TP-Link Archer C7 v2: regarding WiFi speed

[patrakov]

Hello. I have a TP-Link Archer C7 v2, and a Lenovo Yoga 2 Pro laptop which uses an Intel wireless chipset (Intel Corporation Wireless 7260 (rev 6b)). I also have a desktop PC, with Intel Corporation Centrino Advanced-N 6235 (rev 24). Both the laptop and the desktop run Arch Linux.

I think I have a WiFi speed issue. It applies both on 18.06.5 and 19.07-rc2 OpenWRT firmware versions.

Here is a config fragment:

config wifi-device 'radio1'
option type 'mac80211'
option hwmode '11g'
option path 'platform/qca955x_wmac'
option noscan '1'
option legacy_rates '0'
option disabled '0'
option txpower '20'
option channel '9'
option country 'RU'
option htmode 'HT40'

The issue is that the RX rate (from the viewpoint of Intel cards) never goes above 150 Mbps, while TX stays at 300 Mbps, as if the router for some reason only uses one antenna for transmitting. If I build hostapd on the desktop, with 300-noscan.patch applied, and turn the desktop into a new access point, then both TX and RX rate is 300 Mbps, as shown by iw dev wlp1s0 link. So it looks like the router does not realize the full potential of its radio. And, if asymmetry is expected, it is at least strange that it gets 300 Mbps in the wrong direction (from the laptop, not to it).

Is this expected? Is this a known issue? Are there any options to try and fix this?

[patrakov]

Solved. This is not a driver bug.

The router is able to send data to the laptop over a high-bitrate WiFi link, and can be forced to do so using a command like iw dev wlan1 set bitrates ht-mcs-2.4 13 14 15. However, minstrel notices that there are apparently no benefits from using multiple spatial streams, and therefore downgrades to a single stream at the highest rate.