doc.: IEEE /0935r1 Submission July 2011 Fei Tong, CSRSlide 1 An improved non-compressed beamforming feedback format for 11ac Date: Authors:

doc.: IEEE /0935r1 Submission July 2011 Fei Tong, CSRSlide 2 Abstract Propose an improved non-compressed beamforming feedback format Demonstrate that, for equal performance, non- compressed BF offers similar or lower feedback overhead (bits per matrix) to compressed BF, for 1 or 2-antenna beamformee devices Slide 2Fei Tong, CSR

doc.: IEEE /0935r1 Submission July 2011 Fei Tong, CSRSlide 3 Focus on beamforming feedback matrix with one or two column vectors Beamforming matrix has one or two column vectors –The only option in devices with one or two Rx antennas –Feedback matrix dimension is small : (Ntx, 1) or (Ntx, 2) –Complexity of BF matrix calculation is low Why? –A large proportion of portable devices with embedded modules will have one or two Rx antennas due to physical size and power consumption constraints –For middle to long propagation distances, 1 or 2 spatial streams is still preferable even if there are >= 2 Rx antennas for reliable communication and option to reject interference

doc.: IEEE /0935r1 Submission July 2011 Each column vector is normalised by the element with maximum magnitude before quantisation Beamforming vector is norm and phase invariant Benefits Can maximise the quantisation resolution by choosing different scaling for each beamforming vector Reduced bit count with same quantisation accuracy: only feedback (Ntx-1) complex values and one index to represent the position of the maximal magnitude in each vector –1 bit for this index for 2 Tx antennas –2 bits for this index for 3 and 4 Tx antennas –3 bits for this index for 5, 6, 7 and 8 Tx antennas Improved non-compressed feedback format Fei Tong, CSRSlide 4

doc.: IEEE /0935r1 Submission July x1 example Minor change in the quantisation process Minor change in the feedback bit sequence Example of the proposed method Fei Tong, CSRSlide 5

doc.: IEEE /0935r1 Submission July 2011 Proposed change is simple to implement for the beamformee and the beamformer NO change in current beamforming frame exchange procedure –Still explicit beamforming with beamforming matrix feedback We are only proposing changes to the format of the feedback Quick Summary on Proposed Method Fei Tong, CSRSlide 6 Fei Tong, CSR

doc.: IEEE /0935r1 Submission July 2011 Accuracy –Compare the CDF of quantisation error (in dBc) over a set of beamforming matrices (8x1 or 8x2) obtained from the IEEE fading channel B random realisations Overhead –The total number of bits needed with a given accuracy to feedback a beamforming matrix Quantisation accuracy and overhead study Fei Tong, CSRSlide 7

doc.: IEEE /0935r1 Submission July 2011 Ntx x 1 BF matrix, lowest resolution Fei Tong, CSRSlide 8 Compressed format (Feedback type = 0, Codebook Information = 0) (2,4) Non-compressed format with Nb=2 uses fewer bits than compressed format (2,4) Slide 8Fei Tong, CSR

doc.: IEEE /0935r1 Submission July 2011 Ntx x 1 BF vector, medium resolution Fei Tong, CSRSlide 9 Compressed format (Feedback type = 0, Codebook Information = 1) (4,6) Non-compressed format with Nb=4 uses fewer bits than compressed format (4,6) Slide 9Fei Tong, CSR

doc.: IEEE /0935r1 Submission July 2011 Ntx x 1 BF vector, highest resolution Fei Tong, CSRSlide 10 Compressed format (Feedback type = 1, Codebook Information = 1) (7,9) Non-compressed format with Nb=6 and Nb = 7 use fewer bits than compressed format (7,9) Slide 10Fei Tong, CSR

doc.: IEEE /0935r1 Submission July 2011 IEEE Fading channel model B Equal 64 QAM, BCC R = 2/3, 125 Bytes PPDU MMSE receiver with channel estimation SVD to calculate FB matrix Beamforming based on FB; number of streams equals to number of column vector in FB; equal power on each stream Non-compressed FB: 2 or 3 Bits quantisation per real value Compressed FB: lowest resolution feedback format (2,4) SU-MIMO performance simulation setting Fei Tong, CSRSlide 11

doc.: IEEE /0935r1 Submission July 2011 Frame error rate results for 1 SS (1) Fei Tong, CSRSlide 12 Total = 5 bits per tone for Non-comp Nb=2 Total = 7 bits per tone for Non-comp Nb=3 Total = 6 bits per tone for Compressed format Total = 14 bits per tone for Non-comp Nb=2 Total = 20 bits per tone for Non-comp Nb=3 Total = 18 bits per tone for Compressed format

