Abstract: A method to improve communication system performance using an adaptive modem that estimates the communication channel scattering function to select one of several modulation schemes. The scattering function is estimated from the channel's frequency (doppler) and time (multipath) spreading effects on a probe signal. The probe signal is transmitted from a first modem to a second modem. The second modem processes the channel measurements and transmits the channel spreading factors to the first modem. Based upon the channel scattering function estimate, channel characteristic data, propagation models, strategic information, and modem position estimates, the first modem selects one of several modulation schemes. Subsequent data transmissions from the first modem to the second modem contain a modulation mode identifier. The second modem uses the modulation mode identifier to select the correct demodulation scheme.

Abstract: A modem to improve communication system performance that uses multiple modulation schemes comprising modulation technique and encoder combinations. As communication system performance and objectives change, different modulation schemes may be selected. Modulation schemes may also be selected upon the communication channel scattering function estimate, and the modem estimates the channel scattering function from measurements of the channel's frequency (doppler) and time (multipath) spreading characteristics.

Abstract: An undersea vehicle propulsion and attitude control system is used to conl the forward/reverse movement, vertical up/down movement, lateral movement, pitch, roll and yaw of an undersea vehicle. The propulsion and attitude control system includes a forward port at a forward end of the undersea vehicle, an aft port at an aft end of the vehicle, and radial ports extending radially along the undersea vehicle. The propulsion and attitude control system further includes a single pump, either reversible or unidirectional, and a plurality of valves that, through a controller, selectively control fluid flow between the pump and the forward port, aft port, and radial outlet ports in the undersea vehicle, to provide accurate vehicle propulsion and attitude control.