# Path Loss Model for Outdoor Parking Environments at 28 GHz and 38 GHz for 5G Wireless Networks
## 6 Results and Discussions  
### Path Loss Models Results  
Figure 3 shows that the path loss at 28 GHz increased as the separation distance increased; this observation was the same for both single and dual parking lots. The path loss observed in the DPL was much more than in the SPL by an average value of about 7 dB/decade. Using the CI path loss model, the path loss exponent values were 2.7 and 3.4 for SPL and DPL, respectively, as shown in Figure 3. Comparing with FSPL exponent of 2, the path loss values obtained from the parking lot indicate that the most experienced losses were due to the car objects. In the SPL, the PLE obtained values that indicate 7 dB/decade for the signal drop, which doubled (14 dB/decade) for DPL, as shown in Figure 3. The standard deviation values for both scenarios were approximately identical, which means that the shadowing effect for both scenarios was nearly the same. For the 38 GHz band, it can be shown that the PLE for the DPL was greater than the SPL by 3 dB/decade, as shown in Figure 4. The PLE values were 2.8 and 3.1 for SPL and DPL, respectively. Comparing Figures 3 and 4, it can be shown that the PLEs were approximately identical for 28 GHz and 38 GHz bands for a SPL. However, the losses in the 28 GHz band were greater than the 38 GHz for the DPL by 3 dB/decade. This result indicates that  
some of the paths losses at 28 GHz were added up destructively, which caused the degradation of the power level which appears clearly from the distance range from 40 to 50 m, where the path loss at 28  GHz degraded by 10 dB as compared to the 38 GHz at the same range distance. For the FI path loss model, Figures 5 and 6 show the PL models with respect to the separation distance at 28 GHz and 38 GHz. For 28 GHz, the FI path loss model parameters show that the PLE (\(B\) slope) value was approximately identical to the CI model with 3 dB less for the SPL scenario. Additionally, the value was comparable with that of 1 m separation distance, which was lower than the theoretical one by only 4.3 dB. The FI slope values at 38 GHz and 28 GHz for DPL were low as compared to the CI model at 28 GHz and 38 GHz. The reason for this observation is because of small difference between the reference value at 30 m and the maximum FI PL value at 50 m. This implies that the slope of the PL was low, whereas, in the CI model (the reference value is at 1 m), the slope  
Figure 4: CI path loss model at 38 GHz. Figure 3: Close-in (CI) free space reference distance path loss model at 28 GHz. along the PL was large with respect to 50 m PL value. It can be concluded that the FI model showed a tight reflection frequency dependency at 28 GHz and 38 GHz as shown in Figures 5 and 6, respectively. This effect can be described as a wavelength effect, since, if there is a reduction in wavelength, there will be a proportional increase in the rate of reflection. In conclusion, the FI model can be used as an effective model for DPL, and it is highly recommended at the 38 GHz frequency band. Figures 7 and 8 show the proposed PLM path loss model at 28 GHz and 38 GHz for the SPL and DPL scenarios. It can be shown that for the parking lot factor \(k_{f}\) values of 28 GHz were 10.6 dB and 23.1 dB for SPL and DPL, respectively, as depicted in Figure 7. This indicates that the power decay for the DPL was twice that of the SPL at 28 GHz band. Figure 8 shows that the parking lot factor values of 38 GHz are 13.1 dB and 19.1 dB for SPL and DPL, respectively. At 38 GHz band, the effect of the DPL  
Figure 5: Floating-intercept (FI) path loss model at 28 GHz. Figure 6: FI path loss model at 38 GHz. was less than the effect at 28 GHz, where the power decay is 6 dB over the SPL, as shown in Figure 8. This implies that the reflection was better and there was less shadowing effect at 38 GHz compared to the 28 GHz band. The standard deviation values show that the effect at 38 GHz bands was half that of the standard deviation values at 28 GHz band.