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doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 1
Beamforming training for IEEE 802.11ad
Date: 2010-04-30
Name Company Address Phone email
Changsoon Choi +493355625155 [email protected]
Eckhard Grass [email protected]
Rolf Kraemer
IHP Im Technologiepark 25, Frankfurt (oder), Germany
Thomas Derham Orange Labs Tokyo, Shinjuku 160-0022
+81-3-5312-8563 thomas.derham@ orange-ftgroup.com
Sandrine Roblot sandrine.roblot@ orange-ftgroup.com
Laurent Cariou laurent.cariou@ orange-ftgroup.com
Philippe Christin
Orange Labs
4, rue du clos courtel, 35512 Cesson-Sevigne
philippe.christin@ orange-ftgroup.com
Authors:
doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 2
Abstract
• The performance of 60-GHz wireless LAN can be significantly enhanced if the receiver beamforming is capable of interference mitigation.
• In order to do this, beamforming training mechanism should allow for estimation of the full MIMO channel.
• This proposal addresses the number of beamforming training sequence repetition necessary to achieve this, and demonstrates the performance improvement that can be obtained.
doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 3
Beamforming for interference mitigation
• Important to manage mutual interference among different 60-GHz devices /networks. • Even within TGad networks, interference is a main concern for efficient spatial reuse.• Beamforming (BF) needs interference mitigation capability.• IEEE 802.15.3c BF is NOT capable of it due to the nature of codebook approach
• In order to achieve interference mitigation, there should be a mechanism in 802.11ad for the MIMO channel to be estimated
AP
STA
Interference
e.g. IEEE 802.15.3c
doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 4
Beamforming for < 6-GHz and 60-GHz
• 60-GHz BF transceivers would be based on analog beamforming• Baseband does not know the received signals on each antenna individually because
they are combined in analog domain prior to digital baseband elements of MIMO channel matrix cannot be estimated directly
Digitalbaseband
Digitalbaseband
Digitalbaseband
Digitalbaseband
Digitalbaseband
Weightingvector
calculation
Analog phase-shifter
< 6-GHz 60-GHz
doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 5
BF training proposal
• For BF training of an N-element receiver STA, a transmit STA will send N-repetitions of BF training sequences per transmit antenna.
• Receiver STA can estimate channel state information (CSI) in various ways (e.g. LS, MMSE).
BF trainingsymbol #1
BF trainingsymbol #2
SIF
S
BF trainingsymbol #N
SIF
S
BF training time
time
For N-element beamforming receiver
doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 6
BF model for performance evaluation
• For simplicity, we assume SIMO channel.
• This reflects the usage case where one mobile terminal (e.g. smart phone) transmits data to an access point with beamforming capability.
Non- beamforming capable
Beamforming capable
Digitalbaseband
1h
2h
3h
Nh
Tx Rx
*Nc
*3c
*2c
*1cx
y
doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 7
Example: BF training with codebook approach
• Transmit STA sends N-repetitions of a BF training sequence while the receiver cycles through different beamforming vectors from codebook matrix– Codebook matrix (n-element, k-beam) defined as:
• Received baseband signals for k-th beamforming vector
• Collect all baseband signals (or channel estimates) for n-repetition BF training sequences
• Estimation of CSI on each antenna
]c,c,c[C k21
)C(
Tncc ],[c 1
Tn ]h,h[H 1 kHkk nxHcy
NXHCY H
*XY]C[H 1H
)()(C,Y nnkn
)(C kn matrix
matrix, n = k for matrix inversion
doc.: IEEE 802.11-10/0493r0
Submission
System simulation model for BF evaluation
Channel and antenna models
• 60-GHz NLOS residential model (CM2.3) with AoA information (used in IEEE 802.15.3c)
• 100 channel realizations and averaged results. Each channel normalized to unit power
• 90-degree Gaussian beam pattern HPBW (half-power beamwidth) for receiver antenna. No backside emission assumed.
