arXiv subjects

Filip Maksimovic

Publications and source records attributed to Filip Maksimovic.

3 recordsLinked to original sources

arXiv2026

LightCal: Lightweight Optical-Pulse Bootstrap Calibration for Crystal-Free BLE Radios

Crystal-free Bluetooth Low Energy (BLE) radios remove the off-chip high-frequency crystal oscillator and can therefore reduce the cost, size, and integration complexity of Internet of Things (IoT) nodes. However, they face a fundamental bootstrap problem: before a node can communicate over RF, it must first obtain a sufficiently accurate carrier-frequency reference. Existing approaches typically rely on RF beacons, already-connected nodes, or search-based channel acquisition, which can incur long startup latency and provide limited feedback when the initial carrier offset is large. This paper presents LightCal, a lightweight bootstrap calibration method that uses periodic optical pulses as an external timing reference for crystal-free BLE radios. LightCal is designed for highly resource-constrained platforms and requires only simple optical pulse reception. We implement LightCal on scum, a crystal-free IoT platform and use a commercial HTC Lighthouse V1 base station as an unmodified off-the-shelf optical pulse source. Experimental results show that pulse accumulation substantially improves the effective timing stability of Lighthouse sync pulses on SC$\mu$M and enables practical BLE bootstrap calibration. In the current scum prototype, optical calibration brings the RF carrier into a bounded residual-error range, and the remaining offset is resolved by a narrow transmit-time fine sweep. The results demonstrate that optical pulse references can provide a practical pre-RF bootstrap calibration path for crystal-free and highly integrated IoT platforms.

cs.NI↗

arXiv2026

A Digital Twin Platform Enabling Monolithic Crystal-Free Bluetooth Low Energy Single-Chip Sensor Motes

Low-power wireless-capable systems-on-chips (SoCs) are critical for researching many of our current environmental issues. The scale at which these devices are needed for many applications necessitates innovation in their design to reduce the various capital and labor costs involved with operating an extensive sensor network. This can be difficult for devices with novel wireless architectures, as many emerging architectures lack commercially available development platforms. This makes pre-silicon validation challenging, and the impact of a failed tapeout is unacceptable when the cost is of primary concern for these devices. In this work, we propose a digital twin ecosystem for Bluetooth Low-Energy (BLE) with physical-layer (PHY) control intended for novel device development and demonstrated through use with crystal-free single-chip sensor motes. We present this system operating with multiple RF front ends and digital baseband implementations, including a commercially available Software Defined Radio (SDR) with synthesized RTL and embedded firmware, along with an existing crystal-free SoC front end and FPGA digital baseband. These configurations are shown to be capable of communicating sensor data with commercially available BLE devices and achieving receiver sensitivities up to -82 dBm, exceeding the minimum BLE specification. This approach is extendable to other hardware and communication protocols and promises to enable inexpensive, reusable validation and verification tools for novel wireless devices.

eess.SP↗

arXiv2019

Experimental Clock Calibration\\on a Crystal-Free Mote-on-a-Chip

The elimination of the off-chip frequency reference, typically a crystal oscillator, would bring important benefits in terms of size, price and energy efficiency to IEEE802.15.4 compliant radios and systems-on-chip. The stability of on-chip oscillators is orders of magnitude worse than that of a crystal. It is known that as the temperature changes, they can drift more than 50 ppm/{\deg}C. This paper presents the result of an extensive experimental study. First, we propose mechanisms for crystal-free radios to be able to track an IEEE802.15.4 join proxy, calibrate the on-chip oscillators and maintain calibration against temperature changes. Then, we implement the resulting algorithms on a crystal-free platform and present the results of an experimental validation. We show that our approach is able to track a crystal-based IEEE802.15.4-compliant join proxy and maintain the requested radio frequency stability of +/-40 ppm, even when subject to temperature variation of 2{\deg}C/min.

cs.NI↗