Cost-Effective and Energy-Efficient Techniques for Underwater Acoustic Communication Modems

Finally, the modem developed has been tested experimentally in laboratory (aquatic environment) showing that can communicates at different data rates (100..1200 bps) compared to state-of-the-art research modems. The software used include LabVIEW, MATLAB, Simulink, and Multisim (to test the electronic circuit built) has been employed.Underwater wireless sensor networks (UWSNs) are widely used in many applications related to ecosystem monitoring, and many more fields. Due to the absorption of electromagnetic waves in water and line-of-sight communication of optical waves, acoustic waves are the most suitable medium of communication in underwater environments. Underwater acoustic modem (UAM) is responsible for the transmission and reception of acoustic signals in an aquatic channel. Commercial modems may communicate at longer distances with reliability, but they are expensive and less power efficient. Research modems are designed by using a digital-signal-processor (DSP is expensive) and field-programmable-gate-array (FPGA is high power consuming device). In addition to, the use of a microcontroller is also a common practice (which is less expensive) but provides limited computational power. Hence, there is a need for a cost-effective and energy-efficient UAM to be used in budget limited applications. In this thesis different objectives are proposed. First, to identify the limitations of state-of-the-art commercial and research UAMs through a comprehensive survey. The second contribution has been the design of a low-cost acoustic modem for short-range underwater communications by using a single board computer (Raspberry-Pi), and a microcontroller (Atmega328P). The modulator, demodulator and amplifiers are designed with discrete components to reduce the overall cost. The third contribution is to design a web based underwater acoustic communication testbed along with a simulation platform (with underwater channel and sound propagation models), for testing modems. The fourth contribution is to integrate in a single module two important modules present in UAMs: the PSK modulator and the power amplifier

Low cost OFDM based transmitter for underwater acoustic communications

On this work a low cost OFDM transmitter for underwater sensor networks is presented. The transmitter is based on a low power microcontroller that governs a DDS in order to generate the output data -OFDM symbols- avoiding the IFFT computations. This solution represents a new design perspective for the current UWSN -mainly based on FPGAs or DSPs, allowing to reduce the cost, the power consumption and the size of the current transmitters.Peer ReviewedPostprint (author’s final draft

IUmote: A Framework for the Efficient Modelling, Evaluation, and Deployment of Algorithms and Hardware for Underwater Communications

We present an approach for the modelling and simulating of the modem section of underwater sensor networks. The proposal is based on a specially designed modem architecture and the use of simulation tools and models that represent each of the communication elements: the water medium, physical transducers, electronics, and coding/decoding software. The algorithms can be simulated in the modelling environment; this framework does not require recoding and allows the combination of real and modelled elements. In physical terms, the modem engine provides a decoupled pipelined design of the processing path for the algorithms which allows users to run complex algorithms without requiring a highly demanding specific hardware. The proposal includes a methodology that has allowed us to significantly reduce the effort required in the process, from algorithm development to the effective deployment of the system. As a case study, this paper shows its application and results in the evaluation of a multipath and Doppler-shift correction algorithms.The authors gratefully acknowledge financial support from the CICYT ANDREA: Automated Inspection and Remote Performance of Marine Fish Farms (CTM2011-29691-C02-01), RIDeWAM: Research on Improvement of the Dependability of WSN based Applications by developing a hybrid monitoring platform (TIN2011-28435-C03-01), Valencian Regional Government under Research Project GV/2014/012, and Universitat Politecnica de Valencia under Research Project UPV PAID-02-12. The translation of this paper was funded by the Universitat Politecnica de Valencia, Spain.Sánchez Matías, AM.; Perles Ivars, A.; Yuste Pérez, P.; Capella Hernández, JV.; Serrano Martín, JJ. (2015). IUmote: A Framework for the Efficient Modelling, Evaluation, and Deployment of Algorithms and Hardware for Underwater Communications. International Journal of Distributed Sensor Networks. 2015:1-14. https://doi.org/10.1155/2015/358315S114201

Design and implementation of low complexity wake-up receiver for underwater acoustic sensor networks

This thesis designs a low-complexity dual Pseudorandom Noise (PN) scheme for identity (ID) detection and coarse frame synchronization. The two PN sequences for a node are identical and are separated by a specified length of gap which serves as the ID of different sensor nodes. The dual PN sequences are short in length but are capable of combating severe underwater acoustic (UWA) multipath fading channels that exhibit time varying impulse responses up to 100 taps. The receiver ID detection is implemented on a microcontroller MSP430F5529 by calculating the correlation between the two segments of the PN sequence with the specified separation gap. When the gap length is matched, the correlator outputs a peak which triggers the wake-up enable. The time index of the correlator peak is used as the coarse synchronization of the data frame. The correlator is implemented by an iterative algorithm that uses only one multiplication and two additions for each sample input regardless of the length of the PN sequence, thus achieving low computational complexity. The real-time processing requirement is also met via direct memory access (DMA) and two circular buffers to accelerate data transfer between the peripherals and the memory. The proposed dual PN detection scheme has been successfully tested by simulated fading channels and real-world measured channels. The results show that, in long multipath channels with more than 60 taps, the proposed scheme achieves high detection rate and low false alarm rate using maximal-length sequences as short as 31 bits to 127 bits, therefore it is suitable as a low-power wake-up receiver. The future research will integrate the wake-up receiver with Digital Signal Processors (DSP) for payload detection. --Abstract, page iv

