Haeyong Kim

Optimal multi-sink positioning and energy-efficient routing in wireless sensor networks

In wireless sensor networks, the sensors collect data and deliver it to a sink node. Most of the existing proposals deal with the traffic flow problem to deliver data to the sink node in an energy-efficient manner. In this paper, we extend this problem into a multi-sink case. To maximize network lifetime and to ensure fairness, we propose (i) how to position multiple sink nodes in a sensor network and (ii) how to route traffic flow from all of the sensors to these multiple sink nodes. Both of the problems are formulated by the linear programming model to find optimal locations of the multiple sink nodes and the optimal traffic flow rate of routing paths in wireless sensor networks. The improved lifetime and fairness of our scheme are compared with those of the multi-sink aware minimum depth tree scheme.

A Dynamic GTS Allocation Algorithm in IEEE 802.15.4 for QoS guaranteed Real-time Applications

In this paper, we propose a novel QoS guaranteed algorithm for real-time applications in IEEE 802.15.4 protocol. The IEEE 802.15.4 standard provides a Guaranteed Time Slot (GTS) mechanism to allocate a specific duration within a superframe structure for time-critical transmissions. However, there are many weak points to support real-time applications. We suggest a new slot allocation algorithm that enables guaranteed services to be more efficient. The proposed algorithm also allocates a new guaranteed time slot dynamically to support real-time applications which have periodic messages. We evaluate the delay bounds and the throughput of the proposed scheme compared with original protocol. We then show that our proposal improves the bandwidth utilization and guarantees real-time features more strictly.

Multiple Sink Positioning and Routing to Maximize the Lifetime of Sensor Networks

In wireless sensor networks, the sensor nodes collect data, which are routed to a sink node. Most of the existing proposals address the routing problem to maximize network lifetime in the case of a single sink node. In this paper, we extend this problem into the case of multiple sink nodes. To maximize network lifetime, we consider the two problems: (i) how to position multiple sink nodes in the area, and (ii) how to route traffic flows from sensor nodes to sink nodes. In this paper, the solutions to these problems are formulated into a Mixed Integer Linear Programming (MILP) model. However, it is computationally difficult to solve the MILP formulation as the size of sensor network grows because MILP is NP-hard. Thus, we propose a heuristic algorithm, which produces a solution in polynomial time. From our experiments, we found out that the proposed heuristic algorithm provides a near-optimal solution for maximizing network lifetime in dense sensor networks.

DAP: Dynamic Address Assignment Protocol in Mobile Ad-hoc Networks

In general IP networks, addresses can be assigned to hosts manually by a network administrator or automatically by a DHCP server. Mobile ad-hoc network (MANET), which is a self-configuring network, is the union of mobile hosts that form an arbitrary topology. Most research related to the MANET assumes that hosts IP address is configured, prior to the node joining the MANET. However, it is impossible that a network administrator or DHCP server configures host IP addresses in MANETs because there is no infra-structure. For this reason, a dynamic address management protocol is essential in MANETs. Thus, this paper proposes a novel self-configuring address management protocol, referred to as DAP (distributed address pool), in which IP addresses can be dynamically allocated to a newly-joined host in MANETs with no network infra-structure. In DAP, every host in a MANET has a unique IP address pool (a set of unused addresses that will be used for new joined hosts in MANETs) and address assignments are performed locally in the host. The advantage of this method is that it does not generate any broadcasting messages and, in turn, address allocation time can be significantly reduced. From our simulations, DAP showed a superior performance to a random address allocation scheme (RADA) in terms of both address allocation time and message exchange overhead.

Secure multimedia transmission in IPv6 wireless networks

Security is very important during transmission of data in wireless networks. Bit errors frequently occur in wireless networks, which consequently create critical data losses as encrypted data is decrypted. The relation between bit errors and serviced quality after decryption about several encryption algorithms supported by IPv6 was researched. RC4 shows a higher PSNR than DES in CBC mode and AES in CBC mode when JPEG and MPEG multimedia data is transmitted.

