Content has been formatted as TeX source. Click to format for web.

To Appear 

Content has been formatted for web. Click to view raw TeX

To Appear

Content has been formatted as TeX source. Click to format for web.

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
ultra-small 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
180~nm technology, Mbus achieves 8~nW of standby power
and 17.5~pJ/bit/chip.

Content has been formatted for web. Click to view raw TeX

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 ultra-small 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 180 nm technology, Mbus achieves 8 nW of standby power and 17.5 pJ/bit/chip.

Content has been formatted as TeX source. Click to format for web.

We present a $2\times4\times4$~mm$^3$ imaging system
complete with optics, wireless communication, battery, power
management, solar harvesting, processor and memory. The system
features a 160$\times$160 resolution CMOS image sensor with 304~nW
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
456~nW at 10~klux to enable energy autonomous system operation.

Content has been formatted for web. Click to view raw TeX

We present a 2×4×4 mm³ 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 304 nW 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 456 nW at 10 klux to enable energy autonomous system operation.

Content has been formatted as TeX source. Click to format for web.

The second Radio Aurora Explorer satellite, RAX-2, is a triple CubeSat studying the formation of plasma
irregularities in Earth’s ionosphere. The spacecraft was developed jointly by SRI International and the University of 
Michigan, and it is the first satellite funded by the National Science Foundation. RAX-2 launched October 28, 2011 
and is currently operating on orbit. RAX uses a bistatic radar configuration to study the ionospheric irregularities: a 
ground-based incoherent scatter radar station illuminates the irregularities, and the RAX-based radar receiver
measures radar scatter from the irregularities. RAX has successfully measured radar scatter from the ionospheric 
irregularities, providing unprecedented auroral region measurements. In this paper, we review the mission goals and 
satellite development, and discuss initial flight results from the mission. This includes a summary of results from the 
first detection of radar scatter, power system performance, spacecraft attitude dynamics, global UHF noise 
measurements, and data download strategies and results of partnering with the amateur radio community.

Content has been formatted for web. Click to view raw TeX

The second Radio Aurora Explorer satellite, RAX-2, is a triple CubeSat studying the formation of plasma irregularities in Earth’s ionosphere. The spacecraft was developed jointly by SRI International and the University of Michigan, and it is the first satellite funded by the National Science Foundation. RAX-2 launched October 28, 2011 and is currently operating on orbit. RAX uses a bistatic radar configuration to study the ionospheric irregularities: a ground-based incoherent scatter radar station illuminates the irregularities, and the RAX-based radar receiver measures radar scatter from the irregularities. RAX has successfully measured radar scatter from the ionospheric irregularities, providing unprecedented auroral region measurements. In this paper, we review the mission goals and satellite development, and discuss initial flight results from the mission. This includes a summary of results from the first detection of radar scatter, power system performance, spacecraft attitude dynamics, global UHF noise measurements, and data download strategies and results of partnering with the amateur radio community.

Content has been formatted as TeX source. Click to format for web.

RAX-2 is a 3U CubeSat that is studying the formation of plasma irregularities in the ionosphere. 
The primary payload is a UHF radar receiver which is used in conjunction with ground-based 
incoherent scatter radar stations to characterize the irregularities. RAX is the first CubeSat funded 
by the United States National Science Foundation’s Small Satellite Program for Space Weather 
Research. The satellite, launched October 28, 2011, continues the scientific mission started by the 
RAX-1 CubeSat. This paper discusses the mission and the initial operations of the satellite. After 
successful checkout, RAX-2 began scientific operations on November 22, 2011. With the exception 
of an SD card anomaly, the spacecraft has performed well on orbit. 19 radar experiments have been 
performed, and RAX-2 measurements of radar scatter from the ionospheric irregularities have 
already provided unprecedented detail for characterization and improved understanding of the 
formation of the irregularities. 

Content has been formatted for web. Click to view raw TeX

RAX-2 is a 3U CubeSat that is studying the formation of plasma irregularities in the ionosphere. The primary payload is a UHF radar receiver which is used in conjunction with ground-based incoherent scatter radar stations to characterize the irregularities. RAX is the first CubeSat funded by the United States National Science Foundation’s Small Satellite Program for Space Weather Research. The satellite, launched October 28, 2011, continues the scientific mission started by the RAX-1 CubeSat. This paper discusses the mission and the initial operations of the satellite. After successful checkout, RAX-2 began scientific operations on November 22, 2011. With the exception of an SD card anomaly, the spacecraft has performed well on orbit. 19 radar experiments have been performed, and RAX-2 measurements of radar scatter from the ionospheric irregularities have already provided unprecedented detail for characterization and improved understanding of the formation of the irregularities.

Content has been formatted as TeX source. Click to format for web.

The Radio Aurora Explorer (RAX) is a CubeSat that was developed to study space weather in Earth׳s ionosphere. The scientific payload is a bistatic radar system in which an onboard receiver works in cooperation with a ground-based transmitter. Accuracy of the onboard clock is critical for processing the radar measurements. The RAX timing system utilizes commercial off-the-shelf components integrated into custom subsystems. GPS is used to maintain absolute timing accuracy better than 1~μs, but the subsystem is not always available due to power constraints, so a method has been developed to correct the onboard clock error without the use of GPS. The clock correction utilizes range measurements extracted from the pulses emitted by the transmitter, and resulting absolute clock accuracies of better than 0.20~s with drift of less than 21~ns/s have been demonstrated. The RAX timing system and the clock correction algorithm are presented as a reference for other spacecraft designers and are critical for those analyzing RAX data.

