1. HEW Beamforming Enhancements
May 2013
doc.: IEEE /xxxxr0
July 2013
HEW Beamforming Enhancements
Date:
Authors:
James Wang (MediaTek)
James Wang (MediaTek)

2. 2019/6/29
Background
“Area throughput/Average Throughput per STA” is a new metric in HEW for dense deployment scenarios1
Performance enhancement for cell edge has also been highlighted as a key issue in dense deployment2
Current CSMA baseline channel access protocol is based on the omni-directional transmission
This contribution presents some possible beamforming enhancement ideas for HEW
Slide 2
James Wang (MediaTek)

3. Cell-Edge Performance
2019/6/29
Cell-Edge Performance
Improved cell edge performance with TX or RX beamforming, more graceful degradation in dense deployment
James Wang (Mediatek )

4. Beamforming for Cell Edge Performance Enhancement
2019/6/29
Beamforming for Cell Edge Performance Enhancement
Beamforming is an effective way to enhance cell edge performance
Higher phy rate can be achieved (versus non-beamformed)
Reduced interference to OBSS (beamformed transmission)
Reduced interference from OBSS interference (beamformed reception)
Reduced delay spread
When more energy is delivered to the targeted receiver through TX beamforming, the less interference toward others. RX beamforming mitigates the interference level. Higher number of antennas results in less interference.
Potential to increase spatial reuse (higher area throughput)
James Wang (MediaTek)

5. Scenario : Station at the cell edge
2019/6/29
Scenario : Station at the cell edge
STA1 at the cell edge of BSS1 typically suffers from
Difficulty with channel access (CCA busy) due to OBSS interference
Higher packet collision rate from OBSS hidden nodes
STA1 becomes interference to OBSS
Goal: How to use beamforming to improve STA1 situation while reducing interference to OBSS (STA2 and AP2). Specifically, we want to explore the possibility of spatial reuse to improve network capacity
AP1
STA3
STA1
BSS1
STA2
AP2
James Wang (MediaTek)

6. Spatially Reciprocal Transmission
2019/6/29
Spatially Reciprocal Transmission
Define spatial reciprocity as a device capable of transmitting and receiving with same antenna pattern, via implicit or explicit calibration or other means.
Spatially reciprocal devices provides the following benefits :
A spatially reciprocal device can use its channel knowledge derived the received signal in its transmission
It reduces the overhead of the over-the-air calibration if a device has already been calibrated.
AP1
STA3
STA1
BSS1
STA2
AP2
James Wang (MediaTek)

7. Condition 1 - Spatially Orthogonal Condition
2019/6/29
Condition 1 - Spatially Orthogonal Condition
Supposed that OBSS STA2 and AP2 are communicating and STA1 wishes to transmit to AP1 at the same time…
To avoid STA1 interfering with OBSS STAs (STA2 and AP2), STA1 should satisfy spatially orthogonal (SO) condition before it transmits (allowing it to reset NAV)
SO condition: STA1 does not receive AP2 and STA2 signal under beamformed condition during an observation duration
* Note if STA1’s CCA is idle, the STA1 is allowed to transmit.
AP1
STA3
STA1
BSS1
SO condition
STA2
AP2
James Wang (MediaTek)

8. Condition 1- Spatially Orthogonal Condition
2019/6/29
Condition 1- Spatially Orthogonal Condition
STA1 decides the beamforming weight for SO detection based on its knowledge of channel to AP1 and the OBSS interference (STA2&AP2) situations. STA1’s is only interested in communicating to AP1.
SO condition can be established via
beamforming toward AP1 to suppress interference, or
using active nulling toward interference source (STA2/AP2)
AP1
STA3
STA1
BSS1
SO condition
STA2
AP2
James Wang (MediaTek)

9. Condition 2 – Use RTS/CTS to start a SO Frame Exchange
2019/6/29
Condition 2 – Use RTS/CTS to start a SO Frame Exchange
STA1 should start the frame exchange with RTS/CTS with AP1 to avoid AP1 from interfering with AP2 or STA2
Note that the intended recipient of RTS (AP1) will not transmit CTS if its NAV≠0*. AP1 would not cause interference to OBSS STAs (AP2 and STA2).
* REVmb: CTS procedure: If the NAV at the STA receiving the RTS indicates the medium is not idle, that STA shall not respond to the RTS frame.
AP1
CTS
STA3
RTS
STA1
BSS1
STA2
AP2
James Wang (MediaTek)

