Symbol synchronizer for software defined communications system signal combiner

• US 7,369,631 B1
• Filed: 12/15/2003
• Issued: 05/06/2008
• Est. Priority Date: 08/14/2000
• Status: Expired due to Term

• Current Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Original Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Inventors: Kleider, John Eric, Gifford, Carl Steven, Chuprun, Jeffery Scott, Bergstrom, Chad S.
• Primary Examiner(s): Fan; Chieh M.
• Assistant Examiner(s): Perilla; Jason M.
• Application Number:
  US10/736,128
• Time in Patent Office: 1,604 Days
• Field of Search: 375/343, 375/240.24, 375/150, 375/152, 375/144, 375/346, 375/349, 375/350, 375/229
• US Class Current: 375/346
• CPC Class Codes: H04B 2001/71563 Acquisition
• CPC Class Codes: H04B 7/0837 using pre-detection combining H04B7/0868 takes precedence
• CPC Class Codes: H04B 7/0894 using different delays between antennas
• CPC Class Codes: H04L 7/007 detection of error based on maximum signal power, e.g. peak value, maximizing autocorrelation
• CPC Class Codes: H04L 7/0083 taking measures against momentary loss of synchronisation, e.g. inhibiting the synchronisation, using idle words or using redundant clocks
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15

Abstract

A symbol synchronizer (100) is provided for a software-defined communications system (10). The symbol synchronizer (100), when integrated into either a pre- or post-detection diversity signal combiner (108, 208), enables highly accurate signal synchronization with minimal added system complexity. The symbol synchronizer (100) includes a single complex sliding window-matched filter (102) for filtering an input digital signal with a match filtering function based on predetermined signal transfer function characteristics to average out receiver noise from the signal. A signal delay bank (84) includes a plurality of delay blocks each for delaying the digital signal filtered by the single matched filter for a predetermined number of samples. A complex correlator (88) correlates the digital signal filtered by the single complex sliding window matched filter (102) and delayed by the complex correlator (88) with a correlator reference signal, and selects an index of a path having a peak correlator value. As a result of such a configuration, the symbol synchronizer (100) is capable of determining symbol boundaries of channel signals in a multi-channel communications system to enable system signal measurement statistics and demodulated to be more accurately generated.

Claims

1. A diversity signal combiner system for a digital communications system, comprising:

a plurality of channels each for receiving a channel signal of a plurality of channel signals from a spatially diverse antenna array element;

a plurality of downconverters each on one of the plurality of channels for downconverting a corresponding channel signal to baseband;

a co-phasing software block for resolving phase differences among the plurality of channel signals after the plurality of channel signals are downconverted by the plurality of downconverters;

a combiner for combining the plurality of channel signals by weighting and delaying each of the plurality of channel signals after the co-phasing software block resolves the phase differences among the plurality of channel signals;

a symbol synchronizer for determining symbol boundaries of the plurality of channel signals after the combiner combines the plurality of channel signals to enable a system signal to be accurately demodulated to accurately represent transmitted data, wherein the symbol synchronizer includes a single complex sliding window matched filter for filtering the plurality of channel signals after the combiner combines the plurality of channel signals with a match filtering function based on predetermined signal transfer function characteristics to average noise out of the plurality of channel signals and thereby maximize a signal-to-noise ratio of each of the plurality of channel signals; and

an equalizer for receiving the plurality of channel signals from the combiner, for providing channel estimates of complex channel gain when necessary, and for removing channel effects from the plurality of channel signals before the plurality of channel signals are input into the single complex sliding window matched filter;

wherein the symbol synchronizer is for providing a variable step size parameter to the equalizer according to a confidence measure of correct symbol boundary estimation.

2. A diversity signal combiner system for a digital communications system, comprising:

a plurality of channels each for receiving a channel signal of a plurality of channel signals from a spatially diverse antenna array element;

a plurality of downconverters each on one of the plurality of channels for downconverting a corresponding channel signal to baseband;

a co-phasing software block for resolving phase differences among the plurality of channel signals after the plurality of channel signals are downconverted by the plurality of downconverters;

a combiner for combining the plurality of channel signals by weighting and delaying each of the plurality of channel signals after the co-phasing software block resolves the phase differences among the plurality of channel signals;

a symbol synchronizer for determining symbol boundaries of the plurality of channel signals after the combiner combines the plurality of channel signals to enable a system signal to be accurately demodulated to accurately represent transmitted data wherein the symbol synchronizer includes a single complex sliding window matched filter for filtering the plurality of channel signals with a match filtering function based on predetermined signal transfer function characteristics to average noise out of the plurality of channel signals and thereby maximize a signal-to-noise ratio of each of the plurality of channel signals;

an equalizer for receiving the plurality of channel signals from the combiner, for providing channel estimates of complex channel gain when necessary, and for removing channel effects from the plurality of channel signals before the plurality of channel signals are input into the single complex sliding window matched filter; and

an adaptive weight, delay and phase adapter connected between the combiner and the equalizer for estimating and correcting phase gain, frequency and sampling error effects, and for receiving feedback from the single complex sliding window matched filter and the symbol synchronizer for providing a variable step size parameter, and fast error convergence, in the equalizer.

3. The diversity signal combiner system of claim 2, wherein the equalizer is connected to the adaptive weight, delay and phase updater via a feedback loop to accept a new value of the variable step size parameter and to return a combined channel signal estimate to the adaptive weight, delay and phase updater.

