A preview of the PDF is not available
Sensifi: A Wireless Sensing System for Ultra-High-Rate Applications
Preprints and early-stage research may not have been peer reviewed yet.
Abstract and Figures
Wireless Sensor Networks (WSNs) are being used in various applications such as structural health monitoring and industrial control. Since energy efficiency is one of the major design factors, the existing WSNs primarily rely on low-power, low-rate wireless technologies such as 802.15.4 and Bluetooth. In this paper, we strive to tackle the challenges of developing ultra-high-rate WSNs based on 802.11 (WiFi) standard by proposing Sensifi. As an illustrative application of this system, we consider vibration test monitoring of spacecraft and identify system design requirements and challenges. Our main contributions are as follows. First, we propose packet encoding methods to reduce the overhead of assigning accurate timestamps to samples. Second, we propose energy efficiency methods to enhance the system's lifetime. Third, we reduce the overhead of processing outgoing packets through network stack to enhance sampling rate and mitigate sampling rate instability. Fourth, we study and reduce the delay of processing incoming packets through network stack to enhance the accuracy of time synchronization among nodes. Fifth, we propose a low-power node design for ultra-high-rate applications. Sixth, we use our node design to empirically evaluate the system.
Figures - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
ResearchGate has not been able to resolve any citations for this publication.
An important problem of modern Wi-Fis is the interferences caused by hidden stations active in the same area, or in multihop communications. All these issues significantly degrade the efficiency of the random channel access methods. Recent standardization and research activities are focused on solving coordination problems between various Wi-Fi devices. For example, the ongoing development of Wi-Fi 7 includes a coordinated schedule between the access points as a candidate solution. Consequently, Wi-Fi has many deterministic channel access mechanisms, which schedule channel time in a periodic manner well in advance and, thus, are utilized for streaming QoS sensitive data. However, both random traffic intensity and error-prone nature of the wireless channel complicate choosing such reservation parameters, i.e., the duration and the period of the reserved time intervals, that satisfy QoS requirements while minimizing channel time consumption. This paper introduces a general mathematical framework to solve the problem of choosing appropriate reservations parameters. The comparison of the analytical and simulation results show the high accuracy of the proposed framework. Finally, the paper gives an example of how to use the developed framework to maximize the network capacity.
Wireless sensor networks require time synchronization, which is the coordination of events or actions to make a system operate in unison. In this work, real experiments and a theoretical analysis of the behavior of the clock sources, most used in wireless sensor networks, have been carried out. The experiments have been performed on two real platforms from two different manufacturers in real environments with sudden changes in temperature. Complementary metal-oxide-semiconductor oscillators have a low accuracy, bigger than 500 ppm, and a high dependency with temperature. External crystal oscillators have good accuracy, around 20 ppm, and are stable with temperature. Temperature-compensated crystal oscillators are very accurate, around 5 ppm, and the temperature has no influence in their drift. The use of phase-locked loop circuits minimizes the impact of temperature and stabilizes oscillators. We highlight and demonstrate the importance of the early stages of design, especially the selection of the clock source, because that decision has a great impact on the performance of the time synchronization in wireless sensor networks.
Structural health monitoring is the fact of estimating the state of structural healthor detecting the changes in structure that affect its performance. The traditional approach to monitor the structural health is by using centralized data acquisition hub wired to tens or even hundreds of sensors, and the installation and maintenance of these cabled systems represent significant concerns, prompting the move toward wireless sensor network. As cost effectiveness and energy efficiency is a major concern, our main interest is to reduce the amount of overhead while keeping the structural health monitoring accurate. Since most of the compression algorithm is heavy weight for wireless sensor network with respect to payload compression, here we have analyzed an algorithmic comparison of arithmetic coding algorithm and Huffman coding algorithm. Evaluation shows that arithmetic coding is more efficient than Huffman coding for payload compression.
Profiling and minimizing the energy consumption of IoT devices is an essential step towards employing IoT in various application domains. In this paper we propose EMPIOT, an accurate, low-cost, easy to build, and flexible, power measurement platform. We present the hardware and software components of this platform, and study the effect of various design parameters on accuracy. In particular, we analyze the effect of driver, bus speed, input voltage, and buffering mechanism, on sampling rate, measurement accuracy and processing demand. These extensive experimental studies enable us to configure the system in order to achieve its highest performance. We also propose a novel calibration technique and report the calibration parameters under various settings. Using five different IoT devices performing four types of workloads, we evaluate the performance of EMPIOT against the ground truth obtained from high-accuracy devices. Our results show that, for very low-power devices that utilize 802.15.4 wireless standard, measurement error is less than 4%. In addition, for 802.11-based devices that generate short and high power spikes, error is less than 3%.
Despite the ubiquity of WiFi devices, Bluetooth is widely used for communication in low-power, low data-rate devices. This is because Bluetooth consumes much less power than WiFi which results in longer battery life. The higher power consumption of WiFi devices is due to overheads from either establishing or maintaining connections with the access point. Surprisingly, Bluetooth devices require nearly three times as much energy to transmit a bit of data at the physical layer than WiFi devices. In this paper, we propose Wi-LE a WiFi-compatible communication system that avoids the power hungry process of establishing or maintaining a connection. We implement and evaluate Wi-LE using an off-the-shelf WiFi module. Our results show that Wi-LE has power consumption similar to that of Bluetooth Low Energy (BLE). This demonstrates the potential for Wi-LE to be used in place of BLE.
Wireless communication technologies have become widely adopted, appearing in heterogeneous applications ranging from tracking victims, responders and equipments in disaster scenarios to machine health monitoring in networked manufacturing industries. Very often, applications demand a strictly bounded timing response, which, in distributed systems, is generally highly dependent on the performance of the underlying communication technology. These systems are said to have real-time timeliness requirements since data communication must be conducted within predefined temporal bounds, whose unfulfillment may compromise the correct behavior of the system and cause economic losses or endanger human lives. The support of real-time communications over license-free bands in open environments is a challenging task. The support of real-time medium access is achieved by a strict timing control of all communicating stations (real-time and non real-time). However, in open communication environments, the traffic generated by uncontrolled stations cannot be avoided by existing medium access protocols. In this paper, the definition, implementation and validation of a novel MAC technique named bandjacking, allowing a deterministic wireless channel access in industrial environments is presented. The bandjacking effectiveness is assessed using a commercial off-the-shelf based programmable interference synthesizer. The critical data communications are IEEE 802.15.4 based and the technologies chosen to contend for the medium are the IEEE 802.15.4 and the IEEE 802.11. The results demonstrate that the support of low-power deterministic communications is possible in open environments by using the bandjacking technique capable of synthesizing and controlling simultaneously black-burst and protective interference.