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Bits Consideration for SIGNAL fields

Bits Consideration for SIGNAL fields. Date: 2010-05-20. Authors:. Slide 1. Abstract. 10/0382r1 was presented at Orlando meeting last March A couple of motions were passed in TGac Bandwidth and STBC indication bits are located in VHT-SIG-A

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Bits Consideration for SIGNAL fields

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  1. Bits Consideration for SIGNAL fields Date: 2010-05-20 Authors: Slide 1 Joonsuk Kim, et. al..

  2. Abstract • 10/0382r1 was presented at Orlando meeting last March • A couple of motions were passed in TGac • Bandwidth and STBC indication bits are located in VHT-SIG-A • Allow only equal modulation and coding scheme for Single User • With revision r2, we’d like to update the old business that were not agreed nor treated last time • Old business • Only the same modulation and the same coding rate and coding type across all streams for multi user case • 1 bit for STBC indication • Zero value of GroupID for SU and broadcasting (Not treated) • New business • 6 bits for GroupID field • No bits for sounding and smoothing Joonsuk Kim, et. al..

  3. Preamble Structure [1] Rate=6Mbps Length determined by T 2 symbols 1 symbol L-STF L-LTF L-SIG VHTSIGA VHT-STF VHT-LTFs VHTSIGB VHTData T VHT auto-detection Joonsuk Kim, et. al..

  4. Different Natures for VHT-SIGs in MU • VHT-SIGA contains the “common” bits for all clients. • Bits/Fields that deliver common information for all users need to be located in VHT-SIGA • Information on the number of VHT-LTFs to follow also need to be located in VHT-SIGA • Better to indicate the number of spatial streams earlier for a receiver to be prepared for decoding DATA • Bandwidth indication also needs to be informed earlier before VHT-STF. • VHT-SIGB contains user-specific information (e.g. modulation and coding rate) and is spatially multiplexed for different clients. • Typically, VHT-STF,VHT-LTFs and VHT-SIGB are being beamformed in order to minimize the interference terms for other users • It is placed after all the VHT-LTFs to enable better receiver side interference mitigation in DL-MU before decoding VHT-SIGB. Joonsuk Kim, et. al..

  5. Bits/Fields to Consider in VHT-SIGs • Bandwidth  VHT-SIGA • Needs to be informed early before VHT-STF • Group ID Field  VHT-SIGA • It indicates the number of VHT-LTFs and the stream numbers to decode for each STA • MCS  VHT-SIGB • MCS is a user-specific information • STBC  VHT-SIGA • If Nsts is not the same as Nss with STBC encoded symbols, it needs to be informed early for a recipient to be prepared to decode symbols correctly. • Short GI • Sounding • Smoothing • Coding Type • CRC & Tail: Located at both VHT-SIGA and SIGB. Bits in Italic font are not covered in this presentation Other new bits/fields are possible to consider if necessary, for example, MAC ID, Number of Extension Streams and Resolvable/Non-resolvable LTF Indication Joonsuk Kim, et. al..

  6. GroupID Field in VHT-SIG A [2] • VHT-SIG A tells the number of columns of Qk (steering matrix for user k) in the order of assigned user number in the group-definition-field. • All STAs can listen to VHT-SIG A, so each participating user knows when to start to detect its own stream. • VHT-SIG A includes following fields • Some of these bits may be reused for SU-MIMO packet • Usage scenario of GroupID • If it is non–zero • The receiving STA(s) use the GroupID as described above • If it is zero (Only the first 3 bits out of x bits in Nsts field are sufficient to indicate the number of streams), the packet can be either • Single user transmission (SU-MIMO packet) • A transmission when the group membership between the transmitter and the receiving STA(s) is not established yet. • A transmission that needs to bypass a group (for example, a broadcast packet) y bits x bits Qk is the steering matrix for user k Group ID # of columns of Qk (Nsts_k) for k=1,2,3,4 x>0, y >0 x bits indicate the number of columns of Nsts for user 1,2,3 and 4. Details are TBD It is possible Nsts_k = 0 for certain k if STA k is not a recipient of MU-MIMO packet. Joonsuk Kim, et. al..

  7. MCS Field in VHT-SIG B • For 802.11n, we have 77 MCS sets to cover many combinations for up to 4 streams with unequal modulations. • For 802.11ac, we’re talking about 256 QAM and up to 8 streams, which may end up with too many combinations. • For testing purpose, we have too many modes. • With simpler design for MCS table, we don’t need a giant LUT for implementation. • We propose not to allow unequal modulation for 11ac MCS set. Joonsuk Kim, et. al..

