Underwater wireless sensor Networks (UWSN) will provide a variety of attractive working fields such as aquaculture, offshore exploitation, biological monitoring as well as water and seafloor pollution, seismic activity and ocean currents. A practical implementation of these applications will require spreading an important number of nodes to facilitate underwater monitoring by means of data acquiring, so it becomes a challenge to develop simple and reliable modem architectures to reduce both the cost in components and the developing time, still being efficient and robust. Moreover power consumption must be also considered due to energy harvesting difficulties in an underwater environment. This work is focused in the design and implementation of a low cost and energy efficient underwater modem. The paper presents a new acoustic modem design based on an original signal-conditioning model optimally adapted to commercial echo sounder based piezoelectric transducers. It represents a very low-cost solution with a power consumption level similar to current terrestrial wireless sensor networks. The modulation and demodulation algorithms are essential to define the modem architecture. In this work, they have been adapted to a low power microcontroller processing capabilities. The proposed modem architecture includes an 8-bit microcontroller and few external analog components. A binary Coherent-FSK modulation has been chosen because it is more efficient in terms of bandwidth than a non-coherent FSK. Coherent FSK modulation algorithm is quite simple, and can be easily implemented in an 8-bit microcontroller with negligible execution time. Demodulation algorithm is more complex and needs a low-power solution. The paper investigates different alternatives, obtaining a new optimal solution including an additional specific processing unit to the microprocessor core. Compared with previous researches that used microcontrollers, the presented approach also improves energy efficiency without lowering bit rate and bandwidth efficiency. The design has a variable gain reception to measure precisely the incoming signal level and obtaining signal quality indicators similar to RSSI used in wireless RF sensor networks. The circuit has been simulated and experimentally tested too with a prototype. Several tests have been carried out using the different alternatives presented. The goal of the first experiments was to characterize the frequency response of the transducers, and validate acoustic wave generation and amplification models obtained by means of simulation. Measurements were also taken to obtain receiver sensitivity and communication efficiency to power variations. Efficient design of both power amplifier and receiver analog processing stages, combined with optimal microcontroller power saving modes has extended estimated battery. As a conclusion, a worthwhile modem has been designed with the following advantages: Ultra-Low power consumption, a small form factor and a low final cost which enable future low cost deployment of underwater sensor networks.

This paper is focused on the description of the physical layer of a new acoustic modem called ITACA. The modem architecture includes as a major novelty an ultra-low power asynchronous wake-up system implementation for underwater acoustic transmission that is based on a low-cost off-the-shelf RFID peripheral integrated circuit. This feature enables a reduced power dissipation of 10 µW in stand-by mode and registers very low power values during reception and transmission. The modem also incorporates clear channel assessment (CCA) to support CSMA-based medium access control (MAC) layer protocols. The design is part of a compact platform for a long-life short/medium range underwater wireless sensor network.

Although combustion failure diagnosis techniques have been widely developed over the last few years, real-time correction of fuel injection failures, such as drift, are still deficient. In this paper, a controller for the correction of fuel injection failures is presented; the aim of the algorithm is to ensure that the same quantity of fuel is injected in each one of the cylinders. The controller is based on a linear model that relates the low-frequency region of the Fourier transform of a dynamic engine signal and fuel injection unevenness. Model inversion is used as an injection failure observer, and discrepancies in the injected fuel mass in each cylinder can be estimated, even in the case of multiple and simultaneous failures. This observer is used for closing the loop and performing the control action via an integral controller. Theoretical bases are given for the controller, and the stability and settling error are related to the error of the linear engine model assumed. This technique can be used for different engine signals, like crankshaft speed, exhaust manifold pulsation, and turbocharger instantaneous speed. Experimental results obtained on a diesel turbocharged engine, where the turbocharger instantaneous speed was used as input information of the controller, are presented proving the performance of the fuel quantity control algorithm

This paper presents a new Acoustic-Triggered Wake-Up system specially useful to Underwater Wireless Sensor Networks built with low-power consumption architectures. The work includes both the wake-up system description and a comparison with previous works carried out under similar features. These comparisons demonstrate the energy benefits of this new system which requires no additional hardware within the transmission and a single but efficient AT-WUp module in the reception.