SIGNAL BLANKING FOR IMPROVED FREQUENCY DOMAIN CHANNEL ESTIMATION

• US 20100285738A1
• Filed: 02/18/2010
• Published: 11/11/2010
• Est. Priority Date: 05/11/2009
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Gore, Dhananjay Ashok, Howard, Steven J., Wang, Michael Mao, Barriac, Gwendolyn Denise, Jarosinski, Tadeusz, Tian, Tao
• Granted Patent: US 8,380,122 B2
• Time in Patent Office: Days
• US Class Current: 455/9
• CPC Class Codes: H04B 7/15535 Control of relay amplifier gain amplifier gain control in general H03G3/00; gain control reducing self - or loop interference H04B7/15578
• CPC Class Codes: H04B 7/15585 by interference cancellation
• CPC Class Codes: H04L 27/2607 Cyclic extensions
• CPC Class Codes: H04L 27/2613 Structure of the reference signals

Abstract

A wireless repeater includes a channel estimation block to estimate a feedback channel between the antennas of the repeater using frequency domain channel estimation. The repeater includes a pilot signal blanking circuit to blank out a selected number of samples of the pilot signal to improve the accuracy of the channel estimation. In another embodiment, the repeater replaces T samples of the pilot signal with a cyclic prefix.

Claims

1. A method for estimating a feedback channel for a wireless repeater in a wireless communication system, the wireless repeater having a first antenna and a second antenna to receive a receive signal and transmit an amplified signal, the receive signal being a sum of a remote signal to be repeated and a feedback signal resulting from the feedback channel between the first and second antenna of the wireless repeater, the method comprising:

estimating the feedback channel between the first antenna and the second antenna using frequency domain channel estimation and using a signal indicative of the amplified signal as a pilot signal;

grouping samples of the pilot signal into blocks of N samples, N being the size of the fast Fourier transform (FFT) operation performed for the frequency domain channel estimation;

blanking K samples of the pilot signal in each block of N samples, K being much less than N; and

generating a feedback channel estimate using blocks of N samples of the pilot signal, each block of N samples including K blanked samples, and blocks of N samples of the receive signal.

2. The method of claim 1, wherein blanking K samples of the pilot signal in each block of N samples comprises reducing an energy level of the K samples of the pilot signal to zero or a value near zero.

3. The method of claim 2, wherein blanking K samples of the pilot signal in each block of N samples comprises reducing the energy level of the K samples of the pilot signal to zero or a value near zero gradually over two or more samples.

4. The method of claim 1, wherein blanking K samples of the pilot signal in each block of N samples comprises applying a window function to blank the K samples of the pilot signal, the window function having a gradual transition from an ungated state to a gated state and vice versa.

5. The method of claim 4, wherein applying a window function to blank the K samples of the pilot signal comprises applying a window function having a fall interval in which an energy level of a first subset of the K samples is reduced from the ungated state to zero or a value near zero, a zero interval in which the energy level of a second subset of the K samples is maintained at zero or a value near zero, and a rise interval in which the energy level of a third subset of the K samples is increased from the zero or the value near zero to the ungated state.

6. The method of claim 5, wherein applying a window function having a fall interval, a zero interval and a rise interval comprises apply a window function where the fall interval and the zero interval are positioned at the end of the block of N samples and the rise interval is positioned at the beginning of the block of N samples.

7. The method of claim 1, wherein blanking K samples of the pilot signal in each block of N samples comprises blanking the K samples of the pilot signal before the fast Fourier transform operation is performed for the frequency domain channel estimation.

8. The method of claim 1, wherein blanking K samples of the pilot signal in each block of N samples comprises replacing the K samples with T samples of a cyclic prefix.

9. The method of claim 1, wherein generating a feedback channel estimate comprises:

generating the feedback channel estimate using blocks of N samples of the pilot signal, each block of N samples including K blanked samples, and blocks of N samples of the receive signal and applying maximal ratio combining.

10. The method of claim 1, wherein estimating the feedback channel using a signal indicative of the amplified signal as a pilot signal comprises:

taking a signal before or after a transmit filter in a transmit circuitry of the wireless repeater as the pilot signal.

11. The method of claim 3, wherein estimating the feedback channel using a signal indicative of the amplified signal as a pilot signal comprises:

taking a signal before or after a transmit filter in a transmit circuitry of the wireless repeater as the pilot signal.

12. The method of claim 4, wherein estimating the feedback channel using a signal indicative of the amplified signal as a pilot signal comprises:

taking a signal before or after a transmit filter in a transmit circuitry of the wireless repeater as the pilot signal.

