Weighted Centroid Correction Localization in Cellular Systems

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1 Amerca J. of Egeerg ad Appled Sceces 4 (): 37-4, 20 ISSN Scece Publcatos Weghted Cetrod Correcto Localzato Cellular Systems Rog-Zheg L, X-Log Luo ad Ja-Ru L Key Laboratory of Uversal Wreless Network, School of Iformato ad Commucato Egeerg, Bejg Uversty of Posts ad Telecommucatos, Cha Abstract: Problem statemet: There s a large demad for wreless Locato-Based Servce (LBS) ad t s provded by may wreless cellular systems. I process of postog a Moble Stato (MS), the computg speed s as mportat as the postog accuracy ad the algorthm should also be resstat to evrometal flueces. Approach: A ew postog method based o Weghted Cetrod Correcto Localzato (WCCL) for wreless cellular systems s troduced ths artcle. Frstly, referrg to the recevg-state of a MS cellular systems, t computes a weghted cetrod of surroudg Base Statos (BSs) as a rough approxmate posto of the MS. The, accordg to the dstaces betwee the MS ad the BSs beg less or bgger tha the computed dstaces betwee the BSs ad the weghted cetrod, t corrects the coordate of the weghted cetrod towards the drectos of the BSs by movg t closer or farther tur. Results: Accordg to our expermets, WCCL mproves the postog accuracy, as well as to provde a better resstace to evrometal flueces. Cocluso: As a modfed cetrod-based localzato algorthm, WCCL obtas weghtg factors from the recevg-state of MS mult-cells structured cellular systems ad obtas a better postog result cellular systems wthout updatg the etwork equpmet. Therefore, for the cellular postog problem, WCCL algorthm ca be a alterate soluto. Key words: Wreless postog method, Locato-Based Servce (LBS), geometrc dstace, Base Statos (BSs), weghted cetrod correcto localzato (WCCL), cellular systems, Arrval Of Agle (AOA), Locato Measuremet Ut (LMU), Effectve Cells (ECs) INTRODUCTION There s a large demad for wreless Locato-Based Servce (LBS) ad t s provded by may wreless cellular systems (Reed et al., 998; Drae et al., 998; Bas ad Murthy, 2004). I process of postog a Moble Stato (MS), the computg speed s as mportat as the postog accuracy ad the algorthm should also be resstat to evrometal flueces. Cell-ID method s the frst cellular postog techology appled to commercal servces. It adopts the coordate of the Base Stato (BS) whch has the strogest sgal stregth as the posto of the moble stato, but t oly has a low accuracy (Caffery ad Stuber, 998; Drae et al., 998). Aother postog method s the tragle algorthm, whch obtas the postog coordate of a MS by solvg a lear least-square problem based o the dstaces betwee the MS ad surroudg BSs (Luo ad Wu, 200; Zheg et al., 2008). However, the postog accuracy of the tragle method s very sestve to the precso of measured dstaces. I order to obta a better postog result, other postog techologes are developed recet years, such as asssted GPS, Arrval Of Agle (AOA), Tme Of Arrval/Tme Dfferece Of Arrval (TOA/TDOA) (Caffery ad Stuber, 998; Drae et al., 998). The postog techology based o the asssted GPS or AOA eeds to deploy the specal hardware (GPS chp or atea array) a MS or a BS. If a o-sychroous system tres to locate a MS va TOA/TDOA, t eeds to deploy Locato Measuremet Ut (LMU) to mprove the tmg capablty ad the MS also must be upgraded. Aother dsadvatage, they usually take much more tme to respod the request of the postog because of ther complex computg process. Therefore, we eed to vestgate a smple ad effcet method to mprove the postog accuracy wth less tme cost, as well as to provde a better resstace to evrometal flueces. The weghted Correspodg Author: X-log Luo, Key Laboratory of Uversal Wreless Network, School of Iformato ad Commucato Egeerg, Bejg Uversty of Posts ad Telecommucatos, Bejg 00876, Cha 37

cetrod-based localzato algorthm s a good backup approach because of ts smplcty ad effcecy, o the recet advacemet of ths class of postog methods, oe ca refer to (Blumethal et al.

