Implementation of N-VSB training sequences in N-squared QAM receiver structures

• US 6,459,741 B1
• Filed: 10/21/1999
• Issued: 10/01/2002
• Est. Priority Date: 10/21/1999
• Status: Expired due to Term

• Current Assignee: NBC Universal Media LLC (Comcast Corporation)
• Original Assignee: General Electric Company
• Inventors: Hershey, John Erik, Grabb, Mark Lewis, Welles, Kenneth Brakeley II
• Primary Examiner(s): Vo, Don N.
• Application Number:
  US09/422,450
• Time in Patent Office: 1,076 Days
• Field of Search: 375/261, 375/270, 375/298, 375/301, 375/321, 329/304, 329/306, 329/357, 332/103, 332/170
• 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: H04L 27/34 Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
• 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

Training sequences designed for N-VSB systems within the embodiment of an N-squared QAM receiver facilitate designing 8-VSB receivers using methodologies of 64-QAM receiver design. A receiver designed using such methodologies converts the received modulation into a signal which can be accepted by circuitry for decoding 64 level quadrature-amplitude modulation (64-QAM) signals. This process provides a better signal to noise ratio reception than the conventional I-channel only decoding circuitry of most 8-VSB receivers. This process also employs training and equalizing algorithms developed for 64-QAM receivers which are superior to equivalent algorithms for 8-VSB receivers. The invention can be generalized to N-VSB conversion into M-QAM where M=N². Adaptive equalization algorithms for 8-VSB transmissions implemented within the context of the 64 QAM receiver are superior to present single-channel VSP processing receivers. Present 64 QAM equalization strategies can be employed when receiving an 8-VSB waveform, given removal of the pilot tone and time offset, except when employing a training sequence. Modifications to the 8-VSB training sequence specification are employed for operation within a 64 QAM receiver design.

Claims

1. A method of using training sequences designed for an N-VSB (vestigial sideband) modulation signal in which the N-VSB modulation signal is converted into an M-QAM (quadrature amplitude modulation) signal, where M=N², comprising the steps of:

parsing alternating symbol values of training sequences from the N-VSB modulation signal to generate first and second subsequences;

inverting every other symbol in said first and second subsequences; and

converting the N-VSB modulation signal including the first and second subsequences into an M-QAM signal.

2. The method of using training sequences designed for an N-VSB modulation signal in which the N-VSB modulation signal is converted into an M-QAM signal as recited in claim 1, wherein the step of converting the N-VSB modulation signal comprises the steps of:

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

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

offsetting symbol timing between I and O 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 using training sequences designed for an N-VSB modulation signal in which the N-VSB modulation signal is converted into an M-QAM signal as recited in claim 1, further comprising the step of generating said training sequences with an m-sequence generator.

4. The method of using training sequences designed for an N-VSB modulation signal in which the N-VSB modulation signal is converted into an M-QAM signal as recited in claim 3, wherein the step of generating said training sequences with an m-sequence generator comprises generating first and second subsequences.

5. A receiver for using training sequences designed for an N-VSB (vestigial sideband) modulation signal in which the N-VSB modulation signal is converted into an M-QAM (quadrature amplitude modulation) signal, where M=N², comprising:

means for parsing alternating symbol values of training sequences from the N-VSB modulation signal to generate first and second subsequences;

means for inverting every other symbol in said first and second subsequences; and

means for converting the N-VSB modulation signal including the first and second subsequences into an M-QAM signal.

6. The receiver for using training sequences designed for an N-VSB modulation signal in which the N-VSB modulation signal is converted into an M-QAM signal recited in claim 5, wherein the means for converting the N-VSB modulation signal comprises:

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

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

means for offsetting symbol timing between I and Q channels;

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

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