Junchao Ma

Energy Efficient TDMA Sleep Scheduling in Wireless Sensor Networks

Sleep scheduling is a widely used mechanism in wireless sensor networks (WSNs) to reduce the energy consumption since it can save the energy wastage caused by the idle listening state. In a traditional sleep scheduling, however, sensors have to start up numerous times in a period, and thus consume extra energy due to the state transitions. The objective of this paper is to design an energy efficient sleep scheduling for low data-rate WSNs, where sensors not only consume different amounts of energy in different states (transmit, receive, idle and sleep), but also consume energy for state transitions. We use TDMA as the MAC layer protocol, because it has the advantages of avoiding collisions, idle listening and overhearing. We first propose a novel interference-free TDMA sleep scheduling problem called contiguous link scheduling, which assigns sensors with consecutive time slots to reduce the frequency of state transitions. To tackle this problem, we then present efficient centralized and distributed algorithms that use time slots at most a constant factor of the optimum. The simulation studies corroborate the theoretical results, and show the efficiency of our proposed algorithms.

Minimum Latency Broadcast Scheduling in Duty-Cycled Multihop Wireless Networks

Broadcast is an essential and widely used operation in multihop wireless networks. Minimum latency broadcast scheduling (MLBS) aims to find a collision-free scheduling for broadcast with the minimum latency. Previous work on MLBS mostly assumes that nodes are always active, and, thus, is not suitable for duty-cycled scenarios. In this paper, we investigate the MLBS problem in duty cycled multihop wireless networks (MLBSDC problem). We prove both the one-to-all and the all-to-all MLBSDC problems to be NP hard. We propose a novel approximation algorithm called OTAB for the one-to-all MLBSDC problem, and two approximation algorithms called UTB and UNB for the all-to-all MLBSDC problem under the unit-size and the unbounded-size message models, respectively. The approximation ratios of the OTAB, UTB, and UNB algorithms are at most 17|T|, 17|T| + 20, and (Δ + 22)|T|, respectively, where |T| denotes the number of time slots in a scheduling period, and Δ denotes the maximum node degree of the network. The overhead of our algorithms is at most constant times as large as the minimum overhead in terms of the total number of transmissions. We also devise a method called Prune to further reduce the overhead of our algorithms. Extensive simulations are conducted to evaluate the performance of our algorithms.

A novel mobility management scheme for target tracking in cluster-based sensor networks

Target tracking is a typical and important application of wireless sensor networks (WSNs). In the consideration of scalability and energy efficiency for target tracking in large scale WSNs, it has been employed as an effective solution by organizing the WSNs into clusters. However, tracking a moving target in cluster-based WSNs suffers the boundary problem when the target moves across or along the boundary among clusters. In this paper, we propose a novel scheme, called hybrid cluster-based target tracking (HCTT), which integrates on-demand dynamic clustering into a cluster-based WSN for target tracking. To overcome the boundary problem, when the target moves close to the boundary among clusters, a dynamic cluster will be constructed for the management of target tracking. As the target moves, static clusters and on-demand dynamic clusters alternately manage the tracking task. Simulation results show that the proposed scheme performs better in tracking the moving target when compared with other typical target tracking protocols.

A Hybrid Cluster-Based Target Tracking Protocol for Wireless Sensor Networks

Target tracking is a typical and important application of wireless sensor networks (WSNs). In consideration of the network scalability and energy efficiency for target tracking in large-scale WSNs, it has been employed as an effective solution by organizing the WSNs into clusters. However, tracking a moving target in cluster-based WSNs suffers a boundary problem when the target moves across or along the boundaries of clusters, as the static cluster membership prevents sensors in different clusters from sharing information. In this paper, we propose a novel mobility management protocol, called hybrid cluster-based target tracking (HCTT), which integrates on-demand dynamic clustering into a cluster-based WSN for target tracking. By constructing on-demand dynamic clusters at boundary regions, nodes from different static clusters that detect the target can temporarily share information, and the tracking task can be handed over smoothly from one static cluster to another. As the target moves, static clusters and on-demand dynamic clusters alternately manage the target tracking task. Simulation results show that the proposed protocol performs better in tracking the moving target when compared with other typical target tracking protocols.

Duty-Cycle-Aware Minimum Latency Broadcast Scheduling in Multi-hop Wireless Networks

Broadcast is an essential and widely-used operation in multi-hop wireless networks. Minimum latency broadcast scheduling (MLBS) aims to provide a collision-free scheduling for broadcast with the minimum latency. Previous work on MLBS mostly assumes that nodes are always active, and thus is not suitable for duty-cycle-aware scenarios. In this paper, we investigate the duty-cycle-aware minimum latency broadcast scheduling (DCA-MLBS) problem in multi-hop wireless networks. We prove both the one-to-all and the all-to-all DCA-MLBS problems to be NP-hard. We propose a novel approximation algorithm called OTAB for the one-to-all DCA-MLBS problem, and two approximation algorithms called UTB and UNB for the all-to-all DCA-MLBS problem under the unit-size and the unbounded-size message models respectively. The OTAB algorithm achieves a constant approximation ratio of 17|T|, where |T| denotes the number of time-slots in a scheduling period. The UTB and UNB algorithms achieve the approximation ratios of 17|T|+20 and (Δ+22)|T| respectively, where Δ denotes the maximum node degree of the network. Extensive simulations are conducted to evaluate the performance of our algorithms.

