Sang Hoon Lee

Bio: Sang Hoon Lee is an academic researcher from Korea University. The author has contributed to research in topics: Wireless sensor network & Network packet. The author has an hindex of 8, co-authored 23 publications receiving 174 citations.

AMAC: Traffic-Adaptive Sensor Network MAC Protocol through Variable Duty-Cycle Operations

Abstract: Sensor network MAC protocols usually employ periodic sleep and wakeup, achieving low duty-cycle to save energy and to increase the lifetime of battery-powered sensor devices. However, existing protocols require all the sensor nodes to operate on the same static schedule, waking up all the nodes at the same fixed interval periodically. This paper proposes a new media access control protocol called AMAC that can achieve significant energy savings by dynamically changing the schedule of each node depending on the traffic. In AMAC, each node can adjust the duration of the periodic interval as well as the duration of the active period depending on the traffic. Thus, busy nodes can operate with a high duty-cycle while idle nodes can operate with a low duty-cycle at the same time, achieving both low-energy and high-performance. The results of our detailed simulations confirm that AMAC can reduce the average energy consumption by a factor of up to 6.8 compared to an existing fixed duty-cycle MAC protocol while it can also improve the network performance for burst traffic patterns.

SPEED-MAC: speedy and energy efficient data delivery MAC protocol for real-time sensor network applications

Abstract: Although existing wakeup scheduling techniques suggest end-to-end delay guarantees for real-time applications, their fixed wakeup schedules may not meet such constraints when multiple sensors compete for the event delivery at the same time. In this paper we propose a new MAC protocol called SPEED-MAC that can provide real-time delay guarantees with much lower energy consumption for both single-source and multi-source events. The main ideas underlying the protocol are twofold. First, we introduce a novel wakeup technique called signaling wakeup, which is small only enough to detect the event occurrence. By employing the signaling wakeup we can minimize the event report latency as well as the idle listening. Second, to resolve the collisions and contentions incurred by multi-source events, the protocol employs adaptive wakeup that combines static scheduling with contention-based media access control depending on the type of traffic. The result of our analytic evaluation confirms that SPEED-MAC can provide real-time delay guarantees even for a large-scale network assuming a low event rate. We have implemented SPEED-MAC on both NS-2 and MICA2 platforms, and evaluated both the energy and the network performance of the protocol for various scenarios including multi-source, multi-sink, source-to-sink, sink-to-source, multi-cast and broadcast traffic. Our experimentation results show that SPEED-MAC can achieve an order of magnitude energy savings while providing near optimal latency compared to the existing solutions.

SPEED-MAC: Speedy and Energy Efficient Data Delivery MAC Protocol for Real-Time Sensor Network Applications

Abstract: In this paper we consider the design of MAC protocol for real-time sensor network applications. Although existing wakeup scheduling techniques suggest end-to-end delay guarantees for such applications, their fixed wakeup schedules may not meet such constraints when multiple sensors compete for the event delivery at the same time. We propose a new MAC protocol called SPEED-MAC that can provide real-time delay guarantees with much lower energy consumption for both single-source and multi-source events. The main ideas underlying the protocol are two-fold. First, we introduce a novel wakeup technique called signaling wakeup period, which is small enough to detect collisions and contentions. By employing the signaling wakeup we can minimize the event report latency as well as the idle listening. Second, to resolve the collisions and contentions incurred by multi-source events, the protocol employs adaptive wakeups that combines static scheduling with contention-based media access control depending on the type of traffic. Our simulation results show that SPEED-MAC can achieve an order of magnitude energy savings while providing near optimal latency compared to the existing solutions.

Chaining Clock Synchronization: An Energy-Efficient Clock Synchronization Scheme for Wireless Sensor Networks

Abstract: Since WSNs have restricted energy sources, the energy efficiency of a synchronization scheme is as important as the accuracy of a clock. To accomplish both the energy efficiency and the accuracy, we propose a new clock synchronization scheme called Chaining Clock Synchronization (CCS). In CCS, a subset of nodes whose transmission range cover the overall network carries out a two-way message exchange algorithm while the remaining nodes synchronize themselves by overhearing the messages. To reduce the energy consumption associated with the message exchange, CCS integrates a clock request and a clock reply into a single message. Therefore, CCS requires only a single message transmission per node for the synchronization. To increase the accuracy of the clock synchronization, we also propose a new technique called clock skew propagation to reduce the error accumulation associated with multi-hop clock synchronization schemes. According to the results from NS-2, in comparison with TPSN, CCS can effectively reduce the energy consumption by up to 95% while sacrificing 9.2% of the average accuracy of clocks. Moreover, the average clock error accumulation of CCS is reduced by 58% as the hop distance from a reference node increases.

