Spatial Modulation in the Underwater Acoustic Communication Channel
Spatial Modulation in the Underwater Acoustic Communication Channel

Author: Daniel B. Kilfoyle

Publisher:

Published: 2000

Total Pages: 428

ISBN-13:

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A modulation technique for increasing the reliable data rate achievable by an underwater acoustic communication system is presented and demonstrated. The technique, termed spatial modulation, seeks to control the spatial distribution of signal energy such that multiple parallel communication channels are supported by the single, physical ocean channel. Results from several experiments successfully demonstrate higher obtainable data rates and power throughput. Given a signal energy constraint, a communication architecture with access to parallel channels will have increased capacity and reliability as compared to one with access to a single channel. Assuming the use of multiple element spatial arrays at both the transmitter and receiver, an analytic framework is developed that allows a multiple input, multiple output physical channel to be transformed into a set of virtual parallel channels. The continuous time, vector singular value decomposition is the primary vehicle for this transformation. Given knowledge of the channel impulse responses and assuming additive, white Gaussian noise as the only interference, the advantages of using spatial modulation over a deterministic channel may be exactly computed. Improving performance over an ensemble of channels using spatial modulation is approached by defining and then optimizing various average performance metrics including average signal to noise ratio, average signal to noise plus interference ratio, and minimum square error. Several field experiments were conducted. Detailed channel impulse response measurements were made enabling application of the decomposition methodology. The number, strength, and stability of the available parallel channels were analyzed. The parallel channels were readily interpreted in terms of the underlying sound propagation field. Acoustic communication tests were conducted comparing conventional coherent modulation to spatial modulation. In one case, a reliable data rate of 24000 bits per second with a 4 kHz bandwidth signal was achieved with spatial modulation when conventional signaling could not achieve that rate. In another test, the benefits of spatial modulation for a horizontally distributed communication system, such as an underwater network with autonomous underwater vehicles, were validated.

Spatial Modulation in the Underwater Acoustic Channel
Spatial Modulation in the Underwater Acoustic Channel

Author:

Publisher:

Published: 2004

Total Pages: 21

ISBN-13:

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Multiple-input multiple-output (MIMO) communication channels are an active area of research for terrestrial wireless applications. The natural bandwidth limitations of the underwater acoustic channel (UAC) combined with the potential for a rich spatial propagation structure suggest the ocean may be another useful application area for MIMO techniques. An underwater acoustic communications experiment was conducted in the waters surrounding Elba, Italy, using spatially modulated signals. Two frequency regimes (9.5-14.5 kHz and 25-35 kHz) were explored over ranges up to 5 km using vertical line arrays suspended from drifting ships. The UAC had an average depth of 100 m. One-way communication links were established at two sites with one site having a rocky (reverberant) bottom and the other having a muddy (absorbent) bottom. The waveform comprised a single data stream with concatenated codes providing error control. The inner code was a high rate BCH code Trellis-coded modulation was used as the basis for the outer code. Successive coded symbols were multiplexed across the available transducer elements. This coding approach effectively maintains the inherent bandwidth efficiency of MIMO signaling. The receiver was an adaptive recursively updated multichannel decision feedback equalizer operating in conjunction with a digital phase-locked loop A packet-based, transport architecture was used and included a training sequence. A Viterbi algorithm was integrated with the equalizer that supported simultaneous tap-weight update and trellis transversal, thereby affording the decision-directed update partial error control. Using appropriate assumptions, channel capacity using a single transducer was estimated to be 5.4 bits/channel use at the soft bottom site. Capacity was maximized at 15.9 bits/channel use using four transducers. More detailed results will be presented along with performance predictions based on both propagation models and measured channel transfer functions7.