Interference-aware spatio-temporal link scheduling for long delay underwater sensor networks

In underwater sensor networks (UWSNs), acoustic communication is commonly used unlike that in terrestrial wireless networks. The long propagation delay of acoustic signals causes spatio-temporal uncertainty, which makes the link scheduling in UWSNs a challenging problem. To describe the propagation delays of the transmission links and deal with the spatio-temporal uncertainty, we construct a so called slotted spatio-temporal conflict graph. We propose efficient scheduling algorithms with constant approximation ratios to the optimum solutions. We consider both unified and weighted traffic load scenarios when designing the scheduling algorithms. In the weighted traffic load scenario, we consider the scheduling with and without the consecutive constraint. Simulations validate our theoretical results, and show the efficiency of our proposed algorithms.

TSCD: A Novel Secure Localization Approach for Wireless Sensor Networks

Recent advances in wireless networking technologies, along with ubiquitous sensing and computing, have brought significant convenience for location service. The localization issue in wireless sensor networks under the non-adversarial scenario has already been well studied. However, most existing localization schemes cannot provide satisfied location service under the adversarial scenario. In this paper, we propose an attack-resistant localization scheme, called TSCD secure localization, to overcome the distance-consistent spoofing attack in wireless sensor networks. The main idea of the TSCD scheme is to firstly apply the temporal and spatial properties of locators to detect some attacked locators, and then utilize the consistent property of the detected attacked locators to find out other attacked locators. An enhanced TSCD scheme is also presented and analyzed. Simulation results demonstrate that both proposed schemes achieve better performance than existing approaches under the same network parameters.

On interference-aware gossiping in uncoordinated duty-cycled multi-hop wireless networks

Gossiping, which broadcasts the message of every node to all the other nodes, is an important operation in multi-hop wireless networks. Interference-aware gossiping scheduling (IAGS) aims to find an interference-free scheduling for gossiping with the minimum latency. Previous work on IAGS mostly assumes that nodes are always active, and thus is not suitable for duty-cycled scenarios. In this paper, we investigate the IAGS problem in uncoordinated duty-cycled multi-hop wireless networks (IAGS-UDC problem) under protocol interference model and unbounded-size message model. We prove that the IAGS-UDC problem is NP-hard. We propose two novel algorithms, called MILD and MILD-R, for this problem with an approximation ratio of at most 3@b^2(@D+6)|T|, where @b is 23(@a+2), @a denotes the ratio of the interference radius to the transmission radius, @D denotes the maximum node degree of the network, and |T| denotes the number of time slots in a scheduling period. The total numbers of transmissions scheduled by both two algorithms are at most three times as large as the minimum total number of transmissions. Extensive simulations are conducted to evaluate the performance of our algorithms.

Interference-aware gossiping scheduling in uncoordinated duty-cycled multi-hop wireless networks

Gossiping is to broadcast the message of every node to all the other nodes in multi-hop wireless networks (MWNs). This operation plays an important role and is widely used in MWNs. Interference-aware gossiping scheduling (IAGS) aims to provide an interference-free scheduling for gossiping with the minimum latency. Previous work on IAGS mostly assumes that nodes are always active, and thus is not suitable for duty-cycled scenarios. In this paper, we investigate the IAGS problem in uncoordinated duty-cycled multi-hop wireless networks (IAGS-UDC problem) under protocol interference model and unbounded-size message model. We prove that the IAGS-UDC problem is NP-hard. We propose a novel approximation algorithm called MILD for this problem. The MILD algorithm achieves an approximation ratio of 3β2(Δ + 6)|T|, where β is ⌈2/3(α + 2)⌉,α denotes the ratio of the interference radius to the transmission radius, Δ denotes the maximum node degree of the network, and |T| denotes the number of time-slots in a scheduling period. Moreover, the number of transmissions scheduled by the MILD algorithm is at most 3 times as large as the minimum number of transmissions.

Interference-Free Wakeup Scheduling with Consecutive Constraints in Wireless Sensor Networks

Wakeup scheduling has been widely used in wireless sensor networks (WSNs), for it can reduce the energy wastage caused by the idle listening state. In a traditional wakeup scheduling, sensor nodes start up numerous times in a period, thus consuming extra energy due to state transitions (e.g., from the sleep state to the active state). In this paper, we address a novel interference-free wakeup scheduling problem called compact wakeup scheduling, in which a node needs to wake up only once to communicate bidirectionally with all its neighbors. However, not all communication graphs have valid compact wakeup schedulings, and it is NP-complete to decide whether a valid compact wakeup scheduling exists for an arbitrary graph. In particular, tree and grid topologies, which are commonly used in WSNs, have valid compact wakeup schedulings. We propose polynomial-time algorithms using the optimum number of time slots in a period for trees and grid graphs. Simulations further validate our theoretical results.