M-MAC: Mobility-Based Link Management Protocol for Mobile Sensor Networks

Abstract: In wireless sensor networks with mobile sensors, frequent link failures caused by node mobility generate wasteful retransmissions, resulting in increased energy consumption and decreased network performance. In this paper we propose a new link management protocol called M-MAC that can dynamically measure and predict the link quality. Based on the projected link status information each node may drop, relay, or selectively forward a packet, avoiding unnecessary retransmissions. Our simulation results show that M-MAC can effectively reduce the per-node energy consumption by as much as 25.8% while improving the network performance compared to a traditional sensor network MAC protocol in the case of both low and high mobility scenarios.

Survey and Taxonomy of Duty Cycling Mechanisms in Wireless Sensor Networks

Abstract: Motivated by stringent power constraints, duty cycling - the practice of turning a mote's radio on and off to conserve energy - has become a fundamental mechanism in the design of Wireless Sensor Networks. Because of its importance, a variety of approaches to duty cycling have emerged during the last decade and are being now proposed with increasingly ambitious goals, such as achieving ultra low duty cycles as low as 0.1%. Such propositions differ mostly in their reliance on nodes' synchronization, which, in turn, translates into different hardware requirements and implementation complexity. However, duty cycling may also differ in other aspects as topology dependency, network density requirements and increase in end-to-end delay. This paper organizes the most important proposals into a taxonomy and provides insights into their strengths and weaknesses in relation to important characteristics of applications, mote's hardware and network deployments.

A Critical Analysis of Research Potential, Challenges, and Future Directives in Industrial Wireless Sensor Networks

Abstract: In recent years, industrial wireless sensor networks (IWSNs) have emerged as an important research theme with applications spanning a wide range of industries including automation, monitoring, process control, feedback systems, and automotive. Wide scope of IWSNs applications ranging from small production units, large oil and gas industries to nuclear fission control, enables a fast-paced research in this field. Though IWSNs offer advantages of low cost, flexibility, scalability, self-healing, easy deployment, and reformation, yet they pose certain limitations on available potential and introduce challenges on multiple fronts due to their susceptibility to highly complex and uncertain industrial environments. In this paper, a detailed discussion on design objectives, challenges, and solutions, for IWSNs, are presented. A careful evaluation of industrial systems, deadlines, and possible hazards in industrial atmosphere are discussed. This paper also presents a thorough review of the existing standards and industrial protocols and gives a critical evaluation of potential of these standards and protocols along with a detailed discussion on available hardware platforms, specific industrial energy harvesting techniques and their capabilities. This paper lists main service providers for IWSNs solutions and gives insight of future trends and research gaps in the field of IWSNs.

A Simple Improved Distributed Algorithm for Minimum CDS in Unit Disk Graphs

Abstract: Several routing schemes in ad hoc networks first establish a virtual backbone and then route messages via back-bone nodes. One common way of constructing such a backbone is based on the construction of a minimum connected dominating set (CDS). In this paper we present a very simple distributed algorithm for computing a small CDS. Our algorithm has an approximation factor of at most 6.91, improving upon the previous best known approximation factor of 8 due to Wan et al. [INFOCOM'02], The improvement relies on a refined analysis of the relationship between the size of a maximal independent set and a minimum CDS in a unit disk graph. This subresult also implies improved approximation factors for many existing algorithm.

High-Reliability and Low-Latency Wireless Communication for Internet of Things: Challenges, Fundamentals, and Enabling Technologies

Abstract: As one of the key enabling technologies of emerging smart societies and industries (i.e., industry 4.0), the Internet of Things (IoT) has evolved significantly in both technologies and applications. It is estimated that more than 25 billion devices will be connected by wireless IoT networks by 2020. In addition to ubiquitous connectivity, many envisioned applications of IoT, such as industrial automation, vehicle-to-everything (V2X) networks, smart grids, and remote surgery, will have stringent transmission latency and reliability requirements, which may not be supported by existing systems. Thus, there is an urgent need for rethinking the entire communication protocol stack for wireless IoT networks. In this tutorial paper, we review the various application scenarios, fundamental performance limits, and potential technical solutions for high-reliability and low-latency (HRLL) wireless IoT networks. We discuss physical, MAC (medium access control), and network layers of wireless IoT networks, which all have significant impacts on latency and reliability. For the physical layer, we discuss the fundamental information-theoretic limits for HRLL communications, and then we also introduce a frame structure and preamble design for HRLL communications. Then practical channel codes with finite block length are reviewed. For the MAC layer, we first discuss optimized spectrum and power resource management schemes and then recently proposed grant-free schemes are discussed. For the network layer, we discuss the optimized network structure (traffic dispersion and network densification), the optimal traffic allocation schemes and network coding schemes to minimize latency.