Pyeongsoo Mah

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.

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.

RNIndoor: A relay node deployment method for disconnected wireless sensor networks in indoor environments

In a 2D indoor environment, finding the proper location of relay nodes for wireless sensor networks is a difficult and time consuming job because walls, rooms and restricted areas can prevent the placement of nodes. Moreover, the number of relay nodes is an important factor. Too many relay nodes may increase installation cost and communication delays as well as spoil the beauty of the insides of buildings. In this paper, we present a heuristic relay node deployment method for indoor wireless sensor networks (RNIndoor). The method places as few additional relay nodes as possible to provide at least one path among the deployed nodes in a floor using structural information of the floor (indoor environment) and path loss generated from propagation models. The walls and restricted areas are considered in finding the locations of additional relay nodes. Our method can be effectively used in the initial stage of real deployment or a simulator in a wireless sensor network domain to reduce installation time and cost. We compared it with other deployment methods to validate the superiority of our method.

Non-contrast based edge descriptor for image segmentation

We present an efficient object segmentation strategy based on edge information to assist object-based video coding, motion estimation and motion compensation for the MPEG system. Two parameters are introduced and described based on edge information from the analysis of a local histogram. Using these features, a non-contrast based edge function is defined to generate an edge information map, which can be thought as a gradient image. Then, an improved marker-based region growing and merging techniques are derived to separate image regions. The proposed algorithm is tested on several standard images and demonstrates high reliability for object segmentation.

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.

Novel Block Motion Estimation Based on Adaptive Search Patterns

An improved algorithm for fast motion estimation based on the block matching algorithm (BMA) is presented for use in a block-based video coding system. To achieve enhanced motion estimation performance, we propose an adaptive search pattern length for each iteration for the current macro block (MB). In addition, search points that must be checked are determined by means of directional information from the error surface, thus reducing intermediate searches. The proposed algorithm is tested with several sequences and excellent performance is verified.

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.

Performance comparison of MRTOS and VxWorks in MultiBench benchmark suite

Recently, multiple core systems are widely used in various area. To meet the needs of mission-critical applications running on multicore systems, a realtime operating system (RTOS) and verification testing for multicore are absolutely necessary. We have developed the multicore RTOS (MRTOS) for supporting the symmetric multiprocessing. It includes multicore system BSP, multicore kernel, middleware, and IDE. To evaluate the developed RTOS, in this paper, we have compared the performance of the VxWorks and the developed RTOS by using the embedded MultiBench algorithms. We observed that the developed RTOS is able to achieve more than 90% of the performance of VxWorks on average.

Multi-Level Ultra Low-Power Mode Support Mechanisms for Wearable Device

For the convenience of users, thousands of wearable devices with new built-in applications are appearing every year in the field of healthcare, sports, and safety. However, the system of them should be operated by using limited capacity of power because of very small size of battery that can be loaded into a wearable device due to the device properties. For such a reason, Chip Vendors are recently launching MCUs with ultra-low power capability on the market and also MCU that supports 7-step low power mode was appeared at present[1-3]. But now, it is very rare case to completely use Low Power Mode offered by MCU vendor on the operating system (OS) that is applied to wearable devices, and there is no case to support low power mode by the OS at the board level. Therefore, this paper suggests optimal supporting mechanism for ultra-low power multi-step mode at the OS level of wearable device. The mechanism proposed in this paper is largely divided into two parts. First, it is Low Power Mode Governor (LPMG) which is a module used to select an optimal low power mode after computation of retention time in idle mode. Second, we proposed Power-Off Mode, which disconnects power to the board when idle mode lasts for a long time. When integrating these two technologies and applying them to the Tickless nanoQplus[4], the OS for wearable devices developed at our lab, in the same Wearable Application Scenario 2 test, power consumption after passing a certain duration of time is reduced by 98.05% compared to idle mode, and 96.33% compared to sleep mode. These newly proposed two technologies will be able to offer an effective solution required to achieve low power consumption in wearable devices.

MAC-Aware Concentrated Multi-Point Relay Selection Algorithm in Ad Hoc Networks

In OLSR, only selected Multipoint Relays (MPRs) are allowed to forward broadcast data during the flooding process, which reduces the message transmission overhead. Since every node in a network selects its own MPRs independently, many nodes may be MPRs of other nodes, which results in many collisions in the Medium Access Control (MAC) layer especially in the high traffic load condition. In this paper, we propose the concentrated MPR selection mechanism in an ad hoc network. Our proposed MPR selection can reduce the number of MPRs and thus the number of MAC layer collisions. The performance of the proposed MPR selection mechanism is investigated via analysis and simulations. The performance evaluation indicates that the proposed MPR selection is efficient.