Channel Estimation In OFDM Communication Systems

• US 20180013591A1
• Filed: 07/06/2017
• Published: 01/11/2018
• Est. Priority Date: 07/07/2016
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Shafiee, Hamid, Pourkhaatoun, Mohsen, Gowda, Kiran, Shetty, Siddharth, Heidari, Esmael, Fard, Ali, Bagheri, Rahim, Djafari, Masoud
• Granted Patent: US 10,805,117 B2
• Time in Patent Office: Days
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0212 of impulse response
• CPC Class Codes: H04L 25/0216 with estimation of channel length
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/03019 adaptive, i.e. capable of adjustment during data reception
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 27/26526 with inverse FFT [IFFT] or inverse DFT [IDFT] demodulators, e.g. standard single-carrier frequency-division multiple access [SC-FDMA] receiver or DFT spread orthogonal frequency division multiplexing [DFT-SOFDM]

Abstract

Embodiments of the present disclosure include an OFDM receiver circuit, which includes an FFT circuit configured to calculate an FFT of a plurality of sample values received by the receiver circuit, and a smoothing circuit configured to identify equalizer coefficients for the sample values by truncating portions of an impulse response of the FFT.

Claims

1. An OFDM receiver circuit, comprising:

a Fast Fourier Transform (FFT) circuit configured to calculate an FFT of a plurality of sample values received by the receiver circuit; and

a smoothing circuit configured to identify equalizer coefficients for the sample values by truncating portions of an impulse response of the FFT.

2. The OFDM receiver circuit of claim 1, wherein the smoothing circuit is further configured to identify the equalizer coefficients by truncating portions of the impulse response of the FFT beyond a defined length of the impulse response.

3. The OFDM receiver circuit of claim 1, wherein the smoothing circuit is further configured to identify the equalizer coefficients by performing an inverse FFT on channel frequency response of the plurality of sample values, truncating portions of the impulse response in results of the inverse FFT, and performing an FFT on results of the truncation.

4. The OFDM receiver circuit of claim 1, wherein the smoothing circuit is further configured to:

estimate a value of a null sub-carrier in a channel frequency response of the plurality of sample values;

perform an inverse FFT on channel frequency response of the plurality of sample values with the estimated value of the null-subcarrier;

truncate portions of the impulse response in results of the inverse FFT; and

perform an FFT on results of the truncation.

5. The OFDM receiver circuit of claim 1, wherein the smoothing circuit is further configured to:

estimate a value of a null sub-carrier in a channel frequency response of the plurality of sample values;

perform an inverse FFT on channel frequency response of the plurality of sample values with the estimated value of the null-subcarrier;

truncate portions of the impulse response in results of the inverse FFT;

perform an FFT on results of the truncation;

evaluate whether results of the truncation have converged; and

based on whether results of the truncation have converged, determine whether to repeat performance of the inverse FFT, truncation, and performance of the FFT.

6. The OFDM receiver circuit of claim 1, wherein the smoothing circuit is further configured to:

estimate a value of a null sub-carrier in a channel frequency response of the plurality of sample values;

perform an inverse FFT on channel frequency response of the plurality of sample values with the estimated value of the null-subcarrier;

truncate portions of the impulse response in results of the inverse FFT;

perform an FFT on results of the truncation;

based on a determination that results of the truncation have not converged, repeat performance of the inverse FFT, truncation, and performance of the FFT using the channel frequency response of the plurality of sample values and a value of the null sub-carrier resulting from previous performance of the inverse FFT, truncation, and performance of the FFT.

7. The OFDM receiver circuit of claim 1, wherein the smoothing circuit is further configured to truncate portions of the impulse response by applying a least-square estimation matrix operation to the impulse response of the FFT

8. The OFDM receiver circuit of claim 1, wherein the smoothing circuit is further configured to truncate portions of the impulse response by finding a channel impulse response as the least-square solution to an over-determined set of linear equations.

9. The OFDM receiver circuit of claim 1, wherein the smoothing circuit is further configured to perform an inverse FFT and truncate portions of the impulse response by applying the impulse response of the plurality of samples to a matrix operation dimensionally dependent upon expected channel response without null-subcarriers and including an inverse Fourier transform matrix.

10. The OFDM receiver circuit of claim 1, wherein the smoothing circuit is further configured to estimate a value of a null sub-carrier in a channel frequency response of the plurality of sample values by applying a least-square estimation matrix operation to the impulse response of the FFT.

12. The system of claim 10, wherein the smoothing circuit is further configured to identify the equalizer coefficients by truncating portions of the impulse response of the FFT beyond a defined length of the impulse response.

13. The system of claim 10, wherein the smoothing circuit is further configured to identify the equalizer coefficients by performing an inverse FFT on channel frequency response of the plurality of sample values, truncating portions of the impulse response in results of the inverse FFT, and performing an FFT on results of the truncation.

14. The system of claim 10, wherein the smoothing circuit is further configured to:

estimate a value of a null sub-carrier in a channel frequency response of the plurality of sample values;

perform an inverse FFT on channel frequency response of the plurality of sample values with the estimated value of the null-subcarrier;

truncate portions of the impulse response in results of the inverse FFT; and

perform an FFT on results of the truncation.

15. The system of claim 10, wherein the smoothing circuit is further configured to:

estimate a value of a null sub-carrier in a channel frequency response of the plurality of sample values;

perform an inverse FFT on channel frequency response of the plurality of sample values with the estimated value of the null-subcarrier;

truncate portions of the impulse response in results of the inverse FFT;

perform an FFT on results of the truncation;

evaluate whether results of the truncation have converged; and

based on whether results of the truncation have converged, determine whether to repeat performance of the inverse FFT, truncation, and performance of the FFT.

16. The system of claim 10, wherein the smoothing circuit is further configured to:

estimate a value of a null sub-carrier in a channel frequency response of the plurality of sample values;

perform an inverse FFT on channel frequency response of the plurality of sample values with the estimated value of the null-subcarrier;

truncate portions of the impulse response in results of the inverse FFT;

perform an FFT on results of the truncation;

based on a determination that results of the truncation have not converged, repeat performance of the inverse FFT, truncation, and performance of the FFT using the channel frequency response of the plurality of sample values and a value of the null sub-carrier resulting from previous performance of the inverse FFT, truncation, and performance of the FFT.

17. The system of claim 10, wherein the smoothing circuit is further configured to truncate portions of the impulse response by applying a least-square estimation matrix operation to the impulse response of the FFT

18. The system of claim 10, wherein the smoothing circuit is further configured to truncate portions of the impulse response by finding a channel impulse response as the least-square solution to an over-determined set of linear equations.

19. The system of claim 10, wherein the smoothing circuit is further configured to perform an inverse FFT and truncate portions of the impulse response by applying the impulse response of the plurality of samples to a matrix operation dimensionally dependent upon expected channel response without null-subcarriers and including an inverse Fourier transform matrix.

20. The system of claim 10, wherein the smoothing circuit is further configured to estimate a value of a null sub-carrier in a channel frequency response of the plurality of sample values by applying a least-square estimation matrix operation to the impulse response of the FFT.

11. A system, comprising:

a Fast Fourier Transform (FFT) circuit configured to calculate an FFT of a plurality of sample values received by the receiver circuit; and

a smoothing circuit configured to identify equalizer coefficients for the sample values by truncating portions of an impulse response of the FFT.