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I have 3 Raspbian Wi-Fi clients using a Wi-Fi dongle with the rtl8812 chipset. The drivers are working great and I have everything set up to do some performance tests. We ordered a Cisco router for testing purposes after explaining our requirements to them. The router was set to performance mode and the clients connect on a 5GHz band with no interference whatsoever (no other access points around, not even 2.4GHz clients or routers)

When I start sending data to a server via FTP with one client, I get 15 Megabytes per second. That's fine; it's the speed we want. When I start to send with two clients, this 15 Megabytes gets split up into 7.5 Megabytes for each client. Three clients then each transmit with 5 Megabytes and so on. A division like this is expected because bandwidth has to be divided. However when we try a different dongle with a rtl8814chipset, this one has a little antenna, it can reach 30 Megabytes per second.

How is it possible that one client can reach 30 Megabytes per second with this dongle, and that 2 clients with the other dongle only reach 7.5 each (15 megabytes is being split).

I would expect that they would both be able to send with 15 Megabytes per second, as I know 30 Megabytes is achievable with the other dongle. If I mix clients, one with the rtl8814 and two with the rtl8812 dongle, again the 15 megabyte split happens and each client gets 5 Megabytes upload speed. Where is this weird split of 15 megabytes occuring?

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The newer WiFi chip could support newer standards such as "wide" (double bandwidth) channels or things such as short preamble which would increase performance over the older chips. This would account for the increase in speed you are seeing for it.

The subsequent decrease in speed when one of the older chips is seen would be due to the fact that, for compatibility reasons, the router WiFi would fall back to the highest mode supported by all the clients (the 15MBps speed) so that they are all able to communicate effectively.

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  • I thought this too initially, But they're not that far apart in terms of speed, the two chipsets. They're both 802.11ac. For clarification; I'm talking about the EW-7833UAC and the EW-7811UTC. However, the rtl8812 is not MU-MIMO, could this have anything to do with it?
    – Zimano
    Nov 16 '17 at 13:21
  • According to wikidevi.com/wiki/Realtek there are versions of the 8812 that are MU-MIMO, so I'm not convinced that it is the cause. Could be the 4x4 MIMO on the 8814 over the 2x2 on the 8812...
    – Mokubai
    Nov 16 '17 at 14:39

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