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doc.: IEEE 802.11-14/1174r0
Submission Yakun Sun, et. al. (Marvell)Slide 1
PHY Abstraction with Time Varying Interference
Date: 2014-09-15
Authors:
Name Affiliations Address Phone email
Yakun Sun Marvell Semiconductor5488 Marvell Ln, Santa Clara, CA 95054
1-408-222-3847 [email protected]
doc.: IEEE 802.11-14/1174r0
Submission
Introduction
• Basic procedure of PHY abstraction has been accepted in evaluation methodology document [1] in the July meeting.
• The open issue is how to handle the interference varying across the transmission duration of a packet.– This happens due to asynchronous transmission of interfering
packets in OBSS.
• Here we studied this open problem and propose a block-wise PER prediction solution.
Yakun Sun, et. al. (Marvell)Slide 2
doc.: IEEE 802.11-14/1174r0
Submission
Recap of PHY Abstraction Procedure in [1]
Yakun Sun, et. al. (Marvell)Slide 3
1. Generate (both desired and interfering) channels. 2. Calculate the equalizer-output SINR per spatial stream for the n-th tone/t-th OFDM symbol,
SINR(iss,n,t), iss=1…Nss, n=1…N, t=T0…T0+T. a. Equalizer is MRC if Nss=1, or MMSE if Nss>1. b. Definition of T0 and T are TBD.
3. Map N×T×Nss SINRs to 1 RBIR.
0
01 1
1, ;
ss
ss
N T T N
i t T nss
RBIR SINR n t MN T N
4. Reverse map 1 RBIR to 1 effective SNR.
1 ;effSNR RBIR M
5. Estimate PER for based on AWGN PER lookup table.
0
0
0
/
_ ; ,coding scheme, reference packet length
1 1
PL eff
PL PL
PL
PER PER LUT SNR MCS
PER PER
a. In case of BCC, PL0 = 32bytes if PL< 400bytes; or 1458bytes otherwise. b. In case of LDPC, PL0 = 1458bytes.
6. Determine if this PPDU is successfully received.
transmission success0,1
transmission fail
PERUniform
PER
doc.: IEEE 802.11-14/1174r0
Submission
Discussions
• Thorough studies on the basic procedure show good PER prediction.– PHY abstraction works well for frequency selective interference.
• However, the studies focuses on under the assumption of time-constant interference the interferers over the whole packet.– In such a case, the effective SNR based on one SINR vector over one
OFDM symbol is the same as that based on SINR vectors over the packet.
– (T0=1, T=0) = (T0=1, T=packet_len-1) in STEP2-3
• This is not the case if the interferers change over the packet.– How to select T0/T for time-selective interference?
Yakun Sun, et. al. (Marvell)Slide 4
doc.: IEEE 802.11-14/1174r0
Submission
Time Varying Interference
Yakun Sun, et. al. (Marvell)Slide 5
Frame
•In
terf
eren
ce L
evel
• Time• (unit: OFDM • symbols)
• L1• LN
• L2
• Interference Event N• Interference Event 1
• L
• T1=1 • T2• T3
• TN
doc.: IEEE 802.11-14/1174r0
Submission
Potential Solutions
• Whole packet average– T0=1, T=L-1
– May discount strong interference given a short interleaver for BCC.
• Weakest link– T0=argmin_t SINR(t), T=0
– May overestimate strong (but short) interference
• Block-wise PHY abstraction– Balance between the two method above.– For each event n, T0=Tn, T=0 PERn, n=1…N
– Final PER prediction:
Yakun Sun, et. al. (Marvell)Slide 6
1
1 1iN L
Li
i
PER PER
doc.: IEEE 802.11-14/1174r0
Submission
Case 1: 5dB Interference Rise x2
• 20MHz, 1x1, D_NLOS, ideal CE, 8000 bits packet• MCS 0/2/4/7/9• Interference rises 5dB every 1/3 of packet.
Yakun Sun, et. al. (Marvell)Slide 7
Frame
Inte
rfer
ence
Lev
el
time
5dB
L/3 L/3
5dB
L/3
SNR
doc.: IEEE 802.11-14/1174r0
Submission
PER Predict: Whole Packet Avg
Yakun Sun, et. al. (Marvell)Slide 8
• Clearly discounted strong interference too much and underestimate PER
0 5 10 15 20 25 30 35 40 45 5010
-3
10-2
10-1
100
20MHz, MCS0/2/4/7/9, BCC
Simulated PER
Predicted PER, pkt avg
doc.: IEEE 802.11-14/1174r0
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PER Predict: Weakest Link
Yakun Sun, et. al. (Marvell)Slide 9
• Use the last interference level for PHY abstraction• Overweight strong interference and overestimate PER (but closer than whole
packet average)
0 5 10 15 20 25 30 35 40 45 5010
-3
10-2
10-1
100
20MHz, MCS0/2/4/7/9, BCC
Simulated PER
Predicted PER, weakest link
doc.: IEEE 802.11-14/1174r0
Submission
PER Prediction: Block-Wise
• Very accurately predicted PER performance for time-varying interference.
Yakun Sun, et. al. (Marvell)Slide 10
0 5 10 15 20 25 30 35 40 45 5010
-3
10-2
10-1
100
SNR of event 1 (dB)
PE
R
20MHz, MCS0/2/4/7/9, BCC
Simulated PER
Predicted PER, block wise
doc.: IEEE 802.11-14/1174r0
Submission
PER Prediction: LDPC
• Weakest link and block-wise PHY abstraction provides close and accurate PER prediction.
