The reader
164 RFID Handbook: Applications, Technology, Security, and Privacy
pushes query ??????00??™??™ and queries ??????01??™??™ into the queue. At the next reading slot, the reader
transmits query ??????1??™??™ to tags and two tags (110 and 111) reply. Both queries ??????10??™??™ and ??????11??™??™
are pushed into the queue. A tag with its ID ??????001??™??™ is identi?¬?ed successfully at the next
reading slot. At this point, the queue has three queries (01, 10, and 11). The reader transmits
query ??????01??™??™ in the next reading slot. Two tags (010 and 011) which start with ??????01??™??™ reply and
a collision occurs. The reader pushes query ??????010??™??™ and query ??????011??™??™ into the queue. In this
way, tag identi?¬?cation process is continued until the queue is empty. There are ?¬?ve
collided slots, one idle slot, and ?¬?ve readable slots under the query tree protocol.
9.3.2 Binary Tree
The binary tree protocol uses the pseudo-random number generator to divide tags into two
groups. The counter variable in each tag is used for identifying each group. At the
beginning of identi?¬?cation operation, the reader sends a message which noti?¬?es the start
of its cycle to tags. All tags receiving this message generate random numbers of 0 or 1. Tags
set their counter values by adding the generated random number to their counter values.
Pages:
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327