1. Comparisons of HARQ transmission schemes for 11be
9/3/2019
doc.: IEEE yy/xxxxr0
5/8/2019
Comparisons of HARQ transmission schemes for 11be
Date:
Authors:
Name
Affiliations
Address
Phone
Yan Zhang
Hongyuan Zhang 
Sudhir Srinivasa
Liwen Chu
Rui Cao
Mao Yu
Marvell
Yan Zhang et al (Marvell)
John Doe, Some Company

2. 9/3/2019
HARQ Review
HARQ CC is studied in [1][2][3], and show some performance gain over ARQ. To realize the gain, frequency diversity across transmissions is needed to achieve the potential gain via BCC interleaver or LDPC tone mapper patterns varying across transmissions.
HARQ IR is shown to have larger performance gain over ARQ in [4][5]. However, this is done with BCC encoding, which is only applied to RU size less than or equal to 242 tones, and MCS up to 9. Hence the gain cannot be realized for the commonly used applications which utilize larger RU sizes and LDPC encoding.
A modified HARQ CC scheme and HARQ IR for LDPC encoding scheme are explored and evaluated to show the potential gain of HARQ over ARQ.
Hongyuan Zhang et al (Marvell)

3. HARQ Punctured CC outline
9/3/2019
HARQ Punctured CC outline
HARQ Punctured CC is improved upon regular HARQ CC to achieve higher throughput without adding much implementation complexities at both transmitter and receiver.
All coded bits corresponding to an MPDU are transmitted in the first transmission as in regular HARQ CC.
A portion of the coded bits are transmitted in the subsequent retransmissions for soft combining at receiver side.
The percentage of the coded bits transmitted in the subsequent retransmissions can be determined based on the first transmission PER statistics.
Hongyuan Zhang et al (Marvell)

4. 9/3/2019
HARQ IR outline
The HARQ IR for LDPC encoding scheme can support all LDPC code rates and all codeword lengths employed in current WIFI standards.
Rate ½ code designs still use the ones in current standard specs. All code rates higher than ½ will be achieved by puncturing rate ½ code for a given LDPC codeword length.
The information bits and the parity bits which are not punctured are transmitted in the first transmission for a given MCS. Additional information and parity bits are transmitted in the subsequent retransmissions to achieve a lower effective code rate if the initial code rate is higher than 1/2. The lower effective code rates for the subsequent retransmissions can be determined based on either CQI reports or relevant PER statistics.
For MCS values with rate ½ code, use the same retransmission schemes as HARQ Punctured CC.
Yan Zhang et al (Marvell)

5. 9/3/2019
Simulation setup
20MHz 2x2 (2SS) and 80MHz 4x2 (2SS) DNLOS channel (channels are not normalized)
4x HE-LTF, MCS0-11
LDPC encoder
Up to 4 (re)transmissions for each packet, same channel realization is applied across all (re)transmissions for each packet. With HARQ transmission, soft combining is done over all (re)transmissions.
ARQ, HARQ CC, Punctured CC and IR are evaluated.
Yan Zhang et al (Marvell)

6. HARQ vs ARQ Throughput Comparison, with Optimal MCS selection
9/3/2019
HARQ vs ARQ Throughput Comparison, with Optimal MCS selection
HARQ Punctured CC and IR achieves highest throughput due to the efficient retransmissions compared to HARQ CC and ARQ at the same SNR value. There is up to 7dB gain using HARQ Punctured CC or HARQ IR over ARQ, and up to 4dB gain using HARQ CC over ARQ even with optimal link adaptation for the same throughput. HARQ IR improves highest achievable throughput by 21% compared to ARQ.
Yan Zhang et al (Marvell)

7. 9/3/2019
HARQ Punctured CC vs ARQ with link adaptation Throughput Comparison, with first Tx PER varying 10-40%
HARQ Punctured CC throughput values do not vary much even though first Tx PER varies from 10% to 40%, i.e, SNR operating points varies about a few dBs. On the other hand, ARQ throughput values change significantly when first Tx PER varies from 10% to 40%, especially for MCS levels above MCS 6. HARQ Punctured CC still has throughput gain when operating at SNR points resulting in 40% first Tx PER over ARQ while ARQ is operating at SNR points resulting in 10% first Tx PER. See Appendix for detailed results of ARQ and HARQ schemes at each first Tx PER value.
Yan Zhang et al (Marvell)

