Data-aided symbol timing recovery loop decoupled from carrier phase offset

• US 8,761,311 B2
• Filed: 01/14/2008
• Issued: 06/24/2014
• Est. Priority Date: 01/14/2008
• Status: Active Grant

• Current Assignee: InterDigital Madison Patent Holdings (InterDigital, Inc.)
• Original Assignee: Thomson Licensing (Vantiva SA)
• Inventors: Belotserkovsky, Maxim
• Primary Examiner(s): Liu, Shuwang
• Assistant Examiner(s): TAYONG, HELENE E
• Application Number:
  US12/735,385
• Publication Number:
  US 20100283911A1
• Time in Patent Office: 2,353 Days
• Field of Search: 375/326, 375/221, 375/296, 375/298, 375320-321, 375/346, 348/726
• US Class Current: 375/326
• CPC Class Codes: H04L 2027/003 at baseband only
• CPC Class Codes: H04L 2027/0057 quadrature phase
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits
• CPC Class Codes: H04L 7/0029 interpolation of received data signal
• CPC Class Codes: H04L 7/027 extracting the synchronising or clock signal from the received signal spectrum, e.g. by using a resonant or bandpass circuit
• CPC Class Codes: H04L 7/065 and superimposed by modulation

Abstract

A receiver is an ATSC (Advanced Television Systems Committee)-receiver and comprises a staggered quadrature amplitude modulator for providing an staggered quadrature amplitude modulated (SQAM) signal from a received signal; a data-aided carrier tracking loop (CTL) and a data-aided symbol timing recovery (STR) loop. The data-aided STR loop operates such that the data-aided STR loop is now insensitive to carrier phase offset.

Claims

1. Apparatus for use in a receiver, the apparatus comprising;

a staggered quadrature amplitude modulator for providing a staggered quadrature amplitude modulated signal from a received signal;

a carrier tracking loop, for tracking a carrier frequency in the staggered quadrature amplitude modulated signal; and

a data-aided symbol timing recovery loop for tracking symbol timing in the staggered quadrature amplitude modulated signal wherein the symbol timing recovery loop includes

a filter for removing a phase response symmetry in a signal derived from the staggered quadrature amplitude modulated signal for providing a filter output signal, wherein the filter is sensitive to a timing phase offset, while keeping the filter insensitive to a carrier phase offset, and wherein the filter comprises a Hilbert filter that operates on a real signal component of the signal derived from the staggered quadrature amplitude modulated signal; and

a timing phase detector responsive to the filter output signal for driving the symbol timing recovery loop.

2. The apparatus of claim 1, wherein the carrier tracking loop is a data-aided carrier tracking loop.

3. The apparatus of claim 1, wherein the data-aided symbol timing recovery loop further comprises:

a multiplier for derotating the staggered quadrature amplitude modulated signal for providing a derotated staggered quadrature amplitude modulated signal;

an interpolator responsive to the derotated staggered quadrature amplitude modulated signal for providing an interpolated signal;

a demodulator for demodulating the interpolated signal for providing a demodulated signal;

an equalizer for equalizing the demodulated signal for providing an equalized signal;

wherein the filter removes the phase response symmetry from the equalized signal.

4. The apparatus of claim 3, wherein the demodulator translates the interpolated signal back to a vestigial sideband modulated signal before providing the demodulated signal.

5. The apparatus of claim 1, wherein the data-aided symbol timing recovery loop further comprises:

a multiplier for derotating the staggered quadrature amplitude modulated signal for providing a derotated staggered quadrature amplitude modulated signal;

an interpolator responsive to the derotated staggered quadrature amplitude modulated signal for providing an interpolated signal; and

a demodulator for demodulating the interpolated signal for providing a demodulated signal;

wherein the filter removes the phase response symmetry from the demodulated signal.

6. The apparatus of claim 5, wherein the demodulator translates the interpolated signal back to a vestigial sideband modulated signal before providing the demodulated signal.

7. The apparatus of claim 1, wherein the received signal is an ATSC (Advanced Television Systems Committee) VSB (Vestigial Sideband) modulated signal.

14. The apparatus of claim 3, wherein the equalizer provides a training signal and the symbol timing recovery loop is driven as a function of a phase difference between the equalized signal and the training signal.

15. The apparatus of claim 5, wherein the data-aided symbol timing recovery loop further comprises an equalizer for equalizing the demodulated signal for providing an equalized signal and a training signal and wherein the symbol timing recovery loop is driven as a function of a phase difference between the equalized signal and the training signal.

8. A method for use in a receiver, the method comprising:

staggered quadrature amplitude modulating a received signal for providing a staggered quadrature amplitude modulated signal;

tracking a carrier frequency in the staggered quadrature amplitude modulated signal with a carrier tracking loop;

tracking symbol timing in the staggered quadrature ampliture modulated signal with a symbol time loop;

wherein the tracking symbol timing step comprises the steps of

filtering a signal derived from the staggered quadrature amplitude modulated signal to remove a phase response symmetry in the signal for providing a filter output signal, wherein the filtering is sensitive to a timing phase offset, while keeping the filter insensitive to a carrier phase offset, and wherein the filtering performs Hilbert filtering that operates on a real signal component of the signal derived from the staggered quadrature

amplitude modulated signal; and

detecting timing phase differences as a function of the filter output signal for driving a symbol timing recovery loop.

9. The method of claim 8, further comprising:

derotating the staggered quadrature amplitude modulated signal for providing a derotated staggered quadrature amplitude modulated signal;

interpolating the derotated staggered quadrature amplitude modulated signal for providing an interpolated signal;

demodulating the interpolated signal for providing a demodulated signal; and

equalizing the demodulated signal for providing an equalized signal;

wherein the filtering step removes the phase response symmetry from the equalized signal.

10. The method of claim 9, wherein the demodulating step comprises:

converting the interpolated signal back to a vestigial sideband modulated signal before providing the demodulated signal.

11. The method of claim 8, further comprising:

derotating the staggered quadrature amplitude modulated signal for providing a derotated staggered quadrature amplitude modulated signal;

interpolating the derotated staggered quadrature amplitude modulated signal for providing an interpolated signal; and

demodulating the interpolated signal for providing a demodulated signal;

wherein the filtering step removes the phase response symmetry from the demodulated signal.

12. The method of claim 11, wherein the demodulating step comprises:

converting the interpolated signal back to a vestigial sideband modulated signal before providing the demodulated signal.

13. The method of claim 8, wherein the received signal is an ATSC (Advanced Television Systems Committee) VSB (Vestigial Sideband) modulation signal.

16. The method of claim 9, wherein the equalizing step provides a training signal and the symbol timing recovery loop is driven as a function of a phase difference between the equalized signal and the training signal.

17. The method of claim 11 further comprising equalizing the demodulated signal for providing an equalized signal and a training signal, wherein the symbol timing recovery loop is driven as a function of a phase difference between the equalized signal and the training signal.