Determine optimal bandwidth for modulation in underwater communication channel based on PSO

Immune particle swarm optimization of linear frequency modulation in acoustic communication

The Earth is a water planet, two-thirds of which is covered by water. With the rapid developments in technology, underwater communications has become a fast growing field, with broad applications in commercial and military water based systems. The need for underwater wireless communications exists in applications such as remote control in the off-shore oil industry, pollution monitoring in environmental systems, collection of scientific data from ocean-bottom stations, disaster detection and early warning, national security and defense (intrusion detection and underwater surveillance), as well as new resource discovery. Thus, the research of new underwater wireless communication techniques has played the most important role in the exploration of oceans and other aquatic environments. In contrast with terrestrial wireless radio communications, the communication channels in underwater wireless networks can be seriously affected by the marine environment, by noise, and by limited bandwidth and power resources, and by the harsh underwater ambient conditions. Hence, the underwater communication channel often exhibits severe attenuation, multipath effect, frequency dispersion, and constrained bandwidth and power resources, etc., which turn the underwater communication channel into one of the most complex and harsh wireless channels in nature. When facing these unique conditions in diverse underwater applications, many new challenges, which were not encountered in terrestrial wireless communications, are emerging in underwater acoustic, optical, and RF communications for future underwater wireless networks. Of these challenges, acoustic and optical are the most compelling, and somewhat complementary, owing to the potential for longer range and high bandwidth networked communications in sizeand power-constrained modems and unmanned systems.

This work presents a computational framework for the analysis and design of large-scale algorithms utilized in the estimation of acoustic, doubly-dispersive, randomly time-variant, underwater communication channels. Channel estimation results are used, in turn, in the proposed framework for the development of efficient high performance algorithms, based on fast Fourier transformations, for the search, detection, estimation and tracking (SDET) of underwater moving objects through acoustic wavefront signal analysis techniques associated with real-time electronic surveillance and acoustic monitoring (eSAM) operations. Particular importance is given in this work to the estimation of the range and speed of deep underwater moving objects modeled as point targets. The work demonstrates how to use Kronecker products signal algebra (KSA), a branch of finite-dimensional tensor signal algebra, as a mathematical language for the formulation of novel variants of parallel orthogonal matching pursuit (POMP) algorithms, as well as a programming aid for mapping these algorithms to large-scale computational structures, using a modified Kuck’s paradigm for parallel computation.

Multicarrier code division multiple access (MC-CDMA) can be applied in underwater acoustic communication networks to combat the narrow bandwidth of the underwater acoustic channel and multipath fading. Power control is one of the key technologies for the MC-CDMA communication networks. In this paper, we propose a multi-objective power control scheme based on improved particle swarm optimization (PSO) algorithm for underwater acoustic MC-CDMA communication networks. The distance of different nodes to base station (BS) is not same, which can cause near-far effect. So we propose a fitness function which is consisted of power consumption and SINR (the signal to interference plus noise ratio) on the receiver. The method effective reduces the power consumption of nodes and decreases the near-far effect. Comparing with the scheme without power control, our results show that the proposed power control algorithm can be used in underwater acoustic channel. Not only the power consumption is lower, but also the bit error rate (BER) performances are better.

As the dominant information carrier in water, the acoustic wave is widely used for underwater detection, communication and imaging. Even though underwater acoustic communication has been greatly improved in the past decades, it still suffers from slow transmission speeds and low information capacity. The recently developed acoustic orbital angular momentum (OAM) multiplexing communication promises a high efficiency, large capacity and fast transmission speed for acoustic communication. However, the current works on OAM multiplexing communication mainly appear in airborne acoustics. The application of acoustic OAM for underwater communication remains to be further explored and studied. In this paper, an impedance matching pentamode demultiplexing metasurface is designed to realize multiplexing and demultiplexing in underwater acoustic communication. The impedance matching of the metasurface ensures high transmission of the transmitted information. The information encoded into two different OAM beams as two independent channels is numerically demonstrated by realizing real-time picture transfer. The simulation shows the effectiveness of the system for underwater acoustic multiplexing communication. This work paves the way for experimental demonstration and practical application of OAM multiplexing for underwater acoustic communication.

