Abstract: Disclosed is an apparatus and method for estimating a Doppler shift for underwater communication. The apparatus includes: a multipath delay profile determiner for detecting a correlation of a known signal 1 and a received packet signal and time (T1o) at a point having maximum energy of the correlation, and detecting a multipath delay profile at the time (T1o); a correlation calculator for calculating a correlation between a correlation of a known signal 2 and the received packet signal, and the multipath delay profile; a maximum value detector for detecting time (T2o) at a point having maximum energy of the correlation calculated by the correlation calculator; and a Doppler shift estimator for determining a Doppler shift using a difference between the time (T1o) and the time (T2o) at points having respective maximum energy.

Abstract: Disclosed is an apparatus and method for estimating a Doppler shift for underwater communication. The apparatus includes: a multipath delay profile determiner for detecting a correlation of a known signal 1 and a received packet signal and time (T10) at a point having maximum energy of the correlation, and detecting a multipath delay profile at the time (T10); a correlation calculator for calculating a correlation between a correlation of a known signal 2 and the received packet signal, and the multipath delay profile; a maximum value detector for detecting time (T20) at a point having maximum energy of the correlation calculated by the correlation calculator; and a Doppler shift estimator for determining a Doppler shift using a difference between the time (T10) and the time (T20) at points having respective maximum energy.

Abstract: Apparatus and method of transmitting a preamble having additional information in differential modulation packet data communication. The apparatus includes a phase rotator that outputs a phase rotation quantity corresponding to additional information to be applied to a transmission target packet, a transmission-multiplier that multiplies the phase rotation quantity output from the phase rotator by a preamble to be transmitted, a symbol mapper that converts header and payload data to be applied to the transmission target packet into symbols and outputs the same, a multiplexer that processes an output signal of the transmission-multiplier and an output signal of the symbol mapper to be selectively output through an output end to form a symbol stream in units of packets, and a differential symbol converter that converts the symbol stream output from the multiplexer according to a predetermined differential modulation method and outputs the converted symbol stream.

Abstract: Apparatus and method of transmitting a preamble having additional information in differential modulation packet data communication. The apparatus includes a phase rotator that outputs a phase rotation quantity corresponding to additional information to be applied to a transmission target packet, a transmission-multiplier that multiplies the phase rotation quantity output from the phase rotator by a preamble to be transmitted, a symbol mapper that converts header and payload data to be applied to the transmission target packet into symbols and outputs the same, a multiplexer that processes an output signal of the transmission-multiplier and an output signal of the symbol mapper to be selectively output through an output end to form a symbol stream in units of packets, and a differential symbol converter that converts the symbol stream output from the multiplexer according to a predetermined differential modulation method and outputs the converted symbol stream.