Groupid concept for downlink mu mimo transmission
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GroupID Concept for Downlink MU-MIMO Transmission. Authors:. Date: 2010-01-18. Background. Non-resolvable LTFs # LTF symbols = max i (# spatial streams for user i) Each user cannot estimate H i Q i reliably unless ||H i Q j ||=0 We cannot guarantee this assumption in general. Advantage

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GroupID Concept for Downlink MU-MIMO Transmission

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GroupID Concept for Downlink MU-MIMO Transmission

Authors:

Date: 2010-01-18

Joonsuk Kim, Broadcom Corp.


Background

  • Non-resolvable LTFs

    • # LTF symbols = maxi(# spatial streams for user i)

    • 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

    • # of LTF symbols >= total # 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.


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.


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.


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.


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 sounding frame.

  • 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.


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.


Reference

[1] “11-10-0070-00-00ac-802-11ac-preamble.ppt"

Joonsuk Kim, Broadcom Corp.


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