A method, apparatus, system, and computer program product for processing low frequency signals. A communications system comprising a low frequency receiver, a denoiser, and a signal extractor. The low frequency receiver receives low frequency signals in which a communications signal is expected. The denoiser is in communication with the low frequency receiver. The denoiser denoises the low frequency signals received from the low frequency receiver. The denoising results in a generation of denoised signals. The signal extractor in communication with the denoiser. The signal extractor extracts the communications signal from the denoised signal.

An underwater network management system includes a manager corresponding to a management station, and a plurality of agents connected to the manager and corresponding to a gateway and a plurality of underwater devices, wherein each of the manager and the plurality of agents includes an underwater management information base including a plurality of managed objects for managing an underwater network and the plurality of underwater devices, and the manager controls operations for status monitoring and management of the underwater network and the plurality of underwater devices based on information included in managed objects provided from the plurality of agents.

An underwater network management system includes a manager corresponding to a management station, and a plurality of agents connected to the manager and corresponding to a gateway and a plurality of underwater devices, wherein each of the manager and the plurality of agents includes an underwater management information base including a plurality of managed objects for managing an underwater network and the plurality of underwater devices, and the manager controls operations for status monitoring and management of the underwater network and the plurality of underwater devices based on information included in managed objects provided from the plurality of agents.

An aquatic environment audio system for communication of wireless audio signals between a smartwatch and headphones worn by a user includes one or more wireless repeaters. Each of the one or more wireless repeaters includes a waterproof housing, an attachment mechanism for attaching the waterproof housing to the user between the smartwatch and the headphones. Each of the one or more wireless repeaters further includes a first antenna for receiving wireless signals from the smartwatch, repeater circuitry coupled with the first antenna for processing the wireless signals received from the smartwatch, and a second antenna coupled with the wireless repeater circuitry for transmitting the processed wireless signals to the headphones. One or more of the first antenna, repeater circuitry, and second antenna are contained in the waterproof housing.

Transmitting and receiving mud pulse pressure waves at a downhole device. The mud pulse pressure waves may be transmitted from a surface mud pulser and/or by a downhole mud pulser to a downhole device. The mud pulse pressure waves may be detected directly by a transducer or indirectly by detecting physical changes induced in the downhole tool by the pressure waves of the mud pulse. The detected physical changes can be converted to a digital signal for use by the downhole tool. The mud pulse pressure waves may encode information including data, or instructions to the downhole devices.

The invention is to provide an underwater communication device and an underwater communication method that can be applied to mobile communication in water. An underwater communication device 10 includes: a transmitter 12 configured to transmit an electric signal; and a receiver 14 arranged away from the transmitter 12 via water and configured to receive the electric signal, in which the receiver 14 includes an field effect transistor 23 having a channel region 39 provided at a position in contact with the water, and a drive circuit 26 configured to generate a potential difference between a source region 31 and a drain region 33 of the field effect transistor 23.

The invention is to provide an underwater communication device and an underwater communication method that can be applied to mobile communication in water. An underwater communication device 10 includes: a transmitter 12 configured to transmit an electric signal; and a receiver 14 arranged away from the transmitter 12 via water and configured to receive the electric signal, in which the receiver 14 includes an field effect transistor 23 having a channel region 39 provided at a position in contact with the water, and a drive circuit 26 configured to generate a potential difference between a source region 31 and a drain region 33 of the field effect transistor 23.

An underwater acoustic communication system includes a transmission device including N transmitters, and a reception device. The reception device includes M (M is an integer of two or more) receivers configured to receive M reception signal sequences corresponding to N transmission signal sequences transmitted from the N transmitters through sound waves, a beam former configured to suppress multipath waves other than direct waves of the M received reception signal sequences and to generate L (L is an integer of two or more) signal sequences from the M reception signal sequences, and a signal estimation unit configured to estimate the N transmission signal sequences based on the L generated signal sequences.

An underwater acoustic communication system includes a transmission device including N transmitters, and a reception device. The reception device includes M (M is an integer of two or more) receivers configured to receive M reception signal sequences corresponding to N transmission signal sequences transmitted from the N transmitters through sound waves, a beam former configured to suppress multipath waves other than direct waves of the M received reception signal sequences and to generate L (L is an integer of two or more) signal sequences from the M reception signal sequences, and a signal estimation unit configured to estimate the N transmission signal sequences based on the L generated signal sequences.

A communication system includes a repetitive orthogonal frequency-division multiplexing (“ROFDM”)transmitter communicating with an ROFDM receiver. The ROFDM transmitter includes an ROFDM modulator, which includes a K-point Fast Fourier Transform receiving a block of time-domain data symbols and generating an initial orthogonal frequency-division multiplexing symbol. The initial orthogonal frequency-division multiplexing symbol is based on a block of frequency-domain data symbols corresponding to the block of time-domain data symbols. The initial orthogonal frequency-division multiplexing symbol includes an ending part. The ROFDM modulator includes an orthogonal frequency-division multiplexing symbol repeater generating a repetitive orthogonal frequency-division multiplexing symbol by repeatedly reproducing the initial orthogonal frequency-division multiplexing symbol. The modulator includes a cyclic prefix adder pretending a cyclic prefix to the repetitive orthogonal frequency-division multiplexing symbol to generate a baseband transmitted signal. The cyclic prefix includes the ending part of the initial orthogonal frequency-division multiplexing symbol. The ROFDM receiver includes an ROFDM demodulator.