ADAPTIVE KNOWN SIGNAL CANCELLER

• US 20100091822A1
• Filed: 10/10/2008
• Published: 04/15/2010
• Est. Priority Date: 10/10/2008
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: Auvitek International Limited (Qualcomm, Inc.)
• Inventors: YU, Tao, COOKMAN, Jordan Christopher, DONG, Ping
• Granted Patent: US 8,135,058 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/0212 of impulse response
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 27/2657 Carrier synchronisation

Abstract

An adaptive known signal canceller comprising of a known signal canceller filter responsive to a known signal including a known portion of a transmitted signal, the known signal canceller filter operative to generate a filtered known signal, and a subtractor unit responsive to an input signal and operative to generate an output signal, the subtractor unit configured to subtract the filtered known signal from the input signal to generate an output signal, such that the known portion of the transmitted signal is substantially removed from the input signal. The adaptive known signal canceller further comprising of a known signal canceller update unit, responsive to a desired signal and an output signal and operative to continually adjust the coefficients of the known signal canceller filter based on the difference between the output signal and the desired signal, so that the filter coefficients substantially reflect the impulse response of a channel.

Claims

1. A receiver responsive to at least one input signal of a communication channel and operative to generate an equalized signal comprising:

an adaptive known signal canceller responsive to an input signal of a communication channel including frames of information, said input signal including orthogonal sub-carriers and representing a transmitted signal that has been distorted by the communication channel, said adaptive known signal canceller operative to generate a time domain unknown signal, and further operative to generate an estimated channel impulse response signal representing substantially the impulse response of the channel, the adaptive known signal canceller including a known signal canceller filter configured to generate a filtered known signal, the known signal canceller filter configured to receive a coefficient update signal that is used to update the coefficient, the adaptive known signal canceller further including a subtractor responsive to the input signal and operative to generate an output signal, the subtractor configured to subtract the filtered known signal from the input signal, the adaptive known signal canceller further including a known signal canceller update unit responsive to a desired signal, the desired signal representing the desired output signal with the known signal part having been removed, the known signal canceller update unit operative to provide the coefficient update signal to the known signal canceller filter based on the difference between the output signal and the desired signal, so that the coefficients correspond to an estimate of the impulse response of the channel, and a known portion of the transmitted signal is adaptively removed from the input signal; and

a frequency domain equalizer responsive to a frequency representation of the estimated channel impulse response and a frequency representation of a cyclically restored time domain unknown signal and operative to generate an frequency domain equalized signal, the frequency domain equalizer configured to remove the effects of the channel thereby generating a frequency domain estimate of the unknown part of the transmitted signal.

2. A receiver as recited in claim 1, further comprising:

a delay spread estimation block responsive to an estimated channel impulse response and operative to generate an estimated delay spread signal,

a cyclic restoration block responsive to the output signal and operative to generate a cyclically restored signal, the cyclic restoration block configured to add a portion of the output signal to a delayed potion of the output signal to form a single frame that represents a cyclic convolution of the single frame with the channel impulse response;

a first discrete Fourier transformer (DFT) responsive to the cyclically restored time domain unknown signal and operative to generate frequency domain sub-signals for each of the orthogonal sub-carriers, the DFT configured to use Fourier analysis to transform the cyclically restored time domain unknown signal into frequency domain sub-signals for each of the orthogonal sub-carriers; and

a second DFT responsive to the estimated channel impulse response and operative to generate an estimated frequency response signal, which is the frequency representation of the estimated channel impulse response, the second DFT configured to use Fourier analysis to transform the estimated channel impulse response into the estimated frequency response signal.

3. A receiver as recited in claim 2, wherein the delay spread estimation block is configured to generate an estimated delay spread signal by finding the earliest and latest coefficients of the estimated channel impulse response that are above a threshold, and thereafter measuring the distance between the earliest and latest coefficients.

