Kalman Filter For Phase Noise Tracking

• US 20160266186A1
• Filed: 03/12/2015
• Published: 09/15/2016
• Est. Priority Date: 03/12/2015
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Mansour, Mohamed
• Granted Patent: US 10,527,663 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 29/26 Measuring noise figure; Measuring signal-to-noise ratio
• CPC Class Codes: H04B 17/354 Adjacent channel leakage power

Abstract

A forward-backward Kalman filter for estimating phase noise present in a received signal. Both the forward and backward Kalman filters use hard-decision measurements of the received symbols. The phase noise estimate from the forward Kalman filter is used as a coarse phase noise estimate for the backward Kalman filter and vice versa. The final phase noise estimate is an optimal combination of the forward phase noise estimate and backward phase noise estimate.

Claims

1. A phase noise estimation system for estimating phase noise in a received signal, the system comprising:

a hard-decision decoder operable to receive a transmitted symbol and to generate a hard decision regarding the value of the transmitted symbol; and

a forward Kalman filter comprising;

a state transition module operable to generate a forward estimate of the phase noise present in the received signal at a time t based on a forward estimate of the phase noise present in the received signal at a prior time t−

1; and

a measurement module operable to update the forward estimate of the phase noise based on a value of the received symbol and the hard decision generated by the hard decision decoder.

2. The phase noise estimation system of claim 1 wherein the received signal includes known pilot symbols placed in the signal at predetermined intervals, and wherein the phase noise estimation system further comprises a pilot symbol phase-noise estimator operable to estimate the phase noise present at a received pilot symbol and to generate an initial coarse estimate of the phase noise present in the received signal based on the phase noise estimated at one or more pilot symbols, and wherein the forward Kalman filter is operable to generate a forward estimate of the difference between the coarse estimate of the phase noise and the actual phase noise present in the received signal.

3. The phase noise estimation system of claim 2 wherein the forward Kalman filter is operable to add the coarse estimate and the forward estimate of the difference between the coarse estimate and the actual phase noise to generate the forward estimate of the phase noise present in the received signal.

4. The phase noise estimation system of claim 1 wherein the forward Kalman filter is operable to update the forward phase noise estimate at time t based on the prior forward phase noise estimate at time t−

1 and the hard decision generated by the hard decision decoder at time t.

5. The phase noise estimation system of claim 1 wherein the measurement module is operable to update the forward estimate of the phase noise based on the value of the received signal, the hard decision generated by the hard decision decoder, and further based on a measurement variance.

6. The phase noise estimation system of claim 1, further comprising a demodulator operable to receive a transmitted symbol, demodulate said received symbol using a current coarse estimate of the phase noise, and provide the demodulated symbol to the hard decision decoder.

7. The phase noise estimation system of claim 6 wherein the hard decision decoder is operable to determine the distances from the demodulated symbol to a plurality of symbol constellation points, and wherein the hard decision is generated based on said distances and on a current estimate of the phase noise.

8. The phase noise estimation system of claim 7 wherein the hard decision decoder is operable to generate a measurement variance value for the real and imaginary components of each hard decision symbol corresponding to the distance between the generated hard decision and the demodulated symbol and the amplitude of the imaginary and real components of the hard-decision symbols, and to provide said measurement variance value to the measurement module.

9. The phase noise estimation system of claim 8 wherein the hard decision decoder is operable to provide a plurality of the symbol constellation points to the measurement module along with a measurement variance value corresponding to each symbol constellation point.

10. The phase noise estimation system of claim 1, further comprising a backward Kalman filter comprising:

a state transition module operable to generate a backward estimate of the phase noise present in the received signal at a time t−

1 based on a backward estimate of the phase noise present in the received signal at a subsequent time t; and

a measurement module operable to update the backward estimate of the phase noise based on a value of a received symbol and a hard decision generated by the hard decision decoder.

11. The phase noise estimation system of claim 10 wherein the forward Kalman filter uses a backward phase noise estimate generated by a previous iteration of the backward Kalman filter as a coarse phase noise estimate, and wherein the backward Kalman filter uses a forward phase noise estimate generated by a current iteration of the forward Kalman filter as a coarse phase noise estimate.

12. The phase noise estimation system of claim 10, further comprising a phase noise estimate module operable to generate an overall phase noise estimate based on the forward phase noise estimate and the backward phase noise estimate.

