Characteristics Of Acoustic Channel Research Articles

Acoustic detection based on coherence bandwidth

Traditional security systems which include video cameras continuously recording and transmitting data for surveillance systems require a password to prevent entry by unauthorised persons. Actually, such systems have weaknesses such as blind spots or danger of stealth. This reported work focuses on intruder detection in indoor environments, which is based on acoustic channel characteristics. The basic concept of this study is to compute the coherence bandwidth from the measured room impulse response. The coherence bandwidth is influenced by channel delay profiles. Intruders give rise to changes in room channel impulse response inside the room. This variation causes change in the channel delay profile. Experiments have been performed to validate the effectiveness of the proposed method.

中国水声信号处理30年

The advances of new technology and theoretical development in 30 years of underwater acoustic signal processing and its applications in sonar design are presented in this paper. The topics include the research work in the field of underwater acoustic signal modeling, acoustic field matching, ocean waveguide and internal wave, the exaction and processing technique of acoustic vector signal information, space/time correlation characteristics of low frequency acoustic channel, the invariant feature of underwater target radiated noise, the transmission technology of underwater voice/image data, and its anti-interference technique. Some frontier technologies in sonar design are also discussed, including large aperture towed line array sonar, high resolution synthetic aperture sonar, deep sea siren and deep sea manned subsea vehicle, diver detection sonar and demonstration projector of national ocean monitoring system in China, etc.

浅海水声信道动态响应建模与仿真研究<br>Dynamic Response Modeling and Simulation in Shallow Water Acoustic Channel

水声通信系统必须与海洋通信信道相匹配才能达到良好的通信性能，如何对这样一个复杂多变的信道环境进行建模和仿真成为了一个研究的热点。本文主要研究浅海水声信道的仿真建模方法。利用BELLHOP高斯射线束跟踪法，对浅海信道的多途特性进行了建模；针对传统声线模型在信道动态响应建模上的不足，提出了一种新型的动态响应信道建模方法，仿真了信道的多途多普勒效应。分析了不同条件下信号的频谱规律。仿真结果与理论值相符，证明了模型的有效性。 Underwater acoustic communication system must match the communication channel in order to achieve a good performance. How to simulate for such a complex channel has become a hot research. This paper studied the shallow water acoustic channel modeling and simulation method. Using BELLHOP Gauss-ray beam tracing algorithm, modeled the multipath characteristics of the Shallow Water Acoustic Channel. Aiming at the lack of the traditional ray beam method, modeled a dynamic response channel. Simulated and analyzed the Doppler effect of the spectrum. The result showed that the Doppler shift was consistent with the theoretical value, which proved the effectiveness of the design.

2P6-2 Time-Varying Underwater Acoustic Channel Characteristics in Shallow Water(Poster Session)

2P6-2 Time-Varying Underwater Acoustic Channel Characteristics in Shallow Water(Poster Session)

Quality aware image transmission over underwater multimedia sensor networks

With the recent advances in Micro Electro-Mechanical Systems (MEMS) and underwater imaging sensors, and cameras, underwater multimedia sensor networks (UMSNs) have been proposed and drawn the immediate attention of the research community. Underwater multimedia sensor networks enable several new applications, such as target tracking, advanced coastal multimedia surveillance, undersea explorations, image acquisition and classification, environmental monitoring, and disaster prevention. However, the practical realization of these currently designed and envisioned applications directly depends on reliable and quality-aware communication capabilities of the deployed UMSNs. This paper presents a comprehensive performance evaluation of error concealment and error correction algorithms for quality-aware image transmission over UMSNs. Specifically, different combinations of multipath transport,watermarking-based error concealment (EC), forward error correction (FEC) and adaptive retransmission mechanisms have been evaluated to combat underwater channel impairments and mitigate packet losses due to node failures and intrinsic underwater acoustic channel characteristics. In addition, two novel image quality assessment metrics have been proposed to obtain the predicted quality of the image depending on the channel and node failures. Comparative performance evaluations show that the EC approach reconstructs the distorted image as closely as the original one while avoiding the burden of retransmissions and consequent delay.

Sensitivity analysis of acoustic channel characteristics to sea surface spectral uncertainty.

