Hello, first of all I'm not too tech-savvy so I have difficulties troubleshooting my issue. The thing is I'm getting slow transfer rates at 5ghz band, circa 2MB/s download speed. Operating mode is set to "N", swapping channels doesn't help. I'm using 802.11n wireless cards to connect to Xiaomi r3g router with OpenWrt 18.06.2 firmware. When I check 5ghz wireless info in LuCi I see Bitrate: 54 Mbit/s which, I guess should be much higher for 802.11n standart.
One more thing, If i enable "Disassociate On Low Acknowledgement" option in LuCi (IIRC it was enabled by default) I experience random disconnects.
I really would like to resolve this issue, I originally thought it's related to some bugs in OpenWrt but several fw updates did not help.
Are u experiencing the same problems connected to another 5GHz band router?
What tools do you use to measure throughput? Could u try iperf?
Did u try to measure your spectrum. You could look at horst.
What type of client device do you have?
to use 5ghz band router and receiver must be 5Ghz band may u use 2.4 Ghz that may occurs speed down. your laptop only support 2.4Ghz.
Are u experiencing the same problems connected to another 5GHz band router?
Unfortunately I don't have any other 5GHz router to check, but IIRC on a stock fw I had higher speeds. It's been long since I switched to alternative firmwares though.
What tools do you use to measure throughput? Could u try
iperf?
$ iperf -c 192.168.1.1
------------------------------------------------------------
Client connecting to 192.168.1.1, TCP port 5001
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[ 3] local 192.168.1.241 port 39796 connected with 192.168.1.1 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.1 sec 24.1 MBytes 20.1 Mbits/sec
Did u try to measure your spectrum. You could look at
horst.
Will update post with spectrum details later.
What type of client device do you have?
I use mostly Intel Centrino Advanced-N + WiMAX 6250 but I also tried Rosewill RNX-N600UBE USB wi-fi card, I get more or less the same result with it connected to Ubuntu 18 or Windows 7.
to use 5ghz band router and receiver must be 5Ghz band may u use 2.4 Ghz that may occurs speed down. your laptop only support 2.4Ghz.
My cards support 5GHz 802.11n, see above.
You have 20.1 Mbit/sec?
Do you mean MByte/s or Mbp/s?
Yes, around 20Mbits. I see slightly more than 2 Mbytes/sec when I download something. What information I should copy from horst output? Here's the top of the output (I've replaced my network name with "MY_SSID_HERE"):
- 43/0% 40 -39 6 78:11:dc:4b:80:d6 AP n 20 2x2 WPA2 MY_SSID_HERE_5GHZ
- 1/0% 40 -75 6 48:2c:a0:62:6b:34 ST a 20 WPA2 MY_SSID_HERE_5GHZ
/ 7/0% 36 -83 24 40:16:7e:59:60:2c AP ac 80 3x3 WPA2 ASUS_5G
- 1/0% 40 -82 6 ec:89:14:87:12:6d a 20
\ 0/0% 40 -82 24 90:b9:31:e3:a2:c0 a 20
\ 0/0% 1 -66 1 80:38:bc:5e:58:90 AP n 20 0x2 WPA12 mgts113
/ 0/50% 2 -80 1 80:38:bc:c9:32:78 AP n 20 0x2 WPA12 mgts114
\ 0/0% 3 -34 1 78:11:dc:4b:80:d5 AP bg 20 WPA2 MY_SSID_HERE_2.4GHZ
\ 0/0% 3 -82 1 ac:4e:91:17:58:40 AP n 20 0x2 WPA12 MGTS_110
- 0/0% 1 -87 1 94:4a:0c:40:4c:d2 AP n 20 0x2 WPA2 MGTS_GPON_2531
- 0/0% 3 -79 1 e8:37:7a:91:06:58 AP n 40+ 0x2 WPA2 Keenetic-4081
\ 0/0% 5 -83 1 1c:7e:e5:46:08:83 AP n 40- 0x2 WPA12 615
- 0/60% 6 -87 1 00:1e:e5:92:c1:ce AP bg 20 WPA2 linksys
\ 0/0% 6 -64 1 d4:60:e3:21:26:0a AP n 20 0x2 WPA2 MGTS_GPON_3202
- 0/0% 6 -80 1 90:94:e4:37:da:72 AP n 40- 0x2 WPA2 DIR-615
- 0/0% 9 -73 1 40:16:7e:59:60:28 AP n 40+ 0x3 WPA2 ASUS_2G
- 0/0% 9 -88 1 90:8d:78:c7:02:75 AP n 40+ 0x2 WPA2 EZID_2
\ 0/0% 11 -77 1 e0:ce:c3:c7:5a:f9 AP n 20 0x2 WPA12 AKADO-5AF3
\ 0/0% 11 -57 1 1c:7e:e5:94:3f:ba AP n 20 0x2 WPA12 Asus95
- 0/0% 11 -87 1 24:7f:20:ad:f1:2a AP n 20 0x2 WPA2 AKADO-F124
- 0/0% 11 -73 1 58:6d:8f:51:57:87 AP n 20 0x2 WPA2 Stog
Plase look at the MCS Rates and findout the mcs value for your stations. This allow you to find the rate.
