Tropospheric error correction in assisted GPS signals

Transcription

1 Indian Jurnal f Radi & Spac Physics Vl 4, Jun 013, pp rpsphric rrr crrctin in assistd GPS signals Mhammd Mushthaq Ahmd 1,#, Quddusa Sultana 1,$,*, A Supraja Rddy & M A Malik 3 1 Dpartmnt f Elctrnics and Cmmunicatin Enginring, Dccan Cllg f Enginring and chnlgy, Hydrabad , AP, India Rsarch and raining Unit fr Navigatinal Elctrnics (NERU), Osmania Univrsity, Hydrabad , AP, India 3 Dccan Grup f Institutins, Hydrabad , AP, India # mushthaq.md@gmail.cm; $ quddusas@gmail.cm Rcivd 7 Nvmbr 01; rvisd 19 March 013; accptd 3 March 013 hugh standaln cll phn tchnlgy is sufficint t navigat, prsntly, in th dvlpd and th undr dvlpd cuntris f th wrld, almst vry cll phn has a Glbal Psitining Systm (GPS) rcivr mbddd in it. his cmbind systm is calld as assistd GPS. hr ar varius issus t b dalt critically whil using such systms. Fr instanc, cllular ntwrks and GPS signals ncuntr varius typs f rrrs in which trpsphric rrr is n. his papr fcusss n th stimatin f trpsphric rrr and its crrctin in cll phn signals as wll as GPS signals. In rdr t stimat th trpsphric dlay, fur diffrnt trpsphric rrr crrctin mdls ar implmntd. w mdls, namly Hpfild mdl and Eurpan G-statinary Navigatin Ovrlay Srvic (EGNOS) mdl ar implmntd fr GPS signals and thr tw mdls, namly Radi chnical Cmmissin fr Arnautics (RCA) and Lcata rpsphric (LC) mdl ar implmntd fr cllular signals. h rsults indicat that in cas f GPS signals, as th altitud incrass, trpsphric dlay (D) gradually dcrass. h maximum D is bsrvd at th surfac f arth fr Hpfild mdl (13 m) as wll as fr EGNOS mdl (13. m). In cas f cllular signals, D incrass as th altitud incrass sinc th bas statins ar n th grund. At an altitud f 14 km, D is bsrvd fr RCA mdl as 9.08 m and fr LC mdl, it is m. Kywrds: rpsphric rrr crrctin, rpsphric dlay, Assistd GPS signal PACS N: 9.60.hf; Fc 1 Intrductin hr is an incrasing intrst twards lcatin basd mbil srvics. Currntly, glbal systm mbil (GSM) handsts with intgratd GPS navigatr ar availabl n mass lvl in th wrld markt. Mbil phns can stimat thir psitin using tim f arrival (OA), angl f arrival (AOA), tim diffrnc f arrival (DOA) tchniqus 1,. Hwvr, ths ar nt accurat. Hnc, cll phn can b intgratd with GPS rcivr t imprv accuracy. h GPS systm was stablishd by th Unitd Stats Dpartmnt f Dfns (DOD) t prvid ral tim navigatin fr th US military. Civil us was th scndary bjctiv f GPS and civil usrs wr limitd in 1990 but prsntly, th GPS usrs grw at an amazing rat du t its vast applicatins 3. hr ar varius typs f rrrs that affct th cll phn signals as wll as th GPS signals. Sm f th majr rrrs in cllular cmmunicatins ar signal fading, c-channl intrfrnc, multipath and trpsphric rrr. h prminnt rrrs in GPS ar insphric rrr, trpsphric rrr, multipath and clck bias. In this papr, trpsphric rrr is fcusd. Invstigatins ar prfrmd n th stimatin and crrctin f trpsphric tim dlay rrr in cas f cll phn signals as wll as GPS signals. As th trpsphric tim dlay rrr dpnds n th mtrlgical data, this data is cllctd frm varius citis and is incrpratd in trpsphric rrr mdls. rpsphric rrr h layr f th atmsphr which is clsst t th arth is trpsphr. Gnrally, trpsphr xtnds up t 14 kms frm th surfac f th arth. his layr is mst dns than thr layrs and mainly cnsists f gass and watr vapur. Mst f th watr vapur is blw 4 kms. Smtims, th atmsphric layr till 50 kms altitud is knwn as trpsphr 4. h trpsphr thicknss is nt sam vrywhr, it strtchs t 16 kms at quatr and rducs t 9 kms

