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Bit Error Rate performance of coded OFDM with decision feedback on the LTV1 and NOF1 channels, as a function of the delay and Doppler spread estimation thresholds.
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Acoustic underwater channels are very challenging, because of limited bandwidth, long propagation delays, extended multipath, severe attenuation, rapid time variation and large Doppler shifts. A plethora of underwater communication techniques have been developed for dealing with such a complexity, mostly tailoring specific applications scenarios wh...
Citations
... There are many different physical layer protocols for digital acoustic communication, but they are all proprietary and therefore not interoperable, and also the extent to which academic inquiry is possible is limited. Furthermore, in cases where robustness is required, e.g. in noisy environments, the previously mentioned JANUS standard is as of 2021 still the fallback technology [30]. JANUS was developed as a deliberately simple and robust physical layer protocol suited for initial contact, that could be used as a beacon, for discovery and for negotiation of mutually-available higher-performance communication modes, a function demonstrated in [31]. ...
... In [24], second-order statistics of the channel are exploited to derive the signal-to-interference-plus-noise ratio in each sub-carrier, so to realize adaptive coding and bit-power loading. An OFDM acoustic modem is presented in [25], with adaptive modulation being performed based on the channel delay and Doppler spread, measured by using chirp pilots. An information-dependent sub-carrier mapping is proposed for underwater video transmission in [26], so that important data are conveyed on the most reliable OFDM sub-channels, while less useful data are transmitted through the lower quality sub-carriers. ...
Underwater acoustic communications are limited by the following channel impairments: time variability, narrow bandwidth, multipath, frequency selective fading and the Doppler effect. Orthogonal Frequency Division Modulation (OFDM) is recognized as an effective solution to such impairments, especially when optimally designed according to the propagation conditions. On the other hand, OFDM implementation requires accurate channel knowledge atboth transmitter and receiver sides. Long propagation delay may lead to outdated channel information. In this work, we present an adaptive OFDM scheme where channel state information is predicted through a Kalman-like filter so as to optimize communication parameters, including the cyclic prefix length. This mechanism aims to mitigate the variability of channel delay spread. This is cast in a protocol where channel estimation/prediction are jointly considered, so as to allow efficiency. The performance obtained through extensive simulations using real channels and interference show the effectiveness of the proposed scheme, both in terms of rate and reliability, at the expense of an increasing complexity. However, this solution is significantly preferable to the conventional mechanism, where channel estimation is performed only at the receiver, with channel coefficients sent back to the transmit node by means of frequent overhead signaling.
... All the aforementioned modems are capable of ranging and of achieving a bitrate of hundreds of bits per second up to a range of a few hundred meters in a shallow water environment. For a more complete review of both low-cost and expensive acoustic software-defined modems we refer the interested reader to [10] and [11]. ...
The development of small low-cost autonomous underwater and surface vehicles has increased the need for underwater wireless communication and ranging to support swarm operations for collaborative data collection efforts. Specifically, newly available low-cost underwater and surface vehicles make the realization of swarm formation cost effective. However, their mission coordination involves the use of expensive acoustic modems whose price may be higher than that of the vehicle itself. In this paper, we describe and evaluate a low-cost software-defined acoustic modem developed with only off-the-shelf components, able to perform one-way travel-time ranging. The modem is specifically designed for dense mobile networks deployed in shallow water environments, such as rivers, lagoons and lakes. The modular software design of the modem allows us to easily configure parameters such as modulation and coding schemes, scheduling algorithm, source power, carrier frequency and bandwidth. In this paper we evaluate, in a shallow environment, the modem performance in terms of packet detection ratio, packet delivery ratio, and one-way travel-time ranging.
... The first scheme adjusted only the modulation level and evenly distributed power among subcarriers; the second scheme adaptively adjusted the modulation level and power and then gave the effectiveness of UWA link adaptive modulation results through real-time marine experiments for the first time. Mangione [7] and others designed and implemented a software-defined modem, which can dynamically estimate the acoustic channel conditions, adjust the parameters of the OFDM modulator according to the environment, or switch to a more robust JANUS/FSK modulator under harsh propagation conditions. ...
Due to the time-varying and space-varying characteristics of the underwater acoustic channel, the communication process may be seriously disturbed. Thus, the underwater acoustic communication system is facing the challenges of alleviating interference and improving communication quality and communication efficiency through adaptive modulation. In order to select the optimal modulation mode adaptively and maximize the system throughput ensuring that the bit error rate (BER) meets the transmission requirements, this paper introduces deep reinforcement learning (DRL) into orthogonal frequency division multiplexing acoustic communication system. The adaptive modulation is mapped into a Markov decision process with unknown state transition probability. Thereby, the underwater communication channel environment is regarded as the state of DRL, and the modulation mode is regarded as action. The system returns channel state information (CSI) and signal–noise ratio in every time slot through the feedback link. Because the Deep Q-Network optimizes in the changing state space of each time slot, it is suitable for a variety of different CSI. Finally, simulations in different underwater environments (SWellEx-96) show that the proposed adaptive modulation scheme can obtain lower BER and improve the system throughput effectively.
... The main characteristic of S2C communications is that data symbols are transmitted through linear frequency modulated (LFM) waveforms. While higher spectral efficiency modulations like OFDM suffer from high peak-to-average power ratio (PAPR) and might even be unfeasible on the underwater channel [7], S2C transmissions have ideal PAPR, with waveforms modulated with constellations such as quadrature phase shift keying (QPSK). However, relatively few works have developed and investigated S2C communications, despite its usefulness and success in real-world commercial deployments, perhaps because of the patents protecting further implementation and developments [4]. ...
