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

GroupID Concept for Downlink MU-MIMO Transmission

Authors:

Date: 2010-01-18

Joonsuk Kim, Broadcom Corp.


Background

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

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 definition field

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.


An example of sounding mechanism

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.


Stream number indication in vht sig a 1

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

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

Reference

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

Joonsuk Kim, Broadcom Corp.


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