July 2013
doc.: IEEE 802.11-13/0877r0
HEW Beamforming Enhancements
Date: 2013-07-3
Authors:
Name
Company
James Wang
MediaTek
Jianhan Liu
Phone
email
[email protected]
MediaTek
408-526-1899
88109
408-526-1899
Thomas Pare
MediaTek
408-526-1899
[email protected]
Chaochun Wang
MediaTek
408-526-1899
James Yee
MediaTek
408-526-1899
[email protected]
om
[email protected]
Submission
Address
Slide 1
[email protected]
James Wang (MediaTek)
2017/7/28
doc.: IEEE 802.11-13/0877r0
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
• There are some ambiguities related to beamformed
transmission under different scenarios
• This contribution presents some possible performance
beamforming enhancements for HEW
Submission
Slide 2
James Wang (MediaTek)
May 2013
doc.: IEEE 802.11-13/0877r0
Cell-Edge Performance
Improved cell edge
performance with TX or
RX beamforming, more
graceful degradation in
dense deployment
Submission
Slide 3
James Wang (Mediatek )
2017/7/28
doc.: IEEE 802.11-13/0877r0
Beamforming for Cell Edge Performance
Enhancement
•
Beamforming is an effective way to enhance cell
edge performance
– Higher phy rate can be achieved (versus nonbeamformed)
– 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)
Submission
Slide 4
James Wang (MediaTek)
2017/7/28
doc.: IEEE 802.11-13/0877r0
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
Submission
Slide 5
AP1
STA3
STA1
BSS1
STA2
AP2
James Wang (MediaTek)
2017/7/28
doc.: IEEE 802.11-13/0877r0
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
use it in its transmission
– It reduces the overhead of the over-the-air
(explicit or implicit) calibration.
• Note that some vendors are shipping
pre-calibrated devices already.
Submission
Slide 6
AP1
STA3
STA1
BSS1
STA2
AP2
James Wang (MediaTek)
2017/7/28
doc.: IEEE 802.11-13/0877r0
Condition 1 - Spatially Orthogonal Condition
• Supposed 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
AP1
STA3
STA1
BSS1
SO condition
STA2
AP2
* Note if STA1’s CCA is idle, the STA1 is allowed to
transmit.
Submission
Slide 7
James Wang (MediaTek)
2017/7/28
doc.: IEEE 802.11-13/0877r0
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 communicate to AP1.
• STA1 can establish SO condition via
– beamforming toward AP1 to suppress
interference, or
– using active nulling toward interference source
(STA2/AP2)
AP1
STA3
STA1
BSS1
SO condition
STA2
Submission
Slide 8
AP2
James Wang (MediaTek)
2017/7/28
doc.: IEEE 802.11-13/0877r0
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).
AP1
CTS
STA3
RTS
STA1
BSS1
* REVmb: 9.3.2.6 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.
STA2
Submission
Slide 9
AP2
James Wang (MediaTek)
2017/7/28
doc.: IEEE 802.11-13/0877r0
Spatial Reuse of 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 this 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 under this condition , the spatial reuse of the wireless medium can be achieved.
AP1
STA2
STA1
BSS1
STA3
AP3
TXOP
AP
STA
Submission
Bemaformed Transmission and Reception Duration
RTS
WM
Access
(SO Detection)
CTS
Slide 10
WM
Access
(SO Detection)
James Wang (MediaTek)
2017/7/28
doc.: IEEE 802.11-13/0877r0
Beamformed Transmission Issues
• PPDU-based Beamforming: Switching between a omnipreamble to a beamformed-transmission after omnipreamble is also hard for OBSS receiver to predict the
channel conditions
Omni-preamble
AP
Beamformed
Beamformed
Time
STA
Submission
Slide 11
James Wang (MediaTek)
doc.: IEEE 802.11-13/0877r0
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 omnidirectional 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 beamformed
transmission thru the TXOP  minimum interference to OBSS
TXOP
Omni-Beam Duration
Bemaformed Transmission and Reception Duration
AP
STA
WM
Access
WM
Access
NAV
NAV
More
Interference
to OBSS
Submission
Reduced
Interference
to OBSS
Slide 12
James Wang (MediaTek)
July 2013
doc.: IEEE 802.11-13/0877r0
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)
Submission
Slide 13
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)
2017/7/28
doc.: IEEE 802.11-13/0877r0
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
STA
WM
Access
WM
Access
NAV
NAV
Bemaformed Transmission and Reception Duration
STA uses SR Beamformed FX
TXOP
AP uses TXOP-based Beamformed FX
Omni-Beam Duration
AP
STA
Bemaformed Transmission and Reception Duration
CTS
WM
Access
WM
Access
NAV
RTS
NAV
Beamformed Transmission and Reception Duration
STA uses SR beamformed FX
Submission
Slide 14
James Wang (MediaTek)
2017/7/28
doc.: IEEE 802.11-13/0877r0
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
Submission
Slide 15
James Wang (MediaTek)
2017/7/28
doc.: IEEE 802.11-13/0877r0
References
• Ref 1: 11-13-0675 Usage models and requirements for
IEEE 802.11 High Efficiency WLAN study group
(HEW SG) –
Liaison with WFA, Laurent Cariou, Orange
• Ref 2: 11-12-1123-00-0-WNG Carrier-oriented WiFi
for cellular offload, Laurent Cariou, Orange
Submission
Slide 16
James Wang (MediaTek)