Ultrafast adaptive digital modem

Abstract

A receiver includes means for sampling and noncoherently demodulating a received signal to provide digital symbols in each of a first and second channel. An equalization network equalizes the incoming signal and a phase correction network corrects the phase of the equalized signal. In response to the transmission of a preamble in the first channel, a fast learn network derives the phase error by determining the arc tangent of a quotient formed by dividing the signal in the first channel by the signal in the second channel. A course phase jump can be made to insure that the arc tangent is not greater than unity. The timing error of the sampling means can be derived by determining the arc tangent of a quotient formed by dividing the present digital symbol in the one channel by the preceding digital symbol in the one channel. In response to an impulse in the preamble, the lead-in samples of an impulse response can be stored while the phase error is computed from the major sample; then the phase of the lead-in samples can be corrected. Equalization coefficients can be derived from the phase corrected impulse response samples. With this apparatus, in accordance with the preferred method of the present invention, the receiver can be adapted to receive normal data in less than thirty milliseconds.