Where are my megabits gone? (Long-range outdoor wireless)

Installing and Using OpenWrt
1

Hi there,
I am facing WiFi bandwidth problem:

  • my connection is 630m (according Google maps), both ends are TP-LINK WR-1043ND (v1) 300M/GbE routers.
  • both ends are with directional antennas: 2x 16Bd on one end, 16+19dB on other, with 5m H155 cable. Polarisation H +V.

OpenWRT 21.02 on one router OpenWRT 18.06 on other.

Now /network/wireless shows:
Master "adelin3" (wlan1)

74:EA:3A:A7:DE:2A

TP-LINK_WR1043ND_Krzysiek (192.168.1.11)

-76 / -95 dBm

54.0 Mbit/s, 40MHz, MCS 9
90.0 Mbit/s, 40MHz, MCS 4, Short GI

But iperf3 shows 20-30Mbps.

Same result with link measuring page www.speedtest.pl

What should I look for?

Laurent

2

1 byte = 8 bits

therefore,

20-30 Mbps (Megabytes per second) measured should be roughly equal to theoretical 160 - 240 Mbit/s (Megabits per second), which is substantially higher than the 54 and 90 Mbit/s you posted, so my take would be that OpenWRT at the very least measures differently as compared to Iperf....

Edit:

Thanks @mbo2o

3

The 54 and 90 MBit/s numbers look like the raw radio link rates. These are only theoretical numbers (they're quite misleading), in practice you will never achieve them. Getting above half of them is a pretty good start.

Have a look at the output of the command "iwconfig" for each end. See what the counters for invalid messages & retries are like. Every time there is a collision or failed message you effectively lose some of the theoretical bandwidth.

(Obligatory: I don't know where in the world you are, but make sure you're following local laws and regulations regarding high gain antennas. Many jurisdictions require you to lower your transmit power when using them. Above all else: avoid using them near other people using wifi or the same frequencies, as you're more likely than a normal user to cause them interference problems.)

4

Both are megabits per second in this case

1 Like
5

Ok, iwconfig does not report counters on AP interfaces, but provices some info on STA node:


wlan0     IEEE 802.11  ESSID:"adelin3"  
          Mode:Managed  Frequency:2.462 GHz  Access Point: 74:EA:3A:A5:DE:2A   
          Bit Rate=180 Mb/s   Tx-Power=20 dBm   
          RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality=35/70  Signal level=-75 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:354  Invalid misc:89630   Missed beacon:0

root@Laurent_Home_OpenWrt_1043ND_new_Krzysiek:~# uptime 
 18:14:25 up 9 days,  2:19,  load average: 0.22, 0.16, 0.06

Getting half of theoretical in 2R2T config 300Mbps, would be a miracle,
Even half of N-lite 150Mbps.

This is in Poland in rural area so I don't scare about interference.

6

The bottom line is that -76 is not a very good signal. Is it a clear line of sight or are there obstructions?

MCS numbers less than 8 are a 1x1 link with a maximum rate of 150 Mb (MCS 7) on 40 MHz n.

I would use CPEs here. A CPE is a pre-integrated solution with a directional 2x2 antenna and no cable RF loss. There are very few 2 GHz CPEs on the market today, use 5 GHz ac instead.

1 Like
7

LOS is free from other equipments, nearest is 30 deg apart.
But there is (unremovable) obstacle: 50cm of "gas-concrete" wall. (24cm thick but with 45 deg angle to LOS).

For 5GHz I already tried , 2x 23.5dB antennas, USB WiFi cards, 5m of RF240. It would be nicer, as even connected to USB2 port card shows 300Mbps i "A" band.
"Far end" has 300Mbps fiber connection :slight_smile: so getting 10% of this is not enough for me.

But (for now) didn't got any trace of signal...

8

It is in general better to use narrow channels at longer distances or crowded airways. More power. Also, better to have low qeueing delay, at any distance.

A packet capture often shows underlying link interference problems, do a packet capture of your iperf (I use flent tcp-nup, simpler), and do a rtt plot in wireshark.

1 Like
9

Ok, changed to NOT "force 40MHz", now LuCI GUI shows stable 52-78Mbps, ~ -70dBm.
Added 800m to "distance" (remember that I should use TWICE the distance - maybe not with modern OpeWRT?)
Found problem that caused erratic WiFi behawior (ping from 3ms to 1000ms): HDD connected to Orangepi on same SMPS as router.
Fixed.
Now iperf shows (a little less) ~30Mbps.
Is that all that I may expect from 2.4G WiFi on that distance?

10

Was not the miracle of connectivity enough?

30Mbit is good at that distance, yes.

11

OK then :(.

But for given distance (and obstables), it it possible to achieve highrer rate?
"Far end" has 300Mbps fiber connection, I'd like to profit from this :slight_smile:

5GHz? Tried with 2 23.5dB antennas and USB AC cards, but no luck for now. Will do a test with there 2 antennas with clear LOS.

12

I could get more than that via directional nanostation m5s, even through foliage. Integrated directional antennas are helpful.

I just dug up my diary of my wireless journey in 1998, when a local ham sneered at our cable and showed of his heliax and lmr-400. Enjoy:

http://www.rage.net/wireless/diary.html

13

Nice story, reading :slight_smile:
At 1998 I wasn't involved in WiFi, only 2003 and later.
The few Mbps WiFi B connection (~100m). But also Linux as router -> Asus 500gP with X-Wrt.

But now I am faced to given situation. And want most of possible link speed. 50-100Mbps would be nice. What is radiation (-3dB) angle of 23.5dB 5GHz antenna? Tetraant.

14

Look it up in the datasheet of your antenna.

15

I am asking here because I got used antenna and exact type marking usi unreadable.
So I can't use google.

[edit]
This may be this one: https://elboxrf.com/en/product/96/tetraant-5-23-10-hv