  8. STBC Bits in VHT-SIG A Spatial Mapping STBC • 802.11n has a hybrid mode of SDM and STBC (for example, Nss=3 and Nsts=4) • If we allow this with up to 8 streams for 11ac, it also causes a lot of STBC modes (testing issue) • We propose only one bit for STBC mode (Almouti scheme) • If Nsts is even, Nsts = 2*Nss • If Nsts is odd, Nsts = 2*Nss – 1 (only one stream is not STBC encoded) • Whether or not we allow this case (Nsts is odd) is TBD • If it is allowed, the position of spatial-stream that is not encoded by STBC is TBD . . . . . . . . . Nss Nsts Ntx Joonsuk Kim, et. al..

  9. Reference [1] 11-10/0070r5 “802.11ac Preamble.ppt” [2] 11-10/0073r2 “GroupID Concept for Downlink MU-MIMO Transmission.ppt” Joonsuk Kim, et. al..

  10. Straw Poll on Bit Allocation in VHT-SIGs • Do you support including TBD bits for Bandwidth and STBC in VHT-SIGA and including MCS field in VHT-SIGB, and editing the spec framework document, 11-09-0992, accordingly? • This motion passed in TGac Joonsuk Kim, et. al..

  11. Straw Poll on MCS field • Do you support allowing only equal modulation and coding scheme across all streams per user and stating this in the spec framework document, 11-09-0992? • This straw poll failed in PHY adhoc • It was amended in TGac as follows • Move to support allowing only the same modulation and the same coding rate and coding type across all streams for single user case and stating this in the spec framework document, 11-09-0992 • This motion passed in TGac Joonsuk Kim, et. al..

  12. Straw Poll on STBC bit • Do you support to have one bit to indicate STBC mode (Alamouti scheme) and to edit the spec framework document, 11-09-0992, accordingly? • This straw poll failed in PHY adhoc Joonsuk Kim, et. al..

  13. Update Joonsuk Kim, et. al..

  14. Smoothing Bit and Non-sounding Bit • Both bits are in HT-SIG for 11n • Smoothing bit • This bit is to indicate receivers that AP recommends whether to apply smoothing algorithm for the channel estimation or not • We believe it is not necessary • Receivers decide their own channel estimation algorithm anyway • Non-sounding bit • This bit is used to indicate the packet with PHY payload is a sounding PPDU • If NDP sounding is the only option for sounding PPDU, this bit is not necessary • VHT packets with L-SIG length corresponding to zero VHT data symbols indicates sounding packet Joonsuk Kim, et. al..

  15. Bits for GroupID field [2] • The number of bits for GroupID field is not determined • It is mentioned to consider 4 bits for example in [2] • In order to support large network of STAs, we believe it is better to have 6 bits for GroupID field • How to define and to signal the GroupID field is under investigation • Need to look at techniques to manage the GroupID, for example (but not limited to), • Overloading • Multiple sets of STAs per GroupID Joonsuk Kim, et. al..

  16. Straw Poll on Smoothing Bit • Do you support excluding smoothing bit in VHT-SIG and stating this in the spec framework document, 11-09-0992? • Yes: • No: • Abs: Joonsuk Kim, et. al..

  17. Straw Poll on Non-sounding Bit • Do you support excluding non-sounding bit in VHT-SIG and stating this in the spec framework document, 11-09-0992? • Yes: • No: • Abs: Joonsuk Kim, et. al..

  18. Straw Poll on a Specific GroupID Value • Do you support the specific usage of a GroupID value of zero as described in Slide 6 of 11-10-0382r2 and stating this in the spec framework document, 11-09-0992? • Yes: • No: • Abs: Joonsuk Kim, et. al..

  19. Straw Poll on Bits for GroupID Field • Do you support 6 bits for GroupID field (i.e., y=6 in slide 6) and stating this in the spec framework document, 11-09-0992? • Yes: • No: • Abs: Joonsuk Kim, et. al..

  20. Straw Poll on MCS field- Old Business - • Do you support allowing only the same modulation and the same coding rate and coding type across all streams belonging to each user for multi user case as well, and stating this in the spec framework document, 11-09-0992? • Yes: • No: • Abs: Joonsuk Kim, et. al..

  21. Straw Poll on STBC Bit- Old Business - • Do you support to have one bit to indicate STBC mode (Alamouti scheme)and stating this in the spec framework document, 11-09-0992? • Yes: • No: • Abs: Joonsuk Kim, et. al..

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