Software guy trying to understand radio, sorry if this is basic.
For our office pilot someone recommended a small indoor LoRaWAN gateway for around 150 dollars, the “picocell” kind with Semtech inside. Coming from Wi-Fi, where an access point talks to one client at a time on a channel, I don’t get how such a cheap box listens to hundreds of sensors on several channels at the same time. What’s the trick? And is a cheap one like that ok to use with Hermetry?
Also curious from the money side. If one 150 dollar box covers our warehouse, that changes the business case a lot compared to the outdoor ones at 1,000+.
I asked the same thing when we did our first site, so here’s what I learned.
It comes down to the concentrator chip (SX1302/SX1303 family in current gateways, SX1301/1308 in older ones). It isn’t one radio, it’s a baseband that demodulates 8 channels in parallel and on each channel every spreading factor at once. A sensor doesn’t have to “connect” either: it transmits, every gateway in range hears it, done. No association like Wi-Fi. So listening to hundreds of sensors is mostly listening to short bursts that rarely overlap.
The cheap indoor ones use the same chip family. What you give up is the outdoor stuff: enclosure, a good antenna up high, cellular backhaul, GPS.
For Hermetry, check three things before buying:
- A model for your band. Hermetry’s network server follows the gateway’s frequency plan, so the gateway and your sensors just need to be on the same one.
- Basics Station support (LNS). The old UDP packet forwarder isn’t supported.
- It lets you set tc.uri, upload tc.trust and set the token (tc.key). Hermetry doesn’t use CUPS, you configure it once by hand.
On the channels: Hermetry sends the gateway its radio configuration when it connects (on EU868 the 8 channels plus a 250 kHz LoRa channel and an FSK channel), so you don’t set channels yourself.
Keisha, for a warehouse: indoor gateway in the middle, mounted high, and check RSSI/SNR of the furthest sensors in the frames log before you trust coverage. Racking full of metal eats a lot.
The “8 channels times every SF in parallel” bit is what I was missing. Bought one with Basics Station support, followed the Connect a Basics Station gateway page, it showed Online within a minute. Our two test sensors at the far end of the office come in at around -105 dBm, fine for now.
Good to know about the metal racking, I’ll budget a second one for the cold store then.
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