## 3 Results & Observations
### Acknowledgements, Retransmissions and Gateway Availability  
The ACK payload with one retransmission has been shown to work satisfactorily (PDR is 0.95) for deployment of 80 EDs with transmission interval of 10 min and 50 byte  
Figure 8: PDR differentiation derived from payload size and number of EDs relation. Figure 7: DR5 capacity related to transmission interval. payloads. The impact of the ACKs on the gateway side is also active here, independently of the small number of EDs. The gateway is still unable to hear five out of 100 messages, which is the main issue compared to collisions. The aforementioned simulation has been set up in three clusters of nodes, distributed at 1000 m or less, with DR3 to DR5 depending on the distance. We have also tried to scale the above to a 10-times bigger size network that, with the same settings, saw its performance drop to 0.87 PDR. In a parallel simulation we have moved more than half of the devices to DR0 and the PDR has been differentiated a lot and rose to 0.77 and cannot reach more than 0.80 even with one retry. Surely, if we set the transmission interval to 1 h then the PDR is even better than without the DR0 EDs (0.96), which again argues on the importance of rare transmissions for any case. Instead, if we keep the transmission interval the same and reduce the packet size to 10 bytes the PDR increase is not the same (0.84). Based on our analysis, the observation that when we import DR0 EDs on short data acquisition frequency deployments, PDR reduced a lot, occurred in a stepwise fashion. When GW is acknowledging payloads, which are downlinks, in SF12, suddenly a lot more traffic on the same SF occurred, creating a lot more interference. This fact increases the retransmissions on the same SF, which increases the overall traffic that the GW must handle, with the extra drawback that this kind of traffic occupies the channel for a long time. This sequence causes a high transmission failure rate due to the busy condition of the GW. This drawback is always the case when we use ACKs on a medium- or larger-sized network that has DR0 devices in Europe, where SF12 transceiving happens in the same SF as the GW acknowledges the payload receiving success to all nodes. To prove this, we have conducted some targeted simulations with 300 EDs within a 3 km axis, with the goal of getting the most out of the retransmission LoRaWAN feature. We have achieved 0.99 PDR when configuring all EDs to DR5, two retries and a 10 min transmission interval, that falls to 0.97 when all EDs were set to DR3 (due to increased collisions due to ToA). As expected, when we deploy the same network, but with the EDs set to DR0, the PDR rose to 0.58 and even when we increased the interval between transmissions to around 17 min, the PDR was 0.74. In an attempt to scale a network with ACK, we simulated 3000 EDs to transmit every 1 h a short message on DR3 and the results were really satisfying, reaching 0.95 PDR. Achieving as high a PDR as before (0.95) without ACK, with exactly the same settings, can be achieved if we reduce the EDs to 2000. Simultaneously, we can argue here that deployments with medium capacity that require high data acquisition frequency, wide range and acknowledged transmissions can perform (PDR > 0.75) only if more than one GW has been deployed to the network, but we notice that if we use four instead of two gateways, PDR increased only 2%, so it is a useless choice on its own. On the contrary, if we deploy more GWs on a small-capacity network without ACK we can see this is a useless choice because no difference to the PDR is observed. So, applications that need to achieve high QoS, which depends on messages ACK or/and applications that need a lot of downlinks, need to deploy more gateways. This is a necessity because each ED on a network could have a GW fail when trying to listen on an uplink due to being in TX condition (transceiving).