Underwater Acoustic Communication Networks Research Articles

A Kalman Filter-Based Blind Adaptive Multi-User Detection Algorithm for Underwater Acoustic Networks

An underwater acoustic Kalman filter-based blind adaptive multi-user detection algorithm, suitable for underwater acoustic communication networks, is proposed in this paper. The algorithm can be employed to effectively improve the system capacity of multi-user communication in underwater acoustic sensor networks, reduce transmitting power and costs on power control, extend the multi-user communication distance, weaken or eliminate intersymbol interference, multiple access interference and near-far effect, thus effectively utilizing limited underwater frequency band resource. First, the dynamic model of underwater acoustic multi-user communication system and the optimal filter equation of the proposed algorithm are found. Second, computation complexity is analyzed, and convergence analysis is carried out in terms of excess mean output energy. Finally, pool, river, sea, and under-ice asynchronous communication experiments have been carried out for both the scalar and the vector hydrophones. Good experimental results verify the effectiveness of the proposed algorithm.

Adaptive Error-Correction Coding Scheme for Underwater Acoustic Communication Networks

Underwater acoustic communication networks (UWANs) have recently attracted much attention in the research community. Two properties that set UWANs apart from most radio-frequency wireless communication networks are the long propagation delay and the possible sparsity of the network topology. This in turn offers opportunities to optimize throughput through time and spatial reuse. In this paper, we propose a new adaptive coding method to realize the former. We consider time-slotted scheduling protocols, which are a popular solution for contention-free and interference-free access in small-scale UWANs, and exploit the surplus guard time that occurs for individual links for improving transmission reliability. In particular, using link distances as side information, transmitters utilize the available portion of the time slot to adapt their code rate and increase reliability. Since increased reliability trades off with energy consumption per transmission, we optimize the code rate for best tradeoff, considering both single and multiple packet transmission using the incremental redundancy hybrid automatic repeat request (IR-HARQ) protocol. For practical implementation of this adaptive coding scheme, we consider punctured and rateless codes. Simulation results demonstrate the gains achieved by our coding scheme over fixed-rate error-correction codes in terms of both throughput and consumption of transmitted energy per successfully delivered packet. We also report results from a sea trial conducted at the Haifa harbor, which corroborate the simulations.

LMS Blind Adaptive Multiuser Detection for Underwater Acoustic Communication with MMSE and MOE Criteria

In order to solve detection of multi-user detection in underwater acoustic communication networks, blind adaptive multiuser detection method using LMS algorithm was proposed to solve the MAI problem of multi-user detection in underwater acoustic communication channel when users increase. Two type simulations were executed, including synchronous and asynchronous multi-user simulation analysis, to verify the validity of LMS multi-user detection algorithm and inspection machine. The verification of the effectiveness of the MMSE and MOE algorithm for LMS multi-user detection algorithm was done by simulation.

Leveraging spatial diversity to mitigate interference in underwater acoustic communication networks

Many acoustic channels suffer from interference which is neither narrowband nor impulsive. This relatively long duration partial band interference can be particularly detrimental to system performance. We survey recent work in interference mitigation and orthogonal frequency division multiplexing (OFDM) as background motivation to develop a spatial diversity receiver for use in underwater networks. The network consists of multiple distributed cabled hydrophones that receive data transmitted over a time-varying multipath channel in the presence of partial band interference produced by interfering active sonar signals as well as marine mammal vocalizations. In operational networks, many dropped messages are lost due to partial band interference which corrupts different portions of the received signal depending on the relative position of the interferers, information source and receivers due to the slow speed of propagation.

Robust Spatial Reuse Scheduling in Underwater Acoustic Communication Networks

Resource assignment in underwater acoustic communication (UWAC) networks has recently drawn much attention in the research community. Although in most applications the number of nodes in the UWAC network is relatively small, the long propagation delay of acoustic signals underwater motivates the application of spatial reuse in channel access protocols for throughput enhancement. In this paper, we address the problem of spatial-reuse scheduling in UWAC networks that support frequent transmission of broadcast packets and require robustness to inaccurate topology information. Taking the possibility of outdated network topology information into account is of great importance for UWAC applications due to time-varying topologies in the underwater environment. Our main contribution is the derivation of a broadcast scheduling algorithm that combines topology-transparent and topology-dependent spatial-reuse scheduling methodologies to achieve high throughput in static and dynamic topology scenarios. Simulation results demonstrate that our protocol provides a favorable tradeoff between network throughput and robustness to outdated topology information due to topology changes, and that it also achieves fairness in terms of per-node throughput.

