# On the Benefits of Listen before Talk Scheme for NB-Fi Networks
## 8 Conclusions  
This paper considers NB-Fi networks using LBT and non-LBT operation modes. We compared Aloha, persistent CSMA, non-persistent CSMA, non-persistent CSMA with frequency hopping, and \(p\)-persistent CSMA in terms of the PLR, average delay, throughput, and energy consumption of NB-Fi devices. We considered scenarios of a small network of radius \(R=0.4\) km, where all sensors can sense the transmissions of other sensors, and a wide network with an \(R=3\) km radius, where some sensors cannot sense transmissions of some other sensors. Analysis of the simulation results shows that at low rates (50 and 400 bps), LBT achieves almost the same PLR as Aloha, which differs from the classic results of CSMA studies but is explained by the peculiarities of NB-Fi modulation. At rates of 3200 and 25,600 bps in a small network, LBT has a much greater effect; in a large network, the effect is smaller. At high loads, the persistent CSMA always has the highest PLR results among other types of CSMA and should not be used. Note that in a network of a small radius, it is better to use the highest data rate with non-persistent CSMA, while in a network of a large radius, it is better to use \(p\)-persistent with small \(p\). At low data rates, the average delay in LBT modes is a little different from the average delay in the Aloha mode. At a high rate in a small network with a high load, the average delay when using the carrier sensing mode noticeably exceeds the average delay when operating in the Aloha mode. In a large network, the difference in the average delay at high loads becomes smaller. These results contradict the classic studies on CSMA but are explained by the buffering model, which more accurately describes the IoT devices. For feasible loads, the best delay is obtained with the highest data rate and non-persistent CSMA in a small network and p-persistent CSMA in a large network. As predicted by classic papers, CSMA at high loads significantly increases throughput. At the same time, \(p\)-persistent and non-persistent CSMA modes with frequency hopping have the highest throughput at high loads. As can be expected, at a load below one packets/s, the use of CSMA does not reduce the energy consumption compared to Aloha. At high loads (more than 40 packets/s), CSMA can lower the energy consumption more than twice in comparison with Aloha. Among the considered types of CSMA, persistent CSMA has the highest energy consumption at a high load. At the same time, at high loads, non-persistent CSMA shows the lowest energy consumption in networks of small radius, while \(p\)-persistent CSMA with small \(p\) is the most effective in networks of large radius. The practical result of this research is the recommendation to use the non-LBT mode in NB-Fi networks with low loads or in NB-FI networks where devices operate only at low data rates (50 bps or 400 bps), while at higher loads and higher data rates, the best practical solution could be to use non-persistent CSMA in small networks, where all devices can sense each other's transmissions, and to use p-persistent CSMA with an optimized \(p\) parameter in large networks. We see several directions for future work. The first one is studying the performance of NB-Fi in multi-BS scenarios. The second direction is studying approaches to satisfy the quality of service (QoS) requirements for different kinds of traffic that are generated in the same NB-Fi networks. The third direction is to develop rate and power control algorithms that can decrease energy consumption, PLR, and delay in such networks. An important subcase of this problem is when the devices are mobile. Finally, the coexistence of NB-Fi networks with networks of other technologies operating in ISM bands should also be studied. **Author Contributions:** Conceptualization, D.B., E.K., and A.L. ; formal analysis, D.B. and E.K. ; investigation, I.P. and D.B. ; methodology, E.K. and A.L. ; software, I.P. and D.B. ; validation, E.K. and A.L. ; writing--original draft, I.P. ; writing--review and editing, D.B., E.K., and A.L.