A key IoT network deployment requirement: bi-directional communication to upgrade firmware-over-the-air and update security patches to end-devices that have already been deployed in the field.
Bi-directional / FOTA
The three reasons why LoRaWAN is unable to support Firmware-Over-The-Air (FOTA) for a real IoT deployment.
1. With very stringent downlink limitations, LoRaWAN would take an unreasonably long time to update the firmware for a single end device. There are a few elements to take into consideration including the distance of gateway to end device and spreading factor utilised but It could potentially take weeks to send a 200K update to ONE end-device given 20 bytes on a 5-minute polling.
2. LoRaWAN gateway transmissions are uncoordinated. This means if a gateway attempts firmware downlink transmission, it will not be able to listen and receive messages from the rest of the end devices in the network. When you have thousands of end devices deployed, the end-devices won't know the gateway is conducting a firmware upgrade and all messages being sent will be lost. Class B a synchronous mode has a 128 second beacon period.
3. LoRaWAN gateways are duty cycle limited. LoRaWAN gateways can only transmit 1% of the time (ETSI), and will need all of the downlink resource for acknowledgements and MAC control messages. Very, very little would be left over for FOTA multicast. In the US, the 1% duty cycle limit does not apply so the network basically stops functioning to facilitate uplink.
Weightless is a narrowband LPWAN technology which supports FOTA and true bi-directional communication. Duty cycle limitations do not apply as Weightless-P utilises spectrally efficient narrowband operation and frequency hopping.
How does a Weightless, LoRaWAN, and Sigfox base station perform when placed in a large, urban environment?
Our large urban area capacity simulation uses Hata to derive the path loss for a given base station to end device distance. Hata Model is the most widely used radio frequency propagation model for predicting the behaviour of cellular transmissions in built up areas.
Settings: Base Station Height = 30m
End-Device Height = 0.5m
LoRaWAN settings: adaptive data rate assumption given end nodes are spread uniformly throughout a large urban city (2km for EU and 4.5km for US). Thus, the closer nodes are using SF7 and farther nodes are using SF 12. The average data rate is 3200bps so about SF9 average. For optimal performance, LoRaWAN will be using 8 channels (1MHz bandwidth in EU) and 64 channels (8MHz in US).
Europe: 863-870 MHz
Devices / Base Station Calculator (EU)
1. Use slider/manually input end-device message size
2. Use slider/manually input messages sent per day
every 15 mins = 96 messages / day
every minute = 1440 messages / day
Outputs (right): devices supported per base station