2023 Volume 59 Issue 1 Pages 26-36
In this paper, we propose a TOF-based high-resolution ranging method for asynchronous nodes in wireless sensor networks. Localization of sensor nodes is often required in wireless sensor networks to utilize measured data. TOF-based localization method is considered to be desirable since TOF of RF signal is hardly affected by surrounding conditions and no additional hardware is necessary. However, it is difficult to measure TOF with enough resolution because the speed of RF signal is too fast. Although measurement resolution can be improved by operating measurement devise with high frequency clock, it is not practical since high frequency operation leads to high power consumption and high cost. In previous research, high resolution measurement method using vernier effect, which is the principle of vernier caliper, has been proposed so that enough resolution can be achieved even when using low frequency clock. As a problem of the method, however, transmitting clock and receiving clock can't be isolated because they are assumed to be synchronized. If these clocks are put on same node, round-trip TOF has to be measured instead of one-way TOF. In that case, however, there are several problems such as uncertainty of reflecting time and self-interference, which makes it difficult to put the method to practical use. Then, we improve the method to realize TOF measurement between asynchronous nodes. When asynchronous clocks are used, measurement result is affected by phase difference and period difference. Main works of this research are formulating measurement error due to those asynchronous differences and proposing a way to negate the error. In addition, some experiments have been conducted to verify the proposed method. As a result of the experiments, it is confirmed that high-resolution TOF measurement between isolated nodes can be realized.
