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11ah Preamble for 2MHz and Beyond

Jan 2012. 11ah Preamble for 2MHz and Beyond. Authors:. Date: 2012-01-16. Authors continued:. Slide 2. Abstract. This presentation proposes the preamble format for 11ah 2MHz, and wider BW packets, including 4MHz, 8MHz and 16MHz.

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11ah Preamble for 2MHz and Beyond

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  1. Jan 2012 11ah Preamble for 2MHz and Beyond Authors: Date: 2012-01-16 Hongyuan Zhang, et. Al.

  2. Authors continued: Hongyuan Zhang, et al Slide 2

  3. Abstract This presentation proposes the preamble format for 11ah 2MHz, and wider BW packets, including 4MHz, 8MHz and 16MHz. Hongyuan Zhang, et. Al.

  4. 11ac and 11n preambles apply a mixed-mode preamble, which is composed by a legacy portion for legacy device to decode the signal field, and a (V)HT portion. • Legacy portion and (V)HT portion have AGC fields separately. • 11ac also relies on MM preamble for transmitting MU packets. • 11n also defines a green field preamble, in which only HT portion is present, and preamble duration is shorter • Extra protection is required for GF transmissions. Background HT-MM: Legacy portion HT portion L-STF L-LTF L-SIG HT-SIG HT-STF HTLTF1 HTLTF2 HTLTF3 HTLTF4 HT-DATA 2 symb 2 symb 1 symb 2 symb 1 symb 1 symb … HT-GF: HT-STF HTLTF1 HT-SIG HTLTF2 HTLTF3 HTLTF4 HT-DATA 2 symb 2 symb 2 symb 1 symb 1 symb … Hongyuan Zhang, et. Al.

  5. 2/4/8/16MHz signals are basically downclocked versions of 11ac 20/40/80/160MHz. • 11ah is a “green field” system, therefore a green field type of preamble is preferred, at least for regular single user (SU) packet. • Downlink MU-MIMO may be an optional feature for 11ah, its benefit may be limited to WiFi offloading use cases—therefore MU preamble should not burden regular SU frame format • Different from 11ac, in which a common preamble format was defined for both MU and SU • Therefore we propose a different MU “mixed mode” frame format for >=2MHz, which is similar to 11ac MU packet format. Overview: 802.11ah Preamble for >=2MHz Hongyuan Zhang, et. Al.

  6. I. SU Preamble for >=2MHz • The general structure for SU open-loop packet is similar to 11n green field preamble, as below. • Each field is explained in subsequent slides. QBPSK … STF LTF1 SIG LTF2 LTF_NLTF DATA (2 symbols) (2 symbols ) (2 symbols) (1 symbol each) DGI LTS LTS Hongyuan Zhang, et. Al.

  7. Use the same tone design as in 11n, i.e. in each 2MHz, STF occupies 12 non-zero tones in {±4 ±8 ±12 ±16 ±20 ±24}. None-zero tones are mapped to space-time streams using the first column of P matrix, the same way as in 11n GF preamble. STF Field Hongyuan Zhang, et. Al.

  8. Define the 11ah LTF signs for >= 2MHz PPDUs the same as the VHTLTF signs in the corresponding 11ac packets with the same FFT sizes. In data tones of LTF, the mapping from NSTS space-time streams to NLTF LTFs is the same as in 11n green field preamble, with the P matrix. LTF Fields Hongyuan Zhang, et. Al.

  9. 2 symbols, each modulated using Q-BPSK, same as in 11n green field preamble. • 52 data tones, modulated using 11n/11ac MCS0. • Note that 11n HTSIG uses 48 data tones. • Data tones are mapped to multiple space-time streams using the first column of P matrix—the same as in 11n GF preamble. SIG Field Hongyuan Zhang, et. Al.

  10. Propose MU packets using a “mixed-mode” format II. MU Preamble for >=2MHz “Omni” Portion MU Portion … STF LTF1 SIGA MU-STF MU-LTF1 MU-LTF_NLTF SIGB DATA (2 symbols) (2 symbols as 11n GF) (2 symbols) (1 symbol) (1 symbol each) DGI LTS LTS Hongyuan Zhang, et. Al.

  11. LTF1 and SIG field both have 52 data tones. • Different from the legacy portion of 11n MM preamble and 11ac preamble. • STF/LTF1/SIG fields applies single stream in each subcarrier (without the 1st column P matrix mapping as seen in SU preamble), similar to the legacy portion of 11n MM preamble and 11ac preamble. • SIG field subfield definition is different from SU, and the two symbols in SIG field are modulated using QBPSK and BPSK respectively • Refer to later “auto-detection” slide. Omni Portion Hongyuan Zhang, et. Al.

