Abstract: A pair of full duplex modems are connected and each is designed to transmit to the other at the same predetermined band rates. One modem is connected to receive data bits for transmission over the channel at a predetermined first (and fast) rate and to transmit its received data bits at a integral number of first transmission bits per band. The other modem is connected to receive data bits for transmission over the channel at a rate slower than the band rate and is designed to sequentially encode blocks of said slower rate data bits into a larger number of second transmission bits for transmission over said channel at an integral number of second transmission bits per band. Means forming part of said one modem for converting said second transmission bits into the slower rate data bits.

Abstract: Numeric signals appearing on a communication channel are converted in blocks of b signals to a number N. The number N is converted to coordinates in K dimensional space where 40.gtoreq.K<4. The coordinates are selected to provide suitable packing in the dimensional space represented by K. The values of coordinates selected are modulated on a carrier and transmitted. Apparatus is provided which carries out the above steps.Where K=24 the coordinates are selected to be expressible in integral form and in integral form are selected so that they have all even values with a sum of 0 modulo 8 or all odd values with a sum of 4 modulo 8.

Abstract: An encoder treats a block of b bits of binary data as a number N and encodes it into eight values S1, S2 . . . S8 identifying it. The eight values are each selected from positive, negative and zero integer values; and the values are chosen so that a set of eight consists of all even integers or all odd integers and so that the sum of the eight values is 0 modulo 4. In the transmitter these values are modulated on a carrier for transmission. A receiver detects the received versions of the transmitted values, determining the number N and reconstituting the block of b bits.

Abstract: Locations of a desired number of signal points for a double side band-quadrature carrier modulation system occupy the inner intersections of a multiplicity of concentric rings with a triangular grid. The signal point locations of the desired number on the outer partially occupied ring are provided with additional signal points at positions selected to provide that the centroid of the set of locations is at the center of the rings.

Abstract: A sinusoidal component of phase jitter in a communications channel is reduced by apparatus including means providing an oscillator signal at the receiver and modifying the received signal phase in accord therewith. Decision means determine the probable transmitted signal and the signals at the input and output of the decision means are compared to determine the residual phase jitter. The residual phase jitter is compared with a suitably delayed oscillator signal and the results of the comparison are used to alter the modification (by the oscillator signal) of the received signal to further reduce the phase jitter. Preferably the results of the comparison are also used to reduce the frequency difference between the oscillator signal and the phase jitter.

Abstract: Means and method are provided for correcting for the effects of amplitude and phase jitter, in the presence of noise on quadrature signals transmitted over a channel at regular intervals as quadrature pairs. The signal values of respective signal elements of sequentially transmitted quadrature pairs, as received are measured. Responsive to such measurement a first decision is made as to which pair of quadrature signals was transmitted. The measured value and value from the first decision for the same signal are compared for each signal and as a result of such comparison measures of the amplitude and phase errors occurring during transmission. The measures of amplitudeand of phase errors are averaged over respective pluralities of intervals. The measured signal values are transmitted over a line and modified to compensate for the average values of the phase errors and of the amplitude errors. The signal values so modified are used as the basis of a second decision as to the elements modified.