Receiver capable of demodulating multiple digital modulation formats

• US 5,799,037 A
• Filed: 09/27/1996
• Issued: 08/25/1998
• Est. Priority Date: 02/16/1996
• Status: Expired due to Term

• Current Assignee: AmTRAN Technology Co., Ltd.
• Original Assignee: David Sarnoff Research Center, Inc.
• Inventors: Jaffe, Steven T., Strolle, Christopher H.
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US08/721,663
• Time in Patent Office: 697 Days
• Field of Search: 375/232-235, 375/321, 375/324-327, 375/332, 375/343, 375/346, 375/350, 375/371, 375/373, 348/725-726, 329/304, 329/307, 329/356-357
• US Class Current: 375/233
• CPC Class Codes: H03D 3/007 by converting the oscillations into two quadrature related signals H03D3/245 takes precedence
• CPC Class Codes: H03J 7/04 where the frequency control is accomplished by varying the electrical characteristics of a non-mechanically adjustable element or where the nature of the frequency controlling element is not significant
• CPC Class Codes: H04L 2025/03382 Single of vestigal sideband
• CPC Class Codes: H04L 2025/0342 QAM
• CPC Class Codes: H04L 2025/0349 as a feedback filter
• CPC Class Codes: H04L 25/0307 using blind adaptation
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453
• CPC Class Codes: H04L 7/0278 Band edge detection
• CPC Class Codes: H04L 7/0334 Processing of samples having at least three levels, e.g. soft decisions
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence

Abstract

A receiver for demodulating multiple digital modulation formats including vestigial sideband (VSB), quadrature amplitude modulation (QAM), and offset QAM (OQAM). The receiver includes a timing recovery circuit that produces accurate timing information for each modulation format and a signal processor for adaptive equalization and quantization of each modulation format. The adaptive equalizer is a passband equalizer that performs blind equalization using a feed forward equalizer and a decision feedback equalizer.

Claims

1. A signal processing apparatus for processing a passband signal to produce an equalized signal, said signal processing apparatus comprising:

a passband adaptive equalizer, containing a passband feed forward equalizer (FFE) and a passband decision feedback equalizer (DFE), for processing said passband signal to produce said equalized signal;

an equalizer control circuit, coupled to said passband adaptive equalizer, for initializing and updating parameters of said passband adaptive equalizer;

a derotator, coupled to said passband adaptive equalizer and said equalizer control circuit, for derotating the equalized signal to form a baseband signal; and

a quantizer, coupled to said derotator and said equalizer control circuit, for quantizing said baseband signal to produce quantized symbols;

said feed forward equalizer being coupled to said equalizer control circuit and having an output terminal coupled to a signal combiner;

said decision feedback equalizer being coupled to said equalizer control circuit and having an output terminal connected to said signal combiner, where an output signal of said signal combiner is the equalized signal; and

said equalizer control circuit causing said decision feedback equalizer to operate in one of a decision feedback mode and a infinite impulse response (IIR) mode.

2. The signal processing apparatus of claim 1 wherein the passband adaptive equalizer has coefficients that are adjusted using blind equalization in accordance with a constant modulus algorithm.

3. The signal processing apparatus of claim 1 wherein the equalizer control circuit comprises:

an error generator, coupled to the quantizer and the derotator for producing an error signal;

a rotator, coupled to said error generator, for rotating the error signal and coupling the rotated error signal to the passband adaptive equalizer.

4. The signal processing apparatus of claim 1 wherein the feed forward equalizer is a finite impulse response filter and the decision feedback equalizer is an infinite impulse response filter.

5. The signal processing apparatus of claim 1 wherein the passband signal is a quadrature amplitude modulated (QAM) signal, a vestigial sideband (VSB) modulated signal, or a offset QAM (OQAM) signal.