NanoMon: An Adaptable Sensor Network Monitoring Software

In this paper, we present a sensor network monitoring software, named NanoMon, which has a flexible architecture and supports for various user requirements of sensor network applications in an adaptive manner. With NanoMon, users can specify custom GUI plug-ins and internal module parameters by using a simply describable configuration file; and it can be automatically integrated to NanoMon framework to support user-specific sensor network applications. NanoMon employs a widely used database MySQL, to concurrently and correctly manage sensing data and node information of several types of sensor network applications. To show flexibility and adaptability of NanoMon, we implemented two WSN applications- home monitoring and parking lot monitoring systems. By selecting a WSN application name specified in the configuration file, users can easily and dynamically change GUI and internal module parameters such as sensor types and database locations of NanoMon used to display the status of WSN.

A flexible, high-precise time synchronization for multi-hop sensor networks

In recent years, time synchronization in wireless sensor networks (WSN) is important for accurate time stamping of events and fine-tuned coordination of duty cycles to minimize power consumption. This paper presents an on-demand hierarchical mesh-based time synchronization (OHMTS) that is flexible, multi-hop based and high-precise in WSN. OHMTS adopts hierarchical and multi-hop mesh-based network architecture with supporting energy-saving problem for WSN. For the purpose of performance evaluation, we first study the error sources of OHMTS and then we evaluate the performance of OHMTS with respect to synchronization delay error using network simulator (NS-2). The simulation results show that OHMTS provides fine-tuned clock offset mechanism and can be easily applied to real WSN platform

A Dynamic Stack Allocating Method in Multi-Threaded Operating Systems for Wireless Sensor Network Platforms

Typical sensor nodes have a small amount of memory with 2-10 KB and even no hardware devices for memory protection such as MMU. Consider multi-threaded sensor applications running on such a memory-constrained hardware platform. In most sensor operating systems, it is assumed that thread stacks are statically allocated. However, this static allocation is not appropriate for memory constrained sensor hardware because shortage of stack memory space can bring in the stack overflow problem. As an alternative method, this paper proposes a dynamic stack allocating method, which enables to adaptively adjust the stack size of each threads based on the stack usage information. The information of the stack usage is obtained by measurement at run-time. The proposed method also defines a stack reallocating problem and solves it in n steps, where n is the number of thread stacks. Our experimental results showed that the proposed method significantly minimizes the waste of thread stack memory space compared to the static stack allocating method.

Design of large scale network simulator using device emulator for Internet of Things

The term “Internet of Things” (IoT) denotes the interconnected of embedded devices designed to leverage data gathered by sensors. These devices are interconnected to transmit information and control instruction via the internet infrastructure. The development of an IoT system is a complex process due to the large scale and widely distribution of deployed wireless node. The simulator provides infrastructure to easily test and debug the algorithms of the IoT applications before they are to be deployed in actual environment. In this paper, we propose the emulation based network simulator architecture which focus on the large scale IoT system. With the proposed simulator architecture, the IoT application developers can reduce cost by cutting the amount of nodes needed for application test and shortens development time required for deploying a large scale IoT system.

An industrial IoT MAC protocol based on IEEE 802.15.4e TSCH for a large-scale network

IEEE 802.15.4e TSCH MAC is widely used for the industrial market, which require ultra-high reliability and ultra-low power. However, the significance of the TSCH is missing, which is a management function to build and maintain the communication schedule. We address several limitations for Ipv6 over IEEE 802.15.4e TSCH in a large-scale network and propose an enhanced scheme which deals with the configuration of Slotframes, Linkset slots, EB(Enhanced Beacon) management and scheduling information. It supports a dynamic schedule management based on observed resource usage, which achieves industrial-grade performance in terms of jitter, latency, scalability, reliability and low-power consumption.