# An Admission-Control-Based Dynamic Query Tree Protocol for Fast Moving RFID Tag Identification
## 6 Simulation Results
### Fast-Moving Tag Identification  
To evaluate tag recognition performance in a conveyor belt system, we measured from two metrics: throughput and tag lost ratio. Throughput refers to the number of tags recognized per unit of time, and the tag lost ratio is the ratio of tags that are not recognized (lost tags) after they move out of the reader's reading range to the total number of tags passing through. The moving speed of the incoming tag flow of the system (termed tag flow rate) ranges from 0 to 800 tags/s, and the distances between tags are evenly distributed. The performance of ACDQT is compared with the three most related works dealing with moving tag situations, i.e., DCT [29], BFSA [26] and EBD [15]. Simulation results are illustrated in Figure 11.  
Figure 10: Time performance: (**a**) average time for one tag identification; (**b**) time efficiency.  
As can be observed from Figure 11a, the proposed ACDQT algorithm achieves much higher throughput than comparable algorithms, and the highest throughput is about 510 tags/s. Compared with EBD, BFSA and DCT, the throughput is improved by 20%, 85% and 140%, respectively. When tag flow rate is greater than 510, the throughput of ACDQT basically tends to be stable. However, when tag flow rate of BFSA is greater than 160, the fluctuation of throughput is relatively large, and it changes around 150. Since DCT directly repeats the identification process for fast-moving tags, it is limited by the performance of the tree splitting process. When new tags enter the reader's reading range, they join the identification process immediately, which may collide with other participating tags. This greatly lowers the throughput in mobile systems. In EBD, newly arrived tags will participate in the identification process in the next round which relieves the collision situation. It also uses a new bit tracking strategy to accelerate the identification process in each round. Thus, its throughput is higher than DCT and BFSA but lower than ACDQT.  
In Figure 11b, the tag lost ratio of ACDQT is 0 when tag flow moves slower than 470 tags/s, while in DCT, BFSA and EBD, the values are 120, 170 and 290, respectively. After these points, the tag lost ratio increases with the tag flow rate. This is because with the tag flow rate increasing, the reader does not have enough time to identify all tags in the current round before they move out of reading range. In this situation, some tags may leave unrecognized after they move out of the reader's reading range, resulting in a lost tag. With larger tag flow rate, the lost tag situation becomes worse. Nevertheless, the proposed ACDQT has much higher throughput and a lower tag lost ratio than comparable algorithms, which is more suitable to be implemented in fast-moving RFID systems. Finally, Table 7 lists the overall results of the comparable algorithms in single round and fast-moving situations. Note that the bold values refer to the best performance in each group, and the results are in accordance with these in Figures 8-10.  
Figure 11: Identification performance for fast-moving tags: (**a**) throughput; (**b**) tag lost ratio.