6. A receiver for receiving signals having digital modulation formats, said receiver comprising:

an analog-to-digital (A/D) converter for digitizing received signals;

a quadrature demodulator, coupled to said A/D converter, for producing a complex signal having a center frequency in response to the digitized received signals;

a matched filter, coupled to said quadrature demodulator, for filtering said complex signal;

a carrier tracking circuit, coupled to said matched filter, for locking an oscillator to a carrier signal within said complex signal whenever said complex signal contains said carrier signal, and for adjusting the center frequency of said complex signal whenever said complex signal contains said carrier signal;

a passband adaptive equalizer, coupled to said carrier tracking circuit and containing a passband feed forward equalizer (FFE) and a passband decision feedback equalizer (DFE), for equalizing passband signal of said complex signal to produce an equalized signal;

an equalizer control circuit, coupled to said passband adaptive equalizer, for initializing and updating parameters of said passband adaptive equalizer;

a derotator, coupled to said passband adaptive equalizer, for converting said equalized signal to a baseband signal; and

a quantizer, coupled to said derotator and said equalizer control circuit, for quantizing the baseband signal to produce quantized symbols;

said passband adaptive equalizer further comprising a signal combiner, coupled to said passband decision feedback equalizer (DFE) and said passband feed forward equalizer (FFE), for combining output signals from the DFE and FFE to form said equalized signal; and

said equalizer control circuit causing said decision feedback equalizer to operate in one of a decision feedback mode and a infinite impulse response (IIR) mode.

7. The receiver of claim 6 wherein said received signals include quadrature amplitude modulated (QAM) signals, vestigial sideband (VSB) modulated signals, or offset QAM (OQAM) signals.

8. The receiver of claim 6 wherein the passband adaptive equalizer has coefficients that are adjusted using blind equalization in accordance with a constant modulus algorithm.

9. The receiver of claim 6 further comprising:

an error generator, coupled to said derotator and said quantizer, for generating an error signal;

a rotator, coupled to said error generator, for rotating said error signal; and

a signal converter, coupled to said rotator and said passband adaptive equalizer, for converting said rotated error signal into a control signal for said passband adaptive equalizer.

10. The receiver of claim 9 wherein said signal converter comprises:

a complex to real/imaginary converter for converting the rotated error signal into real and imaginary components;

a multiplexer, coupled to the complex to real/imaginary converter, for selecting the imaginary component when a QAM signal is received and no signal when a VSB or OQAM signal is received; and

a make complex converter, coupled to the complex to real/imaginary converter and the multiplexer, for converting the real component and selected signal into the control signal for the passband adaptive equalizer.

11. The receiver of claim 6 further comprising:

a symbol retiming circuit, coupled to said quantizer and said derotator, for retiming said quantized symbols that are generated from received signals carrying either VSB or OQAM modulation, to produce symbol samples.

12. The receiver of claim 11 further comprising:

a carrier recovery circuit, coupled to said symbol retiming circuit and said derotator, for locking an oscillator to said quantized symbols or said symbol samples.

13. The receiver of claim 6 further comprising:

a rotator, coupled to said quantizer, for rotating said quantized symbols;

a multiplexer, coupled to said passband adaptive equalizer and said rotator, for selecting either the equalized signal or the rotated quantized symbols as a multiplexer output signal; and

a signal converter, coupled to said multiplexer and said passband adaptive equalizer, for converting said multiplexer output signal into an input signal for said DFE.

14. The receiver of claim 13 wherein the signal converter comprises:

a delay for delaying said multiplexer output signal;

a complex to real/imaginary converter, coupled to said delay, for converting the delayed signal into real and imaginary components;

a multiplexer, coupled to the complex to real/imaginary converter, for selecting the imaginary component when a QAM signal is received and no signal when a VSB or OQAM signal is received; and

a make complex converter, coupled to the complex to real/imaginary converter and the multiplexer, for converting the real component and selected signal into the input signal for the DFE.

