DETERMINING A RESPONSE OF A RAPIDLY VARYING OFDM COMMUNICATION CHANNEL USING AN OBSERVATION SCALAR

• US 20120114053A1
• Filed: 10/29/2011
• Published: 05/10/2012
• Est. Priority Date: 10/15/2008
• Status: Active Grant

• Current Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV), STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: KARTHIK, Muralidhar, VLANTIS, George A.
• Granted Patent: US 9,130,788 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/0224 using sounding signals
• CPC Class Codes: H04L 25/03821 Inter-carrier interference cancellation [ICI]
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems

Abstract

In an embodiment, a channel estimator includes first and second stages. The first stage is configurable to generate an observation scalar for a communication path of a communication channel, and the second stage is configurable to generate channel-estimation coefficients in response to the first observation scalar. For example, such a channel estimator may use a recursive algorithm, such as a VSSO Kalman algorithm, to estimate the response of a channel over which propagates an OFDM signal that suffers from ICI due to Doppler spread. Such a channel estimator may estimate the channel response more accurately, more efficiently, with a less-complex algorithm, and with less-complex software or circuitry, than conventional channel estimators. Furthermore, such a channel estimator may be able to dynamically account for changes in the number of communication paths that compose the channel, changes in the delays of these paths, and changes in the signal-energy levels of these paths.

Claims

1. A channel estimator, comprising:

a first stage configurable to generate a first observation scalar for a first communication path of a communication channel; and

a second stage configurable to generate channel estimation coefficients in response to the first observation scalar.

2. The channel estimator of claim 1 wherein the first stage is configurable:

to receive a signal having a pilot subcarrier; and

to generate the first observation scalar in response to information carried by the pilot subcarrier.

3. The channel estimator of claim 1 wherein the channel estimation coefficients include a multi dimensional array of frequency-domain channel estimation coefficients for the communication channel.

4. The channel estimator of claim 1, further including:

a third stage configurable to generate a second observation scalar for a second communication path of the communication channel; and

wherein the second stage is configurable to generate the channel estimation coefficients in response to the second observation scalar.

5. The channel estimator of claim 1, further comprising:

a third stage configurable to generate path estimation coefficients for the first communications path in response to the first observation scalar; and

wherein the second stage is configurable to generate the channel-estimation coefficients in response to the path-estimation coefficients.

6. The channel estimator of claim 5 wherein:

the path estimation coefficients comprise time domain coefficients; and

the channel estimation coefficients comprise frequency domain coefficients.

7. The channel estimator of claim 1, further including:

a third stage configurable to generate a second observation scalar for a second communication path of the communication channel;

a fourth stage configurable to generate first path estimation coefficients in response to the first observation scalar;

a fifth stage configurable to generate second path-estimation coefficients in response to the second observation scalar; and

wherein the second stage is configurable to generate the channel estimation coefficients in response to the first and second path estimation coefficients.

8. The channel estimator of claim 1, further including:

a Kalman filter configurable to generate in response to the first observation scalar intermediate coefficients;

a third stage configurable to generate path estimation coefficients in response to the intermediate coefficients; and

wherein the second stage is configurable to generate the channel estimation coefficients in response to the intermediate coefficients.

9. The channel estimator of claim 1, further including:

a first Kalman filter configurable to generate in response to the first observation scalar first intermediate coefficients;

a third stage configurable to generate first path estimation coefficients in response to the first intermediate coefficients;

a fourth stage configurable to generate a second observation scalar for a second communication path of the communication channel;

a second Kalman filter configurable to generate in response to the second observation scalar second intermediate coefficients;

a fifth stage configurable to generate second path estimation coefficients in response to the second intermediate coefficients; and

wherein the second stage is configurable to generate the channel estimation coefficients in response to the first and second path estimation coefficients.

10. A receiver, comprising:

a channel estimator, including;

a first stage configurable to generate an observation scalar for a communication path of a communication channel; and

a second stage configurable to generate channel estimation coefficients in response to the observation scalar.

