March 9, 2009
doc.:IEEE 802.11-09/0309r1
TGac Channel Model Addendum
Highlights
Greg Breit, [email protected]
Hemanth Sampath, [email protected]
Sameer Vermani, [email protected]
Richard Van Nee, [email protected]
Minho Cheong, [email protected]
Naoki Honma, [email protected]
Takatori Yasushi, [email protected]
Yongho Seok, [email protected]
Seyeong Choi, [email protected]
Phillipe Chambelin, [email protected]
John Benko, [email protected]
Laurent Cariou, [email protected]
VK Jones, [email protected]
Allert Van Zelst, [email protected]
Note: The author list will grow to reflect those providing explicit contributions and review comments
Submission
Slide 1
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Introduction
• The TGn task group has developed a comprehensive MIMO
broadband channel models, with support for 40 MHz
channelization and 4 antennas.
• The TGac task group is targeting > 1 Gbps MAC SAP throughput
using one or more of the following technologies:
–
–
–
–
Higher order MIMO (> 4x4)
Multi-User MIMO with > 4 AP antennas
Higher Bandwidth (> 40 MHz)
OFDMA
• We propose some simple modifications to TGn channel models to
enable their use for TGac.
Submission
Slide 2
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Modifications to Handle Large System BW
• TGn systems handled 40 MHz systems BW, assuming tap-spacing
of 10 nsec.
• For TGac systems with larger overall system bandwidth (W), we
propose to decrease channel tap spacing by a factor of
1
2
W

ceiling log 2
40 

• The calculation of W and tap spacing is illustrated in the below
examples:
– Example : A TGac modem can have 2 channels of 40 MHz each that are spaced by
60 MHz for sufficient isolation.
• W = 40*2+60 = 140 MHz. Channel tap spacing = 2.5 nsec.
• The reduced channel tap-spacing is modeled by linearly
interpolating the Cluster channel tap power values, on a cluster by
cluster basis.
Submission
Slide 3
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Higher Order MIMO
• Propose to extend Kronecker models of TGn for higher order
MIMO.
• It has shown by measurements [1] that
– TGn channel models tightly bound and sweep the range of MIMO
performance observed in real environments.
– Randomly rotating the TGn defined cluster AoA and AoDs is
sufficient to emulate the case-by-case variation expected in realworld environments.
• Random AoA offsets were distributed uniformly between ±180°
• Random AoD offsets were distributed uniformly between ±30°.
• For each case, the same offset was applied to all clusters.
Submission
Slide 4
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Higher Order MIMO
Measured Capacity CDFs
in Office Environment [1]
Channel Model B Capacity CDFs
(Random AoA/AoD)
Channel Model D Capacity CDFs
(Random AoA/AoD)
Randomly rotating the TGn defined cluster AoA and AoDs is
sufficient to emulate the case-by-case variation expected in real-world
environments.
In this figure, capacity calculated assuming SNR = 24 dB and
*
C  log 2 det( I Nr  SNR
Nt HH )
Submission
Slide 5
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Multi-User MIMO Extensions
•
Literature Search:
– J-G. Wang, A.S. Mohan, and T.A. Aubrey,” Angles-of-arrival of
multipath signals in indoor environments,” in proc. IEEE Veh. Technol.
Conf., 1996, pp. 155-159.
• For the same RX location, cluster AoA from 2 different TX locations
vary up to 20 degrees in classroom and up to 60 degrees in large halls.
• In Hall, clusters that are relevant for one TX location were absent for
another TX location.
• Results directly applicable to MU-MIMO
Submission
Slide 6
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Multi-User MIMO Extension
AoD/AoA vs. Physical Geometry
Scenario 1: Pure LOS channel
STA-1
STA-2
AoD1
AoD2
AP
From Physics:
•AP has a different AoD to STA-1 and STA-2. Also, each STA has a different AoA from AP.
 The LOS steering vectors to STA-1 and STA-2 are different.
Submission
Slide 7
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Multi-User MIMO Extension
AoD/AoA vs. Physical Geometry
Scenario 2: NLOS channel with scatterers far away from AP
STA-1
AoD1
STA-2
AoD1
AoD2
AoD2
AP
•Different scatterers may be relevant to different STAs.