13. A wireless repeater having a first antenna and a second antenna to receive a receive signal and transmit an amplified signal, the receive signal being a sum of a remote signal to be repeated and a feedback signal resulting from a feedback channel between the first antenna and the second antenna, the repeater comprising:

receive circuitry configured to receive the receive signal from one of the first antenna and the second antenna;

an echo canceller configured to access a feedback signal estimate, and to cancel the feedback signal estimate from the receive signal;

a delay element configured to introduce a first delay before or after the echo canceller; and

transmit circuitry configured to amplify the delayed echo cancelled signal to generate the amplified signal to be transmitted,

wherein the echo canceller comprises;

a channel estimation block configured to estimate the feedback channel using frequency domain channel estimation and using a signal indicative of the amplified signal as a pilot signal, the frequency domain channel estimation operative to perform a fast Fourier transform (FFT) on blocks of N samples of the pilot signal, N being the size of the FFT operation; and

a pilot signal blanking circuit configured to blank K samples of the pilot signal in each block of N samples, K being much less than N,

wherein the channel estimation block is configured to generate a feedback channel estimate using blocks of N samples of the pilot signal, each block of N samples including K blanked samples, and blocks of N samples of the receive signal, the channel estimation block further generates the feedback signal estimate based on the feedback channel estimate.

14. The wireless repeater of claim 13, wherein the echo canceller further comprises a summer to receive the receive signal and the feedback signal estimate, the summer configured to subtract the feedback signal estimate from the receive signal to generate an echo cancelled signal.

15. The wireless repeater of claim 13, wherein the transmit circuitry comprises a transmit filter and the pilot signal blanking circuit blanks the K samples of the pilot signal in each block of N samples before or after the transmit filter.

16. The wireless repeater of claim 13, wherein the pilot signal blanking circuit operative to reduce an energy level of the K samples of the pilot signal to zero or a value near zero to blank the K samples.

17. The wireless repeater of claim 13, wherein the pilot signal blanking circuit operative to reduce an energy level of the K samples of the pilot signal to zero or a value near zero gradually over two or more samples to blank the K samples.

18. The wireless repeater of claim 13, wherein the pilot signal blanking circuit operative to apply a window function to blank the K samples of the pilot signal, the window function having a gradual transition from an ungated state to a gated state and vice versa.

19. The wireless repeater of claim 18, wherein the window function has a fall interval in which an energy level of a first subset of the K samples is reduced from the ungated state to zero or a value near zero, a zero interval in which the energy level of a second subset of the K samples is maintained at zero or a value near zero, and a rise interval in which the energy level of a third subset of the K samples is increased from the zero or the value near zero to the ungated state.

20. The wireless repeater of claim 18, wherein the window function has the fall interval and the zero interval positioned at the end of the block of N samples and the rise interval positioned at the beginning of the block of N samples.

21. The wireless repeater of claim 13, wherein the pilot signal blanking circuit operative to blank the K samples before the fast Fourier transform operation is performed for the frequency domain channel estimation.

22. The wireless repeater of claim 13, wherein the pilot signal blanking circuit operative to replace the K samples with T samples of a cyclic prefix.

23. The wireless repeater of claim 19, wherein the pilot signal blanking circuit comprises:

a blanking controller to generate a fall signal defining a location and a duration of the fall interval and a rise signal defining a location and a duration of the rise interval, the zero interval being position between the fall interval and the rise interval;

an up/down counter to generate a count address in response to the fall signal and the rise signal, the up/down counter being enabled when one of the fall or rise signal is being asserted, the count address counting up from a first count to a last count when the fall signal is asserted and counting down from the last count to the first count when the rise signal is asserted;

a memory to store window coefficients associated with the window function, the memory being indexed by the count address to provide a window coefficient; and

a multiplier to multiply each of the K samples with the window coefficient to blank the K samples in accordance with the window function.

24. The wireless repeater of claim 13, wherein the channel estimation block is configured to generate the feedback channel estimate using blocks of N samples of the pilot signal, each block of N samples including K blanked samples, and blocks of N samples of the receive signal and applying maximal ratio combining.

25. The wireless repeater of claim 17, wherein the transmit circuitry comprises a transmit filter and the pilot signal blanking circuit blanks the K samples of the pilot signal in each block of N samples before or after the transmit filter.

26. The wireless repeater of claim 18, wherein the transmit circuitry comprises a transmit filter and the pilot signal blanking circuit blanks the K samples of the pilot signal in each block of N samples before or after the transmit filter.

27. A wireless repeater having a first antenna and a second antenna to receive a receive signal and transmit an amplified signal, the receive signal being a sum of a remote signal to be repeated and a feedback signal resulting from a feedback channel between the first antenna and the second antenna, the repeater comprising:

means for receiving the receive signal from one of the first antenna and the second antenna;

means for cancelling a feedback signal estimate from the input signal;

means for introducing a first delay before or after the feedback signal estimate is cancelled from the input signal;

means for amplifying the delayed echo cancelled signal to generate the amplified signal to be transmitted,

wherein the means for cancelling comprises;

means for estimating the feedback channel using frequency domain channel estimation and using a signal indicative of the amplified signal as a pilot signal, the frequency domain channel estimation operative to perform a fast Fourier transform (FFT) on blocks of N samples of the pilot signal, N being the size of the FFT operation; and

means for blanking K samples of the pilot signal in each block of N samples, K being much less than N,

wherein the means for estimating the feedback channel generates a feedback channel estimate using blocks of N samples of the pilot signal, each block of N samples including K blanked samples, and blocks of N samples of the receive signal, the means for estimating the feedback channel further generates the feedback signal estimate based on the feedback channel estimate.