Implementation of a wireless underwater video link

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 73-75).Autonomous underwater vehicles (AUVs) are increasingly being considered for remotely supervised missions, primarily for routine subsea inspection tasks currently performed by tethered remotely operated vehicles (ROVs). This project is a step in the development of a high speed, networked wireless communication capability for AUVs using MIT Sea Grant's software defined Reconfigurable Modem (R-Modem) acoustic communications platform. We have demonstrated a test implementation of live streaming video with a digital camera connected to an R-Modem transceiver; and explored a range of tuning parameters for the video link.by James Paul Morash.M.Eng

DSP implementation of OFDM acoustic modem

The success of multicarrier modulation in the form of OFDM in radio channels illuminates a path one could take towards high-rate underwater acoustic communications,and recently there are intensive investigations on underwater OFDM. Processing power has increased to a point where orthogonal frequency division multiplexing (OFDM) has become feasible and economical. Since many wireless communication systems being developed use OFDM, it is a worthwhile research topic. Some examples of applications using OFDM include Digital subscriber line (DSL), Digital Audio Broadcasting (DAB),High definition television (HDTV) broadcasting, IEEE 802.11 (wireless networking standard).OFDM is a strong candidate and has been suggested or standardized in high speed communication systems. In this Thesis in first phase ,we analyzes the factor that affects the OFDM performance. The performance of OFDM was assessed by using computer simulations performed using Matlab7.2 .it was simulated under Additive white Gaussian noise (AWGN) ,Exponential Multipath channel and Carrier frequency offset conditions for different modulation schemes like binary phase shift keying (BPSK), Quadrature phase shift keying (QPSK),16 Quadrature amplitude modulation (16-QAM),64-Quadrature amplitude modulation(64-QAM)which are used for achieving high data rates.In second phase we implement the acoustic OFDM transmitter and receiver design of [4,5] on a TMS320C6713 DSP board. We analyze the workload and identify the most timeconsuming operations. Based on the workload analysis, we tune the algorithms and optimize the code to substantially reduce the synchronization time to 0.2 seconds and the processing time of one OFDM block to 2.7235 seconds on a DSP processor at 225 MHz. This experimentation provides guidelines on our future work to reduce the per-block processing time to be less than the block duration of 0.23 seconds for real time operations

Time Synchronization in Mobile Underwater Sensor Network

Time synchronization plays a critical role in underwater sensor networks (UWSNs). Sensor network consists of static and mobile underwater sensor nodes. Although many time-synchronization protocols have been proposed for terrestrial wireless sensor networks, none of them can be directly applied to UWSNs. This is because most of these protocols do not consider long propagation delays and sensor node mobility, which are important attributes in UWSNs. In addition, UWSNs usually have high requirements in energy efficiency. In this paper, time-synchronization scheme is proposed in mobile underwater sensor networks. The scheme proposes a framework to estimate the Doppler shift caused by mobility, more precisely through accounting the impact of the skew. The time delay and frequency are estimated accurately. To refine the relative velocity estimation, and consequently to enhance the synchronization accuracy, the Kalman filter is employed. Thus by estimating the velocity, the accuracy has been increased

Vector sensors for underwater : acoustic communications

Acoustic vector sensors measure acoustic pressure and directional components separately. A claimed advantage of vector sensors over pressure-only arrays is the directional information in a collocated device, making it an attractive option for size-restricted applications. The employment of vector sensors as a receiver for underwater communications is relatively new, where the inherent directionality, usually related to particle velocity, is used for signal-to-noise gain and intersymbol interference mitigation. The fundamental question is how to use vector sensor directional components to bene t communications, which this work seeks to answer and to which it contributes by performing: analysis of acoustic pressure and particle velocity components; comparison of vector sensor receiver structures exploring beamforming and diversity; quanti cation of adapted receiver structures in distinct acoustic scenarios and using di erent types of vector sensors. Analytic expressions are shown for pressure and particle velocity channels, revealing extreme cases of correlation between vector sensors' components. Based on the correlation hypothesis, receiver structures are tested with simulated and experimental data. In a rst approach, called vector sensor passive time-reversal, we take advantage of the channel diversity provided by the inherent directivity of vector sensors' components. In a second approach named vector sensor beam steering, pressure and particle velocity components are combined, resulting in a steered beam for a speci c direction. At last, a joint beam steering and passive time-reversal is proposed, adapted for vector sensors. Tested with two distinct experimental datasets, where vector sensors are either positioned on the bottom or tied to a vessel, a broad performance comparison shows the potential of each receiver structure. Analysis of results suggests that the beam steering structure is preferable for shorter source-receiver ranges, whereas the passive time-reversal is preferable for longer ranges. Results show that the joint beam steering and passive time-reversal is the best option to reduce communication error with robustness along the range.Sensores vetoriais acústicos (em inglês, acoustic vector sensors) são dispositivos que medem, alem da pressão acústica, a velocidade de partícula. Esta ultima, é uma medida que se refere a um eixo, portando, esta associada a uma direção. Ao combinar pressão acústica com componentes de velocidade de partícula pode-se estimar a direção de uma fonte sonora utilizando apenas um sensor vetorial. Na realidade, \um" sensor vetorial é composto de um sensor de pressão (hidrofone) e um ou mais sensores que medem componentes da velocidade de partícula. Como podemos notar, o aspecto inovador está na medição da velocidade de partícula, dado que os hidrofones já são conhecidos.(...)This PhD thesis was supported by the Brazilian Navy Postgraduate Study Abroad Program Port. 227/MB-14/08/2019