To split
a set of con?¬‚icting tags into two subsets, the reader uses two queries 1 bit longer than the
collision query. By expanding the collision queries, the reader can recognize all tags.
Consider the situation that a reader attempts to recognize three tags whose IDs are 0101,
0110, and 1001, respectively. CQ of the reader has no bit string because the reader resets. In
this case, tag identi?¬?cation of AQS is equal to that of the query tree protocol. Figure 8.3a
shows signals transmitted by the reader and tags for tag identi?¬?cation, and Figure 8.3b is
the tree expression of tag identi?¬?cation. Recognizing three tags causes two collisions, and
at the end of the frame, CQ stores 1, 00, 010, and 011. Thereafter, tag 1101 comes into the
reader??™s reading range, and now the reader attempts to recognize four tags. As shown in
Reader??™s
transmission
Tag
(0101)
Tag
(0110)
Tag
(1001)
Reader??™s
reception
Collision No response
0 1
Tag 1001 Idle
Readable
Collision
(b)
01 00
010 011
Tag 0110 Tag 0101
(a)
Collision
Time
0110 0101 1001
1001
0110 0110 0110
0 1 00 01 010 011
0101 0101 0101
FIGURE 8.3
Tag identi?¬?cation in AQS after the reader resets. (a) Communication between the reader and tags. (b) Tree of tag
identi?¬?cation.
146 RFID Handbook: Applications, Technology, Security, and Privacy
Figure 8.4a and b, the reader recognizes four tags with only one collision.
Pages:
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297