Carrier phase independent symbol timing recovery methods for VSB receivers
The present invention provides a novel symbol timing recovery method for VSB receivers. Systems are described that comprise a timing error detector (TED) that produces an exact symbol timing error even in the presence residual carrier phase offset, loop filter that controls the characteristics of acquisition and tracking of digital PLL loop, Voltage/Numerically Controlled Oscillator (VCO/NCO) that adjusts the sampling instant and phase, A/D converter that samples a continuous VSB input signal, and a interpolating squared root raised cosine filter that performs both matched filtering and a compensation of constant timing offset of quarter symbol caused by the invented TED. The timing error detector in this invention comprises an envelope detector, band pass filter, squaring block, high pass filter, and decimator. It uses both in-phase and quadrature-phase component of received VSB signal, is operated at twice of a symbol frequency F, and guarantees consistent symbol timing error signal resulting in the improvement of receiver's performance.
1. A timing recovery system, comprising:
an interpolator configured to provide an interpolated signal representative of a Vestigial Side Band (“VSB”) signal wherein the interpolated signal includes inter-sample interpolations of a digital representation of the VSB signal; and
a timing error detector configured to receive a complex representation of the interpolated signal and to generate a timing error signal at each of a plurality of symbol periods,
wherein the timing error detector comprises an envelope processor and an envelope detector that computes energy in a complex representation of the VSB signal,
wherein the timing error detector cancels phase offsets in the complex representation of the VSB signal, and
wherein the timing error signal is unaffected by carrier phase offset.
2. The timing recovery system of claim 1 , wherein the envelope detector cancels residual phase offset in the complex representation of the VSB signal.
3. The timing recovery system of claim 2 , wherein the energy is computed using conjugate multiplication of real and imaginary components of the complex representation of the VSB signal.
4. The timing recovery system of claim 1 , wherein the interpolator receives a complex baseband representation of the VSB signal.
5. The timing recovery system of claim 1 , wherein the complex representation of the VSB signal is a baseband representation of the VSB signal.
6. The timing recovery system of claim 5 , and further comprising a phase splitter, the phase splitter receiving the interpolated signal and wherein a carrier signal is recovered from the output of the phase splitter to provide the complex baseband representation of the VSB signal.
7. A timing recovery system, comprising:
an interpolator configured to provide an interpolated signal representative of a Vestigial Side Band (“VSB”) signal wherein the interpolated signal includes inter-sample interpolations of a digital representation of the VSB signal; and
a timing error detector configured to receive a complex representation of the interpolated signal and to generate a timing error signal, wherein the timing error signal is unaffected by carrier phase offset,
wherein the timing error detector comprises an envelope processor and an envelope detector that computes energy in a complex representation of the VSB signal,
wherein the timing error detector cancels phase offsets in the complex representation of the VSB signal, and
wherein the timing error signal is unaffected by carrier phase offset and jitter.
8. A timing recovery system, comprising:
an interpolator configured to provide an interpolated signal representative of a Vestigial Side Band (“VSB”) signal wherein the interpolated signal includes inter-sample interpolations of a digital representation of the VSB signal; and
a timing error detector configured to receive a complex representation of the interpolated signal and to generate a timing error signal,
wherein the timing error signal is unaffected by carrier phase offset,
wherein the timing error detector comprises an envelope detector that computes energy in a complex representation of the VSB signal and an envelope processor that includes a high pass filter, a signal squarer and a decimator, and
wherein the timing error detector cancels phase offsets in the complex representation of the VSB signal.
9. A timing recovery system, comprising:
an interpolator configured to provide an interpolated signal representative of a Vestigial Side Band (“VSB”) signal wherein the interpolated signal includes inter-sample interpolations of a digital representation of the VSB signal; and
a timing error detector configured to receive a complex representation of the interpolated signal and to generate a timing error signal,
wherein the timing error detector cancels phase offsets in the complex representation of the interpolated signal,
wherein the timing error signal is unaffected by carrier phase offset,
wherein the inter-sample interpolations are associated with an offset provided by a numerically controlled oscillator responsive to the timing error signal.
10. A timing recovery system, comprising:
an interpolator configured to provide an interpolated signal representative of a Vestigial Side Band (“VSB”) signal wherein the interpolated signal includes inter-sample interpolations of a digital representation of the VSB signal;
a timing error detector configured to receive a complex representation of the interpolated signal and to generate a timing error signal, wherein the timing error detector cancels phase offsets in the complex representation of the interpolated signal, and wherein the timing error signal is unaffected by carrier phase offset; and
a matched filter configured to compensate for a quarter symbol offset.
11. A timing recovery system, comprising:
a timing error detector configured to generate an error signal representative of timing error in a digitized signal, wherein the timing error detector includes an envelope detector;
an analog-to-digital (“A/D”) converter configured to digitize a Vestigial Side Band (“VSB”) signal at a sampling rate determined by the error signal;
an interpolator configured to provide an interpolated VSB signal that includes the digitized VSB signal and inter-sample interpolations of the digitized VSB signal; and
a phase splitter that receives an output of the A/D converter and provides a complex VSB signal representative of the interpolated VSB signal, wherein
the timing error detector receives a complex baseband VSB signal obtained by removing a carrier signal from the interpolated VSB signal,
wherein the timing error detector cancels phase offsets in the complex baseband VSB signal, and
wherein the timing error detector further includes an envelope processor configured to receive an output of the envelope detector representing an estimate of energy in the complex baseband VSB signal, the envelope processor comprising a signal squarer and one or more of a high pass filter and a decimator.
12. The timing error detector of claim 11 , wherein the envelope processor further comprises a high pass filter.
13. The timing error detector of claim 11 , wherein the envelope processor further comprises a decimator.
14. The timing recovery system of claim 11 , wherein the envelope detector performs conjugate multiplication of real and imaginary components of the complex baseband VSB signal to calculate energy in the VSB signal.