Thanks for posting this here, and adding your own thoughts and simulation!
You need to be very careful in comparing these two technologies. For example, at a first glance it seems that the full bandwidth (200kHz) of a Sigfox gateway is compared to a single channel of a LoRa gateway (but correct me if I’m wrong). Using 8 standard channels, and 2 high-speed for LoRa, the numbers get much closer to each other. Maybe the main conclusion from the analysis is that Sigfox is more spectrum efficient. Although I don’t think that assuming 2000 independent 100Hz channels in a 200kHz bandwidth is realistic: at full power adjacent channels will interfere with each other. Another thing to take into account is that if there is a certain difference in signal strength, LoRa can still decode the strongest signal in case of a collision.
My point is not to claim the analysis is wrong, but just to indicate that there are many factors to take into account, also non capacity related ones.
What is important, and clear from the blog post, is that with too many message, a Lora channel will be congested, and result in unacceptable packet loss. This is the basis for our ‘30 seconds’ fair access policy.
We defined a maximum load per frequency of 5% (duty-cycle) to prevent too many collisions, and a minimum number of 1000 nodes we want to support per gateway. Over 8 frequencies that gives you per node: 8×24×60×60×0.05/1000 = approx. 30 seconds. We don’t make any assumption on the SF distribution, and don’t include a gain based on the orthogonality.
They key is that it is defined in seconds, and not in messages. This will keep the number of (unnecessary) SF12 transmissions minimal, as the blog post clearly shows is problematic.
The TTN model is based on small cells using simple equipment, not large gateways covering entire cities (although that’s great for now). Together with the scalability features of LoRa such as ADR and the ability to regulate node TX power, this will get us quite far.
Let’s keep researching and discussing this, as it is key to the long-term success of TTN.