Yasutaka Kawamoto

Challenges in Real-Time Vital Signs Monitoring for Persons During Exercises

Although there have been a variety of wearable Information and Communication Technology (ICT) devices around us, which are easily connectable to smart phones, unfortunately, very few people are practicing everyday healthcare using them. There must be some causes in it. This paper examines educational and literate causes in the impracticality of everyday healthcare using wearable ICT devices, which may be inherent to Japan, and emphasizes the importance of real-time vital signs monitoring for schoolchildren in classroom learning and physical training, namely, persons during exercises. Then, the paper points out technical problems in its realization in terms of vital sensing and wireless networking, and introduces some solutions which we have been making up to the present. And finally, the paper shows some challenges of the future towards realization of real-time vital signs monitoring for schoolchildren during physical training, with the possibility of wireless multi-hop networking taking the mobility and location of vital sensor nodes into consideration.

Improving reliability of 920 MHz-band wireless networks using advanced source routing function to guarantee real-time property

We investigated the introduction of a source routing method into wireless nodes to improve the reliability of communication when economical 920 MHz-band wireless networks are used for control and sensing applications. In particular, higher real-time property and reliability of communication are required in the application of wireless control networks. We developed a source routing program for control networks such as in process control systems and factory automation systems and conducted an experiment with the wireless nodes implemented in the source routing program. The results of the experiment were that the reliability of wireless communication can be improved by introducing the source routing function.

Clock adjustment for a low power listening wireless infrastructure monitoring system

Sensor networks for infrastructure monitoring systems require battery operated sensing nodes with a lifetime of 10 years, a standardized technology, and low engineering costs. Low Power Listening (LPL) is well known as a technology to extend the lifetime of sensor network nodes. LPL technology is effective for power saving when time synchronization between the nodes is achieved. However, nodes using a Clock Crystal Oscillator cannot maintain time synchronization. The reason is the CXOs clock is skewed. We proposed NES-MAC that is IEEE802.15.4e standards-based MAC protocol with clock correction function. The NES-MAC stack can communicate with the normal IEEE802.15.4e MAC stack with low power consumption. We show that NES-MAC nodes can operate for more than 10 years on two CR123A batteries.

End-to-end reliability- and delay-aware scheduling with slot sharing for wireless sensor networks

Applications that require the stringent reliability with delay constraint such as industrial process automation and patient monitoring have been emerged as new area of applications of wireless sensor networks (WSNs). This paper presents a per-flow reliability- and delay-aware scheduling algorithm for industrial WSNs. The proposed method adds time slots for retransmission to each link in order to satisfy required reliability. Furthermore, by sharing retransmission slots among different flows, the proposed method achieves the required reliability and forwarding delay while suppressing increase in the number of allocated slots. Through simulation-based evaluations, we show that the proposed method can reduce the number of slots allocated to neighbor links of a sink by up to 70% compared with conventional methods, which contributes to shorten the slotframe size, while satisfying the requirements of end-to-end reliability and forwarding delay.

Application of economical 920-MHz band wireless communication to power routing in HVDC networks

Data centers face problems with concerns about instability in power supply systems caused by sharp changes in load such as power consumption by servers and diversification patterns in their power consumption. We have investigated a method of switching power flows by using power semiconductors via economical 920-MHz band wireless communication to control rises and falls in power in real time as a solution to such problems. We fabricated a testbed and used it to test the basic operating sequence. We report basic guidelines for using this system to improve the real-time performance of an economical wireless communication system and a source routing technique to improve reliability.

MAC protocol with clock synchronization correction for a practical infrastructure monitoring system

Sensor networks for infrastructure monitoring systems require battery-operated sensing nodes with a lifetime of 10 years, a standardized technology, and low engineering costs. Receiver-initiated transmission and coordinated sampled listening are promising power-saving communication methods that can be used for infrastructure monitoring. First, we compared receiver-initiated transmission and coordinated sampled listening from the viewpoint of power consumption and communication success probability. The results of the comparison showed that if we can continue coordinated sampled listening synchronous communication mode, we can satisfy the low power consumption performance required for infrastructure monitoring. However, coordinated sampled listening synchronous communication cannot be maintained for a longer period owing to performance variations of the clock crystal oscillator (CXO). We solved this problem by developing energy efficient system-media access control protocol (NES MAC), a MAC protocol with the additional function of correcting the dispersion of CXO and maintaining synchronization for a long time. NES-MAC is fully compatible with coordinated sampled listening. Furthermore, NES-MAC also has a high power-saving effect when communicating with normal coordinated sampled listening. Therefore, it is possible to expand the network easily and economically without affecting the power-saving performance. In addition, we found that through actual equipment evaluation that sensor nodes that adopt NES-MAC can operate for more than 10 years with two CR123A-type batteries.

NES-SOURCE: Indoor small-scale wireless control network protocol that has a communication failure point avoidance function

Wireless control network require delay guarantees and low packet error rates. The reason for communication delay and error is packet loss, and TDMA is used by many wireless control network technologies to avoid packet loss. However, TDMA protocols are difficult to implement. Besides, TDMA cannot avoid communication failure points due to changes in the environment caused by human intervention. We propose NES-SOURCE as a CSMA/CA based control network protocol. NES-SOURCE uses a source routing protocol, and if the NES-SOURCE node fails to communicate using primary route, the node avoid the communication failure point by to use secondary bypass route. NES-SOURCE is a low delay protocol. The reason is that NES-SOURCE can change the communication route at high speed. In addition, NES-SOUCE is implemented using a protocol stack that is compatible with IEEE 802.15.4 g. We show that NES-SOURCE systems can be used for wireless control network systems, and in an environment where people moving are in and out, path change is more advantageous than retransmission from the point of view of the packet error rate.