D. K. Arvind

SpeckMAC: low-power decentralised MAC protocols for low data rate transmissions in specknets

This paper introduces SpeckMAC, a novel low-power distributed, unsynchronised, random-access MAC protocol for a wireless mobile ad-hoc network of miniature specks called specknet. Two variations of the SpeckMAC protocol were compared theoretically with the well-known B-MAC protocol. All three MAC protocols were implemented on a larger speck prototype called the ProSpeckz for a logical location maintenance algorithm for two types of batteries with differing current drain profiles. ProSpeckz utilizing SpeckMAC-B and SpeckMAC-D showed improvements in lifetime over those using the B-MAC protocol by 27.4% and 38.0%, respectively when Polymer Li-ion batteries were used; and by 83.5% and 117.9%, respectively, when CR1220 button cells were employed.

Orient-2 : a realtime wireless posture tracking system using local orientation estimation

A realtime posture tracking system has been developed using a network of compact wireless sensor devices worn by the user. Each device is a complete inertial/magnetic tracking unit which performs in situ orientation estimation based on its own sensor readings, using a complementary quaternion-based filter. Compared to existing systems which transmit raw sensor data to a PC for processing, it is shown that this technique reduces bandwidth requirements by 79% for typical usage. In combination with a time division multiple access scheme, this reduction allows for full-body tracking using 15 devices at a 64Hz update rate through a single 250kbps receiver. The data is applied to a rigid body model of the subject to provide a realtime display, and can be exported for use in major animation packages.

Speckled computing: disruptive technology for networked information appliances

Speckled Computing is an emerging technology in which data will be sensed in minute (ultimately around one cubic millimetre) semiconductor grains called Specks. Information will be extracted, exchanged and processed in a collaborative fashion in a wireless network of thousands of Specks, called a Specknet. The impact of Speckled Computing on consumer electronics, especially future information appliances, will be disruptive. Objects and the surrounding environment when treated with Specks, or “Speckled”, will be endowed with sensing, processing and wireless networking capabilities. This would effectively “smarten” everyday objects and surroundings post hoc, transforming them into networked information appliances. This paper introduces the concepts of Specks, Specknets and Speckled Computing, and outlines the challenges to be overcome to realise this technology. A prototype for Specks called ProSpeckz (Programmable Specks over Zigbee Radio) which is currently used as a rapid development platform for Speckled Computing is described. ProSpeckz is also intended as an enabler for integrating the technology of Speckled Computing into consumer electronics applications and some illustrative examples are described in this paper. Index Terms — Networked Information Appliances, Smart Home applications and protocols, Speckled Computing, Wireless computational networks

Respiratory Rate and Flow Waveform Estimation from Tri-axial Accelerometer Data

There is a strong medical need for continuous, unobstrusive respiratory monitoring, and many shortcomings to existing methods. Previous work shows that MEMS accelerometers worn on the torso can measure inclination changes due to breathing, from which a respiratory rate can be obtained. There has been limited validation of these methods. The problem of practical continuous monitoring, in which patient movement disrupts the measurements and the axis of interest changes, has also not been addressed. We demonstrate a method based on tri-axial accelerometer data from a wireless sensor device, which tracks the axis of rotation and obtains angular rates of breathing motion. The resulting rates are validated against gyroscope measurements and show high correlation to flow rate measurements using a nasal cannula. We use a movement detection method to classify periods in which the patient is static and breathing signals can be observed accurately. Within these periods we obtain a close match to cannula measurements, for both the flow rate waveform and derived respiratory rates, over multi-hour datasets obtained from wireless sensor devices on hospital patients. We discuss future directions for improvement and potential methods for estimating absolute airflow rate and tidal volume.

The speckled golfer

This paper describes the application of the first fully wireless network of inertial sensors for full-body 3-D motion capture -- the Orient-2 system, to real-time on-body analysis of the golf swing. The golfer-club system is modelled as a double pendulum. The factors which affect the efficiency of the golf swing are outlined, such as the length of the back swing, the wrist-cock angle, swing plane and club-head speed and methods are described for monitoring them using a wireless network of Orient-2 specks. The implementation of the Speckled Golfer System is described and two motion rules are illustrated for executing efficient golf swings.

