An Enhanced Posterior Probability Anti-Collision Algorithm Based on Dynamic Frame Slotted ALOHA for EPCglobal Class1 Gen2

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1 Joural of Commucatos Vol. 9,. 0, October 204 A Ehaced Posteror Probablty At-Collso Algorthm Based o Dyamc Frame Slotted ALOHA for EPCglobal Class Ge2 Lta Dua,Wewe Pag 2, ad Fu Dua 2 College of Iformato Egeerg, Tayua Uversty of Techology, Tayua , Cha 2 College of Computer Scece ad Techology, Tayua Uversty of Techology, Tayua , Cha Emal: dlt @26.com; pagwewe2008@26.com; duafu@tyut.edu.c Abstract I a Rado Frequecy Idetfcato (RFID) System, collso betwee tags s oe of the core problems that we must cosder about. I geeral, a collso wll occur whe more tha oe tag commucates wth the reader smultaeously, reducg the system effcecy. To solve ths, dyamc frame slotted ALOHA (DFSA) s wdely adopted owadays, ad as a varat of DFSA algorthm, Q-algorthm s accepted by the EPCglobal specfcatos for RFID ar terface Class Ge2 protocol. Based o ths, we provde a ew algorthm called EPP-Q to adjust the parameter Q more accurate as well as mata hgh system effcecy whe tags are o more tha 2 Q - (Q belogs to 0 to 5). The smulato provdes a obvous mprovemet whe EPP-Q s compared wth other two mastream algorthms, ot oly system effcecy, but also the quatty of tme slots used. Idex Terms Tag at-collso, RFID, Posteror probablty, EPCglobal Class Ge2 I. ITRODUCTIO RFID techology wth ultra-hgh frequecy (UHF) passve tags s a powerful tool for automatc object detfcato, whch eables the seamless ad automatc coecto betwee real-world objects ad ther vrtual represetatos prevously eabled by maual data etry. I recet years, sce tags are much cheaper tha before, the applcatos of RFID techology has become a vable alteratve for detfyg object automatcally ad wdely deployed vetory cotrol, dstrbuto dustry, ad supply cha maagemet ad so o. So far, RFID techology has bee establshed a lot of domas. For stace, GS Italy ad GS Hog Kog have completed a project by usg EPC Ge2 RFID tags ad readers to track shpmets of we from Europe to Asa. However, before RFID techology becomes ubqutous the ear future, there are also some problems eed to deal wth. auscrpt receved Jue 27, 204; revsed October 20, 204. Ths work was supported by the Key Scetfc ad Techologcal Projects of Shax Provce ( ad ). Correspodg author emal: duafu@tyut.edu.c. do:0.2720/jcm I RFID systems, f oly oe tag exsts reader s detfcato zoe, tag ca be detfed easly. However, f two or more tags exst zoe ad respod to reader smultaeously, o tags ca be detfed ad ths pheomeo s called tag collso. To settle ths problem, at-collso algorthm s very ecessary. Curretly, RFID at-collso algorthms ca be categorzed to two groups: tree-based ad ALOHAbased oes []. Tree based algorthms [2]-[5], such as bary tree protocol (BT) ad query tree protocols (QT), repeatedly separate collded tags to two subsets utl each set has oly oe tag or o tag. The performace of these algorthms s stable, but IDs should ot be log. Otherwse, t wll cost too much tme to detfy all tags. I ALOHA algorthms [6]-[8], tags respod to reader by trasmttg IDs a probablstc maer. All tags wll radomly pck a umber, ad f there s o more tha 2 tags selectg the same umber, ths tag wll be detfed, otherwse othg happes [9], [0]. The effcecy of ALOHA algorthm s low wth hgh traffc load. Such as pure aloha (PA), slotted aloha (SA), basc frame slotted aloha (BFSA), dyamc frame slotted aloha (DFSA). Amog these, DFSA algorthm wll lead to a hgher effcecy ad a better stablty because the reader