# Wake-Up Receiver with Equal-Gain Antenna Diversity +
## 4 Experimental Results
### Measurements in Multipath Environment  
For the second test, the diversity node was equipped with antennas and the 868 MHz wake-up message was transmitted wirelessly, but generated by a signal generator to be able to accurately control the output power. Figure 12 depicts the test setup. The sender was placed at a fixed position in the laboratory, and the receiver was positioned at several different locations. Inside the laboratory were several randomly placed objects like chairs, tables, shelfs and general laboratory equipment. In summary, the objects generated an multipath environment suitable to test the diversity wake-up system.  
Table 3 reports the measurement results at the six positions. The first column gives the position, the second column gives the required transmit power to wake-up the node with one antenna connected in straight position. The third column is the required transmit power to wake-up the node with one antenna connected in angular position and the last column was the required transmit powers when both antennas are connected to the node.  
Assume that a selection diversity system chooses the signal with the highest RSSI value. In this particular experiment, the equal-gain diversity system presented here outperformed both single antenna solutions about approximately 0.2 dB to 2.5 dB and consequently successfully demonstrated its superior performance compared to selection diversity. Figure 13 illustrates the required transmitter powers at the 20 locations graphically. The blue circles show the results for the straight antenna system, the green squares for the angular antenna system and the yellow markers depict the equal-gain diversity results. In this particular experiment, the equal-gain system outperformed both of the other configurations in all measurements, as can be seen in Figure 12.  
To visualize the benefit of the equal-gain diversity wake-up system compared to a selection diversity wake-up system, Figure 14 plots the signal strengths differences required to wake-up the wireless node using the equal-gain diversity method compared to selection diversity in ascending order for the 20 observed locations. It can be seen that the gain of the equal-gain diversity system lies between 0.2 dB and 2.5 dB. Adding signals received by both antennas in an equal manner is also a possible drawback of the equal-gain diversity system. For example, if one antenna receives a strong noise signal, the effective signal-to-noise-ratio at the receiver input will be reduced compared to the signal strength that would be received with only one receiving antenna that has a high signal-to-noise ratio. On the other hand, most selection diversity systems choose the channel with the apparent highest received input signal strength, but not the channel with the highest signal-to-noise-ratio.  
Figure 12: Multipath laboratory setup with randomly placed objects.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Location** & **Straight Antenna (dBm)** & **Angular Antenna (dBm)** & **Both Antennas (dBm)** \\ \hline
1 & \(-\)4.2 & \(-\)16.3 & \(-\)17.1 \\
2 & \(-\)7.7 & \(-\)3.9 & \(-\)9.1 \\
3 & +0.3 & +4.8 & \(-\)0.7 \\