8. 9/3/2019
HARQ IR vs ARQ with link adaptation Throughput Comparison, with first Tx PER around 10-40%
HARQ IR throughput values are almost the same even though first Tx PER varies from 10% to 40%. On the other hand, ARQ throughput values change significantly when first Tx PER varies from 10% to 40%, especially for MCS levels above MCS 6. HARQ IR still has throughput gain when operating at SNR points resulting in 40% first Tx PER over ARQ when ARQ is operating at SNR points resulting in 10% first Tx PER. Note that first Tx PERs of HARQ IR transmission for some MCS values are higher than those with ARQ transmission since the punctured LDPC codes are not optimized for code rates higher than ½.
Yan Zhang et al (Marvell)

9. HARQ vs ARQ Throughput Comparison, with Optimal MCS selection
9/3/2019
HARQ vs ARQ Throughput Comparison, with Optimal MCS selection
HARQ IR and Punctured CC achieves highest throughput due to the efficient retransmissions compared to HARQ CC and ARQ at the same SNR value. There is up to 7dB gain using HARQ Punctured CC or IR over ARQ, up to 3dB gain over HARQ CC even with optimal link adaptation for the same throughput. HARQ IR improves highest achievable throughput by 11% compared to HARQ CC, and by 17% compared to ARQ.
Yan Zhang et al (Marvell)

10. 9/3/2019
HARQ Punctured CC vs ARQ with link adaptation Throughput Comparison, with first Tx PER around 10-40%
HARQ Punctured CC throughput values do not vary much even though first Tx PER varies from 10% to 40%, i.e, SNR operating points varies about a few dBs. On the other hand, ARQ throughput values change significantly when first Tx PER varies from 10% to 40%, especially for MCS levels above MCS 6. See Appendix for detailed results of ARQ and HARQ schemes at each first Tx PER value.
Yan Zhang et al (Marvell)

11. 9/3/2019
HARQ IR vs ARQ with link adaptation Throughput Comparison, with first Tx PER around 10-40%
HARQ IR throughput values are almost the same even though first Tx PER varies from 10% to 40%, i.e, SNR operating points varies about a few dBs. On the other hand, ARQ throughput values change significantly when first Tx PER varies from 10% to 40%, especially for MCS levels above MCS 6. HARQ IR still has throughput gain when operating at SNR points resulting in 40% first Tx PER over ARQ when ARQ is operating at SNR points resulting in 10% first Tx PER.
Yan Zhang et al (Marvell)

12. Discussions and Conclusions
9/3/2019
Discussions and Conclusions
As shown in slides 7-8, and 14-15, both HARQ Punctured CC and HARQ IR are very robust to the channel variations, i.e., the throughput values are hardly affected even though the variations of MCS assignments based on SNR measurements result in first Tx PER varying from 10% to 40%. On the other hand, ARQ throughput relies heavily on how good link adaptation can be, i.e., predicted MCS matches channel condition. ARQ throughput values varies significantly for a given MCS when SNR operating points varies within a few dBs range.
Frequency diversity has to be applied to HARQ CC scheme with time varying LDPC tone mapper for each transmissions in order to achieve most of the gain, while it is not needed for HARQ Punctured CC and HARQ IR schemes.
HARQ Punctured CC and HARQ IR outperforms HARQ CC if receiver buffer capacity can support soft combining up to 4 transmissions.
HARQ IR has significant gain over HARQ CC and Punctured CC for MCS 10 and 11 by reducing effective code rate via retransmissions when first transmission PER is higher than 20%.
Yan Zhang et al (Marvell)

13. 9/3/2019
Reference
[1] IEEE /1955r0 “HARQ for EHT – Further Information”
[2] IEEE /2029r1 “HARQ in EHT”
[3] IEEE /1992r1 “HARQ feasibility”
[4] IEEE /354r0 “Consideration on HARQ”
[5] IEEE /390r0 “Effect of Preamble Decoding on HARQ in be”
Yan Zhang et al (Marvell)

14. 9/3/2019
Appendix
20MHz, 2x2, 2SS simulation results for different first Tx PERs
80MHz, 4x2, 2SS simulation results for different first Tx PERs
Yan Zhang et al (Marvell)

15. HARQ vs ARQ Throughput Comparison, with first Tx PER around 10%
9/3/2019
HARQ vs ARQ Throughput Comparison, with first Tx PER around 10%
If MCS is selected with first transmission PER around 10%, there is up to 6.5dB gain using HARQ Punctured CC or IR over ARQ without rate drop, and up to 5.5dB gain over ARQ with rate drop for the same throughput. *MCS 10 and 11 are not simulated since no SNR can achieve first Tx PER around 10%. *First Tx PER is greater than 10% for HARQ IR transmission since punctured LDPC codes are not optimized as regular LDPC codes.
Yan Zhang et al (Marvell)

