Acoustic propagation is characterized by three major factors: attenuation that increases with signal frequency, time-varying multipath propagation, and low speed of sound (1500 m/s). The background noise, although often characterized as Gaussian, is not white, but has a decaying power spectral density. The channel capacity depends on the distance, and may be extremely limited. Because acoustic propagation is best supported at low frequencies, although the total available bandwidth may be low, an acoustic communication system is inherently wideband in the sense that the bandwidth is not negligible with respect to its center frequency. The channel can have a sparse impulse response, where each physical path acts as a time-varying low-pass filter, and motion introduces additional Doppler spreading and shifting. Surface waves, internal turbulence, fluctuations in the sound speed, and other small-scale phenomena contribute to random signal variations. At this time, there are no standardized models for the acoustic channel fading, and experimental measurements are often made to assess the statistical properties of the channel in particular deployment sites.
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机译:声传播的特征在于三个主要因素:随信号频率增加的衰减,随时间变化的多径传播和低声速(1500 m / s)。尽管背景噪声通常被描述为高斯,但它不是白色的,但具有衰减的功率谱密度。信道容量取决于距离,并且可能非常有限。因为在低频下最好地支持声传播,尽管总的可用带宽可能很低,但从带宽相对于其中心频率不可忽略的意义上来说,声通信系统本身就是宽带。该信道可能具有稀疏的脉冲响应,其中每个物理路径都充当时变的低通滤波器,并且运动会引入额外的多普勒扩展和频移。表面波,内部湍流,声速波动以及其他小范围现象会导致随机信号变化。目前,还没有用于声信道衰落的标准化模型,并且经常进行实验测量以评估特定部署站点中信道的统计特性。
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