doc.: IEEE /0935r1 Submission July 2011 Frame error rate results for 2 SS (1) Fei Tong, CSRSlide 13 Total = 10 bits per tone for Non-comp Nb=2 Total = 14 bits per tone for Non-comp Nb=3 Total = 6 bits per tone for Compressed format Total = 28 bits per tone for Non-comp Nb=2 Total = 40 bits per tone for Non-comp Nb=3 Total = 30 bits per tone for Compressed format

doc.: IEEE /0935r1 Submission July 2011 Complexity of compressed format Fei Tong, CSRSlide 14 Count the number of complex multiplications and arctan/arccos operations for one BF matrix The number of arctan/arccos is quite large Complexity is at both the beamformer and beamformee

doc.: IEEE /0935r1 Submission July 2011 IEEE Fading channel model B 2 Rx antenna per user, total 2 users Each user feedback the vector corresponding to the strongest spatial stream ZF beamforming based on FB vector from 2 users Equal 64 QAM, BCC R = 2/3, 125 Bytes PPDU for all users MMSE receiver with channel estimation per user MU-MIMO performance simulation setting Fei Tong, CSRSlide 15

doc.: IEEE /0935r1 Submission July 2011 FER results for 1 SS (Ntx x 1 FB) Fei Tong, CSRSlide 16 Total = 9 bits per tone per user for Non-comp Nb=4 Total = 12 bits per tone per user for Compressed format (5,7) Total = 26 bits per tone per user for Non-comp Nb=4 Total = 36 bits per tone for Compressed format

doc.: IEEE /0935r1 Submission July 2011 For 1 or 2 column BF matrix, non-compressed feedback has similar or lower overhead (with all quantisation resolution level) than compressed feedback with similar BF performance No extra complexity to beamformee and beamformer to implement non-compressed feedback Including non-compressed feedback format does not require changes to BF frame exchange procedure Conclusions Fei Tong, CSRSlide 17

doc.: IEEE /0935r1 Submission July 2011 Extra bit is needed to indicate the feedback format in VHT MIMO control field; reserved bits are available Extra bit is needed to indicate the compressed feedback format is supported in VHT capabilities field; reserved bits are available Only minor changes needed to the draft Fei Tong, CSRSlide 18

doc.: IEEE /0935r1 Submission July 2011 Fei Tong, CSRSlide 19 Strawpoll 1 Specify in the standard that non-compressed feedback format support as described in slides 4 and 5 of this presentation is mandatory at a beamformer; but is optional at a beamformee. Yes No Abstain

doc.: IEEE /0935r1 Submission July 2011 Fei Tong, CSRSlide 20 Strawpoll 2 Specify in the standard that non-compressed feedback format support as described in slides 4 and 5 of this presentation is the only option if Nc ≤ 2, where Nc is the number of columns of a feedback matrix. For Nc > 2, compressed feedback format remains the only option. Yes No Abstain

doc.: IEEE /0935r1 Submission July 2011 Fei Tong, CSRSlide 21 Appendix A: Detailed Simulation Results Slide 21Fei Tong, CSR

doc.: IEEE /0935r1 Submission July 2011 Ntx x 2 BF matrix, lowest resolution Fei Tong, CSRSlide 22 For greater than 3 Tx antennas, non-compressed format with Nb=2 requires fewer bits than compressed format (2,4). Slide 22Fei Tong, CSR

doc.: IEEE /0935r1 Submission July 2011 Ntx x 2 BF vector, medium resolution Fei Tong, CSRSlide 23 For greater than 3 Tx antennas, non-compressed format with Nb=4 requires fewer bits than compressed format (4,6). Slide 23Fei Tong, CSR

doc.: IEEE /0935r1 Submission July 2011 Ntx x 2 BF vector, highest resolution Fei Tong, CSRSlide 24 For greater than 3 Tx antenna, non-compressed format with Nb=6 uses fewer bits than compressed format (7,9) Slide 24Fei Tong, CSR

doc.: IEEE /0935r1 Submission July 2011 Frame error rate results for 1 SS (2) Fei Tong, CSRSlide 25 Total = 23 bits per tone for Non-comp Nb=2 Total = 33 bits per tone for Non-comp Nb=3 Total = 30 bits per tone for Compressed format Total = 31 bits per tone for Non-comp Nb=2 Total = 45 bits per tone for Non-comp Nb=3 Total = 42 bits per tone for Compressed format

doc.: IEEE /0935r1 Submission July 2011 Frame error rate results for 2 SS (2) Fei Tong, CSRSlide 26 Total = 46 bits per tone for Non-comp Nb=2 Total = 66 bits per tone for Non-comp Nb=3 Total = 54 bits per tone for Compressed format Total = 62 bits per tone for Non-comp Nb=2 Total = 90 bits per tone for Non-comp Nb=3 Total = 78 bits per tone for Compressed format