Question 3x3 router with 2x2 devices

[wm3797]

Regarding a 3x3 MU-MIMO router, with two laptops, each with 2x2 MU-MIMO, does the second laptop have to wait till the first laptop is finished, or itll use the remaining antenna in the router at the same time that the first laptop is using the 2 antennas?

 

[DeauteratedDog]

I'm not sure, but I think the 2 laptops will be in separate groups - that is the 2nd laptop will wait for the 1st.

I have the question in to my local CWNE and will update when I get a conclusive answer.

 

[bill001g]

Kinda both and the answer is different if you have the newer 802.11ax (wifi6).

First all the equipment must support mu-mimo to take advantage of this feature.

What it does is actually transmit the data at the same time...sorta mixing it together. I am pretty sure what it does is have a 1x1 mimo session with each device. It then say transmit a packet for pc 1 on antenna 1 and a packet for pc 2 on antenna 2.

In theory at least 2 1x1 overlapping sessions can send more data than a 2x2 session with the data being sent sequentially. In real world tests there is not a lot of difference. You sometime get a small difference minimum latency but any increased data throughput tends to be very inconsistent in real world installs.

Now the reason the answer is both mu-mimo only runs on traffic from the router to the client. The client must wait for both the router and the other client to send data back to the router.

This is one of the areas that wifi6 is suppose to have great advantages. It uses a different method to allocate radio frequencies and allow mu-mimo to function in both direct as well as other changes.

I have my doubts. The wifi industry promises all kinds of stuff and when people actually take it home they get only a tiny fraction. We will see how much better it really is over the next year or so.

 

[wm3797]

I'm not sure, but I think the 2 laptops will be in separate groups - that is the 2nd laptop will wait for the 1st.

I have the question in to my local CWNE and will update when I get a conclusive answer.

Thankyou very much. Please remember to get back to me. I really need to know this.

 

[bill001g]

You are going to have to go study the mu-mimo documents. I always thought if it runs mu-mimo it only runs 1x1. If you had say 4 antenna I don't know if it can run 2 groups of 2x2.

In general from real world testing mu-mimo makes little to no difference.

This is a couple years old but explains some of the issues.

https://www.smallnetbuilder.com/wireless/wireless-features/33100-why-you-don-t-need-mu-mimo

Maybe 803.11ax stuff will work better since it has some improvements but the wifi industry promises a lot but never seems to actually perform.

 

[DeauteratedDog]

Thankyou very much. Please remember to get back to me. I really need to know this.

OK, looks like I was wrong. I have matching answers from two genuine experts who tell me that the AP may service both clients in one transmission, with one spatial stream dedicated to each client.

Hope this helps.

In reference to bil001g's comments, it looks like the standard allows multiple streams to individual clients in a transmission, but it isn't clear that any real world MU-MIMO APs implement that (maybe Meraki's 8-stream AP?).

 

[wm3797]

OK, looks like I was wrong. I have matching answers from two genuine experts who tell me that the AP may service both clients in one transmission, with one spatial stream dedicated to each client.

Hope this helps.

In reference to bil001g's comments, it looks like the standard allows multiple streams to individual clients in a transmission, but it isn't clear that any real world MU-MIMO APs implement that (maybe Meraki's 8-stream AP?).

So youre saying one laptop will use the full 2 antennas while the remaining one has to WAIT for the first one to finish ?

 

[DeauteratedDog]

So youre saying one laptop will use the full 2 antennas while the remaining one has to WAIT for the first one to finish ?

No, the opposite. It is possible that both clients will be transmitted to in the same transmission, with one stream to each client. There is no guarantee that the AP will group them, but it MAY.

 

[wm3797]

No, the opposite. It is possible that both clients will be transmitted to in the same transmission, with one stream to each client. There is no guarantee that the AP will group them, but it MAY.

So one laptop will use the remaining 3rd antenna while the other laptop is fully using the first 2 antennas ? the 3rd antenna will not just be idle?

 

[DeauteratedDog]

So one laptop will use the remaining 3rd antenna while the other laptop is fully using the first 2 antennas ? the 3rd antenna will not just be idle?

Not 'idle', but the three antennas (really radio chains) will be used to encode 2 streams, one for each client.

I'm afraid that I can't explain further, but I struggled with linear algebra in college and that was decades ago... 🙂