is achieved thanks to two factors. First, the nature of wireless communications enables a sender to distribute the message to multiple nodes with a single transmission. Second, DiBS exploits such a single transmission in constructing the broadcast backbone. A set of extensive simulations is conducted to show the performance of DiBS as well as its improvement over existing ones in terms of total number of transmissions.

Delay-sensitive flooding based on expected path quality in low duty-cycled wireless sensor networks

Flooding in low duty-cycled wireless sensor networks suffers from a large transmission delay because a sender has to wait until a receiver becomes active to forward a packet. With the presence of unreliable radio links, the delay performance is even more severely degraded. In this article, we aim to reduce the flooding delay in low duty-cycled wireless sensor networks in relation to link unreliability. The key idea is to build a delay-sensitive flooding tree in which a node receives packet through the shortest path in terms of the total expected number of transmissions. In addition, the algorithm allows multiple senders to send through links outside of the tree if they can provide earlier expected delivery time. To give priorities to potential senders, we employ an energy-balancing mechanism which dynamically distributes the sending role among them. The mechanism not only makes sure senders start to acquire the channel at different times to prevent collisions but also lets them alternatively take turns based on residual energy, in order to lengthen network lifetime. Compared with the best known schemes, the proposed algorithm achieves up to 8% improvement in terms of flooding delay, energy consumption, and network lifetime.

Restructuring binomial trees for delay-aware and energy-efficient data aggregation in wireless sensor networks

Energy conservation is a fundamental problem in wireless sensor networks that has attracted a great attention in recent years, as each sensor node is battery powered. In this paper, we consider an excessive energy consumption scenario like data transmission between sensor node and far off destination, and present distributed control data aggregation and energy efficiency scheme. Our scheme maintains the strengths of existing algorithms like Restructuring Binomial Trees (RBT) scheme and improves the energy conservation performance in wireless sensor networks. When a node is inserted or deleted in the network, tree rotations are used in a number of tree data structures such as AVL trees and red-black trees. These trees keep the tree balanced by using the rotation method that does not affect the surrounding. The proposed scheme utilizes the rotation mechanism for rebuilding a binomial tree, in which the sensor nodes swap the role partly and then reduce tree cost while keeping the tree structure. Swapping is performed between the parent and child nodes. The proposed scheme maintains the minimum data aggregation delay and increases the energy efficiency of the sensor nodes. Simulation results show that, the cost of building trees by DADC and DEDA is decreased by 45.84% and 14.28% on average respectively, by using the proposed scheme.

A distributed lifetime-maximizing scheme for connected target coverage in WSNs

In this paper, we consider the problem of scheduling sensor activity to prolong the network lifetime while guaranteeing both discrete target coverage and connectivity among all the active sensors and the sink, called connected target coverage (CTC) problem. We proposed a distributed scheme called Distributed Lifetime-Maximizing Scheme (DLMS) to solve the CTC problem. In our proposed scheme, at first the source nodes are selected to ensure the target coverage. After that, energy-efficient paths to transmit the sensory data from source nodes to the sink will be built. The cost of the construction of the connected cover graphs is significantly reduced in comparison with the some conventional schemes since the number of targets (i.e., the necessary number of source nodes) is much smaller than the number of sensor nodes in the practical environment. In addition, the energy consumption is more balanced so that the network lifetime will be increased. Our simulation results show that DLMS scheme performs much better than the conventional schemes in terms of the network lifetime.

Critical-Path Aware Scheduling for Latency Efficient Broadcast in Duty-Cycled Wireless Sensor Networks

Minimum latency scheduling has arisen as one of the most crucial problems for broadcasting in duty-cycled Wireless Sensor Networks (WSNs). Typical solutions for the broadcast scheduling iteratively search for nodes able to transmit a message simultaneously. Other nodes are prevented from transmissions to ensure that there is no collision in a network. Such collision-preventions result in extra delays for a broadcast and may increase overall latency if the delays occur along critical paths of the network. To facilitate the broadcast latency minimization, we propose a novel approach, critical-path aware scheduling (CAS), which schedules transmissions with a preference of nodes in critical paths of a duty-cycled WSN. This paper presents two schemes employing CAS which produce collision-free and collision-tolerant broadcast schedules, respectively. The collision-free CAS scheme guarantees an approximation ratio of in terms of latency, where denotes the maximum node degree in a network. By allowing collision at noncritical nodes, the collision-tolerant CAS scheme reduces up to 10.2 percent broadcast latency compared with the collision-free ones while requiring additional transmissions for the noncritical nodes experiencing collisions. Simulation results show that broadcast latencies of the two proposed schemes are significantly shorter than those of the existing methods.