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 inner CDD input to the receiver FFT outputs (CID 3962)
H_eff = HQCcsd
Ccsd is CDD block between STBC and Spatial Mapping block in Figure n51
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 and Ccsd, to feedback either the full effective channel or beamforming matrix V.
Ccsd is CDD block between STBC and Spatial Mapping block in Figure n51
Joonsuk Kim, Broadcom

6. July 2006
Proposed solution
Beamformee may return HQCcsd for full channel feedback (CSI feedback), or V for beamforming matrix feedback where V is found from HQ (Uncompressed/Compressed V feedback).
CSI feedback
When Beamformee sends back the measured channel, the measured channel includes the Q matrix, which is used in the sounding packet, as well as Ccsd.
We should define Heff = HQCcsd, which is the effective channel including the spatial mapping matrix and inner CDD (CID 11959, 952, 4145, 10286, 3962,11979)
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 x Ccsd*= 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 Heff and Qsteer.
July 2006
Conclusions
We can resolve it by introducing Heff and Qsteer.
Heff includes Q and Ccsd for CSI feedback.
Qsteer is a special name of Q, when Q is used as a beamforming steering matrix.
Beamforming matrix V is found from Heff Ccsd* for the feedback, and Qsteer = QV is new steering matrix for beamformed packets.
Normative text is provided in 06/1335
Joonsuk Kim, Broadcom

9. Proposal for Heff Measured channel is HQCcsd
July 2006
Proposal for Heff
Measured channel is HQCcsd
For CSI feedback, the measured channel Heff, where Heff = HQCcsd,, will be fedback.
For Uncompressed and Compressed feedback, the beamformee strips out Ccsd from the measured channel before it finds the beamforming matrix V for feedback. The beamformer applies new steering matrix Q_steer = QV, where Q is the spatial mapping matrix used for the sounding packet.
Joonsuk Kim, Broadcom

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