Masumi Ichien

Isochronous MAC using Long-Wave Standard Time Code for Wireless Sensor Networks

This paper proposes isochronous-MAC (I-MAC), which utilizes low-frequency radio waves time synchronization for sensor networks. Using IMAC, based on the low power listening (LPL), all sensor nodes wake and listen channel periodically and synchronously. Since a sender can easily predict wakeup time of an intended receiver, it can shorten the length of preamble to make the receiver prepare for reception of the following data packet. This saves power consumption for the sender to rendezvous with the receiver. In the paper, we use an analytical model to investigate the impact of the data transmission frequency, the number of neighboring nodes, the wakeup period, the clock drift, and the time-synchronization frequency on the power consumption for consideration of the power overhead to perform the time synchronization. Those results demonstrate that I-MAC allows determination of any arbitrary wakeup period without much difficulty, whereas LPL requires a much more careful setting of the wakeup period because its optimum wakeup period is sensitive to the frequency of data transmission as well as to the number of neighboring nodes. Therefore, IMAC has a great potential to reduce the power consumption in most situations compared with LPL, in spite of the overhead to perform time synchronization.

Cross-Layer Design for Low-Power Wireless Sensor Node Using Wave Clock

We propose Isochronous-MAC (I-MAC) using the Long-Wave Standard Time Code (so called “wave clock”), and introduce cross-layer design for a low-power wireless sensor node with I-MAC. I-MAC has a periodic wakeup time synchronized with the actual time, and thus we take the wave clock. However, a frequency of a crystal oscillator varies along with temperature, which incurs a time difference among nodes. We present a time correction algorithm to address this problem, and shorten the time difference. Thereby, the preamble length in I-MAC can be minimized, which saves communication power. For further power reduction, a low-power crystal oscillator is also proposed, as a physical-layer design. We implemented I-MAC on an off-the-shelf sensor node to estimate the power saving, and verified that the proposed cross-layer design reduces 81% of the total power, compared to Low Power Listening.

Data Transmission Scheduling Based on RTS/CTS Exchange for Periodic Data Gathering Sensor Networks

SUMMARY One challenging issue of sensor networks is extension of overall network system lifetimes. In periodic data gathering applications, the typical sensor node spends more time in the idle state than active state. Consequently, it is important to decrease power consumption during idle time. In this study, we propose a scheduling scheme based on the history of RTS/CTS exchange during the setup phase. Scheduling the transmission during transfer phase enables each node to turn off its RF circuit during idle time. By tracing ongoing RTS/CTS exchange during the steady phase, each node knows the progress of the data transfer process. Thereby, it can wait to receive packets for data aggregation. Simulation results show a 160–260% longer system lifetime with the proposed scheduling scheme compared to

A power-variation model for sensor node and the impact against life time of wireless sensor networks

We introduce manufacturing variation into a power model for a wireless sensor network node. Network protocols for the wireless sensor networks such as media access control and routing should be evaluated in terms of life time in a whole system. In fact, there exists power variation node by node due to the manufacturing variation. In the previous researches, however, this effect has not been investigated at all since it has been supposed that all nodes have a same power. In this paper, we develop a power model for a sensor node, in which we consider threshold-voltage variation derived from a manufacturing process. We take both a microprocessor and an RF part into account for the model, and implement it to QualNet in order to evaluate the impact against a life time of a wireless sensor network. The simulation results show that the conventional model has overestimated the life time longer than our model when nodes are randomly deployed. In contrast, if we make an optimum deployment of nodes by exploiting the power variation, the network life time is extended by 12.7% compared to the case of the conventional model.

Cross-Layer Design for Low-Power Wireless Sensor Node Using Long-Wave Standard Time Code

We propose isochronous-MAC (I-MAC) using the long-wave standard time code, and introduce cross-layer design for a low-power wireless sensor node with I-MAC. I-MAC has a periodic wakeup time synchronized with the actual time, and thus requires a precise timer. However, a frequency of a crystal oscillator varies along with temperature, from node to node. We utilize a time correction algorithm to shorten the time difference among nodes. Thereby, the preamble length in I-MAC can be minimized, which saves a communication power. For further power reduction, a low-power crystal oscillator is also proposed, as a physical-layer design. We implemented I-MAC on an off-the-shelf sensor node to estimate the power saving, and verified that I-MAC reduces 81% of the total power, compared to low power listening.