# Reader-Tag Commands via Modulation Cutoff Intervals in RFID Systems +
## 5 Performance Evaluation  
### Anti-Collision Protocols  
In this section, the MCI process is applied to two main anti-collision protocols, probabilistic (ALOHA-based) and deterministic (tree-based) protocols. The MCI process effect on the performance of these protocols is evaluated for 40 sets of tag populations, starting from 100 tags up to 4000 tags (with an increment of 100 tags). In our evaluation, all the timing values are based on EPC standardized specifications (reader symbol duration of 25 \(\upmu\)s, PIE encoding, and divide ratio of 8) [16]. Note that there will be a specific number of collision, empty, and single slots by the end of any identification process. Ideally, all slots will be single slots; however, this scenario is not possible due to a lack of communication between the tags. Therefore, all identification protocols aim at minimizing the number of non-valuable slots (collision and empty slots) to reduce the identification time and reader power consumption. In addition, the MCI process further reduces the effect of these non-valuable slots by ending them early. In probabilistic protocols, the number of collision slots depends on the total slots (frame size) that the tag competes to transmit their IDs within. If the frame is larger than the tag population, empty slots and single slots will be dominant. Similarly, frames that are smaller than the tag population will be dominated by collision and single slots. In the standardized identification protocols, the Q-Algorithm is used to maintain an equal proportion of collision, single, and empty slots by adaptively changing the frame size [17; 18], as shown in Figure 10. For example, if 2000 tags are identified, around 6000 slots will be used by the end of the identification process, of which collision, single, and empty slots are roughly 2000 each. In other words, two-thirds of the identification process is wasted on empty and collision slots, where the MCI process effect is accentuated. In deterministic (tree-based) protocols, the total number of collision and empty slots depends on the tag population's pre-knowledge [14; 19]. Therefore, the ratio of collision and empty slots to the total slots consumed in the identification process will be smaller if the tag population is known when compared to an unknown tag population. In such deterministic protocols, the advanced knowledge of the tag population allows for query optimization while traversing the tree of tag IDs. This optimization aims at reaching single slots (the leaves in the tree) while skipping the tree's internal nodes (which cause collision and empty slots). The total number of collision slots in the tree-based protocols for different tag populations is plotted in Figure 10.  
Figure 9: MCI process in anti-collision protocols with PIE encoding to accommodate MCI commands and other commands that are sent explicitly not through the MCI. The performance of the identification protocols is evaluated based on the average identification time for different tag populations with and without the MCI process. Figures 11 and 12 show average identification time after simulating probabilistic and deterministic (with known and unknown tag population) protocols under EPC-standardized timing [16]. In Figure 11, the average identification time for the Q-algorithm is shown with a speedup of 35.9% with the MCI process. Consequently, since the reader is transmitting CW and data during the identification process [9; 14; 15], 35.9% of the power consumption is saved by the MCI process. In Figure 12, the average identification times for different tag populations in the deterministic tree-based protocol for unknown tag populations are shown. The reported results are the simulation of this protocol with and without the MCI process based on standardized timing [16]. The speedup of the MCI process is 50.1% compared to the none  
Figure 11: Average identification time for different tag population in the standardized Q-Algorithm.