R-TWR:一种基于时钟频率比的TOA测距新方案

R-TWR:Frequency Ratio Based TOA Ranging Scheme in IEEE802.15.4a Compliant Devices

TWR(Two Way Ranging)和SDS-TWR(Symmetric Double Side-Two Way Ranging)是IEEE802.15.4a中定义的两种TOA测距方案,主要用于无基础设施和额外同步机制条件下的节点定位/跟踪等应用.通过分析指出:TWR测距方案具有较高的测距容量且对节点移动的敏感度低,但其测距误差较大;SDS-TWR虽然能有效降低时钟频偏带来的测距误差,但其测距容量较低并且对节点移动的敏感度高.在此基础上,提出一种基于时钟频率比的TOA测距新方案R-TWR(Frequency Ratio BasedTWR).分析及仿真证明,该方案能达到SDS-TWR方案的测距准确度,并和TWR一样对节点移动的具有较高的测距容量和较低的移动敏感度.

The principal interest of IEEE 802.15.4a is in providing communications and high precision ranging / location capability.In the IEEE 802.15.4a,Two Way Ranging（TWR） scheme and Symmetric Double Side-Two Way Ranging（SDS-TWR） scheme are designed for the applications like positioning/tracking without infrastructure.In the two schemes,Time of Arrival（TOA） is the basic measurement for estimating the distance between nodes.In this paper,we present the performance metrics for ranging schemes as follows.For the TWR scheme,due to its turn around time,the frequency offset results in significant ranging error.For canceling the ranging error caused by the frequency offset in TWR,the SDS-TWR is proposed.However,since SDS-TWR takes more than two times bandwidth of that by TWR,which results in not only lower capacity,but also higher sensitivity to mobility than that of TWR.We cancel the ranging error from the frequency offset in a different way.We introduce a frequency Ratio based TWR（R-TWR） scheme,which cancels the ranging error based on the ratio of the frequency on the originator side to the frequency on the responder side.We prove that the ranging accuracy of R-TWR scheme can reach the same order as that of SDS-TWR,while the capacity and sensitivity to mobility keep same as TWR scheme.