Application of Spatial Modulation to the Underwater Acoustic Communication Component of Autonomous Underwater Vehicle Networks
Application of Spatial Modulation to the Underwater Acoustic Communication Component of Autonomous Underwater Vehicle Networks

Author:

Publisher:

Published: 2005

Total Pages: 8

ISBN-13:

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There have been two fundamental advances in underwater acoustic communication in the last two decades. The first occurred in the early 1980's with the introduction of digital signaling techniques 1. That facilitated both error correction and reverberation mitigation. The second advance has been the successful application of coherent signaling techniques 2. That facilitated dramatic improvements in bandwidth efficiency and, hence, data rates. Since the introduction of coherent systems in the early 1990's, however, performance gains have been moderate and mostly attributed to important but largely technical algorithm improvements 3. Spatial modulation offers the hope of yet another fundamental advance in performance by both enabling higher data rates and offering a strategy for improving performance in intersymbol interference (ISI) limited channels. The research conducted in this program seeks to define both the potential for spatial modulation in U.S. Navy underwater communication systems and develop practical prototypes suitable to meet U.S. Navy needs.

Digital Underwater Acoustic Communications
Digital Underwater Acoustic Communications

Author: Lufen Xu

Publisher: Academic Press

Published: 2016-09-16

Total Pages: 292

ISBN-13: 0128030291

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Digital Underwater Acoustic Communications focuses on describing the differences between underwater acoustic communication channels and radio channels, discusses loss of transmitted sound in underwater acoustic channels, describes digital underwater acoustic communication signal processing, and provides a comprehensive reference to digital underwater acoustic communication equipment. This book is designed to serve as a reference for postgraduate students and practicing engineers involved in the design and analysis of underwater acoustic communications systems as well as for engineers involved in underwater acoustic engineering. Introduces the basics of underwater acoustics, along with the advanced functionalities needed to achieve reliable communications in underwater environment Identifies challenges in underwater acoustic channels relative to radio channels, underwater acoustic propagation, and solutions Shows how multi-path structures can be thought of as time diversity signals Presents a new, robust signal processing system, and an advanced FH-SS system for multimedia underwater acoustic communications with moderate communication ranges (above 20km) and rates (above 600bps) Describes the APNFM system for underwater acoustic communication equipment (including both civil and military applications), to be employed in active sonar to improve its performance

OFDM for Underwater Acoustic Communications
OFDM for Underwater Acoustic Communications

Author: Sheng Zhou

Publisher: John Wiley & Sons

Published: 2014-03-21

Total Pages: 498

ISBN-13: 1118693817

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A blend of introductory material and advanced signal processing and communication techniques, of critical importance to underwater system and network development This book, which is the first to describe the processing techniques central to underwater OFDM, is arranged into four distinct sections: First, it describes the characteristics of underwater acoustic channels, and stresses the difference from wireless radio channels. Then it goes over the basics of OFDM and channel coding. The second part starts with an overview of the OFDM receiver, and develops various modules for the receiver design in systems with single or multiple transmitters. This is the main body of the book. Extensive experimental data sets are used to verify the receiver performance. In the third part, the authors discuss applications of the OFDM receiver in i) deep water channels, which may contain very long separated multipath clusters, ii) interference-rich environments, where an unintentional interference such as Sonar will be present, and iii) a network with multiple users where both non-cooperative and cooperative underwater communications are developed. Lastly, it describes the development of a positioning system with OFDM waveforms, and the progress on the OFDM modem development. Closely related industries include the development and manufacturing of autonomous underwater vehicles (AUVs) and scientific sensory equipment. AUVs and sensors in the future could integrate modems, based on the OFDM technology described in this book. Contents includes: Underwater acoustic channel characteristics/OFDM basics/Peak-to-average-ratio control/Detection and Doppler estimation (Doppler scale and CFO)/Channel estimation and noise estimation/A block-by-block progressive receiver and performance results/Extensions to multi-input multi-output OFDM/Receiver designs for multiple users/Cooperative underwater OFDM (Physical layer network coding and dynamic coded cooperation)/Localization with OFDM waveforms/Modem developments A valuable resource for Graduate and postgraduate students on electrical engineering or physics courses; electrical engineers, underwater acousticians, communications engineers

Combined Spatial Diversity and Time Equalization for Broadband Multiple Channel Underwater Acoustic Communications
Combined Spatial Diversity and Time Equalization for Broadband Multiple Channel Underwater Acoustic Communications