regulates the frame sze accordg to the umber of tags. EPCglobal adopts the at-collso algorthm called Q- algorthm [], whch s also a varat of DFSA algorthm. However, Q value Q-algorthm has to be adjusted frequetly the evet of more tha oe tag choose the same radom umber. I order to decrease the frequecy of Q adjustmet, we proposed a ehaced posteror probablty algorthm based o the Q-algorthm. I our algorthm, after makg a assessmet of the system s curret state, we use a posteror probablty ad take the past kowledge to cosderato to estmate the tags quatty slot by slot ad acheve -frame Q adjustmet. The corporato of the past kowledge to the estmato wll mprove the accuracy, ad the -frame adjustmet acheve the -tme adjustmet whe the frame sze s ot approprate, reducg the uecessary tme waste. The -frame adjustmet our algorthm depeds o the accurate estmato results, stead of the 204 Egeerg ad Techology Publshg 798

2 Joural of Commucatos Vol. 9,. 0, October 204 fxed parameter C, whch s more flexble. By smulato, t s testfed that our algorthm mproves the effcecy of the tag detfcato. The rest of our paper s orgazed as follows: Secto II, we descrbe ad aalyze several algorthms based o Q-algorthm. I Secto III, we propose ad descrbe our algorthm. I Secto IV, extesve smulatos are doe to compare those dfferet algorthms. The umber of slots to detfy all tags ad the system effcecy are adopted to measure the commucato performace. Fally, cocluso s draw Secto V. II. BACKGROUD (TAG ATI-COLLISIO ALGORITHS I EPCGLOBAL CLASS GE2) EPC Ge2 passve RFID systems operate o the UHF frequecy wth a effectve detfcato rage of 7 to 0 meters []. I order to esure Q-algorthm could be acheved EPCglobal Class Ge2 protocol, several commads are desged to realze t, cludg Select, Query, QueryAdj, QueryRep ad ACK. A detfcato process may beg wth the Select commad sedg by reader, ad the reader wll select a partcular tag group for recogto. After that, the reader wll sed a Query commad to detfy the selected tags. I ths Query commad, a prmary parameter Q s cotaed, whch s the rage of 0 to 5 ad represets a frame legth of 2 Q. Whe the Query commad s receved, each tag geerates a 6-bt radom umber called R6, ad extracts a Q-bt subset from R6 as the tag s slot couter. Ths couter has to mus oe mmedately that a QueryRep s receved. R6 wll be trasmtted as soo as the couter reaches to zero. Actually, the real ID of a tag s 96-bt EPC (electroc product code), ad the 6-bt R6 could be vewed as tag s temporary ID to shorte the collso terval at the arbtrate state. Qfp=max(0,Qfp-C) Qfp=4.0 Q=roud(Qfp) Query(Q) 0 # of Tag > Resposes Qfp=Qfp+0 Fg.. echasm of Q-algorthm. Qfp=m(5,Qfp+C) Sce tags respod to a reader a backscattered way, Q-algorthm cotas 2 other varables besdes Q, Q fp stads for a floatg-pot Q ad C s a very small costat for the frame legth adjustmet. Fg. shows the basc mechasm of Q-algorthm. Detals are descrbed as follows: By Query commad to tate a ew roud, a slotcout parameter Q s cotaed, meag that the frame sze s =2 Q, cludg 2 Q tme slots. For stace, Q s gve as 4, meag that the frame sze of ths roud s 6 ad cludg 6 tme slots. After recevg the Query or QueryRep(query repeat) or QureyAdj(query adjust) commad, all tags wll select a value the rage [0, -] radomly, ad tags wth value 0 could commucate wth reader, otherwse, tags wth ozero values have to wat the ext roud to re-pck radom umbers. Durg the respose process, there could be 3 stuatos: empty, collso ad success. I Fg., Q fp wll mus C frstly ad the maxmum oe betwee 0 ad Q fp -C wll be chose as a ew Q fp whe empty stuato happes; Dfferet wth the former stuato, Q fp wll be selected the mmum oe of 5 ad Q fp +C the stuato of collso; Ad success stuato, Q fp wll keep the same, reader wll mplemet Select commad to read the data of ths successful tag. After ay of these three, t wll go back to Step.