Abstract: A random access technique for one way channels. With the apparatus and method of this system, each user sends an initial message of stated length to a central receiver. The message is then retransmitted a specified number of times in a pre-determined interval reserved for the retransmission process. The time interval between each successive retransmission of a given message is randomly generated. The random access protocol with retransmissions improves the probability of successful message transmission in a one way communication environment where observation (retransmission) periods for all users do not overlap.

Abstract: An apparatus for automatically controlling the active power produced by the generator of a hydraulic turbine-generator unit, comprising a frequency-responsive summing means having its inputs respectively connected to a reference signal source which develops an assigned power signal, to a power measuring means responsive to the active power produced by the generator, and to a gate opening sensing means responsive to the degree of opening of the hydraulic turbine gate apparatus, and its output connected to a control means for controlling the degree of opening of the gate apparatus. The frequency-responsive summing means is adapted to develop at its output a signal representative of an algebraic sum of the signal applied to its input connected to the reference signal source, the low-frequency components of the signal applied to its input connected to the power measuring means and the high-frequency components of the signal applied to its input connected to the gate opening sensing means.