•AP may have a completely independent AoD for clusters corresponding to STA-1 and STA-2
•STAs may have completely independent AoA depending on location and device orientation
Submission
Slide 8
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Multi-User MIMO Extension
AoD/AoA vs. Physical Geometry
Scenario 3: NLOS channel with scatterers close to AP
STA-1
STA-2
AoD2
AoD1
AP
•AP may have a similar AoDs for clusters regardless of transmission to STA-1 or STA-2.
•STAs may have independent AoAs depending on location and device orientation
Submission
Slide 9
March 9, 2009
doc.:IEEE 802.11-09/0309r1
MU-MIMO Channel Model Proposal
•
Assume TGn-defined cluster AoDs and AoAs for link level simulations.
•
For Multi-User MIMO system simulations:
– Assume TGn-defined cluster AoDs and AoAs as baseline.
– For each client, a single pseudo-random offset is added to all cluster AoDs and
AoAs.
• Pseudo-random selection allows comparison across proposals.
• Single offset retains TGn angular spacing between clusters.
– NLOS Cluster AoD offsets uniformly distributed between ±30°
• Based on experimental results from Wang et al.
• Compromises scenarios outlined in slides 3,4,5.
– NLOS Cluster AoA offsets uniformly distributed between ±180°
• Clients can see independent AoA depending on orientation and location.
– LOS tap AoA and AoD offsets uniformly distributed between ±180°.
• Direct LOS path to each client can have independent AoA/AoD depending on location.
•
Pros:
– Physically realistic – Introduces statistical AoA/AoD variation across clients
– Minimal change to TGn channel model
– Simulation complexity increase is reasonable: TX/RX correlation matrix need to be
computed only once per client, for the entire simulation run.
Submission
Slide 10
March 9, 2009
doc.:IEEE 802.11-09/0309r1
MU-MIMO Simulation Overview
• Assumptions:
– 16 TX antennas, 8 STAs, 2 RX antennas per STA
– TGn channel models B, D (LOS and NLOS scenarios) used as baseline
• AoD and AoA as specified in the channel model document
– Composite multi-user channel matrix constructed from vertical concatenation of 8
2x16 channel matrices
• Clients are effectively uncorrelated from each other
• Capacity Analysis:
– For each channel model, 5 cases of random per-user AoA and AoD generated
– 200 channel realizations generated per case
– MMSE precoder applied to each 16x16 channel instance
• Post-processing SINRs calculated for each stream and subcarrier
• PHY capacity for each stream/subcarrier calculated as log2(1+SINR)
– For each instance, sum-average channel capacity calculated by averaging across
subcarriers and summing across spatial streams
– CDFs generated across all 200 channel instances
Submission
Slide 11
March 9, 2009
doc.:IEEE 802.11-09/0309r1
MU-MIMO Model B Results – Capacity CDFs
•
Model B: 2 clusters, 0dB K factor in LOS case
•
Capacity CDF varies by +20% depending on user selection and their AoA/AoD
–
Submission
Note #1: AoD variation in LOS channel component leads to variation of steering vectors across clients
and hence improves MU-MIMO capacity.
Slide 12
March 9, 2009
doc.:IEEE 802.11-09/0309r1
MU-MIMO Model D Results – Capacity CDFs
•
•
Model D: 3 clusters, 3dB K factor in LOS case
Capacity CDF varies by +/-10% depending on user selection and their AoD/AoA.
–
–
Note #1: Artifact of TGn model: TGn AoA specification result in optimal per-user MIMO capacity.
Any AoA offset tends to degrade per-user MIMO capacity.
Note #2: AoD variation in LOS channel component leads to variation of steering vectors across clients
and hence improves MU-MIMO capacity.
Submission
Slide 13
March 9, 2009
doc.:IEEE 802.11-09/0309r1
MU-MIMO Model F Results – Capacity CDFs
•
•
Model F: 6 clusters, 6 dB K factor in LOS case
Capacity CDF varies by negligible amount depending on user selection and their AoD/AoA.
–
Note #1: 6 clusters, each with a large AS of 30-60 degrees, make the capacity CDF less sensitive to
AoA/AoD variations.
Submission
Slide 14
March 9, 2009
doc.:IEEE 802.11-09/0309r1
MU-MIMO Summary
•
Equal AoD for all STAs is not physically realistic.
