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TGac Channel Model Addendum Highlights

TGac Channel Model Addendum Highlights. Greg Breit, gbreit@qualcomm.com Hemanth Sampath, hsampath@qualcomm.com Sameer Vermani, vermani@qualcomm.com Richard Van Nee, rvannee@qualcomm.com Minho Cheong, minho@etri.re.kr Naoki Honma, honma.naoki@lab.ntt.co.jp

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TGac Channel Model Addendum Highlights

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  1. TGac Channel Model Addendum Highlights Greg Breit, gbreit@qualcomm.com Hemanth Sampath, hsampath@qualcomm.com Sameer Vermani, vermani@qualcomm.com Richard Van Nee, rvannee@qualcomm.com Minho Cheong, minho@etri.re.kr Naoki Honma, honma.naoki@lab.ntt.co.jp Takatori Yasushi, takatori.yasushi@lab.ntt.co.jp Yongho Seok, yhseok@lge.com Seyeong Choi, seyeong.choi@lge.com Phillipe Chambelin, philippe.chambelin@thomson.net John Benko, john.benk@orange.com Laurent Cariou, laurent.cariou@orange-ftgroup.com VK Jones, vkjones@qualcomm.com Allert Van Zelst, allert@qualcomm.com Note: The author list will grow to reflect those providing explicit contributions and review comments

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. Multi-User MIMO ExtensionAoD/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 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 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 • 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.

  11. 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

  12. MU-MIMO Model B Results – Capacity CDFs • Model B: 2 clusters, 0dB K factor in LOS case • Capacity CDFvaries 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. 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.

  14. 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.

  15. 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°.

  16. 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.

  17. Incorporating Dual Polarized AntennasMeasurements 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

  18. References • Breit, G. et al. “802.11ac Channel Modeling.” Doc. IEEE802.11-09/0088r1. • Erceg, V. et al. “TGn Channel Models.” Doc. IEEE802.11-03/940r4. • Kenny, T., Perahia, E. “Reuse of TGn Channel Model for SDMA in TGac.” Doc.IEEE802.11-09/0179r0. • 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, 2002. The 13th IEEE International Symposium on , vol.2, no., pp. 587-592 vol.2, 15-18 Sept. 2002. • 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. • Offline discussions with Vinko Erceg (Broadcom) and Eldad Perahia (Intel).

  19. AppendixMU-MIMO Code Changes

  20. 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 H1 and H2 • Each user channel formed assuming different cluster AoA and AoDs • Form the composite 8x8 channel:

  21. MU-MIMO Code Changes

  22. MU-MIMO Code Changes

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