Pilot signal control for digital television DTV transmission

• US 6,539,062 B1
• Filed: 10/21/1999
• Issued: 03/25/2003
• Est. Priority Date: 10/21/1999
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Hershey, John Erik, Grabb, Mark Lewis, Welles, Kenneth Brakeley II
• Primary Examiner(s): VO, DON NGUYEN
• Application Number:
  US09/422,440
• Time in Patent Office: 1,251 Days
• Field of Search: 375/321, 375/298, 375/261, 375/270, 375/301, 329/304, 329/357, 332/103, 332/170, 455/47, 348/641
• US Class Current: 375/261
• 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: H04N 21/2383 Channel coding or modulation of digital bit-stream, e.g. QPSK modulation arrangements for detecting or preventing errors in the information received by adapting the channel coding H04L1/0009; analogue front ends or means for connecting modulators, demodulators or transceivers to a transmission line H04L27/0002
• CPC Class Codes: H04N 21/426 Internal components of the client ; Characteristics thereof H04N5/44 takes precedence
• CPC Class Codes: H04N 21/4382 Demodulation or channel decoding, e.g. QPSK demodulation analog front ends or means for connecting modulators, demodulators or transceivers to a transmission line H04L27/0002

Abstract

An Advanced Television Standards Committee (ATSC)-compliant pilot tone is generated within an 8-VSB (eight level vestigial sideband) transmission in order to enable Quadrature Amplitude Modulation (QAM) receiver designs to more efficiently process the transmitted/received 8-VSB signal. The method and apparatus also efficiently removes the pilot tone before using conventional QAM demodulator equipment for directly demodulating the 8-VSB signal.

Claims

1. A method of generating a pilot tone within an N-VSB (vestigial sideband) transmission that enables an M-QAM (quadrature amplitude modulation) receiver to efficiently process a received N-VSB signal, where M=N², comprising the steps of:

generating the pilot tone at a phase of 90+180·

n degrees, where n is any integer, so that a zero-crossing of the pilot tone will coincide with precise symbol decisions in I and Q channels of the M-QAM receiver; and

inserting the generated pilot tone into the N-VSB transmission.

2. A method of removing a pilot tone within an N-VSB (vestigial sideband) modulation signal and converting the N-VSB signal into an M-QAM (quadrature amplitude modulation) signal, where M=N², comprising the steps of:

deriving the pilot tone at the receiver from a wideband overlay signal transmitted with the N-VSB signal;

additively canceling the pilot tone in the N-VSB signal with the derived pilot tone before processing the N-VSB signal;

shifting a symbol rate frequency of the received N-VSB modulation signal to center the waveform spectrum about zero Hertz prior to complex demodulation so that data symbols will alternately appear on the I and Q channel of the complex demodulation process;

removing the pilot tone of the received N-VSB modulation signal to eliminate any bias in both I and Q channels;

offsetting symbol timing between I and Q channels;

quadrature amplitude demodulating the I and Q channels to generate alternating I and Q channel data symbols; and

alternating inversion of the alternating I and Q channel data symbols to recover the N-VSB symbol data.

3. The method of claim 2, wherein N=8, M=64 and the symbol rate of the received N-VSB modulation signal is shifted by ¼

symbol rate.

4. The method of claim 2, further comprising the step of combining the alternating inversion of the I and Q channel data.

5. A digital television receiver for converting an N-VSB (vestigial sideband) modulation signal containing a pilot tone into an M-QAM (quadrature amplitude modulation) signal, where M=N2, comprising:

a first circuit for deriving the pilot tone at the receiver from a wideband overlay signal transmitted with the N-VSB signal;

a second circuit connected to the first circuit for additively canceling the pilot tone in the N-VSB signal with the derived pilot tone before the N-VSB signal is processed;

a third circuit connected to the second circuit for shifting a symbol rate frequency of a received N-VSB modulation signal to center the waveform spectrum about zero Hertz prior to complex demodulation so that data symbols will alternately appear on each of an I and Q channel during the complex demodulation process;

a fourth circuit connected to the third circuit for removing the pilot tone of the received N-VSB modulation signal to eliminate any bias in both of the I and Q channels;

a fifth circuit connected to the fourth circuit for offsetting symbol timing between the I and Q channels;

a quadrature amplitude demodulator connected to the fifth circuit for demodulating the I and Q channels to generate alternating I and Q channel data symbols; and

an inverter circuit connected to the quadrature amplitude demodulator for inverting alternating I and Q channel data symbols to recover the N-VSB symbol data.

6. The digital television receiver recited in claim 5, wherein the first circuit comprises a squarer for generating a spectral line from which the pilot tone is derived.

7. The digital television receiver recited in claim 6, wherein the third circuit includes first and second mixers for receiving an intermediate frequency signal and further includes an in phase and quadrature phase local oscillator signal to generate, respectively, I and Q channel output signals at baseband.

8. The digital television receiver recited in claim 7, wherein the fourth circuit includes in each of said I and Q channels, a pilot signal detector and a subtractor for subtracting a detected pilot signal from respective I and Q channel output signals.

9. The digital television receiver recited in claim 8, wherein the fifth circuit comprises a first delay.

10. The digital television receiver recited in claim 9, further comprising a sign generator and a symbol clock generator responsive to one of said pilot signal detectors and a second delay responsive to a symbol clock from the symbol clock generator to delay a sign output signal of the sign generator.

11. The digital television receiver recited in claim 10, wherein the quadrature amplitude demodulator is adapted to demodulate signals in the I and Q channels in response to the symbol clock generator and the inverter is responsive to the delayed sign output signal to generate I and Q output signals.

12. The digital television receiver recited in claim 11, further comprising a multiplexer responsive to the symbol clock for combining the I and Q output signals of the inverter to recover the N-VSB symbol data.

13. The digital television receiver recited in claim 12, wherein N=8 and M=64.

14. A digital television receiver for converting an N-VSB (vestigial sideband) modulation signal containing a pilot tone into an M-QAM (quadrature amplitude modulation) signal, where M=N2, comprising:

a first circuit for deriving the pilot tone at the receiver from a wideband overlay signal transmitted with the N-VSB signal;

a second circuit connected to the first circuit for additively canceling the pilot tone in the N-VSB signal with the derived pilot tone before the N-VSB signal is processed;

a third circuit connected to the second circuit for shifting a symbol rate frequency of a received N-VSB modulation signal to center the waveform spectrum about zero Hertz prior to complex demodulation so that data symbols will alternately appear on each of an I and Q channel during the complex demodulation process;

a fourth circuit connected to the third circuit for removing the pilot tone of the received N-VSB modulation signal to eliminate any bias in both of the I and Q channels;

a delay circuit connected to the fourth circuit for offsetting symbol timing between the I and Q channels;

a quadrature amplitude demodulator connected to the delay circuit demodulating the I and Q channels to generate alternating I and Q channel data symbols;

an inverter circuit connected to the quadrature amplitude demodulator for inverting alternating I and Q channel data symbols to recover the N-VSB symbol data; and

a multiplexer connected to the inverter circuit and responsive to a symbol clock for combining the I and Q output signals of the inverter circuit to recover the N-VSB symbol data.