## 4 Investigation Results
### Indoor Operational Range Evaluations  
The performance of the WuRx is influenced by various environmental parameters. Especially indoors, various influencing factors can affect the communication between  
Figure 19: Packet error rate depending on input power. Figure 18: Amplification level of BJT and TIA architecture. nodes. The wake-up receiver has been tested in the building of Faculty of Engineering of Leipzig University of Applied Science (Figure 20a) to ensure the reliability of the complete wake-up system when transmitting the complete WuPt with 16 bit node address. The building provides a challenging environment to explore limits of wireless communication with WuRx. Materials such as stone, glass, concrete, and steel are built in and restrict the propagation of waves. The experimental investigation is performed in different rooms and floors. Among other things, the PER and RSSI are used as comparison values to investigate influences of masonry and furniture. Although the SAW filter at the input of the WuRx provides higher immunity to signal interference and the passive amplifier increases sensitivity, the maximum range and reliability of delivered packets are still affected. The main receiver of the BJT and TIA boards was located on the second floor in the middle of the corridor, while the main transmitter was placed on two floors. Firstly, the same floor as the receiver was located, and, secondly, the floor underneath and the adjacent rooms. The experimental study was conducted at a room temperature of 25 \({}^{\circ}\)C and a distance starting from 0 m. The transmitter was moved towards the WuRx in 4-m increments in the corridor and in 2-m increments in the rooms (see Figure 20b). Once the WuRx boards were placed--marked in figures with (x)--the transmitter was started to send the wake-up packets. For each configuration, a result grid was created representing the packet error rate. The WuPt signals were transmitted every 50 ms with a transmission power of 11 dBm. For each grid point, the receiver counts the arriving packets and records the RSSI. The maximum distance (\(d\)) on the plane was 34 m with a maximum orthogonal distance of 8 m and a height difference of 0.5 m between transmitter and receiver. Figure 20: Setup of indoor range test. (**a**) Range test at the Faculty of Engineering of HTWK Leipzig (credit: [PERSON]/HTWK Leipzig); (**b**) Schematic side view of the measurement setup. Figures 21 and 22 display the receiving and transmitting device placed in the same floor. The x-axis represents the east-west direction of each floor. The y-axis represents the north-south direction of each floor, where southwards are limited by zero. If both units--transmitter and receiver--are located on the same floor, a lower PER value for distance is displayed. This applies to BJT and TIA amplifiers. The maximum reception rate is displayed when the devices are close to each other. Expanding the distance by placing one of the devices on another floor, the PER between WuRx with BJT amplifiers is almost higher than 10%, even at the ideal horizontal distance. By communication over floors, at a distance of 22 m in the west direction (W22) and of 18 m in the east direction (E18), the PER between WuRx with TIA amplifier at 100% means no signal is received. Additionally, with the TIA amplifier, the PER increases rapidly when the devices are placed in different rooms. Comparing the BJT and TIA amplifiers, it can be seen that the amplifier circuitry is very sensitive to vertical and horizontal distances. In ideal positions, both amplifiers provide a similar PER between WuRx of about 0%. In the indoor corridor case, reliable awakening was found up to a distance of 34 m, where awakening success was 90% or more. At a distance greater than 20 m and placement of each equipment in different floors, with the TIA amplifier, not a single packet was received. The second comparison criterion is the RSSI provided by the AS3933. When a signal is detected, the value is set between 0 and 31.