Prasant Misra

Safety assurance and rescue communication systems in high-stress environments: A mining case study

Effective communication is critical to the success of response and rescue operations; however, unreliable operation of communication systems in high-stress environments is a significant obstacle to achieving this. The contribution of this article is threefold. First, it outlines those common characteristics that impair communication in high-stress environments and then evaluates their importance, specifically in the underground mine environment. Second, it discusses current underground mine communication techniques and identifies their potential problems. Third, it explores the design of wireless sensor network based communication and location sensing systems that could potentially address current challenges. Finally, preliminary results are presented of an empirical study of communication using a WSN constructed from commercially available wireless sensor nodes in an underground mine near Parkes, New South Wales, Australia.

Building the Internet of Things with bluetooth smart

The Internet of Things, or the IoT, is an emerging, disruptive technology that enables physical devices to communicate across disparate networks. IP has been the de facto standard for seamless inte ...

Efficient cross-correlation via sparse representation in sensor networks

Cross-correlation is a popular signal processing technique used in numerous localization and tracking systems for obtaining reliable range information. However, a practical efficient implementation has not yet been achieved on resource constrained wireless sensor network platforms. We propose cross-correlation via sparse representation: a new framework for ranging based on l1-minimization. The key idea is to compress the signal samples on the mote platform by efficient random projections and transfer them to a central device, where a convex optimization process estimates the range by exploiting its sparsity in our proposed correlation domain. Through sparse representation theory validation, extensive empirical studies and experiments on an end-to-end acoustic ranging system implemented on resource limited off-the-shelf sensor nodes, we show that the proposed framework, together with the proposed correlation domain achieved up to two order of magnitude better performance compared to naive approaches such as working on DCT domain and downsampling. Furthermore, compared to cross-correlation results, 30-40% measurements are sufficient to obtain precise range estimates with an additional bias of only 2-6cm for high accuracy application requirements, while 5% measurements are adequate to achieve approximately 100cm precision for lower accuracy applications.

Energy efficient GPS acquisition with sparse-gps

Following rising demands in positioning with GPS, low-cost receivers are becoming widely available; but their energy demands are still too high. For energy efficient GPS sensing in delay-tolerant applications, the possibility of offloading a few milliseconds of raw signal samples and leveraging the greater processing power of the cloud for obtaining a position fix is being actively investigated. In an attempt to reduce the energy cost of this data offloading operation, we propose Sparse-GPS: a new computing framework for GPS acquisition via sparse approximation. Within the framework, GPS signals can be efficiently compressed by random ensembles. The sparse acquisition information, pertaining to the visible satellites that are embedded within these limited measurements, can subsequently be recovered by our proposed representation dictionary. By extensive empirical evaluations, we demonstrate the acquisition quality and energy gains of Sparse-GPS. We show that it is twice as energy efficient than offloading uncompressed data, and has 5-10 times lower energy costs than standalone GPS; with a median positioning accuracy of 40 m.

Improving the coverage range of ultrasound-based localization systems

Location awareness is of benefit to a rich set of applications in indoor environments such as asset tracking, resource discovery, interactive virtual games, location-aware sensor networking, navigation support for humans and robots, etc. There exists a vast array of location sensing systems, but they mostly operate under dense indoor deployment due to the limited range and coverage of the sensing device. In this paper, we focus on improving coverage range - a critical prerequisite for localization. Our experiments using the existing Cricket [1] system reveals many of its limitations. We overcome these hurdles, and present the design, implementation and evaluation of a custom designed omni-directional ultrasonic receiver unit integrated with the existing Cricket motes. The modified Cricket system improves the coverage range by ≈20% in comparison to the original Cricket. The lessons and experiences also provide an analytical and system-level understanding of how various factors affect the ranging characteristics.