(2) tll all tags are recogzed. te: Query A commad sedg by reader to tate a roud; QueryRep A commad sedg by reader to repeat query wthout chagg; QueryAdj A commad sedg by reader to repeat query wth crease or decrease Q by oe. It s mportat to emphasze empty slots S E, successful slots S S, ad collsoal slots S C, should satsfy the equalty that S E +S S +S C =. Sce Q-algorthm s a varat of DFSA, the dfferece s that the reader wll estmate the umber of uread tags ad adjust the frame sze. I [2], we see the followg algorthms ca be used EPCglobal protocol, ad t s cocluded that the algorthm Che [3] s approprate for populatos over 300 tags ad Vogt [4] s otherwse preferable. Therefore, we compare these two algorthms wth our algorthm the secto 4. (a) Vogt presets two fuctos to estmate tags umber. Oe s based o the collsos tme slots whch volved at least two tags, hece they used S S +2S C to estmate. O the other had, Vogt proposes a dfferet estmato fucto [4], whch uses the dstace betwee the read result set (S E,S C,S S ) ad the expected value to determe the value of for whch the dstace becomes mmal. The the Q parameter s derved accordg to the value of. (b) Che presets a ew estmato fucto [3], whch s the posteror probablty fucto. Ths alteratve estmato fucto utlzes the posteror probablty ρ( S E,S C,S S,) derved from the result set (S E,S C,S S ) to set the tag estmato, whe ρ( S E,S C,S S,) s maxmum. Later, Bueo mgrates the algorthm to EPC protocol [2]. (c) I [5], Schoute aalyzed the procedure of the DFSA algorthm, the clamed the umber of competg tags follows a Posso dstrbuto. Therefore, they oly 204 Egeerg ad Techology Publshg 799

3 Joural of Commucatos Vol. 9,. 0, October 204 S E, S S, SC,, use formato of the latest frame to estmate of the umber of tags by SS+2.39SC. As show [2], the algorthm does t acheve good performace as the above two algorthms, but t s smple ad easly mplemeted. Therefore, we adopted ths approach the case SC= where the posteror probablty approach caot accomplsh estmato. SE SS S E! S S! SC!! III. EHACED POSTERIOR PROBABILITY ALGORITH BASED O Q-ALGORITH (6) SC We use the posteror probablty to determe the value of Q whe the posteror becomes maxmal. Whe ( se, ss, sc,, ) s maxmum, we set. The posteror probablty fucto possesses a maxmum for all possble results except for the case of SE=SS=0. The case of SE=SS=0 meas all slots are collded. Fg. 2 shows the posteror probablty versus umber of tags, usg (6) whe ot all slots are collso just as SE 0 or SS 0. Four dfferet evet set are outle ths fgure, they are: (a) <=28, =80, SE=70, SS=8, SC=2>, (b) <=28, =80, SE=5, SS=6, SC=59>, (c) <=64, =60, SE=0, SS=20, SC=30>, (d) <=64, =40, SE=5, SS=5, SC=30>. Based o the aalyss above, Q value Q-algorthm has to be adjusted frequetly whe more tha oe tag chooses the same radom umber, whch of ths wll brg the egatve fluece for system effcecy ad tme cost. Therefore, to decrease the frequecy of Q adjustmet, we proposed a ehaced posteror probablty algorthm based o Q-algorthm, called EPPQ algorthm. At the begg, let s troduce several key part of our algorthm: the estmato of tag umber, the approach for I-frame Adjustmet, determato for ext roud. The we wll descrbe the geeral procedure, whch s show Fg. 4. A. The Estmato of