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GroupID Concept for Downlink MU-MIMO Transmission

GroupID Concept for Downlink MU-MIMO Transmission. Authors:. Date: 2010-01-18. Background. Non-resolvable LTFs The number of LTFs should be sufficient for each STA to estimate the channel for its own spatial streams Each user cannot estimate H i Q i reliably unless ||H i Q j ||=0

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GroupID Concept for Downlink MU-MIMO Transmission

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  1. GroupID Concept for Downlink MU-MIMO Transmission Authors: Date: 2010-01-18 Joonsuk Kim, Broadcom Corp.

  2. Background • Non-resolvable LTFs • The number of LTFs should be sufficient for each STA to estimate the channel for its own spatial streams • Each user cannot estimate HiQi reliably unless ||HiQj||=0 • We cannot guarantee this assumption in general. • Advantage • Shorter preamble • Disadvantage • Incompatible with high-performance MU downlink algorithms • Incompatible with certain antenna configurations • Incompatible with interference suppression • Resolvable LTFs • The number of LTFs >= total number of spatial streams • Each user can measure both its signal channel and all interference channels • We can enhance the MU-MIMO performance that cannot be obtained with unresolvable LTFs at the cost of longer preamble. • For resolvable LTFs, we need a mechanism to identify which streams are for which user. Joonsuk Kim, Broadcom Corp.

  3. Group ID Definition • A group ID (y bits) is used to specify a group of K MU-MIMO users in a specified order • Group ID is defined by AP and is communicated to STAs • Group ID may be transmitted within the body of a management frame • Management frame may be a sounding frame or a non-sounding frame • Management frame without sounding may be used to indicate AID list for a Group ID without requesting channel measurement feedback frame (when the management frame transmitter already has CSI information) • A group ID is modified or created by transmitting group-definition-field • See next slide • Group ID may be overloaded. AP may assign same Group ID to mutually exclusive sets of users if necessary • A station can be member of up to 2^y groups Joonsuk Kim, Broadcom Corp.

  4. Group ID AID1 AID2 AID3 AID4 Group-definition-field • Group-definition-field is defined as following • K number of MU-MIMO users per group (K=4 for example) • Several group-definition-fields may be transmitted in one management or sounding frame • Another field indicates how many group-definition-fields are included in the management or sounding frame • Upon reception of Group-definition-field, each STA knows its own STA number (one to four in this example) associated with group ID. • Group ID is managed by AP. AID stands for Associated Identifier AID may be replaced by some other field that identifies STAs Joonsuk Kim, Broadcom Corp.

  5. Group-definition-field in DATA or MAC header In sounding packet, four AIDs are included in MAC header or DATA. Each AID represents MAC address to sound for MU-MIMO From this order, each destination STA knows the assigned number (1 to 4) AP MU-MIMO Packet Sounding Feedback Frames - Details are TBD - STA1 Group-ID-field in VHT-SIG A STA2 STA3 STA4 time An Example of Sounding Mechanism • Sounding packet includes the MAC addresses of recipients to sound (possible candidates for MU-MIMO packet recipients) • The order of AIDs (Associated ID) in Group-definition-field in the PHY payload indicates the station number (1 to 4). • AP will choose the participating STAs for MU-MIMO packet based on available downlink traffic and current channel state information for all the STAs • All of STAs that were included in Group-definition-field are not required to be recipients of MU-MIMO packet. Joonsuk Kim, Broadcom Corp.

  6. 1 bit y bits x bits MU indication Group ID # of columns of Qk (Nsts_k) for k=1,2,3,4 Stream Number Indication in VHT-SIG A [1] • VHT-SIG A tells the number of columns of Qk (steering matrix for user k) in the order of assigned user number in the group-definition-field. • All STAs can listen to VHT-SIG A, so each participating user knows when to start to detect its own stream. • VHT-SIG A may include following bits (called MU-MIMO bits) • Some of these bits may be reused for SU-MIMO packet Qk is the steering matrix for user k x bits indicate the number of columns of Nsts for user 1,2,3 and 4. Details are TBD It is possible Nsts_k = 0 for certain k if STA k is not a recipient of MU-MIMO packet. Joonsuk Kim, Broadcom Corp.

  7. Summary • MU-MIMO with resolvable LTFs requires a mechanism to indicate which streams are for which user. • Group ID and MU-MIMO bits in VHT-SIG field are introduced for this information • In MU-MIMO bits, • For SU, MU-MIMO indication bit is set to 0 • Some of MU-MIMO bits may be reused for other purpose • For MU, MU-MIMO indication bit is set to 1. Joonsuk Kim, Broadcom Corp.

  8. Reference [1] “11-10-0070-00-00ac-802-11ac-preamble.ppt" Joonsuk Kim, Broadcom Corp.

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