Because of broad signal spectrum LoRa has a built-in problem of handling large number of devices. I hope Amazon came up with something narrow-band, like SigFox.
Could you elaborate? I was under the impression that LoRa's slow updates result in a large number of devices being able to operate smoothly. Also, while the ISM band may be considered "broad," in a sense, LoRa takes a small amount of the band's width (low bandwidth), which translates into a long-range.
The problem is two-fold. First, LoRa is a spread spectrum technology that also has a problem with collisions. Spread spectrum is where the signal bandwidth of your transmission is higher than the information bandwidth, meaning your transmission's spectral efficiency is terrible. But usually spread spectrum systems are designed such that multiple transmissions can occur at the same time without colliding, so the network spectral efficiency is just as good as a narrowband system. But LoRa is a spread spectrum technology that still suffers from collisions, so the network spectral efficiency is really bad.
Second, LoRaWAN uses an ALOHA medium access scheme, which also suffers from poor network spectral efficiency compared to basically every other medium access scheme out there. So these two things combined mean that a LoRaWAN network probably won't be able to handle much traffic.
Almost all of the media I see about LoRa and LoRaWAN talk about the great range, which is really good, but then gloss over the network performance. So in my opinion LoRa is a bit too hyped at the moment. I also think that when LoRa came out, it was the only PHY that bothered to go down to really low bit-rates, and then the range basically comes from the Shannonn-Hartley theorem. People think that LoRa gets its range from some fancy signal processing tricks or whatever, but I think it's just the fact that they bothered to drop the bit-rate very low. That's basically what SigFox is doing as well, but they're using a more typical narrowband PHY and so probably won't suffer from the same network capacity problems.
The problem of LoRa is that is just slotted ALOHA, which maximum data throughput is only 36.8% of the available bandwidth. The more you transmit the more packets collide and data must be retransmitted in a spyral of death, so the system needs to operate using a small portion of the bandwidth not to collapse. Practically if everyone in New York would use LoRa and have dozen of devices in their homes using those bands, the bands would be jammed and nothing would work.
LoRa is just a PHY, LoRaWAN is the MAC. And last I checked LoRaWAN used ALOHA, not slotted-ALOHA, which is even worse. But I knew a few years ago they were talking about adding beacons to the MAC to enable slotted-ALOHA, so maybe my knowledge is out-of-date?
