Junhee Ryu

Design and QoS of a Wireless System for Real-Time Remote Electrocardiography

Quality of service (QoS) and, in particular, reliability and a bounded low latency are essential attributes of safety-critical wireless systems for medical applications. However, wireless links are typically prone to bursts of errors, with characteristics which vary over time. We propose a wireless system suitable for real-time remote patient monitoring in which the necessary reliability and guaranteed latency are both achieved by an efficient error control scheme. We have paired an example remote electrocardiography application to this wireless system. We also developed a tool chain that uses a formal description of the proposed wireless medical system architecture in the architecture analysis and design language to assess various combinations of system parameters: we can determine the QoS in terms of packet-delivery ratio and the service latency, and also the size of jitter buffer required for seamless ECG monitoring. A realistic assessment, based on data from the MIT-BIT arrhythmia database, shows that the proposed wireless system can achieve an appropriate level of QoS for real-time ECG monitoring if link-level error control is correctly implemented. Additionally, we present guidelines for the design of energy-efficient link-level error control, derived from energy data, obtained from simulations.

Rapid Prototyping and Evaluation of Intelligence Functions of Active Storage Devices

Active storage devices further improve their performance by executing “intelligence functions,” such as prefetching and data deduplication, in addition to handling the usual I/O requests they receive. Significant research has been carried out to develop effective intelligence functions for the active storage devices. However, laborious and time-consuming efforts are usually required to set up a suitable experimental platform to evaluate each new intelligence function. Moreover, it is difficult to make such prototypes available to other researchers and users to gain valuable experience and feedback. To overcome these difficulties, we propose IOLab, a virtual machine (VM)-based platform for evaluating intelligence functions of active storage devices. The VM-based structure of IOLab enables the evaluation of new (and existing) intelligence functions for different types of OSes and active storage devices with little additional effort. IOLab also supports real-time execution of intelligence functions, providing users opportunities to experience latest intelligence functions without waiting for their deployment in commercial products. Using a set of interesting case studies, we demonstrate the utility of IOLab with negligible performance overhead except for the VMs virtualization overhead.

Randomized clinical trial of immersive virtual reality tour of the operating theatre in children before anaesthesia

A virtual reality (VR) tour of the operating theatre before anaesthesia could provide a realistic experience for children. This study was designed to determine whether a preoperative VR tour could reduce preoperative anxiety in children.

Bounding End-to-End Delay for Real-Time Environmental Monitoring in Avionic Systems

Timing guarantees and predictive early analysis are essential considerations for the design of reliable and verified real-time avionics systems. In this paper, we consider an environmental monitoring avionic system, which allows physical circumstances to be visually monitored continuously in real-time. We analyze timing aspects on the partitions of front-end and back-end nodes, and intermediate node which interconnects those systems. On the end nodes, we use ASIIST to evaluate the worst-case delay for PCI bus analysis. And then, we propose a novel real-time switching algorithm which ensures the delay bound on the intermediate node. Finally, we derive the end-to-end delay on the whole system accurately and show how it can be bounded. A predictive analysis on the worst-case end-to-end delay of a system, before deployment, can result in more reliable and well-verified environmental monitoring systems. We also expect this to reduce the cost of designing and implementing environmental monitoring avionic systems.

Scalable management of storage for massive quality-adjustable sensor data

The quality-adjustable nature of sensor data and gradually decreasing access pattern foster a new data archiving scheme that can cope with rapidly increasing data generation rates by sensors. We propose a scalable quality management of massive sensor data, which handles less frequent data access through discarding supplementary layers as time elapses for efficient usage of storage space. The efficacy of our scheme is shown by its capability to offer multiple fidelity levels compactly utilizing spatio-temporal correlation, without compromising key features of sensor data. In order to store a huge amount of data from various sensor types efficiently, we also study the optimal storage configuration strategy using analytical models that can capture characteristics of our scheme. This strategy helps storing sensor data blocks while minimizing total distortion under a given total rate budget.

