Towards underwater video transmission

Català: Aquest projecte consisteix en la implementació d'un sistema acústic OFDM (Orthogonal Frequency-Division Multiplexing; Multiplexació per Divisió de Freqüències Ortogonals) per a transmissions de vídeo submarines. El sistema està dissenyat per a enllaços de curta distància, amb retards breus i un ample de banda relativament gran. La recerca realitzada en aquest projecte es divideix en quatre parts diferenciades: 1. Recerca en tècniques de compressió de vídeo. 2. Recerca en tècniques de modulació i detecció. 3. Disseny de tècniques de processament de senyal destinades a compensar l'efecte Doppler. 4. Recerca en tècniques per reduir la codificació de canal. Pel que fa al primer punt (1), cal destacar que és important trobar un mètode de compressió de vídeo adequat que redueixi substancialment la quantitat d'informació a transmetre, per tal d'aprofitar al màxim la capacitat de transmissió de dades del canal submarí. La tècnica seleccionada ha estat el codificador VLBV (Very Low Bitrate Video) de l'estàndard MPEG-4, dissenyat per treballar amb seqüències d'imatges de vídeo rectangulars amb una alta eficiència de codificació, robustesa enfront els errors de canal, baixa latència i baixa complexitat per a aplicacions a temps real. Pel que es refereix al segon punt (2), la tècnica de modulació OFDM ha estat seleccionada per les seves excel·lents propietats per sistemes de comunicació d'alta velocitat en canals acústics submarins, caracteritzats per ser selectius en freqüència. No obstant, els problemes de sincronització i desplaçaments de freqüència causats pel moviment entre transmissor i receptor ?l'anomenat efecte Doppler? ha creat la necessitat de dissenyar un algorisme eficient (3) que faci front a aquesta distorsió. Pel que fa a l'últim punt (4), l'estàndard MPEG-4 ofereix un conjunt d'eines de protecció enfront els errors que ha estat incorporat al codificador de vídeo del sistema. Aquestes eines faciliten una comunicació segura en canals wireless sorollosos, oferint una protecció addicional contra les ràfegues d'error i mantenint una bona qualitat visual per al vídeo descodificat. D'aquesta manera, es pot reduir la codificació de canal aplicada a la informació transmesa, incrementant així la velocitat de transferència de dades del sistema.Castellano: Este proyecto consiste en la implementación de un sistema acústico OFDM (Orthogonal Frequency-Division Multiplexing; Multiplexación por División de Frecuencias Ortogonales) para transmisiones de video submarinas. El sistema esta diseñado para enlaces de corta distancia, con retardos breves y anchos de banda relativamente grandes. La investigación realizada en este proyecto se divide en cuatro partes diferenciadas: 1. Investigación en técnicas de compresión de video. 2. Investigación en técnicas de modulación y detección. 3. Diseño de técnicas de procesado se señal destinadas a compensar el efecto Doppler. 4. Investigación en técnicas para reducir la codificación de canal. Por lo que al punto (1) se refiere, cabe destacar que es importante encontrar un método de compresión adecuado que reduzca sustancialmente la cantidad de información a transmitir, con el objetivo de aprovechar al máximo la capacidad de transmisión de datos del canal submarino. La técnica seleccionada es el codificador VLBV (Very Low Bitrate Video) del estándar MPEG-4, diseñado para trabajar con secuencia de imágenes de video rectangulares con un alta eficiencia de codificación, robustez enfrente de errores de canal, baja latencia y baja complejidad para aplicaciones en tiempo real. En cuanto al segundo punto (2), la técnica de modulación OFDM ha sido seleccionada por sus excelentes habilidades para sistemas de comunicación de alta velocidad en canales acústicos submarinos, caracterizados por ser selectivos en frecuencia. Sin embargo, los problemas de sincronización y desplazamientos de frecuencia causados por el movimiento entre transmisor y receptor ?el conocido efecto Doppler? ha creado la necesidad de diseñar un algoritmo eficiente (3) que aborde esta distorsión. En cuanto al último punto (4) se refiere, el estándar MPEG-4 ofrece un conjunto de herramientas de protección contra errores que ha sido incorporado al codificador de video del sistema. Estas herramientas facilitan una comunicación segura en canales wireless ruidosos, ofreciendo una protección adicional contra las ráfagas de errores y manteniendo una buena calidad visual para el video decodificado. De esta forma, se puede reducir la codificación de canal aplicada a la información transmitida, incrementando así la velocidad de transferencia de datos del sistema.English: This project addresses the implementation of an acoustic OFDM (Orthogonal Frequency-Division Multiplexing) system for underwater video transmissions aimed to work over short distance links, with short delays and relatively high available bandwidth. This work includes research on four main approaches: 1. Research on video compression techniques. 2. Research on modulation and detection techniques. 3. Design of signal processing techniques aimed to compensate for the Doppler effect caused by motion. 4. Research on techniques to reduce the channel coding applied to the video data. Regarding (1), it is important to find a suitable video compression technique that substantially reduces the amount of video data to be transmitted in order to properly utilize the limited bit rate capacity of the underwater channel. The chosen compression technique has been the VLBV (Very Low Bitrate Video) coder offered by the MPEG-4 standard due to its efficient low bit rate compression capabilities, aimed to work with conventional rectangular image sequences with high coding efficiency, high error robustness, low latency and low complexity for real-time applications. Concerning (2), the OFDM modulation technique has been considered for its excellent capabilities applicable to high speed communication systems in wireless acoustic underwater channels, characterized by frequency selectivity. However, the motion-induced Doppler distortion makes it important to design an efficient algorithm (3) that deals with the synchronization problems and frequency shifts caused by the accentuated Doppler effect in underwater channels. With regard to (4), a set of error resilience tools offered by the MPEG-4 standard has been implemented at the video encoder. These tools enable robust video communication over noisy wireless channels by offering additional protection over error bursts and maintaining the visual quality of the decoded video. This allows the conventional channel coding applied to the video data to be reduced, thus increasing the available data rate of the system

