Carrier recovery system for a vestigial sideband signal

• US 5,894,334 A
• Filed: 09/05/1996
• Issued: 04/13/1999
• Est. Priority Date: 03/21/1994
• Status: Expired due to Term

• Current Assignee: RCA Thomson Licensing Corporation
• Original Assignee: RCA Thomson Licensing Corporation
• Inventors: Jaffe, Steven Todd, Strolle, Christopher Hugh
• Primary Examiner(s): Peng, John K.
• Assistant Examiner(s): Reed, Jr., James
• Application Number:
  US08/702,529
• Time in Patent Office: 950 Days
• Field of Search: 348/725, 348/726, 348/735, 348/639, 348/470, 348/500, 348/537, 375/355, 455/204
• US Class Current: 348/725
• CPC Class Codes: H04L 2025/03382 Single of vestigal sideband
• CPC Class Codes: H04L 2025/0363 Feature restoration, e.g. constant modulus
• CPC Class Codes: H04L 25/0305 using blind adaptation
• CPC Class Codes: H04L 25/0307 using blind adaptation
• CPC Class Codes: H04L 25/061 providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset removal of dc offset in coupling arrangements H04L25/029, H04L25/0296
• CPC Class Codes: H04L 25/067 providing soft decisions, i.e. decisions together with an estimate of reliability H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178
• CPC Class Codes: H04L 27/02 Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation H04L27/32 takes precedence
• CPC Class Codes: H04L 27/066 Carrier recovery circuits H04L27/2271 takes precedence
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 5/211 Ghost signal cancellation H04N23/81 takes precedence
• CPC Class Codes: H04N 5/455 Demodulation-circuits

Abstract

A television signal receiver for processing an HDTV signal transmitted in a vestigial sideband (VSB) format includes input complex filters shared by a timing recovery network (30) and a carrier recovery network (50). The filter network includes a pair of upper and lower band edge filters (20, 22) mirror imaged around the upper and lower band edges of the VSB signal for producing suppressed subcarrier AM output signals. The timing recovery network includes a phase detector (28, 38, 62) and responds to an AM signal derived from the two filters (via 26) for synchronizing a system clock (CLK). The carrier recovery network (50) also includes a phase detector (54, 60, 62, 64), and responds to outputs from one or both of the filters for producing an output error signal (Δ) representing a phase/frequency offset of the VSB signal. The error signal is used to reduce or eliminate the offset to produce a recovered baseband or near baseband signal. A subsequent equalizer eliminates any residual phase offsets in the recovered signal.

Claims

1. In a system for receiving a high definition television (HDTV) signal transmitted as a modulated vestigial sideband (VSB) signal formatted as a one-dimensional data constellation of symbols representing digital image data and subject to exhibiting a carrier offset, a carrier recovery network (50) for frequency shifting said received VSB signal toward baseband, said carrier recovery network being capable of achieving carrier recovery without reliance on a pilot component if present in said received signal, said carrier recovery network comprising:

an input network (14,16) for processing said VSB signal;

a filter network (20,22) responsive to an output signal from said input network and having a band edge response with respect to at least one of upper and lower band edges of a frequency spectrum of said VSB signal for producing a double sideband amplitude modulated (AM) signal at an output of said filter network;

a phase detector network (54) for processing said double sideband AM output signal to produce a control signal (Δ

) representing a carrier offset when present; and

an output processor (71,74,75) responsive to said control signal for producing a demodulated output signal at or near baseband.

2. A system according to claim 1, wherein

said filter network comprises a first band edge filter (20) and a second band edge filter (22) having band edge responses respectively associated with upper and lower band edges of a frequency spectrum of said VSB signal for producing double sideband amplitude modulated (AM) signals at respective outputs of said first and second filters.

3. A system according to claim 1, wherein

said filter network is a digital filter network comprising first and second filters with responses that are complementary to the frequency spectrum of said received VSB signal at band edges said first and second filters respectively filter.

4. A system according to claim 1, wherein

said received VSB signal exhibits a frequency spectrum with band edge responses at a frequencies f_c -1/4 f_st and f_c +1/4 f_st respectively, with respect to a mid-band carrier frequency f_c +/-Δ

; and

said first filter exhibits a band edge response at a Nyquist frequency f_c -1/4 f_st and said second filter exhibits a band edge response at a Nyquist frequency f_c +1/4 f_st, where

f_c is the carrier frequency of said transmitted VSB signal;

f_st is the transmitted symbol frequency; and

Δ

is said carrier offset when present.

5. A system according to claim 2 and further including

a multiplier (45) having first and second inputs for 25 receiving output signals from said first and second filters, respectively, and an output coupled to an input of said phase detector network;

wherein

an output signal of said multiplier is a suppressed carrier double sideband AM signal (FIG.

     6) centered around a frequency 2f_c where f_c is the carrier frequency of said transmitted VSB signal, said centered frequency subject to exhibiting a carrier offset (Δ

).

6. A system according to claim 1, wherein

said input signal to said phase detector network is a complex signal having real and imaginary components;

and

said phase detector network includes means (55,56,57) for cancelling said imaginary component in an output signal from said phase detector network.

7. A system according to claim 1, wherein said output processor comprises:

a first translating network (74) responsive to an output signal from said input network for producing a translated near baseband VSB signal; and

a second translating network (71) responsive to said near baseband VSB signal from said first translating network and responsive to said control signal from said carrier recovery network for producing a signal at or near baseband.

8. A system according to claim 7 and further including

an equalizer (75) for removing residual offsets from an output signal from said second translating network to produce a baseband VSB signal.

9. A system according to claim 7 wherein

said first and second translating networks are signal multipliers;

and

said first translating network receives an input VSB signal in double sideband form, and responds to a clock signal at a frequency related to f_sr, where f_sr is a receiver sampling frequency for producing an output single sideband near baseband VSB signal.

10. A system according to claim 1, wherein

said received VSB signal is an 8-VSB signal having a one dimensional data constellation defined by the following eight data symbols:

-7 -5 -3 -1 1 3 5 7.