Department of Electrical Engineering and Computer Science, MIT, Cambridge, MA 02139, USA.
Sensors (Basel). 2020 Mar 9;20(5):1489. doi: 10.3390/s20051489.
Determination of indoor position based on fine time measurement (FTM) of the round trip time (RTT) of a signal between an initiator (smartphone) and a responder (Wi-Fi access point) enables a number of applications. However, the accuracy currently attainable-standard deviations of 1-2 m in distance measurement under favorable circumstances-limits the range of possible applications. An emergency worker, for example, may not be able to unequivocally determine on which floor someone in need of help is in a multi-story building. The error in position depends on several factors, including the bandwidth of the RF signal, delay of the signal due to the high relative permittivity of construction materials, and the geometry-dependent "noise gain" of position determination. Errors in distance measurements have unusal properties that are exposed here. Improvements in accuracy depend on understanding all of these error sources. This paper introduces "frequency diversity," a method for doubling the accuracy of indoor position determination using weighted averages of measurements with uncorrelated errors obtained in different channels. The properties of this method are verified experimentally with a range of responders. Finally, different ways of using the distance measurements to determine indoor position are discussed and the Bayesian grid update method shown to be more useful than others, given the non-Gaussian nature of the measurement errors.
基于信号往返时间 (RTT) 的精细时间测量 (FTM) 确定室内位置，可以实现许多应用。然而，目前可达到的精度——在有利情况下距离测量的标准偏差为 1-2 米——限制了可能的应用范围。例如，紧急救援人员可能无法在多层建筑物中明确确定需要帮助的人所在的楼层。位置误差取决于多个因素，包括 RF 信号的带宽、由于建筑材料的高相对介电常数导致的信号延迟，以及与几何形状相关的位置确定的“噪声增益”。距离测量误差具有这里揭示的异常特性。精度的提高取决于对所有这些误差源的理解。本文介绍了“频率分集”，这是一种使用不同通道中获得的具有不相关误差的测量值的加权平均值将室内位置确定精度提高一倍的方法。通过一系列响应器的实验验证了该方法的特性。最后，讨论了使用距离测量值来确定室内位置的不同方法，并表明贝叶斯网格更新方法比其他方法更有用，因为测量误差具有非高斯性质。