10. Spatial Reuse of the Wireless Medium
2019/6/29
Spatial Reuse of the Wireless Medium
A spatially reciprocal (SR) HEW device should be allowed to gain access to the channel when SO condition is satisfied, with beamforming weights determined by the HEW device based on its channel knowledge
Under the SO condition, the HEW device can start a SO frame exchange by employing the beamformed (preamble & payload) transmission and reception for the TXOP starting with a RTS/CTS
Note that spatial re-use of the wireless medium is be achieved in this condition.
AP1
STA2
STA1
BSS1
STA3
AP3
TXOP
RTS
Bemaformed Transmission and Reception Duration AP WM
Access
(SO Detection) WM
Access
(SO Detection)
CTS
STA
James Wang (MediaTek)

11. Beamformed Transmission Issues
2019/6/29
Beamformed Transmission Issues
PPDU-based Beamforming: Switching between a omni-preamble to a beamformed-transmission after omni-preamble is also hard for OBSS receiver to predict the channel conditions
Omni-preamble AP
Beamformed
Time
Beamformed
STA
James Wang (MediaTek)

12. TXOP-based Beamformed Frame Exchange
When an AP is engaged in a frame exchange with a selected STA, it should inform all STAs within the BSS defer properly. This requires some omni-directional transmission.
TXOP-based beamformed frame exchange: A proposed solution is to employ the omni-beam transmission at the beginning of an TXOP to set up protection duration (NAV) and then to switch to the beamformed (both preamble and payload) transmission and reception for the remainder of the TXOP duration
Desirable to have minimum omni-beam duration and then to maintain beamformed transmission thru the TXOP  minimum interference to OBSS
TXOP
Omni-Beam Duration
Bemaformed Transmission and Reception Duration AP WM
Access
NAV WM
Access
STA
NAV
More Interference to OBSS
Reduced Interference to OBSS
James Wang (MediaTek)

13. TXOP-based Beamformed and SO Frame Exchange
July 2013
TXOP-based Beamformed and SO Frame Exchange
During a TXOP-based beamformed frame exchange (AP1 & STA2), an OBSS device (STA3 or AP3) should be allowed to start a frame exchange starting with a RTS/CTS if the SO condition is satisfied  spatial reuse cab be achieved
AP1 can have more antennas for beamforming resulting in less interference
TXOP-based beamformed FX enable simple STAs to spatially re-use the medium (only need to detect SO condition either with or without beamforming)
AP1
STA2
BSS1
STA1
STA3
AP3
An OBSS STA can start a SO frame exchange (RTS/CTS) upon detecting the SO condition
James Wang(MediaTek)

14. Combined SR beamformed and TXOP-based Beamformed FXs
2019/6/29
Combined SR beamformed and TXOP-based Beamformed FXs
Note that the beamformed FX (by STA) and the TXOP-based beamformed FX (by AP) can be combined in an TXOP
TXOP
AP uses TXOP-based Beamformed FX
Omni-Beam Duration
Bemaformed Transmission and Reception Duration AP WM
Access
NAV WM
Access
STA
NAV
Bemaformed Transmission and Reception Duration
STA uses SR Beamformed FX
TXOP
AP uses TXOP-based Beamformed FX
Omni-Beam Duration
Bemaformed Transmission and Reception Duration AP
CTS WM
Access
NAV WM
Access
STA
RTS
NAV
Beamformed Transmission and Reception Duration
STA uses SR beamformed FX
James Wang (MediaTek)

15. 2019/6/29
Summary
Discuss potential beamforming enhancement ideas with the following benefits:
increase likelihood of channel access under dense deployment condition
reduce interference to OBSS
reduce collision during reception
increase likelihood of spatial re-use in dense deployment scenario, leading to higher network throughput
The proposed beamforming enhancement is suitable for HEW, because
there is no control of the WLNA deployment scenario due to unlicensed spectrum
no BSS-BSS coordination is required
distributed algorithm accommodates mobile APs/devices and changing channel conditions
James Wang (MediaTek)

16. 2019/6/29
References
Ref 1: Usage models and requirements for IEEE High Efficiency WLAN study group (HEW SG) – Liaison with WFA, Laurent Cariou, Orange
Ref 2: WNG Carrier-oriented WiFi for cellular offload, Laurent Cariou, Orange
James Wang (MediaTek)