• Journal of Information Processing Systems
• /
• 제5권3호
• /
• pp.135-144
• /
• 2009

Most of the tasks in wireless sensor networks (WSN) are requested to run in a real-time way. Neither EDF nor FIFO can ensure real-time scheduling in WSN. A real-time scheduling strategy (RTS) is proposed in this paper. All tasks are divided into two layers and endued diverse priorities. RTS utilizes a preemptive way to ensure hard real-time scheduling. The experimental results indicate that RTS has a good performance both in communication throughput and over-load.

• Journal of information and communication convergence engineering
• /
• 제10권1호
• /
• pp.21-26
• /
• 2012

As the new requirements for wireless sensor networks are emerging, real-time communications is becoming a major research challenge because resource-constrained sensor nodes are not powerful enough to accommodate the complexity of the protocol. In addition, an efficient energy management scheme has naturally been a concern in wireless sensor networks for a long time. However, the existing schemes are limited to meeting one of these two requirements. To address the two factors together, we propose real-time communications with two approaches, a protocol for satisfied conditions and one for unsatisfied. Under the satisfied requirement, existing real-time protocol is employed. On the other hand, for the unsatisfied requirement, the newly developed scheme replaces the existing scheme by adjusting the transmission range of some surplus nodes. By expanding the transmission range, the end-to-end delay is shortened because the number of intermediate nodes decreases. These nodes conserve their energy for real-time communications by avoiding other activities such as sensing, forwarding, and computing. Finally, simulation results are given to demonstrate the feasibility of the proposed scheme in high traffic environments.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• 제8권10호
• /
• pp.3423-3438
• /
• 2014

In recent years, wearable sensor devices are reshaping the way people live, work, and play. A wearable sensor device is a computer that is subsumed into the personal space of the user, and is always on, and always accessible. Therefore, among the most salient aspects of a wearable sensor device should be a small form factor, long battery lifetime, and real-time characteristics. Thereby, sophisticated applications of a wearable sensor device use real-time operating systems to guarantee real-time deadlines. The deterministic multi-dimensional task scheduling algorithms are implemented on ARC (Actual Remote Control) with relatively limited hardware resources. ARC is a wearable wristwatch-type remote controller; it can also serve as a universal remote control, for various wearable sensor devices. In the proposed algorithms, there is no limit on the maximum number of task priorities, and the memory requirement can be dramatically reduced. Furthermore, regardless of the number of tasks, the complexity of the time and space of the proposed algorithms is O(1). A valuable contribution of this work is to guarantee real-time deadlines for wearable sensor devices.

• 한국정보통신학회논문지
• /
• 제11권8호
• /
• pp.1493-1499
• /
• 2007

센서 네트워크 환경에서 실시간 응용이 원활하게 동작하기 위해서는 센싱 노드에서부터 싱크 노드까지의 실시간 전송이 요구된다. 기존의 혼잡 제어 기 법들은 센서 네트워크에서 혼잡 문제를 해결하기 위한 방법들을 제안하였으나 보고주기를 변경하거나 중간노드에서 전송을 억제하는 방식이므로 전송 지연 발생이 가능하여 실시간 센서네트워크 응용에는 적합하지 않다. 본 논문에서는 실시간 데이터에 대해 전송 지연을 감소시키고 throughput을 증가시킬 수 있는 새로운 메커니즘을 제안하였다. 이 메커니즘에서는 데이터를 실시간성을 기준으로 분류하여 실시간성을 유지하고 있는 데이터를 우선 처리하고 실시간성을 잃은 데이터는 비실시간성 데이터와 함께 처리토록 하였다. 또한 본 논문에서 제안한 전송 지연 개선 기법을 IEEE 802.15.4 MAC 계층에 적용하기 위해 수정된 프레임 포맷도 함께 제안하였다. 또한 본 논문에서 제안한 기법을 적용하는 경우 전송지연 및 throughput 측면에서 어느 정도의 성능개선이 이루어지는지를 확인하기 위해 ns-2를 기반으로 시뮬레이션을 수행하였으며 본 논문에서 제안한 기법이 실시간성이 중요한 응용에 적용될 경우 기존의 기법에 비해 우수한 성능을 나타냄을 확인하였다.

• Nuclear Engineering and Technology
• /
• 제55권3호
• /
• pp.814-826
• /
• 2023

Sensor faults in nuclear power plant instrumentation have the potential to spread negative effects from wrong signals that can cause an accident misdiagnosis by plant operators. To detect sensor faults and make accurate accident diagnoses, prior studies have developed a supervised learning-based sensor fault detection model and an accident diagnosis model with faulty sensor isolation. Even though the developed neural network models demonstrated satisfactory performance, their diagnosis performance should be reevaluated considering real-time connection. When operating in real-time, the diagnosis model is expected to indiscriminately accept fault data before receiving delayed fault information transferred from the previous fault detection model. The uncertainty of neural networks can also have a significant impact following the sensor fault features. In the present work, a pilot study was conducted to connect two models and observe actual outcomes from a real-time application with an integrated system. While the initial results showed an overall successful diagnosis, some issues were observed. To recover the diagnosis performance degradations, additive logics were applied to minimize the diagnosis failures that were not observed in the previous validations of the separate models. The results of a case study were then analyzed in terms of the real-time diagnosis outputs that plant operators would actually face in an emergency situation.

