Laurent Segers

SoundCompass: A Distributed MEMS Microphone Array-Based Sensor for Sound Source Localization

Sound source localization is a well-researched subject with applications ranging from localizing sniper fire in urban battlefields to cataloging wildlife in rural areas. One critical application is the localization of noise pollution sources in urban environments, due to an increasing body of evidence linking noise pollution to adverse effects on human health. Current noise mapping techniques often fail to accurately identify noise pollution sources, because they rely on the interpolation of a limited number of scattered sound sensors. Aiming to produce accurate noise pollution maps, we developed the SoundCompass, a low-cost sound sensor capable of measuring local noise levels and sound field directionality. Our first prototype is composed of a sensor array of 52 Microelectromechanical systems (MEMS) microphones, an inertial measuring unit and a low-power field-programmable gate array (FPGA). This article presents the SoundCompass’s hardware and firmware design together with a data fusion technique that exploits the sensing capabilities of the SoundCompass in a wireless sensor network to localize noise pollution sources. Live tests produced a sound source localization accuracy of a few centimeters in a 25-m2 anechoic chamber, while simulation results accurately located up to five broadband sound sources in a 10,000-m2 open field.

Ultrasonic multiple-access ranging system using spread spectrum and MEMS technology for indoor localization.

Indoor localization of persons and objects poses a great engineering challenge. Previously developed localization systems demonstrate the use of wideband techniques in ultrasound ranging systems. Direct sequence and frequency hopping spread spectrum ultrasound signals have been proven to achieve a high level of accuracy. A novel ranging method using the frequency hopping spread spectrum with finite impulse response filtering will be investigated and compared against the direct sequence spread spectrum. In the first setup, distances are estimated in a single-access environment, while in the second setup, two senders and one receiver are used. During the experiments, the micro-electromechanical systems are used as ultrasonic sensors, while the senders were implemented using field programmable gate arrays. Results show that in a single-access environment, the direct sequence spread spectrum method offers slightly better accuracy and precision performance compared to the frequency hopping spread spectrum. When two senders are used, measurements point out that the frequency hopping spread spectrum is more robust to near-far effects than the direct sequence spread spectrum.

An Ultrasonic Multiple-Access Ranging Core Based on Frequency Shift Keying Towards Indoor Localization

This paper describes a new approach and implementation methodology for indoor ranging based on the time difference of arrival using code division multiple access with ultrasound signals. A novel implementation based on a field programmable gate array using finite impulse response filters and an optimized correlation demodulator implementation for ultrasound orthogonal signals is developed. Orthogonal codes are modulated onto ultrasound signals using frequency shift keying with carrier frequencies of 24.5 kHz and 26 kHz. This implementation enhances the possibilities for real-time, embedded and low-power tracking of several simultaneous transmitters. Due to the high degree of parallelism offered by field programmable gate arrays, up to four transmitters can be tracked simultaneously. The implementation requires at most 30% of the available logic gates of a Spartan-6 XC6SLX45 device and is evaluated on accuracy and precision through several ranging topologies. In the first topology, the distance between one transmitter and one receiver is evaluated. Afterwards, ranging analyses are applied between two simultaneous transmitters and one receiver. Ultimately, the position of the receiver against four transmitters using trilateration is also demonstrated. Results show enhanced distance measurements with distances ranging from a few centimeters up to 17 m, while keeping a centimeter-level accuracy.

Microbenchmarks for GPU Characteristics: The Occupancy Roofline and the Pipeline Model

In this paper we present microbenchmarks in OpenCL to measure the most important performance characteristics of GPUs. Microbenchmarks try to measure individual characteristics that influence the performance. First, performance, in operations or bytes per second, is measured with respect to the occupancy and as such provides an occupancy roofline curve. The curve shows at which occupancy level peak performance is reached. Second, when considering the cycles per instruction of each compute unit, we measure the two most important characteristics of an instruction: its issue and completion latency. This is based on modeling each compute unit as a pipeline for computations and a pipeline for the memory access. We also measure some specific characteristics: the influence of independent instructions within a kernel and thread divergence. We argue that these are the most important characteristics for understanding the performance and predicting performance. The results for several Nvidia and AMD GPUs are provided. A free java application containing the microbenchmarks is available on www.gpuperformance.org.

Efficient Key Pre-distribution for 6LoWPAN

The Internet of Things is imposing an evolution of the capabilities of wireless sensor networks. The new IP-based 6LoWPAN standard for low power sensor networks allows an almost seamless connection of local sensor networks to the Internet. On the other hand, the connection to the Internet also opens doors for unauthorized nodes to become part of the local network. The most important challenge in preventing this, is the implementation of a key management architecture, keeping in mind that the sensor nodes are constrained in power consumption and data storage capacity. This paper builds on a previously proposed symmetric key management scheme for 6LoWPAN networks presented by Smeets et al.in [1]. The original scheme is based on wired bootstrapping for the enrollment of new nodes, while the paper at hand proposes a wireless method. We analyze the original wired scheme and propose an improved wireless scheme, elaborating on the practical implementation on Zolertia Z1 nodes running Contiki-OS. We show that it is possible to provide end-to-end security using wireless bootstrapping within the constraints of the tiny nodes at hand.

A runtime reconfigurable FPGA-based microphone array for sound source localization

Microphone arrays are able to recognize, profile and locate sound-sources in noisy environments, but their quality is determined by the number of microphones. A higher number of microphones increases the computational demand, making real-time response challenging. In this demo, we present a scalable and runtime reconfigurable architecture able to support a variable number of microphones and orientations in order to provide accurate sound-source localization in real-time.

A cryptographic key management architecture for dynamic 6LowPan networks

Wireless sensor networks are becoming an important facilitator for the Internet of Things. These embedded devices can harvest dierent types of information such as temperature, pressure and humidity, which oer important data for making decisions regarding various applications such as healthcare, logistics and smart homes. Dierent sensors working together act as a local sensor network. With the advent of the new 6LowPan standard the sensor nodes can even participate in Internet communications, opening up even more possibilities. The downside is that these networks are more prone to intrusion by unwanted parties. Furthermore implementing security is not straightforward due to the constrained nature of the sensor nodes, although dierent solutions have been proposed. One of the remaining and most challenging issues is the key management problem. In this paper, we propose a symmetric key management scheme for wireless sensor networks that uses tamper-proof hardware for key generation and distribution. The scheme requires no deployment knowledge before enrolling and makes use of a trusted central entity for key negotiation to provide end-to-end security. Our implementation and evaluation were performed on the tiny Zolertia Z1 hardware platform, running Contiki-OS. The performance and security evaluation show This work is funded by the IWT-TETRA project 120105: 6LoWPAN - Towards zero