# Performance Evaluation of Directional Antennas in ZigBee Networks under NLOS Propagation Conditions
## 3 Results
### Location 1--Terrace  
For location 1, we chose two types of orientation for the transmit directional antenna. The first was to orient the transmit antenna toward the room door, approximately in line with most receiver positions (Directional--orientation 1). In the second case, we pointed the transmit antenna in a direction that provides the highest average RSSI and PDR (Directional--orientation 2). In this situation, the antenna pointed to the window mentioned in Figure 1. We moved the receiving antenna during measurements within a radius of about 10 cm around the central position to obtain the average. For the directional antenna, we rotated the receiving antenna to find the highest average RSSI and PDR. In this case, orienting the antenna toward the building in front of the window provided the best results. We recorded about one hundred packets in each measurement session. Figure 5 shows the average RSSI as a function of the distance to the transmitter for the three studied situations. The labels inserted in the graph relate the distance with the receiver position shown in Figure 1b. The expected values of received power under free  
Figure 4: The radiation patterns: (**a**) 17.5 dBi gain antenna; (**b**) 9.5 dBi gain antenna. space conditions are also represented in Figure 5a to determine the attenuation introduced by the medium. This attenuation was almost constant except for distances close to the transmitter. The high attenuation was due to the structure of the building. The directional antenna--orientation 2--provided the highest average RSSI values, with an average of 5 dB above the omnidirectional one. However, the expected received power under free-space conditions would be 7.5 dB higher. Despite the XBee sensitivity being \(-100\) dBm, the lowest measured RSSI was \(-90\) dBm because of the Wi-Fi interference. Figure 5b shows the PDR for the three situations. All antennas have similar results for the first four receiver positions. However, the directional antenna--orientation 2--Iost some packets in the first positions because the antenna pointed directly to the Wi-Fi source. Above the fourth position, the directional antenna--orientation 1--had the lowest performance. The systems were not able to receive packets above the last point. We also performed a set of measurements to assess the signal distribution around the receiver. The technique described in Section 2.3 allowed for extracting the received signal as a function of the azimuth angle. We used the transmitter's direction for the angle count, and the rotation was clockwise. Figure 6a shows the received power for position 2, and Figure 6b shows the received signal after removing the antenna radiation pattern effect. These results demonstrated that the highest components of the received signal were in the same direction as that obtained for the RSSI. However, the antenna received many signal reflections from other directions. The omnidirectional antenna spreads the transmitted power more in multiple directions. The received signal was lower for the directional antenna--orientation 1. In this case, we can observe in Figure 6a signal peaks for angles around \(-120\) degrees. This result confirmed the Wi-Fi interference observed during measurements, which occurred as bursts of high signal levels. The received signal also allowed the received power for each antenna to be estimated. For this, Equation (1) was employed with \(g(\theta)\) as the radiation diagram of the respective antenna. Figure 7 shows the result for the directional antenna--orientation 2--in position 2. The estimated power level in the maximum direction was \(-80\) dBm. Applying the procedure to the omnidirectional antenna gave an estimated power of 5 dB below the value of the directional antenna. Applying it to the case of the directional antenna--orientation 1--the estimated power was \(10\) dB below. The received power was measured using the signal generator and the spectrum analyzer to evaluate the one estimated by the previous procedure.