# An Admission-Control-Based Dynamic Query Tree Protocol for Fast Moving RFID Tag Identification
## 6 Simulation Results
### Single Round Identification
#### 6.1.2 Number of Transmitted Message Bits  
In the comparable algorithms, the frame structure and messages transmitted in each slot are different. Only the number of collisions and idle slots are not enough to evaluate the overall performance of these algorithms. The communication overhead of the RFID tag identification protocol refers to the number of message bits sent and received by the reader and tags during the identification process. The reader side overhead refers to the total number of message bits sent by the reader, and the tag side overhead refers to the total number of message bits in tag replies to the reader. In the simulation, a tag uses a 96-bit ID, and the reader needs to send two necessary commands during the identification process, i.e., the Query and Qrep commands. Since the identification time highly depends on the number of transmitted message bits, we give the comparison results of these algorithms in Figure 9.  
The average number of command bits transmitted by the reader for one tag identification (i.e., communication overhead on the reader side) is shown in Figure 9a. It can be observed that ACDQT and MCT transmit smaller numbers of command bits on the reader side, and the communication overheads are stable at around 42 and 45 bits, respectively. This is because ACDQT and MCT both use a multi-branch tree structure. Compared with 180 bits of CwT and 68 bits of DPPS, communication overhead of ACDQT on the reader side is reduced by about 75% and 33.8%, respectively. This is because the proposed ACDQT protocol uses the number of consecutive collision bits to divide colliding tags into different groups in a new frame. In each frame, only one _Query_ command and several _Qrep_ commands are sent. This greatly saves the amount of command bits needed to send. Although the DPPS algorithm uses a _Query_ command in each frame with two consecutive slots, the amount of command bits transmitted in each frame is small, but DPPS requires more frames to identify tags than ACDQT does. Thus, communication overhead on the reader side of DPPS is higher than that of ACDQT. In CwT, each slot comes with a _Query_  
Figure 9: Average number of message bits needed for one tag identification: (**a**) on the the reader side; (**b**) on the tag side.  
command. With more slots, CwT transmits more command bits on the reader side than comparable algorithms.  
Figure 9b illustrates the average number of message bits transmitted by the tag for one tag identification (i.e., communication overhead at each tag). As shown, a tag transmits fewer message bits in ACDQT and CwT than in the MCT and DPPS algorithms. This is because ACDQT takes the least number of collision slots. Thus, the response time for each tag is reduced accordingly. Secondly, a tag only needs to reply part of the ID information in each slot, which greatly reduces the number of message bits transmitted. Therefore, the communication overhead of each tag by implementing ACDQT is much lower than comparable algorithms. In CwT, a tag replies short messages in each slot. Therefore, although CwT takes more slots, the number of message bits transmitted by each tag is small.