– In pure LOS scenarios, such a model will “break” MU-MIMO by
mandating equal steering matrices across clients.
•
Diversity of AoD/AoA across STAs impacts MU-MIMO performance:
– Capacity improves in LOS scenarios and models with small # of clusters.
• 20% improvement in LOS channel model B.
•
Recommend using a pseudo-randomly selected AoDs/AoA offset across
users in MU-MIMO model
– NLOS Cluster AoD offsets uniformly distributed between ±30°
– NLOS Cluster AoA offsets uniformly distributed between ±180°
– LOS tap AoA and AoD offsets uniformly distributed between ±180°.
Submission
Slide 15
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Incorporating Dual Polarized Antennas
•
Dual-Pol antennas are likely to be employed in TGac devices.
– Dual-polarized antennas improve MIMO channel capacity, especially in LOS
channel conditions. E.g: Hallways.
– Co-located dual-pol antennas minimize real estate in devices.
•
Measurements indicate that Dual-Pol TGn channel models suggested in
Erceg et al., is applicable to 8x8 MIMO.
– We assumed the following, while comparing measured data with
simulation results:
• XPD value of 10 dB for the steering matrix HF,
• XPD value of 3 dB for the variable matrix Hv.
• 0.2 correlation for co-located cross-polarized antenna elements.
Submission
Slide 16
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Incorporating Dual Polarized Antennas
Measurements vs. Simulations
• CDFs in “light lines” indicate measured capacity CDFs in office environment [1]
• TGn channel models B, used as baseline with AoD and AoA as specified in the
channel model document
Submission
Slide 17
March 9, 2009
doc.:IEEE 802.11-09/0309r1
References
1. Breit, G. et al. “802.11ac Channel Modeling.” Doc. IEEE802.11-09/0088r1.
2. Erceg, V. et al. “TGn Channel Models.” Doc. IEEE802.11-03/940r4.
3. Kenny, T., Perahia, E. “Reuse of TGn Channel Model for SDMA in TGac.”
Doc.IEEE802.11-09/0179r0.
4. Schumacher, L.; Pedersen, K.I.; Mogensen, P.E., "From antenna spacings to
theoretical capacities - guidelines for simulating MIMO systems," Personal,
Indoor and Mobile Radio Communications, 2002. The 13th IEEE International
Symposium on , vol.2, no., pp. 587-592 vol.2, 15-18 Sept. 2002.
5. Jian-Guo Wang; Mohan, A.S.; Aubrey, T.A., "Angles-of-arrival of multipath
signals in indoor environments," Vehicular Technology Conference, 1996.
'Mobile Technology for the Human Race'., IEEE 46th , vol.1, no., pp.155-159
vol.1, 28 Apr-1 May 1996.
6. Offline discussions with Vinko Erceg (Broadcom) and Eldad Perahia (Intel).
Submission
Slide 18
March 9, 2009
doc.:IEEE 802.11-09/0309r1
Appendix
MU-MIMO Code Changes
Submission
Slide 19
March 9, 2009
doc.:IEEE 802.11-09/0309r1
MU-MIMO Code Changes
•
Channel generation by offsetting TGn-defined cluster AoAs/AoDs
– IEEE_802_11_Cases.m function altered
• Four new function arguments defining angular offsets: Delta_AoD_LOS_deg,
Delta_AoA_LOS_deg, Delta_AoD_NLOS_deg, Delta_AoA_NLOS_deg
– “LOS” arguments specify offset in degrees added to steering matrix AoD
and AoA
– “NLOS” arguments specify common offset in degrees added to all cluster
AoDs and AoAs
•
Composite MU-MIMO channel generation
– Example scenario
• 8 TX antenna, 2 users, 4 RX antennas per user
• Generate independent 4x8 channel matrices for each user, denoted as H 1 and
H2
– Each user channel formed assuming different cluster AoA and AoDs
• Form the composite 8x8 channel:
H 
H   1
H 2 
Submission
Slide 20
March 9, 2009
doc.:IEEE 802.11-09/0309r1
MU-MIMO Code Changes
Submission
Slide 21
March 9, 2009
doc.:IEEE 802.11-09/0309r1
MU-MIMO Code Changes
Submission
Slide 22