Tag umber Gve frame sze= ad the umber of competg tags=, the tags are bomally dstrbuted the slots wth parameters ad / [4], therefore the probablty that oe gve slot s occuped by tags s as follow: r -r B r = Cr - () It stads to reaso that the probabltes of empty, success, ad collso for the slot s: E B 0 C E S S B Fg. 2. The posteror probablty for SE 0 or SS 0. (2) (3) (4) As show [2], the approach proposed by Che [3] represets the best performace. Che s approach ca be geeralzed to partly observed slots ( observed slots out of slots) ad dcates the path to take full advatage of the -frame adjustmet of the frame sze eabled by EPCglobal protocol. Wth slots out of frame sze, the probablty, that exactly SE empty slots, SS successful slots, ad SC collsoal slot where SE+SS+SC=, ca be derved wth the parameter as E S C :! SE, SS, SC,, ESE SSS CSC SE! SS! SC! Fg. 3. The posteror probablty for SE=SS=0. From the shape of the fucto, we ca see that a sgle maxmum exsts, a sgle ca be derved whch s most close to the observed result whe the probablty s maxmum. We wll take ths as our estmato of the tag quatty. Whe SE=SS=0, the posteror probablty fucto s a mootoe creasg fucto ad wth the (5) From formulas (2) (3) (4) ad (5), we ca obvous derve the posteror probablty as follow: 204 Egeerg ad Techology Publshg 800

4 Joural of Commucatos Vol. 9,. 0, October 204 value creasg, the probablty s ftely close to. Ths case was outled Fg. 3 for a dfferet evet, whch are: (a) <=8, =8, S C =8>, (b) <=6, =0, S C =0>, (c) <=32, =2, S C =2>, (d) <=64, =40, S C =40>. I ths case, we caot get the estmato value of through the posteror probablty fucto. Therefore we adopted the approach proposed by Schoute [5] settg ñ= S S +2.39S C. B. The Approach for I-frame Adjustmet I [2], the author made a lot of smulatos ad derved the approprate Q set for dfferet value of as show Table I. Let us deote the process by ChooseQ(). After every slot of the a roud, we wll record the result (S E,S S,S C,,), ad use t to evaluate the curret state. The case of S E >S S +S C meas that maybe the curret value of Q s too large. Take to cosderato of the smplcty, we adopt the Schoute approach ad the egato method to verfy the hypothess. O the egatve lmtg assumpto that the remader slots - are all collso. Wth the approach proposed by Schoute [5], a estmato of the tag quatty s E =2.39S E +2.39(-)+S S. If E s less tha the left boudary that the curret value of Q correspods to, t verfes the hypothess the curret value of Q s too large ad adjustmet of Q s eeded. The case of S C >S E +S S meas that maybe the curret value of Q s too small. Smlarly, we adopt the Schoute approach ad the egato method to verfy the hypothess. O the egatve lmtg assumpto that the remader slots - are all empty. A estmato of the tag quatty s C =2.39S C +S S. If C s greater tha the rght boudary that the curret value of Q correspods to, t verfes the hypothess the curret value of Q s too small ad Adjustmet of Q s eeded. TABLE I: APPROPRIATE Q Approprate Q Left Boudary Rght Boudary Rage = < 3 3< 6 6< < 22 22< 44 44< 89 89< 77 77< < 70 70< < < < < < I all cases except for the two cases metoed above, the reader wll acquesce that t s ot ecessary to adjust the value of Q ad sed a QueryRep commad. After estmatg the value of competg tags, reader eeds to choose a approprate value of Q for ths estmato result. Wth the estmated result ñ ad the approprate Q for dfferet the Table I, we ca get Q correspodg to ñ. If Q s equal to the Q cluded the Query commad whch tated a roud, the reader wll sed a QueryRep