• Constant total gain from beamformers assumed
0 20 40 60 80
-60
-50
-40
-30
-20
-10
0
10
time index
rela
tive
re
spon
se [d
B]
-100 0 100
-60
-50
-40
-30
-20
-10
0
10
angle-of-arrival [deg]
rela
tive
re
spon
se [d
B]
0.2
0.4
0.6
0.8
1
30
210
60
240
90
270
120
300
150
330
180 0
Time response Angular response
Antenna pattern(90-degree HPBW)
Changsoon Choi, IHP microelectronics
doc.: IEEE 802.11-10/0493r0
Submission
BF performance with full CSI(no interference)
• Maximum signal-to-interference plus noise (SINR) beamformer is used for this work.
• IEEE 802.15.3c beamformer is included for comparison
• Improved beamforming gain is obtained with full MIMO CSI
2 4 6 8 101
2
3
4
5
6
7
8
9
10
Codebook, AWGN
This work, AWGN
Codebook, 60-GHz CM2.3
This work, 60-GHz CM2.3
Codebook: IEEE 802.15.3c standard
No interferenceSNR = 10-dB
Number of antenna element
Bea
mfo
rmin
g ga
in [d
B]
Beamforming gain vs. number of RX antennas
2
2
2
2
22
2
wwwRw
wRw
www]ii[w
w]hh[w
]wnnw[]wiiw[
]whhssw[
]nw[]iw[
]hsw[
Hnii
H
Hhh
Hs
Hn
HH
HHHs
HHHH
HHH
HH
H
E
E
EE
E
EE
ESINR
Interference covariance
Changsoon Choi, IHP microelectronics
CSI covariance matrix
doc.: IEEE 802.11-10/0493r0
Submission
BF performance with full CSI(with co-channel interference)
-100 -80 -60 -40 -20 0 20 40 60 80 100-20
-15
-10
-5
0
5
10
angle-of-arrival [deg]
rela
tive
resp
onse
[dB
]
This work
Codebook
CIR
Interferenceat 45-degree
0 5 10 15 20 25 30 350
5
10
15
20
25
30
35
40
Out
put s
igna
l-to-
inte
rfer
ence
noi
se r
atio
(S
INR
) [d
B]
Input SNR per element [dB]
Codebook, AWGN
This work, AWGN
Codebook, 60-GHz CM2.3
This work, 60-GHz CM2.3
Codebook: IEEE 802.15.3c standard
Interference at 45-deg AoAInput SIR = 6-dB
• Co-channel interference– Assume that angle of arrival (AoA) of co-channel interference was ideally estimated in receiver– Random signals (AWGN-like) with random AoA were generated for co-channel interference.
• Beamforming provides efficient interference nulling with full MIMO CSI.• Higher SINR can be expected with the help of interference mitigation.• No interference mitigation capability in IEEE 802.15.3c codebook BF.
Array factors for full CSI beamforming and codebook Output SINR vs. Input SNR
Changsoon Choi, IHP microelectronics
doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 11
Full MIMO CSI estimation
• Method for estimating SIMO channel can be extended to MIMO– usage case: both transmit and receiver STAs have beamforming capability– Tx has M elements, Rx has N elements
• Transmit STA sends:– repetitions of training sequence
• for each repetition, receive STA uses a different beamforming vector from codebook matrix
– where the above repetitions are repeated times• for each repetition, transmit STA uses a different beamforming vector from codebook
matrix
– Codebook matrices should be orthogonal
• Complex received signal on subcarrier i for each repetition placed in corresponding element of matrix
• Full MIMO channel state information
N
*XWY]C[H 11i
Hi
MC
W
iY
doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 12
Conclusion
• This proposal addresses required number of beamforming training sequences for full MIMO channel estimation.
• There are several use cases where transmit DEV has no beamforming capability whereas receive DEV has powerful beamforming.
• To facilitate BF in receiver, all devices including no beamforming capable devices are required to send N-repetitions of BF training sequence for N-element beamforming receiver
doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 13
Acknowledgement
• This work has been supported by the European Community’s Seventh Framework Programs referred to as MIMAX and OMEGA
doc.: IEEE 802.11-10/0493r0
Submission
May 2010
Changsoon Choi, IHP microelectronicsSlide 14
Straw poll
• Do you support inclusion of the technique “beamforming training for IEEE 802.11ad” as described in 10/000r0 in the TGad draft amendment?
– Yes
– No
– Abstain
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