  12. MU-STF is the same as (downclocked) 11ac VHT-STF. • Modulation flows of MU-STF, MU-LTFs, and SIGB are the same as 11ac MU packets. • i.e. all streams for all users are trained by MU-LTFs. • Up to 4 space-time stream across all users (refer to [2]). MU Portion Hongyuan Zhang, et. Al.

  13. For >=2MHz SU and MU packets, the 1st SIG symbol is always QBPSK • Used for autodetection between 1MHz and 2MHz preamble—refer to [1]. • The 2nd SIG symbol is used for autodetection between SU and MU packets. Auto-Detections QBPSK QBPSK GI SIG1 GI SIG2 DGI LTS LTS 64FFT SIG for SU: SU/MU detection by SIG2 rotation. QBPSK BPSK GI SIGA1 GI SIGA2 DGI LTS LTS 64FFT SIG for MU: 1st 1MHz/2MHz autodetection approach using LTF sequences, refer to[1] 2nd 1MHz/2MHz autodetection approach using QBPSK rotation, refer to [1] 1MHz LTF1: (refer to [1]) DGI LTS LTS GI LTS GI LTS Hongyuan Zhang, et. Al.

  14. For 4MHz, 8MHz, and 16MHz packets, the STF/LTF/SIG field designs are similar to 11ac 40/80/160MHz. • STF/SIG fields are repeated and phase rotated (same as in 11ac) over each 2MHz subband. • LTF signs in the tones of each 2MHz subband, when overlapping with the tones with a stand-alone 2MHz LTF, have the same values as the corresponding signs in 2MHz LTF. Wider BW Hongyuan Zhang, et. Al.

  15. 2MHz SIG(A) • Recall that SU and MU are differentiated by autodetection Jan 2012 III. SIG Field Content (new in r2) Hongyuan Zhang, et. Al.

  16. LENGTH/DURATION: in num of symbols when aggregation is 1, is in num of bytes when aggregation is 0, Mandate AMPDU for packet sizes > 511 bytes and for MU. STBC: Same as in 11ac (Alamouti code on all streams or none). Nsts: for SU (2 bits), represents 1~4 STS; for MU (8 bits), represents 0~3 STS per user for the 4 users. Coding: for SU 1 bit indicates BCC/LDPC, the other bits indicates additional symbol during LDPC encoding process; for MU, 4 bits indicates BCC/LDPC of 4 clients, and 1 bit indicates whether additional symbols happens for any user when encoding LDPC (same as 11ac). MCS: for SU, 4 bit MCS index; for MU, reuse 3 bits for BCC/LDPC indicator for users 2~4—similar as in 11ac VHTSIGA. Aggregation: Mainly applicable for SU, reserved for MU. CRC: 4 bits of CRC should be enough as shown in the Appendix GID: 6-bit GID as in 11ac for MU, not needed for SU. PAID: 12 bits PAID to accommodate more clients than 11ac, not needed for MU. Subfield Descriptions: Hongyuan Zhang, et. Al.

  17. 2MHz SIGB (MU) Hongyuan Zhang, et. Al.

  18. Do you agree with the “green field” type preamble structure for >=2MHz SU open-loop packets, as shown in slide 6~9? Straw Poll – 1 (from Nov Meeting) Hongyuan Zhang, et. Al.

  19. Do you agree with the MU preamble structure for >=2MHz packets, as shown in slide 10~12? Straw Poll – 2 (from Nov Meeting) Hongyuan Zhang, et. Al.

  20. Do you agree with the SU/MU autodetection mechanism, as shown in slide 13? Straw Poll – 3 (from Nov Meeting) Hongyuan Zhang, et. Al.

  21. Do you agree with the 4/8/16 MHz frame format description, as shown in slide 14? Straw Poll – 4 (new in r2) Hongyuan Zhang, et. Al.

  22. Do you agree with the >=2MHz SIG field content as shown in slides 15~17? • Bit ordering and grouping are TBD. • PAID number of bits and detailed content are TBD. • Reserved field could be used for additional TBD MAC and PHY signaling Straw Poll – 5 (new in r2) Hongyuan Zhang, et. Al.

  23. [1] 11-11-1482-03-00ah-preamble-format-for-1-MHz [2] 11-11-1275-01-00ah-spatial-stream-support References Hongyuan Zhang, et. Al.

  24. Results below shows that the false positive prob of 1MHz SIG when using 4-bit CRC is approx. one magnitude lower than the error rate of 1MHz SIG field. Appendix: 4-Bit CRC Jan 2012

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