# US 2010/0166118 A1 · Channel estimation for a wireless communication system with multiple parallel data streams > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2010/0166118 A1 - Document ID: US20100166118A1 - Status: Published application - Kind: A1 - Application number: 12/702,007 - Filed: 2010-02-08 - Published: 2010-07-01 - Earliest claimed: 2004-02-05 - Assignees: QUALCOMM Incorporated - Inventors: Ashok Mantravadi; Aamod Khandekar - Web page: https://patentgrep.com/patent/US20100166118A1 ## CPC - H04L 25/022: {of frequency response} - H04J 11/004: {using regenerative subtractive interference cancellation} - H04L 25/023: {with extension to other symbols} - H04L 27/3488: {Multiresolution systems} - H04L 2001/0093: {Point-to-multipoint} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S) ## Abstract To recover multiple data streams transmitted simultaneously, a first channel estimate is derived for a wireless channel based on received pilot symbols. Detection is performed on received data symbols using the first channel estimate to obtain detected symbols for a first data stream. These detected symbols are decoded to obtain a decoded first data stream, which is re-encoded to obtain remodulated symbols. A second channel estimate is derived based on the remodulated symbols. The first and second channel estimates are combined to obtain a third channel estimate having higher quality. Interference due to the first data stream is estimated using the third channel estimate and canceled from the received data symbols. Detection is performed on interference-canceled symbols using the third channel estimate to obtain detected symbols for a second data stream. These detected symbols are further decoded to obtain a decoded second data stream. ## Claims ### Claim 1 A method of recovering first and second data streams transmitted simultaneously via a wireless channel in a wireless communication system, comprising: deriving a first channel estimate for the wireless channel based on received symbols; performing detection for the first data stream using the first channel estimate; deriving a second channel estimate based on the detected first data stream; deriving a third channel estimate based on the first and second channel estimates; and performing detection for the second data stream using the third channel estimate. ### Claim 2 (depends on 1) The method of claim 1, wherein the first channel estimate for the wireless channel is derived based on received pilot symbols. ### Claim 3 (depends on 1) The method of claim 1, further comprising: estimating interference due to the first data stream using the third channel estimate, and wherein the detection for the second data stream is performed with the estimated interference from the first data stream canceled. ### Claim 4 (depends on 3) The method of claim 3, wherein the first and second data streams are combined prior to transmission via the wireless channel. ### Claim 5 (depends on 1) The method of claim 1, wherein the deriving a first channel estimate includes obtaining a frequency response estimate for the wireless channel based on the received pilot symbols, deriving a time-domain impulse response estimate for the wireless channel based on the frequency response estimate, and deriving the first channel estimate based on the time-domain impulse response estimate. ### Claim 6 (depends on 5) The method of claim 5, wherein the time-domain impulse response estimate is derived by performing an inverse fast Fourier transform (IFFT) on the frequency response estimate, and wherein the first channel estimate is derived by performing a fast Fourier transform (FFT) on the time-domain impulse response estimate. ### Claim 7 (depends on 1) The method of claim 1, wherein the deriving a second channel estimate includes obtaining a frequency response estimate for the wireless channel based on the detected first data stream, deriving a time-domain impulse response estimate for the wireless channel based on the frequency response estimate, and deriving the second channel estimate based on the time-domain impulse response estimate. ### Claim 8 (depends on 1) The method of claim 1, wherein the first and second channel estimates are time-domain impulse response estimates, and wherein the third channel estimate is a frequency response estimate derived by combining and transforming the time-domain impulse response estimates for the first and second channel estimates. ### Claim 9 (depends on 1) The method of claim 1, wherein the first channel estimate comprises channel gain estimates for a first group of subbands and the second channel estimate comprises channel gain estimates for a second group of subbands, and wherein the third channel estimate is derived based on a concatenation of the channel gain estimates for the first and second groups of subbands. ### Claim 10 (depends on 9) The method of claim 9, wherein the third channel estimate is derived by frequency interpolation of the channel gain estimates for the first and second groups of subbands. ### Claim 11 (depends on 9) The method of claim 9, wherein the first group of subbands is used for pilot transmission and the second group of subbands is used for data transmission. ### Claim 12 (depends on 1) The method of claim 1, wherein the detection for the first data stream is performed on received data symbols and provides detected symbols for the first data stream. ### Claim 13 (depends on 12) The method of claim 12, further comprising: decoding the detected symbols for the first data stream to obtain decoded data for the first data stream; and re-encoding the decoded data to obtain remodulated symbols for the first data stream, and wherein the second channel estimate is derived based on the remodulated symbols and the received data symbols. ### Claim 14 (depends on 12) The method of claim 12, further comprising: mapping the detected symbols for the first data stream to modulation symbols based on a modulation scheme used for the first data stream, and wherein the second channel estimate is derived based on the modulation symbols and the received data symbols. ### Claim 15 (depends on 1) The method of claim 1, wherein the deriving a third channel estimate includes scaling the first channel estimate with a first scaling factor, scaling the second channel estimate with a second scaling factor, and combining the scaled first channel estimate and the scaled second channel estimate to obtain the third channel estimate. ### Claim 16 (depends on 