16. HARQ vs ARQ Throughput Comparison, with first Tx PER around 20%
9/3/2019
HARQ vs ARQ Throughput Comparison, with first Tx PER around 20%
If MCS is selected with first transmission PER around 20%, there is up to 23dB gain using HARQ Punctured CC or IR over ARQ without rate drop and up to 18dB gain over ARQ with rate drop for the same throughput. Due to SNR sensitivity requirement for 1024AQM combined with high code rate, the throughput of MCS10 is even lower than that of MCS 9 using HARQ CC. On the other hand, HARQ IR MCS 10 still achieves higher throughput since it reduces effective code rate via retransmissions, resulting in lower SNR sensitivity requirement. HARQ IR improves highest achievable throughput by 77% compared to HARQ CC. *MCS11 is not simulated since no SNR can achieve first Tx PER around 20%.
Yan Zhang et al (Marvell)

17. HARQ vs ARQ Throughput Comparison, with first Tx PER around 30%
9/3/2019
HARQ vs ARQ Throughput Comparison, with first Tx PER around 30%
If MCS is selected with first transmission PER around 30%, there is up to 22dB gain using HARQ Punctured CC and IR over ARQ without rate drop, and up to 16dB gain over ARQ with rate drop for the same throughput. HARQ IR improves highest achievable throughput by almost 100% compared to HARQ CC.
Yan Zhang et al (Marvell)

18. HARQ vs ARQ Throughput Comparison, with first Tx PER around 40%
9/3/2019
HARQ vs ARQ Throughput Comparison, with first Tx PER around 40%
If MCS is selected with first transmission PER around 40%, there is up to 23dB gain using HARQ Punctured CC or IR over ARQ without rate drop, and up to 17dB gain over ARQ with rate drop for the same throughput. HARQ IR improves highest achievable throughput by almost 100% compared to HARQ CC.
Yan Zhang et al (Marvell)

19. HARQ vs ARQ Throughput Comparison, with first Tx PER around 10%
9/3/2019
HARQ vs ARQ Throughput Comparison, with first Tx PER around 10%
If MCS is selected with first transmission PER around 10%, there is up to 6-7dB gain using HARQ punctured CC or IR over ARQ without rate drop, and up to dB gain over ARQ with rate drop for the same throughput. HARQ IR has slight loss at MCS levels lower than 9, and slight gain at MCS 9 compared to HARQ Punctured CC. HARQ punctured CC or HARQ IR improves highest achievable throughput by 11% compared to HARQ CC, and by 27% compared to ARQ. *MCS 10 and 11 are not simulated since no SNR can achieve first Tx PER around 10%. *First Tx PER is greater than 10% for HARQ IR transmission since punctured LDPC codes are not optimized as regular LDPC codes.
Yan Zhang et al (Marvell)

20. HARQ vs ARQ Throughput Comparison, with first Tx PER around 20%
9/3/2019
HARQ vs ARQ Throughput Comparison, with first Tx PER around 20%
If MCS is selected with first transmission PER around 20%, there is up to 9-9.5dB gain using HARQ Punctured CC or HARQ IR over ARQ without rate drop, and up to 7-7.5dB gain over ARQ with rate drop for the same throughput. HARQ punctured CC or HARQ IR improves highest achievable throughput by 17% compared to HARQ CC, and by 40% compared to ARQ with rate drop. *MCS10 and 11 are not simulated since no SNR can achieve first Tx PER around 20%.
Yan Zhang et al (Marvell)

21. HARQ vs ARQ Throughput Comparison, with first Tx PER around 30%
9/3/2019
HARQ vs ARQ Throughput Comparison, with first Tx PER around 30%
If MCS is selected with first transmission PER around 30%, there is up to 22dB gain using HARQ Punctured CC or IR over ARQ without rate drop, and up to 14.5dB gain over ARQ with rate drop for the same throughput. HARQ IR improves highest achievable throughput by 90% compared to ARQ with rate drop, more than 65% compared to HARQ CC, and more than 20% compared to HARQ IR.
Yan Zhang et al (Marvell)

22. HARQ vs ARQ Throughput Comparison, with first Tx PER around 40%
9/3/2019
HARQ vs ARQ Throughput Comparison, with first Tx PER around 40%
If MCS is selected with first transmission PER around 40%, there is up to 20dB gain using HARQ Punctured CC or IR over ARQ without rate drop, and up to 13dB gain over ARQ with rate drop for the same throughput. HARQ IR improves highest achievable throughput by 100% compared to ARQ with rate drop, more than 60% compared to HARQ CC, and more than 24% compared to HARQ Punctured CC.
Yan Zhang et al (Marvell)