High-speed Underwater Communication Research Articles

Ray tracing of long-range underwater acoustic vortex wave propagation

The underwater acoustic communications environment is severely band-limited, which leads to a bottleneck in data transfer. Existing methods of data transfer in underwater acoustic communications applications typically rely primarily on conventional temporal and frequency modulation techniques and achieve bit rates peaking at approximately 40 kb/s. One method of easing the bottleneck and increasing the data rate is to explore further potential degrees of freedom which may be utilized. Acoustic orbital angular momentum (OAM) is a physical quantity that characterizes the rotation in a propagating helical pressure wavefront. The unique phase patterns of OAM carrying vortex waves form an orthogonal basis which may be useful as an additional degree of freedom in acoustics communications applications; however, the long-distance propagation of these waves is largely unstudied. By employing BELLHOP’s ray tracing algorithm, the dominant features of a propagating OAM carrying vortex wave are tracked over long ranges (to and beyond 1 km) under various environmental conditions. This provides essential guidance in the design of the sending and receiving arrays of high-speed underwater communications systems, which rely on multiplexing acoustic OAMs.

Compact acoustic monolayered metadecoder for efficient and flexible orbital angular momentum demultiplexing

Detecting the orders of an orbital angular momentum (OAM)-carrying beam is of fundamental interest and practical importance in wave physics. Yet accurate and fast demultiplexing of free-space OAM beams within physical space comparable to wavelength still remains challenging. Here, a passive monolayered metadecoder with compactness, high efficiency and flexibility is designed systematically and demonstrated experimentally for real-time demultiplexing of multiple OAM modes in free space. A simple yet effective mechanism of simultaneously untwisting and reshaping the synthesized vortex beams is presented to remarkably downsize the device and arbitrarily modulate the propagation path of output beam with amplified intensity and intact information, whose detection needs no sensor array or postprocessing. Consequently, the resulting device features the ultra-compact size, enhanced signal-to-noise ratio, high spectral and spatial selectivity, controllable detection locations, and furthermore, the compatibility to existing multiplexing methods. The effectiveness of proposed mechanism is demonstrated numerically and experimentally via parallel and real-time demultiplexing of a synthesized acoustic vortex using a planar metadecoder much more compact than existing devices in all three dimensions. The realization of metadecoder offers the possibility of high-capacity and miniaturized passive devices harnessing OAM and may promise important applications, including advances in high-speed underwater communication and optical on-chip signal process.

Acoustic MIMO communications in a very shallow water channel

Underwater acoustic channels pose significant difficulty for the development of high speed communication due to highly limited band-width as well as hostile multipath interference. Enlightened by rapid progress of multiple input multiple output (MIMO) technologies in wireless communication scenarios, MIMO systems offer a potential solution by enabling multiple spatially parallel communication channels to improve communication performance as well as capacity. For MIMO acoustic communications, deep sea channels offer substantial spatial diversity among multiple channels that can be exploited to address simultaneous multipath and co-channel interference. At the same time, there are increasing requirements for high speed underwater communication in very shallow water area (for example, a depth less than 10 m). In this paper, a space-time multichannel adaptive receiver consisting of multiple decision feedback equalizers (DFE) is adopted as the receiver for a very shallow water MIMO acoustic communication system. The performance of multichannel DFE receivers with relatively small number of receiving elements are analyzed and compared with that of the multichannel time reversal receiver to evaluate the impact of limited spatial diversity on multi-channel equalization and time reversal processing. The results of sea trials in a very shallow water channel are presented to demonstrate the feasibility of very shallow water MIMO acoustic communication.

근거리 수중통신을 위한 가시광 LED 적용에 관한 연구

Robust and high speed underwater communication is severely limited when compared to communications in terrestial. In free space, RF communication operates over long distances at high data rates. However, the obstacle in seawater is the severe attenuation due to the conducting nature. Acoustic modems are capable of long range communication up to several tens of kilometers, but it has low data-rate, high power consumption and low propagation speed. An alternative means of underwater communication is based on optics, wherein high data rates are possible. In this paper, the characteristics of underwater channel in the range of visible wavelength is investigated. And the possibility of optical wireless communication in underwater is also described. The LED-based transceiver and CMOS sensor module are integrated in the system, and the performance of image transmission was demonstrated.

A Study on Multi-Path Channel Response of Acoustic Propagation in Northwestern Arabian Sea

Multi-path interference due to boundary reflection and variation of sound speed profile in underwater water acoustic communication pose the major barrier to reliable high-speed underwater communication system. Based on the sound speed profiles and the bathymetry data of northwestern Arabian Sea, Multipath impulse response profiles of the area have been obtained using Bellhop. The derived parameters like delay structure, effective transmit and receive angles suitable depths etc. from the obtained impulse responses have also been discussed. The impulse responses have been obtained for different scenarios of transmitter and receiver geometry to arrive at optimal configuration of wireless Acoustic communication/telemetry system for that area. This work can be used as a guide for the practical design of underwater acoustic wireless communication/telemetry system to be operated in this area which is critical to world oil exports.