2 cetrod-based localzato algorthm s a good backup approach because of ts smplcty ad effcecy, o the recet advacemet of ths class of postog methods, oe ca refer to (Blumethal et al., 2007) for the Weghted Cetrod Localzato (WCL), (Behke ad Tmmerma, 2008) for the adaptve WCL (AWCL), (Schuhma et al., 200) for the mproved WCL (IWCL) ad so o. MATERIALS AND METHODS I ths study, we proposed a ew localzato algorthm for wreless cellular systems, whch s called the Weghted Cetrod Correcto Localzato (WCCL). Compared wth other weghted cetrodbased algorthms, the dfferet characterstc of WCCL s that ts weghtg factors are obtaed from the recevg-state of a MS mult-cells structured cellular systems. I order to mprove the postog accuracy of a MS, we use the dstaces betwee the MS ad surroudg BSs to correct ts prmary computed posto. I wreless cellular systems, drectoal ateas are wdely deployed ad every BS usually has three or four drectoal ateas ad each atea ams toward dfferet drecto (Taka et al., 2002; Vasquez ad Hao, 200). We usually use a cell to express the electromagetc wave trasmtted by a atea. If a MS s the coverage of a BS, t may receve sgals from mult-cells of that BS. We call those cells as Effectve Cells (ECs) ad call that BS as a Effectve Base Stato (EBS). If a solated BS has three drectoal ateas whch am to three dfferet drectos wth the spacg of 20 respectvely, the coverage of three ateas overlap each other some regos. We dvded the coverage of a BS to several regos whch are marked by A-G, as depcted Fg.. The coverage radus of ma lobe R 3 s bgger tha back-lobe s coverage radus R sce the ga of a atea s ma-lobe s stroger tha that of back-lobe. R 2 s a boudary of the two types of regos, where a MS ca receve sgals from two ateas or oe atea. Therefore, the recevg-states of a MS dfferet regos A-G are lsted Table. From Table, we ca coclude that the umber of effectve cells s 3 whe a MS s a rego of R ad the umber of effectve cells s 2 f the dstace betwee the MS ad the BS rages from R -R 2 ad the umber of effectve cells s f the MS s beyod the rego of R 2 but stll the coverage of the BS. I a cellular system, order to guaratee the cotuous coverage of a etwork ad the successful Am. J. Egg. & Appled Sc., 4 (): 37-4, Fg. : The aalyss of a base stato s coverage hadover of a MS, the spacg betwee BSs s usually set wth the rage from R 2 -R 3. Therefore, we take the umber of effectve cells of a BS as a weghtg factor of that BS. Ths basc feature s mportat for WCCL. Publczed algorthms of the cetrod locato methods use the cetrod to calculate the posto of a MS (Blumethal et al., 2007; Schuhma et al., 200; Bulusu et al., 2000). For example, a MS receves sgals from mult-cells at the posto M (x,y) ad the cells belog to BSs wth postos of B (x,y) (,2,,.), the the approxmated posto M (x,y) of the MS ca be calculated by Eq. : M'(x,y) B (x,y) () The postog error e s defed as the dstace betwee the exact posto M(x,y) ad the approxmated posto M (x, y) of a MS by Eq. 2: e + ( x' x) 2 ( y' y) 2 (2) A cetrod locato method oly uses the average of the coordates of BSs to approxmate the locato of a MS. A WCL (Blumethal et al., 2007) uses the weghted coeffcets to esure a mproved localzato whch s formulated by Eq. 3: M ''(x, y) { w B (x,y) } (3) w where the weght w s defed by: w (d dstace betwee MS ad BS, gdegree) g (4) (d )

