Downlink Spreading Factor Gateway Config

#1

HI

I have a fully working setup with both uplink and downlink working fine. However I have a question I cant find the answer to.

What determines the Downlink (gateway to node) spreading factor/power and frequency?

I ask because both gateways I use allow me to set this (Dragino and Microchip Development Kit) as well as frequency. But I see in gateway profiles on the application server that I can set desired channel and SF so I wonder how this comes in to play as it appears to have no effect. Messages are all sent depending on how I configure the physical gateway as opposed to whatever config I have in chirpstack.

Thanks

#2

Gateway-Profiles only really take into effect if you are using concentratord (tested) and i dont remember if basic station also takes this into account.
The config get’s pushed to the gateway and applied. Even if you do not use concentratord, I would recommend that your gw-profile matches what you defined at the gateway. It can affect the “advertised” frequencies and proper scheduling of downlinks.

#3

Hi
Yeah thats what I was thinking.

One thing that is confusing me is I have changed the spreading factor to 9 on the gateway but it is still showing SF12 in the downlink gateway message in the application manager

chirp
chirp1911Ă—973 93.3 KB

#4

Hi,
you really don’t need to use gateway-profiles unless you have concentratord on the gateway or if you want to adjust gateway stats interval so that you can see active/inactive gateway conut on dashboard properly.
And in latter case you do not even need to fill correct channel seting anyways (tested).

Settings you looking for are part of network-server config: https://www.chirpstack.io/network-server/install/config/ and depends on your regional parameters too.

Most inportant part of config regarding downlink settings would be[network_server.network_settings]

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#5

The downlink spreading-factor and frequency is based on the uplink sent by the device. For EU868 uplink freq. = downlink freq. By default the DR is equal, unless you have configured the rx1_offset config option. For US915 the downlink channels = uplink channel (not freq.) % 8. All this information, including how the uplink DR maps to the downlink DR can be found in the LoRaWAN Regional Parameter specs.