Hiroyuki Okuhata

An object code compression approach to embedded processors

A low-power processor architecture is described dedicatedly for embedded application programs by means of an object code compression approach. This approach unifies duplicated instructions existing in the embedded program and assigns a compressed object code to such an instruction. An instruction decompressor is constructed so as to generate an object code from each compressed object code (pseudo code) input. A single-chip implementation of this decompressor together with a processor core can effectively reduce the bandwidth required for the I/O interface. To demonstrate the practicability of the proposed approach, experiments are applied to an embedded processor ARM610 which attains 62.5% code compression, and hence 42.3% of the power consumption of instruction memory can be reduced.

Cancellation of motion artifact induced by exercise for PPG-based heart rate sensing

Heart rate (HR) sensing during exercise is essential for medical, healthcare and sport physiological purposes. Photo-Plethysmo-Graphy (PPG) is a simple and non-invasive technique for HR sensing, but it is highly sensitive to motion artifact. This paper proposes a cancellation technique of motion artifact in PPG-based HR sensing for a man during exercise. The canceller is equipped with two sensors; one is a normal PPG sensor where an LED/Photo-Detector (PD) contacts the skin to detect Blood Volume Pulse (BVP) (+motion artifact) and the other is a motion artifact sensor where an LED/PD does not contact the skin to detect only motion artifact. Experimental results show that the proposed technique, which is implemented in adaptive algorithms, can sense HR correctly by cancelling motion artifact induced by exercises such as running and jumping.

ASK digital demodulation scheme for noise immune infrared data communication

A high performance architecture is proposed for the ASK (Amplitude Shift Keying) digital demodulation, which is dedicated to the noise immune wireless infrared data communication. In this architecture, an infrared subcarrier detected by a photodetector is digitized into TTL interface level pulses, and the digitized subcarrier is demodulated by a 1‐bit digital demodulator. To improve the noise immunity against fluorescent lamps, the optical noises from the lamps are analyzed and the behavior of an ASK infrared communication link is modeled under these noises. On the basis of this model, a digital demodulator is synthesized by means of a high level synthesis tool, aiming at implementing an algorithm of discriminating the subcarrier from optical noises. A part of experimental results shows that the ASK receiver realized with the use of this digital demodulator can achieve an error free infrared link even under the intense noises from fluorescent lamps.

Application of the real-time Retinex image enhancement for endoscopic images

This paper presents a real-time image enhancement technique for gastric endoscopy, which is based on the variational approach of the Retinex theory. In order to efficiently reduce the computational cost required for image enhancement, processing layers and repeat counts of iterations are determined in accordance with software evaluation result, and as for processing architecture, the pipelining architecture can handle high resolution pictures in real-time. To show its potential, performance comparison between with and without the proposed image enhancement technique is shown using several video images obtained by endoscopy for different parts of digestive organ.

Development of a real-time vital data collection system from players during a football game

In order to plan effective training menus and avoid injuries and diseases, vital signs monitoring for athletes during training and game is essential, where a key issue is how to collect vital data reliably and in real-time from many people spread in a large field. To realize such a real-time vital data monitoring system, we developed prototype wireless vital sensor nodes, and conducted twice field experiments to evaluate the packet success rate (PSR), where we put the sensor nodes to the waists of 22 players and collected packets from all of them during a football game. In this paper, we present the detail of the real-time vital data collection system composed of the prototype sensor nodes and data collection nodes, and discuss the experimental results in terms of PSR and diversity gain.

Motion artifact cancellation and outlier rejection for clip-type ppg-based heart rate sensor

Heart rate sensing can be used to not only understand exercise intensity but also detect life-critical condition during sports activities. To reduce stress during exercise and attach heart rate sensor easily, we developed a clip-type photoplethysmography (PPG)-based heart rate sensor. The sensor can be attached just by hanging it to the waist part of undershorts, and furthermore, it employs the motion artifact (MA) cancellation technique. However, due to its low contact pressure, sudden jumps and drops, which are called “outliers,” are often observed in the sensed heart rate, so we also developed a simple outlier rejection technique. By an experiment using five male subjects (4 sets per subject), we confirmed the MA cancellation and outlier rejection capabilities.

Elements of a real-time vital signs monitoring system for players during a football game

We have developed a real-time vital signs monitoring system for two years in 2012 and 2013. Just by putting a single vital sensor node to the back waist position of each player and placing four data collection nodes around a field, the system can monitor at a note PC heart rate (HR), energy expenditure (EE) and body temperature (BT) for all players during a football game in real-time, periodically and reliably. The system is based on novel vital sensing technique and wireless data transmission technique. This paper introduces the two techniques in the system, presents some problems encountered in the system development and discusses solutions for them.

Performance evaluation of packet forwarding methods in real-time vital data collection for players during a football game

Real-time vital data monitoring for athletes during training and game is essential for planning effective training menus and avoiding injuries and diseases. Especially for team sports such as footfall and rugby, how to reliably collect vital data from many players spread in a large field is a key issue. In our previous work [1], we developed a real-time vital data collection system in which a wireless sensor node attached at the waist position of each player broadcasts packets to data collection nodes placed around a football field. Our field experiments showed that, (1) for the 920 MHz band, the packet success rate can be almost 1.0 when using 3 or 4 data collection nodes, whereas for the 2.4 GHz band, the packet success rate is less than 0.85 even when using 6 data collection nodes, and (2) the suitable antenna height of the data collection node is 2 meters. In this paper, we discuss a suitable packet forwarding method from the data collection nodes to a sink node at a technical trainer or a coach. By field experiments, we compare the packet error rate between a single-hop packet forwarding in the 920 MHz band and a multi-hop packet forwarding in the 2.4 GHz band. Furthermore, we show some interesting events on the packet error rates for different player positions such as forward, midfielder, defender and goalkeeper.

Dependable embedded processor core for higher reliability

We are developing a 32bit embedded processor core with soft error detection and recovery mechanisms. Soft errors caused by atmospheric neutron hits or performance aging in an embedded processor core make the mission-critical embedded system to produce dangerous results like system failure. Our research goal is to investigate soft error rates in the proposed embedded processor core through fault injection tests using a neutron beam or an electromagnetic pulse generator.

Low-power implementation of H.324 audiovisual codec dedicated to mobile computing

A VLSI implementation of the H.324 audiovisual codec is described. A number of sophisticated low-power architectures have been devised dedicatedly for the mobile use. A set of specific functional units, each corresponding to a process of H.263 video codec, is employed to lighten different performance bottlenecks. A compact DSP core composed of two MAC units is used for both ACELP and MP-MLQ coding schemes of the G.723.1 speech codec. The proposed audiovisual codec core has been implemented by using 0.35 /spl mu/m CMOS 4LM technology, which contains totally 420 K transistors with the dissipation of 224.32 mW from single 3.3 V supply.