Green compressive sampling reconstruction in IoT networks

In this paper, we address the problem of green Compressed Sensing (CS) reconstruction within Internet of Things (IoT) networks, both in terms of computing architecture and reconstruction algorithms. The approach is novel since, unlike most of the literature dealing with energy efficient gathering of the CS measurements, we focus on the energy efficiency of the signal reconstruction stage given the CS measurements. As a first novel contribution, we present an analysis of the energy consumption within the IoT network under two computing architectures. In the first one, reconstruction takes place within the IoT network and the reconstructed data are encoded and transmitted out of the IoT network; in the second one, all the CS measurements are forwarded to off-network devices for reconstruction and storage, i.e., reconstruction is off-loaded. Our analysis shows that the two architectures significantly differ in terms of consumed energy, and it outlines a theoretically motivated criterion to select a green CS reconstruction computing architecture. Specifically, we present a suitable decision function to determine which architecture outperforms the other in terms of energy efficiency. The presented decision function depends on a few IoT network features, such as the network size, the sink connectivity, and other systems’ parameters. As a second novel contribution, we show how to overcome classical performance comparison of different CS reconstruction algorithms usually carried out w.r.t. the achieved accuracy. Specifically, we consider the consumed energy and analyze the energy vs. accuracy trade-off. The herein presented approach, jointly considering signal processing and IoT network issues, is a relevant contribution for designing green compressive sampling architectures in IoT networks

A holographic system for subsea recording and analysis of plankton and other marine particles

