# US 9,439,161 B2 · Physical layer design for uplink (UL) multiuser multiple-input, multiple-output (MU-MIMO) in wireless local area network (WLAN) systems > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,439,161 B2 - Document ID: US9439161B2 - Status: Granted - Kind: B2 - Application number: 14/332,301 - Filed: 2014-07-15 - Published: 2015-01-22 - Granted: 2016-09-06 - Earliest claimed: 2013-07-17 - Applicants: QUALCOMM Incorporated - Inventors: Sameer Vermani; Rahul Tandra; Didier Johannes Richard Van Nee; Albert Van Zelst; Hemanth Sampath; Bin Tian - Web page: https://patentgrep.com/patent/US9439161B2 ## CPC - H04W 56/0035: {detecting errors in frequency or phase} - H04B 7/0404: the mobile station comprising multiple antennas, e.g. to provide uplink diversity - H04B 7/0452: Multi-user MIMO systems - H04B 7/0684: {using different training sequences per antenna} - H04L 27/26: Systems using multi-frequency codes (H04L27/32 takes precedence) - H04L 27/261: {Details of reference signals} - H04L 27/2613: {Structure of the reference signals} - H04L 27/2657: {Carrier synchronisation} - H04L 5/0048: {Allocation of pilot signals, i.e. of signals known to the receiver (allocation of control signalling H04L5/0053; use of control signalling H04L5/0091)} - H04L 27/26132: {using repetition} - H04W 84/12: WLAN [Wireless Local Area Networks] - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract Certain aspects of the present disclosure provide methods and apparatus for uplink (UL) multiuser multiple-input, multiple-output (MU-MIMO) transmissions in a High Efficiency WLAN (HEW) system. One example method generally includes generating a packet having a preamble portion and transmitting the packet. The preamble portion typically includes a long training field (LTF); a first signal (SIG) field subsequent to the LTF; one or more other LTFs located subsequent to the first SIG field; and at least one second SIG field, wherein all SIG fields in the preamble portion, other than the first SIG field, are subsequent to the one or more other LTFs. Another example method generally includes receiving, from an apparatus, a packet having a preamble portion comprising tone-interleaved LTFs; and performing frequency offset adjustment on the packet based on the tone-interleaved LTFs. ## Claims ### Claim 1 A method for handling residual frequency offset error, comprising: receiving, at an apparatus, a packet having a preamble portion comprising tone-interleaved long training fields (LTFs) having interleaved tones designated for each spatial stream of each user in an uplink (UL) multiuser (MU) transmission, wherein in each tone-interleaved LTF, each spatial stream is associated with a subset of tones, wherein a first spatial stream is associated with a first subset of tones and a second spatial stream is associated with a second subset of the tones interleaved with the first subset of the tones, wherein the interleaved tones are arranged in a pattern, and wherein the pattern is shifted between two consecutive tone-interleaved LTFs; and performing frequency offset adjustment on the packet based on the tone-interleaved LTFs. ### Claim 2 (depends on 1) The method of claim 1, wherein a number of the LTFs is one more than a number of spatial streams received by the apparatus. ### Claim 3 (depends on 2) The method of claim 2, wherein a last one of the tone-interleaved LTFs is a copy of the first one of the tone-interleaved LTFs. ### Claim 4 (depends on 3) The method of claim 3, wherein performing the frequency offset adjustment comprises using phase differences for a number of tone subsets between the first and the last ones of the tone-interleaved LTFs to determine a frequency offset, wherein the number of the tone subsets equals the number of spatial streams. ### Claim 5 (depends on 1) The method of claim 1, wherein performing the frequency offset adjustment comprises performing a phase offset adjustment to correct for phase offsets that arise due to frequency errors. ### Claim 6 (depends on 1) The method of claim 1, wherein at least one of the tone-interleaved LTFs comprises a symbol having a duration greater than 4 μs. ### Claim 7 (depends on 1) The method of claim 1, wherein the pattern of the interleaved tones is shifted by one tone. ### Claim 8 (depends on 1) The method of claim 1, wherein the pattern of the interleaved tones is shifted by 2 or by 4 tones. ### Claim 9 (depends on 8) The method of claim 8, wherein each spatial stream covers one half or one quarter of all tones for the tone-interleaved LTFs. ### Claim 10 (depends on 9) The method of claim 9, further comprising interpolating missing tones before performing the frequency offset adjustment. ### Claim 11 (depends on 2) The method of claim 2, wherein a last one of the tone-interleaved LTFs is a copy of different portions of one or more prior LTFs of the tone-interleaved LTFs, according to a pattern. ### Claim 12 (depends on 11) The method of claim 11, wherein performing the frequency offset adjustment comprises correcting phase differences for a number of tone subsets between the different portions of the one or more prior LTFs and the last one of the tone-interleaved LTFs, according to the pattern. ### Claim 13 (depends on 12) The method of claim 12, wherein correcting the phase differences comprises determining a phase offset for each of the prior LTFs for each of the spatial streams. ### Claim 14 (depends on 11) The method of claim 11, further comprising: extracting information in a signal (SIG) field embedded in the last one of the tone-interleaved LTFs; and processing the packet based on the information in the SIG field. ### Claim 15 (depends on 