Abstract: An apparatus and method provides efficient parallel processing for use with a single-bit sampler that provides single-bit samples at a high sample rate. A serial-to-parallel converter converts the single-bit samples into parallel single-bit samples at a reduced sample rate. A digital quadrature mix performs a frequency shift to the parallel single-bit samples and simultaneously performs a real-to-complex conversion of the parallel single-bit samples from the serial-to-parallel converter to provide parallel I and Q output values at an intermediate frequency. The serial-to-parallel converter has shift register stages that provide a memory for use in functional realization of a boxcar filter and decimation-by-two in the digital quadrature mix. The digital quadrature mix utilizes logic to route and invert the parallel single-bit samples resulting in the parallel I and Q single-bit output values. Additional filter and decimate stages may be used to process the parallel I and Q single-bit output values.

Abstract: A data communications receiver incorporating soft decision error correction decoding and a means to set the amplitude or threshold for quantized soft decisions in a near-optimum manner to a soft decision decoder. In one embodiment the means for setting the amplitude or threshold measures the soft decisions from a quantizer and marks data bits as weak or strong. The gain or threshold is automatically adjusted to achieve a desired fraction if each marking. The desired fraction is chosen as the value that optimizes performance of the soft decision decoder.

Abstract: The invention is a way to detect and correct data inversions or other phase ambiguities in a modem's data, without incurring a significant penalty in error rate performance, throughput, or overhead, by making a particular use of the error detection and correction (EDAC) code which would typically be used for random errors. The decoder is set up so that the inverted data or out-of-phase data generates a distinctive syndrome which signals to a phase corrector.

Abstract: Pseudorandom noise having a predetermined frequency spectrum is generated by implementing a finite impulse response filter as an integral part of a feedback shift register sequence generator.

Abstract: Audio beat notes produced by sampling a square wave in a digital quadrature FM demodulator are reduced by adding filtered random noise, or dither, to the signal to be demodulated to randomly vary the width of successive pulses in the square wave. Filtration of the random noise prevents feedthrough of noise which would degrade the demodulated signal.

Abstract: FM signals are demodulated with lower distortion and expenditure of less computing time by digitizing the signals using an A/D converter of predetermined sample frequency and down-converting the signals to their base band quadrature components. The quadrature components are delayed by one sample period, and the complex cross-product of current quadrature components and the delayed quadrature components from the immediately preceding A/D sample period is taken. The arctangent of the resulting cross-product is taken by calculating the ratio of the imaginary and real components thereof to produce a value which is representative of the original modulating signal.