# Ultra-Low-Power Wide Range Backscatter Communication Using Cellular Generated Carrier +
## 5 Results and Discussion
For reducing the harvesting time, outdoor BDs can also be implemented with components that can harvest the energy from sources other than incoming RF signal, e.g., solar and wind energy. whereas, indoor BDs can take the advantage of the energy available from indoor lights fluorescent and indoor RF signals, such as TV and WiFi. Currently available BDs require quite high received power level e.g., -25 dBm for harvesting the energy, and the results that are presented here emphasize the need of developing the BDs that can harvest the energy with good efficiency with considerably low received power levels for supporting the battery free deployment of BDs. Figure 6: CDF of received power at backscatter device for different frequencies, (**a**) Outdoor, and (**b**) Indoor. Figure 7: CDF of time required for energy harvesting at outdoor LoRa backscatter device with different energy harvest efficiencies at, (**a**) 200 MHz, (**b**) 500 MHz. The received power at the reader is the next metric that is considered here, as it defines the coverage and outage of the AmBC system. Figure 8a shows the mean received power at the reader for the case of outdoor BD with outdoor reader, where the \(x\)-axis is the distance between the BD and the reader in \(meter\), and \(y\)-axis is the received power at the BD in \(dBm\). It can be seen that, by increasing the distance between the BD and the reader, the mean received power decreases. The slope of the graph changes due to the LoS probability, as in the case of ITU outdoor D2D model the LoS probability is defined as a function of distance between the BD and the reader, and a transition distance of 20 m is used in our simulations. From the acquired results, it is clearly evident that the cellular based AmBC system is able to provide a significantly high received power to the reader in an outdoor environment at 200 MHz with BD-reader distances up to 60 m. However, at 500 MHz, the mean received power is above -140 dBm for the outdoor BD-reader up to 50 m distance. For the medium range distance, i.e., up to 40 m between the BD and a reader, a BC link with at least -140 dBm receiver sensitivity can be obtained by using, as an ambient source, an existing cellular network operating at 900 MHz. Figure 8: Mean received power with different BD-Rx distance at the receiver for different frequencies, (**a**) Outdoor, and (**b**) Indoor. Similarly, Figure 8b shows the mean received power at the reader while using low and high BPL in the case of indoor BD communicating with the indoor reader. For up to 60 m BD-reader separation the mean received power level is clearly higher than -140 dBm for indoor readers at 200 MHz centre frequency, even with high BPL. It highlights the usage of 200 MHz band for IoT and machine type communication in an urban environment for long and medium range distances. The radio propagation condition is slightly challenging at 500 MHz for indoor BD and reader as the mean received power is almost -140 dBm at 40 m BD-reader separation with high BPL model, and the coverage area shrinks with higher frequencies. Similarly, for other frequencies and BPL models, the mean received power levels at the reader can be found in Figure 8b. The outage ratio is defined as the ratio of the locations with a received power below a receiver sensitivity threshold to the total number of receiver points considered in the area. Here, we have considered three thresholds i.e., -149 dBm, -141 dBm, and -97 dBm with respect to the receiver sensitivity of LoRa, NB-IoT, and BLE 5 technology, respectively, for computing the outage ratio of the considered AmBC system. Figure 9a-f show the outage ratio for outdoor and indoor BDs, respectively, while considering different backscatter technologies. Interestingly, it was found that there is zero outage with LoRa and NB-IoT at 200 MHz in outdoor environment, even for 60 m BD-reader distance, and that shows that both LoRa and NB-IoT are good candidate technologies for deploying AmBC network at 200 MHz in an urban macro cellular outdoor environment.