1. Distributed MU-MIMO and HARQ Support for EHT
Month Year
doc.: IEEE yy/xxxxr0
July 2018
Distributed MU-MIMO and HARQ Support for EHT
Date:
Authors:
Ron Porat (Broadcom)
John Doe, Some Company

2. Abstract July 2018 Summary of thoughts and observations
Proposed Timeline
Proposal for two technologies for discussion in EHT
Ron Porat (Broadcom)

3. Discussion and Observations
July 2018
Discussion and Observations
We think that we hit a wall in terms of standardizing simpler technologies. We propose that time is spent in a study phase/group to investigate more sophisticated technologies and we provide our recommendation for two such technologies in this presentation.
Wider BW and larger number of antennas may take a long time for market adoption
160MHz adoption on STA side slow (7 years after being standardized in 11ac)
8 antenna market traction still very weak (7 years after being standardized in 11ac)
 Enhancements along those directions will not help typical next generation products
The new 6GHz spectrum may require APs to have dedicated radios serving 2.4 GHz, 5 Ghz and 6 Ghz  ( triband APs) which will make high order antenna configurations challenging from a cost, form factor and power perspective.  
Ron Porat (Broadcom)

4. July 2018
Cont.
Limitations in Backhaul Tput limit peak WiFi network Tput enhancements (WiFi already supports peak network Tput of 10Gbps).
Point to point Tput already limited by device BW and number of antennas limitations
Mesh AP is a hot and growing trend in home deployments which EHT can build on
Our preferences for EHT:
We prefer technologies that provide an evolution for typical STA and typical AP devices (regardless of number of antennas and BW)
We would like to see that EHT develops a clear mandatory technology to differentiate it from 11ax (similar to OFDMA in 11ax and 80MHz in 11ac)
Ron Porat (Broadcom)

5. Proposed Timeline July 2018
11ax TG started May 2014 with D1.0 on Jan 2017
Adding 5 years –> EHT TG start May 2019, D1.0 Jan 2022
It would be beneficial to spend the time until May 2019 in a study phase to explore technologies that can improve typical WiFi products
No need to rush the timeline beyond what’s proposed above as 11ax has been a large and complex project and is taking more time for market adoption
Future amendments beyond EHT can follow a cadence of roughly 2.5 years by starting the study phase during the last year of the currently running project
Ron Porat (Broadcom)

6. Constrained Distributed MU-MIMO
July 2018
Constrained Distributed MU-MIMO
Distributed MU-MIMO means MU-MIMO running jointly on multiple distributed APs.
Constrained – we propose that we study this topic with a constraint that all AP participating can hear one of the APs (which we call the master AP).
Note this doesn’t necessarily mean all AP can hear all AP
Why is this a topic of interest?
Distributed MU-MIMO transmission and beamforming and nulling are two flavors of AP coordination in the spatial domain that promise the highest gains. Beamforming and nulling requires AP to have at least 4 antennas to have some degrees of freedom dedicated to nulling and joint transmission require that all AP have the data for all participating STA.
Distributed MU-MIMO in particular leverages the mesh AP trend in the home to provide better performance and is more suitable for AP with small (2-4) antenna count
Improve rate at distance - more uniform very high rate (hundreds of Mbps) is currently desired in home deployments  need multiple AP
Improve all AP configurations (especially 2 and 4 antenna mainstream AP)
Evolve 11ac MU-MIMO technology and provide evolution for WiFi well into the next decade
Ron Porat (Broadcom)

7. Cont. July 2018 Why the constraint?
We think that it doesn’t restrict deployments while at the same time provides a more bounded problem that can be solved wirelessly using techniques currently used in WiFi and without the need for network synchronization or accurate clocks at the APs
Similarly to STA synchronization to the AP in UL MU, participating APs can synchronize to the master AP right before a distributed MU-MIMO transmission
Ron Porat (Broadcom)

8. Link Adaptation and HARQ
July 2018
Link Adaptation and HARQ
Link adaptation is a known weak point of WiFi, already discussed in HEW and observed in many cases whereby throughput drops very fast with changes in interference.
While improvements can be done by mandating some feedback elements (e.g. MCS, CQI), even better performance may be achieved by adding HARQ.
Why is this a topic of interest?
Benefit is broad - all SNR ranges, MIMO configurations and transmission modes and in particular the more complex MU-MIMO technology
Improvements and design effort orthogonal to all other improvements done in 11ax or currently envisioned for EHT
Potential gains – as seen from internal LTE measurements in AWGN 4-6dB in one or two retries.
Complexity - due to the required memory and potentially LDPC changes for IR-HARQ more investigations are needed to better assess gains with practical product limitations
Ron Porat (Broadcom)

9. July 2018
Summary
Recommend that the group starts a study phase to investigate advanced technologies leading to an EHT TG start in May 2019 and targeting D1.0 in January 2022.
Recommend that the group targets technologies that improve mainstream STA and mainstream AP
Recommend two advanced technologies with broad appeal:
Constrained distributed MU-MIMO for mainstream AP evolution of 11ac MU-MIMO
Link adaptation and HARQ for mainstream STA and AP evolution
Ron Porat (Broadcom)

10. July 2018
Straw poll #1
Do you support starting a study group to investigate technologies for EHT targeting TG start in May 2019?
Ron Porat (Broadcom)