# RFID Authentication System Based on User Biometric Information +
## 4 System Design
### Experiment and Evaluation  
In this section, we first implement RF-Ubia, and then verify its performance through extensive experiments. The RF-Ubia consists of a commercial reader, a directional antenna and several passive tags. The RFID reader we use is Impinj R420 commercial reader, the antenna model is Laird S9028 PCR, and the tag model is Alien-9629. The software of RF-Ubia ran on a computer with an Intel(R) Core(TM) i5-3230M processor (2.60 GHz) and 12 GB RAM. Experimental setupsWe carry out the experiment in a conference room. As shown in Figure 6, the tag array formed by 9 Alien-9629 tags is fixed on the top of the box, and the antenna connected to the reader is placed at the bottom of the box to read the tag data. Finally, the data are processed by the computer. Parameter SettingIn the data preprocessing stage, we take the first 10 phases of the tag as the signal data when it is stable, and set the size of the sliding window to 6, that is,  
Figure 6: Experimental environment for testing RF-Ubia system. there are six phases in the window. The sliding window size used in the anomaly detection algorithm is set to 0.5, indicating that the window contains 0.5 s of tag data. The settings for the remaining parameters in the preprocessing and exception detection algorithms are shown in Table 1.  
_Metric._ We use three major indicators to describe the performance of RF-Ubia, namely True Positive Rate (TPR), False Positive Rate (FPR) and Accuracy. TPR [4], as shown in Equation (8), is used to measure the accuracy of a single password identification performance. FPR, as shown in Equation (9), is used to measure the ratio of illegal users that pass the validation of RF-Ubia to all illegal users. Accuracy refers to the combination of the validation results, including the first stage and second stage of RF-Ubia. \[TPR=\frac{ture\ positives}{ture\ positives+false\ negatives} \tag{8}\]  
\[FPR=\frac{false\ positives}{false\ positives+ture\ negatives} \tag{9}\]  
First, we evaluate the performance of the system for password identification (i.e., identifying the tags touched by the user). We collected 360 sets of data for evaluation. The TPR of each password (i.e., tag) from 1 to 9 is shown in Figure 7. The average accuracy of the system in identifying passwords exceeds 96.9%, indicating that RF-Ubia can effectively distinguish the tags touched by the user and enable the function of entering passwords. We verify the validity of RF-Ubia when multiple users use the same password. As shown in Figure 8, the FPR of the RF-Ubia does not exceed 0.04 when the password length is 2, indicating that RF-Ubia can effectively distinguish different users. In addition, we also evaluate the accuracy of RF-Ubia in identifying users with the same password when the password is longer. When the password length is 3, the identification accuracy of users with the same password is 98.75%. When the password length is 4, the accuracy reaches 100%. The longer the password is, the more user features can be utilized and therefore the higher the accuracy of user identification is. Considering password identification and user differentiation, the average accuracy of RF-Ubia system exceeds 92.8%. \begin{table}
\begin{tabular}{l c} \hline \hline
**Parameter Name** & **Parameter Values** \\ \hline \(\mathit{thres}_{1}\) & \(\pi-1\) \\ \(\mathit{thres}_{2}\) & \(\pi+1\) \\ \(\mathit{thres}_{3}\) & 1.5 \\ \(\mathit{thres}_{4}\) & 2 \\ m & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Algorithm parameter setting. Figure 7: The TPR of RF-Ubia’s password identification. DiscussionIn this section, we propose a solution that uses a fusion of user information and biometric information for user authentication, which achieves a high user identification accuracy rate even when using only a simple password. However, it has some drawbacks--we still need to use passwords, which is not friendly to people who usually forget their passwords, such as elderly people with poor memory and those who do not use the authentication system regularly.