3 Am. J. Egg. & Appled Sc., 4 (): 37-4, 20 Table : Recevg-states of a MS regos A-G Rego Cell Cell 2 Cell 3 Num of ECs d A receved receved receved 3 d<r B receved - receved 2 R <d<r 2 C receved receved - 2 R <d<r 2 D - receved receved 2 R <d<r 2 E receved - - R 2 <d<r 3 F - receved - R 2 <d<r 3 G - - receved R 2 <d<r 3 I order to mprove the postog accuracy, we gve a ew cetrod-based localzato algorthm,.e., the Weghted Cetrod Correcto Localzato (WCCL). Its weghted factor w s obtaed from the recevg-state of a MS mult-cells structured cellular systems. The approxmated weghted cetrod M wc (x,y) s computed by Eq. 5, where the weght of the -th BS w equals the umber of effectve cells whch belog to that BS: Table 2: Statstcal results of test pots Num of EBSs Color Quatty Percetage red 9 3.8% 2 yellow % 3 gree % 4-7 blue % M wc (x,y) { w' B (x,y) } (5) w' The, accordg to the dstace d betwee the -th BS B (x,y) ad the MS M(x,y) beg less or bgger tha the computed dstace d betwee that BS B (x,y) ad the weghted cetrod M wc (x,y), we correct the coordate of the weghted cetrod towards the drecto of the -th BS by movg t closer or farther. The above process s executed for every the effectve base stato by turs. Therefore, the fal corrected posto M wcc (x,y) s obtaed by: Fg. 2: Dstrbuto of test pots ad base statos M (x,y) M (x,y) v (d' d ) M B wc wcc wc + (6) MwcB where, v s a correctg factor whch relates wth the umber of effectve base statos. RESULTS I order to verfy the performace of postog methods real cellular etwork, we choose a rego wth 4 2 km aroud Jme Brdge Hada Dstrct Bejg Cha as a test evromet. The test moble stato moves alog seve ma roads whch are dcated Fg. 2. Those test expermets were performed a GSM etwork ad we obtaed 3744 vald test pots. 39 Fg. 3: CDF of postog error by WCCL expermetal model The test moble stato ca receve wreless sgals from seve cells at most, some of whch may belog to same BSs. We dvded those test pots to four classes accordg to the Num of EBSs ad the dfferet classes of test pots are marked by dfferet colors Fg. 2, respectvely. Ther statstcal results are lsted Table 2.

4 Postog error s the geometrc dstace betwee the exact posto M(x,y) ad the approxmated posto M wcc (x,y) of a MS computed by (5-6). We chose the parameters v 2 0.5, v ad v 0.4 ( 4, 5, 6, 7) (6). The Cumulatve Dstrbuto Fucto (CDF) of the postog error by WCCL expermetal model s show by Fg. 3 ad the postog error acheves 20 meters wth the successful postog probablty of 67%. DISCUSSION The dstace d betwee a MS ad the -th BS s very mportat for tragle algorthm, WCL ad WCCL. Because of multpath ad o-lght-of-sght parameters, the estmatg error s evtably. We deote the exact dstace betwee a MS ad the -th base stato as d 0 ad the estmatg error Δd reflects the devato level from d 0 to d, whch s obtaed by: Δ d d0 d (7) The precso of the estmated dstace affects the accuracy of postog. Therefore a good postog algorthm should be resstat to evrometal flueces as well as mprecse dstaces. I order to quatfy evrometal mpacts, we propose a parameter R Δdmax defed by (8), whch s called the maxmum relatve error rate of estmated dstace: [ ] Δd 0,d0 R Δ dmax (8) I order to compare WCCL wth other popular postog algorthms, we estmate the coordates of all the test pots wth more tha two EBSs, by cell-id, CL, WCL, WCCL ad the tragle algorthm, respectvely. Fgure 4 llustrates the postog errors wth the probablty of 67% by dfferet localzato algorthm our expermetal model ad the curves show the treds of postog errors by dfferet localzato algorthms, whch chage wth the creasg of R Δdmax. From Fg. 4, owg to the absece of dstace formato localzato computg, we fd that cell- ID ad CL ca oly roughly localze the coordate of a MS wth low precso. The tragle algorthm ca obta a good postog result f the dstace estmatg error s low ad the postog error wll deterorate sharply wth the creasg of R Δdmax. Therefore, the tragle algorthm caot be resstat to evrometal flueces. WCL algorthm mproves the postog accuracy of a MS ad the postog error ca be reduced to Am. J. Egg. & Appled Sc., 4 (): 37-4, Fg. 4: Postog errors wth the probablty of 67% by dfferet localzato algorthms expermetal model almost a half from CL wth the probablty of 67% ad also be resstat to the creasg of R Δdmax. As a ew cetrod-based localzato algorthm, WCCL obtas weghtg factor w from the recevgstate of a MS mult-cells structured cellular systems whch s dscussed the secod secto ad uses the dstaces betwee the MS ad BSs to correct the approxmated weghted cetrod. As s llustrated Fg. 4, WCCL algorthm ca reduce the postog error by ear 30% from WCL wth the probablty of 67% ad Fg. 4 also shows that the posto accuracy of WCCL s ot sestve to the maxmum relatve error R Δdmax. Before R Δdmax creases to 0.5, the postog result of WCCL s always much better tha that of WCL. CONCLUSION I comparso wth several other popular postog methods, WCCL obtas a better postog result cellular systems ad t also shows a good resstace to evrometal flueces. Furthermore, WCCL ca be easly mplemeted a wreless cellular system ad t does ot eed to update the equpmet of the etwork or MS. Therefore, for the cellular postog problem, WCCL algorthm ca be a alterate soluto. ACKNOWLEDGEMENT Ths study s supported by Grat YBWL20052 from Research Fud for Huawe Techologes Co., Ltd

