Abstract: An acoustic receiver is provided for receiving acoustic signals from an acoustic communication channel. The acoustic receiver comprises a waveguide; and at least first and second sensors for sensing the acoustic signals, the sensors being in acoustic communication with the waveguide. The first and second sensors are acoustically coupled to the waveguide at respective first and second positions spaced from each other along a length of the waveguide. The length of the waveguide between the first and second positions follows a path that changes direction to thereby limit an extent of the waveguide.

Abstract: A method of decoding a received communication signal is provided. The method may comprising converting the received communication signal to the frequency domain to provide frequency domain data. The method may further comprise combining amplitudes of one or more selected frequency components of the frequency domain data, the one or more frequency components being selected according to a predefined communication symbol comprising one or more selected frequency tones corresponding to the one or more selected frequency components. The method may further comprise detecting the predefined communication symbol in the received communication signal depending on the combined amplitudes of the one or more selected frequency components of the frequency domain data.

Abstract: An apparatus for determining a suitability of a frequency band for data communication with a node by way of a communication channel may be provided. The apparatus may comprise a receiver configured to receive first and second signals from the node by way of the communication channel, the first and second signals having frequencies within the frequency band. The apparatus may comprise processing circuitry communicatively coupled to the receiver, the processing circuitry being configured to determine a calibration function depending on the first signal, process the second signal depending on the calibration function, determine the suitability of the frequency band for data communication with the node by way of the communication channel depending on the processed second signal and output an indication of the said suitability.