The fast temporal variations, long multipath delay spreads, and severe frequency-dependent attenuations of underwater acoustic communication channels are extremely complex that impedes underwater acoustic (UWA) data transmission. To alleviate this problem, channel coding is indispensable in UWA communication system to increase the reliability. In this paper, performances of LDPC codes with different parameters over different underwater acoustic communication channels are presented, which is to know how to adjust the encoding and decoding parameters according to different underwater acoustic channels. The results indicate that LDPC codes have a good performance of the estimated BER on the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> either in positive sound velocity gradient (PSVG) underwater channel or negative sound velocity gradient (NSVG) one, even invariable sound velocity gradient (ISVG) one. In addition, whatever the encoding or decoding parameters is adopted, performance of the LDPC codes over the NSVG underwater channel is the best, compared with PSVG one and ISVG one. Furthermore, in the desired performance of BER of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> , the encoding and decoding parameters according to the three different underwater channels specifications are summarized.

Underwater acoustic communications are required for controlling and networking a variety of underwater or sea surface objects. Due to the unique characteristics of the underwater acoustic channel, e.g., complicated multipath propagation, selective frequency fading, extreme Doppler effect and heavy ambient noise, FH-MFSK techniques play a vital role in robust underwater acoustic communication, especially in shallow water. However, based on detecting the frequency of the receiving signals, the demodulation scheme for FH-MFSK may be sensitive to the frequency shifting caused by underwater Doppler shifts. This paper focuses on how to design the frequency demodulation scheme and to improve the performance of underwater FH-MFSK acoustic communication system. By using an original Double-Line Interpolation algorithm with Hanning window, we propose a demodulation scheme to enhance the tolerance of the Doppler shift and improve the detection rate. Simulations and demodulation performance were tested. Experimental results show a promising future for FH-MFSK demodulation in underwater acoustic communication system.

At the physical layer, Underwater Acoustic Communication (UWAC) channels present many challenges for efficient communications, which feature both long delay spreads and serious Doppler effects. The waves and motions at the surface of the sea are the main causes for these effects. The complexity at the receiver increases along with the symbol rate, thereby increasing the burden of the channel. Orthogonal Frequency Division Multiplexing (OFDM) which is a form of multicarrier modulation has been effectively used for UWAC recently because of its ability to handle long dispersive channels reducing the complexity of the channel equalization. However, Inter Carrier Interference (ICI) is introduced by the Doppler effects that destroy the orthogonality of the subcarriers. To overcome the effects of OFDM, an emerging technique known as Filter Bank Multicarrier Communication system (FBMC) is used in UWAC. The high capacity of the transmission bandwidth in FBMC systems can be accomplished by applying Offset Quadrature Amplitude Modulation (OQAM). Because of cyclic prefix deletion, FBMC/OQAM can arrange higher spectral efficiency when compared to OFDM. This paper worked on both OFDM and FBMC/OQAM by considering the losses and noise effects in UWAC environment and explained their performances with respect to Bit Error Rate (BER).

A signal transmitted in an Underwater Acoustic Communication (UAC) system operating in a shallow-water channel suffers from strong time dispersion due to multipath propagation. This causes the Inter-Symbol Interference (ISI) observed in the received signal, which significantly limits the communication system’s reliability and transmission rate. In such propagation conditions, the Direct-Sequence Spread Spectrum (DSSS) method is one of the solutions that make reliable data transmission possible. In systems with one-to-one communication, it ensures communication with a satisfactory Bit Error Rate (BER). Additionally, it makes it possible to implement the Code-Division Multiple Access (CDMA) protocol in underwater acoustic networks. This paper presents the results of simulation and experimental communication tests on a DSSS-based UAC system using three types of spreading sequence, namely m-sequences, Kasami codes and Gold codes, and occupying different bandwidths from 1 kHz to 8 kHz around a carrier frequency equal to 30 kHz. The UAC channel was simulated by impulse responses calculated by the virtual sources method and the UAC chanel models available in the Watermark simulator. The experimental tests were conducted in a model pool. Based on the obtained results, a transmission rate was estimated, which is possible to achieve in strong multipath propagation conditions, assuming reliability expressed as BER less than 0.001.

Underwater acoustic communication channels are characterized by a large variety of propagation conditions. Designing a reliable communication system requires knowledge of the transmission parameters of the channel, namely multipath delay spread, Doppler spread, coherence time, and coherence bandwidth. However, the possibilities of its estimation in a real-time underwater communication system are limited, mainly due to the computational time of implementations of the digital signal processing algorithms. The article presents the results of analysis of probe signals measured during a shallow water experiment. The implementation issues of estimation algorithms are discussed, assuming floating point arithmetic, and with both single-core and multi-core digital signal processors as the target platforms.

