1. doc.: IEEE 802.11-11/0064r0 Submission Shogo Fujita, Kyushu Inst. Of Tech. Slide 1 Modulo Precoding for 11ac Date: 2011-01-17 Authors: January 2011

2. doc.: IEEE 802.11-11/0064r0 Submission Shogo Fujita, Kyushu Inst. Of Tech. Slide 2 Introduction Precoding Techniques for MU-MIMO Linear precoding - Low complexity, Low data rate (capacity) –Channel Inversion –MMSE Precoding –Block Diagonalization Non-linear precoding – High Complexity, High data rate (capacity) –Vector Perturbation Sphere encoding (NP-hard) Lattice reduction aided (Suboptimal but still full diversity) –Tomlinson Harashima Precoding Equivalent to a low complexity vector perturbation but the diversity order is the same as Linear Precoding January 2011

3. doc.: IEEE 802.11-11/0064r0 Submission Shogo Fujita, Kyushu Inst. Of Tech. Slide 3 Introduction The main disadvantage of Linear Precoding is that the normalization constant  (to maintain constant average power) is often very large. This happens when the transmit vector lies along the singular vectors of the precoding matrix H -1 with high singular value [1]. Solution. Make sure the transmit signal does not lie along the singular vectors associated with large singular value of H -1. Vector Perturbation can provide such transmit signal Vector Perturbation.This presentation is a proposal for non-linear precoding method like Vector Perturbation. This technique can minimize the quantity γ January 2011

4. doc.: IEEE 802.11-11/0064r0 Submission Shogo Fujita, Kyushu Inst. Of Tech. Slide 4 Simulation Result Vector Perturbation : BER Performance ( Channel :Rayleigh ) Note: Perfect CSI, Ideal Conditions January 2011

5. doc.: IEEE 802.11-11/0064r0 Submission Shogo Fujita, Kyushu Inst. Of Tech. Slide 5 Simulation Result Vector Perturbation : Signal Power Modulation =64 QAM Channel Model = Rayleigh 4 x [1 1 1 1] MU- MIMO case Vector Perturbation can reduce the unnormalized transmit power which increases the effective receive SNR. January 2011

6. doc.: IEEE 802.11-11/0064r0 Submission Shogo Fujita, Kyushu Inst. Of Tech. Slide 6 Vector Perturbation MU-MIMO System Model VP is analogous to doing MLD in the receiver. The AP is free to use any algorithm to find the perturbing vector. Complexity can range from a simple O(n) modulo operation to MLD-like complexity Regardless of the algorithm used by the transmitter, the receiver needs only a predefined modulo lattice operation. Manufacturer specific STAs doesn’t need to know how the perturbing vector was generated January 2011

7. doc.: IEEE 802.11-11/0064r0 SubmissionSlide 7 Review-Vector Perturbation- This technique can minimize the quantity γ Choose l in such a way that x=H -1 has smaller unnormalized transmit power than x=H -1 u –τ : positive real value –l : Perturbation vector each element is composed of a + jb(a and b are integers) Receiver use modulo operation because a constellation is expanded τ -1+1j0+1j1+1j -1+0j -1-1j0-1j1-1j 1+0j0+0j τ Im Re n th stream’s decoded symbol : Modulo operation : January 2011

8. doc.: IEEE 802.11-11/0064r0 Submission Shogo Fujita, Kyushu Inst. Of Tech. Proposals for TGac Allow the AP to perform vector perturbation to prevent huge attenuation of transmit signals Add one bit in the VHT-SIG-A Field to indicate that vector perturbation was performed. –all modulo decode-capable STAs will modulo decode if the bit is set. –The element of l corresponding to modulo decode-incapable STAs can be forced to zero. – Alternatively, the AP will not use VP when one user doesn’t support modulo lattice decoding. Slide 8 January 2011

9. doc.: IEEE 802.11-11/0064r0 Submission Shogo Fujita, Kyushu Inst. Of Tech. Slide 9 Reference [1] Christian B. Peel, Bertrand M. Hochwald and A. Lee Swindlehurst, “A Vector-Perturbation Technique for Near- Capacity Multiantenna Multiuser Communication -Part II: Perturbation, ” IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 53, NO.3, MARCH 2005 January 2011

10. doc.: IEEE 802.11-11/0064r0 Submission Shogo Fujita, Kyushu Inst. Of Tech. Strawpoll #1 Would you support to allot one bit in the VHT-SIG-A to indicate that modulo lattice decoding is needed after channel equalization? Yes No Abstain Slide 10 January 2011

11. doc.: IEEE 802.11-11/0064r0 Submission Shogo Fujita, Kyushu Inst. Of Tech. Strawpoll #2 Would you support allowing the AP to have the capability of reducing the signal attenuation by doing vector perturbation ? Yes No Abstain Slide 11 January 2011