What will be the bets fixed WiFi data rate mode for long range communication?

[Miyuki]

Hello,
I want to ask if you can help me to choose the best, I assume fixed, data rate mode for long-range transfers 500-1000m
I need to transfer a few KB/s of UDP packets with as low loss as possible over a relatively large distance

I'm considering using something like 2 Mbps with long preamble  or G mode at 6 Mbps

It will be star-like topology. One ESP32 as a central hub in AP moce. Few ESP clients. And optional one setup interface over WiFi from Phone or so.
All with small omnidirectional antennas.

What will give me better reliability?
Have you any experience?

[NiHaoMike]

I need to transfer a few KB/s of UDP packets with as low loss as possible over a relatively large distance

Take a look at LoRa.

[vu2tve]

If you don't need high data rates, typically, with low data rates and low data modes you get the maximum wiggle room in SNR.

If you can set it, 802.11b will be the best mode in terms of noise/range.
If you can't set that, then try 802.11g (and within that MCS0).

I'm assuming you're working at 2.4GHz.

Good luck!

[ahbushnell]

Do you have to have Wifi.  If you used a digital radio link you could do it with this

https://irlock.com/products/rfd900-telemetry-bundle

It runs on 900 MHz.  No license in the US.  1 watt (30 dbm).  56 kbaud. 

Andy

[2N3055]

Cheap Mikrotik Wifi Routers do that job easy..

[A.Z.]

fixed, data rate mode for long-range transfers 500-1000m
[...]
All with small omnidirectional antennas.

I doubt that omnidirectional antennas will "cut the mustard", you'd better consider antennas like this one

https://www.tp-link.com/us/business-networking/antenna-and-accessory/tl-ant2424b/

on BOTH sides of the data link and possibly placing the AP unit straight at the back of the antenna (and using network cable to both carry down the data stream and power the AP using PoE) , be careful about the height of the antennas since at WiFi frequencies, it's important to keep the Fresnel zone away from obstacles, otherwise (e.g.) a passing truck may disrupt your link

[TheUnnamedNewbie]

(...) data rate mode for long-range transfers 500-1000m
I need to transfer a few KB/s of UDP packets with as low loss as possible over a relatively large distance
(...)
All with small omnidirectional antennas.

I think within the Wi-Fi protocol it is impossible to do this. You simply do not have enough output power in the standard to cover that range with omnidirectional antennas. You can't fix this with better RX because you run into the thermal noise floor (unless it works in antartica at -50 C, that might give you some thermal noise wiggle room).

That said, with such low data-rates, there are more appropriate standards like LoRaWAN and Zigbee that might be an option.

[2N3055]

Again, Mikrotik.
You get one with omni antenna as a hub and directional ones as spokes. They even sell a set like that...
500-1000m is simple. You can easily do 5 km.
Provided optical visibility of course. If you don't have optical line of sight than it won't be easy. You will need to go down with frequency and place repeaters..

[cdev]

I second the recommendation of microtik HAP APs for good value. Their best selling model goes for around $24 or less and includes two radios and a good four port 100 MBPS switch, they even throw in a TDR. Modifying it to allow the use of external antennas is quite simple. One needs to use existing footprint for RF connectors that let you use external antennas instead of the supplied monopoles. Its a very simple mod as the traces are already there. This can give you an access point that has a diversity radio - two sets of two antennas each can be pointed in two different directions. That gives you diversity transmission and reception. You can do something similar with an HP thin client. Get an upgrade by mains of a high end wifi card, like an alfa if you want spectacular long range.

And linksys. WRT54 series..

The record if you have line of sight is over 200 miles.. 300 kmn. This was in South America on the slopes of a volcano in the Andes. . Using a linksys totally generic off the shelf router.

Adam 9A4QV (of LNA4all fame) himself was successful in bridging wifi over a channel between two islands in the Adriatic, more than 20 miles, his antenna was simply the access point and two gain antennas on it and a paraboloid (curved metal sheeting or even chicken wire will do) thats all he needed as the reflector, he said.

No extra power, just a straight shot and the simplest way of beefing up an access point, putting it in front of a conductive surface. (a parabolic curve/ A curved piece of sheet metal works fine for this.)

Over water is the best. The salt water multiplies the gain  by reflection. Ive heard so many tales illustrating how well this works, it doesnt surprise me any more.