Simultaneous Activity and Respiratory Monitoring Using an Accelerometer

Simultaneous monitoring of respiratory function and activity level would be of benefit in the monitoring of chronic conditions such as chronic obstructive pulmonary disorder (COPD), but is ill-addressed by existing methods. Current solutions for monitoring respiratory function are obtrusive and not suitable for pervasive monitoring in the home, while existing activity monitors, not equipped to measure parameters of respiration, do not differentiate between causes of sedentary behaviour. Previous work has validated a method for obtaining angular rates of breathing motion of the chest wall using a tri-axial accelerometer against nasal pressure. We have used this method to perform respiratory monitoring during periods of low activity while simultaneously monitoring activity using a single wireless device. We observe that the optimal placement for respiratory monitoring does not preclude successful activity monitoring. We propose an activity monitoring algorithm based on direct estimation of motion energy observed by the device. We show favourable comparison against three commercial activity monitors validated against indirect calorimetry during a programme of exercise activities in healthy subjects.

Comparative study of segmentation of periodic motion data for mobile gait analysis

Two approaches are presented and compared for segmenting motion data from on-body Orient wireless motion capture system for mobile gait analysis. The first is a basic, model-based algorithm which operates directly on the joint angles computed by the Orient sensor devices. The second is a model-free, Latent Space algorithm, which first aggregates all the sensor data, and then embeds them in a low-dimensional manifold to perform segmentation. The two approaches are compared for segmenting four different styles of walking, and then applied in a hospital-based clinical study for analysing the motion of elderly patients recovering from a fall.

Validation of a new non-invasive automatic monitor of respiratory rate for postoperative subjects

BACKGROUND Respiratory rate is an important measurement in patient care but frequently poorly assessed. We set out to develop a simple non-invasive device to reliably measure respiratory movements and estimate respiratory rate, in clinical circumstances. METHODS Respiratory movement was detected with an encapsulated tri-axial accelerometer (Orient speck) and the data transmitted wirelessly to a computer for analysis. We studied subjects after gynaecological surgery who received opioid analgesia, and compared the derived signal with a signal from nasal cannula using directly matched breaths and within the same 5 min epoch. We analysed the signals for 5 min epochs over a 15 h recording period. RESULTS For matched breath analysis, the instantaneous respiratory rates matched within 2 bpm on 86% of occasions. A similar match was found between epoch averages of the respiratory rate. The mean absolute difference between the respiratory rate measured by nasal cannula and Orient speck was 0.6 bpm. The Orient speck generated reliable measures of respiratory rate every 5 min in 95.4% of epochs. CONCLUSIONS The Orient speck provides a reliable measure of respiratory rate at frequent intervals in subjects receiving patient-controlled morphine analgesia after surgery.

Instruction-Level Parallelism in Asynchronous Processor Architectures

Publisher Summary Centralized controls have been traditionally used to correctly sequence information within processor architectures. However, the ability to sustain this design style is under pressure from a number of directions. This chapter examines the effect of relaxing this strict synchrony on the design and performance of processor architectures. The micronet-based Asynchronous Processor (MAP) is a family of processor architectures that are based on the micronet model of asynchronous control. Micronets are a generalization of Sutherlands micropipeline that dynamically control which stages communicate with each other. Thus, micronets can be viewed not just as a pipeline but rather as a network of communicating stages. Micronets distribute the control amongst the functional units that enables the exploitation of fine-grained concurrency, both between and within program instructions. Micronets are controlled at two levels: (1) The data transfer between microagents is controlled locally, and (2) the type of operation carried out by a microagent (called a micro-operation) and the destination of its result is controlled by the sequencer or by other microagents. Microagents can communicate either across dedicated lines or via shared buses, where arbitration is provided either by the sequencer or some other decentralized mechanism such as a token ring. This chapter also introduces the micronet model and evaluates the performance of micronet-based data paths using behavioral simulations. By viewing the datapath as a network of microagents that communicate asynchronously, fine-grain concurrency between and within instructions can be extracted. The micronet can be easily implemented using simple self-timed elements such as Muller C-elements and conventional gates.

Distributed estimation of linear acceleration for improved accuracy in wireless inertial motion capture

Motion capture using wireless inertial measurement units (IMUs) has many advantages over other techniques. Achieving accurate tracking with IMUs presents a processing challenge, especially for real time tracking. Centralised approaches are bandwidth-intensive and prone to error from packet loss. Methods based solely on local knowledge have poor dynamic accuracy, due to ambiguities introduced by linear acceleration. First we analyse the effect of linear acceleration on orientation accuracy. We then present an efficient distributed method which uses a model of the subjects body structure to estimate and correct for linear acceleration. We validate the behaviour of this method on data from combined optical/inertial capture experiments, and show improved gravity vector estimation and a corresponding increase in orientation accuracy. We estimate the runtime, memory, communication and power requirements of our method, and show that it is a practical software modification to an existing system. The proposed solution is the first to use collaboration between wireless IMUs to improve accuracy.