1. Haiguang Wang, Jaya Shankar, Zhongding Lei
A Method for Data Transmission Protection on the IEEE ac MU-MIMO Downlink
Haiguang Wang, Jaya Shankar, Zhongding Lei

2. Content
Background
Protect Data Transmission on IEEE ac MU-MIMO downlink
Summary

3. IEEE 802.11ac IEEE 802.11ac focus on high speed data transmission
Transmission speed up to 1 Gbps
Radio bandwidth up to 160 MHz
Use MU-MIMO technology
With MU-MIMO technology, AP can transmit multiple data packets to multiple stations at the same time.

4. Issues with MU-MIMO Technology
One of the problems with MU-MIMO technology is how to protect data transmission.
IEEE use contention-based data transmission.
Legacy RTS/CTS can only provide partial protection over the MU-MIMO downlink transmission.
Collision may happen when legacy stations is hidden to ac stations.
RTS protection range
CTS protection
range
RTS
Collision
CTS
AP1
STA1
STA3
AP2
STA2
STA4
MU-MIMO Downlink

5. Possible Transmission Protection for 802.11ac MU-MIMO Downlink
A few schemes can be used for transmission protection of ac MU-MIMO downlink, they are:
Legacy RTS/CTS
Single RTS Multiple CTS
Multiple RTS Multiple CTS

6. Single RTS Multiple CTS (1)

7. Single RTS Multiple CTS (2)
We can also consider to send CTS at the same time.
NAV protection AP
RTS
xIFS time
STA1
CTS
xIFS time
STA2
CTS
xIFS time
STA3
CTS
NAV distributing

8. Addressing Multiple Stations in RTS
Single RTS multiple CTS can provide a better protection on data transmission than legacy RTS/CTS scheme. However, we need solve following issues:
Address multiple stations in RTS.
Compatible with legacy stations

9. Group Address
IEEE ac task group has defined a group ID at PHY layer.
A group of stations may be assigned to the same group ID, which indicates that data transmitted in the packet are sent to the stations in this group.
Group ID is sent in PHY layer

10. Using RTS-to-Self and Group ID for Addressing
AP uses group ID directly as group MAC address.
To avoid confusion caused by station with MAC address that is equivalent to a group ID, we propose to use RTS-To-Self with group ID in TA field.
RTS
AP1
STA1
AP2
STA3
STA2
STA4

11. Advantage Simple in the implementation.
Save the signaling exchange for group addressing.
Compatible with legacy system

12. Summary
In this proposal, we have propose a solution for IEEE ac standard in addressing multiple stations with a single RTS packet. The solution is compatible to legacy stations. We have also proposed solutions that may encounter in designing of Single RTS Multiple CTS.