Content has been formatted for web. Click to view raw TeX

The Radio Aurora Explorer (RAX) is a CubeSat that was developed to study space weather in Earth׳s ionosphere. The scientific payload is a bistatic radar system in which an onboard receiver works in cooperation with a ground-based transmitter. Accuracy of the onboard clock is critical for processing the radar measurements. The RAX timing system utilizes commercial off-the-shelf components integrated into custom subsystems. GPS is used to maintain absolute timing accuracy better than 1 μs, but the subsystem is not always available due to power constraints, so a method has been developed to correct the onboard clock error without the use of GPS. The clock correction utilizes range measurements extracted from the pulses emitted by the transmitter, and resulting absolute clock accuracies of better than 0.20 s with drift of less than 21 ns/s have been demonstrated. The RAX timing system and the clock correction algorithm are presented as a reference for other spacecraft designers and are critical for those analyzing RAX data.

Content has been formatted as TeX source. Click to format for web.

The Radio Aurora Explorer CubeSat detected the first radar echoes during the solar storm of March 8, 2012. The 300~s ground-to-space bi-static radar experiment was conducted in conjunction with the Poker Flat Incoherent Scatter Radar in the local morning (~8~am) over Poker Flat, Alaska. The geomagnetic conditions for the E region field-aligned irregularity generation were optimal due to strong (about 1500~m/s) F region ion drifts and sufficient E region ionization (electron densities were ~2~×~1011~m−3). The corresponding E region electric field of ~80~mV/m was larger than the excitation threshold for the Farley-Buneman instability. An auto-correlation analysis resolved, for the first time, the distribution of auroral E region backscatter with 3~km resolution in altitude and sub-degree resolution in aspect angle. Moreover, the measured Doppler velocities of the UHF scatter shows the phase speed saturation of the meter-scale plasma waves. The measured Doppler velocity is in excellent agreement with the Cs cos θ formula for auroral E region irregularities.

Content has been formatted for web. Click to view raw TeX

The Radio Aurora Explorer CubeSat detected the first radar echoes during the solar storm of March 8, 2012. The 300 s ground-to-space bi-static radar experiment was conducted in conjunction with the Poker Flat Incoherent Scatter Radar in the local morning ( 8 am) over Poker Flat, Alaska. The geomagnetic conditions for the E region field-aligned irregularity generation were optimal due to strong (about 1500 m/s) F region ion drifts and sufficient E region ionization (electron densities were  2 × 1011 m−3). The corresponding E region electric field of  80 mV/m was larger than the excitation threshold for the Farley-Buneman instability. An auto-correlation analysis resolved, for the first time, the distribution of auroral E region backscatter with 3 km resolution in altitude and sub-degree resolution in aspect angle. Moreover, the measured Doppler velocities of the UHF scatter shows the phase speed saturation of the meter-scale plasma waves. The measured Doppler velocity is in excellent agreement with the Cs cos θ formula for auroral E region irregularities.

Content has been formatted as TeX source. Click to format for web.

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 tag’s 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.

Content has been formatted for web. Click to view raw TeX

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 tag’s 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.

Content has been formatted as TeX source. Click to format for web.

We introduce {\em Harmonia}, a new RF-based localization scheme
that provides the simplicity, cost, and power advantages of
traditional narrowband radios with the decimeter-scale
accuracy of ultra wideband localization techniques. Harmonia is
an asymmetric {\em tag} and {\em anchor} system, requiring
minimal modifications to existing low-power wireless devices
to support high-fidelity localization with comparatively
modest infrastructure costs.  A prototype Harmonia design offers
location estimates with an average-case error of 53.4~cm in
complex, heavy-multipath, indoor environments and captures
location estimates at 56~Hz while requiring only 1.7~mA
additional power draw for each tag and complying with all
US~UWB regulations.  We believe this architecture's
combination of accuracy, update rate, power draw, and system
complexity will lead to a new point in the design space.

Content has been formatted for web. Click to view raw TeX

We introduce Harmonia, a new RF-based localization scheme that provides the simplicity, cost, and power advantages of traditional narrowband radios with the decimeter-scale accuracy of ultra wideband localization techniques. Harmonia is an asymmetric tag and anchor system, requiring minimal modifications to existing low-power wireless devices to support high-fidelity localization with comparatively modest infrastructure costs. A prototype Harmonia design offers location estimates with an average-case error of 53.4 cm in complex, heavy-multipath, indoor environments and captures location estimates at 56 Hz while requiring only 1.7 mA additional power draw for each tag and complying with all US UWB regulations. We believe this architecture’s combination of accuracy, update rate, power draw, and system complexity will lead to a new point in the design space.

Content has been formatted as TeX source. Click to format for web.

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~x~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.

Content has been formatted for web. Click to view raw TeX

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 x 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.

Content has been formatted as TeX source. Click to format for web.

Recent advances in RF ranging techniques have shown superior performance in difficult RF environments but either lack the practicality of a real-time implementation or lack flexibility through purpose-built hardware. We present SR2, a super-resolution ranging platform developed for the software radio environment. SR2 achieves low resource utilization and hardware complexity requirements through a coherent RF design, making SR2 realizable on commodity software radios.

Content has been formatted for web. Click to view raw TeX

Recent advances in RF ranging techniques have shown superior performance in difficult RF environments but either lack the practicality of a real-time implementation or lack flexibility through purpose-built hardware. We present SR2, a super-resolution ranging platform developed for the software radio environment. SR2 achieves low resource utilization and hardware complexity requirements through a coherent RF design, making SR2 realizable on commodity software radios.