TUNING ALGORITHM FOR MULTI-TAP SIGNAL CANCELLATION CIRCUIT

• US 20140204808A1
• Filed: 01/17/2014
• Published: 07/24/2014
• Est. Priority Date: 01/18/2013
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Kumu Networks, Inc.
• Inventors: Jain, Mayank, Choi, Jung-il
• Granted Patent: US 9,520,985 B2
• Time in Patent Office: Days
• US Class Current: 370/278
• CPC Class Codes: H04L 5/143 for modulated signals H04L5/1469 takes precedence
• CPC Class Codes: H04L 5/1461 Suppression of signals in the return path, i.e. bidirectional control circuits

Abstract

A self-interference signal cancellation circuit includes a transmitter for transmitting a transmit signal, a plurality of signal paths, a controller, and a receiver for receiving a signal. Each signal path includes a delay element and a variable attenuator having attenuation levels set by the controller. A combiner generates an output signal by combining outputs of the signal paths. The circuit computes a matrix based on first and second output signals associated with first and second attenuation levels. The controller concurrently varies the attenuation level of each signal path so that a product of the matrix and the attenuation levels of the signal paths is substantially equal to the received signal. The circuit may iteratively compute the matrix using different transmit signal frequencies or with an FFT. The controller iteratively varies the attenuation level of the attenuators until a sum of the product and the received signal satisfies a predefined condition.

Claims

1. A circuit comprising:

a transmitter adapted to transmit a transmit signal;

a plurality of signal paths, each signal path including a delay element and a variable attenuator and adapted to receive a portion of the transmit signal;

a control unit adapted to set one or more signal paths to a first attenuation level and a second attenuation level;

a combiner adapted to generate an output signal by combining outputs of the plurality of signal paths; and

a receiver adapted to receive a signal,

wherein the circuit computes a matrix based on first and second output signals associated with the respective first and second attenuation levels, and

wherein the control unit concurrently varies an attenuation level of each signal path so that a product of the matrix and the attenuation level of each signal path is substantially equal to the received signal.

2. The circuit of claim 1, further comprising:

at least one antenna for receiving the signal.

3. The circuit of claim 2, wherein each of the signal paths is adapted to receive a sample of the transmit signal and generate a delayed and weighted sample of the transmit signal.

4. The circuit of claim 3, further comprising:

a plurality of passive couplers adapted to change a phase of one or more delayed and weighted signal paths in relation to the transmit signal; and

a coupler adapted to subtract the product from a received signal.

5. The circuit of claim 1, wherein the matrix is determined by applying sequentially a number of transmit signals having different frequencies to the signal paths.

6. The circuit of claim 1, wherein the matrix is determined with a fast Fourier transform (FFT) of a single wideband transmit signal.

7. The circuit of claim 5, wherein the matrix is a complex M×

N matrix, M and N being positive integers, where M is the number of the different frequencies, and N is the number of the signal paths.

8. The circuit of claim 7, wherein the received signal is a complex M×

1 column vector and the attenuation level of each signal path is an element of a real N×

1 column vector.

9. The circuit of claim 1, further comprising a circulator having a first port coupled to an antenna, a second port coupled to a transmit line of the circuit, and a third port coupled to a receive line of the circuit.

10. The circuit of claim 9, wherein the third port of the circulator is disconnected from the receiver while the circuit is computing the matrix.

11. The circuit of claim 10, wherein the third port of the circulator is connected to the receiver while the control unit concurrently varies the attenuation level of each signal path to minimize the sum of the product and the received signal.

12. The circuit of claim 1, wherein the first attenuation level is a maximum attenuation level and the second attenuation level is a minimum attenuation level.

13. The circuit of claim 1, wherein the control unit iteratively varies the attenuation level of each variable attenuator until a sum of the product and the received signal satisfies a predefined condition.

14. A method for performing a self-interference signal cancellation in a full-duplex wireless communication system with a cancellation circuit having a plurality of parallel signal paths, each of the signal paths including a delay element and a variable attenuator, the method comprising:

supplying a first sample of a transmit signal at a first frequency by a transmitter to the cancellation circuit;

setting a first attenuation level to one or more of the variable attenuators;

obtaining a first output signal of the cancellation circuit;

setting a second attenuation level to the one or more of the variable attenuators;

obtaining a second output signal of the cancellation circuit;

generating a matrix based on the first and second output signals;

receiving a signal at a receiver; and

varying an attenuation level of each of the variable attenuators so that a product of the matrix and the attenuation levels of the variable attenuators is substantially equal to the received signal.

15. The method of claim 14, wherein varying an attenuation level of each of the variable attenuators is performed concurrently.

16. The method of claim 14, wherein generating a matrix comprises iteratively performing the following steps:

supplying a second sample of the transmit signal at a second frequency by the transmitter to the cancellation circuit;

setting the first attenuation level to the one or more of the variable attenuators;

obtaining a third output signal of the cancellation circuit;

setting the second attenuation level to the one or more of the variable attenuators;

obtaining a fourth output signal of the cancellation circuit; and

expanding the matrix based on the third and fourth output signals.

17. The method of claim 16, wherein the matrix is a complex M×

N matrix, M and N being positive integers, where M is a number of different frequencies of the transmit signal and N is a number of the plurality of signal paths.

18. The method of claim 14, wherein generating a matrix is without connecting the transmitter to an antenna.

19. The method of claim 14, wherein the received signal at the receiver is through an antenna while a maximum attenuation level is applied to the attenuators.

20. The method of claim 14, wherein the first output signal or the second output signal is obtained by combining outputs from all of the plurality of signal paths.

21. The method of claim 14, wherein the first attenuation level is a maximum attenuation.

22. The method of claim 14, wherein the second attenuation level is a minimum attenuation.

23. The method of claim 14, wherein the first and second attenuation levels are applied to all variable attenuators of the plurality of parallel signal paths.

24. The method of claim 14, wherein the transmit signal is a complex signal.

25. The method of claim 14, wherein varying an attenuation level of each of the variable attenuators comprises iteratively carrying out a tuning of the attenuation of each of the variable attenuators until a sum of the product and the received signal satisfies a predefined condition.