• 통합자연과학논문집
• /
• 제10권4호
• /
• pp.232-239
• /
• 2017

The researcher set up multiple sensor units on the road slope such as national highway and highway where there is a possibility of loss, and using the acceleration sensor built into the sensor unit the researcher will sense whether the inclination of the road slope occur in real time, and Based on the sensed data, the researcher tries to implement a system that detects collapse of road slope and dangerous situation. In the experiment of measuring the error between the actual measurement time and the judgment time of the monitoring system when judging the warning of the sensor and falling rock detection by using the acceleration sensor, the error between measurement time and the judgment time at the sensor warning was 0.34 seconds on average, and an error between measurement time and judgment time at falling rock detection was 0.21 seconds on average. The error is relatively small, the accuracy is high, and thus the change of the slope can be clearly judged.

• Journal of information and communication convergence engineering
• /
• 제9권2호
• /
• pp.244-250
• /
• 2011

Gossip is a well-known protocol which was proposed to implement broadcast service with a high reliability in an arbitrarily connected network of sensor nodes. The probabilistic techniques employed in gossip have been used to address many challenges which are caused by flooding in wireless sensor networks (WSNs). However, very little work has yet been done on real-time wireless sensor networks which require not only highly reliable packets reception but also strict time constraint of each packet. Moreover, the unique energy constraining feature of sensor makes existing solutions unsuitable. Combined with unreliable links, redundant messages overhead in real-time wireless sensor networks is a new challenging issue. In this paper, we introduce a Reliable Gossip Zone, a novel fine-tailored mechanism for real-time wireless sensor networks with unreliable wireless links and low packet redundancy. The key idea is the proposed forwarding probability algorithm, which makes forwarding decisions after the realtime flooding zone is set. Evaluation shows that as an oracle broadcast service design, our mechanism achieves significantly less message overhead than traditional flooding and gossip protocols.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2003년도 추계학술발표대회 논문집
• /
• pp.154-157
• /
• 2003

Precision displacement of less than a few nm resolution was measured in real-time using fiber optic EFPI sensor. The novel method for real-time processing of analyzing EFPI output signal was developed and verified. Linearity in the mean values of interferometric light intensity among adjacent fringes was shown, and the sinusoidal approximation algorithm that estimates past and coming fringe values was verified through the linearity. Real-time signal processing program was developed, and the intensity signal of the EFPI sensor was transformed to the phase shift with this program. The resolution below 0.4 ~ 10 nm in the displacement range of $0 ~ 300\mu\textrm{m}$ was obtained by reducing the photodetector noise using low-pass filter and signal averaging. The nano-translation stage with a Piezo-electric actuator and the EFPI sensor system was designed and tested. This stage successfully reached to the desired destination in $15\mu\textrm{m}$ range within 1 nm accuracy.

• 한국정보과학회논문지:데이타베이스
• /
• 제37권6호
• /
• pp.324-332
• /
• 2010

실시간 임베디드 센서 네트워크 시스템에서의 이벤트 감지는 대부분 현실세계에서 수집된 센서 데이터들의 조합에 기반한다. 이에 최근에 이루어진 연구들에선 센서 데이터들을 수집, 집계하는 낮은 수준의 다양한 메커니즘들을 제안하였다. 그러나 실시간에서 연속적으로 발생하는 복잡한 이벤트들의 감지와 다양한 종류의 센서들로부터 입력되는 실시간 데이터의 처리를 위한 시스템에 대한 솔루션은 보다 많은 연구를 필요로 한다. 즉, 경량의 데이터 혼합이 가능하고 많은 컴퓨팅 자원을 필요로 하지 않는 실시간 이벤트 감지 기법이 필요하다. 이벤트 감지 프레임워크는 실시간 모니터링과 센서 데이터의 도착으로 일어나는 데이터 융합 메커니즘을 통하여 적시성과 임베디드 센서 네트워크의 자원 요구량을 감소시킬 수 있는 잠재력을 지니고 있다. 또한 임베디드 센서 네트워크 시스템이 신뢰성을 지닐 수 있도록 하기 위한 기반 기술인 프라이버시를 보장할 수 있는 익명화 기술을 설명한다.

• 한국정보과학회논문지:컴퓨팅의 실제 및 레터
• /
• 제16권4호
• /
• pp.437-441
• /
• 2010

무선 센서 네트워크가 적용되는 새로운 응용분야는 점점 더 정교하고 복잡한 태스크 수행과 정해진 시간내에 태스크 수행을 완료해야 한다는 조건 만족을 요구하고 있다. 그러나 현재까지, 무선 센서 네트워크에서 센서 노드의 자원 제약성과 수행 작업 특성을 고려한 실시간 센서 운영체제 기반의 인터럽트 처리 기법에 관한 연구는 미비하다. 본 논문에서는 센서 운영체제에서 실시간성을 만족시키기 위한 요구 사항들을 분석하고, 이를 바탕으로 시스템을 설계 및 구현한다. 또한 다양한 검증을 통해, 제안하는 기법의 신뢰성 제공을 확인하며, 시뮬레이션을 통해 실시간 특성에 대한 요구사항 충족 및 성능의 효율성을 검증한다.