1. doc.: IEEE 802.11-10/0493r0 Submission May 2010 Changsoon Choi, IHP microelectronicsSlide 1 Beamforming training for IEEE 802.11ad Date: 2010-04-30 Authors:

2. 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.

3. 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

4. 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 Digital baseband Digital baseband Digital baseband Digital baseband Digital baseband Weighting vector calculation Analog phase-shifter < 6-GHz 60-GHz

5. 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). For N-element beamforming receiver

6. 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

7. 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 matrix matrix, n = k for matrix inversion

8. 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 Time responseAngular response Antenna pattern (90-degree HPBW) Changsoon Choi, IHP microelectronics

9. 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 Beamforming gain vs. number of RX antennas Interference covariance Changsoon Choi, IHP microelectronics CSI covariance matrix

10. doc.: IEEE 802.11-10/0493r0 Submission BF performance with full CSI (with co-channel interference) 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 codebookOutput SINR vs. Input SNR Changsoon Choi, IHP microelectronics

11. 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

12. 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

13. 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

14. 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