Underwater acoustic modem using OFDM

Ankara : The Department of Electrical and Electronics Engineering and the Graduate School of Engineering and Sciences of Bilkent University., 2012.Thesis (Master's) -- Bilkent University, 2012.Includes bibliographical references leaves 52-55.This thesis is about design, simulation and testing of an underwater acoustic modem using OFDM. The thesis work combines a theoretical part, whose objective is to understand the appropriate techniques to deal with the characteristics of the targeted channel, simulations and a practical part regarding the system deployment and experimental tests. There has been a great growing interest in transmitting real-time data and video. Unmanned underwater vehicles (UUVs) for military and scientific applications have become important. Building distributed and scalable underwater wireless sensor networks (UWSN) that will bring significant advantages and benefits to underwater applications, such as ocean observation for scientific exploration, commercial exploitation, coastline protection and target detection in military events has been in the scope of researchers. Based on these, designing a concrete system with high data rate will benefit many underwater acoustic (UWA) applications. The existing systems in literature use single carrier transmission and rely on linear or non-linear equalization techniques to suppress inter-symbol interference (ISI), however this requires complex equalizers and results in low data rates. Therefore we concentrate on multicarrier modulation. In this thesis ZP-OFDM (Zero Padded-Orthogonal Frequency Division Multiplexing) receiver is built, where CFO (Carrier Frequency Offset) compensation, pilot-tone based channel estimation, and data demodulation are carried out on the basis of each OFDM block. The implemented OFDM system has been developed in MATLAB. MATLAB scripts generate a data burst that contained OFDM blocks, and then they are transmitted to the hardware from a laptop by using a Data Acquisition (DAQ) Card. At the other side of the system, the receiver laptop gets the data by using a DAQ Card. As the data is received, MATLAB scripts are demodulated and data is detected. Simulations aim to provide correct implementation of all the algorithms by coupling the generated OFDM signal to a channel using Bellhop underwater channel model and noise addition algorithm, that artificially introduces some of the real channel effects into the signal. The method is tested in a shallow-water experiment at Bilkent Lake. Over a bandwidth of 12 kHz, the data rate is 13.92 kb/s with QPSK modulation, when the number of subcarriers was 1024. Bit-error-rate (BER) is less than 9x10−2 without any coding.Yüksel, Mine MerveM.S

Mobile underwater acoustic communications with multicarrier modulation in very shallow waters

Master'sMASTER OF ENGINEERIN

Underwater Acoustic MIMO OFDM: An experimental analysis

Projecte fet en col.laboració amb Massachusetts Institute of TechnologyResearch e orts over the past several years have provided ample proof that orthogonal frequency division multiplexing (OFDM) represents a viable alternative to single-carrier modulation which has traditionally been used for high rate communications over underwater acoustic channels. The main attraction of OFDM lies in its simplicity of implementation via FFT modulation/demodulation, which makes it a candidate for implementation in the next generation of acoustic modems

Physical Layer Techniques for Wireless Communication Systems

The increasing diffusion of mobile devices requiring, everywhere and every time, reliable connections able to support the more common applications, induced in the last years the deployment of telecommunication networks based on technologies capable to respond effectively to the ever-increasing market demand, still a long way off from saturation level. Multicarrier transmission techniques employed in standards for local networks (Wi-Fi) and metropolitan networks (WiMAX) and for many years hot research topic, have been definitely adopted beginning from the fourth generation of cellular systems (LTE). The adoption of multicarrier signaling techniques if on one hand has brought significant advantages to counteract the detrimental effects in environments with particularly harsh propagation channel, on the other hand, has imposed very strict requirements on sensitivity to recovery errors of the carrier frequency offset (CFO) due to the resulting impact on correct signal detection. The main focus of the thesis falls in this area, investigating some aspects relating to synchronization procedures for system based on multicarrier signaling. Particular reference will be made to a network entry procedure for LTE networks and to CFO recovery for OFDM, fltered multitone modulation and direct conversion receivers. Other contributions pertaining to physical layer issues for communication systems, both radio and over acoustic carrier, conclude the thesis

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

Analysis of and techniques for adaptive equalization for underwater acoustic communication

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2011Underwater wireless communication is quickly becoming a necessity for applications in ocean science, defense, and homeland security. Acoustics remains the only practical means of accomplishing long-range communication in the ocean. The acoustic communication channel is fraught with difficulties including limited available bandwidth, long delay-spread, time-variability, and Doppler spreading. These difficulties reduce the reliability of the communication system and make high data-rate communication challenging. Adaptive decision feedback equalization is a common method to compensate for distortions introduced by the underwater acoustic channel. Limited work has been done thus far to introduce the physics of the underwater channel into improving and better understanding the operation of a decision feedback equalizer. This thesis examines how to use physical models to improve the reliability and reduce the computational complexity of the decision feedback equalizer. The specific topics covered by this work are: how to handle channel estimation errors for the time varying channel, how to use angular constraints imposed by the environment into an array receiver, what happens when there is a mismatch between the true channel order and the estimated channel order, and why there is a performance difference between the direct adaptation and channel estimation based methods for computing the equalizer coefficients. For each of these topics, algorithms are provided that help create a more robust equalizer with lower computational complexity for the underwater channel.This work would not have been possible without support from the O ce of Naval Research, through a Special Research Award in Acoustics Graduate Fellowship (ONR Grant #N00014-09-1-0540), with additional support from ONR Grant #N00014-05- 10085 and ONR Grant #N00014-07-10184

Analysis of and techniques for adaptive equalization for underwater acoustic communication

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and the Woods Hole Oceanographic Institution), 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 203-215).Underwater wireless communication is quickly becoming a necessity for applications in ocean science, defense, and homeland security. Acoustics remains the only practical means of accomplishing long-range communication in the ocean. The acoustic communication channel is fraught with difficulties including limited available bandwidth, long delay-spread, time-variability, and Doppler spreading. These difficulties reduce the reliability of the communication system and make high data-rate communication challenging. Adaptive decision feedback equalization is a common method to compensate for distortions introduced by the underwater acoustic channel. Limited work has been done thus far to introduce the physics of the underwater channel into improving and better understanding the operation of a decision feedback equalizer. This thesis examines how to use physical models to improve the reliability and reduce the computational complexity of the decision feedback equalizer. The specific topics covered by this work are: how to handle channel estimation errors for the time varying channel, how to use angular constraints imposed by the environment into an array receiver, what happens when there is a mismatch between the true channel order and the estimated channel order, and why there is a performance difference between the direct adaptation and channel estimation based methods for computing the equalizer coefficients. For each of these topics, algorithms are provided that help create a more robust equalizer with lower computational complexity for the underwater channel.by Ballard J. S. Blair.Ph.D