Furthere, this given rates are just a upper bound! They are far away from the actual throughput.
Further, you use 20 MHz channel. You can go to 40 MHz with 802.11n! 
That gives you more speed (but only in 5 GHz).
You are interfering with the ASUS_5G! (it is using 80 MHz) Go to some other channel that is not interfering.
AHHHHHH:
Your own laptop is a 802.11a station. It does not support 802.11n. 802.11a is the same as 802.11g in 5 Ghz. 802.11a only supports up to 54 Mbit/sec. This explains all. 
So you are interferring with another AP and only have some 802.11a. I think the throughput for that is alright.
Something is strange. This card should support 802.11n.
Can you give the iw output?
iw list
Wow, thank's for your help. It's a client 48:2c:a0:62:6b:34 which is connected to AP and using Legacy 802.11 standart? That's not my laptop because I disabled all connections from it before making horst scanning. It's one of my phones, but can it connect to 5ghz network with "N" mode set in LuCi? Could it be a reason of slow network performance on my laptop? Thanks for the suggestion about interference, not sure if I can change to a less clogged channel, there's a limited set of 5GHz channels allowed to use in my country and there's some interference in all of them.
iw list output:
Wiphy phy0
max # scan SSIDs: 20
max scan IEs length: 223 bytes
max # sched scan SSIDs: 0
max # match sets: 0
max # scan plans: 1
max scan plan interval: -1
max scan plan iterations: 0
Retry short limit: 7
Retry long limit: 4
Coverage class: 0 (up to 0m)
Device supports RSN-IBSS.
Supported Ciphers:
* WEP40 (00-0f-ac:1)
* WEP104 (00-0f-ac:5)
* TKIP (00-0f-ac:2)
* CCMP-128 (00-0f-ac:4)
* CCMP-256 (00-0f-ac:10)
* GCMP-128 (00-0f-ac:8)
* GCMP-256 (00-0f-ac:9)
Available Antennas: TX 0 RX 0
Supported interface modes:
* IBSS
* managed
* AP
* AP/VLAN
* monitor
Band 1:
Bitrates (non-HT):
* 1.0 Mbps
* 2.0 Mbps (short preamble supported)
* 5.5 Mbps (short preamble supported)
* 11.0 Mbps (short preamble supported)
* 6.0 Mbps
* 9.0 Mbps
* 12.0 Mbps
* 18.0 Mbps
* 24.0 Mbps
* 36.0 Mbps
* 48.0 Mbps
* 54.0 Mbps
Frequencies:
* 2412 MHz [1] (15.0 dBm)
* 2417 MHz [2] (15.0 dBm)
* 2422 MHz [3] (15.0 dBm)
* 2427 MHz [4] (15.0 dBm)
* 2432 MHz [5] (15.0 dBm)
* 2437 MHz [6] (15.0 dBm)
* 2442 MHz [7] (15.0 dBm)
* 2447 MHz [8] (15.0 dBm)
* 2452 MHz [9] (15.0 dBm)
* 2457 MHz [10] (15.0 dBm)
* 2462 MHz [11] (15.0 dBm)
* 2467 MHz [12] (15.0 dBm) (no IR)
* 2472 MHz [13] (15.0 dBm) (no IR)
Band 2:
Bitrates (non-HT):
* 6.0 Mbps
* 9.0 Mbps
* 12.0 Mbps
* 18.0 Mbps
* 24.0 Mbps
* 36.0 Mbps
* 48.0 Mbps
* 54.0 Mbps
Frequencies:
* 5180 MHz [36] (15.0 dBm) (no IR)
* 5200 MHz [40] (15.0 dBm) (no IR)
* 5220 MHz [44] (15.0 dBm) (no IR)
* 5240 MHz [48] (15.0 dBm) (no IR)
* 5260 MHz [52] (15.0 dBm) (no IR, radar detection)
* 5280 MHz [56] (15.0 dBm) (no IR, radar detection)
* 5300 MHz [60] (15.0 dBm) (no IR, radar detection)
* 5320 MHz [64] (15.0 dBm) (no IR, radar detection)
* 5500 MHz [100] (15.0 dBm) (no IR, radar detection)
* 5520 MHz [104] (15.0 dBm) (no IR, radar detection)
* 5540 MHz [108] (15.0 dBm) (no IR, radar detection)
* 5560 MHz [112] (15.0 dBm) (no IR, radar detection)
* 5580 MHz [116] (15.0 dBm) (no IR, radar detection)
* 5600 MHz [120] (15.0 dBm) (no IR, radar detection)
* 5620 MHz [124] (15.0 dBm) (no IR, radar detection)
* 5640 MHz [128] (15.0 dBm) (no IR, radar detection)
* 5660 MHz [132] (15.0 dBm) (no IR, radar detection)
* 5680 MHz [136] (15.0 dBm) (no IR, radar detection)
* 5700 MHz [140] (15.0 dBm) (no IR, radar detection)
* 5745 MHz [149] (15.0 dBm) (no IR)
* 5765 MHz [153] (15.0 dBm) (no IR)
* 5785 MHz [157] (15.0 dBm) (no IR)
* 5805 MHz [161] (15.0 dBm) (no IR)
* 5825 MHz [165] (15.0 dBm) (no IR)
Supported commands:
* new_interface
* set_interface
* new_key
* start_ap
* new_station
* new_mpath
* set_mesh_config
* set_bss
* authenticate
* associate