The Research of Cross-Layer Architecture for Cognitive UACN

Underwater acoustic communication network (UACN) has been considered as one of the main technologies for underwater communication. But underwater environmental is complex, water is a worse communication medium than the air, and in limited bandwidth. Thus, it is necessary to explore higher communication and network intelligence such as cognitive radio (CR) in UACN. In this paper, a concept of environment-adaptive CR-based UACN is proposed. Furthermore, the design of cross-layer network architecture, cognitive system processing cycle and the obstacle of CR-based UACN realization are described and discussed.

Underwater Acoustic Networks: The FP7 UAN Project

The EU-funded project UAN - Underwater Acoustic Network aims at conceiving, developing and testing at sea an innovative and operational concept for integrating in a unique communication system submerged, surface and aerial sensors with the objective of protecting off-shore and coastline critical infrastructures. A crucial aspect of the project consisted in the use of autonomous underwater vehicles (AUVs) as mobile nodes in the underwater acoustic communication network. In particular, AUVs have the role of adapting the network geometry to the variation of the acoustic channel. This paper reports on the project concept and vision as well as on the progress of its various development phases. The recent at-sea successes that have been demonstrated within the UAN framework are detailed and results of the final UAN project demonstration, UAN11, held in the May of 2011, are reported. The UAN network was in operation for five continuous days with up to five nodes, of which three of them were mobile nodes.

Spatial Reuse Time-Division Multiple Access for Broadcast Ad Hoc Underwater Acoustic Communication Networks

Underwater acoustic communication (UWAC) is often the only viable solution to establish an ad hoc underwater communication network. The specific features of UWAC, arising from the physics of underwater acoustics, make the design of resource-efficient media access control (MAC) protocols important as well as challenging. In this paper, we tackle this task considering ad hoc UWAC networks that support high-traffic broadcast communication. To this end, we propose the application of the spatial reuse concept and the exploitation of direct sequence spread spectrum used at the UWAC physical layer to obtain a new hybrid spatial reuse time-division multiple-access (HSR-TDMA) protocol. By tracking the time-varying network topology, our protocol adaptively optimizes the set of active communication nodes and overcomes problems of UWAC networks such as the near-far problem, flickering, and formation of islands. Pertinent performance parameters, namely network availability, message reliability, and transmission rate, are analyzed for the proposed protocol. Evaluation of these analytical performance expressions demonstrates the significant advantages of HSR-TDMA over commonly used conventional TDMA for broadcast UWAC networks. We also report performance results for both the HSR-TDMA and the conventional TDMA protocol from a sea trial at the Haifa harbor, which corroborate the results obtained from the analysis.

Direct sequence spread spectrum point-to-point communication scheme in underwater acoustic sparse channels

Owing to multiple access capability, low probability of intercept and immunity against inter symbol interference (ISI) caused by multipath propagation, direct sequence spread spectrum (DSSS) techniques have been utilised in both underwater acoustic (UWA) communication networks and reliable point-to-point communications. To overcome the severe impact of ISI in the UWA channels, we propose a novel multiple pseudo noise (PN) sequence DSSS scheme and analyse its performance in sparse time varying UWA channels. Analytical and simulation results show that using a few PN sequences can remove most of the multipath induced ISI. To further alleviate the ISI effect, we propose a simple ISI reduction algorithm. Numerical results show that our proposed algorithm along with the proposed DSSS scheme can effectively mitigates the effect of remaining ISI, especially in sparse multipath channels.

Underwater acoustic localization by principal components analyses based probabilistic approach

In this paper, the underwater localization is given from wireless acoustic communication signals by probabilistic pattern recognition in eigenspace of PCA (principal components analyses). It should be emphasized that our underwater localization is from existing wireless acoustic communication signals, but not from additional localization systems. Our underwater localization scheme is based on fingerprinting and contains two stages, i.e., the off-line (i.e., training) and on-line (i.e., predicting) stages. In general, the received acoustic signals fluctuate seriously in underwater environments. To reduce the complexity and noise effects, all received signals are projected onto the eigenspace of PCA. Each projected feature is assumed to have Gaussian probabilistic distributions. Therefore, the location information can be easily obtained by probabilistic pattern recognition of projected features in PCA space. Note that our underwater localization scheme is not affected by reflected signals. To illustrate such a benefit, experiments were conducted in a bounded water pool where reflected signals exist near the walls. Experimental results show that the proposed underwater localization scheme is efficient and accurate. The proposed localization scheme is useful for underwater acoustic communication networks, and then in underwater technologies.