commad to set up the ext slot; coversely, f Q s dfferet wth the Q cluded the tated Query commad, further estmato s eeded ad the past kowledge would be take to cout. The corporatg of the past kowledge wll acheve some amedmets to the estmato ad lead to accuraces. Wth the observed results ad the posteror probablty approach, a seres of estmated value of ca be derved as ñ (, ),..., ñ (, ). The estmato fucto s as follow: adjust m m (, ) (7) Lkewse, the value of Q adjust ca be obtaed combg the value ñ adjust ad Table. If Q adjust s equal to the Q cluded the Query commad whch tated ths roud, the reader wll sed a QueryRep commad to set up the ext slot; Coversely, the reader wll sed a QueryAdjust commad to adjust the Q value (frame sze) for the uread tags. C. Determato for the Followg Rouds After a roud, the posteror probablty s also used to estmate the umber of tags, as show (8). Take to accout of the past kowledge, the formula s as follow: m m (, ) (8) Therefore, the reader ca work out the umber of uread tags by subtractg the sgly occuped slots. The uread tag quatty s ñ-s S, the the Q ew value for the ext roud s easy to draw Q ew =ChooseQ(ñ-S S ). A ew roud starts utl all tags selected by Select commad are detfed. The algorthm s sketched Fg. 4. ) Italze Q=4.0. 2) Reader seds Query(Q) to actvated tags based o the selected Q value. 3) Tags pck radom values from 0 to 2Q- after Step. 2) ad set varat Step=0. 4) Tags wth the value 0 wll commucate wth reader ad at the meawhle Step adds. 5) After the former steps, f Step=2Q ad S C =0, whch meas all tags have bee recogzed ad o collso occurred, the process could be eded; else f Step=2 Q but collso stll happe, Q should be reassged based o estmated mus S S ad the go back to Step.(2); else Q 204 Egeerg ad Techology Publshg 80

5 Joural of Commucatos Vol. 9,. 0, October 204 mght be usutable, whch meas Q mght be too large or too small, Q wll be decded by. 6) If Q equals to curret Q, reader wll sed QueryRep to actvated tags ad go back to Step 4); else, a further estmato, corporatg the past kowledge s eeded to obta the amedatory Qadjust ad f Qadjust s equal to curret Q, reader wll also sed QueryRep to actvated tags ad go back to Step.(4), but f Qadjust s dfferet from curret Q, reader wll sed QueryAdjust to actvated tags ad go back to Step 3). te: Estmated umber of tags; Estmated umber of tags Step=; adjust Estmated umber of tags by further estmato; SE The expected umber of o tag respose; SS The expected umber of tags recogzed; SC The expected umber of more tha two tags respose; Q Q value decded by ; Qadjust Q value decded by adjust. Fg. 5. The umber of slots eeded versus the umber of tags. Q=4.0 Query(Q) Q=ChooseQ(-SS) Tags pck a radom value Step=0 Estmate the tag quatty Tags wth slots couter of 0 reply Step=Step+ Fg. 6. The system effcecy versus the umber of tags. Fg. 5 shows a comparso of tme slots eeded to detfy all tags three dfferet approaches, that s the approach derved by Vogt [4], the approach proposed by Che [3] ad the approach we proposed ths paper(whch s called EPP-Q). Geerally to say, the umber of slots eeded s postve correlated to the umber of tags. I detals, recogzg more tags wll requre more tme slots total. It s observed that our proposed approach takes the mmal slots to complete ths procedure ad ths drop s more ad more dramatcally sce the umber of tags crease. For example, Vogt s wll eed,350 slots total to recogze 400 tags ad Che s wll requre,450 tme slots the same tag sze; however, t wll oly use less tha,200 tme slots whe detfyg 400 tags by usg the EPP-Q algorthm. I total, fewer tme slots eeded meas less tme cost, ad wth the growth of the umber of competg tags, the advatage of our approach has become creasgly evdet. I [6], Che clamed that the RFID systems wth dyamc frame-slotted algorthm wthout capture effect reach ther theoretcal maxmum 36.