15) The method of claim 15, wherein the first and second scaling factors are selected based on reliability of the first channel estimate relative to reliability of the second channel estimate. ### Claim 17 (depends on 1) The method of claim 1, further comprising: filtering the first channel estimate, and wherein the third channel estimate is derived based on the filtered first channel estimate. ### Claim 18 (depends on 1) The method of claim 1, further comprising: filtering the second channel estimate, and wherein the third channel estimate is derived based on the filtered second channel estimate. ### Claim 19 (depends on 1) The method of claim 1, further comprising: filtering the third channel estimate, and wherein the detection for the second data stream is performed using the filtered third channel estimate. ### Claim 20 (depends on 1) The method of claim 1, further comprising: filtering the first, second, or third channel estimate in time domain or frequency domain. ### Claim 21 (depends on 20) The method of claim 20, wherein the filtering is performed with an infinite impulse response (IIR) filter. ### Claim 22 (depends on 20) The method of claim 20, wherein the filtering is performed with a finite impulse response (FIR) filter. ### Claim 23 (depends on 1) The method of claim 1, wherein the wireless communication system utilizes orthogonal frequency division multiplexing (OFDM). ### Claim 24 (depends on 23) The method of claim 23, wherein the received pilot symbols are obtained in each OFDM symbol period and for a set of subbands used for pilot transmission. ### Claim 25 (depends on 23) The method of claim 23, wherein the received pilot symbols are obtained for OFDM symbol periods used for pilot transmission, wherein the first channel estimate is derived for each OFDM symbol period used for pilot transmission, and wherein the second channel estimate is derived for each OFDM symbol period used for data transmission. ### Claim 26 (depends on 1) The method of claim 1, wherein the wireless communication system is a multiple-input multiple-output (MIMO) communication system, and wherein the first and second data streams are transmitted simultaneously from a plurality of antennas. ### Claim 27 An apparatus operable to recover first and second data streams transmitted simultaneously via a wireless channel in a wireless communication system, comprising: a channel estimator operative to derive a first channel estimate for the wireless channel based on received symbols, derive a second channel estimate based on detected symbols for the first data stream, and derive a third channel estimate based on the first and second channel estimates; and a detector operative to perform detection for the first data stream using the first channel estimate, provide the detected symbols for the first data stream, perform detection for the second data stream using the third channel estimate, and provide detected symbols for the second data stream. ### Claim 28 (depends on 27) The apparatus of claim 27, wherein the detector is further operative to estimate interference due to the first data stream using the third channel estimate and to perform detection for the second data stream with the estimated interference from the first data stream canceled. ### Claim 29 (depends on 27) The apparatus of claim 27, further comprising: a receive data processor operative to decode the detected symbols for the first data stream to obtain decoded data for the first data stream and to re-encode the decoded data to obtain remodulated symbols for the first data stream, and wherein the channel estimator is operative to derive the second channel estimate based on the remodulated symbols and received data symbols. ### Claim 30 An apparatus operable to recover first and second data streams transmitted simultaneously via a wireless channel in a wireless communication system, comprising: means for deriving a first channel estimate for the wireless channel based on received symbols; means for performing detection for the first data stream using the first channel estimate; means for deriving a second channel estimate based on the detected first data stream; means for deriving a third channel estimate based on the first and second channel estimates; and means for performing detection for the second data stream using the third channel estimate. ### Claim 31 (depends on 30) The apparatus of claim 30, further comprising: means for estimating interference due to the first data stream using the third channel estimate, and wherein the detection for the second data stream is performed with the estimated interference from the first data stream canceled. ### Claim 32 (depends on 30) The apparatus of claim 30, further comprising: means for decoding detected symbols for the first data stream to obtain decoded data for the first data stream, and means for re-encoding the decoded data to obtain remodulated symbols for the first data stream, and wherein the second channel estimate is derived based on the remodulated symbols and received data symbols. ### Claim 33 A computer-readable medium storing instructions for recovering first and second data streams transmitted simultaneously via a wireless channel in a wireless communication system, the computer-readable medium comprising: code for causing a computer to derive a first channel estimate for the wireless channel based on received symbols; code for causing a computer to perform detection for the first data stream using the first channel estimate; code for causing a computer to derive a second channel estimate based on the detected first data stream; code for causing a computer to derive a third channel estimate based on the first and second channel estimates; and code for causing a computer to perform detection for the second data stream using the third channel estimate. ### Claim 34 A processor configured to execute instructions for recovering first and second data streams transmitted simultaneously via a wireless channel in a wireless communication system, wherein the processor executing the instructions is operable to: derive a first channel estimate for the wireless channel based on received symbols; perform detection for the first data stream using the first channel estimate; instructions to derive a second channel estimate based on the detected first data stream; derive a third channel estimate based on the first and second channel estimates; and perform detection for the second data stream using the third channel estimate.