15. A receiver for receiving signals having digital modulation formats such as quadrature amplitude modulated (QAM) signals, vestigial sideband (VSB) modulated signals, or offset QAM (OQAM) signals, said receiver comprising:

an analog-to-digital (A/D) converter for digitizing received signals;

a quadrature demodulator, coupled to said A/D converter, for producing a complex signal having a center frequency in response to the digitized received signals;

a matched filter, coupled to said quadrature demodulator, for filtering said complex signal;

a carrier tracking circuit, coupled to said matched filter, for locking an oscillator to a carrier signal within said complex signal whenever said complex signal contains said carrier signal and for adjusting the center frequency of said complex signal whenever said complex signal contains said carrier signal;

a passband adaptive equalizer, coupled to said carrier tracking circuit, for equalizing said complex signal, said passband adaptive equalizer comprising a feed forward equalizer (FFE), a decision feedback equalizer (DFE) and a signal combiner, coupled to said DFE and FFE, for combining output signals from the DFE and FFE to form an equalized signal;

a derotator, coupled to said passband adaptive equalizer, for converting said equalized signal to a baseband signal;

a quantizer, coupled to said derotator, for quantizing the baseband signal to produce quantized symbols;

a symbol retiming circuit, coupled to said quantizer and said derotator, for retiming said quantized symbols generated from received VSB or OQAM signals to produce symbol samples, said symbol retiming circuit being bypassed for received QAM signals;

a carrier recovery circuit, coupled to said symbol retiming circuit and said derotator, for locking an oscillator to said quantized symbols or said symbol samples;

an error generator, coupled to said derotator and said symbol retiming circuit, for generating an error signal in response to said symbol samples or said quantized symbols and said baseband signal;

a first rotator, coupled to said error generator, for rotating said error signal;

a first signal converter, coupled to said first rotator and said passband adaptive equalizer, for converting said rotated error signal into a control signal for said passband adaptive equalizer;

a second rotator, coupled to said symbol retiming circuit, for rotating said symbol samples or said quantized symbols;

a multiplexer, coupled to said passband adaptive equalizer and said second rotator, for selecting either the equalized signal or the rotated symbol samples or the quantized symbols as a multiplexer output signal; and

a second signal converter, coupled to said multiplexer and said passband adaptive equalizer, for converting said multiplexer output signal into an input signal for said DFE.

16. The receiver of claim 15 wherein the passband adaptive equalizer has coefficients that are adjusted using blind equalization in accordance with a constant modulus algorithm.

17. The receiver of claim 16 wherein said first signal converter comprises:

a complex to real/imaginary converter for converting the first rotated error signal into real and imaginary components;

a multiplexer, coupled to the complex to real/imaginary converter, for selecting the imaginary component when the QAM signal is received and no signal when the VSB or the OQAM signal is received; and

a make complex converter, coupled to the complex to real/imaginary converter and the multiplexer, for converting the real component and selected signal into the control signal for the passband adaptive equalizer.

18. The receiver of claim 16 wherein the second signal converter comprises:

a delay for delaying said multiplexer output signal;

a complex to real/imaginary converter, coupled to said delay, for converting the delayed signal into real and imaginary components;

a multiplexer, coupled to the complex to real/imaginary converter, for selecting the imaginary component when the QAM signal is received and no signal when the VSB or OQAM signal is received; and

a make complex converter, coupled to the complex to real/imaginary converter and the multiplexer, for converting the real component and selected signal into the input signal for the DFE.

19. A signal processing apparatus for processing a passband signal to produce an equalized signal, said signal processing apparatus comprising:

a passband adaptive equalizer, containing a passband feed forward equalizer (FFE) and a passband decision feedback equalizer (DFE), for processing said passband signal to produce said equalized signal;

an equalizer control circuit, coupled to said passband adaptive equalizer, for initializing and updating filter coefficients of said passband adaptive equalizer;

a derotator, coupled to said passband adaptive equalizer and said equalizer control circuit, for derotating said equalized signal to form a baseband signal; and

a quantizer, coupled to said derotator and said equalizer control circuit, for quantizing said baseband signal to produce quantized symbols;

said equalizer control circuit causing said decision feedback equalizer to operate in one of a decision feedback mode and a infinite impulse response (IIR) mode.

20. The signal processing apparatus of claim 19, wherein said quantizer operates in one of a quadrant mode, an octant mode and a decision directed mode, and said equalizer control circuit causes said decision feedback equalizer to operate in said decision feedback mode when said quantizer operates in said decision directed mode.