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.
In (Page 221, Line 16), when using a transmit steering matrix Qk , it needs an estimate of the effective channel HkQk , where Qk is in this case a NtxxNSTS orthonormal steering matrix.
The sounding PPDU sounds the effective channel that includes spatial mapping matrix Qk at the transmitter.
Joonsuk Kim, Broadcom

4. explicit feedback with current sounding packet
July 2006
explicit feedback with current sounding packet
We may have a spatial mapping matrix, Q, for sounding PPDU in explicit feedback
Beamformee may estimate the channel, which is HQ, not H, to feedback either the full effective channel or beamforming matrix V, where V is determined using HQ.
For example of SVD BF, HQ = USV*
Joonsuk Kim, Broadcom

5. 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.
Note (CID3962) that H_eff is defined as a transfer function from the transmitter spatial mapper input to the receiver FFT outputs
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.
Joonsuk Kim, Broadcom

6. Proposed solution (cont.)
July 2006
Proposed solution (cont.)
V matrix feedback (either compressed or uncompressed)
Beamformee sends back V and Beamformer needs to modify it to account for Q in H_eff, where V is found from H_eff.
We introduce Q_steer. (CID 947, 948, 949, 950, 951, 4144, 1072, 954, 4147, 957, 4150, 969, 1073, 4161, 968, 970)
Tx shall use Q_steer = QV for new steering matrix by modifying fedback V with the original Q used in the sounding PPDU.
H_eff = HQ = USV* for the example of SVD operation
HQQ*QV = USV*Q*QV  HQV = HQ_steer = US
Joonsuk Kim, Broadcom

7. How to resolve We can resolve it by introducing H_eff and Q_steer.
July 2006
How to resolve
We can resolve it by introducing H_eff and Q_steer.
In (Page 124, line 15), change the sentence to “the sequence is initiated by an AP which sends a sounding PPDU for CSI feedback request.”
Proposed Names
Q: Spatial mapping matrix
Q_steer: Steering matrix
V: Beamforming feedback matrix
Normative text will be provided
Joonsuk Kim, Broadcom

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