Phase noise and additive noise estimation in a QAM demodulator

• US 6,249,180 B1
• Filed: 04/17/2000
• Issued: 06/19/2001
• Est. Priority Date: 09/08/1999
• Status: Expired due to Term

• Current Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Hamman, Emmanuel, Maalej, Khaled, Demol, Amaury, Levy, Yannick
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US09/550,885
• Time in Patent Office: 428 Days
• Field of Search: 329/304-310, 375/261, 375/324-329, 375/345-351
• US Class Current: 329/304
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 2027/0032 at baseband and passband
• CPC Class Codes: H04L 2027/0036 using a recovered symbol clock
• CPC Class Codes: H04L 2027/0038 using an equaliser
• CPC Class Codes: H04L 2027/0055 single phase
• CPC Class Codes: H04L 2027/0057 quadrature phase
• CPC Class Codes: H04L 2027/0071 Control of loops
• CPC Class Codes: H04L 2027/0081 between loops of different bandwidths
• CPC Class Codes: H04L 27/3809 Amplitude regulation arrangements
• CPC Class Codes: H04L 27/3827 in which the carrier is recovered using only the demodulated baseband signals
• CPC Class Codes: H04L 27/3872 Compensation for phase rotation in the demodulated signal
• CPC Class Codes: H04L 7/0029 interpolation of received data signal

Abstract

A QAM demodulator having a carrier recovery circuit that includes a phase estimation circuit and an additive noise estimation circuit which produces an estimation of the residual phase noise and additive noise viewed by the QAM demodulator. The phase noise estimation is based on the least mean square error between the QAM symbol decided by a symbol decision circuit and the received QAM symbol. The additive noise estimation is based on the same error as in the phase noise estimation, except that it is based only on QAM symbols having the minimum amplitude on the I and Q coordinates. The additive noise estimation is not dependent on the phase of the signal, thus, is independent of the phase noise estimator.

Claims

1. A quadrature amplitude modulation (QAM) type demodulator comprising:

an analog-to-digital converter receiving an input signal and producing a first signal,

a baseband conversion circuit being electrically coupled to the analog-to-digital converter and receiving the first signal and producing a baseband signal,

a carrier recovery circuit being electrically coupled to the baseband conversion circuit and receiving the baseband signal and producing a QAM signal, the carrier recovery circuit including a phase noise estimation circuit and an additive noise estimation circuit, and

a symbol decision circuit being electrically coupled to the carrier recovery circuit and receiving the QAM signal,

whereby an output signal of the symbol detection circuit is a demodulated data output signal.

2. A demodulator, as in claim 1, wherein the phase noise estimation circuit produces a phase noise estimated signal based on a first least mean square error and wherein the additive noise estimation circuit produces an additive noise estimated signal based on a second least mean square error.

3. A demodulator, as in claim 2, wherein the first and second least mean square error signals are defined as a difference between a point in I/Q coordinates of the received QAM signal and a point in I/Q coordinates of a decided QAM signal, the decided QAM signal being determined by the symbol decision circuit.

4. A demodulator, as in claim 2, wherein the first least mean square error is based on a set of QAM symbols having a maximum amplitude on I and Q coordinates and a set of QAM symbols having a same amplitude on I and Q coordinates.

5. A demodulator, as in claim 2, wherein the second least mean square error is based on a set of QAM symbols having a minimum amplitude on I and Q coordinates.

6. A demodulator, as in claim 2, wherein the phase noise estimated signal is independent of the additive noise estimated signal.

7. A demodulator, as in claim 1, further including a receive filter electrically coupled to an output of the baseband conversion circuit and to an input of the carrier recovery circuit.

8. A quadrature amplitude modulation (QAM) type demodulator comprising:

an analog-to-digital converter receiving an input signal and producing a first signal,

a baseband conversion circuit being electrically coupled to the analog-to-digital converter and receiving the first signal and producing a baseband signal,

a carrier recovery circuit being electrically coupled to the baseband conversion circuit and receiving the baseband signal and producing a QAM signal, the carrier recovery circuit including a phase noise estimation circuit and an additive noise estimation circuit, the phase noise estimation circuit producing a phase noise estimated signal based on a first least mean square error, the additive noise estimation circuit producing an additive noise estimated signal based on a second least mean square error, wherein the phase noise estimated signal is independent of the additive noise estimated signal, and

a symbol decision circuit being electrically coupled to the carrier recovery circuit and receiving the QAM signal,

whereby an output signal of the symbol detection circuit is a demodulated data output signal.

9. A demodulator, as in claim 8, wherein the first and second least mean square error signals are defined as a difference between a point in I/Q coordinates of the received QAM signal and a point in I/Q coordinates of a decided QAM signal, the decided QAM signal being determined by the symbol decision circuit.

10. A demodulator, as in claim 8, wherein the first least mean square error is based on a set of QAM symbols having a maximum amplitude on I and Q coordinates and a set of QAM symbols having a same amplitude on I and Q coordinates.

11. A demodulator, as in claim 8, wherein the second least mean square error is based on a set of QAM symbols having a minimum amplitude on I and Q coordinates.

12. A demodulator, as in claim 8, further including a receive filter electrically coupled between the baseband conversion circuit and the carrier recovery circuit.

13. A quadrature amplitude modulation (QAM) type demodulator comprising:

an analog-to-digital converter receiving an input signal and producing a first signal,

a baseband conversion circuit being electrically coupled to the analog-to-digital converter and receiving the first signal and producing a baseband signal,

a carrier recovery circuit being electrically coupled to the baseband conversion circuit and receiving the baseband signal and producing a QAM signal, the carrier recovery circuit including a phase noise estimation circuit and an additive noise estimation circuit, the phase noise estimation circuit producing a phase noise estimated signal based on a first least mean square error, the additive noise estimation circuit producing an additive noise estimated signal based on a second least mean square error, wherein the phase noise estimated signal is independent of the additive noise estimated signal, and wherein the first and second least mean square error signals are defined as a difference between a point in I/Q coordinates of the received QAM signal and a point in I/Q coordinates of a decided QAM signal, the decided QAM signal being determined by the symbol decision circuit, and

a symbol decision circuit being electrically coupled to the carrier recovery circuit and receiving the QAM signal after filtering,

whereby an output signal of the symbol detection circuit is a demodulated data output signal.

14. A demodulator, as in claim 13, wherein the first least mean square error is based on a set of QAM symbols having a maximum amplitude on I and Q coordinates and a set of QAM symbols having a same amplitude on I and Q coordinates.

15. A demodulator, as in claim 13, wherein the second least mean square error is based on a set of QAM symbols having a minimum amplitude on I and Q coordinates.