# US 7,609,786 B2 · Channel estimation for a communication system using spectral estimation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,609,786 B2 - Document ID: US7609786B2 - Status: Granted - Kind: B2 - Application number: 11/021,292 - Filed: 2004-12-22 - Published: 2005-07-28 - Granted: 2009-10-27 - Earliest claimed: 2004-01-28 - Assignees: QUALCOMM Incorporated - Inventors: Arvind Vijay Keerthi - Web page: https://patentgrep.com/patent/US7609786B2 ## CPC - H04L 25/0248: {Eigen-space methods} - H04L 25/0224: {using sounding signals} - H04L 27/2647: {Arrangements specific to the receiver only (equalisation H04L27/01)} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract Techniques for performing channel estimation in a multi-carrier system are described. A frequency response estimate is initially obtained for a wireless channel based on a narrowband pilot sent on different sets of subbands in different symbol periods or a wideband pilot sent on all or most subbands in the system. Spectral estimation is performed on the frequency response estimate to determine at least one frequency component of the frequency channel estimate, with each frequency component being indicative of a delay for a channel tap in an impulse response estimate for the wireless channel. A channel estimate for the wireless channel is then obtained based on the frequency component(s) determined by the spectral estimation. This channel estimate may be a channel profile, the impulse response estimate, an improved frequency response estimate, a signal arrival time, or some other pertinent information regarding the wireless channel. ## Claims ### Claim 1 A method of performing channel estimation for a communication channel in a communication system, comprising: obtaining a first channel estimate by a detector for the communication channel; performing spectral estimation on the first channel estimate to determine at least one frequency component of the first channel estimate; and obtaining a second channel estimate for the communication channel based on the determined at least one frequency component of the first channel estimate, wherein obtaining the second channel estimate comprises obtaining at least one channel tap delay for an impulse response estimate for the communication channel. ### Claim 2 (depends on 1) The method of claim 1, wherein obtaining the first channel estimate comprises determining a frequency response estimate for the communication channel, and wherein spectral estimation is performed on the frequency response estimate. ### Claim 3 (depends on 2) The method of claim 2, wherein each of the at least one frequency component is indicative of a delay for a channel tap in an impulse response estimate for the communication channel. ### Claim 4 (depends on 2) The method of claim 2, further comprising: obtaining a plurality of partial frequency response estimates for a plurality of different sets of subbands, wherein each partial frequency response estimate is for a portion of a total bandwidth for the system and is obtained from one set of subbands, and wherein the spectral estimation is performed on the plurality of partial frequency response estimates to determine the at least one frequency component. ### Claim 5 (depends on 4) The method of claim 4, wherein each set of subbands includes a subset of N total subbands for the system, where N is an integer greater than 1. ### Claim 6 (depends on 4) The method of claim 4, wherein each set of subbands includes M consecutive subbands in the system, where M is an integer greater than 1. ### Claim 7 (depends on 4) The method of claim 4, wherein each set of subbands includes M subbands uniformly distributed across N total subbands for the system, where M and N are integers greater than one, and M is less than N. ### Claim 8 (depends on 4) The method of claim 4, wherein the different sets of subbands are determined by a pseudo-random sequence used for frequency hopping. ### Claim 9 (depends on 2) The method of claim 2, wherein determining the frequency response estimate is obtained based on a wideband pilot and comprises channel gain estimates for all or a large number of subbands for the system. ### Claim 10 (depends on 1) The method of claim 1, wherein obtaining the second channel estimate further comprises obtaining at least one channel tap gain at the at least one channel tap delay. ### Claim 11 (depends on 1) The method of claim 1, wherein obtaining the second channel estimate comprises obtaining a plurality of channel gains for a plurality of subbands of the communication channel. ### Claim 12 (depends on 1) The method of claim 1, wherein obtaining the second channel estimate comprises obtaining a delay value indicative of an arrival time of a signal transmitted via the communication channel. ### Claim 13 (depends on 12) The method of claim 12, further comprising: using the delay value for time synchronization of a data transmission received via the communication channel. ### Claim 14 (depends on 1) The method of claim 1, wherein performing the spectral estimation comprises performing based on a multiple signal classification (MUSIC) technique. ### Claim 15 (depends on 1) The method of claim 1, wherein performing the spectral estimation comprises performing based on a periodogram technique, a Prony estimator, or a Pisarenko harmonic decomposition technique. ### Claim 16 (depends on 1) The method of claim 1, wherein the communication system utilizes orthogonal frequency division multiplexing (OFDM). ### Claim 17 (depends on 1) The method of claim 1, wherein the communication system is an orthogonal frequency division multiple access (OFDMA) system. ### Claim 18 An apparatus operable to perform channel estimation for a communication channel in a communication system, comprising: a detector operative to obtain a first channel estimate for the communication channel; a spectral estimator operative to perform spectral estimation on the first channel estimate to determine at least one frequency component of the first channel estimate; and a processor operative to obtain a second channel estimate for the communication channel based on the determined at least one frequency component of the first channel estimate, wherein the second channel estimate comprises at least one channel tap delay for an impulse response estimate for the communication channel. ### Claim 19 (depends on 18) The apparatus of claim 18, wherein the first channel estimate comprises a frequency response estimate for the communication channel, and wherein each of the at least one frequency component is indicative of a delay for a channel tap in the impulse response estimate for the communication channel. ### Claim 20 (depends on 18) The apparatus of claim 