2 160 INDIAN J RADIO & SPACE PHYS, JUNE 013 abv th pl. Du t th rfractiv indx (N 1 > 1) f th arth s nutral atmsphr, GPS signals suffr frm trpsphric prpagatin dlays. h ttal trpsphric dlay in th dirctin f a particular satllit, i.. slant path dlay (SPD) can b dividd int a hydrstatic () and a cmpnnt 5. Abut 90% f th trpsphric rfractin is du t cmpnnt and abut 10% is du t cmpnnt. hugh th trpsphric dlay is much smallr than th insphric dlay at L-band frquncis, it gratly affcts th signal prpagatin. 3 rppshric rrr crrctin mdls applicabl t GPS signals Many mdls ar prpsd in th availabl litratur but fw prminnt and fficint mdls fr stimating th trpsphric dlay in GPS signals ar cnsidrd in this papr. w mdls, namly Hpfild mdl 6 and Eurpan G-statinary Navigatin Ovrlay Srvic (EGNOS) mdl 7 ar implmntd fr th GPS signals. w mdls Radi chnical Cmmissin fr Arnautics (RCA) 8 and Lcata rpsphric (LC) mdls 9 ar implmntd fr cllular signals. 3.1 Hpfild mdl h Hpfild mdl was basically prpsd by a scintist, Hln Hpfild 6. his mdl is basd n th rlatinship btwn th rfractivity at hight h t th surfac f arth. h thicknss f th layr, h, is givn as: h = ( ) (1) whr,, is th tmpratur ( K) at th surfac f arth; and h, th layr thicknss, i.. whr humidity xists. It is calculatd fr Hydrabad city n 8 Fb 01 as 4 km. h ttal trpsphric dlay ( rp ) in znith dirctin is xprssd as: rp whr, = + () = 10 6 / 5*[ N * h + N * h ] (3) N = K1* p / (4) = K* / K3* / (5) N + h cnstants ar givn as K1 = Kmb, K = Kmb and K3 = 3.718*10 5 ; P, is th ttal prssur (mb); and, is th partial prssur f watr vapur bth in milli bar at surfac. If θ is th lvatin angl (in dg) f th satllit with rspct t th usr thn mapping functins can b includd in Eq. (3) t gt th rspctiv dlay as: rp 6 = 10 /5*[ N * h * m ( θ ) + N d, * h * m ( θ )] w.(6) whr, m d (θ ) and m w (θ ), ar th mapping functins fr and cmpnnt dlays fr Hpfild mdl. hs ar givn as: md ( θ ) = 1/sin θ (7) m ( ) = 1/sin +. 5 w θ θ (8) 3. Eurpan G-statinary Navigatin Ovrlay Srvic (EGNOS) mdl h EGNOS mdl is th Eurpan cntributin t th Glbal Navigatin Satllit Systm (GNSS). h EGNOS trpsphric crrctin mdl is cnsidrd as a pssibl tl fr stimating and crrcting th trpsphric dlay in rdr t btain rrr fr GPS signals 7. h ttal trpsphric dlay du t and cmpnnts, using mapping functin (θ ) is mdlld as is in Eq. (). h znith and dlays ar cmputd as 10 : g β H Rdβ = Z * [1 ] = Z β H *[1 ] ( λ+ 1) g 1 R β d (9) (10) whr, g, is acclratin du t gravity ( m s - ); H, hight f th rcivr abv man sa lvl (m); λ = -.6 mb km -1, th tmpratur laps rat (.6 mb km -1 ); and R d = J kg -1 K -1. h tw xprssins fr th znith dlay and th znith dlay at man sa lvl ar as fllws: Z = (10-6 *y 1 *R d *P )/g m 6 1 Z = [( 10 * y * Rd )/ gm( λ + 1) βrd ]* 0 / 0 whr, y 1, y and g m, ar cnstants: y 1 = k mb -1 ; y = k mb -1 ; g m = 9.78 m s -. h mapping functin (MF) at lvatin angl (θ ) is xprssd as: MF ( θ ) = sin( θ ) (11)