4. A receiver responsive to at least one input signal and operative to generate an equalized signal comprising:

an adaptive known signal canceller responsive to an input signal of a communication channel including frames of information, said input signal representing a transmitted signal that has been distorted by the communication channel, said adaptive known signal canceller operative to generate a time domain unknown signal, and further operative to generate an estimated channel impulse response signal representing substantially the impulse response of the channel, the adaptive known signal canceller including a known signal canceller filter configured to generate a filtered known signal, the known signal canceller filter configured to receive a coefficient update signal that is used to update the coefficients, the adaptive known signal canceller further including a subtractor responsive to the input signal and operative to generate an output signal, the subtractor configured to subtract the filtered known signal from the input signal, the adaptive known signal canceller further including a known signal canceller update unit responsive to a desired signal, the desired signal representing the desired output signal with the known signal part having been removed, the known signal canceller update unit operative to provide the coefficient update signal to the known signal canceller filter based on the difference between the output signal and the desired signal, so that the coefficients correspond to an estimate of the impulse response of the channel, and a known portion of the transmitted signal is adaptively removed from the input signal;

a equalizer coefficient computation block responsive to the estimated channel impulse response and operative to compute and generate time domain equalizer coefficients; and

a time domain equalizer responsive to the time domain equalizer coefficients and to the output signal, and operative to generate an equalized signal, the time domain equalizer configured to filter the output signal using the time domain equalizer coefficients to yield an equalized signal.

5. A receiver as recited in claim 4, wherein the equalizer coefficient computation block generates the coefficients according to minimum mean squared error (MMSE) criterion, wherein equations are set up to minimize the mean squared error between equalizer outputs and transmitted symbols given the channel impulse response and an estimate of the signal to noise ratio (SNR), and further wherein the equations are solved for the equalizer coefficients.

6. An adaptive known signal canceller adaptive for use in a receiver configured to receive at least one channel carrying information, said adaptive known canceller comprising:

a known signal canceller filter responsive to a known signal including a known portion of a transmitted signal, the known signal canceller filter operative to generate a filtered known signal;

a subtractor unit responsive to an input signal and operative to generate an output signal, the subtractor unit configured to subtract the filtered known signal from the input signal to generate an output signal, such that the known portion of the transmitted signal is substantially removed from the input signal; and

a known signal canceller update unit, responsive to a desired signal and an output signal and operative to adjust the coefficients of the known signal canceller filter based on the difference between the output signal and the desired signal, so that the filter coefficients substantially reflect the impulse response of a channel.

7. An adaptive known signal canceller as recited in claim 6, wherein the desired signal is an all-zero signal.

8. An adaptive known signal canceller as recited in claim 6, wherein the desired signal is a null signal.

9. An adaptive known signal canceller as recited in claim 6, wherein the adaptive known signal canceller is operative to perform channel estimation and to provide an output signal in response to an input signal and a known signal.

10. An adaptive known signal canceller as recited in claim 6, further comprising a known signal generator, operative to generate a known signal including a known portion of a transmitted signal.

11. An adaptive known signal canceller as recited in claim 6, further comprising a signal subtractor, responsive to the input signal and the filtered known signal, and operative to compute the difference between the input signal and the filtered known signal to generate an output signal.

12. An adaptive known signal canceller, as recited in claim 6, wherein the known signal includes a quasi-cyclic pseudo-random number (PN) sequence.

13. An adaptive known signal canceller, as recited in claim 6, wherein the known signal includes a non-cyclic pseudo-random (PN) sequence.

14. An adaptive known signal canceller as recited in claim 6, wherein said known signal generator is further operative to stop generating signals during a time corresponding to an unknown portion of a transmitted signal.

15. An adaptive known signal canceller as recited in claim 6, wherein the known signal canceller update unit adjusts the filter coefficients using the LMS algorithm.

16. An adaptive known signal canceller as recited in claim 6, wherein the desired signal consists of a discrete time signal whose values are all zero.

17. An adaptive known signal canceller as recited in claim 6, wherein the known portion of the transmit signal is a frame header.

18. The adaptive known signal canceller as recited in claim 17, wherein the frame header consists of a PN sequence.

19. The adaptive known signal canceller as recited in claim 6, wherein the known signal canceller filter is a finite impulse response filter.

20. The adaptive known signal canceller as recited in claim 19, wherein the known signal canceller filter includes only addition and subtraction elements.

21. An adaptive known signal canceller operative to perform channel estimation and to provide an output signal in response to an input signal, comprising:

a known signal generator, operative to generate a known signal consisting of a known portion of a transmitted signal;

a known signal canceller filter, responsive to the known signal and operative to generate a filtered known signal;

a signal subtractor, responsive to an input signal and the filtered known signal, and operative to compute the difference between the input signal and the filtered known signal to generate an output signal; and

a known signal canceller update unit, responsive to a desired signal and an output signal, and operative to continually adjust the coefficients of the known signal canceller filter based on the difference between the output signal and a desired signal, to generate an estimated channel impulse response.

