In Fig. 6 we show the failure probability for two representative cell loads, i.e., 10 H2H UEs (low load) and 40 H2H UEs (high load).
The failure probability for a smart object is defined as the ratio between the number of CoAP responses received with success and the total number of CoAP requests sent. Failure occurs because of some of the RLC PDUs being lost at the UE/eNB level, due to either node/cell congestion or channel fading effects.
In a more complex simulation scenario with multiple cells co-located in the same region and using the same frequency bands, which is not considered here, inter-cell interference would also contribute to these failures.