# HARE: Supporting Efficient Uplink Multi-Hop Communications in Self-Organizing LPWANs
## 7 Results
### Power Regulation Mechanism Performance  
The previous test was also useful to analyze the performance of the PRM when setting it with RSSI\({}_{min}=-110\) dBm and RSSI\({}_{max}=-100\) dBm. It is worth noting here that Zolertia\({}^{\text{TM}}\) RE-Mote devices use up to 31 different power levels (from \(-16\) dBm to 14 dBm with steps of 1 dB [51]) and are programmed by default with the maximum transmission power level.  
Figure 22 shows the clear reduction of transmission power in most of the analyzed STAs during 50 _primary beacons_, the most significant examples being STAs #7, #8, #9 and #10; that is, the nearest ones to the GW. This fact results in a lower energy consumption, as \(I_{TX}=61\) mA when transmitting at 14 dBm, but almost half (\(I_{TX}=39\) mA) when doing it at -16 dBm.  
The effects of switching off nodes are also visible in the transmission power, as shown in (**A**) and (**B**) from Figure 22. While STA #1 in (**A**) simply stopped working, nodes involved in the shutdown  
Figure 21: Network topology before and after shutdown of nodes #1 and #4. (**a**) logical network topology after the _network association primary beacon_; (**b**) logical network topology from beacon #15 until beacon #50.  
Figure 22: Temporal evolution of STAs’ transmission power level in multi-hop setting.  
of STA #4 in (**B**) experienced notable changes. Thus, STAs #2, #3 and #5 _disappeared_ along with the shutdown of STA #4. However, they became associated again between beacons #13 and #15 with maximum transmission power. For its part, when STA #6 became a parent of STA #2, it set the maximum power level to establish connection with its new child.  
The PRM also proved its good performance against channel alterations as shown in area (**C**). In this case, and due to the test execution on a real scenario, the presence of people in the floor corridor may have disturbed channel conditions. To overcome this situation, some STAs (#9, #10, #11, and #12) selected greater transmission power levels temporarily, which were reestablished once the detected channel issues were finished.  
To evaluate the effectiveness of the PRM in single-hop networks, this test was repeated with the same configuration except from the network topology, which was forced to be single-hop. As it can be seen in Figure 23, only STAs located very close to the GW and/or with favorable channel propagation conditions (that is, STAs #4, #8, and #9) managed to noticeably reduce their transmission power over the test's duration. As for the rest of STAs, they could not decrease significantly their power level, and tended to stabilize them from half of the test.  
Lastly, it is relevant to note the behavior of STA #9, whose final power level was well over that of the multi-hop test, when that STA belonged to the first network ring. This difference is due to the inherent operation of the PRM, which increases in one unit the power level in each successive retransmission, and is consistent with reliability results from Section 7.2, where measured PDR in first transmission windows is always higher in multi-hop approaches.