Disclosed are apparatus and methods for enhancing operation of an ultrasonic sensing device for determining the status of an object near such ultrasonic sensing device. From the ultrasonic sensing device, an emission signal having a current frequency or band in an ultrasonic frequency range is emitted. Ultrasonic signals are received and analyzed to detect one or more objects near or contacting the ultrasonic sensing device. After expiration of a predefined time period of emitting the emission signal, a background noise signal is detected from an environment of the ultrasonic device and background noise metrics are estimated based on the background noise signal. It is then determined whether the current frequency of the emission signal is optimized based on the background noise metrics. A next frequency or band is selected and the emission signal is emitted at the next frequency or band if it is determined that the current frequency or band is not optimum. The operations of detecting, estimating, determining, and selecting are repeated after each time a next frequency or band is selected and the emission signal is emitted at such next frequency or band.

Relationship discovery can include receiving at a first mobile device a pair of ultrasonic signals conveyed at different frequencies from a second mobile device. The pair of ultrasonic signals can convey, respectively, a second user's contact information in an encrypted form and a key indicator. A contact number can be selected from a first user's contact list electronically stored on the first mobile device. The contact number can be selected based on the key indicator. A mutual contact can be identified in response to decrypting the second user's contact information using the contact number as a decryption key.

An optical network element includes a connection to an optical fiber in an optical line system including a coherent receiver; a microphone configured to detect sound; and circuitry connected to the microphone and configured to cause transmission of information related to sounds detected by the microphone to a receiver at an end of the optical line system, wherein the transmission is over the optical fiber in the optical line system to the coherent receiver. The optical network element can include a polarization controlling device connected to the circuitry and configured to modulate a state-of-polarization (SOP) envelope for the transmission.

A signal processing method includes: receiving, by a first reception unit, an acoustic signal transmitted via a first transmission path, the acoustic signal received by the first reception unit being a first acoustic signal; receiving, by a second reception unit, the acoustic signal transmitted via a second transmission path different from the first transmission path, the second transmission path having a longer delay time for transmission than the first transmission path, and the acoustic signal received by the second reception unit being a second acoustic signal; calculating, by a delay amount calculation unit, a transmission delay amount that is a relative delay amount between the first acoustic signal and the second acoustic signal; and delaying, by a delay amount addition unit, the first acoustic signal based on the calculated transmission delay amount and outputting the delayed first acoustic signal.

A signal processing method includes: receiving, by a first reception unit, an acoustic signal transmitted via a first transmission path, the acoustic signal received by the first reception unit being a first acoustic signal; receiving, by a second reception unit, the acoustic signal transmitted via a second transmission path different from the first transmission path, the second transmission path having a longer delay time for transmission than the first transmission path, and the acoustic signal received by the second reception unit being a second acoustic signal; calculating, by a delay amount calculation unit, a transmission delay amount that is a relative delay amount between the first acoustic signal and the second acoustic signal; and delaying, by a delay amount addition unit, the first acoustic signal based on the calculated transmission delay amount and outputting the delayed first acoustic signal.

A data encoding and decoding method for underwater acoustic networks (UANs) based on an improved online fountain code, including: in a build-up phase, subjecting all original packets to sequential encoding according to their serial numbers to generate and send encoded packets with degree 2; merging k original packets to k/8 connected components with a size of 8; performing random encoding until a largest connected component is successfully decoded; in a completion phase, sending, by a receiver, a feedback packet according to a current decoding graph; according to a feedback packet containing decoding states of all the original packets, sending, by a sender, encoded packets with degree m; and randomly selecting original packets for recursive encoding to generate and send encoded packets with degree 1 or 2; and setting, by the receiver, a threshold to restrict the number of feedback packets.

An embodiment communication system includes: one or more slave stations, each of the slave stations including a sensor configured to detect a sensor signal, a controller configured to generate a first electrical signal at a predetermined frequency using the sensor signal, and a sound wave transmitter configured to convert the first electrical signal into a sound wave signal and to emit the sound wave signal; and a master station including a sound wave receiver configured to receive the sound wave signal and to convert the sound wave signal into a second electrical signal, and a controller configured to detect that the sensor of one of the slave stations has detected the sensor signal based on the second electrical signal.

An embodiment communication system includes: one or more slave stations, each of the slave stations including a sensor configured to detect a sensor signal, a controller configured to generate a first electrical signal at a predetermined frequency using the sensor signal, and a sound wave transmitter configured to convert the first electrical signal into a sound wave signal and to emit the sound wave signal; and a master station including a sound wave receiver configured to receive the sound wave signal and to convert the sound wave signal into a second electrical signal, and a controller configured to detect that the sensor of one of the slave stations has detected the sensor signal based on the second electrical signal.

An underwater communication method includes creating an air column in a water body using a device including a device body, an air column-generating component, and a transceiver, thereby forming an air column to a surface of the water body. A signal is transmitted, received, or a combination of transmitted and received using the transceiver through the air column to the surface of the water body.

An exemplary method includes a computing system receiving an audio message generated by a first device, determining a physical location of the first device when the audio message is generated, and associating the audio message with the physical location. The method further includes the computing system identifying a target recipient of the audio message, identifying a second device associated with the target recipient, and providing, based on a proximity of the second device to the physical location, the audio message to the second device.