532 Mobile Netw Appl (2014)19:524-533 2500 9 ARCP PRCP 8 2000 BRCR CRCP ECRC 500 5 1000 4 3 500 50 100150200250300 ARCP PRCP BRCP CRCPECRCP Number of rules Protocols Fig.9 Number of verified category IDs under different number of rules Fig.11 Average Number of verified category IDs used to check a rule collision slots to get more category IDs.Besides,Fig.11 properly adjust the length of the Bloom filter and the num- shows that ECRCP only needs about 1.7 verified related ber of hash functions used in the Bloom filter to meet the categories to check a rule on average,which is only 21 of requirement. that needed in RRCP,BRCP,CRCP.This is because RCRCP verifies the most popular categories,which affect more rules'Boolean values.ECRP only verifies part of the related 9 Discussion categories,which is consistent with Fig.9.Therefore,it achieves the best performance. Bit-level collision detection is important to CRCP and ECRCP.While considering the realistic environments, 8.5 Accuracy of checking all the rules detecting a collision bit can be affected by the capture effect. channel error,etc. Figure 12 illustrates the accuracies of checking all the rules. Capture Effect:When tagl sends bit'0'and tag2 sends The accuracies of ARCP and PRCP are higher than those bit'1'simultaneously,the expected mixed result is a of BRCP,CRCP and ECRCP.Because BRCP,CRCP and collision bit x.However,if the signal strength of tagl is ECRCP use the Bloom filter,which has the probability of much more strong than that of tag2,the reader is likely false positive.It can result in decoding the category IDs to get bit'0',capture effect occurs.At this time,CRCP wrongly,leading to wrong result of the correlated rule. and ECRCP may consider that tag2 is missing,leading However,the accuracy of 96%can be achieved by CRCP to an error. and ECRCP,which is high enough in many applications. Aiming to relieve capture effect,we can check the Furthermore,the accuracy of 98 can be achieved by rules in a mobile way to change the distance between ECRCP.When the number of rules is 300,the accuracy of the tags and the antenna,which affects the tag's signal ECRCP is 99.5 %If a higher accuracy is needed,we can strength.If a tag can be detected at least one time,then the reader considers that it exists.Moreover,in our pro- posed protocols CRCP and ECRCP,there may be more 5 4.5 PRCP 10 4553 2 1 0.5 ARCP PRCP BRCP CRCPECRCP 50 100 150 200 250 300 Protocols Number of rules Fig.10 Average Number of category IDs verified in a response slot Fig.12 Accuracy under different number of rules ②SpringerFig. 9 Number of verified category IDs under different number of rules collision slots to get more category IDs. Besides, Fig. 11 shows that ECRCP only needs about 1.7 verified related categories to check a rule on average, which is only 21 % of that needed in RRCP, BRCP, CRCP. This is because RCRCP verifies the most popular categories, which affect more rules’ Boolean values. ECRP only verifies part of the related categories, which is consistent with Fig. 9. Therefore, it achieves the best performance. 8.5 Accuracy of checking all the rules Figure 12 illustrates the accuracies of checking all the rules. The accuracies of ARCP and PRCP are higher than those of BRCP, CRCP and ECRCP. Because BRCP, CRCP and ECRCP use the Bloom filter, which has the probability of false positive. It can result in decoding the category IDs wrongly, leading to wrong result of the correlated rule. However, the accuracy of 96 % can be achieved by CRCP and ECRCP, which is high enough in many applications. Furthermore, the accuracy of 98 % can be achieved by ECRCP. When the number of rules is 300, the accuracy of ECRCP is 99.5 %. If a higher accuracy is needed, we can Fig. 10 Average Number of category IDs verified in a response slot Fig. 11 Average Number of verified category IDs used to check a rule properly adjust the length of the Bloom filter and the num￾ber of hash functions used in the Bloom filter to meet the requirement. 9 Discussion Bit-level collision detection is important to CRCP and ECRCP. While considering the realistic environments, detecting a collision bit can be affected by the capture effect, channel error, etc. – Capture Effect: When tag1 sends bit ’0’ and tag2 sends bit ’1’ simultaneously, the expected mixed result is a collision bit x. However, if the signal strength of tag1 is much more strong than that of tag2, the reader is likely to get bit ’0’, capture effect occurs. At this time, CRCP and ECRCP may consider that tag2 is missing, leading to an error. Aiming to relieve capture effect, we can check the rules in a mobile way to change the distance between the tags and the antenna, which affects the tag’s signal strength. If a tag can be detected at least one time, then the reader considers that it exists. Moreover, in our pro￾posed protocols CRCP and ECRCP, there may be more Fig. 12 Accuracy under different number of rules 532 Mobile Netw Appl (2014) 19:524–533