How To Improve Gps Locatg Accuracy On A Cell Phone

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1 GPS Localzato Improvemet of Smartphoes Usg Bult- Sesors Soyoug Hwag ad Doghu Yu* Departmet of Multmeda Egeerg Catholc Uversty of Pusa, South Korea {soyoug, Abstract Locato awareess ad avgato are becomg oe of the most mportat features moble phoes ad smartphoes. Persoal avgato ad locato based servces are elargg the scope of moble applcatos. GPS s the most effcet postog techology. Thaks to the reducto the sze of the GPS recevers ad the tegrato of GPS wth moble phoes, GPS s oe of the most mportat servce provders LBS. By the way, sce moble phoes ad smartphoes usually have relatvely low cost GPS chps, the performace of locatg accuracy s hghly depedet o evrometal factors. I addto, the accuracy of GPS vares depedg o the umber of GPS satelltes ad s reduced GPS terferg spots such as a forest or aroud buldgs. Ths paper proposes a localzato mprovemet algorthm GPS terferg spots by tegratg formato of multple sesors smartphoes. The proposed algorthm s mplemeted a smartphoe ad the performace s evaluated o a campus. The proposed algorthm has better performace tha oly the GPS locato formato GPS terferg spots ad matas reasoable performace ope spaces where the GPS recever s accurate. Keywords: localzato, GPS, smartphoe, sesors. Itroducto Locato awareess ad avgato are becomg oe of the most mportat features moble phoes ad smartphoes. Persoal avgato ad locato based servces are elargg the scope of moble applcatos. GPS (Global Postog System) s the most effcet postog techology. Thaks to the reducto the sze of the GPS recevers ad tegrato of GPS wth moble phoes, GPS s oe of the most mportat servce provders for LBS. By the way, sce moble phoes ad smartphoes usually have relatvely low cost GPS chps, the performace of locatg accuracy s hghly depedet o evrometal factors. I addto, the accuracy of GPS vares depedg o the umber of GPS satelltes ad s reduced GPS terferg spots such as a forest or aroud buldgs. Ths paper proposes a localzato mprovemet algorthm GPS terferg spots by tegratg formato of multple sesors such as gyroscope ad compass smartphoes. The proposed algorthm s mplemeted a smartphoe ad the performace s evaluated o a campus. The rest of ths paper s orgazed as follows. I Secto 2, motvato ad related work are dscussed. Secto 3 proposes the desg of the localzato algorthm to mprove localzato accuracy smartphoes usg multple sesors. Net, performace of the proposed algorthm s evaluated Secto 4. Fally, we coclude ths paper Secto 5.

2 2. Motvato ad Related Work 2.. Motvato The reducto the sze of GPS recevers ad the tegrato of GPS wth moble phoes have made locato based servce applcato more ad more popular. There have bee may case studes of locato based servces usg moble phoes ad smartphoes wth GPS. A applcato study o a ta callg ad dspatchg system s proposed []. Ths s a prototype of a LBS applcato based o GPS moble phoes. It gves the basc desg, modules dvso, GIS dsplay algorthm desg, test results ad feature aalyss of the proposed system. Aother moble applcato based o provdg LBS usg GPS as a locato provder s to locate famly members ad alert whe freds are earby [2]. The applcatos work ope space areas oly sce t reles o GPS. A dstrbuted trajectory smlarty search framework s preseted [3]. It focuses o GPS trace search smartphoe etworks by decetralzed ad -stu data. [4] gves a ew method for precse W-F AP localzato usg GPS formato of smartphoes ad the receved sgal stregth (RSS) formato from W-F APs. Sce GPS s the most effcet postog techology, most moble LBS applcatos utlze GPS as a locato provder. But, as metoed before moble phoes ad smartphoes have relatvely low cost GPS chps, therefore the performace of locatg accuracy s hghly depedet o evrometal factors such as weather or GPS terferg areas. To crease the utlzato of such varous moble LBS applcatos, t s mportat to mprove GPS accuracy. Fgure shows GPS postog error a smartphoe whe the user s ear hgh rse buldgs. So we cosdered a study to overcome ths GPS error. Fgure. Postog Error GPS Iterferg Spot 2.2. Related Work As GPS s wdely used for outdoor localzato, there have bee efforts to aalyze GPS performace cases ad to overcome GPS errors. 2