File-system-level flash caching for improving application launch time on logical hybrid disks

Application launch time is an important performance metric to user experience in desktop environment. The launch time mostly depends on the performance of secondary storage. There is a cost-performance trade-off in using hard disk drive (HDD) or solid-state drive (SSD). Thus, application launch times can be reduced by utilizing SSDs as caches for slow HDDs. We propose a new SSD caching scheme which migrates data blocks from HDDs to SSDs. Since our scheme operates entirely in the file system level and does not require an extra layer for mapping SSD-cached data, which is essential in most other schemes, our scheme does not incur mapping overheads that cause significant burdens on main memory, CPU, and SSD cache itself. Experimental results demonstrate our scheme yields 56% of performance gain in application launch.

Accommodating the Variable Timing of Software AES Decryption on Mobile Receivers

Broadcast and multicast services in CDMA2000 wireless networks restrict the provision of high-quality multimedia services to their intended recipients by encrypting the content using the advanced encryption standard (AES) block cipher in the security layer of the broadcast protocol suite. We profile the execution time and the energy of each transformation within the AES decryption process and propose a novel analytic model for predicting the time and energy that are required to decrypt the content at a mobile receiver. The model uses the cross-layer information, including the characteristics of error control in the MAC layer and the varying conditions of the fading channel in the physical layer. In particular, we find that the decryption time varies significantly with the condition of the physical channel. Rate control is, therefore, required to smooth out these variations in the decryption time. For this purpose, we propose the introduction of a jitter buffer into the security layer and estimate the size of this jitter buffer to provide seamless multimedia services.

Strategy to Reduce I/O Access Time of Applications in Virtual Machines

An input/output (I/O) device can incorporate mechanical devices that require physical movements, such as a hard drive seeking a track for a data read or write. Hence I/O operations on a computer can be extremely slow compared to data processing. When a program conducts many I/O operations, the processor often spends most idling as it waits for the I/O operations to complete. The same holds true for a virtual machine (VM), and to improve the overall performance of a VM, this problem needs to be addressed. In this paper, we propose a pinning technique, which migrates frequently accessed disk blocks from hard disks to flash memories, to reduce the I/O waiting time. Experimental results show that the start-up times dramatically decrease by up to 38% on average when using this method.

Improving Application Launch Performance on Solid State Drives

Application launch performance is of great importance to system platform developers and vendors as it greatly affects the degree of users’ satisfaction. The single most effective way to improve application launch performance is to replace a hard disk drive (HDD) with a solid state drive (SSD), which has recently become affordable and popular. A natural question is then whether or not to replace the traditional HDD-aware application launchers with a new SSD-aware optimizer. We address this question by analyzing the inefficiency of the HDD-aware application launchers on SSDs and then proposing a new SSD-aware application prefetching scheme, called the Fast Application STarter (FAST). The key idea of FAST is to overlap the computation (CPU) time with the SSD access (I/O) time during an application launch. FAST is composed of a set of user-level components and system debugging tools provided by Linux OS (operating system). Hence, FAST can be easily deployed in any recent Linux versions without kernel recompilation. We implement FAST on a desktop PC with an SSD running Linux 2.6.32 OS and evaluate it by launching a set of widely-used applications, demonstrating an average of 28% reduction of application launch time as compared to PC without a prefetcher.

Toward energy-efficient error control in 3G broadcast video

Energy use is a key issue in battery-operated mobile devices. In order to extend battery life, mobiles showing video often allow a controlled drop in quality, which is tolerable when the shortcomings of a small screen are combined with the imperfections of visual perception. Both energy consumption and video quality are affected by the Reed-Solomon codes and interleaving levels used in 3G video broadcast services. We explore the effect of these elements of MAC-layer error control, and show how they can be manipulated to save energy while maintaining acceptable video quality through a controlled reduction in the number of parity symbols in the Reed-Solomon code and the level of interleaving.