# US 9,520,985 B2 · Tuning algorithm for multi-tap signal cancellation circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,520,985 B2 - Document ID: US9520985B2 - Status: Granted - Kind: B2 - Application number: 14/158,711 - Filed: 2014-01-17 - Published: 2014-07-24 - Granted: 2016-12-13 - Earliest claimed: 2013-01-18 - Assignees: Kumu Networks, Inc. - Applicants: Kumu Networks - Inventors: Jung-il Choi; Mayank Jain - Web page: https://patentgrep.com/patent/US9520985B2 ## CPC - H04L 5/1461: {Suppression of signals in the return path, i.e. bidirectional control circuits} - H04L 5/143: {for modulated signals (H04L5/1469 takes precedence)} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## 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 ### Claim 1 A circuit comprising: a transmitter that transmits a transmit signal; a plurality of signal paths, each signal path including a delay element and a variable attenuator; wherein each signal path receives a portion of the transmit signal; a control unit that sets one or more signal paths to a first attenuation level and a second attenuation level; a combiner that generates an output signal by combining outputs of the plurality of signal paths; and a receiver that receives 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; wherein the matrix is determined by applying sequentially a number of transmit signals having different frequencies to the signal paths; 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; 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. ### Claim 2 (depends on 1) The circuit of claim 1, further comprising: at least one antenna for receiving the signal. ### Claim 3 (depends on 2) The circuit of claim 2, wherein each of the signal paths receives a sample of the transmit signal and generates a delayed and weighted sample of the transmit signal. ### Claim 4 (depends on 3) The circuit of claim 3, further comprising: a plurality of passive couplers that change a phase of one or more delayed and weighted signal paths in relation to the transmit signal; and a coupler that subtracts the product from a received signal. ### Claim 5 (depends on 1) The circuit of claim 1, wherein the matrix is determined with a fast Fourier transform (FFT) of a single wideband transmit signal. ### Claim 6 (depends on 1) 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. ### Claim 7 (depends on 6) The circuit of claim 6, wherein the third port of the circulator is disconnected from the receiver while the circuit is computing the matrix. ### Claim 8 (depends on 7) The circuit of claim 7, 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. ### Claim 9 (depends on 1) 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. ### Claim 10 (depends on 1) 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. ### Claim 11 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; 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. ### Claim 12 (depends on 11) The method of claim 11, wherein varying an attenuation level of each of the variable attenuators is performed concurrently. ### Claim 13 (depends on 11) The method of claim 11, 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. ### Claim 14 (depends on 11) The method of claim 11, wherein generating a matrix is without connecting the transmitter to an antenna. ### Claim 15 (depends on 11) The method of claim 11, wherein the received signal at the receiver is through an antenna while a maximum attenuation level is applied to the attenuators. ### Claim 16 (depends on 11) The method of claim 11, wherein the first output signal or the second output signal is obtained by combining outputs from all of the plurality of signal paths. ### Claim 17 (depends on 11) The method of claim 11, wherein the first attenuation level is a maximum attenuation. ### Claim 18 (depends on 11) The method of claim 11, wherein the second attenuation level is a minimum attenuation. ### Claim 19 (depends on 11) The method of claim 11, wherein the first and second attenuation levels are applied to all variable attenuators of the plurality of parallel signal paths. ### Claim 20 (depends on 11) The method of claim 11, wherein the transmit signal is a complex signal. ### Claim 21 (depends on 11) The method of claim 11, 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. ### Claim 22 A circuit comprising: a transmitter that transmits a transmit signal; a plurality of signal paths, each signal path including a delay element and a variable attenuator; wherein each signal path receives a portion of the transmit signal; a control unit that sets one or more signal paths to a first attenuation level and a second attenuation level; a combiner that generates an output signal by combining outputs of the plurality of signal paths; 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; and a receiver that receives 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; wherein the third port of the circulator is disconnected from the receiver while the circuit is computing the matrix; 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. ### Claim 23 (depends on 22) The circuit of claim 22, further comprising: at least one antenna for receiving the signal. ### Claim 24 (depends on 23) The circuit of claim 23, wherein each of the signal paths receives a sample of the transmit signal and generates a delayed and weighted sample of the transmit signal. ### Claim 25 (depends on 24) The circuit of claim 24, further comprising: a plurality of passive couplers that change a phase of one or more delayed and weighted signal paths in relation to the transmit signal; and a coupler that subtracts the product from a received signal. ### Claim 26 (depends on 22) The circuit of claim 22, wherein the matrix is determined with a fast Fourier transform (FFT) of a single wideband transmit signal. ### Claim 27 (depends on 22) The circuit of claim 22, wherein the first attenuation level is a maximum attenuation level and the second attenuation level is a minimum attenuation level. ### Claim 28 (depends on 22) The circuit of claim 22, 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.