# A Real-Time BLE/PDR Integrated System by Using an Improved Robust Filter for Indoor Position
## 4 Experiments and Analysis  
### BLE Fingerprint Position Experiments and Error Analysis  
The experiments were set up on the second floor of the C7 test site which has three floors in the 54 th Research Institute of China Electronics Technology Group Corporation as shown in Figure 8. The second-floor test site is 24.92 m long and 27.49 m wide which consists of a rectangular corridor and several rooms. The center part of Figure 8 is a hollow space enclosed with glass. When the radio signal of BLE propagates, there is a severe multipath effect. There are 54 Bluetooth beacons installed on the whole C7 test site and 18 on each floor. The deployment of the Bluetooth beacon in Figure 8 is based on the principle of optimizing beacon placement by maximizing localization accuracy and satisfying a predefined coverage degree [23]. The HUAWEI P20 smartphone was chosen as the test device. In Figure 8, the blue triangle refers to the Bluetooth low energy beacon and there are 18 BLE beacons were installed on the second-floor test site. For the BLE fingerprint position method, all of the BLE beacons installed on the C7 test site were utilized to collect signals for the experiment. Another scenario called 331 test site had been chosen to conduct a comparison experiment. The test site is 21.72 m long and 7.75 m wide. The deployment of the Bluetooth beacon in the 331 test site is upon the same optimization solution as C7. Then we carried out a BLE fingerprint positioning experiment in this position scenario. The BLE fingerprint database was constructed in advance. People stranded with the HUAWEI P20 at each known RP to collect data for 7 s, the time is set randomly. Then the data was processed per second into real-time fingerprint data. In the actual acquisition process, only 6 s of data were collected at some RPs. There were real-time 332 BLE fingerprint data collected at 48 RPs for fingerprint position. We calculated the positioning results through the KNN matching method and compared them with the true coordinates of RPs to obtain the position error. We analyzed the gross error of the BLE fingerprint method, whose error is larger than twice the standard deviation under the Gaussian distribution. Then we picked out the gross error caused by the few numbers of scanning RSSI which is less than 5 and we eliminate the corresponding fingerprint. Finally, we recalculate the position error, and both position errors were obtained and they were illustrated in Table 1 and Figure 9.  
Figure 7: The BLE/PDR integrated system localization framework. Figure 8: The two location scenarios. (**a**) The location scenario of the second floor of the C7 test site. (**b**) The location scenario of the 331 test site. As shown in Table 1, after eliminating the few numbers of scanning RSSI real-time fingerprints, the mean position accuracy and the root-mean-square error (RMSE) were 2.312 m and 2.043 m, respectively. Compared with all data on the BLE fingerprint method, the position accuracy was reduced by 0.5220 m and RMSE decreased by 1.064 m. In Figure 8, the blue line refers to the result of all real-time fingerprint data and the green line refers to eliminating the few numbers of scanning RSSI real-time fingerprints. The red dashed line represents twice the standard deviation which means the position error that exceeds the red dashed line is a gross error. From Figure 9a, the gross error number shown in the green line is greatly reduced compared with the blue line. Figure 9b indicates that the method of eliminating the few numbers of scanning RSSI has a higher confidence level than the BLE fingerprint method. From the statistics of gross errors, the total number of gross errors is 31. Among them, the number of gross errors caused by the few numbers of scanning RSSI is 10.0  
scanning RSSI is 17, accounting for about 54.8%. Therefore, we can conclude that the causes of gross errors in the BLE fingerprint method are not only caused by signal fluctuations, but also affected by the few numbers of scanning RSSI.