3 AHMED t al.: ROPOSPHERIC ERROR CORRECION IN ASSISED GPS SIGNALS rppshric rrr crrctin mdls applicabl t cllular signals h cllular ntwrk is a grund basd systm, hnc, th signals frm th bas statin prpagat thrugh th trpsphric layr and rach th rcivr n grund. hrfr, th mdls which culd stimat th trpsphric dlay in such grund basd systms ar RCA mdl 8 and LC mdl 9. RCA and LC mdls ar basically dvlpd fr th ara f navigatin, hwvr, in this papr thir fasibility is invstigatd fr cllular signals. 4.1 RCA mdl RCA has dfind a trpsphric dlay mdl fr us with lcal ara augmntatin systms (LAAS) 8. h trpsphric crrctin cnsists f a (hydrstatic) and a cmpnnt xprssd as is in Eq.. h quatin fr and dlays ar givn as: 6 = 10 * N * D *[1 ( hms hbs ) / h, 6 = 10 * N * D*[1 ( h h ) / h, MS BS ] ] (1) (13) whr, h MS stands fr usr hight (m); h BS, stands fr th bas statin twr hight (m); and D, is th slp distanc (m) btwn th usr and th twr. Rfractivity N fr is calculatd as in Eq. (5) and cmpnnts is givn as: ( 0 73)/( ) * f / *10 N =.77*10 (14) whr, f, is humidity (%) which is givn as: f = ( ) / 0.01* xp( * * 4. Lngth basd trpsphric (LB) mdl A mdifid lngth rati basd trpsphric (LB) mdl is rfrrd as th Lcata rpsphric Mdl (LC) 9. h LC mdl uss th principl f LB mdl. It is intrducd fr us in lcata psitining, and its prfrmanc is invstigatd fr us during th Knwn Pint Ambiguity Rslutin (KPAR) prcdur. his mdl uss nw cnstants fr calculating rfractivity indx (N). Hr, th trpsphric crrctin is givn as: ) 4.3 Lcata rpsphric (LC) mdl In LC, th trpsphric crrctin is applid t th diffrnc btwn th distanc f transmittr and usr and th distanc f transmittr and th knwn pint (Fig. 1). By taking th diffrnc btwn th tw distancs, LC taks car f th distancs that ar nt includd in th ambiguity rslutin and als rmvs th radi intrfrnc and biass. Mathmatically, th trppshtric rrr can b calculatd as in Eq. (15). whr, D = D 1 D (18) whr, D 1, is th slp distanc btwn th bas statin and usr rcivr; D, th slp distanc btwn th bas statin and a knwn pint. 5 Intrplatin f mtrlgical data rpsphric mdls dpnd upn ME data. Mtrlgical (ME) data cnsists f ttal prssur, tmpratur, partial prssur du t watr vapur and rlativ humidity. If th airbrn data is availabl, it can b dirctly usd by diffrnt trpsphric mdls t find th trpsphric dlay at diffrnt hights. Othrwis, th surfac mtrlgical data shuld b intrplatd at varius hights fr trpsphr, trppaus and stratsphr 11 (abl 1). 6 Rsults and Discussin Availabl surfac ME data fr varius citis f India is intrplatd at diffrnt altituds f th atmsphr 1. Balln data, which is cllctd frm a suthrn rgin f India is cmpard with th ME data btaind using intrplatin tchniqus. If th ral mtrlgical data is nt availabl, thn th Minimum Opratinal Prfrmanc Standards (MOPS) trpsphric algrithm can als b applid. his apprach uss standard mtrlgical data dpndnt n latitud and taks sasnal variatins int accunt 13. h advantag f this mdl is that th = 10 6 * N D (15) rp * whr, N = 71.96* / * / N = * ( P ) / (16) (17) Fig. 1 Lcata trpsphric mdl (LC) principl

4 16 INDIAN J RADIO & SPACE PHYS, JUNE 013 Mtrlgical paramtr mpratur () abl Surfac ME data cllctd frm thr diffrnt citis S N Lcatin im, hrs IS mpratur, K Prssur, mb PP, mb 1. Hydrabad 0: Mumbai 0: Dlhi 1: abl 1 Intrplatin f th mtrlgical paramtrs rpsphr ( h 1km ) rppaus (1-16 km) = + β h = + β h β = 6 ± 0.5 dg km -1 β = 0 Stratsphr (16-50 km) = + β h β =1 r C km -1 Prssur (p) 3. 5 p = p 1+ β h / ) p = p xp[( Mg ( h h ) / R ] ( g ff * ff U =.784( cs λ h ) 9 Partial prssur f watr vapr () = * (( λ + 1) / R d β ) 1 / [1 β h / ] in trms f rlativ humidity (f) = 0.01* f *xp( * * ) whr, h, is th altitud; h, th hight f th usr at th surfac; and [%] p, and h, th prssur (mb), tmpratur ( K ) and hight (m) at th lwr trppaus ( 1km ). β is th tmpratur laps rat (dg km -1 ); R, th univrsal gas cnstant ( kj (kml K) -1 ; U M, th mlar mass f th air in th stratsphr ( 8.96kg / kml ); g, th ffctiv fr fall acclratin in th stratsphr; λ, th usr ff latitud (dg); R d, th gas cnstant fr air (=87.05 J kg -1 km -1 ); λ, th laps rat in partial prssur du t watr vapur. mtrlgical masurmnts ar nt ncssary and mtrlgical paramtrs ar mdlld with th hlp f dfault data sts. Hwvr, th accuracy f this mdl is nt sufficint. 