Angle of arrival (AoA) analysis is essential for the statistical characterization of the underwater (UW) channel where the acoustic signal propagation is confined to a restricted geometry. In UW channels, the acoustic signal reaches the receiver either through the line of sight path or through scattering from the sea surface and bottom. Low-frequency acoustic signals (few Hz) undergo reflection from the sea surface and bottom. This is called coherent scattering, where the scattered paths are assumed to be in phase and concentrated around the specular paths. At relatively higher frequencies (above 10 kHz), incoherent scattering occurs, resulting in an omnidirectional scattering pattern at each point of interaction with the sea surface. In this work, we derive a closed-form expression for the AoA distribution for a single bounce (SB) path that undergoes incoherent scattering from the surface/bottom in an UW channel. The analysis is extended to the case of paths involving multiple bounces (MB). The AoA distribution is further used to evaluate the Doppler spread in an UW channel.

This paper applies the full tail-biting (FTB) convolutional codes to short data packets and evaluates their performance in underwater acoustic communication by computer simulation and an ocean experiment. The simulation results for AWGN channels show that the FTB codes achieve the similar bit error rate (BER) performance as the zero-tailing convolutional (ZTC) codes regardless of block lengths, while the direct-truncate convolutional (DTC) codes suffer from BER degradation, specially with short block lengths. Both simulation and ocean experimental results demonstrate that the FTB codes are excellent candidates for underwater acoustic communication systems where short data blocks and strong error correction codes are needed.

The achievement of efficient data transmissions via underwater acoustic channels, while dealing with large data packets and real-time data fed by underwater sensors, requires a~high data rate. However, diffraction, refraction, and reflection phenomena, as well as phase and amplitude variations, are common problems experienced in underwater acoustic (UWA) channels. These factors make it difficult to achieve high-speed and long-range underwater acoustic communications. Due to multipath interference caused by surface and ocean floor reflections, the process of modeling acoustic channels under the water's surface is of key importance. This work proposes a~simple geometry-based channel model for underwater communication. The impact that varying numbers of reflections, low water depth values, and distances between the transmitter and the receiver exert on channel impulse response and transmission loss is examined. The high degree of similarity between numerical simulations and actual results demonstrates that the proposed model is suitable for describing shallow underwater acoustic communication environments.

The recent growing interest in underwater acoustic communication (UAC) requires an in depth understanding of a vast and diverse water medium. The UAC channel presents many difficulties such as high frequency, space, and time selectivity, frequency dependent noise, and significant range and band limitation on transmission. The existing channel models may not be sufficient to cover the entire UAC channel domain and its many applications. In addition, the choice of channel model from the existing ones may not always be accurate to represent the channel environment. Thus, it is necessary to explore higher communication intelligence in the mapping of UAC channel models according to environment. This paper will present novel cognitive intelligent (CI) algorithm in accurate selection of UAC channel models. To the best knowledge of the authors, cognitive intelligence in the mapping of UAC environment to channel models has not been presented in the literature. Thus this research presents a valuable work.

This paper focuses on the wake-up signal detection design for underwater acoustic communication (UAC) terminals. A wake-up signal detection unit can considerably reduce the power consumption of the terminals. Compared with terrestrial wireless counterparts, the wake-up signal detection design for UAC terminals is challenged by the severe underwater acoustic channels, which is characterized as doubly selective fading and low signal-to-noise ratio (SNR). This paper proposes a wake-up signal detection approach called channel-adaptive detection and location-assisted joint decision (ChAD-LaJD), for UAC terminals. ChAD-LaJD applies a group of linear frequency modulation (LFM) signals as a wake-up signal. In order to increase the detection probability while keeping a low false alarm rate, ChAD-LaJD consists of two procedures: channel-adaptive detection (ChAD) and location-assisted joint decision (LaJD). Besides a pre-determined threshold, ChAD procedure defines two special parameters which reflect instantaneous channel states to detect wake-up signals adaptively. LaJD procedure further exploits the location relationships of LFM signals detected by ChAD to achieve a joint decision. The simulations and field experiments are conducted to evaluate the performance of ChAD-LaJD. The results show that ChAD-LaJD outperforms the conventional methods that consider a fixed threshold (FixTh) and/or constant false alarm rate (CFAR).