18, wherein the detector is operative to obtain a plurality of partial frequency response estimates for a plurality of different sets of subbands, and wherein the spectral estimator is operative to perform spectral estimation on the plurality of partial frequency response estimates to determine the at least one frequency component. ### Claim 21 (depends on 19) The apparatus of claim 19, further comprising: a timing unit operative to obtain from the spectral estimator a delay value indicative of an arrival time of a signal transmitted via the communication channel and to use the delay value for time synchronization of a data transmission received via the communication channel. ### Claim 22 An apparatus operable to perform channel estimation for a communication channel in a communication system, comprising: means for obtaining a first channel estimate for the communication channel; means for performing spectral estimation on the first channel estimate to determine at least one frequency component of the first channel estimate; and means for obtaining a second channel estimate for the communication channel based on the determined at least one frequency component of the first channel estimate, wherein the second channel estimate comprises at least one channel tap delay for an impulse response estimate for the communication channel. ### Claim 23 (depends on 22) The apparatus of claim 22, wherein the first channel estimate comprises a frequency response estimate for the communication channel, and wherein each of the at least one frequency component is indicative of a delay for a channel tap in the impulse response estimate for the communication channel. ### Claim 24 A method of performing channel estimation for a communication channel in a communication system, comprising: obtaining a frequency response estimate by a detector for the communication channel; deriving a correlation matrix based on the frequency response estimate; obtaining T noise eigenvectors based on the correlation matrix, where T is an integer one of greater; and obtaining a channel estimate for the communication channel based on the T noise eigenvectors. ### Claim 25 (depends on 24) The method of claim 24, further comprising: obtaining a plurality of partial frequency response estimates for a plurality of different sets of subbands, wherein each partial frequency response estimate is for a portion of a total bandwidth for the system and is obtained from one set of subbands, and wherein the frequency response estimate for the communication channel comprises the plurality of partial frequency response estimates. ### Claim 26 (depends on 25) The method of claim 25, wherein the deriving a correlation matrix comprises computing an outer product matrix for each of the plurality of partial frequency response estimates, and averaging a plurality of outer product matrices computed for the plurality of partial frequency response estimates to obtain the correlation matrix. ### Claim 27 (depends on 24) The method of claim 24, wherein the obtaining T noise eigenvectors comprises performing eigenvalue decomposition of the correlation matrix to obtain a diagonal matrix of eigenvalues and a unitary matrix of eigenvectors, and wherein the T noise eigenvectors are T eigenvectors in the unitary matrix corresponding to T smallest eigenvalues in the diagonal matrix. ### Claim 28 (depends on 24) The method of claim 24, wherein the obtaining a channel estimate for the communication channel comprises computing a cost value for each of N hypothesized delay values based on a cost function of the T noise eigenvectors and the hypothesized delay value, where N is an integer greater than T, and wherein N cost values are computed for the N hypothesized delay values, identifying L largest cost values among the N cost values, where L is an integer one of greater, and providing L hypothesized delay values for the L largest cost values as delays of L channel taps in an impulse response estimate for the communication channel, and wherein the channel estimate for the communication channel comprises the L channel tap delays. ### Claim 29 (depends on 28) The method of claim 28, wherein the obtaining a channel estimate for the communication channel further comprises deriving gains of the L channel taps in the impulse response estimate based on the L tap delays and the frequency response estimate, and wherein the channel estimate for the communication channel further comprises the L channel tap gains. ### Claim 30 (depends on 29) The method of claim 29, wherein the obtaining a channel estimate for the communication channel further comprises obtaining a full frequency response estimate for N total subbands of the communication channel based on the impulse response estimate. ### Claim 31 An apparatus operable to perform channel estimation for a communication channel in a communication system, comprising: a detector operative to obtain a frequency response estimate for the communication channel; and a spectral estimator operative to derive a correlation matrix based on the frequency response estimate, obtain T noise eigenvectors based on the correlation matrix, where T is an integer one of greater, and obtain a channel estimate for the communication channel based on the T noise eigenvectors. ### Claim 32 (depends on 31) The apparatus of claim 31, wherein the detector is operative to obtain a plurality of partial frequency response estimates for a plurality of different sets of subbands, wherein each partial frequency response estimate is for a portion of a total bandwidth for the system and is obtained from one set of subbands, and wherein the spectral estimator is operative to derive the correlation matrix based on the plurality of partial frequency response estimates. ### Claim 33 An apparatus operable to perform channel estimation for a communication channel in a communication system, comprising: means for obtaining a frequency response estimate for the communication channel; means for deriving a correlation matrix based on the frequency response estimate; means for obtaining T noise eigenvectors based on the correlation matrix, where T is an integer one of greater; and means for obtaining a channel estimate for the communication channel based on the T noise eigenvectors. ### Claim 34 (depends on 33) The apparatus of claim 33, further comprising: means for obtaining a plurality of partial frequency response estimates for a plurality of different sets of subbands, wherein each partial frequency response estimate is for a portion of a total bandwidth for the system and is obtained from one set of subbands, and wherein the frequency response estimate for the communication channel comprises the plurality of partial frequency response estimates.