We report here details of the design, development, initial testing and field-deployment of the HOLOMAR system for in-situ subsea holography and analysis of marine plankton and nonliving particles. HOLOMAR comprises a submersible holographic camera ("HoloCam") able to record in-line and off-axis holograms at depths down to 100 m, together with specialised reconstruction hardware ("HoloScan") linked to custom image processing and classification software. The HoloCam consists of a laser and power supply, holographic recording optics and holographic plate holders, a water-tight housing and a support frame. It utilises two basic holographic geometries, in-line and off-axis such that a wide range of species, sizes and concentrations can be recorded. After holograms have been recorded and processed they are reconstructed in full three-dimensional detail in air in a dedicated replay facility. A computer-controlled microscope, using video cameras to record the image at a given depth, is used to digitise the scene. Specially written software extracts a binarised image of an object in its true focal plane and is classified using a neural network. The HoloCam was deployed on two separate cruises in a Scottish sea loch (Loch Etive) to a depth of 100 m and over 300 holograms were recorded

HoloCam: A subsea holographic camera for recording marine organisms and particles

The HoloCam system is a major component of a multi-national multi-discipline project known as HoloMar (funded by the European Commission under the MAST III initiative). The project is concerned with the development of pulsed laser holography to analyse and monitor the populations of living organisms and inanimate particles within the world's oceans. We describe here the development, construction and evaluation of a prototype underwater camera, the purpose of which is to record marine organisms and particles, in-situ. Recording using holography provides several advantages over conventional sampling methods in that it allows non-intrusive, non-destructive, high-resolution imaging of large volumes (up to 10^5 cm^3) in three dimensions. The camera incorporates both in-line and off-axis holographic techniques, which allows particles from a few micrometres to tens of centimetres to be captured. In tandem with development of the HoloCam, a dedicated holographic replay system and an automated data extraction and image processing facility are being developed. These will allow, optimisation of the images recorded by the camera, identification of species and particle concentration plotting

Cellular Underwater Wireless Optical CDMA Network: Potentials and Challenges

Underwater wireless optical communications is an emerging solution to the expanding demand for broadband links in oceans and seas. In this paper, a cellular underwater wireless optical code division multiple-access (UW-OCDMA) network is proposed to provide broadband links for commercial and military applications. The optical orthogonal codes (OOC) are employed as signature codes of underwater mobile users. Fundamental key aspects of the network such as its backhaul architecture, its potential applications and its design challenges are presented. In particular, the proposed network is used as infrastructure of centralized, decentralized and relay-assisted underwater sensor networks for high-speed real-time monitoring. Furthermore, a promising underwater localization and positioning scheme based on this cellular network is presented. Finally, probable design challenges such as cell edge coverage, blockage avoidance, power control and increasing the network capacity are addressed.Comment: 11 pages, 10 figure

The Hierarchic treatment of marine ecological information from spatial networks of benthic platforms

Measuring biodiversity simultaneously in different locations, at different temporal scales, and over wide spatial scales is of strategic importance for the improvement of our understanding of the functioning of marine ecosystems and for the conservation of their biodiversity. Monitoring networks of cabled observatories, along with other docked autonomous systems (e.g., Remotely Operated Vehicles [ROVs], Autonomous Underwater Vehicles [AUVs], and crawlers), are being conceived and established at a spatial scale capable of tracking energy fluxes across benthic and pelagic compartments, as well as across geographic ecotones. At the same time, optoacoustic imaging is sustaining an unprecedented expansion in marine ecological monitoring, enabling the acquisition of new biological and environmental data at an appropriate spatiotemporal scale. At this stage, one of the main problems for an effective application of these technologies is the processing, storage, and treatment of the acquired complex ecological information. Here, we provide a conceptual overview on the technological developments in the multiparametric generation, storage, and automated hierarchic treatment of biological and environmental information required to capture the spatiotemporal complexity of a marine ecosystem. In doing so, we present a pipeline of ecological data acquisition and processing in different steps and prone to automation. We also give an example of population biomass, community richness and biodiversity data computation (as indicators for ecosystem functionality) with an Internet Operated Vehicle (a mobile crawler). Finally, we discuss the software requirements for that automated data processing at the level of cyber-infrastructures with sensor calibration and control, data banking, and ingestion into large data portals.Peer ReviewedPostprint (published version