tailieunhanh - Current Trends and Challenges in RFID Part 11

Tham khảo tài liệu 'current trends and challenges in rfid part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 290 Current Trends and Challenges in RFID EDFSA Enhanced Dynamic Framed Slotted ALOHA This algorithm estimates the number of unread tags instead of number of tags to determine the frame size. H. Vogt s algorithm shows poor performance when the number of tags becomes large because the variance of the tag number estimation is increased according to the number of tags increase Rom90 . Therefore to handle the poor performance of large number of tag identification EDFSA algorithm restricts the number of responding tags as much as the frame size. Conversely if the number of tags is too small as compared with the frame size it reduces the frame size. To estimate the number of unread tags equation 2 is used. The procedure of EDFSA algorithm s read cycle is shown in Figure 12. Fig. 12. Read Cycle of EDFSA Algorithm Evaluating delays To evaluate the implementation of the BFSA protocol I first evaluated the total census delay of the tag reading process. It is comprised of three different delays success delay collision delay and idle delay. Thus the total census delay is defined as T n n C n I n 6 where n is success delay C n is collision delay and I n is idle delay Cappelletti06 . The unit of delay can be defined as a slot duration T sec and it is defined as T ID bits 7 data_rate bps where ID bits is the size of the packet containing tag s ID and data_rate bps is the data rate from tag to reader. 291 RFID Model for Simulating Framed Slotted ALOHA Based Anti-Collision Protocol for Muti-Tag Identification BFSA-non-muting It is necessary that evaluating of the read cycles satisfying the confidence level a since it is used to determine total census delay. The assurance level a is the probability of identifying all tags in the reader s interrogation range Vogt02 . if a which means one or more missing tags less than 1 of all are allowed. The probability of r tags responding in a slot in the ith read cycle is given by Bin05 8 where N is the given frame size .