# Path Loss Measurements of Indoor LTE System for the Internet of Things
## 4 Evaluation Results  
Figure 6 illustrates the modified path loss model obtained from the field trial in the laboratory, where the solid curve is the ITU-R indoor office path loss model; the circle dotted and solid curves are the average LOS path loss measurement and the modified LOS path loss model, respectively; and the square dotted and solid curves are the average NLOS path loss measurement and the modified NLOS path loss model, respectively. The modified LOS and NLOS path loss models are generated by using the linear least square method, fitting the solid curve to the scattered path loss measurements.  
Figure 4: The LOS test scenario while the Tx-Rx distance is 4 m.  
Figure 5: 16 Quadrature Amplitude Modulation (QAM) constellation at the receiver.  
Figure 3: The LOS test scenario while the Tx-Rx distance is 1 m.  
As shown in Figure 7a,b, the probability density functions (PDFs) of the receive power are verified to be lognormal distributed for both LOS testing and NLOS testing at a distance of 6 m. The mean and standard deviation for LOS testing are \(-62.88\) dBm and 0.557 dBm, respectively; the mean and standard deviation for NLOS testing are \(-72.84\) dBm and 2.1534 dBm, respectively. The standard deviations of the shadow fading at a distance of 0-15 m for the LOS and NLOS are listed in Tables 2 and 3, respectively, which are obtained from the measured PDF.  
Based on the measurement results, the formula of the LOS path loss model is given as:  
\[PL(d)=20\log_{10}(f)+19.5\log_{10}(d)-36, \tag{8}\]  
where the average standard deviation of the received shadow fading signal and the path loss exponent are 0.93 dB and 1.95, respectively. Then, using the average standard deviation and path loss exponent, the FM for 90% SR [15] is calculated to be about 0 dB.  
Now, consider the NLOS results in Figure 6. The square dotted and solid curves represent the NLOS average path loss measurement and the modified NLOS path loss model, respectively. Based on the measurement results, the formula of the ITU path loss model represented in Equation (1) is modified as:  
\[PL(d)=20\log_{10}(f)+28\log_{10}(d)-36, \tag{9}\]  
where the average standard deviation of the received shadow fading signal and the path loss exponent are 2.748 dB and 2.8, respectively. In comparison with Reference [15], it is noted that the path loss  
Figure 6: Path loss versus distance for the LOS and NLOS scenarios.  
Figure 7: Probability density function (PDF) of Rx power for (**a**) LOS and (**b**) NLOS scenarios at a distance of 6 m.  
parameters of the measured path loss model are not the same as the ITU path loss model. Finally, using the average standard deviation and path loss exponent, the FM for 90% SR is calculated as 0.728 dB. Based on the previous results, the coverage range could be calculated by using the coverage range model described in Section 2.2. The parameter represented in Equation (3) is modified as:  
\[A^{\prime}=P_{t}-L_{t}+G_{t}+G_{r}-\left[20\log_{10}(f)-36\right]-L_{r}. \tag{10}\]  
Figure 7 shows the probability density function (PDF) of Rx power for (a) LOS and (b) NLOS scenarios at a distance of 6 m. This figure validates the lognormality of the shadowing fading samples in our experiments.  
Figure 8 shows the coverage range of the eNB deployed in the laboratory. It is shown that the coverage range increases with the transmit power. Under the same transmit power, the coverage range of the NLOS testing is smaller than the LOS testing. At a coverage range of 10 m, the required transmit power of eNB for LOS testing, NLOS testing and ITU model are \(-19\) dBm, \(-10\) dBm and \(-1\) dBm, respectively.