Author: Violeta Skoro Kaskarovska

Publisher:

Published: 2015

Total Pages: 136

ISBN-13:

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High data rate acoustic communications become feasible with the use of communication systems that operate at high frequency. The high frequency acoustic transmission in shallow water endures severe distortion as a result of the extensive intersymbol interference and Doppler shift, caused by the time variable multipath nature of the channel. In this research a Single Input Multiple Output (SIMO) acoustic communication system is developed to improve the reliability of the high data rate communications at short range in the shallow water acoustic channel. The proposed SIMO communication system operates at very high frequency and combines spatial diversity and decision feedback equalizer in a multilevel adaptive configuration. The first configuration performs selective combining on the equalized signals from multiple receivers and generates quality feedback parameter for the next level of combining. The second configuration implements a form of turbo equalization to evaluate the individual receivers using the feedback parameters as decision symbols. The improved signals from individual receivers are used in the next iteration of selective combining. Multiple iterations are used to achieve optimal estimate of the received signal. The multilevel adaptive configuration is evaluated on experimental and simulated data using SIMO system with three, four and five receivers. The simulation channel model developed for this research is based on experimental channel and Rician fading channel model. The performance of the channel is evaluated in terms of Bit Error Rate (BER) and Signal-to-Noise-and-Interference Ratio (SNIR). Using experimental data with non-zero BER, multilevel adaptive spatial diversity can achieve BER of 0 % and SNIR gain of 3 dB. The simulation results show that the average BER and SNIR after multilevel combining improve dramatically compared to the single receiver, even in case of extremely high BER of individual received signals. The results demonstrate the ability of the proposed multilevel adaptive combining approach to significantly improve the performance of the shallow water acoustic channel, while preserving the same transmission power and channel bandwidth.

Harvesting Time-frequency-space Diversity with Coded Modulation for Underwater Acoustic Communications
Harvesting Time-frequency-space Diversity with Coded Modulation for Underwater Acoustic Communications

Author: Konstantinos Pelekanakis

Publisher:

Published: 2009

Total Pages: 360

ISBN-13:

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(Cont.) Both systems are combined with specific space-time block codes (STBC) when two or three transmit antennas are used. Moreover, pilot-symbol-aided channel estimation is performed by using a robust 2-D Wiener filter, which copes with channel model mismatch by employing appropriate time and frequency correlation functions. The following result was obtained by testing the aforementioned systems using both simulated and experimental data from RACE '08: the BICM scheme performs better when the UWA channel exhibits limited spatial diversity. This result implies that coded modulation schemes emphasizing higher Hamming distances are preferred when there is no option for many receive/transmit hydrophones. The TCM scheme, on the other hand, becomes a better choice when the UWA channel demonstrates a high spatial diversity order. This result implies that coded modulation schemes emphasizing higher free Euclidean distances are preferred when multiple receive/transmit hydrophones are deployed.

Advanced Spatial Modulation Systems
Advanced Spatial Modulation Systems

Author: Anirban Bhowal

Publisher: Springer Nature

Published: 2020-12-12

Total Pages: 246

ISBN-13: 9811599602

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This state-of-the-art book deals with advanced spatial modulation (ASM), which are a special class of recent Multiple-Input Multiple-Output MIMO techniques, for various applications like radio frequency (RF) based body area network (BAN) communication, free-space optical (FSO) communication, underwater optical wireless communication (UOWC) and hybrid FSO/RF communication. The performance analysis of such systems is achieved in terms of certain performance metrics and compared with other techniques available in the literature. Such SM based schemes can find its application in advanced 5G and 6G communications. The diagrams of the system models of the different schemes along with tables and examples will help readers get a clear understanding of this approach. This book elucidates required derivations, examples, and links various concepts related to this field so that readers can gain comprehensive knowledge. Pseudo codes or algorithms or MATLAB/MATHEMATICA programs are also provided so that readers can easily implement the concepts which they learn. This volume will be useful for students, researchers, and industry alike.