# Wireless Access

MVP

## MU-MIMO syntax clarification

Hi community,

Recently I have seen this syntax about MU-MIMO:

axb:c:d:e, for example, 4x4:4:3:3.

I understand the first two numbers are the transmit and receive chains, and the third one is the number of spatial streams. What's the meaning of the fourth and fifth numbers?

Regards,

Julián

Highlighted
MVP Guru

## Re: MU-MIMO syntax clarification

The fourth number references how many (MU) multi user streams can be transmitted and the fifth number represents a MU-MIMO group or how many MU-MIMO clients are receiving the transmission at the same time.

ACMP, ACSA, ACDX #985
MVP

## Re: MU-MIMO syntax clarification

Hi zailon0,

Then, the third number represents the total spatial streams for a single client and the fourth number represents the spatial streams to different clients simultaneously?

Regards,

Julián

MVP Guru

## Re: MU-MIMO syntax clarification

Correct, the fourth number is how many multi user streams can be
transmitted at once. For example 3 spatial streams can be used to transmit
to 3 clients at the same time all receiving a single stream.

ACMP, ACSA, ACDX #985
MVP

## Re: MU-MIMO syntax clarification

Then, with the fourth and fifth numbers you can figure out how the AP can distribute the streams across different clients simultaneously? For instance, in the case of 4x4:4:4:3, you can transmit 4 streams to a single client, but not 4 streams to 4 clients simultaneously, each receiving one stream, because the AP supports up to 3 clients simultaneously. Although I suppose the fourth and fifth numbers are normally the same in practice?

Regards,
Julián
MVP Guru

## Re: MU-MIMO syntax clarification

In your example, with the fourth number (4), this would mean that 4 spatial streams are available for MU-MIMO clients. So this could be 4 clients all with a single stream. The fifth number (3) represents how many clients could belong to the MU-MIMO Group.

So, I believe an example would look like this

1x SS - MU-MIMO User

1x SS - MU-MIMO User

2x SS - MU-MIMO Group

Have you checked out the 802.11ax whitepaper, this explains it far better then I ever can :)

https://www.arubanetworks.com/assets/wp/WP_802.11AX.pdf

Also take a look at the below, this details further on combinations of valid groups.

https://www.networkcomputing.com/wireless-infrastructure/how-does-mu-mimo-work/748964231

All of the above is from my research and i'm certainly no expert :)

ACMP, ACSA, ACDX #985
MVP

## Re: MU-MIMO syntax clarification

Hi zailon0,

In your example, with the fourth number (4), this would mean that 4 spatial streams are available for MU-MIMO clients. So this could be 4 clients all with a single stream. The fifth number (3) represents how many clients could belong to the MU-MIMO Group.

Are you sure 4 clients simultaneously all with a single stream? Because the fifth number is 3 and then the AP will support up to 3 MU-MIMO clients simultaneously, but not 4.

Regards,

Julián

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