22. An adaptive known signal canceller as recited in claim 21, wherein said known signal generator is operative to generate a null signal corresponding to an unknown portion of a transmitted signal.

23. An adaptive known signal canceller as recited in claim 21, wherein the null signal consists of a discrete time signal whose values are all zero.

24. An adaptive known signal canceller as recited in claim 21, wherein said known signal generator is further operative to stop generating signals during a time corresponding to an unknown portion of a transmitted signal.

25. An adaptive known signal canceller as recited in claim 21, wherein the known signal canceller update unit adjusts the filter coefficients using the LMS algorithm.

26. An adaptive known signal canceller as recited in claim 21, wherein the desired signal consists of a discrete time signal whose values are all zero.

27. An adaptive known signal canceller as recited in claim 21, wherein the known portion of the transmit signal is a frame header.

28. The adaptive known signal canceller as recited in claim 27, wherein the frame header consists of a PN sequence.

29. The adaptive known signal canceller as recited in claim 21, wherein the known signal canceller filter is a finite impulse response filter.

30. The adaptive known signal canceller as recited in claim 29, wherein the known signal canceller filter includes only addition and subtraction elements

31. The adaptive known signal canceller as recited in claim 29, wherein the finite impulse response filter consists of a plurality of segments, wherein each segment is responsive to a delayed sample of the known signal, and wherein the finite impulse response filter further consists of a filter block for filtering the delayed samples by using coefficients which are updated based on a step size generated for each segment.

32. An adaptive known signal canceller operative to provide an output signal in response to a input signal, comprising:

a known signal generator, operative to generate a known signal consisting of a known portion of a transmitted signal;

a known signal canceller filter, responsive to the known signal and operative to generate a filtered known signal;

a carrier rotation block, responsive to an input signal and operative to generate a rotated signal, wherein said rotated signal represents the input signal with a carrier phase rotation;

a signal subtractor, responsive to the rotated signal and the filtered known signal, and operative to compute the difference between the rotated signal and the filtered known signal to generate an output signal;

a known signal canceller update unit, responsive to a desired signal and an output signal, and operative to adjust the coefficients of the known signal canceller filter based on the difference between the output signal and a desired signal, to generate an estimated channel impulse response; and

a phase error detection block, responsive to the rotated signal and the filtered known signal, and operative to generate a phase error signal;

wherein the carrier rotation block is further operative to use said phase error signal to update the phase rotation for a subsequent value of the input signal.

33. An adaptive known signal canceller as recited in claim 32, wherein the known signal generator is further operative to generate a null signal corresponding to an unknown portion of a transmitted signal.

34. An adaptive known signal canceller as recited in claim 32, wherein the null signal consists of a discrete time signal whose values are all zero.

35. An adaptive known signal canceller as recited in claim 32, wherein the known signal generator is further operative to stop generating signals during a time corresponding to an unknown portion of a transmitted signal.

36. An adaptive known signal canceller as recited in claim 32, wherein the known signal canceller update unit adjusts the filter coefficients using the LMS algorithm.

37. An adaptive known signal canceller as recited in claim 32, wherein the desired signal consists of a discrete time signal whose values are all zero

38. An adaptive known signal canceller as recited in claim 32, wherein the known portion of the transmit signal is a frame header.

39. An adaptive known signal canceller as recited in claim 32, wherein the frame header consists of a PN sequence.

40. An adaptive known signal canceller as recited in claim 32, wherein the known signal consists of a sequence of values in the set {−

1, +1}

41. An adaptive known signal canceller of claim 32, wherein the known signal canceller filter is a finite impulse response filter.

42. An adaptive known signal canceller of claim 41, wherein the known signal canceller filter is implemented using only addition and subtraction.

43. An adaptive known signal canceller of claim 42, wherein the finite impulse response filter consists of a plurality of segments, wherein each segment is responsive to a delayed sample of the known signal, and wherein the finite impulse response filter further consists of a filter block for filtering the delayed samples by using coefficients which are updated based on a step size generated for each segment.

44. An adaptive known signal canceller comprising:

means for generating a known signal consisting of a known portion of a transmitted signal;

means for receiving the known signal;

means for generating a filtered known signal;

means for receiving an input signal and the filtered known signal;

means for computing the difference between the input signal and the filtered signal to generate an output signal

means for receiving a desired signal and an output signal;

means for adjusting the coefficients of the known signal canceller filter based on the difference between the output signal and a desired signal, to generate an estimated channel impulse response.

