Abstract: A high speed modem system which utilizes multiple carriers to successively transmit frames containing data such that the frames are transmitted so that the level of the signal is minimized, and is preferably zero, at the borders between individual frames thus, reducing or eliminating interframe discontinuities and the accompanying distortion and interframe interference. The modem system includes a circuit to successively combine together the modulated carrier signals of each set to produce a frame waveform which includes an inphase signal and a quadrature signal for each carrier signal as is known in the art. The components of the inphase signal and the quadrature signal are grouped to form an I odd/Q even group and an I even/Q odd group. In order to restore the missing components in the I odd/Q even group, the I odd and the Q even components are duplicated and combined with the I odd/Q even group.

Abstract: A system and method for reducing echoes on a duplex communication channel having both transmitted and received signals carried thereon, particularly a telephone channel having digital data transmitted thereon by way of a modem. The transmitted signal is converted from a time domain signal to a frequency domain transmitted signal by a fast fourier transform process. The frequency domain transmitted signal is multiplied by a set of filter coefficients to generate estimated echo coefficients. The estimated echo coefficients are converted from the frequency domain to the time domain by an inverse fast fourier transform process and then subtracted from the received signal to generate a residual echo signal. The residual echo signal is converted to a frequency domain residual echo signal by a fast fourier transform process and then multiplied by the complex conjugate of the frequency domain transmitted signal to generate correlation frequency components.

Abstract: A modem system includes a transmitter section having generators for successively generating sets of carrier signals where each carrier signal of a set has a different frequency and a modulator for modulating each carrier signal of a set with a different portion of digital data to be transmitted where all such portions used to modulate a set of carrier signals comprise a frame of digital data. Also included are an adder for successively combining together the modulated carrier signals of each set to produce a frame waveform, an inverse Fast Fourier Transform circuit for transforming each waveform from a frequency domain signal to a time domain signal, a rotate and match buffer circuit for rotating each transform waveform so that its beginning point amplitude and slope substantially match the ending point amplitude and slope of the immediately preceding transformed waveform, and a transmitter for successively and continuously transmitting the transformed and rotated waveforms over a telephone channel.