% for a EPCglobal UHF Class Ge2 system. Compared wth ths maxmum throughput, the easy-to-mplemet advatage of EPP-Q algorthm comes at the expese of oly % reducto. Fg. 6 shows the system effcecy for detfyg all tags. It s obvously that EPP-Q s closest to the theoretcal maxmum throughput every horzotal axs. What s more, wth the creasg of tags quatty, EPP-Q could stll output satsfactory system effcecy. ore SC=0 Fsh Step=2^Q The curret value Q s too large Estmate the tag quatty The curret value Q s too small Q=ChooseQ() Q=Q Further estmate the tag quatty adjust Qadjust=ChooseQ(adjust) Qadjust=Q QueryRep QueryAdjust(Qadjust) Fg. 4. EPP-Q algorthm s procedure to read tags. IV. SIULATIO RESULTS AD PERFORACE VERIFICATIO We compared the performace of two algorthms (Vegt s ad Che s) wth EPP-Q algorthm the total umber of slots for detfes all gve tags ad the system effcecy. The smulato evromet s matlab 2009 wth wdows 7. I our smulato, the tal value of parameter Q s set to 4.0 as the EPC protocol. 204 Egeerg ad Techology Publshg 802

6 Joural of Commucatos Vol. 9,. 0, October 204 specfcally, there s a bref comparso amog these three algorthms showg Table II ad Table III. By adoptg EPP-Q algorthm, the system effcecy has dfferet degrees of crease o matter comparg wth Vogt s or Che s. TABLE II: SYSTE EFFICIECY COPARISO BETWEE VOGT S AD EPP-Q S umber of Tags Vogt's EPP-Q s Effcecy Icrease % 34.6% 20.% % 34.6% 3.8% % 34.8% 6.0% % 34.7% 7.2% % 34.5% 5.4% % 34.3% 5.9% % 34.5% 6.9% TABLE III: SYSTE EFFICIECY COPARISO BETWEE CHE S AD EPP-Q S umber of Tags Che's EPP-Q s Effcecy Icrease % 34.6% 0.5% % 34.6% 7.8% % 34.8% 8.7% % 34.7% 3.8% % 34.5% 2.7% % 34.3% 5.5% % 34.5% 6.9% V. COCLUSIO EPP-Q represets a better performace tha other oes, ad t loads to accuraces of the estmato to take to cosderato of the kowledge from the past slots. Whe frame sze s too small or too large, the adjustmet frame wll reduce uecessary waste ad mprove the effcecy of the system. Our result s smulated matlab, however, real applcatos the effcecy would be better due to capture effect (The capture effect o RFID refers to the evet that oe of multple tags s able to trasmt wth the reader successfully because t has a hgher trasmsso power spte of that multple tags try to trasmt smultaeously to a reader). I cocluso, more researches are requred to reach the future that RFID systems become ubqutous. For example, the tal Q value (frame sze) wll affect the performace of at-collso algorthms. aybe some researches are eeded to tue the tal Q accordg to the cotextual formato. ACKOWLEDGEET Ths work has bee supported by the Key Scetfc ad Techologcal Projects of Shax Provce ( ad ). Fally, we thak revewers for ther atteto ad tme for ths work, ad we wll apprecate ay useful commets they could gve us. REFERECES [] L. Zhu ad T. S. P. Yum, "The optmal readg strategy for EPC Ge-2 RFID at-collso systems," IEEE Trasactos o Commucatos, vol. 58, pp , 200. [2] J. yug, W. J. Lee, ad J. Srvastava, "Adaptve bary splttg for effcet RFID tag at-collso," IEEE Commucatos Letters, vol. 0, pp , arch [3] Y. C. La ad C. C. L, Two couple-resoluto blockg protocols o adaptve query splttg for RFID tag detfcato, IEEE Tras. oble Computg, vol., o. 0, pp , Oct [4] W. J. Pa, Q. S. Xe, S. B. L, G. C. Yag, ad. Feg, "Atcollso algorthm based o dyamc groupg mechasm RFID systems," Joural of Covergece Iformato Techology, vol. 7, pp , 202. [5] C.. Yag ad J. Y. He, "A effectve 6-bt radom umber aded query tree algorthm for RFID tag at-collso," IEEE Commucatos Letters, vol. 5, pp , 20. [6]. V. Bueo-Delgado ad J. Vales-Aloso, "O the optmal frame-legth cofgurato o real passve RFID systems," Joural of etwork ad Computer Applcatos, vol. 34, pp , ay 20. [7] B. L ad J. Wag, Effcet at-collso algorthm utlzg the capture effect for ISO C RFID protocol, IEEE Commucato Letters, vol. 5, o. 3, pp , ar. 20. [8] J. Vales-Aloso, V. Bueo-Delgado, E. Egea-Lopez, F. J. Gozalez-Castaño, ad J. Alcaraz, ultframe maxmumlkelhood tag estmato for RFID atcollso protocols, IEEE Tras. Idustral Iformatcs, vol. 7, o. 3, pp , Aug. 20. [9] Y. agure ad R. Pappu, "A optmal Q-algorthm for the ISO C RFID protocol," IEEE Trasactos o Automato Scece ad Egeerg, vol. 6, pp. 5-24, [0] C. Y. Wag, C. C. Lee, ad. C. Lee, "A ehaced dyamc framed slotted ALOHA at-collso method for moble RFID tag detfcato," Joural of Covergece Iformato Techology, vol. 6, pp , 20. [] EPCglobal, "EPC rado-frequecy detty protocols class- geerato-2 UHF RFID protocol for commucatos at 860Hz- 960Hz verso.2.0," ed, [2]. V. Bueo-Delgado, J. Vales-Aloso, ad F. J. Gozalez- Castaño, "Aalyss of DFSA at-collso protocols passve RFID evromets," preseted at the Idustral Electrocs, IECO '09. 35th Aual Coferece of IEEE, [3] W. T. Che, "A accurate tag estmate method for mprovg the performace of a RFID at-collso algorthm based o dyamc frame legth ALOHA," IEEE Trasactos o Automato Scece ad Egeerg, vol. 6, pp. 9-5, [4] H. Vogt, "Effcet object detfcato wth passve RFID tags," Proc. Frst Iteratoal Coferece o Pervasve Computg, Lodo, UK, 2002, pp [5] F. C. Schoute, "Dyamc frame legth ALOHA," IEEE Trasacto Commucato, vol. 3, pp , 983. [6] W. T. Che, "A feasble ad easy-to-mplemet at-collso algorthm for the EPCglobal UHF Class- Geerato-2 RFID protocol," IEEE Trasactos o Automato Scece ad Egeerg, vol., o. 2, pp , 204. Lta Dua was bor Shax Provce, Cha, 989. He receved the B.Sc. Iformato System from Bejg Isttute of Techology (BIT), Bejg, Cha, 20 ad the.sc. Iformato System aagemet from Cty Uversty of Hog Kog (CtyU), Hog Kog, 202. I addto, he was oe of 204 Egeerg ad Techology Publshg 803

7 Joural of Commucatos Vol. 9,. 0, October 204 the frst batches of exchage studets to Tawa, Chug Yua Chrsta Uversty, Tawa, 20. Curretly, he s a doctoral studet the college of Iformato Egeerg, Tayua Uversty of Techology (TYUT). Hs research terests clude RFID mplemetato for at-collso algorthm ad formato securty. techology. Wewe Pag was bor Shax Provce, Cha, 986. She receved the B.E. Computer Scece from Tayua Uversty of Techology (TYUT), Tayua, Cha, 200 ad the.e. Computer Scece from Tayua Uversty of Techology (TYUT), Tayua, Cha, 204. Her research terests clude IoT (teret of thgs) ad RFID Fu Dua was bor Shax Provce, Cha. He receved the B.E. computer scece from Tayua Uversty of Techology (TYUT), Tayua, Cha, 983 ad the.e. Computer Scece from Tayua Uversty of Techology (TYUT), Tayua, Cha, 986 ad the Ph.D. Electroc Iformato Egeerg from Tayua Uversty of Techology (TYUT), Tayua, Cha, 200. w he s a professor ad supervsor of aster studets the college of Computer Scece ad Techology, Tayua Uversty of Techology, Tayua, Cha. Hs curretly research cludes the techology of IoT(teret of thgs), the applcato of tellget optmzato algorthm ad the techology of RFID recogto. 204 Egeerg ad Techology Publshg 804