The Aerospace Corporation

Gee L Lui

Kuang Tsai

Jack K Holmes

Chit-Sang Tsang

Milton K Sue

Data aided carrier phase and symbol timing synchronizers are implemented at baseband as digital modulators isolating input signal inphase and quadrature component signals fed into inphase and quadrature Laurent transforms that function as data detector to provide odd and even data bit multiplexed output data signal while cross coupling the inphase and quadrature transformed outputs for removing data modulation in error signals to correct phase errors and timing errors in the received signal so as to provide reliable data demodulation of noisy received signals having dynamic carrier phase and symbol timing errors as found in continuous phase modulation communications systems such as Gaussian minimum shift keying communications systems.

Data aided symbol timing system for precoded continuous phase modulated signals

A communications receiver receives a received continuous phase modulation (CPM) signal having an original modulation index of h and includes a filter, a continuous phase reconstructor using phase unwrapping, and a modulation index scaler for generating a reconstructed CPM signal having a scaled modulation index H from the received CPM signal having a small modulation index h, with the scaled modulation index H preferably being greater than the original modulation index h, so that, the transmitted CPM signal occupies a narrow bandwidth, yet, during reception, the reconstructed CPM signal with the high modulation index H can be reliably data demodulated for improved performance with reduced demodulation complexity.

Binary continuous phase modulation (CPM) data demodulation receiver

A symbol clock recovery subsystem uses a tap delay line having a set of delays, uses a clock bank of samplers providing time-staggered sampled noncoherently received signals, and uses a set of mean magnitude generators, in channelized form, for providing a set of mean magnitudes to a maximum selector for selecting a maximum one of the time-staggered sampled received signals having the greatest signal to noise ratio so as to provide a signal effectively occurring at symbol epoch time for demodulating a symbol stream in a digital communication system receiver.

Noncoherent symbol clock recovery subsystem

Data aided carrier phase and symbol timing synchronizers are implemented at baseband as digital modulators isolating input signal inphase and quadrature component signals fed into inphase and quadrature. Laurent transforms that function as data detector to provide odd and even data bit multiplexed output data signal while cross coupling the inphase and quadrature transformed outputs for removing data modulation in error signals to correct phase errors and timing errors in the received signal so as to provide reliable data demodulation of noisy received signals having dynamic carrier phase and symbol timing errors as found in continuous phase modulation communications systems such as Gaussian minimum shift keying communications systems.

A receiver generates log-likelihood-ratio-based soft bit metrics of precoded quaternary continuous phase modulation signals using four state-constrained trellises and a streamlined maximum likelihood sequence estimation Viterbi algorithm requiring no survivor state storage elements for a preferred error correction-coded quaternary Gaussian minimum shift keying communication system employing reduced-complexity pulse-amplitude modulation matched-filtering and soft-decision decoding.

Quaternary precoded continuous phase modulation soft bit metric demodulator

An improved AGC subsystem for preferred use in quadrature amplitude modulation receivers offers improved automatic gain control of received signals in fading channels by generating an error signal only from constellation signal points having large signal-to-noise ratios for increase the signal-to-noise ratio of the gain control error signal for lowering dispersion of symbol signals in the constellation signal space for improving data detection of symbol signals with the improved performance with as much as one dB in the signal-to-noise ratio.

Automatic gain control 16-ary quadrature amplitude modulation subsystem

A premodulation precoding method precodes a data sequence in a Gaussian minimum shift keying (GMSK) modulator to improve the bit error rate performance of a coherent Viterbi receivers generating estimates of the communicated data sequence without the use of differential decoding while preserving the spectrum of 2-ary and 4-ary GMSK signals over a wide range of bandwidth time products.

Gaussian minimum shift keying (GMSK) precoding communication method

Data aided carrier phase tracking system for precoded continuous phase modulated signals

A method and processing system for determining a soft decision metric for each input symbol, including and/or performing the steps of: computing trellis branch metrics based on a received sample sequence; updating initial state metrics from time (n&minus;1) with a Viterbi algorithm (VA); constraining M trellises differently at time n such that only state transitions caused by an input value associated with a particular trellis are allowed; executing the VA on the M constrained trellises for a finite number (N ) steps; and computing likelihood ratios by taking a difference of a maximum state metric at time (n&plus;N ) for each trellis with a maximum state metric of a reference trellis.

Method and processing system for estimating likelihood ratios for input symbol values

Unambiguous carrier phase estimation for frequency hop signals of a frequency hopping Gaussian minimum shift keying (GMSK) communication system using coherent demodulation is enabled by channel zeroing bits and channel guard bits positioned between each pair a preceding data portion and a succeeding synch word, functioning as cumulative data phase zero forcing bits that force the accumulative data phase to zero at the end of the synch word for determining the carrier phase for subsequent data demodulation so that each synch word may be arbitrarily placed within a hop of the hopping signal having an unknown carrier phase for improved interference immunity.

Method of determining the carrier reference phase of coherent demodulation of frequency hopped continuous phase modulated signals with synch words arbitrarily located within the hop

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Westminster, CA, United States of America

Gee L Lui