Benjamin P. Kempke

A millimeter-scale wireless imaging system with continuous motion detection and energy harvesting

We present a 2×4×4mm3 imaging system complete with optics, wireless communication, battery, power management, solar harvesting, processor and memory. The system features a 160×160 resolution CMOS image sensor with 304nW continuous in-pixel motion detection mode. System components are fabricated in five different IC layers and die-stacked for minimal form factor. Photovoltaic (PV) cells face the opposite direction of the imager for optimal illumination and generate 456nW at 10klux to enable energy autonomous system operation.

PolyPoint: Guiding Indoor Quadrotors with Ultra-Wideband Localization

We introduce PolyPoint, the first RF localization system which enables the real-time tracking and navigating of quadrotors through complex indoor environments. PolyPoint leverages the new ScenSor transceiver from DecaWave to acquire the timestamps necessary for accurate time-based location estimation and leverages the benefits of antenna and frequency diversity to iteratively refine a tags position. PolyPoint produces quadrotor position estimates at a rate of 20 Hz with median error below 40 cm and average error of 56 cm in line-of-sight conditions. PolyPoint approaches the localization accuracy necessary to safely navigate quadrotors indoors, a feat currently achieved by costly and delicate optical motion capture systems.

MBus: A 17.5 pJ/bit/chip portable interconnect bus for millimeter-scale sensor systems with 8 nW standby power

We propose an ultra-low power interconnect bus for millimeter-scale wireless sensor nodes. Using only 4 IO pads, the bus minimizes the required chip real estate, enabling ultrasmall form factors in modular sensor node designs. Low power is achieved using a “clockless” design of member nodes while aggressive power gating allows an ultra-low power standby mode with only 53 gates powered on. An integrated wakeup scheme is compatible with PMUs that have a special low power standby mode. The MBus is fully synthesizable and uses robust timing. Implemented in a 3 module system in 180nm technology, Mbus achieves 8nW of standby power and 17.5 pJ/bit/chip.

Harmonium: asymmetric, bandstitched UWB for fast, accurate, and robust indoor localization

We introduce Harmonium, a novel ultra-wideband RF localization architecture that achieves decimeter-scale accuracy indoors. Harmonium strikes a balance between tag simplicity and processing complexity to provide fast and accurate indoor location estimates. Harmonium uses only commodity components and consists of a small, inexpensive, lightweight, and FCC-compliant ultra-wideband transmitter or tag, fixed infrastructure anchors with known locations, and centralized processing that calculates the tags position. Anchors employ a new frequency-stepped narrowband receiver architecture that rejects narrowband interferers and extracts high-resolution timing information without the cost or complexity of traditional ultra-wideband approaches. In a complex indoor environment, 90% of position estimates obtained with Harmonium exhibit less than 31 cm of error with an average 9 cm of inter-sample noise. In non-line-of-sight conditions (i.e. through-wall), 90% of position error is less than 42 cm. The tag draws 75 mW when actively transmitting, or 3.9 mJ per location fix at the 19 Hz update rate. Tags weigh 3 g and cost

Calibration-free network localization using non-line-of-sight ultra-wideband measurements

4.50 USD at modest volumes. Harmonium introduces a new design point for indoor localization and enables localization of small, fast objects such as micro quadrotors, devices previously restricted to expensive optical motion capture systems.

Demo: Ultra-constrained sensor platform interfacing

We present a method for calibration-free, infrastructure-free localization in sensor networks. Our strategy is to estimate node positions and noise distributions of all links in the network simultaneously -- a strategy that has not been attempted thus far. In particular, we account for biased, NLOS range measurements from UWB devices that lead to multi-modal noise distributions, for which few solutions exist to date. Our approach circumvents cumbersome a-priori calibration, allows for rapid deployment in unknown environments, and facilitates adaptation to changing conditions. Our first contribution is a generalization of the classical multidimensional scaling algorithm to account for measurements that have multi-modal error distributions. Our second contribution is an online approach that iterates between node localization and noise parameter estimation. We validate our method in 3-dimensional networks, (i) through simulation to test the sensitivity of the algorithm on its design parameters, and (ii) through physical experimentation in a NLOS environment. Our setup uses UWB devices that provide time-of-flight measurements, which can lead to positively biased distance measurements in NLOS conditions. We show that our algorithm converges to accurate position estimates, even when initial position estimates are very uncertain, initial error models are unknown, and a significant proportion of the network links are in NLOS.