Cyclic shift keying spread spectrum underwater acoustic communication

Aimed at solving the problem of low data rate of direct sequence spread spectrum underwater acoustic communication and that of complexity of the receivers of M-ary spread spectrum underwater acoustic communication, cyclic shift keying spread spectrum underwater acoustic communication is proposed based on the good characteristic of spread sequences. At the transmitter, base waveform is cyclically shifted according to the input information. At the receiver, only one correlator is used to estimate the time delay and decode. Multi-code spread spectrum based on cyclic shift is presented. Lake experiments at both middle and long range were conducted for the proposed methods. Single and two code cyclic shift keying underwater acoustic communication were realized in the range of 15 km and the bandwidth of 2 kHz. The data rate was 438 bit/s with bit error ratio around 10-2—10-5. The result demonstrated the bandwidth efficiency and low complexity of the proposed methods and the applicability for long range underwater acoustic communication and multi-user underwater acoustic communication network.

A novel architecture for multihops routing ad hoc underwater acoustic sensor networking

Underwater acoustic communication networks are an innovative issue, which faces difficult medium problems, such as long propagation time and dynamic network topology. In addition, due to high error probabilities typical for this channel it is preferred to use anti collision network mechanism. Because of the long propagation time, methods such as CTS/RTS, requiring transmissions of pre‐messages, achieve relatively low network efficiency. Moreover, TDMA methods do not utilize the network resources allowing reuse in the code domain (using CDMA) and in the spatial domain in case of nonhomogenic network topology which includes obstructions in the acoustic line of sight. In this paper we introduce a network concept based on the CDMA method confronting the acoustic underwater network challenges, such as the “near‐far” problem, fast time varying topology, multihops routing and message distribution protection. Using this concept, a sea trial including broadcast, multicast and unicast transmissions of SMS and navigation control messages was carried out in various scenarios including multihops near the shores of Israel. We present results from this sea trial demonstrating the efficacy of the proposed networking scheme.

Acoustic propagation considerations for underwater acoustic communications network development

The underwater environment is widely regarded as one of the most difficult communication channels. Underwater acoustic communications systems are challenged by the characteristics of acoustic propagation through the underwater environment. There are a wide range of physical processes that impact underwater acoustic communications and the relative importance of these processes are different in different environments. In this paper some relevant propagation phenomena are described in the context of how they impact the development and/or performance of underwater acoustic communications networks. The speed of sound and channel latency, absorption and spreading losses, waveguide effects and multipath, surface scattering, bubbles, and ambient noise are all briefly discussed.

The influence of underwater data transmission sounds on the displacement behaviour of captive harbour seals (Phoca vitulina)

To prevent grounding of ships and collisions between ships in shallow coastal waters, an underwater data collection and communication network (ACME) using underwater sounds to encode and transmit data is currently under development. Marine mammals might be affected by ACME sounds since they may use sound of a similar frequency (around 12 kHz) for communication, orientation, and prey location. If marine mammals tend to avoid the vicinity of the acoustic transmitters, they may be kept away from ecologically important areas by ACME sounds. One marine mammal species that may be affected in the North Sea is the harbour seal (Phoca vitulina). No information is available on the effects of ACME-like sounds on harbour seals, so this study was carried out as part of an environmental impact assessment program. Nine captive harbour seals were subjected to four sound types, three of which may be used in the underwater acoustic data communication network. The effect of each sound was judged by comparing the animals' location in a pool during test periods to that during baseline periods, during which no sound was produced. Each of the four sounds could be made into a deterrent by increasing its amplitude. The seals reacted by swimming away from the sound source. The sound pressure level (SPL) at the acoustic discomfort threshold was established for each of the four sounds. The acoustic discomfort threshold is defined as the boundary between the areas that the animals generally occupied during the transmission of the sounds and the areas that they generally did not enter during transmission. The SPLs at the acoustic discomfort thresholds were similar for each of the sounds (107 dB re 1 microPa). Based on this discomfort threshold SPL, discomfort zones at sea for several source levels (130-180 dB re 1 microPa) of the sounds were calculated, using a guideline sound propagation model for shallow water. The discomfort zone is defined as the area around a sound source that harbour seals are expected to avoid. The definition of the discomfort zone is based on behavioural discomfort, and does not necessarily coincide with the physical discomfort zone. Based on these results, source levels can be selected that have an acceptable effect on harbour seals in particular areas. The discomfort zone of a communication sound depends on the sound, the source level, and the propagation characteristics of the area in which the sound system is operational. The source level of the communication system should be adapted to each area (taking into account the width of a sea arm, the local sound propagation, and the importance of an area to the affected species). The discomfort zone should not coincide with ecologically important areas (for instance resting, breeding, suckling, and feeding areas), or routes between these areas.

