Performance Of Underwater Communication System Research Articles

A novel cooperative spectrum signal detection algorithm for underwater communication system

In order to further improve the spectrum resource detection probability and increase the spectrum utilization rate in underwater wireless communication systems, this paper designs a novel multi-layer cooperative spectrum sensing algorithm based on compressed sensing, which uses compressed sensing technology to estimate the spectrum to reduce the sampling rate and the overhead of sonar signals. This new algorithm seeks the optimal hyper-parameter through Bayesian model. The multi-layer Bayesian model is introduced into the Dirichlet process to realize the automatic grouping of compressed perceptual data with the information from the non-parametric grouping mechanism, and the optimal super-parameters are selected through the fusion center to determine the spectrum. Simulation results show that the proposed algorithm fully considers the temporal correlation of compressed perceptual data and effectively improves spectral sensing performance of underwater communication system.

Predicting surface scattering from surface elevation time series

Surface reverberation in mid-frequency bands (we are considering 3–15 kHz) can be an important determinant for the performance of underwater communications systems operating in surface scattering environments. At these frequencies and at relatively short ranges (order 10 water depths), gravity waves focus sound energy incident on the surface, creating intensifications, Doppler shifts and phase shifts in the reflected field, all of which impact the performance of underwater acoustic communications systems. Observations of the time-varying arrival intensity structure from an experiment conducted in the Martha's Vineyard Coastal Observatory will be presented along with model calculations made using the Kirchhoff approximation. The sensitivity of the reflected field to the distribution of energy in the surface wave field and short wavelength gravity waves will will be discussed. [Work supported by the ONR Ocean Acoustics Program.]

수중 센서 네트워크에서 저전력 통신을 위한 변조기법의 적용성 연구

In this paper, we propose the result of PSSK(Phase Silence Shift Keying) modulation scheme that is mixed PSK(Phase Shift Keying) modulation and PPM(Pulse Position Modulation) method. The performance of underwater communication systems are influenced underwater channel characteristics. In particular, delay spread can make ISI(Inter Symbol Interference) because of reverberation and multi path. It degrade the performance of the communication system. Also underwater sensor networks consider about power efficient due to the particularities of their operating environment. PSSK modulation method transmit two orthogonal symbol and using silence period in a period so it can reduce the power. Increasing the distance of between modulation symbols, to enhance the performance of BER(Bit Error Rate) as well as to improve power efficient. The result of sea trial, QPSK modulation BER is and PSSK modulation BER is .

수중에서 OFDM 변조를 이용한 음향 통신의 성능분석

The performance of underwater communication system is influenced on channel characteristic. Delay spread cause by reverberation and multi-path happen the ISI (Inter Symbol Interference) and reduces the communication performance. In this paper, we analyze the performance of acoustic communication experiment in underwater to use the OFDM (Orthogonal Frequency Division Multiplexing) technique for overcome the reverberation and multi-path. As a result, we acquired the BER of modulation techniques. The BER of 2kbps data rate is and BER of 4 kbps data rate is .

Frequency and Temporal Coherence Variation for Sea Surface Fluctuation

Sea surface fluctuation by the wind has an effect on the performance of underwater communication systems since it induces time-variant scattering. Such scattering gives the time spread and consequently the signal fading in the amplitude and phase of the transmitted signal. In this study, such signal fading is examined experimentally on the basis of frequency and temporal coherence variations under wind speeds of about 15–16 kn at a 15.5 m height from the sea level. The frequency coherence bandwidth of surface reflection scattered signals is found to be about 300 Hz at a 3 dB bandwidth. The mean coherence is about 0.9 for a grazing angle of 16° and at wind speed of 15–16 kn. The dominant coherence variation frequency is consistent with the dominant sea surface wave frequency.

Quasi-deterministic forward scattering from the sea surface

Gravity waves create focal regions and caustics in sound forward-scattered from the sea surface. Focal regions are associated with rapid variations in amplitude and Doppler shift, which can impact the performance of underwater communications systems and sonars operated near the shore. Single-bounce focal regions consist of a superposition of up to 3 micro-paths, each of which is associated with its own amplitude, time delay, and Doppler shift. Focal regions move systematically through the water column as the wave propagates. Studies of these effects in near-shore ocean experiments and a laboratory flume have shown that a quasi-deterministic analysis of wave scattering can lead to valuable insights about the underlying scattering process. [Work supported by ONR.]

Gravity wave focusing in the littoral zone

One of the unique environmental factors impacting acoustic propagation in the littoral zone is the presence of shoaling surf. Surface gravity waves act as acoustic mirrors, creating high‐intensity cusps and caustics in the reflected sound field. The focal points of sound move through the water column as the gravity waves shoal, and can disrupt the performance of underwater communications systems and impact sonar performance. Analytical and numerical calculations of the focusing properties of shoaling gravity waves are described and used to predict the motion of the focal regions through time. [Work supported by ONR.]

Theory and experiments for surface-wave focused acoustic arrivals: A deterministic view

Statistical descriptions of surface wave scattering are now highly developed, and have proven very effective in relating the first and second order statistics of surface-reflected acoustic arrivals to surface conditions. Notwithstanding this success, the deterministic features of surface-scattered arrivals are of considerable importance. The limits of performance of underwater communications systems in very shallow water, for example, are determined by the frequency and properties of extreme surface focusing events. The analysis of data from the Wavefronts I, II, and V series of experiments has led to an understanding of the wave properties controlling the focusing events, as well as their impact on acoustic channel estimators. Data from the wavefronts experiments (SIO pier, 7 m deep, 40 m range) and the SPACE02 experiment (Martha’s Vineyard, 15 m depth, 250–1000 m range) will be presented and discussed. [Work supported by ONR.]

Modeling the acoustical focusing properties of shoaling surf

Shoaling surf focuses sound, creating high intensity caustics that impact the performance of underwater communications systems and sonars in the very near shore region. Simple expressions for the time-varying caustic locus and amplitude can be derived from the Kirchhoff–Helmholtz scattering integral. The analysis shows that a focus is formed at a range equal to one-half the crests radius of curvature when the wave is directly over a shallow water source, and moves toward the crest and decreases in intensity as the wave shoals shoreward. The analysis is compared with numerical scattering calculations based on measured surface gravity wave profiles, and also with experimental data in which 10-kHz, single cycle pulses were transmitted over a 40 m path in 6 m of water just north of Scripps Pier. The impact of the caustics on sonar performance will be discussed. [Work supported by ONR.]