Min Choi

Experimental link channel characteristics in wireless body sensor systems

In the resource-constrained environment such as wireless body sensor networks (WBSNs), all sensor nodes operating with limited battery need the very-low-power wireless technologies. The representative approach to reduce energy consumption in WBSNs is transmission power control (TPC). The TPC technique is used to maintain acceptable packet delivery performance with the low power consumption. So, it has been widely researched as the important subject in WSNs. However, the TPC algorithms which have been researched in WSNs are not directly applicable in WBSNs which deploy sensor nodes in, on, or around a human body. This is because instantaneous channel condition is frequently changed due to sensor mobility resulting from human movements in WBSNs. Therefore, we need a sophisticated TPC technology to achieve reliable communication in WBSNs. To do this, in this paper, we investigate link layer channel characteristics in WBSNs. For understanding link characteristics in terms of power and placement, we conducted diverse experiments with real sensor devices. Through the analysis of experimental results, we knew that RSSI values are deeply depended on the transmission power and sensor placement in WBSNs.

Improving performance of a dynamic load balancing system by using number of effective tasks

Efficient resource usage is a key to achieving better performance in cluster systems. Previously, most research in this area has focused on balancing the load if each node to use the resources of an entire system more effectively. However, we can achieve further improvement in performance when the load balancing system considers the resource requirement according to the task being assigned. This kind of load balancing system, known as an initial job placement system, requires knowledge of the resource usage of a task in order to fit the job to the most suitable node. Since the initial placement requires that the tasks be scheduled before execution, all resource usage must be provided in terms of the prediction. This approach can severely affect the execution time when it uses an inaccurate prediction. We propose a novel load metric termed number of effective tasks in order to resolve the problem arising from inaccurate predictions. Thus, the initial job placement system can work without knowing job resource usage in priori. Simulation results show that the system incurs 11% shorter execution time that the conventional approach using historical behavior-based estimates.

Different Characteristics of Radio Modules in Wireless Body Sensor Network Systems

Wireless body sensor network systems (WB-SNSs) can use diverse radio modules. However, previous studies did not consider different characteristics of radio modules, which deeply impact the performance of WB-SNSs. In this paper, we analyze the performance of WB-SNSs using the representative radio modules CC2420 and CC1000. In this environment, we collected log data from real sensor devices deployed on the human body. After log data collection, we first show that CC2420 and CC1000 have different radio characteristics from diverse views, such as the received signal strength indication (RSSI) average and deviation, transmission power levels, and body movement. Through the analysis, we also find that an efficient transmission power control (TPC) algorithm should consider these diverse factors due to different radio modules.

Cluster computing environment supporting single system image

Single system image (SSl) systems have been the mainstay of high-performance computing for many years. SSI requires the integration and aggregation of all types of resources in a cluster to present a single interface to users. We describe a cluster computing environment supporting SSI, constructed through three components: single process space (SPS), process migration, and dynamic load balancing. These components attempt to share all available resources in the cluster among all executing processes, so that the cluster operates like a single node with much more computing power. The most important goal is to combine these constructs in innovative ways for building cluster computing environment for SSI, as well as individually take an approach to improve performance or functionality. Our implementation of process migration has the capability of resolving broken pipe problems and bind errors on server socket reconstruction. We realize SPS based on block PID allocation. We also designed and implemented a dynamic load balancing scheme which resolves the limitations of our previous work by continuously tracing the job resource usage at runtime. The experimental results show that these three constructs for SSI clusters realized scalability, functionality and performance improvement. The cluster computing environment allows these constructs to cooperate implicitly so that they create a synergy effect at the SSI cluster system level and successfully provide a single system image to users and administrators.

An Energy Efficient Instruction Window for Scalable Processor Architecture

Modern microprocessors achieve high application performance at the acceptable level of power dissipation. In terms of power to performance trade-off, the instruction window is particularly important. This is because enlarging the window size achieves high performance but naive scaling of the conventional instruction window can severely increase the complexity and power consumption. In this paper, we propose low-power instruction window techniques for contemporary microprocessors. First, the small reorder buffer (SROB) reduces power dissipation by deferred allocation and early release. The deferred allocation delays the SROB allocation of instructions until their all data dependencies are resolved. Then, the instructions are executed in program order and they are released faster from the SROB. This results in higher resource utilization and low power consumption. Second, we replace a conventional issue queue by a direct lookup table (DLT) with an efficient tag translation technique. The translation scheme resolves the instruction dependency, especially for the case of one producer to multiple consumers. The efficiency of the translation scheme stems from the fact that the vast majority of instruction dependency exists within a basic block. Experimental results show that our proposed design reduces the power consumption significantly for SPEC2000 benchmarks.

Design and Implementation of an ONVIF Proxy Server

The Open Network Video Interface Forum (ONVIF) has created a standard protocol for improving compatibility between the protocols employed by heterogeneous network cameras. The aim of this study was to design and implement a proxy server to reduce the management cost of network video transmitters (NVTs) by reducing the load of NVTs as well as the network load of NVTs.

An Efficient AP Selection Scheme for Wireless Distributed Systems

In this paper, we propose an efficient access point (AP) selection scheme for wireless multi-hop networks. Some previous IEEE 802.11 studies have used multi-hop techniques to solve the shadow region and to cover the wide region in the area where the AP is deployed. However, users employing these techniques are unable to determine which AP is more efficient among the number of APs in the wireless multi-hop networks. In addition, it is very difficult to capture the status of the current channel using only the received signal strength indication (RSSI) in the existing AP selection scheme. Therefore, in this paper, we propose a new AP selection algorithm with the hop count for wireless multi-hop networks. We built a wireless distributed system (WDS) that can be easily constructed as a wireless multi-hop network without expert knowledge. Then, we measured the throughput and evaluated the performance of our AP selection scheme in UDP Downlink and UDP Uplink. Based on the results of our measurements, our AP selection scheme can increase the performance of all stations in wireless multi-hop networks.

A low-cost recovery scheme for dynamically scheduled processors

Although todays branch predictors show high accuracy, the branch misprediction penalty is getting larger due to aggressive speculation and deeper pipelining. In order to reduce the miss penalty, we propose a fast and low-cost branch recovery scheme using the incremental register renaming (IRR) and the bit-vector based rename map table (BVMT). The IRR enforces the destination register number of the instruction stream to appear in non-decreasing order. With this incremental property of the IRR, the BVMT recovery scheme completely eliminates the roll-back overhead on branch misprediction. Thus, the instruction fetcher does not stop and it fetches instructions from the correct path immediately after the misprediction detected. The goal of our scheme is to prevent a processor from flushing the pipeline, even under branch misprediction. Consequently, the BVMT instantly reconstructs the map table to any mispredicted branch and it outperforms the conventional approach by an average of 10.93%.

Performance Improvement using Effective Task Size Calculation in Dynamic Load Balancing Systems

In distributed systems like cluster systems, in order to get more performance improvement, the initial task placement system precisely estimates and correctly assigns the resource requirement by the process. The resource-based initial job placement scheme needs the prediction of resource usage of a task in order to fit it to the most suitable hosts. However, the wrong prediction of resource usage causes serious performance degradation in dynamic load balancing systems. Therefore, in this paper, to resolve the problem due to the wrong prediction, we propose a new load metric. By the new load metric, the resource-based initial job placement scheme can work without priori knowledge about the type of process. Simulation results show that the dynamic load balancing system using the proposed approach achieves shorter execution times than the conventional approaches.