An evaluation of 802.11 error-correcting codes March 2018 doc.: IEEE 802.11-18/0303r5 November 2018 An evaluation of 802.11 error-correcting codes Date: 11/12/2018 Authors: Sigurd Schelstraete, Quantenna Dorothy Stanley (HP Enterprise)

Introduction: 802.11 FEC generations November 2018 Introduction: 802.11 FEC generations 802.11a defines BCC codes with coding rates 1/2, 2/3 and ¾ BCC is the only FEC scheme 802.11n added BCC with rate 5/6 and introduced LPDC codes as an optional FEC scheme Block sizes 648, 1296 and 1944 bits 802.11ac maintained the 802.11n FEC schemes 802.11ax makes LPDC mandatory for a majority of cases Sigurd Schelstraete, Quantenna

How well does the current FEC perform? November 2018 How well does the current FEC perform? Typically, coding performance is measured against the Shannon limit Theoretical SNR limit at which error-free transmission can be achieved Any gap between the performance of the code at a given BER (e.g. 10-6) and the Shannon limit can be seen as a measure of quality for the code Some caveats: Comparing error-free performance vs. performance at chosen BER is not unambiguous The Shannon limit does not assume any specific modulation Sigurd Schelstraete, Quantenna

November 2018 The Shannon limit The Shannon limit defines the capacity of the channel at a given SNR as: 𝐶=𝑙𝑜𝑔 1+ 𝑆 𝑁 There is also a discrete-constellation version of the Shannon limit that applies when the modulation is fixed (e.g. QAM, PAM, …) Needs to be derived numerically For K equiprobable signal points: 𝐶=𝑙𝑜𝑔 𝐾 − 1 𝐾 𝑎 𝑘 𝑛 𝑙𝑜𝑔 𝑎 𝑘 ′ 𝑒𝑥𝑝 − 𝑛− 𝑎 𝑘 ′ + 𝑎 𝑘 2 − 𝑛 2 2 𝜎 2 Sigurd Schelstraete, Quantenna

November 2018 The Shannon limit(s) Uncoded performance at 10-6 is about 8-10 dB away for the Shannon limit Sigurd Schelstraete, Quantenna

Performance of current coding schemes November 2018 Performance of current coding schemes LDPC improves about 2 dB over BCC About 1.5 to 2 dB gap with the “discrete constellation” limit About 3.5 dB gap to “unconstrained” Shannon limit Sigurd Schelstraete, Quantenna

November 2018 Conclusions Current 802.11 FEC compare relatively well to Shannon limit LDPC has narrowed the gap Some gap to full capacity remains “Anecdotical evidence” that further coding gain is possible The complexity needed to narrow this gap is unknown Possible considerations: Typically, longer LDPC codes improve performance Note that 802.3ca has already adopted a 18K LDPC block code [1] 3GPP has defined LDPC with block size 8448 [2] Would TCM in combination with LDPC result in further improvement? Sigurd Schelstraete, Quantenna

November 2018 Recommendation Incremental improvement in coding gain may be possible over the currently defined codes for 802.11 Given that: Current FEC schemes haven’t been updated in 10 years Other projects have adopted newer codes Further improvements appear possible We recommend that EHT considers review of FEC within scope of the project Sigurd Schelstraete, Quantenna

November 2018 References [1] FEC Proposal for NGEPON, laubach_3ca_1a_1117, http://www.ieee802.org/3/ca/public/meeting_archive/2017/11/laubach_3ca_1a_1117.pdf [2] 3GPP TS 38.212, NR; Multiplexing and channel coding Sigurd Schelstraete, Quantenna