Yakun Sun, et. al. (Marvell)Slide 11
0 5 10 15 20 25 30 35 40 45 5010
-3
10-2
10-1
100
SNR of event 1 (dB)
PE
R
20MHz, MCS0/2/4/7/9, LDPC
Simulated PER
Predicted PER, block-wisePredicted PER, weakest link
doc.: IEEE 802.11-14/1174r0
Submission
Case 2: 10dB Rise
• 20MHz, 1x1, D_NLOS, ideal CE, 8000 bits packet• MCS 0/2/4/7/9• Interference rises 10dB for the last ¼ of the packet.
Yakun Sun, et. al. (Marvell)Slide 12
Frame
Inte
rfer
ence
Lev
el
time
10dB
3L/4 L/4
doc.: IEEE 802.11-14/1174r0
Submission
PER Prediction: BCC
• Block-wise PHY abstraction still work well, while weakest link still overestimate PER.
Yakun Sun, et. al. (Marvell)Slide 13
0 5 10 15 20 25 30 35 40 45 5010
-3
10-2
10-1
100
SNR of event 1 (dB)
PE
R
20MHz, MCS0/2/4/7/9, BCC
Simulated PER
Predicted PER, block-wise
Predicted PER, weakest link
doc.: IEEE 802.11-14/1174r0
Submission
PER Prediction: LDPC
• Again, weakest link ≈ block-wise ≈ true PER
Yakun Sun, et. al. (Marvell)Slide 14
0 5 10 15 20 25 30 35 40 45 5010
-3
10-2
10-1
100
SNR of event 1 (dB)
PE
R
20MHz, MCS0/2/4/7/9, LDPC
Simulated PER
Predicted PER, block-wise
Predicted PER, weakest link
doc.: IEEE 802.11-14/1174r0
Submission
Case 3: Short 15dB Rise
• 20MHz, 1x1, D_NLOS, ideal CE, 8000 bits packet• MCS 0/2/4/6/9• Interference rises 15dB for the last 6 OFDM symbols
Yakun Sun, et. al. (Marvell)Slide 15
Frame
Inte
rfer
ence
Lev
el
time
15dB
3L/4 6
doc.: IEEE 802.11-14/1174r0
Submission
PER Prediction: BCC
• Same conclusion even for such a short interference pulse.
Yakun Sun, et. al. (Marvell)Slide 16
10 15 20 25 30 35 40 45 50 55 6010
-3
10-2
10-1
100
SNR of event 1 (dB)
PE
R
20MHz, MCS0/2/4/7/9, BCC
Simulated PER
Predicted PER, block-wise
Predicted PER, weakest link
doc.: IEEE 802.11-14/1174r0
Submission
Discussions on Block-Wise PHY Abstraction
• It provides much better PER prediction than other methods.
• The additional complexity is minimal.– Post-equalization SINR calculation is anyway required for each
interference event, for all methods.– Effective SNR mapping and PER lookup for each event is trivial.
• If interferences are assumed to change significantly, block-wise can be related to weakest-link by:
Yakun Sun, et. al. (Marvell)Slide 17
1
1
1 1 1 min 1i iN L L
L Li ii N
i
PER PER PER
doc.: IEEE 802.11-14/1174r0
Submission
Conclusion
• Propose to update the basic PHY abstraction to block-wise PHY abstraction.
Yakun Sun, et. al. (Marvell)Slide 18
doc.: IEEE 802.11-14/1174r0
Submission
Proposed Text Change in [1]
Yakun Sun, et. al. (Marvell)Slide 19
Assume N interference events happen during the transmission, each starts from Tn and lasts Ln OFDM symbols.
For each interference event over [Tn, Tn+1), n=1…N:
1. Generate (both desired and interfering) channels. 2. Calculate the equalizer-output SINR per spatial stream for the n-th tone/t-th OFDM symbol,
SINR(iss,n,t), iss=1…Nss, n=1…N, t=Tn,T=0. a. Equalizer is MRC if Nss=1, or MMSE if Nss>1. b. Definition of T0 and T are TBD.
3. Map N×T×Nss SINRs to 1 RBIR.
0
01 1
1, ;
ss
ss
N T T N
i t T nss
RBIR SINR n t MN T N
4. Reverse map 1 RBIR to 1 effective SNR.
1 ;effSNR RBIR M
5. Estimate PER for based on AWGN PER lookup table.
0
_ ; ,coding scheme, reference packet lengthPL effPER n PER LUT SNR MCS
a. In case of BCC, PL0 = 32bytes if PL< 400bytes; or 1458bytes otherwise. b. In case of LDPC, PL0 = 1458bytes.
After iterated over all events,
6. Calculate the final PER
0 0
0
/
1
/
1 1
1 1
nN L L
PL PLn
PL PL
PL
PER PER n
PER PER
7. Determine if this PPDU is successfully received.
transmission success0,1
transmission fail
PERUniform
PER
doc.: IEEE 802.11-14/1174r0
Submission
Reference
• [1] 11-14-0571-03-00ax-evaluation-methodology
Yakun Sun, et. al. (Marvell)Slide 20
