1. Switch-to-Beamform Power Step
January 2005
doc.: IEEE /1581r0
March 2005
Switch-to-Beamform Power Step
Date:
Authors:
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Mark Webster, Conexant Systems
Dave Hedberg, Conexant Systems

2. January 2005
doc.: IEEE /1581r0
Abstract
March 2005
This presentation gives a couple of examples where the switch-to-beamform power-step can be more than 10 dB. The power step can be upward or downward. The impact of this behavior on legacy OFDM reception may warrant further analysis and testing. Legacy radios may not be certified to handle this behavior. Unlike b, OFDM does not have a CRC check on the Signal Field (header).
Mark Webster, Conexant Systems
Dave Hedberg, Conexant Systems

3. Outline Introduction Line-of-Sight Scenario Non-Line-of-Sight scenario
March 2005
Outline
Introduction
Line-of-Sight Scenario
Non-Line-of-Sight scenario
Conclusions
Mark Webster, Conexant Systems

4. Introduction Many possible beamforming scenarios exist
March 2005
Introduction
Many possible beamforming scenarios exist
This presentation looks at only a couple of “quick-to-analyze” scenarios
No impairments are included
Only one type of beamforming is examined: one spatial stream
A small set of channel types are examined
All preambles/antenna transmission options are not examined
The impact of multiple, small cyclic shifts is not examined
The objective is to merely illustrate potential behavior
More work will be required to fully scope this issue in terms of legacy radio behavior
Mark Webster, Conexant Systems

5. TGn Sync Packet Structure with Beamforming
March 2005
TGn Sync Packet Structure with Beamforming
Power
Discontinuity
L-STF
8 us
L-LTF
8 us
L-SIG
4 us
HT-SIG
8 us
H-STF
2.4 us
H-STF
7.2 us
DATA
Omni-Directional
Beamformed
Mark Webster, Conexant Systems

6. Line-of-Sight Scenario Described All STA’s are LOS (Multipath ignored)
March 2005
Line-of-Sight Scenario Described All STA’s are LOS (Multipath ignored)
Antenna Pattern
Beamform-Mode
LOS Target
11n Client
Radio
11n AP 4 Element
Linear Array
Experiences
Upward
Power Step
Antenna Pattern
Omni-Mode
LOS Legacy
11n Client
Radio
Experiences Downward
Power Increase
Mark Webster, Conexant Systems

7. LOS, 2 Element, 0.5 l, Beampatterns
March 2005
LOS, 2 Element, 0.5 l, Beampatterns
Target
STA at
0 deg
Target
STA at
30 deg
Target
STA at
90 deg
Target
STA at
60 deg
Mark Webster, Conexant Systems

8. LOS, 4 Element, 0.5 l, Beampatterns, Linear Array
March 2005
LOS, 4 Element, 0.5 l, Beampatterns, Linear Array
Target
STA at
30 deg
Target
STA at
0 deg
Target
STA at
90 deg
Target
STA at
60 deg
Mark Webster, Conexant Systems

9. Power-Step CDF’s Around Azimuth One Spatial Stream
March 2005
Power-Step CDF’s Around Azimuth One Spatial Stream
Target
STA
sees
13% of STA’s see greater
than 10 dB drop in power
23% of STA’s see greater
than 10 dB drop in power
+3 dB
Point
+6 dB
Point
2 Tx Antennas
4 Tx Antennas
Caused by
Sidelobes
Mainlobe
Jump dB
Jump dB
-10 dB
Point
0 dB
Point
-10 dB
Point
0 dB
Point
Mark Webster, Conexant Systems

10. NLOS Scenario Described All STA’s are NLOS
March 2005
NLOS Scenario Described All STA’s are NLOS
Antenna Pattern
Beamform-Mode
LOS Target
11n Client
Radio
Experiences
Upward
Power Step
Multipath
Reflectors
11n AP 4 Element
Linear Array
Antenna Pattern
Omni-Mode
Multipath
Reflectors
LOS Legacy
11n Client
Radio
Experiences
Power Step
Mark Webster, Conexant Systems

11. March 2005
Flat Rayleigh Chan A: Total Tx Power Held Constant Individual Element Power Allowed to Vary
2 Tx Antennas
4 Tx Antennas
7% of STA’s see
greater than
10 dB drop
in power
Zoomed
Zoomed
Mark Webster, Conexant Systems

12. March 2005
Conclusion
This submission has illustrated that more than a 10 dB power jump can occur in switch-to-beamform packets in some cases
More work will be required to fully scope the impact on legacy OFDM packet reception
Unlike b, OFDM does not have a CRC check on the Signal Field (header)
Legacy OFDM radios may not have been certified for this behavior
Mark Webster, Conexant Systems

13. March 2005
References
IEEE / n, “TGnSync Proposal Technical Specification,” Syed Aon Mujtaba, March 4, 2005
IEEE / n, “WWiSE Complete Proposal Presentation,” S. Coffey et al., March 14, 2005
Mark Webster, Conexant Systems