Adaptive Modulation Schemes for Underwater Acoustic OFDM Communication

High data rate communication is challenging in underwater acoustic (UA) communication as UA channels vary fast along with the environmental factors. A real-time Orthogonal frequency-division multiplexing (OFDM) based adaptive UA communication system is studied in this research employing the National Instruments (NI) LabVIEW software and NI CompactDAQ device. The developed adaptive modulation schemes enhance the reliability of communication, guarantee continuous connectivity, ensure maximum performance under a fixed BER at all times and boost data rate

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

Real-Time Adaptive Modulation Schemes for Underwater Acoustic OFDM Communication

Adaptive modulation received significant attention for underwater acoustic (UA) communication systems with the aim of increasing the system efficiency. It is challenging to attain a high data rate in UA communication, as UA channels vary fast, along with the environmental factors. For a time-varying UA channel, a self-adaptive system is an attractive option, which can choose the best method according to the channel condition to guarantee the continuous connectivity and high performance constantly. A real-time orthogonal frequency-division multiplexing (OFDM)-based adaptive UA communication system is presented in this paper, employing the National Instruments (NI) LabVIEW software and NI CompactDAQ device. In this paper, the received SNR is considered as a performance metric to select the transmission parameters, which are sent back to the transmitter for data transmission. In this research, a UA OFDM communication system is developed, employing adaptive modulation schemes for a nonstationary UA environment which allows to select subcarriers, modulation size, and allocate power adaptively to enhance the reliability of communication, guarantee continuous connectivity, and boost data rate. The recent UA communication experiments carried out in the Canning River, Western Australia, verify the performance of the proposed adaptive UA OFDM system, and the experimental results confirm the superiority of the proposed adaptive scheme

Space-time-frequency methods for interference-limited communication systems

textTraditionally, noise in communication systems has been modeled as an additive, white Gaussian noise process with independent, identically distributed samples. Although this model accurately reflects thermal noise present in communication system electronics, it fails to capture the statistics of interference and other sources of noise, e.g. in unlicensed communication bands. Modern communication system designers must take into account interference and non-Gaussian noise to maximize efficiencies and capacities of current and future communication networks. In this work, I develop new multi-dimensional signal processing methods to improve performance of communication systems in three applications areas: (i) underwater acoustic, (ii) powerline, and (iii) multi-antenna cellular. In underwater acoustic communications, I address impairments caused by strong, time-varying and Doppler-spread reverberations (self-interference) using adaptive space-time signal processing methods. I apply these methods to array receivers with a large number of elements. In powerline communications, I address impairments caused by non-Gaussian noise arising from devices sharing the powerline. I develop and apply a cyclic adaptive modulation and coding scheme and a factor-graph-based impulsive noise mitigation method to improve signal quality and boost link throughput and robustness. In cellular communications, I develop a low-latency, high-throughput space-time-frequency processing framework used for large scale (up to 128 antenna) MIMO. This framework is used in the world's first 100-antenna MIMO system and processes up to 492 Gbps raw baseband samples in the uplink and downlink directions. My methods prove that multi-dimensional processing methods can be applied to increase communication system performance without sacrificing real-time requirements.Electrical and Computer Engineerin

TS-MUWSN: Time synchronization for mobile underwater sensor networks

Time synchronization is an important, yet challenging, problem in underwater sensor networks (UWSNs). This challenge can be attributed to: 1) messaging timestamping; 2) node mobility; and 3) Doppler scale effect. To mitigate these problems, we present an acoustic-based time-synchronization algorithm for UWSN, where we compare several message time-stamping algorithms in addition to different Doppler scale estimators. A synchronization system is based on a bidirectional message exchange between a reference node and a slave one, which has to be synchronized. Therefore, we take as reference the DA-Sync-like protocol (Liu et al., 2014), which takes into account node's movement by using first-order kinematic equations, which refine Doppler scale factor estimation accuracy, and result in better synchronization performance. In our study, we propose to modify both time-stamping and Doppler scale estimation procedures. Besides simulation, we also perform real tests in controlled underwater communication in a water test tank and a shallow-water test in the Mediterranean Sea.Peer ReviewedPostprint (author's final draft