45. A method of channel impulse response estimation comprising:

a. receiving an input signal sample;

b. determining if said sample corresponds to a known portion of the signal, and if it does, generating a sample of the known portion of the signal;

c. generating a filtered known sample using one or more samples of the known portion of the signal;

d. generating an output sample by subtracting the sample of the filtered known signal from the sample of the input signal;

e. updating the filter coefficients of the known signal canceller filter block based on the difference between the output signal and the desired signal; and

f. repeating steps a.-e. so long as the input signal is received.

46. A computer-readable medium containing a description expressed in a hardware description language which is interpreted by a computer to specify a circuit that performs a method to generate an equalized signal comprising:

an adaptive known signal canceller responsive to an input signal of a communication channel including frames of information, said input signal including orthogonal sub-carriers and representing a transmitted signal that has been distorted by the communication channel, said adaptive known signal canceller operative to generate a time domain unknown signal, and further operative to generate an estimated channel impulse response signal representing substantially the impulse response of the channel, the adaptive known signal canceller including a known signal canceller filter configured to generate a filtered known signal, the known signal canceller filter configured to receive a coefficient update signal that is used to update the coefficient, the adaptive known signal canceller further including a subtractor responsive to the input signal and operative to generate an output signal, the subtractor configured to subtract the filtered known signal from the input signal, the adaptive known signal canceller further including a known signal canceller update unit responsive to a desired signal, the desired signal representing the desired output signal with the known signal part having been removed, the known signal canceller update unit operative to provide the coefficient update signal to the known signal canceller filter based on the difference between the output signal and the desired signal, so that the coefficients correspond to an estimate of the impulse response of the channel, and a known portion of the transmitted signal is adaptively removed from the input signal; and

a frequency domain equalizer responsive to a frequency representation of the estimated channel impulse response and a frequency representation of a cyclically restored time domain unknown signal and operative to generate an frequency domain equalized signal, the frequency domain equalizer configured to remove the effects of the channel thereby generating a frequency domain estimate of the unknown part of the transmitted signal.

47. A computer-readable medium containing a description expressed in a hardware description language which is interpreted by a computer to specify a circuit that performs a method of channel impulse response estimation comprising:

an adaptive known signal canceller responsive to an input signal of a communication channel including frames of information, said input signal representing a transmitted signal that has been distorted by the communication channel, said adaptive known signal canceller operative to generate a time domain unknown signal, and further operative to generate an estimated channel impulse response signal representing substantially the impulse response of the channel, the adaptive known signal canceller including a known signal canceller filter configured to generate a filtered known signal, the known signal canceller filter configured to receive a coefficient update signal that is used to update the coefficients, the adaptive known signal canceller further including a subtractor responsive to the input signal and operative to generate an output signal, the subtractor configured to subtract the filtered known signal from the input signal, the adaptive known signal canceller further including a known signal canceller update unit responsive to a desired signal, the desired signal representing the desired output signal with the known signal part having been removed, the known signal canceller update unit operative to provide the coefficient update signal to the known signal canceller filter based on the difference between the output signal and the desired signal, so that the coefficients correspond to an estimate of the impulse response of the channel, and a known portion of the transmitted signal is adaptively removed from the input signal;

a equalizer coefficient computation block responsive to the estimated channel impulse response and operative to compute and generate time domain equalizer coefficients; and

a time domain equalizer responsive to the time domain equalizer coefficients and to the output signal, and operative to generate an equalized signal, the time domain equalizer configured to filter the output signal using the time domain equalizer coefficients to yield an equalized signal.

48. A computer-readable medium containing a description expressed in a hardware description language which is interpreted by a computer to specify a circuit that performs a method to receive at least one channel carrying information, said circuit comprising:

a known signal canceller filter responsive to a known signal including a known portion of a transmitted signal, the known signal canceller filter operative to generate a filtered known signal;

a subtractor unit responsive to an input signal and operative to generate an output signal, the subtractor unit configured to subtract the filtered known signal from the input signal to generate an output signal, such that the known portion of the transmitted signal is substantially removed from the input signal; and

a known signal canceller update unit, responsive to a desired signal and an output signal and operative to adjust the coefficients of the known signal canceller filter based on the difference between the output signal and the desired signal, so that the filter coefficients substantially reflect the impulse response of a channel.