The Aerospace Corporation

Communications Satellite Corporation

Comsat Corporation

John James Poklemba

Gregory S Mitchell

Chester J Wolejsza, Jr

James R Thomas

Mark Robert Gramann

Ronald F Smith

Certain embodiments of the invention may include systems and methods for implementing a multirate digital decimating filter for filtering received symbol data. The method may include sampling the received symbol data at a selected sample rate, pre-averaging the sampled received data to provide two samples per symbol; convolving the pre-averaged samples with decimated finite impulse response (FIR) aperture impulse response coefficients to produce detected output samples, convolving the pre-averaged samples with shifted decimated FIR aperture impulse response coefficients to produce zero-crossing transition samples, and adjusting the sample rate based at least in part on averaging the zero-crossing transition samples.

Systems and methods for pre-averaged staggered convolution decimating filters

Certain embodiments of the invention may include systems and methods for implementing a multirate digital interpolating filter. According to an example embodiment of the invention, the method includes sampling symbol data from one sample per symbol to N samples per symbol, wherein sampling includes: convolving the symbol data with a decimated finite impulse response (FIR) aperture impulse response coefficient set, convolving the symbol data with one or more shifted decimated FIR aperture impulse response coefficient sets, and summing the convolution results to produce interpolated bandlimited data.

Systems and methods for sliding convolution interpolating filters

A quadrature vestigial-sideband (QVSB) method and system with correlated noise removal are embodied in a QVSB receiver with a correlated-noise estimator-subtractor configured to obtain I/Q channel correlated noise estimates for receive-filtered I/Q signals in the QVSB receiver, and to subtract the I/Q channel correlated noise estimates from the receive-filtered I/Q signals to whiten noises entering a quadrature-crosstalk, maximum-likelihood-sequence-estimator (QC-MLSE) of the QVSB receiver.

Quadrature vestigial sideband digital communications method and system with correlated noise removal

A quadrature vestigial sideband (QVSB) communication system provide bandwidth efficient data transmission using cross coupled data signaling during both transmit and receive having controlled intersymbol interference. The QVSB modem includes cross coupled arm transmit and receive data filtering on both of the I&Q channels providing a bandwidth efficient QVSB spectra. A quadrature crosstalk maximum likelihood sequence estimator implements a Viterbi decoding algorithm for providing estimated data sequence outputs. The receiver is a coherently aided demodulator synchronized by a synchronization loop providing time and phase references using the estimated data sequence outputs.

Quadrature vestigial sideband digital communications method

A sampling method, denoted continuously variable IF sampling (CVIFS), implemented in digital transmission and reception components is characterized by sampling a bandpass signal which is centered at an intermediate frequency f.sub.IF that is related to both the data transmission symbol rate (R.sub.s) and sample rate (NR.sub.s) by integer ratios. Moreover, the CVIFS method is characterized in that the sample rate NR.sub.s is constrained to be four times the IF center frequency, and both the sample rate NR.sub.s and the IF center frequency are constrained to be within a range of a factor of 1.5 of their maximum values. To maintain this high sample rate as the data symbol rate is lowered, a 'gear shifting' technique is utilized whereby the integer number of samples-per-symbol, N, is increased as the symbol rate decreases. Moreover, the sample rate NR.sub.s is always between 3.0 to 4.5 times the maximum data symbol rate (R.sub.smax), and the IF center frequency is always between 3/4 to 9/8 times (R.sub.smax), irrespective of the actual data rate R.sub.s.

Continuously variable if sampling method for digital data transmission

A coherent phase and frequency recovery method capable of rapidly recovering the phase and frequency of bursts of received signals from plural sources. The received signal is applied to a first input of a mixer, the output of which is amplified and applied to two feedback paths, one for frequency and the other for phase. The frequency path contains a loop filter driving a voltage-controlled oscillator, and the phase path a loop filter and amplifier. Initial estimates of the phase and frequency of the present burst are derived and injected into the respective feedback paths. The output of the phase path is applied to correct the phase of the output of the frequency path, which is then applied to a second input of the mixer.

Coherent phase and frequency recovery method and circuit

A symbol timing recovery circuit with a clock synchronization loop for variable rate data signals utilizes a frequency synthesizer for setting the frequency of the recovered clock signal. The received data signal, representing the modulating waveform of a transmitted modulated wareform, is estimated by passage through a data filter and sampling comparator sampled by the recovered clock. The received data signal is also delayed and multiplied by the time derivative of the estimated data signal to produce an error signal representing the difference between the incoming data rate and the output of a narrow pull range voltage controlled oscillator, VCO. The error signal is input to the VCO to correct the VCO output. A programmable frequency synthesizer provides timing signals having a range of the symbol rate divided by n. The VCO output is mixed with the frequency synthesizer output and the sum signals removed by a low pass signal to produce the difference signals which will correspond to the clock signal of the data signal.

Rate synchronized symbol timing recovery for variable rate data

Concurrent carrier and clock synchronization are derived from an input signal in interdependent loops without the use of phase look loop (PLL) circuitry in order to improve operation at higher bit rates. An acquisition detection signal is generated only in response to predetermined minimum errors in both the received signal amplitude and the recovered carrier phase.

Non-PLL concurrent carrier clock synchronization

The present invention is directed to circuitry for achieving concurrent synchronization of carrier phase and clock timing in double-sideband, suppressed carrier transmissions systems. A phase-lock loop (PLL) is used in the respective carrier and clock recovery networks. The carrier recovery loop is similar to the conventional 'Costas Loop'. The PLLs are cross coupled in an interdependent recovery structure to enable a more effective clock and carrier regeneration.

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Ijamsville, MD, United States of America

John James Poklemba