11. The receiver of claim 10, further comprising:

an antenna configurable to receive an orthogonal frequency divisional multiplexed signal over the communication channel; and

wherein the first stage of the channel estimator is configurable to generate the observation scalar in response to the received signal.

12. The receiver of claim 10, further comprising:

a transform unit operable to convert an orthogonal frequency divisional multiplexed signal from the communication channel into frequency domain coefficients; and

wherein the first stage of the channel estimator is operable to generate the observation scalar in response to the frequency domain coefficients.

13. The receiver of claim 10, further comprising a data recovery unit configurable to recover data carried by an orthogonal frequency divisional multiplexed signal from the communication channel in response to the channel estimation coefficients.

14. The receiver of claim 10, further comprising:

a data recovery unit configurable to recover coded data carried by an orthogonal frequency divisional multiplexed signal from the communication channel in response to the channel estimation coefficients; and

a decoder operable to decode the recovered coded data.

15. The receiver of claim 10, further comprising a controller configurable to control at least one function of the channel estimator.

16. The receiver of claim 10, further comprising a controller configurable to implement the channel estimator.

17. A communication unit, comprising:

a receiver configurable to receive a first orthogonal frequency division multiplexed signal from a communication channel having a communication path, the receiver including;

a channel estimator, including;

a first stage configurable to generate from the first signal an observation scalar for the communication path; and

a second stage configurable to generate channel estimation coefficients in response to the observation scalar; and

a transmitter configurable to transmit a second orthogonal frequency division multiplexed signal.

18. The communication unit of claim 17, further comprising an antenna configurable:

to provide the first signal to the receiver; and

to receive the second signal from the transmitter.

19. A system, comprising:

a first communication unit, including;

a first receiver configurable to receive a first orthogonal frequency division multiplexed signal from a communication channel having a communication path, the receiver including;

a channel estimator, including;

a first stage configurable to generate from the first signal an observation scalar for the communication path; and

a second stage configurable to generate channel estimation coefficients in response to the observation scalar; and

a first transmitter configurable to transmit a second orthogonal frequency division multiplexed signal; and

a second communication unit, including;

a second receiver configurable to receive the second signal from the first transmitter; and

a second transmitter configurable to transmit the first signal to the first receiver.

20. A computer-readable medium storing instructions that when executed by a computing apparatus cause the apparatus:

to generate an observation scalar for a communication path of a communication channel; and

to generate channel estimation coefficients in response to the observation scalar.

21. A method, comprising:

receiving a signal over a communication channel having a number of communication paths;

generating in response to the signal a first observation scalar for a first one of the communication paths; and

estimating channel coefficients in response to the first observation scalar.

22. The method of claim 21 wherein receiving the signal comprises receiving an orthogonal-frequency-division-multiplexed signal that is experiencing Doppler spread.

23. The method of claim 21 wherein receiving the signal comprises receiving the signal at a destination that is moving relative to a source of the signal.

24. The method of claim 21 wherein receiving the signal comprises receiving the signal from a source that is moving relative to a destination at which the signal is being received.

25. The method of claim 21 wherein the number of communication paths equals one.

26. The method of claim 21 wherein the number of communication paths is greater than one.

27. The method of claim 21 wherein:

receiving the signal comprises receive a number of pilot subcarriers of the signal; and

generating the first observation scalar comprises generating the first observation scalar in response to information carried by the number of pilot subcarriers.

28. The method of claim 21, further comprising:

generating in response to the signal a second observation scalar for a second one of the communication paths; and

estimating the channel coefficients in response to the second observation scalar.

29. The method of claim 21 wherein estimating the channel coefficients comprises:

estimating path coefficients for the first path in response to the first observation scalar; and

estimating the channel coefficients in response to the path coefficients.

30. The method of claim 21 wherein estimating the channel coefficients comprises estimating the channel coefficients in response to a Kalman algorithm that is responsive to the observation scalar.