1. TGac Channel Model Addendum Highlights
Month Year
doc.: IEEE yy/xxxxr0
March 9, doc.:IEEE /0309r0
TGac Channel Model Addendum Highlights
Greg Breit,
Hemanth Sampath,
Sameer Vermani,
Richard Van Nee,
Minho Cheong,
Naoki Honma,
Yongho Seok,
Seyeong Choi,
Phillipe Chambelin,
John Benko,
Tomo Adachi,
Laurent Cariou,
VK Jones,
Allert Van Zelst,
John Doe, Some Company

2. Month Year
doc.: IEEE yy/xxxxr0
March 9, doc.:IEEE /0309r0
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.
John Doe, Some Company

3. Modifications to Handle Large System BW
Month Year
doc.: IEEE yy/xxxxr0
March 9, doc.:IEEE /0309r0
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
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.
John Doe, Some Company

4. Month Year
doc.: IEEE yy/xxxxr0
March 9, doc.:IEEE /0309r0
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 real-world 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.
John Doe, Some Company

5. Higher Order MIMO March 9, 2009 doc.:IEEE 802.11-09/0309r0
Month Year
doc.: IEEE yy/xxxxr0
March 9, doc.:IEEE /0309r0
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
John Doe, Some Company

6. Multi-User MIMO Extensions
March 9, doc.:IEEE /0309r0
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
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

7. Multi-User MIMO Extension AoD/AoA vs. Physical Geometry
March 9, doc.:IEEE /0309r0
Multi-User MIMO Extension AoD/AoA vs. Physical Geometry
Scenario 1: Pure LOS channel
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.

8. Multi-User MIMO Extension AoD/AoA vs. Physical Geometry
March 9, doc.:IEEE /0309r0
Multi-User MIMO Extension AoD/AoA vs. Physical Geometry
Scenario 2: NLOS channel with scatterers far away from 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

9. Multi-User MIMO Extension AoD/AoA vs. Physical Geometry
March 9, doc.:IEEE /0309r0
Multi-User MIMO Extension AoD/AoA vs. Physical Geometry
Scenario 3: NLOS channel with scatterers close to 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

10. MU-MIMO Channel Model Proposal
March 9, doc.:IEEE /0309r0
MU-MIMO Channel Model Proposal
For Link Level simulations:
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 random offset is added to cluster AoDs and AoAs
Pseudorandomly chosen from a pre-determined set of client offsets to allow comparison across proposals.
All cluster angles for a single client are rotated by the same offset
Retain cluster spacing from TGn
AoD offsets uniformly distributed between ±30°
Reasonable compromise across scenarios mentioned in slides 3,4,5.
AoA offsets uniformly distributed between ±180°
STAs that are not co-located will see independent AoA (see slides 3,4,5).
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.

11. Multi-User MIMO Extensions Simulation Overview
March 9, doc.:IEEE /0309r0
Multi-User MIMO Extensions 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

12. Multi-User MIMO Extension Model B Results – Capacity CDFs
March 9, doc.:IEEE /0309r0
Multi-User MIMO Extension 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
Note #1: AoD variation in LOS channel component leads to variation of steering vectors across clients and hence improves MU-MIMO capacity.

13. Multi-User MIMO Extension Model D Results – Capacity CDFs
March 9, doc.:IEEE /0309r0
Multi-User MIMO Extension Model D Results – Capacity CDFs
Model D: 3 clusters, 3dB K factor in LOS case
Capacity CDF varies by +/-15% 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.

14. Multi-User MIMO Extension Summary
March 9, doc.:IEEE /0309r0
Multi-User MIMO Extension 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.
Artifact: TGn AoA specification is optimal, especially in Model D. Any deviation tends to degrades performance.
Up to 15% capacity loss noted in channel model D.
Recommend using a pseudo-randomly selected AoDs/AoA offset across users in MU-MIMO model
AoD offsets uniformly distributed between ±30°
AoA offsets uniformly distributed between ±180°

15. Incorporating Dual Polarized Antennas
March 9, doc.:IEEE /0309r0
Incorporating Dual Polarized Antennas
Dual-polarized antennas allow for maximal MIMO channel capacity while minimizing real estate in devices with large number of antennas.
We believe Dual-Pol antennas are likely to be employed in TGac devices.
Measurements indicate that polariation diversity extensions to the TGn channel model suggested in Erceg et al., is applicable to 8x8 MIMO.
We can assume the following:
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.

16. Incorporating Dual Polarized Antennas Measurements vs. Simulations
March 9, doc.:IEEE /0309r0
Incorporating Dual Polarized Antennas Measurements vs. Simulations
Notes:
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

17. References March 9, 2009 doc.:IEEE 802.11-09/0309r0
Breit, G. et al. “802.11ac Channel Modeling.” Doc. IEEE /0088r1.
Erceg, V. et al. “TGn Channel Models.” Doc. IEEE /940r4.
Kenny, T., Perahia, E. “Reuse of TGn Channel Model for SDMA in TGac.” Doc.IEEE /0179r0.
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, The 13th IEEE International Symposium on , vol.2, no., pp vol.2, Sept
Jian-Guo Wang; Mohan, A.S.; Aubrey, T.A., "Angles-of-arrival of multipath signals in indoor environments," Vehicular Technology Conference, 'Mobile Technology for the Human Race'., IEEE 46th , vol.1, no., pp vol.1, 28 Apr-1 May 1996.
Offline discussions with Vinko Erceg (Broadcom) and Eldad Perahia (Intel).