Apparatus and method of eliminating vestigial sideband pilot tone in vestigial sideband/quadrature amplitude modulation system

• US 6,944,241 B1
• Filed: 08/24/2000
• Issued: 09/13/2005
• Est. Priority Date: 08/24/1999
• Status: Expired due to Fees

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Oh, Ji-sung
• Primary Examiner(s): Bocure, Tesfaldet
• Assistant Examiner(s): Tran, Khanh
• Application Number:
  US09/644,540
• Time in Patent Office: 1,846 Days
• Field of Search: 455/47, 455/109, 455202-204, 375/316, 375/320, 375/229, 375/232, 375/235, 375/231, 375/270, 375/261, 375/277, 375/285, 375/298, 375/301, 375/321, 375/327, 375/326, 375/346, 375/324, 375/350, 375/365, 375/325, 375/344, 375/355, 375/343, 348/500, 348/513, 348/512, 348/521, 348/725, 348/726, 329/304, 329/306, 329/307, 329/357, 708/300, 708/323, 708/425
• US Class Current: 375/321
• CPC Class Codes: H04L 27/06 Demodulator circuits; Receiver circuits

Abstract

An apparatus and method for eliminating a vestigial sideband (VSB) pilot tone in a vestigial sideband/quadrature amplitude modulation (VSB/QAM) receiving system, is provided. This apparatus eliminates a vestigial sideband (VSB) pilot tone in a vestigial sideband/quadrature amplitude modulation (VSB/QAM) shared receiving system including a VSB/QAM shared modulator for demodulating a received VSB signal and outputting I-axis VSB symbols and Q-axis VSB symbols. This apparatus includes an I-axis pilot tone eliminating unit for dividing the I-axis VSB symbols into a plurality of groups according to the sign of a pilot tone which remains in each symbol, obtaining the size of a pilot tone by calculating the average of VSB symbols in each group, and eliminating a pilot tone by adding the size of a pilot tone to or subtracting it from the I-axis VSB symbols, and a Q-axis pilot tone eliminating unit for dividing the Q-axis VSB symbols into a plurality of groups according to the sign of a pilot tone which remains in each symbol, obtaining the size of a pilot tone by calculating the average of VSB symbols in each group, and eliminating a pilot tone by adding the size of a pilot tone to or subtracting it from the Q-axis VSB symbols. In a VSB/QAM shared receiver, a VSB signal is demodulated in synchronization with the center frequency of a VSB signal, similar to a QAM signal, in the VSB/QAM shared receiver, so that a pilot tone signal component, which, in the prior art, remained in VSB symbol values even after demodulation, can be completely eliminated.

Claims

1. An apparatus for eliminating a vestigial sideband (VSB) pilot tone in a vestigial sideband/quadrature amplitude modulation (VSB/QAM) shared receiving system including a VSB/QAM shared demodulator for demodulating a received VSB signal and outputting I-axis VSB symbols and Q-axis VSB symbols, the apparatus comprising:

an I-axis pilot tone eliminating unit for dividing the I-axis VSB symbols into a first plurality of groups according to the sign of an I-axis pilot tone which remains in each symbol, obtaining the value of the I-axis pilot tone by calculating the average of VSB symbols in each of the first plurality of groups, and eliminating the I-axis pilot tone by adding the value of the I-axis pilot tone to or subtracting the value of the I-axis pilot tone from the I-axis VSB symbols; and

a Q-axis pilot tone eliminating unit for dividing the Q-axis VSB symbols into a second plurality of groups according to the sign of a Q-axis pilot tone which remains in each symbol, obtaining the value of the Q-axis pilot tone by calculating the average of VSB symbols in each of the second plurality of groups, and eliminating the Q-axis pilot tone by adding the value of the Q-axis pilot tone to or subtracting the value of the Q-axis pilot tone from the Q-axis VSB symbols.

2. The apparatus of claim 1, wherein the I-axis pilot tone eliminating unit comprises:

a first switch unit dividing the I-axis VSB symbols output by the VSB/QAM shared demodulator into two groups according to the sign of the I-axis pilot tone which remains in each of the I-axis VSB symbols;

first and second average arithmetic units for calculating the average of I-axis VSB symbols in each group divided by the first switch unit to extract the direct current (DC) value of the I-axis pilot tone which remains in the I-axis VSB symbols of each group;

a first adder for adding the DC value of a first pilot tone extracted by the first average arithmetic unit to the DC of a second pilot tone extracted by the second average arithmetic unit to output a third pilot tone;

a divider for dividing the DC value of the third pilot tone, which is output by the first adder, by 2 to output the DC value of the I-axis pilot tone which remains in a VSB symbol;

second and third adders for adding the DC value of the I-axis pilot tone, which is the output of the divider, to or subtracting the I-axis pilot tone from each of the I-axis symbols of each group classified by the first switch unit, to eliminate the I-axis pilot tone, and

a second switch unit for outputting I-axis VSB symbols form which the I-axis pilot tone output by each of the second and third adders has been removed, in one bitstream.

3. The apparatus of claim 1, wherein the Q-axis pilot tone eliminating unit comprises:

a first switch unit for dividing the Q-axis VSB symbols output by the VSB/QAM shared demodulator into two groups according to the sign of the Q-axis pilot tone which remains in each of the Q-axis symbols;

first and second average arithmetic units for calculating the average of Q-axis VSB symbols in each group divided by the first switch unit to extract the direct current (DC) value of the Q-axis pilot tone which remains in the Q-axis VSB symbols of each group;

a first adder for adding the DC value of a first pilot tone extracted by the first average arithmetic unit to the DC value of a second pilot tone extracted by the second average arithmetic unit to output a third pilot tone;

a divider for dividing the DC value of the third pilot tone, which is output by the first adder, by 2 to output the DC value of the Q-axis pilot tone which remains in a VSB symbol;

second and third adders for adding the DC value of the Q-axis pilot tone, which is the output of the divider, to or subtracting the Q-axis pilot tone from each of the Q-axis VSB symbols of each group classified by the first switch unit, to eliminate the Q-axis pilot tone; and

a second switch unit for outputting Q-axis VSB symbols from which the Q-axis pilot tone output by each of the second and third adders has been removed, in one bitstream.

4. A method of eliminating a vestigial sideband (VSB) pilot tone in a vestigial sideband/quadrature amplitude modulation (VSB/QAM) shared receiving system including a VSB/QAM shared demodulator for demodulating a received VSB signal and outputting I-axis VSB symbols and Q-axis VSB symbols, the method-comprising:

(a) classifying the I-axis and Q-axis VSB symbols into a plurality of groups;

(b) obtaining the DC value of a pilot tone which remains in each VSB symbol, by calculating the average of VSB symbols in each of the divided groups; and

(c) eliminating a pilot tone by adding the calculated pilot tone DC value to or subtracting the calculated pilot tone DC value from the I-axis and Q-axis VSB symbols.

5. The method of claim 4, wherein in the step (a), the I-axis VSB symbols and the Q-axis VSB symbols demodulated by the VSB/QAM shared demodulator are each classified in two groups according to the sign of the pilot tone which remains in the VSB symbols.