Waymark in the Depths: Baseband Signal Transmission and OFDM in Underwater Acoustic Propagation Channel Models

In the intricate environment of underwater acoustic propagation, establishing reliable communication channels stands as a formidable challenge, primarily due to the medium's inherent properties, such as high path loss, multipath propagation, and time-varying channel characteristics. "Waymark in the Depths: Baseband Signal Transmission and OFDM in Underwater Acoustic Propagation Channel Models" presents an innovative exploration into enhancing underwater communication systems by leveraging advanced signal processing techniques and channel modeling strategies. At the core of this research lies the integration of Orthogonal Frequency Division Multiplexing (OFDM) with baseband signal transmission, aiming to mitigate the detrimental effects of the underwater acoustic environment on signal integrity and throughput. By dissecting the acoustic channel's unique attributes, the study devises a comprehensive channel model that encapsulates the dynamic nature of underwater acoustics, including the impact of temperature, salinity, and pressure on sound speed and signal dispersion. This model serves as a waymark, guiding the development of tailored OFDM techniques that are optimized for the underwater medium, focusing on maximizing spectral efficiency and minimizing error rates. The research meticulously examines the interplay between baseband signal processing and OFDM in this context, illustrating how their synergistic application can overcome the bandwidth limitations and frequency-selective fading characteristic of underwater channels. Through extensive simulation and experimental validation, the study demonstrates the feasibility of achieving high-speed, reliable underwater communication, highlighting significant improvements in data rates and link stability. Furthermore, the research delves into adaptive modulation schemes and coding strategies, optimized for the derived channel model, to bolster the robustness of the communication link against the unpredictable underwater environment. This pioneering work not only sheds light on the complexities of underwater acoustic signal transmission but also charts a path forward for the next generation of underwater communication systems. By pushing the boundaries of current technological capabilities and offering a solid theoretical foundation, this research contributes significantly to the field of underwater acoustics and opens new horizons for marine exploration, environmental monitoring, and submarine communication networks. Through its comprehensive analysis and innovative approaches, "Waymark in the Depths" not only addresses the technical challenges of underwater signal transmission but also lays down a crucial waymark for future endeavors in the uncharted territories of the ocean's depths

Adaptive OFDM-based acoustic underwater transmission: system design and experimental verification

In this paper, we present the design and implementation of a software defined orthogonal frequency division multiplexing (OFDM)-based underwater acoustic (UWA) communication system with link adaptation. Our system implementation is based on the customized versions of National Instruments Universal Software Radio Peripheral (USRP). The modified USRPs are interfaced with hydrophone front-ends for acoustic transmission. We investigate the performance of various adaptive algorithms where both modulation order/type and power on each subcarrier are selected based on channel conditions in order to maximize throughput. The experimental in-pool test results verify the superiority of adaptive transmission

Adaptive OFDM-based acoustic underwater transmission: system design and experimental verification

In this paper, we present the design and implementation of a software defined orthogonal frequency division multiplexing (OFDM)-based underwater acoustic (UWA) communication system with link adaptation. Our system implementation is based on the customized versions of National Instruments Universal Software Radio Peripheral (USRP). The modified USRPs are interfaced with hydrophone front-ends for acoustic transmission. We investigate the performance of various adaptive algorithms where both modulation order/type and power on each subcarrier are selected based on channel conditions in order to maximize throughput. The experimental in-pool test results verify the superiority of adaptive transmission

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

Komunikace viditelným světlem (VLC) pro LED veřejné osvětlení a další venkovní aplikace

This diploma thesis focuses on visible light communications, mainly in outdoor appliances. Whole text is divided into two blocks. First segment serves as a research, focusing on experiments carried by different university teams all over the world, which are published as IEEE conference papers. Another half discuss our own VLC prototyping, its limitations and possible upgrade paths.Tato práce se zabývá problematikou komunikace viditelným spektrem světla. Celý text je rozvržen do dvou velkých bloků, přičemž první slouží jako rešerše prací jiných týmů ze všech koutů světa, publikovaných na IEEE konferencích. Druhá část pojednává o samotném měření a prototypu komunikačního řetězce. Zmíněna je konstrukce, limitace i možnosti budoucích vylepšení.440 - Katedra telekomunikační technikyvýborn