5 Am. J. Egg. & Appled Sc., 4 (): 37-4, 20 ad Grat BUPT2009RC08 from the Fudametal Research Fuds for the Cetral Uverstes. REFERENCES Bas, H.M.A. ad M.B.R. Murthy, A smple scheme for mproved performace of fxed outage rate cellular system. Am. J. Appled Sc., : DOI: / Behke, R. ad D. Tmmerma, AWCL: Adaptve weghted cetrod localzato as a effcet mprovemet of coarse graed localzato. Proceedg of the WPNC 5th Workshop o Postog, Navgato ad Commucato, March 27-27, IEEE Xplore Press, Haover, pp: Blumethal, J., R. Grossma, F. Golatowsk ad D. Tmmerma, Weghted cetrod localzato zgbee-based sesor etworks. Proceedg of the IEEE Iteratoal Symposum o Itellget Sgal Processg, Oct. 3-5, IEEE Xplore Press, Alcala de Heares, pp: -6. DOI: 0.09/WISP Bulusu, N., J. Hedema ad D. Estr, GPSless low-cost outdoor localzato for very small devces. IEEE Persoal Commu. Maga., 7: DOI: 0.09/ Caffery, J.J. ad G.L. Stuber, 998. Overvew of radolocato CDMA cellular systems. IEEE Commu. Maga., 36: DOI: 0.09/ Drae, C., M. Macaughta ad C. Scott, 998. Postog GSM telephoes, IEEE Commu. Maga., 36: DOI: 0.09/ Luo, X.L. ad Z.J. Wu, 200. Least-squares approxmatos geometrc buldup for solvg dstace geometry problems, J. Optm. Theory Appl., Accepted. Reed, J.H., K.J. Krzma, B.D. Woerer ad T.S. Rappaport, 998. A overvew of the challeges ad progress meetg the E-9 requremet foe locato servce. IEEE Commu. Maga., 36: DOI: 0.09/ Schuhma, S., K. Herrma, K. Rothermel, J. Blumethal ad D. Tmmerma, 200. Improved weghted cetrod localzato smart ubqutous evromets. Ubqutous Itell. Comput., 560: DOI: 0.007/ _4 Taka, M., J. Mart, R. Bagroda ad A. Re, Drectoal vrtual carrer sesg for drectoal ateas moble ad hoc etworks. Proceedgs of the 3rd ACM Iteratoal Symposum o Moble Ad Hoc Networkg ad Computg, (ISMAHNC 02), ACM MobHoc, USA., pp: DOI: 0.45/ Vasquez, M. ad J.K. Hao, 200. A heurstc approach for atea postog cellular etworks. J. Heurstcs, 7: DOI: 0.023/A: Zheg, Z., X. Luo ad Z. Wu, A Two-phase geometrc buldup algorthm for the soluto of the sesor etwork localzatom. ACM Trasactos o Computatoal Logc, 20:

Zigbee wireless sensor network localization evaluation scheme with weighted centroid method

Zigbee wireless sensor network localization evaluation scheme with weighted centroid method Zgbee wreless sesor etwork localzato evaluato scheme wth weghted cetrod method Loesy Thammavog 1, Khamphog Khogsomboo 1, Thaadol Tegthog 2 ad Sathapor Promwog 2,* 1 Departmet of Electrocs ad Telecommucato