Toshihiko Matsunaga

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.

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.