13. The phase noise estimation system of claim 12 wherein the forward Kalman filter is operable to generate a forward estimate variance value and the backward Kalman filter is operable to generate a backward estimate variance value, and wherein the phase noise estimate module is operable to calculate the overall phase noise estimate based on the forward phase noise estimate, the forward variance value, the backward phase noise estimate, and the backward variance value.

14. The phase noise estimation system of claim 10 wherein the forward Kalman filter and the backward Kalman filter operate between two successive pilot symbols, and wherein the forward Kalman filter moves in the forward direction between successive pilot symbols and the backward Kalman filter moves in the backward direction between successive pilot symbols.

15. A method of estimating the phase noise present in a received signal, comprising:

receiving a transmitted signal;

generating a hard decision regarding a transmitted value of a symbol in the received signal;

generating a forward estimate of the phase noise present in the received signal at a time t based on a forward estimate of the phase noise present in the received signal at a prior time t−

1; and

updating the forward estimate of the phase noise based on a value of the received symbol and the hard decision.

16. The method of claim 15, further comprising:

determining a coarse estimate of the phase noise present in the received signal;

wherein generating a forward estimate of the phase noise comprises generating a forward estimate of a difference between the coarse estimate of the phase noise and the actual phase noise present in the received signal at a time t based on a forward estimate of the difference between the coarse estimate of the phase noise and the actual phase noise present in the received signal at a prior time t−

1;

and wherein updating the forward estimate of the phase noise comprises updating the forward estimate of the difference between the coarse estimate of the phase noise and the actual phase noise based on the value of the received symbol and the hard decision.

17. The method of claim 16 wherein the received signal includes pilot symbols placed in the signal at predetermined intervals, the pilot symbols being of a predetermined known value, the method further comprising:

determining the phase noise present at a pilot symbol in the received signal; and

determining an intial coarse estimate of the phase noise present at a non-pilot symbol in the received signal based on the phase noise present at the pilot symbol.

18. The method of claim 17, further comprising adding the coarse estimate and the forward estimate of the difference between the coarse estimate and the actual phase noise to generate a forward estimate of the phase noise present in the received signal.

19. The method of claim 15, further comprising demodulating said received signal using a current coarse estimate of the phase noise and provide the demodulated signal to the hard decision decoder.

20. The method of claim 15 wherein said generating a hard decision comprises determining the distances from the received symbol to a plurality of symbol constellation points, and wherein the hard decision is generated based on said distances and on a current estimate of the phase noise.

21. The method of claim 20 wherein said generating a hard decision comprises generating a measurement variance value corresponding to the generated hard decision and wherein said updating the forward estimate comprises updating the forward estimate of the phase noise based on a value of the received symbol, the hard decision, and the measurement variance value.

22. The method of claim 20 wherein said generating a hard decision comprises generating a plurality of the symbol constellation points along with a measurement variance value corresponding to each symbol constellation point, and wherein said updating the forward estimate comprises updating the forward estimate of the phase noise based on a value of the received symbol, the plurality of symbol constellation points, and the measurement variance values corresponding to each symbol constellation point.

23. The method of claim 15, further comprising:

generating a backward estimate of the phase noise present in the received signal at a time t−

1 based on an estimate of the phase noise present in the received signal at a subsequent time t; and

updating the backward estimate of the phase noise based on a value of a received symbol and the hard decision regarding the transmitted value of the symbol.

24. The method of claim 23 wherein said generating a forward estimate of the phase noise and said updating the forward estimate of the phase noise are performed iteratively to generate an iteratively updated forward estimate of the phase noise present in the received signal, and wherein said generating a backward estimate of the phase noise and said updating the backward estimate of the phase noise are performed iteratively to generate an iteratively updated backward estimate of the phase noise present in the received signal.

25. The method of claim 24 wherein a backward estimate of the phase noise present in the received signal at a prior time t−

1 is used as a coarse estimate in generating a forward estimate of the phase noise present in the received signal at a time t, and wherein a forward estimate of the phase noise present in the received signal at a time t is used as a coarse estimate in generating a backward estimate of the phase noise at said time t.

26. The method of claim 23, further comprising generating an overall phase noise estimate based on the forward phase noise estimate and the backward phase noise estimate.

27. The phase noise estimation system of claim 26 further comprising generating a forward estimate variance value and a backward estimate variance value, and wherein generating the overall phase noise estimate comprises calculating the overall phase noise estimate based on the forward phase noise estimate, the forward variance value, the backward phase noise estimate, and the backward variance value.