Eco-WakeLoc: An Energy-Neutral and Cooperative UWB Real-Time Locating System

TL;DR

Eco-WakeLoc achieves energy-neutral, centimeter-precision indoor localization by marrying ultra-low-power wake-up radios with UWB ranging, solar harvesting, and cooperative localization. The system activates anchors on demand and enables passive tags to reuse active exchanges, while an AIMD-based energy-aware scheduler adapts localization rates to harvested energy to sustain operation. hardware demonstrations and year-long simulations show sustained performance (up to ~2031 localizations per day per tag) with end-of-year battery levels around 7%, confirming practical viability in GPS-denied indoor environments. This approach offers scalable, maintenance-free RTLS suitable for mobile robotics and large IoT deployments without continuous infrastructure operation.

Abstract

Indoor localization systems face a fundamental trade-off between efficiency and responsiveness, which is especially important for emerging use cases such as mobile robots operating in GPS-denied environments. Traditional RTLS either require continuously powered infrastructure, limiting their scalability, or are limited by their responsiveness. This work presents Eco-WakeLoc, designed to achieve centimeter-level UWB localization while remaining energy-neutral by combining ultra-low power wake-up radios (WuRs) with solar energy harvesting. By activating anchor nodes only on demand, the proposed system eliminates constant energy consumption while achieving centimeter-level positioning accuracy. To reduce coordination overhead and improve scalability, Eco-WakeLoc employs cooperative localization where active tags initiate ranging exchanges (trilateration), while passive tags opportunistically reuse these messages for TDOA positioning. An additive-increase/multiplicative-decrease (AIMD)-based energy-aware scheduler adapts localization rates according to the harvested energy, thereby maximizing the overall performance of the sensor network while ensuring long-term energy neutrality. The measured energy consumption is only 3.22mJ per localization for active tags, 951uJ for passive tags, and 353uJ for anchors. Real-world deployment on a quadruped robot with nine anchors confirms the practical feasibility, achieving an average accuracy of 43cm in dynamic indoor environments. Year-long simulations show that tags achieve an average of 2031 localizations per day, retaining over 7% battery capacity after one year -- demonstrating that the RTLS achieves sustained energy-neutral operation. Eco-WakeLoc demonstrates that high-accuracy indoor localization can be achieved at scale without continuous infrastructure operation, combining energy neutrality, cooperative positioning, and adaptive scheduling.

Figures (9)

• Figure 1: Overview of the developed sensor node used for anchors and tags.
• Figure 2: WakeLoc localization scheme as shown in cortesi25_wakel, combining *TWR with *TDOA. Messages in green are transmissions, orange represents receptions.
• Figure 3: State diagram of the *FSM-based adaptive sampling algorithm: $k/2$ means that $k$ halves in the next step; $k++$ means that $k$ increases by a fixed rate in the next step, in our case by one; $k$ means that $k$ stays the same in the next step.
• Figure 4: Experimental setup for evaluating the localization accuracy. $A$ represents anchors, $V$ the cameras of the Vicon system.
• Figure 5: Solar cell and harvester characteristics. (a) shows the IV-curve of the KXOB201K04 solar cell, and (b) shows the measured relation between light intensity and harvested power into a 3.7 sink together with a fitted polynomial function.