A single-channel gateway is a LoRa device that acts as a gateway by forwarding LoRa packets to the network. As it’s usually built using a SX1272/SX1276 instead of SX1301/SX1257, it’s a lot cheaper than a full gateway, making it a favorite choice for people to start with LoRaWAN. However, single-channel gateways are very limited compared to a real gateway. Using a single-channel gateways often leads to undesired design choices for device implementations, but also cause a lot of issues in the network as a whole.
As a reminder: Single-Channel gateways are not LoRaWAN compliant and are currently not officially supported by The Things Network.
Problems of SCGs
Single-channel gateways can only receive on one channel and one spreading factor at the same time, whereas a full gateway can receive on eight channels and six spreading factors at the same time. Some single-channel gateways can “hop” between frequencies and spreading factors to simulate a real gateway, but they still have less than 2% of the capacity of a real gateway. As mentioned in another thread by @kersing, single channel gateways project a false coverage image. Putting single-channel gateways on the map confuses many people (“why is my LoRaWAN compliant node not working when there is a gateway 60 meters away?”). Furthermore, we need multiple channels to make the network scale (using Adaptive Data Rate).
Many single-channel gateways do not have downlink support. This may lead to lost downlink messages if the network tries to schedule a downlink on such gateway, confusing people even more (“the gateway that is 60 meters away receives my message with great signal, a downlink is sent, but never received?”). Furthermore, downlink support is required for OTAA (“why does my LoRaWAN compliant device say “join denied” when I’m 60 meters from the gateway?”) and for using Adaptive Data Rate (ADR). Without downlink support, devices close to the single-channel gateway will not go to more efficient spreading factors, but instead, pollute the spectrum with unnecessary SF12 transmissions.
What I think we need to do
- Add Downlink Support to all SCGs: In my opinion, the biggest problem is the fact that many single-channel gateways do not support downlink. Although the hardware supports downlink just fine, the forwarder that is used, does not. As far as I know, @JBraam’s ESP8266 based single-channel gateway and the LoPy are the only ones that do support downlink. If we eventually want to support other single-channel gateways, these projects should also add downlink support.
- Define Single-Channel Frequency Plans: I think we should define a single-channel frequency plan (per region) outside the existing frequency plan, and use that for all single-channel gateways. Currently, most SCGs in EU are fixed to 868.1, which is one of the 3 join frequencies that are used by all LoRaWAN networks, putting significantly more load on this one channel than on the 7 other channels, which is harmful for the entire network. If we would define a completely separate frequency that will exclusively be used by single-channel gateways, we won’t harm the rest of the (LoRaWAN compliant) network anymore.
Let’s start the discussion with that.