* deauthenticate
* disassociate
* join_ibss
* join_mesh
* set_tx_bitrate_mask
* frame
* frame_wait_cancel
* set_wiphy_netns
* set_channel
* set_wds_peer
* probe_client
* set_noack_map
* register_beacons
* start_p2p_device
* set_mcast_rate
* connect
* disconnect
* set_qos_map
* set_multicast_to_unicast
Supported TX frame types:
* IBSS: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* managed: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* AP: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* AP/VLAN: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* mesh point: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* P2P-client: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* P2P-GO: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
* P2P-device: 0x00 0x10 0x20 0x30 0x40 0x50 0x60 0x70 0x80 0x90 0xa0 0xb0 0xc0 0xd0 0xe0 0xf0
Supported RX frame types:
* IBSS: 0x40 0xb0 0xc0 0xd0
* managed: 0x40 0xd0
* AP: 0x00 0x20 0x40 0xa0 0xb0 0xc0 0xd0
* AP/VLAN: 0x00 0x20 0x40 0xa0 0xb0 0xc0 0xd0
* mesh point: 0xb0 0xc0 0xd0
* P2P-client: 0x40 0xd0
* P2P-GO: 0x00 0x20 0x40 0xa0 0xb0 0xc0 0xd0
* P2P-device: 0x40 0xd0
software interface modes (can always be added):
* AP/VLAN
* monitor
valid interface combinations:
* #{ managed } <= 1, #{ AP } <= 1,
total <= 2, #channels <= 1, STA/AP BI must match
* #{ managed } <= 2,
total <= 2, #channels <= 1
HT Capability overrides:
* MCS: ff ff ff ff ff ff ff ff ff ff
* maximum A-MSDU length
* supported channel width
* short GI for 40 MHz
* max A-MPDU length exponent
* min MPDU start spacing
Device supports TX status socket option.
Device supports HT-IBSS.
Device supports SAE with AUTHENTICATE command
Device supports scan flush.
Device supports per-vif TX power setting
Driver supports full state transitions for AP/GO clients
Driver supports a userspace MPM
Device supports configuring vdev MAC-addr on create.
Is this the client or AP?
I'm a bit confused because normally some HT-Data Rates are given.
Typically something like that
HT Max RX data rate: 300 Mbps
HT TX/RX MCS rate indexes supported: 0-15
All IEE 802.11 standards are backward compatible. A 802.11a can connect to a 802.11n AP. I'm not sure, but I think this is the reason for the 20 MHz channel width. Please disconnect that phone and measure again.
There is a huge problem with legacy devices having a huge impact on the whole network. Just google for performance anomaly or stuff like that.
Depending in which country you are living it could be that some mobile operator is deploying LTE base-station with duty cycle in your network, lowering your throughput.
If you want to get really fancý, you could try to buy a SDR and look at a waterfall diagramm. It must support 5 GHz (or you need a down converter) and a bandwidth up to 160 MHz. Unfortunately, they are very expensive.
Wait, you need 2 times sampling rate. So you would need at least 10 Gbps sampling frequency.
Is this the client or AP?
I'm a bit confused because normally some HT-Data Rates are given.
Typically something like that
It's a client (laptop). No idea why it doesn't show HT-Data rates.
Please disconnect that phone and measure again.
Unfortunately performance stays the same. Btw, when I try to use 40MHz band it becomes unstable, so you're probably right and there is some industrial interference. Will try to switch to another fw to be absolutely sure I can't do anything about it. Thanks PolynomialDivision and eveyone else who tried to help for your input!
I'm not sure. LTE-U is not deployed widely. You can look at rx and tx stats (error stats). Maybe driver issues... Is the signal strength good? Weak signal strength is killing your data rate (typical problem of 5GHz band)
I don't know if it's what you meant but iw wlan0 station dump outputs are:
tx failed: 0
signal: -43 dBm
signal avg: -43 dBm
Use an analyzer app to find a clearer 5.4 GHz channel.