The influence of acoustic emissions for underwater data transmission on the behaviour of harbour porpoises (Phocoena phocoena) in a floating pen

To prevent grounding of ships and collisions between ships in shallow coastal waters, an underwater data collection and communication network is currently under development: Acoustic Communication network for Monitoring of underwater Environment in coastal areas (ACME). Marine mammals might be affected by ACME sounds since they use sounds of similar frequencies (around 12 kHz) for communication, orientation, and prey location. If marine mammals tend to avoid the vicinity of the transmitters, they may be kept away from ecologically important areas by ACME sounds. One marine mammal species that may be affected in the North Sea is the harbour porpoise. Therefore, as part of an environmental impact assessment program, two captive harbour porpoises were subjected to four sounds, three of which may be used in the underwater acoustic data communication network. The effect of each sound was judged by comparing the animals' positions and respiration rates during a test period with those during a baseline period. Each of the four sounds could be made a deterrent by increasing the amplitude of the sound. The porpoises reacted by swimming away from the sounds and by slightly, but significantly, increasing their respiration rate. From the sound pressure level distribution in the pen, and the distribution of the animals during test sessions, discomfort sound level thresholds were determined for each sound. In combination with information on sound propagation in the areas where the communication system may be deployed, the extent of the 'discomfort zone' can be estimated for several source levels (SLs). The discomfort zone is defined as the area around a sound source that harbour porpoises are expected to avoid. Based on these results, SLs can be selected that have an acceptable effect on harbour porpoises in particular areas. The discomfort zone of a communication sound depends on the selected sound, the selected SL, and the propagation characteristics of the area in which the sound system is operational. In shallow, winding coastal water courses, with sandbanks, etc., the type of habitat in which the ACME sounds will be produced, propagation loss cannot be accurately estimated by using a simple propagation model, but should be measured on site. The SL of the communication system should be adapted to each area (taking into account bounding conditions created by narrow channels, sound propagation variability due to environmental factors, and the importance of an area to the affected species). The discomfort zone should not prevent harbour porpoises from spending sufficient time in ecologically important areas (for instance feeding areas), or routes towards these areas.

Multicarrier code division multiple access (MC-CDMA) technique for underwater acoustic communication networks using short spreading sequences

Code division multiple access (CDMA) techniques have recently been utilised to achieve reliable multiuser communication in asynchronous shallow water acoustic networks. The authors consider this type of communication technique, which has its origins in spread spectrum principles. The performance of multicarrier (MC) CDMA for short length complex spreading sequences, which demonstrate both good cross-correlation and auto-correlation properties, has been evaluated by means of computer simulations. In MC-CDMA, a set of carrier frequencies is employed to achieve frequency diversity. The proposed adaptive receiver architectures integrate the functions of despreading, multi-access and narrowband interference cancellation, equalisation, and phase-carrier tracking. Results show the effectiveness of the system in a rapidly time-varying, frequency-selective channel.

Implementation of multiuser detection strategies for coherent underwater acoustic communication

This paper presents multiple access interference cancellation techniques based on joint implementation of spatial-beamforming and multiuser detection strategies for coherent underwater acoustic communication network. Performances of adaptive multiuser detection strategies based on weighted parallel, successive, and recursive successive interference cancellation techniques are compared using experimental sea-trial data. Results show that the receiver structure adopting weighted recursive successive interference cancellation (RSIC) exhibits robustness in extracting useful data for weak users in the presence of co-channel interference from strong users. In addition, this type of structure simultaneously suppresses the summed interference effects contributed by weaker users toward the strongest user. The RSIC structure is therefore a potential candidate for multiple access interference suppression in coherent shallow water acoustic communication systems.