14) The method of claim 14, wherein the extracting comprises detecting polarity changes on tones in the last one of the tone-interleaved LTFs. ### Claim 16 (depends on 1) The method of claim 1, wherein in each tone-interleaved LTF, the first and second subsets of the tones are associated with a first set of one or more subbands, a third spatial stream is associated with a third subset of tones, a fourth spatial stream is associated with a fourth subset of tones interleaved with the third subset of the tones, and the third and fourth subsets of the tones are associated with a second set of one or more subbands different than the first set. ### Claim 17 An apparatus for handling residual frequency offset error, comprising: a receiver configured to receive a packet having a preamble portion comprising tone-interleaved long training fields (LTFs) having interleaved tones designated for each spatial stream of each user in an uplink (UL) multiuser (MU) transmission, wherein in each tone-interleaved LTF, a first spatial stream is associated with a first subset of tones and a second spatial stream is associated with a second subset of the tones interleaved with the first subset of the tones, wherein the interleaved tones are arranged in a pattern, and wherein the pattern is shifted between two consecutive tone-interleaved LTFs; and a processing system configured to perform frequency offset adjustment on the packet based on the tone-interleaved LTFs. ### Claim 18 (depends on 17) The apparatus of claim 17, wherein in each tone-interleaved LTF, the first and second subsets of the tones are associated with a first set of one or more subbands, a third spatial stream is associated with a third subset of tones, a fourth spatial stream is associated with a fourth subset of tones interleaved with the third subset of the tones, and the third and fourth subsets of the tones are associated with a second set of one or more subbands different than the first set. ### Claim 19 (depends on 17) The apparatus of claim 17, wherein the processing system is configured to perform the frequency offset adjustment by performing a phase offset adjustment to correct for phase offsets that arise due to frequency errors. ### Claim 20 (depends on 17) The apparatus of claim 17, wherein a number of the LTFs is one more than a number of spatial streams received by the apparatus. ### Claim 21 (depends on 20) The apparatus of claim 20, wherein a last one of the tone-interleaved LTFs is a copy of the first one of the tone-interleaved LTFs. ### Claim 22 (depends on 21) The apparatus of claim 21, wherein the processing system is configured to perform the frequency offset adjustment by using phase differences for a number of tone subsets between the first and the last ones of the tone-interleaved LTFs to determine a frequency offset, wherein the number of the tone subsets equals the number of spatial streams. ### Claim 23 (depends on 17) The apparatus of claim 17, wherein at least one of the tone-interleaved LTFs comprises a symbol having a duration greater than 4 μs. ### Claim 24 (depends on 20) The apparatus of claim 20, wherein a last one of the tone-interleaved LTFs is a copy of different portions of one or more prior LTFs of the tone-interleaved LTFs, according to a pattern. ### Claim 25 (depends on 17) The apparatus of claim 17, wherein the pattern of the interleaved tones is shifted by one tone. ### Claim 26 (depends on 17) The apparatus of claim 17, wherein the pattern of the interleaved tones is shifted by 2 or by 4 tones. ### Claim 27 (depends on 26) The apparatus of claim 26, wherein each spatial stream covers one half or one quarter of all tones for the tone-interleaved LTFs. ### Claim 28 (depends on 27) The apparatus of claim 27, wherein the processing system is further configured to interpolate missing tones before performing the frequency offset adjustment. ### Claim 29 (depends on 24) The apparatus of claim 24, wherein the processing system is further configured to: extract information in a signal (SIG) field embedded in the last one of the tone-interleaved LTFs; and process the packet based on the information in the SIG field. ### Claim 30 (depends on 24) The apparatus of claim 24, wherein the processing system is configured to perform the frequency offset adjustment by correcting phase differences for a number of tone subsets between the different portions of the one or more prior LTFs and the last one of the tone-interleaved LTFs, according to the pattern. ### Claim 31 (depends on 30) The apparatus of claim 30, wherein correcting the phase differences comprises determining a phase offset for each of the prior LTFs for each of the spatial streams. ### Claim 32 (depends on 29) The apparatus of claim 29, wherein the processing system is configured to extract the information by detecting polarity changes on tones in the last one of the tone-interleaved LTFs. ### Claim 33 An apparatus for handling residual frequency offset error, comprising: means for receiving a packet having a preamble portion comprising tone-interleaved long training fields (LTFs) having interleaved tones designated for each spatial stream of each user in an uplink (UL) multiuser (MU) transmission, wherein in each tone-interleaved LTF, a first spatial stream is associated with a first subset of tones and a second spatial stream is associated with a second subset of the tones interleaved with the first subset of the tones, wherein the interleaved tones are arranged in a pattern, and wherein the pattern is shifted between two consecutive tone-interleaved LTFs; and means for performing frequency offset adjustment on the packet based on the tone-interleaved LTFs.