Demo: PolyPoint: High-Precision Indoor Localization with UWB

In this work we expose the challenges of interfacing both conventional and new systems with an extremely resource constrained platform. We find that even when attempts are made to utilize an industry standard protocol (I2C), necessary protocol modifications for ultra-low power design means that interfacing remains non-trivial. We present a functional 0.4mm × 0.8mm ARM Cortex M0 with 3KB of RAM, 24 GPIOs, and an ultra-low power I2C interface. This chip is part of the Michigan Micro Mote (M3) project, which is designed to build a complete software and hardware platform for general purpose sensing at the millimeter scale. We demo an I2C interface circuit allowing commercial hardware to program and interact with the chip and present the beginning of the millimeter scale sensing revolution.

Circuit and System Designs of Ultra-Low Power Sensor Nodes With Illustration in a Miniaturized GNSS Logger for Position Tracking: Part II—Data Communication, Energy Harvesting, Power Management, and Digital Circuits

We demonstrate PolyPoint, a high-fidelity RF-based indoor localization system that achieves 28~cm accuracy indoors and tracks a fast-moving quadcopter with only 56~cm average error. PolyPoint uses ultra-wideband signals to achieve high precision RF time-of-flight estimates between nodes. To further improve accuracy, PolyPoint exploits two forms of diversity: frequency diversity, which leverages several ultra-wideband channels to improve channel response, and antenna diversity, which adds three antennas at 120 degree offsets to mitigate the effects of antenna polarization and nulls. PolyPoint introduces an efficient, novel ranging protocol that maximizes these diversity sources with a minimal number of packets. Additionally, this work introduces a new hardware platform that provides ranging and localization as a service. The minimal TriPoint module integrates an ultra-wideband transceiver and microcontroller with firmware that implements the protocol. The TriTag carrier board adds Bluetooth and batteries to create a complete mobile tag, and the TriBase anchor platform integrates a TriPoint with an Intel Edison to act as anchors for the system.

Circuit and System Designs of Ultra-Low Power Sensor Nodes With Illustration in a Miniaturized GNSS Logger for Position Tracking: Part I—Analog Circuit Techniques

This two-part paper reviews recent innovations in circuit design that have accelerated the miniaturization of sensor nodes. In this second part of the paper, we focus on key building blocks of miniaturized sensor nodes, such as data transceivers, energy harvesters, power management units, and digital logic circuits. System level design considerations are also discussed to provide guidelines for the design of a miniaturized system. As an example prototype design, a 2.7-cm3 global navigation satellite system (GNSS) logger is proposed. This paper includes a die-stacked sensor platform composed of an ARM cortex M0 processor, energy harvester, power management unit, solar cell, optical receiver, sensor layer, and RF transmitter that exploits the discussed design techniques for ultra-low power operation. The GNSS logger can store GNSS signals of >1 k positions on a single battery charging without additional energy harvesting.

Demo: Michigan's IoT Toolkit

This paper, split into Parts I and II, reviews recent innovations in circuit design that have accelerated the miniaturization of sensor nodes. Design techniques for key building blocks, such as sensor interfaces, timing reference, data communication, energy harvesting, and power management are reviewed. In particular, Part I introduces analog circuit techniques and sensor interfaces for miniaturized sensor nodes. The energy budget of such system is highly restricted due to the small battery volume. Therefore, ultra-low power design techniques are critical enablers and are reviewed. Design techniques for compact monolithic integration are also discussed.