3 Systematc statstcal aalyss of GPS movg measuremets ope sky ad uder tree shadg evromets was reported [5]. The objectve of the research was to develop a robust localzato system. So t s cosdered that the frst step to acheve such a objectve s testg sesor performace through tree folage evromets that preset codtos that are ot optmal. Recetly, the wreless dustry s movg towards covergece of rado techology to cater for mult stadards o a sgle platform such as moble phoe, PDA (Persoal Dgtal Assstat) ad smartphoe. These platforms provde a wde varety of wreless servces, such as voce, data, vdeo ad posto fg. May wreless stadards such as 2G/3G, W-F, buetooth ad GPS, have bee mplemeted o these platforms. For moble purposes, the equpmet must be small volume, lght weght ad low power cosumpto. These lead to complcated problems wth dgtal ad RF operatos. The sestvtes GPS ad 2G/3G are tested ad the mprovemets of GPS recever sestvtes PDA platforms are preseted [6]. Applcatos usg locato based servces have bee eplored due to safety ad emergecy requremets wreless commucatos servces. The terworkg amog heterogeeous systems duces the hybrd postog cocept wth multple postog techologes. [7] focuses o the mprovemet of GPS orbt accuracy to ehace hybrd posto computato. The results suggest that the proposed approach has a potetal real tme applcatos. LfeMap, a smartphoe-based cotet provder s proposed [8]. It s mplemeted o commercal smartphoes ad ca provde advaced locato based servces for moble users. LfeMap uses ertal sesors the smartphoe to overcome the lmtatos of GPS ad provde door locato formato. The formato s combed wth GPS ad W-F postog systems to geerate user cotet daly lfe. I a urba evromet, the sgals from a bult- GPS o a smart phoe are always so weak that t causes cosderably low posto ad headg accuracy. [9] presets a approach usg the bult- sesor to smooth the avgato process. Our work also focuses o GPS localzato mprovemet smartphoes by tegratg the formato from bult- sesors wth the GPS the smartphoe. 3. Desg of Localzato Algorthm 3.. Structure of Algorthm The proposed algorthm cossts of three steps: fdg the correct drecto of movemet, obtag the dstace moved, ad tegratg the pror results ad GPS locato formato. To obta the drecto of movemet, we get the headg from the bult- compass the smartphoe. However, the compass s hghly depedet o the ambet magetc feld so t has lower accuracy. To obta more accurate values of the user's headg, we stablze the headg value of the compass by recurrece processg of the data. After obtag the drecto of the movemet of the user, the dstace moved s calculated by the summato of the dstaces of each coordate from the GPS locato formato. The GPS locato formato shows the dfferece compared to the actual path moved as preseted Fgure 2. So the calculated movg dstace s greater tha the actual dstace moved f t s calculated by the summato of the dstaces betwee each coordate from the GPS locato formato. 3

4 Fgure 2. Path ad Dstace Moved To f ths problem, we estmate the movemet dstace by usg a trgoometrc fucto as show Fgure 3. Fgure 3. Calculato of Movg Dstace The proposed method estmates the path moved by tegratg the GPS locato formato ad sesor data ad t prevets the accumulato of locato error Recurrece Processg Fucto of Compass Headg The measuremets of the compass smartphoe are hghly depedet o the ambet magetc feld so ts accuracy s low. For ths reaso, we stablze the measuremets of the compass by averagg as show equato (). a ( ( a ) / 2 a ) /( ) : accumulated headg value a : a ew compass value () 4

5 a ( ( d d a a ) /( ) : accumulated headg value a : a ew compass value d : dfferece of headg ) / 2 The headg value of the compass ca be stablzed wth equato (). But the real headg of a user vares cotuously as the user moves. To adjust ths value, we apply the dfferece betwee the prevous headg ad curret headg ad process t recursvely as show equato (2). The dfferece the headg d s obtaed from the bult- gyroscope the smartphoe. Although the gyroscope caot measure the absolute headg lke a compass, t has hgh accuracy measurg varato of the headg. Evetually, through the pror processg, effcet stablzato of the data s possble. 4. Performace Evaluato I ths secto we dscuss the performace evaluato of the proposed localzato mprovemet algorthm. We mplemeted the proposed method o commercal smartphoe ad performed a epermet by walkg through a campus. (2) Fgure 4. Epermet Evromet We traced the path of movemet the smartphoe ad the path s dsplayed o the map. There are two kds of trace: tracg by the proposed method ad oly tracg by the GPS locato formato. Fgure 4 shows the epermetal evromet as a GPS terferg spot. The accuracy of GPS s reduced GPS terferg spots such as a forest or aroud buldgs. The epermetal results the GPS terferg spot s preseted Fgure 5. As show the results, the GPS locato formato devates from the real path moved. O the other had, the adjusted locato formato through the proposed algorthm ca trace the movemet path more accurately. 5

6 Fgure 5. Epermetal Result GPS Iterferg Area Fgure 6. Epermetal Result Ope Space Fgure 6 shows the epermetal results o a soccer feld as a ope space. I ths case, the GPS locato formato has hgh accuracy. The proposed algorthm also has reasoable results sce t has feedback from the GPS locato formato. 6

