Method and apparatus for demodulation of a desired signal in the presence of nonlinear-distorted interference

• US 9,071,313 B2
• Filed: 11/06/2013
• Issued: 06/30/2015
• Est. Priority Date: 11/07/2012
• Status: Active Grant

• Current Assignee: Datum Systems, Inc.
• Original Assignee: Datum Systems, Inc.
• Inventors: Monsen, Peter
• Primary Examiner(s): NEFF, MICHAEL R
• Application Number:
  US14/073,374
• Publication Number:
  US 20140126675A1
• Time in Patent Office: 601 Days
• Field of Search: 375/350, 375/343
• US Class Current: 1/1
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04L 25/03012 operating in the time domain H04L25/03165, H04L25/03178 take precedence

Abstract

The present disclosure provides methods and apparatuses for demodulating discrete-time desired signals in a period-T_d bandpass desired signal in the presence of interference that results from a period-T bandpass interference signal that has been nonlinear distorted. Estimation of the nonlinear-distorted interference and subsequent cancellation from a received signal, that includes the interference and desired signal, produces residual-interference signals. The demodulation of the residual-interference signals uses an equalization technique when T_d is not equal to T. The estimation, cancellation, and demodulation are adapted for changing nonlinear distortion effects.

Claims

1. A receiver, comprising:

a receiver filter/sampler for filtering, with a matched filter, a received signal containing a bandpass desired signal and a bandpass distorted-interference signal to produce period-T discrete-time receiver signals that include distorted-interference signals associated with the bandpass distorted-interference signal, and desired signals associated with the bandpass desired signal, wherein the matched filter has a complex conjugate, time-inverted impulse response of a waveform filter, wherein T is a positive real number or value;

a synchronizer for tracking from the period-T discrete-time receiver signals a timing phase of the desired signals, and adjusting an interference-signal timing clock to produce a timing alignment between the desired signals and the distortion-interference signals;

a block generator for producing, for each receiver signal, an associated block of successive interference signals that includes a center signal that is sequence-aligned with an associated distorted-interference signal in the receiver signal;

an estimator signal generator for producing estimator signals that include signals that are products of one or more real values of products of interference signals in the block;

an estimator weight calculator for producing estimator weights, each associated with a respective estimator signal, and that depend on previous receiver signals;

a dot-product multiplier for multiplication of each of the estimator signals by the associated estimator weight and summation of the products to produce an estimate of the associated distorted-interference signal;

a combiner for summation of the estimate and the associated receiver signal to produce a sequence of residual-interference signals; and

a desired-signal demodulator for demodulation of the sequence of residual-interference signals to produce desired-signal estimates and for detection of said estimates to produce decision estimates of the desired digital-data;

wherein the receiver is in a digital-data communication system including the receiver, a desired-signal transmitter, and an interference-signal transmitter,

the desired-signal transmitter for modulation of desired digital-data into the bandpass desired signal including a sequence of desired signals that belongs to a complex constellation alphabet, and

the interference-signal transmitter for modulation, using the waveform filter and the interference-signal timing clock, of interference digital-data into a bandpass interference signal that includes a sequence of interference signals that have period T and belong to a complex constellation alphabet, and that the bandpass interference signal traverses a nonlinear channel to produce the bandpass distorted-interference signal.

2. The receiver of claim 1, wherein the estimator weight calculator periodically calculates the estimator weights by a Least-Mean-Squares direct solution that uses a sequence of error signals derived from subtracting from a previous receiver signal an associated decision estimate.

