1. Simultaneous Beam Training
Month Year
March, doc.:IEEE ad
Simultaneous Beam Training
Date: March 2010
Authors:
Name
Affiliations
Address
Phone
M. Hossein Taghavi
Qualcomm
San Diego
Avinash Jain
Hemanth Sampath

2. March, doc.:IEEE ad
Background
Beamforming is necessary to achieve multi-Gbps throughput in 60 GHz band.
Necessary to overcome severe path loss & directionality in 60 GHz.
For a robust 60 GHz network:
STAs needs to beam-train periodically to account for blockage, movement, change of orientation, etc.
STAs need to use dedicated service (time) periods to beam-train, to prevent traffic disruption to other 60 GHz devices.
The beam training overhead can be significant for 60 GHz network with multiple STAs.

3. Example Beam-Training Overhead Calculation
March, doc.:IEEE ad
Example Beam-Training Overhead Calculation
Consider a conference Room scenario with 4 pairs of STAs communicating:
Assume beam training uses 15.3c long preamble (4.7μs)
Beam training by 4 pairs of STAs using separate dedicated times can lead to significant overhead.
This significantly reduces perceived network throughput
Training Overhead
Beam Training Periodicity (ms)
(% of Total Channel) 5 10 20 40 60
Total # of Tx/Rx
Beams or
Directions 16
15.04
7.52
3.76
1.88
1.25 32
30.08
2.50 64
60.16
5.01
128
120.3
10.02
256
240.6
20.05

4. Solution: Simultaneous Beam Training
March, doc.:IEEE ad
Solution: Simultaneous Beam Training
Allow multiple pairs of STAs to perform beam training simultaneously
Each pair of STAs uses a different training sequence in order to mitigate interference
The different training sequences may be based on different Golay codes
It is easy to generate multiple Golay codes using the same hardware with good cross-correlation properties
Example: Two complementary Golay sequences of length 128 with good correlation properties
Simultaneous training of even 2 pairs of devices can reduce the beam training overhead by 50%

5. Conference Room Simulation Setup
March, doc.:IEEE ad
Conference Room Simulation Setup
We will demonstrate performance of simultaneous Tx beam training of 2 pairs & 3 pairs of STAs
Channels generated using the TGad Conference Room channel model, and as defined in the TGad evaluation methodology
Transmitter parameters:
Training sequence is transmitted across each of Tx beams in a random order
19 Tx beams total of 60o HPBW, covering the half-space z>0
Receiver parameters:
Training sequence is received in an omni-directional mode (covering z>0) and using a simple correlator detector
Receiver selects the best Tx beam by comparing the strength of the received training sequences across all beam directions.
A random delay of chips has been added to model in-room propagation delays.
Performance results are averaged over 100 channel realizations, and 10 noise realizations and beam-ordering per channel realization.

6. Case #1: Simultaneous Training of 2 Pairs of STAs
March, doc.:IEEE ad
Case #1: Simultaneous Training of 2 Pairs of STAs
Assume STA2STA1 training uses Golay code a128 from c
Assume STA7STA8 training uses Golay code b128 from c
To illustrate benefit of interference suppression using distinct Golay codes, performance is compared to the case where every STA uses a128 as the training sequence
50% reduction of training overhead with no performance degradation
Training of 2 pairs
PBest
PFailure
STAs using the same training sequence
STA2→STA1
6.8%
88.%
STA7→STA8
100%
0.0%
STAs using different training sequences
PBest =
Probability of correctly selecting the best beam
PFailure =
Probability of selecting a wrong beam that is at least 3 dB worse compared to the best beam.

7. Case #2: Simultaneous Training of 3 Pairs of STAs
March, doc.:IEEE ad
Case #2: Simultaneous Training of 3 Pairs of STAs
Assume STA2STA1 and STA7 STA8 trainings use Golay codes a128 and b128 respectively, from c.
The third pair STA6STA3 training uses concatenation of Golay codes a64 and b64 from c
Note: Failure events can be readily flagged as they correspond to low measured SINR of the selected beam.
67% reduction of training overhead with minimal performance degradation.
Training of 3 pairs
PBest
PFailure
STAs using the same training sequence
STA2→STA1
10.3%
84.2%
STA7→STA8
100%
0.0%
STA6→STA3
5.9%
87.9%
STAs using different training sequences
98.6%
0.3%
PBest =
Probability of correctly selecting the best beam
PFailure=
Probability of selecting a wrong beam that is at least 3 dB worse compared to the best beam.

8. Enabling Simultaneous Beam Training in TGad
March, doc.:IEEE ad
Enabling Simultaneous Beam Training in TGad
The Simultaneous Beam training concept can be overlayed on any beam training protocol:
Standard specifies a few Golay based training-sequences with good cross-correlation properties.
AP allocates the same service (time) period to more than one pair of STAs for beam training.
AP allocates distinct training sequences to these pairs of STAs
Alternately, STAs pseudo-randomly pick a distinct training sequence (e.g: based on STA-ID).
STAs can re-use existing HW to generate and detect these additional Golay based training-sequences.
Each STA needs to generate or detect only one Golay based training sequence, at any given time.

9. March, doc.:IEEE ad
Conclusion
Enabling simultaneous beam training of multiple pairs of STAs using different Golay-based training sequences can significantly reduce network overhead
Presented examples from the Conference Room Scenario where 3 pairs of STAs can simultaneously perform beam training, resulting in 67% training overhead reduction.
The additional Golay-based training sequences can be generated and detected without change to existing hardware
We are open to comments/suggestions to incorporate this concept in TGad.

10. March, doc.:IEEE ad
References
[1] A. Maltsev et al., “Channel Models for 60 GHz WLAN Systems,” /0334r6, [2] E. Perahia, “TGad Evaluation Methodology,” /0296r16,

11. March, doc.:IEEE ad
Straw Poll
Do you support inclusion of the technique,     - Simultaneous Beam Training as described in 10/0252r0 in the TGad draft amendment? Y: N: A: