Round-trip delay ranging with OFDM signals — Performance evaluation with outdoor experiments

Ranging accuracy and reliability is crucial for any cooperative- and non-cooperative positioning system applied for unmanned vehicle localization, and formation estimation. State of the art systems exploit received signal strength (RSS) from WiFi devices, or ultra-wide bandwidth (UWB) timing based range estimation. RSS proved to be unreliable in environments with multipath, and UWB combats multipath at the cost of high bandwidth and specialized hardware. We tackle this problem with round-trip delay (RTD) based range estimation with orthogonal frequency division multiplex (OFDM) modulated signals which are widely used in WiFi and 3GPP-LTE. In this paper, we present our developed prototype and two different outdoor environments with varying multipath conditions. Measurements along ground truth points are collected for each environment and post-processed. We apply four different estimators, two based on cross-correlation and interpolation, and two based on Maximum-likelihood (ML) multipath estimation. Our analysis reveals that a simple correlation based estimator with interpolation and smart thresholding is sufficient and a very good trade-off between computational complexity and accuracy compared to ML multipath estimators. These outdoor experiments show that our simple ranging technique is suitable for peer-to-peer distance estimation with low bandwidth, low transmit power, and can be exploited for localization and formation estimation in cyber-physical systems.