Wideband Semiconductors, Inc.

Wideband Computers, Inc.

Byron Esten Danzer

David Bruce Isaksen

Mark Fong

Richard W Koralek

A method for frequency estimation in a QAM modem comprising the following steps: (1) receiving inphase and quadrature components of a QAM symbol from a carrier recovery block; (2) mapping received QAM symbol to a nearest QAM plant point using a slicer; (3) determining an instant error power of the received QAM point; (4) averaging the instant error power over a plurality of incoming QAM symbols in time domain; (5) excluding a DC component from the averaged error power; (6) translating the averaged error power without DC component from time domain into a frequency domain in order to determine the frequency spectrum of the averaged error power; (7) selecting the frequency spectrum component of the averaged error power with the maximum amplitude by using a peak detection; and (8) determining the frequency offset as the maximum frequency spectrum component of the averaged error power.

Frequency estimation based on constellation error in QAM modems

In a system comprising a subscriber (sub) carrier tracking loop and a hub carrier tracking loop, a method and apparatus for resolving phase equivocation. The method comprises the following steps: (A) acquiring a phase and a frequency of a hub carrier frequency by utilizing the sub carrier tracking loop; (B) estimating an instant absolute frequency offset between a received symbol point and a corresponding plant point; (C) averaging the instant absolute frequency offset over a plurality of received symbols; (D) storing the averaged estimated frequency offset in a frequency register of the sub carrier tracking loop; (E) locking the sub carrier tracking loop on the hub carrier frequency by compensating for the stored averaged estimated frequency offset; (F) estimating an instant absolute phase error between a received symbol point and a corresponding plant point; (G) averaging the instant absolute phase error over a plurality of received symbols; (H) resolving phase equivocation by adjusting the averaged absolute phase error, if the averaged absolute phase error is at least equal to a predetermined equivocation phase threshold; and (I) completing the tracking of the hub carrier frequency by the locked sub carrier tracking loop.

Minimization of phase equivocation in burst modems

A method of baseband/passband digital modulation for a data transmission system wherein a plurality of data symbols is transmitted over a transmission channel at a symbol rate. The method comprises the following steps: (1) generating a plurality of I and Q components of symbols by mapping an input bit stream comprising a plurality of digital codewords into a QAM constellation; (2) selecting a passband or a baseband mode; and (3) generating an analog output signal in the passband or baseband mode. The step of selecting the passband or the baseband mode depends on the complexity of QAM constellation. If QAM constellation includes less than 64 QAM plant points, the passband mode is selected, and if QAM constellation includes more than 64 QAM plant points, the baseband mode is selected. If the QAM constellation includes less than 64 QAM plant points, initially selecting the passband mode until a D/A conversion speed reaches a maximum passband conversion speed, and until an output symbol rate reaches a maximum passband symbol output rate, and subsequently switching to the baseband mode in order to double the maximum passband conversion speed and to double the maximum passband symbol output rate.

Flexible multimode QAM modulator

In a QAM demodulator including an adaptive equalizer, a method of carrier tracking comprising the following steps is disclosed: (A) sampling a QAM signal received from a transmission channel; (B) recovering a symbol clock function from the sampled QAM signal; (C) applying the sampled QAM signal to the adaptive equalizer in order to obtain a QAM equalized signal in a Blind Equalization (BE) mode; (D) using a slicer to locate a nearest plant point for the QAM Blind equalized signal for each recovered symbol clock; (E) using a complex conjugate multiplier to obtain an instantaneous inphase component and an instantaneous quadrature component of a phase angle error signal; (F) using a linear phase detector to obtain an instantaneous phase angle error for each symbol clock; (G) averaging the instantaneous phase angle error signal by using a carrier loop filter; (H) using a complex multiplier to insert an inverse of the averaged phase angle error signal into the QAM Blind equalized signal to compensate for the carrier phase angle error; and (I) repeating the steps (D-H) to close a carrier frequency loop.

Linear phase robust carrier recovery for QAM modems

Method for predistortion compensation for nonlinear distortion produced by the non-linear power amplifier of the QAM signal at the transmitter side of the direct digital communication channel. The out-of-band signal power is monitored by the existent receiver at the receive side of the direct propagation channel. The nonlinear distortion compensation signal is generated at the receiver/demodulator side of the direct propagation channel and transmitted across the direct propagation channel to an input of a pre-distortion block at the transmitter/modulator side of the direct propagation channel. The nonlinear distortion compensation signal is used to adjust the set of parameters of the pre-distortion block in order to minimize the out-of-band power produced by the non-linear amplifier (NLA).

Nonlinear pre-distortion modulator and long loop control

A digital automatic gain control (AGC) system comprising an AGC amplifier configured to scale an input signal by a scale factor, and configured to generate an analog scaled input signal. An analog-to-digital (A/D) converter is configured to sample and convert the analog scaled input signal into a digital scaled input signal. The frequency down converted digital scaled input signal is processed by a power level detector circuit to detect its power level. The logarithmic comparison circuit (LCC) is configured to compare the detected power level of the digital scaled input signal to a predetermined reference signal and configured to generate a digital error signal. Finally, an error processing circuit is configured to process the digital error signal and configured to determine the scale factor of the AGC circuit. The test results show that for any applicable QAM constellation the AGC circuit of the present invention can control the broadest fades (or decreases) in the power level of the input signal with an accuracy up to 200 dB/per second.

All digital automatic gain control circuit

A timing recovery system and method for QAM signals having different symbol rates are disclosed. After sampling the QAM baseband signal, a symbol timing recovery logic including a generator of a weighting function is utilized to develop a local error signal. The local error signal averaged over a predetermined time period is utilized to make a global decision regarding the sampling point position relative to the baseband signal maximum/minimum.

Growing community of inventors

Aptos, CA, United States of America

Byron Esten Danzer