4. A diversity signal combiner system for a digital communications system, comprising:

a plurality of channels each for receiving a signal from a spatially diverse antenna array element;

a plurality of downconverters each on one of the plurality of channels for downconverting a corresponding plurality of channel signals to baseband;

a plurality of matched filters each being located on one of the plurality of channels for filtering the plurality of channel signals after the plurality of channel signals are downconverted by the plurality of downconverters with a match filtering function based on predetermined signal transfer function characteristics to average noise out of the plurality of channel signals to maximize a signal-to-noise ratio of each of the plurality of channel signals;

a combiner for combining each of the plurality of channel signals output from the plurality of matched filters by appropriately weighting and delaying each of the plurality of channel signals;

a symbol synchronizer for determining symbol boundaries of the plurality of channel signals output from the plurality of matched filters as the combiner weights and delays each of the plurality of channel signals, thereby causing a single combined signal to be output from the combiner;

an adaptive delay/phase updater for receiving digitally sampled signals from a variable delay in each of the plurality of channels; and

an equalizer for generating a signal phase/delay estimation error and for inputting the signal phase/delay estimation error into the adaptive phase/delay updater;

wherein the symbol synchronizer is further for generating a confidence measure and inputting the confidence measure into the adaptive phase/delay updater; and

wherein the adaptive phase/delay updater measures and updates the signal phase/delay estimation error based on the confidence measure.

5. A diversity signal combiner system for a digital communications system, comprising:

a plurality of channels each for receiving a signal from a spatially diverse antenna array element;

a plurality of downconverters each on one of the plurality of channels for downconverting a of channel signal to baseband;

a plurality of matched filters each being located on one of the plurality of channels for filtering the plurality of channel signals after the plurality of channels signals are downconverted by the plurality of downconverters with a match filtering function based on predetermined signal transfer function characteristics to average noise out of the plurality of channel signals to maximize a signal-to-noise ratio of each of the plurality of channel signals;

a combiner for combining each of the plurality of channel signals output from the plurality of matched filters by appropriately weighting and delaying each of the plurality of channel signals;

a symbol synchronizer for determining symbol boundaries of the plurality of channel signals output from the plurality of matched filters as the combiner weights and delays each of the plurality of channel signals, thereby causing a single combined signal to be output from the combiner;

an equalizer for receiving the combined channel signals from the combiner and for providing combiner weight updating on the plurality of channels signals; and

a sampling time update block for executing a sampling time update equation and for outputting results of the executed sampling time update equation to the plurality of downconverters to control a sampling time of the plurality of channel signals input to the plurality of downconverters.

6. The diversity signal combiner system of claim 5, wherein the symbol synchronizer is further for providing confidence measures to both the equalizer and the sampling time update block to provide adjustable step size in both the sampling time update block and the equalizer.

7. A diversity signal combiner system for a digital communications system, comprising:

a plurality of channels each for receiving a signal from a spatially diverse antenna array element;

a plurality of downconverters each on one of the plurality of channels for downconverting a corresponding channel signal to baseband;

a plurality of matched filters each being located on one of the plurality of channels for filtering the plurality of channel signals after the plurality of channel signals are downconverted by the plurality of downconverters with a match filtering function based on predetermined signal transfer function characteristics to average noise out of the plurality of channel signals to maximize a signal-to-noise ratio of each of the plurality of channel signals;

a combiner for combining each of the plurality of channel signals output from the plurality of matched filters by appropriately weighting and delaying each of the plurality of channel signals;

a symbol synchronizer for determining symbol boundaries of the plurality of channel signals output from the plurality of matched filters as the combiner weights and delays each of the plurality of channel signals, thereby causing a single combined signal to be output from the combiner; and

an equalizer for receiving the combined channel signals from the combiner and for providing combiner weight updating on the plurality of channels signals;

wherein the equalizer further includes a vector line for accepting output samples from the plurality of matched filters, the equalizer further for estimating a complex channel gain for each of the plurality of channels based on the accepted output samples; and

wherein the equalizer is further for generating a weight vector output for correcting channel complex gain errors.

8. A diversity signal combiner system for a digital communications system, comprising:

a plurality of channels each for receiving a signal from a spatially diverse antenna array element;

a plurality of downconverters each on one of the plurality of channels for downconverting a corresponding channel signal to baseband;

a plurality of matched filters each being located on one of the plurality of channels for filtering the plurality of channel signals after the plurality of channel signals are downconverted by the plurality of downconverters with a match filtering function based on predetermined signal transfer function characteristics to average noise out of the plurality of channel signals to maximize a signal-to-noise ratio of each of the plurality of channel signals;

a combiner for combining each of the plurality of channel signals output from the plurality of matched filters by appropriately weighting and delaying each of the plurality of channel signals;

a symbol synchronizer for determining symbol boundaries of the plurality of channel signals output from the plurality of matched filters as the combiner weights and delays each of the plurality of channel signals, thereby causing a single combined signal to be output from the combiner; and

an equalizer for receiving the combined channel signals from the combiner and for providing combiner weight updating on the plurality of channels signals;

wherein the symbol synchronizer is further for providing a control signal to the equalizer for providing optimal sampling at an output of the equalizer to minimize a demodulated data bit error rate.