# Ultra-Low-Power Wide Range Backscatter Communication Using Cellular Generated Carrier +
## 6 Conclusions  
With the rapid worldwide urbanization, the need to efficiently manage the resources and infrastructure of cites is increasing. The utilization of the Internet of Things (IoT) in smart cities improves the quality of life by sensing, computing, and networking. Backscatter communication has high potential for commercial usage in cities, while it also has certain constraints from a practical implementation point of view. This article evaluated the coverage and outage performance of a practical cellular carrier based bi-static backscatter communication system through simulations. The simulation environments included both indoor and outdoor spaces and four different sub-GHz frequencies were applied in a real world urban city environment. For the considered system and homogeneous distribution of BDs, the 3D ray tracing simulations showed that, in an outdoor environment, the mean received power levels at BDs are around -33 dBm, -42 dBm, -45.5 dBm, and -48 dBm at 200 MHz, 500 MHz, 700 MHz, and 900 MHz, respectively. Whereas, while considering modern building infrastructure and indoor backscatter devices, the mean received power of -54.5 dBm, -58.5 dBm, and -61 dBm at 200 MHz, 500 MHz, 700 MHz, and 900 MHz, respectively, were found. The simulation results show that, at 200 MHz, the received power levels at the BDs in an outdoor environment are good enough for the purpose of energy harvesting for LoRa backscatter technology, as the power consumption for LoRa backscatter device is only 9.25 \(\upmu\)W. However, already at 500 MHz, the time that is required for harvesting the energy is quite high for a practical backscatter communication system. It was found that, for the given scenario and setup in an outdoor environment, the mean time that is required for harvesting the energy with 40% energy harvesting efficiency  
Figure 9: Outage ratio, (**a**) Outdoor LoRa, (**b**) Outdoor NB-IoT, (**c**) Outdoor BLE5, (**d**) Indoor LoRa, (**e**) Indoor NB-IoT, and (**f**) Indoor BLE5. is around 86 s and 880 s at 200 MHz and 500 MHz, respectively. It is emphasized that energy harvesting time can be improved by developing BDs with better energy harvesting efficiency, and by integrating the components in the BDs which can harvest the energy from sources other than incoming RF signal. We have used a hybrid approach of ray tracing and ITU-R D2D model for computing the received signal power at the reader in an outdoor environment, and for indoor receiver a hybrid approach of RT and 3 GPP indoor hotspot model was used. Presented results show that 200 MHz band is well-suited for IoT and machine type communication in an urban environment for long and medium range distances in both the indoor and outdoor environment for both LoRa backscatter and NB-IoT technology. However, the simulation results also indicate that the considered bi-static BC system with NB-IoT BDs becomes coverage limited at 500 MHz in the case of indoor BDs even with 40 m or larger BD-reader separation. The coverage outage ratio of zero percent was achieved with LoRa backscatter technology in both an indoor and outdoor environment at 200 MHz for BD-reader separation up to 60 m. Whereas, at 200 MHz, in an indoor environment for NB-IoT technology, the outage ratio was found around 1.4% for 60 m BD-reader separation. The acquired results highlight the importance and potential of using lower frequency band i.e., 200 MHz and 500 MHz for IoT and backscatter communication type of services. Conceptualization, M.U.S., K.R., H.Y. and R.J.; methodology, M.U.S., K.R., H.Y., R.J., J.H. ; software, M.U.S. ; validation, M.U.S., H.Y., K.R. and R.J.; formal analysis, M.U.S., B.X., K.R., H.Y., R.J. and J.H. ; investigation, M.U.S., K.R., H.Y., R.J. and J.H. ; resources, M.U.S., B.X., H.Y., R.J. and J.H. ; data curation, M.U.S., K.R., H.Y., R.J. and J.H. ; writing--original draft preparation, M.U.S., B.X. and H.Y. ; writing--review and editing, M.U.S., B.X., K.R., H.Y., R.J. and J.H. ; visualization, M.U.S., K.R., H.Y. and R.J.; supervision, R.J. and J.H.