基于时隙ALOHA的标签识别机制-5 Tag inventory and access Upon receiving RN16,the reader will echo RN16 in an ACK command If the tag successfully receives RN16,it will backscatter its ID information(PC+EPC+CRC16).Then a subsequent QueryRep command will be sent to the tag,signaling the end of the slot and toggling an inventoried flag in the tag to make it keep silent in the following rounds. Interrogator cw Select CW Query Cw Ack Cw QueryRep NAK Cw Tag PC+EPC +CRC16 Interrogator cw Query Cw QueryRep Cw QueryRep Cw QueryRep Cw INo Reply Collision Detected Single Reply Tag N16 RN16 Fig.2.C1G2 protocol
基于时隙ALOHA的标签识别机制-5 • Tag inventory and access – Upon receiving RN16, the reader will echo RN16 in an ACK command. If the tag successfully receives RN16, it will backscatter its ID information (PC+EPC+CRC16). Then a subsequent QueryRep command will be sent to the tag, signaling the end of the slot and toggling an inventoried flag in the tag to make it keep silent in the following rounds
基于时隙ALOHA的标签识别机制-6 Tag inventory and access If the ID is not successfully received by the reader,an NAK command is sent which resets the tag so as to keep the tag active in the next round Upon receiving the QueryRep command,the remaining tags will decrement their slot counters,and respond with RN16 if their slot counters are set to 0.When the number of QueryReps is equal to 2, the current QueryRound ends Interrogator cw Select Cw Query CW Ack Cw QueryRep NAK Tag RN16 PC+EPC +CRC16 Interrogator Query cw QueryRep CW QueryRep Cw QueryRep INo ReplyI Collision Detected I single Reply Tag RN16 RN16 Fig.2.C1G2 protocol
基于时隙ALOHA的标签识别机制-6 • Tag inventory and access – If the ID is not successfully received by the reader, an NAK command is sent which resets the tag so as to keep the tag active in the next round. – Upon receiving the QueryRep command, the remaining tags will decrement their slot counters, and respond with RN16 if their slot counters are set to 0. When the number of QueryReps is equal to 2" , the current QueryRound ends
Query f=3 Query Round 1 RN16 RN16 RN16 Slot.=0 Frame size f=3 Tag 1 PC+EPC+CR C16 RN16 QueryRep Tag 2 RN16 RFID Reader RN16 RN16 DA1C Slo8kdt =0 Tag3 RN16 QueryRep
RFID Reader Tag 1 Tag 2 Tag 3 Query f=3 QueryRep RN16 RN16 RN16 RN16 RN16 RN16 RN16 Frame size f=3 PC+EPC+CR C16 RN16 RN16 QueryRep Slot =0 Slot =1 Slot=1 Slot =0 Slot =0
Query f=2 Query Round 2 RN16 Frame size f=2 Keep Tag1 RN16 PC+EPC+CR RN16 C16 Tag 2 QueryRep RFID Reader RN16 RN16 RN16 Slot=0 Tag 3 PC+EPC+CR C16
Query f=2 RN16 QueryRep RN16 RFID Reader Tag 1 Tag 2 Tag 3 RN16 RN16 Frame size f=2 RN16 PC+EPC+CR C16 RN16 PC+EPC+CR C16 Slot =1 Slot =0 Keep silent Slot =0
基于时隙ALOHA的标签识别机制-7 Efficiency Problem: How to select an optimized frame size ffor each query round such that the overall scanning time can be minimized? overall scanning time Minimized! Query Query Query f=? 000000 Rep Rep
基于时隙ALOHA的标签识别机制-7 • Efficiency Problem: – How to select an optimized frame size f for each query round such that the overall scanning time can be minimized? Query �=? Query Rep Query Rep …… overall scanning time Minimized!