11ac 80MHz Transmission Flow

1. 11ac 80MHz Transmission Flow Date: 2010-05-17 Authors: Slide 1 Sudhir Srinivasa et al.

2. Introduction • Core features of 11ac Basic PHY • Higher bandwidth (at least 80MHz) • Higher order constellations (256QAM) • Data and pilot tone mappings for both 80MHz and higher bandwidths have been discussed in [1, 2]. • This presentation will discuss the 80MHz MIMO-OFDM transmission flow in Data field for BCC encoding, including: • Encoder and stream parsing • Interleaver design Sudhir Srinivasa et al.

3. Preliminaries • We assume that PPDU duration is signaled in number of symbols in the SIG field [3]. • MAC/PHY Padding is required to ensure that the coded bits fit inside an integer number of OFDM symbols • Some details about MAC and PHY padding has been presented in previous meetings [3] • The following slides describe the 80MHz MIMO-OFDM transmitter flow in detail. Sudhir Srinivasa et al.

4. Transmitter Block Diagram for 11ac PHY padding Sudhir Srinivasa et al.

5. Padding bits are added to ensure that the coded bits fit inside an integer number of OFDM symbols. This is done as follows (details refer to [3]) : MAC adds required 4-byte null sub-frames and 0-3 bytes of final MAC pad to fill the frame to the last byte PHY adds the remaining 0-7 padding bits to the end of the OFDM symbol. PHY padding before encoder parser. (Service bits + MAC payload + MAC/PHY padding bits) are passed to the scrambler. Add Tail, Encoding & Puncturing Encoder Parser Stream Parser AMPDU (with MAC pad) Add 0-7 PHY padding bits Scrambler Padding Sudhir Srinivasa et al.

6. With multiple encoders, scrambled data bits are distributed evenly among all the encoders, exactly like the encoder parser in 11n Every consecutive block of NES bits divided among the NES encoders in a round robin fashion, i.e., one bit assigned per encoder in one cycle (identical to 11n). The overall number of bits after padding should be divided to equal number of bits allocated to each encoder. 6 tail bits are added at each BCC encoder Note that padding bits are scrambled, but the tail bits are not. Encoded bits are punctured based on the coding rate Add Tail, Encoding & Puncturing Encoder Parser Stream Parser AMPDU (with MAC pad) Add 0-7 PHY padding bits Scrambler Encoder Parser Sudhir Srinivasa et al.

7. The same stream parsing as 11n: Consecutive blocks of  s (num of bits on each constellation axis) bits are assigned to different spatial streams in a round robin fashion. If multiple encoders per user are present, the output of each encoder is used alternately in a round robin cycle, i.e., at the beginning S=NSSs bits from the output of first encoder are fed into all spatial streams, and then S bits from the output of the next encoder are used and so on. Stream Parser Add Tail, Encoding & Puncturing Encoder Parser Stream Parser AMPDU (with MAC pad) Scrambler 0-7 bits PHY padding Sudhir Srinivasa et al.

8. Same interleaver structure as 11n, i.e. 3 permutations (characterized by three parameters NROW, NCOL and NROT) NROW/NCOL Chosen as a good tradeoff for all constellations from BPSK through 256QAM Simulations (backup slides) show that a good choice for these parameters in 80MHz (234 data tones) is NCOL = 26, NROW = 9 * NBPSCS, where NBPSCS is the number of coded bits per subcarrier per stream. We also propose to define NROT as below: When Nss <=4: NROT = floor(234/4)=58, so cyclic shift [0, 2 NROT*NBPSCS, NROT*NBPSCS, 3 NROT*NBPSCS]) for NSS=1,2,3,4 respectively. When NSS >4: the stream cyclic rotation rule is TBD. Frequency Interleaver for 80MHz Sudhir Srinivasa et al.

9. Conclusions • 80MHz MIMO-OFDM Tx Flow is given, with emphasis on: PHY padding, BCC encoder parser, interleaver. • Summarizing our proposed parameters: • Encoder Parser with 1 bit round-robin, equal number of bits per encoder. • Same stream parser as in 11n • Interleaver: NCOL=26; for Nss<=4, NROT= 58 and [0 2 1 3]* NROT cyclic permutation is applied for each stream, as in 11n. Sudhir Srinivasa et al.

10. Straw Poll 1 (20/40MHz Interleaver) • Do you support adding the following to the specification framework document (11-09/0992, Section 3.2.4.x (VHT Data Field)): • For BCC encoding, the interleaver parameters for 20/40MHz 802.11ac packets will remain unchanged from 20/40MHz 802.11n, i.e., the NCOL and NROT parameters for 20/40MHz are as in the table below: • Yes: • No: • Abstain: Sudhir Srinivasa et al.

11. Straw Poll 2 (80MHz Interleaver NCOL) • Do you support adding the following to the specification framework document (11-09/0992, Section 3.2.4.x (VHT Data Field)): • For BCC encoding, the NCOL value for 80 MHz 11ac is given by NCOL = 26 • Yes: • No: • Abstain: Sudhir Srinivasa et al.

12. Straw Poll 3 (80MHz Interleaver NROT) • Do you support adding the following to the specification framework document (11-09/0992, Section 3.2.4.x (VHT Data Field)): • For BCC encoding, the NROT value for 80 MHz 11ac is given by NROT = 58 for 4 or fewer streams • The cyclic shifts applied on the different streams are given by [0 2 1 3]* NROT, identical to 11n • Yes: • No: • Abstain: Sudhir Srinivasa et al.

13. Straw Poll 4 (Encoder Parsing) • Do you support adding the following to the specification framework document (11-09/0992, Section 3.2.4.x (VHT Data Field)): • For BCC encoding, the encoder parsing done in the same way as in 11n, i.e., • The encoder parser cycles through all the encoders in a round robin fashion assigning one bit to each encoder in each cycle. • Each encoder is therefore assigned an equal number of bits. • Yes: • No: • Abstain: Sudhir Srinivasa et al.

14. Straw Poll 5 (Stream Parsing) • Do you support adding the following to the specification framework document (11-09/0992, Section 3.2.4.x (VHT Data Field)): • For BCC encoding, stream parsing done in the same way as 11n, i.e., • Consecutive blocks of  s(iss) bits are assigned to different spatial streams in a round robin fashion. • If multiple encoders are present per user, the output of each encoder is used in a round robin cycle, i.e., • At the beginning S bits from the output of first encoder are fed into all spatial streams, • Then S bits from the output of the next encoder are used and so on. S is a sum of s(iss) over all streams) • Yes: • No: • Abstain: Sudhir Srinivasa et al.

15. References [1] 11-10-0370-00-00, 80MHz Tone Allocation [2] 11-10-0378-00-00, 160MHz PHY Transmission [3] 11-10-0064-04-00, VHT Frame Padding [4] IEEE802.11-09/0992r3, R. Stacey et al., Proposed Specification Framework for TGac Sudhir Srinivasa et al.

16. Backup Slides Sudhir Srinivasa et al.

17. Simulation Results 1 Sudhir Srinivasa et al.

18. Simulation Results 2 Sudhir Srinivasa et al.

19. Simulation Results 3 Sudhir Srinivasa et al.

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