3. A receiver, comprising;

a receiver filter/sampler with a receiver-timing clock for filtering, with a matched filter, a received signal containing a bandpass desired signal and a bandpass distorted-interference signal to produce period-T/2 discrete-time receiver signals that include distorted-interference signals associated with the bandpass distorted-interference signal, wherein the matched filter has a complex conjugate, time-inverted impulse response of a waveform filter, wherein T is a positive real number or value;

a synchronizer for tracking from the period-T/2 discrete-time receiver signals a transmission time delay, and adjusting a receiver-timing clock such that for each period T, the two receiver signals include a synchronized-receiver signal and an antisynchronized-receiver signal;

a block generator for producing, for each synchronized and antisynchronized receiver signal, an associated block of successive interference signals that includes within the block a center signal that is sequence-aligned with an associated distorted-interference signal in the receiver signal;

an estimator signal generator for producing synchronized and antisynchronized estimator signals that include signals that are products of one or more real values of products of interference signals in the associated block;

an estimator weight calculator for producing synchronized and antisynchronized estimator weights, each associated with a respective estimator signal, and that depend on previous receiver signals;

a synchronized/antisychronized dot-product multiplier for multiplication of each of the synchronized/antisynchronized estimator signals by the associated estimator weight and summation of the products to produce a synchronized/antisynchronized estimate of the associated distorted-interference signal;

a combiner for summation of each synchronized/antisynchronized estimate and the associated receiver signal to produce a sequence of residual-interference signals;

a desired-signal demodulator for demodulation of the sequence of residual-interference signals to produce desired-signal estimates and for detection of said estimates to produce decision estimates of the desired digital-data;

wherein the receiver is in a digital-data communication system including the receiver, a desired-signal transmitter, and an interference-signal transmitter,

the desired-signal transmitter for modulation of desired digtal-data into the bandpass desired signal including a sequence of desired signals that belongs to a complex constellation alphabet, and

the interference-signal transmitter for modulation, using the waveform filter, of interference digital-data into a bandpass interference signal that includes a sequence of interference signals that have period T and belong to a complex constellation alphabet, and that the bandpass interference signal traverses a nonlinear channel to produce the bandpass distorted-interference signal.

4. The receiver of claim 3, wherein the desired signals have a period nominally equal to T and the desired-signal demodulator includes an interpolator for producing the desired-signal estimates by interpolation of the residual-interference signals.

5. The receiver of claim 3, wherein the desired signals have a period of greater than or less than T and the desired-signal demodulator includes an equalizer for producing the desired-signal estimates.

6. The receiver of claim 3, wherein the estimator weight calculator periodically calculates the estimator weights by a Least-Mean-Squares direct solution that uses a sequence of error signals derived from subtracting from a previous receiver signal a bias signal that is derived from a plurality of associated decision estimates.

7. A method, comprising:

receiving, at a receiver in a digital-data communication system, a received signal containing a bandpass desired signal and a bandpass distorted-interference signal;

filtering and sampling, with a matched filter, the received signal to produce discrete-time receiver signals that include distorted-interference signals associated with the distorted-interference signal, and desired-signals associated with the bandpass desired signal, wherein the matched filter has a complex conjugate, time-inverted impulse response of a waveform filter;

generating, for each receiver signal, an associated block of successive interference signals, one of which is a center signal that is sequence-aligned with an associated distorted-interference signal in the receiver signal;

producing estimator signals that include signals that are products of one or more real values of products of interference signals in the block;

calculating estimator weights, each associated with a respective estimator signal, and that depend on previous receiver signals;

multiplying an estimator signal by an associated estimator weight and summing products to produce an estimate of the distorted-interference signal;

combining the estimate and the associated receiver signal to produce a residual-interference signal; and

demodulating a sequence of the residual-interference signals to produce digital-data estimates of the desired digital-data,

wherein the digital-data communication system includes transmission of desired digital-data that has been modulated into a bandpass desired signal that includes a sequence of desired signals that belongs to a complex constellation alphabet, and which further includes transmission of interference digital-data that has been modulated, using the waveform filter, into a bandpass interference signal that includes a sequence of interference signals that have period T and belong to a complex constellation alphabet, and that the bandpass interference signal traverses a nonlinear channel to produce the bandpass distorted-interference signal, wherein T is a positive real number or value.

8. The method of claim 7, wherein the desired signals have a period nominally equal to T and the combining step further includes interpolating the residual-interference signals to produce residual-interference signals that are time-aligned with the desired signals in the received signal.

9. The method of claim 7, wherein the desired signals have a period of greater than or less than T and the demodulating step includes equalization of the residual-interference signals.