Bluetooth smart: An enabling technology for the Internet of Things

The past couple of years have seen a heightened interest in the Internet of Things (IoT), transcending industry, academia and government. As with new ideas that hold immense potential, the optimism of IoT has also exaggerated the underlying technologies well before they can mature into a sustainable ecosystem. While 6LoWPAN has emerged as a disruptive technology that brings IP capability to networks of resource constrained devices, a suitable radio technology for this device class is still debatable. In the recent past, Bluetooth Low Energy (LE) - a subset of the Bluetooth v4.0 stack - has surfaced as an appealing alternative that provides a low-power and loosely coupled mechanism for sensor data collection with ubiquitous units (e.g., smartphones and tablets). When Bluetooth 4.0 was first released, it was not targeted for IP-connected devices but for communication between two neighboring peers. However, the latest release of Bluetooth 4.2 offers features that makes Bluetooth LE a competitive candidate among the available low-power communication technologies in the IoT space. In this paper, we discuss the novel features of Bluetooth LE and its applicability in 6LoWPAN networks. We also highlight important research questions and pointers for potential improvement for its greater impact.

Acoustical ranging techniques in embedded wireless sensor networked devices

Location sensing provides endless opportunities for a wide range of applications in GPS-obstructed environments, where, typically, there is a need for a higher degree of accuracy. In this article, we focus on robust range estimation, an important prerequisite for fine-grained localization. Motivated by the promise of acoustic in delivering high ranging accuracy, we present the design, implementation, and evaluation of acoustic (both ultrasound and audible) ranging systems. We distill the limitations of acoustic ranging and present efficient signal designs and detection algorithms to overcome the challenges of coverage, range, accuracy/resolution, tolerance to Dopplers effect, and audible intensity. We evaluate our proposed techniques experimentally on TWEET, a low-power platform purpose-built for acoustic ranging applications. Our experiments demonstrate an operational range of 20m (outdoor) and an average accuracy ≈2cm in the ultrasound domain. Finally, we present the design of an audible-range acoustic tracking service that encompasses the benefits of a near-inaudible acoustic broadband chirp and approximately two times increase in Doppler tolerance to achieve better performance.

An empirical study of asymmetry in low-power wireless links

Experimental studies of wireless sensor networks have shown that asymmetry in low-power wireless links has a significant effect on the performance of WSN protocols. Protocols that work well in simulation studies often fail when link asymmetry is encountered in real-world deployments. Thus, characterization of asymmetry is of importance for the design of resilient WSN protocols that will work in practice. The contribution of this article is twofold. First, it identifies some of the hardware and physical factors that can contribute to link asymmetry, and gives an experimental assessment of their relative importance. Second, it examines the impact of packet length and interpacket interval on protocol operation, and identifies possible interactions that also cause asymmetrical behavior.

Spray: A multi-modal localization system for stationary sensor network deployment

We present a localization system that targets rapid deployment of stationary wireless sensor networks (WSN). The system uses a particle filter to fuse measurements from multiple localization modalities, such as RF ranging, neighbor information or maps, to obtain position estimations with higher accuracy than that of the individual modalities. The system isolates different modalities into separate components which can be included or excluded independently to tailor the system to a specific scenario. We show that position estimations can be improved with our system by combining multiple modalities. We evaluate the performance of the system in both an indoor and outdoor environment using combinations of five different modalities. Using two anchor nodes as reference points and combining all five modalities, we obtain RMS (Root Mean Square) estimation errors of approximately 2.5 m in both cases, while using the components individually results in errors within the range of 3.5 and 9 m.

Characterization of asymmetry in low-power wireless links: an empirical study

Experimental studies in wireless sensor network (WSN) have shown that asymmetry in low-power wireless links have a significant effect on the performance of WSN protocols. Protocols, which work in simulation studies often fail when link asymmetry is encountered in real deployments. Therefore, characterization of link asymmetry is of importance for the design and operation of resilient WSN protocols in real scenarios. This paper details an empirical study to characterize link asymmetry in WSNs. It presents a systematic approach to measure the effects of hardware performance and environmental factors on link asymmetry using off-the-shelf WSN devices. It shows that, for the given hardware platform, transmitter power and receiver sensitivity are the major factors responsible for asymmetry in low-power wireless links, while frequency misalignment in the transmitter and power variations in the antenna are unlikely causes for it.