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Interleaver for Nss>4

Interleaver for Nss>4. Date: 2011-01-18. Authors:. Background. BCC interleaver permutations are characterized by three parameters N ROW , N COL and N ROT as in 11n. In 11ac, N ROW , N COL and N ROT need to be modified to accommodate higher bandwidths and/or more streams.

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Interleaver for Nss>4

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  1. Interleaver for Nss>4 Date: 2011-01-18 Authors:

  2. Background • BCC interleaver permutations are characterized by three parameters NROW, NCOL and NROT as in 11n. • In 11ac, NROW, NCOL and NROT need to be modified to accommodate higher bandwidths and/or more streams. • Column depth for 80MHz is 26, i.e., (NCOL = 26, NROW = 9 * NBPSCS) • NROT and Stream Permutaions: • When Nss <=4 20/40MHz: NROT and permutation are the same as 11n. • When Nss <=4 80MHz: NROT = floor(234/4)=58, so cyclic shift [0, 2, 1, 3]* NROT*NBPSCS) for Nss=1,2,3,4 respectively (as in current spec framework). • When Nss >4: the SS permutation and NROT are TBD.

  3. Best set of SS permutation and NROT for Nss >4 based on largest D (1/4) • Given BW and Nss >4, find SS permutation and NROT such that average subcarrier distance (D) of two adjacent SS is maximized. Specifically, where ``” means the third interleaver permutation, i.e., freq. rotation based on SS permutation and NROT, A is the normalization factor, i is the data tone index before the third permutation, k,m are the exact tone index after the permutation. |a| is to take the absolute value of a. Note: Objective criterion of the best set of SS permutation and NROTis to provide best PER performance.

  4. Best set of SS permutation and NROT for Nss >4 based on largest D (2/4) One practical issue: More than one set of SS permutation and Nrot give the same D value. For example, for (80M, 7SS), 58*[0 6 4 1 3 5 2], and 58*[0 2 5 3 1 4 6] give the same D of 115.6. Break the tie:Check the average distance of the j-th adjacent SS, where j =2,3… until the tie is resolved. Specifically, Using the above method, we get one best set of SS permutation and Nrot for most of pair (BW, Nss), except few case such as (80M, 5 ss). For (80M, 5 ss), 47*[0 2 4 1 3] and 47*[ 0 3 1 4 2] give the same D’s for all possible j.

  5. 80M 8ss Best D corresponds to 28*[0 5 2 7 3 6 1 4] Best set of SS permutation and NROT for Nss >4 based on largest D (3/4) • One example of the simulation curves: two dimensional search for best SS permutation and NROT for (80M, 8 ss): each ``*” corresponds the largest D (j=1) for a given Nrot among all the possible SS permutations.

  6. Best set of SS permutation and Nrot for Nss >4 based on largest D (4/4) Some considerations • The criterion based on largest D requires different Nrot and SS permutation for each pair of (BW, Nss). • This criterion may not provide best PER performance, but can be used as a reference of a good PER curve. • Nss>4 has stringent SNR requirement and already very high complexity in basic Tx/Rx HW, interleaver design hence should focus on the PER performances.

  7. Candidate Nrot and SS permutation for Comparisons • Selection based on largest D for each (BW, Nss) combination. • Selection based on the second largest D for each (BW, Nss) combination • Subset of Nrot*[0 4 2 6 1 5 3 7] for 5~8SS. • Nrot=floor(Ndata-tone/8) • Extension of exiting 4ss selection, i.e., subset of floor (N_data_carr/4) *[ 0 2 1 3 0 2 1 3] • Subset of Nrot*[0 5 2 7 3 6 1 4], Nrot = 28, 13, 6 for 80M, 40M and 20M, respectively. • i.e. optimize Nrot and permutation based on 8SS for different BW respectively, then take subset for 4<Nss<8.

  8. Simulation setup • Packet length: 1000 byes • MIMO: 5x8, 6x8, 7x8, 8x8 for 5, 6, 7, 8ss, respectively • Channel: 11ac DNLOS • 1000 channel realizations for each PER curve • Therefore, PER > 1% is accountable • MCS3 (16QAM ½), and MCS7 (64QAM 5/6) for different (BW, Nss) combinations. • 5 sets of Nrot and SS permutation for each (BW, Nss, MCS), as previously discussed.

  9. Summary of simulation results (1/2) • Nrot and SS permutation based on larges D provide best and close to best PER performance in all cases. • Bottom line: Their PER performance can serve as the reference for good selection of Nrot and SS permutation. • PER performance depends on many factors including BW, Nss, MCS, etc, in addition to the selection of Nrot and SS permutation. • None of the 5 sets of Nrot and SS permutation under test provide the best PER performance in all cases. But some sets show severe degradation in certain configurations, such as Set 4 for (80M, 5ss, MCS3).

  10. Summary of simulation results (2/2) By checking with the simulation results available, we propose Set 5 to be the selection of Nrot and SS permutation for Nss>4. • Recall: Set 5 is the subset of Nrot *[0 5 2 7 3 6 1 4], Nrot =28, 13 and 6 for 80M, 40M and 20M, respectively. Specifically, Set 5 has following advantages: • Good PER performance in most simulated cases, compared with the reference Set 1 and other sets • No severe degradation in any case • Systematic and Simple formulation by using the subset of 8SS.

  11. Math Expressions of the Proposal • At interleaver: if Nss>4, • At deinterleaver: if Nss>4

  12. Pre-motion #1 • Do you agree to insert the following text in 3.2.4.3.3 Frequency interleaver of the spec framework? • “For BCC encoding, when Nss>4, the third permutation of the interleaver uses the following parameters: • Permutation as the first Nss values of [0 5 2 7 3 6 1 4]*Nrot *NBPSCS. • NROT =28, 13 and 6 for 80MHz, 40MHz and 20MHz, respectively.” -Yes -No -Abstain

  13. Appendix: simulation results

  14. 29*[04261537]

  15. 29*[04261537]

  16. 29*[0426153]

  17. 29*[0426153]

  18. 29*[042615]

  19. 29*[042615]

  20. 29*[04261]

  21. 29*[04261]

  22. 13*[04261537]

  23. 13*[04261537]

  24. 13*[0426153]

  25. 13*[0426153]

  26. 13*[042615]

  27. 13*[042615]

  28. 13*[04261]

  29. 13*[04261]

  30. 6*[04261537]

  31. 6*[04261537]

  32. 6*[0426153]

  33. 6*[0426153]

  34. 6*[042615]

  35. 6*[042615]

  36. 6*[04261]

  37. 6*[04261]

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