Abstract: A noninterruptive noise measurement technique wherein the absolute value of the amplitude error from a modem slicer is compared to a reference, the number of events in excess of said reference over a selected interval are counted and the range within which said count falls is determined as a particular signal to noise ratio value.

Abstract: Disclosed is a modulation-demodulation system and method for transmitting a plurality of sequentially received information bit sequences, the system including a transmitter having a state machine for expanding by a coding process each information bit sequence into an expanded bit sequence with a coded bit group portion and, in some cases, an uncoded bit group portion. The transmitter further includes a modulator for modulating a carrier signal by one of a plurality of multilevel symbols in a two-dimensional complex plane in response to each sequentially applied expanded bit sequence, with the coded bit group portion being used to specify a subset of the multilevel symbols which when rotated in the complex plane maps upon another subset for each adverse angular rotation and the uncoded bit group portion being used to specify for a selected multiple symbol subset the transmitted multilevel symbol of the carrier signal.

Abstract: A two-bus, two instruction type, pipelined microprocessor having a control means which orders application of instruction and data addresses to a memory and further interleaves instructions and data on a single bus to achieve maximum efficiency in operation.

Abstract: An automatic adaptive equalizer operative on a test pattern including a carrier-only period, clock-only period and a single test impulse. The equalizer employs a transversal filter under control of a microprocessor. Samples of in-phase and quadrature phase components of the received impulse response are cross correlated and autocorrelated to form elements of a complex matrix equation describing the optimum equalizer tap settings. The microprocessor performs a special interative operation utilizing elements of this equation to rapidly and exactly calculate the optimum initial settings for the tap constants. The clock-only portion of the test pattern is analyzed to accurately set a sampling clock to properly sample the received impulse so that matrix formation can be carried out within the duration of the received impulse. Initial equalization can be achieved in a time on the order of 30 milliseconds at a data rate of 9600 bits per second.

Abstract: A digital timing recovery circuit operative upon digital samples of the input signal to a data receiver provided at the sample rate to produce a clock correction signal at the symbol rate utilizing a digital periodic filter providing a double restrictive bandpass characteristic about the band edge frequencies and outputting to a nonlinear device followed by a digital sampling filter designed to require only addition and subtraction of the nonlinear device outputs.

Abstract: Circuitry for detecting and correcting false equilibrium conditions generated in data modems by sudden changes in gain of an associated transmission system including a false gain detector which detects a low rate of production of symbols of largest magnitude and triggers a final gain circuit which initially jumps the overall system gain and thereafter adaptively adjusts the gain jump to the correct value.

Abstract: A circuit for maintaining proper sampling timing in a data modem wherein main channel equalizer error is correlated with a derivative channel signal to drive a clock correction signal. The derivative channel signal is derived from an equalizer using fewer coefficients than required to derive the main channel equalized signal, and calculation of the equalized derivative and clock correction signal is performed only once every other Baud.

Abstract: An automatic gain control circuit having a coarse analog gain adjustment section producing discrete increments of db gain and a fine digital gain adjustment section. The digital section provides for adjustment of gain through a final increment of db gain to achieve precise gain setting. The output of the digital section is squared and compared to a reference signal to derive an error signal whose value is fed to an apparatus which iteratively determines the precise coarse increment and fine digital settings to achieve the final desired gain setting.