7 5. Coclusos Locato awareess ad avgato are becomg oe of the most mportat features moble phoes ad smartphoes. Persoal avgato ad locato based servces are elargg the scope of moble applcatos. GPS s the most effcet postog techology. Thaks to the reducto the sze of the GPS recevers ad the tegrato of GPS wth moble phoes, GPS s oe of the most mportat servce provders for LBS. Sce moble phoes ad smartphoes usually have relatvely low cost GPS chps, the performace of locatg accuracy s hghly depedet o evrometal factors. Ths paper proposes a localzato mprovemet algorthm GPS terferg spots by tegratg formato of multple sesors such as gyroscope ad compass the smartphoe. The proposed algorthm s mplemeted a smartphoe ad the performace s evaluated o a campus. The proposed algorthm has better performace tha oly the GPS locato formato GPS terferg spots ad matas reasoable performace ope spaces where the GPS recever s accurate. As a future work, we cosder localzato mprovemet method for smartphoes usg other bult- sesors such as accelerometer ad camera. Refereces [] Y. Ja, Z. Xaom ad Z. Hogyu, Desg ad Implemetato of Ta Callg ad Dspatchg System based o GPS Moble Phoe, Proceedgs of the 4th Iteratoal Coferece of Computer Scece & Educato, (29), July 25-28, Nag, Cha. [2] G. B. Al-Suwad ad M. J. Zemerly, Locatg Freds ad Famly Usg Moble Phoes Wth Global Postog System (GPS), Proceedgs of 7th ACS/IEEE Iteratoal Coferece o Computer Systems ad Applcatos Program (29), May -3, Rabat, Morocco. [3] D. Zealpour-Yazt, C. Laoudas, M. I. Adreou ad D. Guopulos, Dsclosure-free GPS Trace Search Smartphoe Networks, Proceedgs of the 2th IEEE Iteratoal Coferece o Moble Data Maagemet, (2), Jue 6-9, Luleå, Swede. [4] S. M. Chu, S. Mu Lee, J. W. Nah, J. H. Cho ad J. T. Park, Localzato of W-F Access Pot usg Smartphoe s GPS Iformato, Proceedgs of 2 Iteratoal Coferece o Selected Topcs Moble ad Wreless Networkg, (2), October -2, Shagha, Cha. [5] Y. Morales ad T. Tsubouch, GPS Movg Performace o Ope Sky ad Forested Paths, Proceedgs of the 27 IEEE/RSJ Iteratoal Coferece o Itellget Robots ad Systems, (27), October 29- November 2, Sa Dego, USA. [6] Y. H. Kao ad H. C. Yag, Iterfereces of GPS Recepto PDA Phoe, Proceedgs of 2 Asa- Pacfc Mcrowave Coferece, (2), December 7-, Yokohama, Japa. [7] C. S. Ho, A Effectve Approach Improvg A-GPS Accuracy to Ehace Hybrd Postog Computato, Proceedgs of the 7th IEEE Iteratoal Coferece o Embedded ad Real-Tme Computg Systems ad Applcatos, (2), Auguest 28-3, Toyama, Japa [8] Y. Cho ad H. Cha, LfeMap: A Smartphoe-Based Cotet Provder for Locato-Based Servces, IEEE Pervasve Computg, vol., o. 2, (2). [9] L. Pe, R. Che, J. Lu, Z. Lu, H. Kuusem, Y. Che ad L. Zhu, Sesor Asssted 3D Persoal avgato o a Smart Phoe GPS Degraded Evromets, Proceedgs of the 9th Iteratoal Coferece o Geoformatcs, (2), Jue 24-26, Shagha, Cha. 7

8 Authors Soyoug Hwag receved the B.S., the M.S., ad the Ph.D. degrees Computer Scece from Pusa Natoal Uversty, Busa, Korea 999, 2 ad 26 respectvely. From 26 to 2, she was a seor researcher ETRI, Daejeo, Korea. Sce 2, she has bee a professor of Departmet of Multmeda Egeerg at Catholc Uversty of Pusa, Korea. Her research terests clude embedded systems ad sesor etworks. Doghu Yu receved the B.S., the M.S., ad the Ph.D. degrees Computer Scece from Pusa Natoal Uversty, Busa, Korea 992, 994, 2 respectvely. From 994 to 997, she was a researcher ETRI (Electrocs ad Telecommucatos Research Isttute), Daejeo, Korea. From 23, she has bee a faculty of Departmet of Multmeda Egeerg at Catholc Uversty of Pusa, Korea. Her research terests are tme sychrozato ad moble systems. 8