The interaction of sound with the sea surface is important for underwater acoustic communications. The high‐frequency sound used, 10 kHz and above, is sensitive to surface wave frequencies well above the ∼0.5‐Hz upper limit routinely measured by wave buoys. Accurately measuring the surface in the short gravity wave regime is difficult and even the general shape of the spectrum is uncertain. The primary measurement challenge is to disentangle the effects of the instrument, including its supporting structure, from what one is attempting to measure. There have been attempts to combine the copious data at low frequencies and the sparse data at higher frequencies to produce model spectra depending on a few parameters that describe the spectrum in the short gravity wave region and above. In this work we study the sensitivity of the acoustic channel characteristics such as the channel impulse response to our uncertain spectral knowledge. We merge low‐frequency surface wave spectra measured at NDBC 44014, with various modeled higher‐frequency spectra generated from measured environmental parameters to get unified spectra. For each unified spectrum we generate surface realizations, feed them into a rough surface parabolic equation model to compute a channel impulse response, and compare the impulse responses under different surfaces.

Measurement of angular power profile at an array receiver in a shallow underwater acoustic channel

In the design of broadband underwater acoustic communication system, proper analysis of underwater acoustic channel characteristics is required to determine communication system parameters. Especially for high channel capacity transmissions such as multiinput multioutput (MIMO) systems, the spatial correlation characteristics among multiple sensors determine communication performance and they are affected by the angular power distribution of the incoming acoustic waves. In this study, we suggest a model‐based array signal processing technique for measuring the angular power profile and apply it to experimental data gathered from very shallow water of 20 to 30 m water depth near the southern coast of South Korea. At first we show the variation of the angular power profile over different transmitter/receiver ranges and then its impact on the spatial correlation characteristics between two different array elements. Finally we discuss the expected spatial diversity effects from the viewpoint of underwater acoustic channel modeling.

Modeling and evaluation of coherent equalizer performance in the surf zone environment

The environmental conditions encountered in the surf zone give rise to acoustic channel characteristics which can vary significantly. A state space model is developed which describes these characteristics in sufficient accuracy for evaluating their effect on the performance of a coherent acoustic communications system in the surf zone environment. Using techniques developed by the author and presented at the two prior ASA meetings, the impact of the acoustic channel characteristics on coherent communications system performance is analyzed. The theoretical results are compared to experimental data collected at the Scripps Pier during the Fall of 2000 over several regimes of environmental conditions. [Work supported by ONR.]

Underwater acoustic networks

With the advances in acoustic modem technology that enabled high-rate reliable communications, current research focuses on communication between various remote instruments within a network environment. Underwater acoustic (UWA) networks are generally formed by acoustically connected ocean-bottom sensors, autonomous underwater vehicles, and a surface station, which provides a link to an on-shore control center. While many applications require long-term monitoring of the deployment area, the battery-powered network nodes limit the lifetime of UWA networks. In addition, shallow-water acoustic channel characteristics, such as low available bandwidth, highly varying multipath, and large propagation delays, restrict the efficiency of UWA networks. Within such an environment, designing an UWA network that maximizes throughput and reliability while minimizing the power consumption becomes a very difficult task. The goal of this paper is to survey the existing network technology and its applicability to underwater acoustic channels. In addition, we present a shallow-water acoustic network example and outline some future research directions.

Signaling characteristics of the surf zone acoustic communications channel

The Near Shore Acoustic Network Experiment (NSANE) was conducted at the Scripps Pier in May 1999 to ascertain the physical properties of the very shallow water and surf zone environments which enable or constrain acoustic communications. Results of the analysis of the experimental data will be presented focusing on the properties of the environment which are of particular relevance to the performance of acoustic communications systems. Communications channel characteristics such as multipath spread, coherence time, and channel outage and signal attenuation characteristics will be examined. These characteristics will be related to observable environmental conditions and their effect on the performance of acoustic communications systems will be discussed.

Vertical distribution of the sound speed in the Gulf Stream system

Using archived historical data on the temperature/salinity distribution, this paper describes the structure of the mean seasonal and the actual field of the computed speed of sound in the Gulf Stream region. The formation of acoustic channels of large, medium, and small size is considered, depending on the vertical thermohaline structure of waters. The paper provides statistical characteristics of the sound speed field and acoustic channels of waters interacting in the Gulf Stream system.