Channel estimation and BER studies for an underwater acoustic OFDM system using time reversal mirror in shallow waters

Trivedi

2015 IEEE Underwater Technology (UT)

2015

Underwater acoustic communication is essential in applications like remote control in the offshore oil industry, pollution monitoring in environmental systems, collection of scientific data recorded at ocean-bottom stations, disaster detection and early warning and underwater surveillance. Research on underwater wireless communication techniques plays a vital role in further exploring oceans and other marine environments. There has been an extensive growth in the volume of literature for underwater acoustic (UWA) communication but still it remains to be one of the most challenging areas of wireless communication. Over the years attention has turned on applying modified versions of multicarrier (MC) communication to underwater channel. This paper reviews the recent developments in the area of UWA communication related to multicarrier communication and particularly to orthogonal frequency division multiplexing (OFDM) with respect to applied, theoretical and simulation studies. An attempt has been made to present a compact yet exhaustive literature survey that will serve as a standard reference for researchers working in the area. Stress has been laid on the physical layer issues as it works as the basic foundation of any network. The focus areas of research activities have been identified and a summary of the ongoing activities and future trends has been presented.

Section: A Time Reversal and Passive-phase Conjugation Methods For Umentioning

confidence: 99%

Recent trends in multicarrier underwater acoustic communications

Trivedi

2015 IEEE Underwater Technology (UT)

2015

“…Equalization is a one of the techniques to resist the distortion. Adaptive equalizations are the widely used equalizations in underwater acoustic communication [7]- [10]. The underwater acoustic communication channel exhibits a long delay spread because of a large amount of multipath arrivals resulting from surface and bottom interactions.…”

Section: Introductionmentioning

confidence: 99%

A Novel Carrier Waveform Inter-Displacement Modulation Method in Underwater Communication Channel

Ren,

Zhao

2013

Preprint

As the main way of underwater wireless communication, underwater acoustic communication is one of the focuses of ocean research. Compared with the free space wireless communication channel, the underwater acoustic channel suffers from more severe multipath effect, the less available bandwidth and the even complex noise. The underwater acoustic channel is one of the most complicated wireless communication channels. To achieve a reliable underwater acoustic communication, Phase Shift Keying (PSK) modulation and Passive Time Reversal Mirror (PTRM) equalization are considered to be a suitable scheme. However, due to the serious distortion of the received signal caused by the channel, this scheme suffers from a high Bit Error Rate (BER) under the condition of the low Signal to Noise Ratio (SNR). To solve this problem, we proposes a Carrier Waveform Inter-Displacement (CWID) modulation method based on the Linear Frequency Modulation (LFM) PSK and PTRM scheme. The new communication scheme reduces BER by increasing the difference from the carrier waveform for different symbols. Simulation results show the effectiveness and superiority of the proposed method.

“…Con objeto de acercar e impulsar los avances en materia de comunicaciones acústicas (Ribas, Sura, & Stojanovic, 2010;Vadde, Indushree, & Sequeira, 2011) a estos sistemas, la cuarta propuesta plantea el estudio y propuesta de una plataforma de comunicación OFDM apta para estos entornos.…”

Section: Monitorización Con Dispositivos Acústicos 133unclassified

Sistemas inalámbricos para la monitorización continua del comportamiento de especies marinas

