1. Explicit feedback with sounding packet
May 2006
doc.: IEEE /0xxxr0
July 2006
Explicit feedback with sounding packet
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Joonsuk Kim, Broadcom
Matthew Fischer, Broadcom

2. CIDs to cover in LB84 comments
July 2006
CIDs to cover in LB84 comments
CID numbers to cover
11959, 947, 948, 949, 950, 951, 4144, 1072, 952, 4145, 10286, 954, 4147, 957, 4150, 969, 1073, 4161, 968, 970, 4526, 2697
Joonsuk Kim, Broadcom

3. July 2006
Current draft D1.0
Current draft D1.0 has conflicts in PHY and MAC sections
In (Page 124, line 15), the sequence is initiated by an AP which sends an un-steered sounding PPDU for CSI feedback request.
We don’t have this issue anymore with 06/886r2 accepted.
In (Page 221, Line 16), when using a spatial mapping matrix Qk , it needs an estimate of the effective channel HkQk , where Qk is in this case a NtxxNSTS orthonormal spatial mapping matrix.
The sounding PPDU sounds the effective channel that includes spatial mapping matrix Qk at the transmitter.
Joonsuk Kim, Broadcom

4. July 2006
Definitions
H_eff: a transfer function from the transmitter spatial mapper input to the receiver FFT outputs (CID 3962)
H_eff = HQ
Q: Spatial mapping matrix used at beamformer
It can be either direct mapping, spatial expansion or beamforming steering matrix
Q_steer: Steering matrix used for beamformed packet transmission (special name of Q only if Q is used for steering matrix)
Q_steer = QV
V: Beamforming feedback matrix to be fedback from beamformee to beamformer
Joonsuk Kim, Broadcom

5. The explicit feedback with current sounding packet
July 2006
The explicit feedback with current sounding packet
We may have a spatial mapping matrix, Q, for sounding packet in the explicit feedback
Beamformee may estimate the channel, where the measured channel includes Q, to feedback either the full effective channel or beamforming matrix V.
For example of SVD BF, HQ = USV*
Joonsuk Kim, Broadcom

6. July 2006
Proposed solution
Beamformee may return HQ for full channel feedback, or V for beamforming matrix feedback.
CSI feedback
When Beamformee sends back the measured channel, the measured channel includes the Q matrix which is used in the sounding packet.
We should define H_eff = HQ, which is the effective channel including the spatial mapping matrix (CID 11959, 952, 4145, 10286, 3962,11979)
The beamformee removes the CSD in table n67 from the measured channel matrix before it returns CSI feedback with H_eff.
Joonsuk Kim, Broadcom

7. Proposed solution (cont.)
July 2006
Proposed solution (cont.)
V matrix feedback (either compressed or uncompressed)
The beamformee removes the CSD in table n67 from the measured channel matrix before it determines the beamforming feedback matrix V.
The beamformee sends back V and Beamformer needs to modify it to account for Q which is originally used in the sounding packet.
We introduce Q_steer. (CID 947, 948, 949, 950, 951, 4144, 1072, 954, 4147, 957, 4150, 969, 1073, 4161, 968, 970)
The beamformer shall use Q_steer = QV for new steering matrix by multiplying fedback V with the original Q used in the sounding packet.
H_eff = HQ = USV* for the example of SVD operation
HQQ*QV = USV*Q*QV  HQV = HQ_steer = US
Joonsuk Kim, Broadcom

8. Conclusions We can resolve it by introducing H_eff and Q_steer.
July 2006
Conclusions
We can resolve it by introducing H_eff and Q_steer.
H_eff includes Q but not Ccsd in frequency domain.
Q_steer is a special name of Q, when Q is used as a beamforming steering matrix.
Beamforming matrix V is found from H_eff for the feedback, and Q_steer = QV is new steering matrix for beamformed packets.
Normative text is provided in 06/1335
Joonsuk Kim, Broadcom

9. Question to ask at the adhoc group
July 2006
Question to ask at the adhoc group
Measured channel is HQCcsd , where Ccsd is taken out at the beamformee before the beamformee sends the feedback either Heff, uncompressed or compressed V matrix, where Heff = HQ and V is found from Heff.
Otherwise, the beamformer should consider Ccsd from the measured channel before it finds the new steering matrix.
So, it is a matter of choice, whether the action is taken at the beamformee or the beamformer.
When the beamformee takes it out
Heff = HQ, Q_steer = QV
When the beamformer takes it out
Heff = HQCcsd, Q_steer = QCcsdV
Joonsuk Kim, Broadcom

10. Advantages when Ccsd is taken care of at the beamformee
July 2006
Advantages when Ccsd is taken care of at the beamformee
The steering matrix block, Spatial Mapping Q in Figure n51, is the place where the packet is beamformed. Conceptually, it makes much sense to define the channel, which the steering matrix is found from.
Ccsd is a phase-shift matrix which can be easily handled by the beamformee.
Joonsuk Kim, Broadcom

11. July 2006
Straw Poll
Who do you think needs to take out Ccsd from the measured channel (Heff is the channel to be fedback from the beamformee)?
*NOTE: Ccsd refers to the CDD block located between STBC and Spatial Mapping blocks in Figure n51 (D1.03)
The beamformee (i.e., Heff = HQ, Q_steer = QV)
Votes:
The beamformer (i.e., Heff = HQCcsd, Q_steer = QCcsdV)
Joonsuk Kim, Broadcom

12. July 2006
References
n-tgn-d1-0-lb84-beamforming-and-adapation.xls
Joonsuk Kim, Broadcom