ReLoki: Infrastructure-free Distributed Relative Localization using On-board UWB Antenna Arrays

TL;DR

ReLoki addresses infrastructure-free 3D relative localization for multi-robot teams in GPS-denied environments by integrating on-board UWB sensing with AoA estimation. The approach co-designs Two-Way Ranging (TWR) and Phase Difference of Arrival (PDoA) measurements on a Regular Tetrahedral Antenna Array (RTA) to estimate the relative position between agents in 3D, yielding estimates $\widehat{q}_{i,j}$ of the true relative position $q_{i,j}$. Hardware proof-of-concept demonstrates a lightweight node (~65 g) and enables comparisons with prior orthogonal-array methods, achieving sub-decimeter range accuracy and bearing errors in the tens of degrees under realistic conditions; experiments include two moving agents and one static agent. The work advances plug-and-play, infrastructure-free relative localization, with potential applications in indoor aerial and ground robotics, while highlighting elevation-angle limitations and avenues for antenna and algorithmic refinements.

Abstract

Coordination of multi-robot systems require some form of localization between agents, but most methods today rely on some external infrastructure. Ultra Wide Band (UWB) sensing has gained popularity in relative localization applications, and we see many implementations that use cooperative agents augmenting UWB range measurements with other sensing modalities (e.g., ViO, IMU, VSLAM) for infrastructure-free relative localization. A lesser researched option is using Angle of Arrival (AoA) readings obtained from UWB Antenna pairs to perform relative localization. In this paper we present a UWB platform called ReLoki that can be used for ranging and AoA-based relative localization in~3D. ReLoki enables any message sent from a transmitting agent to be localized by using a Regular Tetrahedral Antenna Array (RTA). As a full scale proof of concept, we deploy ReLoki on a 3-robot system and compare its performance in terms of accuracy and speed with prior methods.

Figures (8)

• Figure 1: Illustration of the relative localization problem with ReLoki attached to any existing motion platform. Here the RX agent senses the relative positions $q_{i, j}$ of the TX agents w.r.t its body frame whenever a message is received from $j$.
• Figure 2: Examples of two 4-antenna antenna configurations that can be used with ReLoki.
• Figure 3: Regular Tetrahedral Array with three 3 sample incidence angles used to estimate the bearing angle.
• Figure 4: On the left we have ReLoki hardware block diagram showing the components. Here we start with the agent $i$ initiating communication request. ReLoki connected to Agent $i$ transmits the data, ReLoki broadcasts the information to all agents in the neighborhood, the receiving ReLoki decodes the message and the localization data and intimates the receiving agent $j$. On the right we have the ReLoki PCB
• Figure 5: Timing Diagram showing the different phases of transmissions. Message phase is shown in red, ranging phase in blue and bearing phase in green.