... There are many different physical layer protocols for digital acoustic communication, but they are all proprietary and therefore not interoperable, and also the extent to which academic inquiry is possible is limited. Furthermore, in cases where robustness is required, e.g. in noisy environments, the previously mentioned JANUS standard is as of 2021 still the fallback technology [26]. JANUS was developed as a deliberately simple and robust physical layer protocol suited for initial contact, that could be used as a beacon, for discovery and for negotiation of mutually-available higher-performance communication modes, a function demonstrated in [27]. ...
Secure digital wireless communication underwater has become a key issue as maritime operations shift towards employing a heterogeneous mix of robotic assets and as the security of digital systems becomes challenged across all domains. At the same time, a proliferation of underwater signal coding and physical layer options are delivering greater bandwidth and flexibility, but mostly without the standards necessary for interoperability. We address here an essential requirement for security, namely a confirmation of asset identities also known as authentication. We propose, implement, verify and validate an authentication protocol based on the first digital underwater communications standard. Our scheme is applicable primarily to AUVs operating around offshore oil and gas facilities, but also to other underwater devices that may in the future have acoustic modems. It makes communication including command and control significantly more secure and provides a foundation for the development of more sophisticated security mechanisms.
... Acoustic signals are of interest in the telecommunications industry for various remote applications, such as sonar for underwater civilian/military scenarios [1][2][3], modems for both aerial and underwater communications [4][5][6], as well as echography and other medical applications involving image reconstruction [7][8][9]. Networks of acoustic sensors, called wireless acoustic sensor networks (WASNs), are increasingly adopted to support sensing and monitoring applications in the emerging paradigm of the smart cities. Prominent examples include the monitoring of urban noise [10,11], the deployment of advanced acoustic surveillance systems [12], and more generally indoor and outdoor applications benefiting from the extraction of contextual information (e.g., proximity, ranging) from acoustic communications [13]. ...
Acoustic communications are experiencing renewed interest as alternative solutions to traditional RF communications, not only in RF-denied environments (such as underwater) but also in areas where the electromagnetic (EM) spectrum is heavily shared among several wireless systems. By introducing additional dedicated channels, independent from the EM ones, acoustic systems can be used to ensure the continuity of some critical services such as communication, localization, detection, and sensing. In this paper, we design and implement a novel acoustic system that uses only low-cost off-the-shelf hardware and the transmission of a single, suitably designed signal in the inaudible band (18-22 kHz) to perform integrated sensing (ranging) and communication. The experimental testbed consists of a common home speaker transmitting acoustic signals to a smartphone, which receives them through the integrated microphone, and of an additional receiver exploiting the same signals to estimate distance information from a physical obstacle in the environment. The performance of the proposed dual-function system in terms of noise, data rate, and accuracy in distance estimation is experimentally evaluated in a real operational environment.
... The error bits N ei are calculated by comparingp i with the fixed 32-bit preamble p (lines 11). Only the peak resulting in the least error bits (lines[12][13][14][15][16][17][18][19] ...
This article presents extensive field tests of a fast-mode operation of the JANUS acoustic communication standard where the signals occupy high-frequency bands of 38 kHz spanning from 96 to 134 kHz instead of the nominal frequency band of 4.1 kHz spanning from 9.44 to 13.6 kHz specified in the standard. The fixed 32-chip preamble and the 144-chip baseline JANUS packet utilize the frequency-hopped binary frequency shift keying with 13 frequency pairs as defined in the standard while the cargo packets use the single-carrier
M
-ary phase shift keying modulation with a center frequency of 115 kHz and a symbol rate of 23 ksps or up to 34.5 kb/s information data rate with high-order phase shift keying (PSK) and rate-1/2 forward error correction codes. The original JANUS receiver algorithm is modified to improve the frame/symbol synchronization for the fast mode and increase the decoding success rate of the baseline JANUS packet in difficult multipath channels. More than 10 experiments were conducted using a field-programmable-gate-array-based hardware platform consisting of a single transmit projector and a single receive hydrophone. The experiment results show that the JANUS fast mode worked well with both the original JANUS receiver algorithm and the modified receiver algorithm, yielding zero bit error in most of the baseline JANUS packets. The modified receiver algorithm is able to reduce 30% of error packets to zero error in the experiment experiencing difficult multipath channels where the original JANUS receiver algorithm suffers from large bit error rates (BER). Meanwhile, the cargo packets utilize the linear minimum mean-square error turbo equalizer and achieve a BER around 10
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... Commonly used underwater modulation methods include frequency-shift keying (FSK), phase-shift keying (PSK), and orthogonal frequency-division multiplexing (OFDM). Compared with other modulation methods, OFDM has advantages due to its resilience against frequency selective channels with long delay spreads [61][62][63][64]. In addition, although underwater acoustic communication has been relatively mature, it also faces some problems. ...
As the ocean development process speeds up, the technical means of ocean exploration are being upgraded. Due to the characteristics of seawater and the complex underwater environment, conventional measurement and sensing methods used for land are difficult to apply in the underwater environment directly. Especially for the seabed topography, it is impossible to carry out long-distance and accurate detection via electromagnetic waves. Therefore, various types of acoustic and even optical sensing devices for underwater applications have come into use. Equipped by submersibles, those underwater sensors can sense underwater wide-range and accurately. Moreover, the development of sensor technology will be modified and optimized according to the needs of ocean exploitation. This paper has made a summary of the ocean sensing technologies applied in some critical underwater scenarios, including geological surveys, navigation and communication, marine environmental parameters, and underwater inspections. In order to contain as many submersible-based sensors as possible, we have to make a trade-off on breadth and depth. In the end, the authors predict the development trend of underwater sensor technology based on the future ocean exploration requirements.