Sarriá Gandul

In this Thesis, new methods for monitoring marine species using optical, radio frequency and acoustic technologies have been proposed and evaluated for biological studies in the laboratory and open sea. A study of the current technologies for monitoring species has been carried out, analyzing the advantages and disadvantages of each one. Although optical technologies allow a non-contact (non-invasive) species monitoring, they require a correct positioning of the elements and they are limited to some factors such as the distance (range), the environmental conditions and the biofouling. Radiofrequency devices allow the study of species that come to the surface, or those that live in freshwater environments. But this technology is restricted in the marine environment due the high absorption of the electromagnetic signals in that environment. Acoustic devices facilitate the monitoring of species in open sea and large areas, allowing location and tracking of the animals, but this technology has to challenge different aspects such as the multipath, the temporal and spatial variation of the channel or the Doppler effect, among others. This research has been divided in three parts according the above technologies, in which have been proposed, designed and evaluated successfully different systems to monitoring species. First, the infrared detectors and low-cost cameras have been evaluated for laboratory applications. The proposal provides different solutions such the expansion and the auto configuration to make the system independent of the aquaria size. Likewise, through different algorithms proposed have been reduced false activity detections caused by changes in water quality (turbidity), the presence of particles that obstruct the line of sight between the transmitter and the receiver, and the deterioration of the transducers. In the second part of this work, solutions have been proposed using RFID (Radio Frequency IDentification) technology through the design and experimental validation of a system for tracking species in experimental aquaria. The proposal provides solutions applied to make the system independent of the aquaria size. The results have demonstrated the validity of this technology to locate and track benthic species in confined spaces with a resolution of several centimeters. Finally, the performance of a commercial acoustic monitoring system in shallow waters and near an artificial reef environment where complex and numerous reflections occur, has been evaluated. Due to the lack of standards, the incompatibility between manufacturers and the need to improve the previous results, this part of the research has been directed to build and evaluated an acoustic underwater transducer prototype and an open OFDM (Orthogonal Frequency Division Multiplexing) communication platform, approaching the current advances in underwater acoustics towards the species monitoring systems. En este trabajo de Tesis se proponen y evalúan nuevos métodos para la monitorización de especies marinas, empleando tecnologías ópticas, por radiofrecuencia y acústicas para estudios biológicos en laboratorio (acuarios de experimentación) y en espacios abiertos. Se ha realizado un estudio de las tecnologías empleadas para la monitorización de especies, presentado y analizado las ventajas e inconvenientes de cada una de ellas. Aunque la tecnología óptica permite el estudio de especies sin contacto (no invasiva), requiere un correcto posicionamiento de sus elementos y está limitada por el alcance, las condiciones cambiantes del medio y la bioincrustación. Los dispositivos de radiofrecuencia permiten el estudio de especies que emergen a la superficie, o las que habitan en entornos de agua dulce; en el entorno marino esta tecnología se encuentra restringida debido a la gran absorción que sufren las señales electromagnéticas en ese medio. Los dispositivos acústicos facilitan la monitorización de especies en espacios abiertos de gran extensión, permitiendo su localización y seguimiento; sin embargo, esta tecnología presenta una gran sensibilidad a diferentes factores que impone el medio marino como el multicamino, la variación temporal y espacial del canal o el efecto Doppler, entre otros. La investigación se ha estructurado en tres partes donde, utilizando las tecnologías citadas, se han propuesto, diseñado y validado con éxito diferentes sistemas de medida. En primer lugar, se han evaluado los detectores de infrarrojos y las cámaras de bajo coste para la monitorización de especies en laboratorio. La propuesta contempla diferentes soluciones que independizan el sistema de las dimensiones del acuario, permitiendo su ampliación y configuración automática. Así mismo, mediante los algoritmos de procesado programados se han reducido las detecciones erróneas causadas por alteraciones de la calidad del agua (turbiedad), la presencia de partículas que obstruyen la línea de vista entre el par emisor-receptor y el deterioro de los transductores. En la segunda parte del trabajo de Tesis se han propuesto soluciones aplicando la tecnología RFID (Radio Frequency IDentification), mediante el diseño y validación experimental de un sistema de localización y seguimiento de especies en acuarios de experimentación. La propuesta realizada plantea mecanismos que independizan el sistema del tamaño del acuario, y permiten la autoconfiguración de sus componentes. Los resultados obtenidos han demostrado la validez de esta tecnología para localizar y seguir la trayectoria de especies bentónicas en espacios reducidos y con una resolución de varios centímetros. Finalmente, se ha evaluado el rendimiento de un equipo acústico comercial en mar abierto, a baja profundidad y en las proximidades de un entorno con arrecifes artificiales, donde ocurren complejas y numerosas reflexiones. Debido a la falta de estándares, la incompatibilidad entre fabricantes y con objeto de mejorar los resultados anteriores, en esta parte de la investigación se ha propuesto, construido y evaluado un prototipo de transductor acústico y una plataforma abierta de comunicaciones OFDM (Ortogonal Frequency Division Multiplexing), acercando la tendencia y los avances actuales en materia de comunicaciones acústicas a los sistemas de monitorización de especies marinas.