6.1 Intrplatin f mtrlgical data and cmparisn with balln data h surfac mtrlgical data is cllctd frm varius citis f India n 8 Fbruary 01 (abl ). mpratur f thr diffrnt citis is intrplatd and cmpard at diffrnt altituds f trpsphr, trppaus and stratsphr (Fig. ). h data prvidd by th MOPS data sht and balln data is als usd t cmpar intrplatd tmpratur at diffrnt altituds. It can b bsrvd that th tmpratur is maximum at th surfac f arth (apprximatly 99 K) fr all thr citis and starts dcrasing in th trpsphr, i.. up t a hight f 14 km and rmains cnstant in trppaus, i.. up t 18 km. hraftr, th tmpratur gradually incrass t 78 K apprximatly in stratsphr up t 50 km. hr is a slight variatin in th surfac tmpratur f th thr diffrnt citis. Frm th balln data, th tmpratur is fund t b 310 K at th surfac and starts dcrasing till 16 km and it slwly incrass Fig. Intrplatin f tmpratur with rspct t altitud Fig. 3 Intrplatin f surfac prssur with rspct t altitud up t 1 K in stratsphr (balln data culd b cllctd till 3 km altitud nly du t varius cnstraints). h intrplatin f prssur at diffrnt altituds is shwn in Fig. 3. h prssur is invrsly prprtinal t altitud, i.. as th altitud incrass th prssur dcrass. h prssur is maximum at th surfac f arth. It can b bsrvd that th prssur dcrass frm 1000 mb at surfac t 0 mb at

5 AHMED t al.: ROPOSPHERIC ERROR CORRECION IN ASSISED GPS SIGNALS 163 an altitud f 45 km and thn rmains cnstant (0 mb) up t 50 km. hr is an insignificant diffrnc in prssur f thr citis and MOPS. Frm th givn balln data, th prssur is maximum at th surfac (1000 mb) and dcrass gradually and bcms 0 mb at 3 km altitud. h intrplatin f partial prssur (PP) du t watr vapur with rspct t altitud is shwn in Fig. 4. PP dcrass with incras in altitud. It is apprximatly 1 mb at th surfac f arth fr all thr citis. It is sn that th PP is significant within 5 km and abv it bcms ngligibl. Frm balln data, PP fluctuats randmly and is bsrvd as 17 mb at surfac and rmains cnstant till 1.5 km altitud. It suddnly rducs t 7.5 mb at apprximat km, thn it gradually incrass till 3.8 km altitud and again rducs t apprximatly 0 mb at apprximat 4 km. Aftr fw mr variatins it bcms 0 mb at 5 km altitud. Accrding t MOPS prvidd data sht, th PP is 6 mb at surfac and bcms 0 mb at 10 km altitud. 6. Estimatin f trpsphric dlay in GPS signals using intrplatd mtrlgical data Fr invstigating th trpsphric dlay (D) crrctins in th GPS signals, th GPS rcivr intgratd with mbil phn may apply th trpsphric rrr crrctin mdls. In this papr tw prminnt mdls, namly Hpfild mdl and EGNOS mdl ar usd t stimat th trpsphric dlay in signals transmittd by th GPS satllit t th mbil rcivr. Fr th analysis, initially, Hydrabad surfac and intrplatd ME data and vntually balln data is utilizd. Estimatin f D with rspct t lvatin angl is shwn in Fig. 5. As th lvatin angl incrass, D xpnntially dcrass. Whn lvatin is 5, th trpsphric dlay is fund t b maximum fr Hpfild mdl (.5 m) as wll as fr EGNOS mdl (15.5 m). h D rducs t apprximatly 1.5 m fr Hpfild mdl and 3 m fr EGNOS mdl, whn lvatin incrass t 90. h stimatin f D with rspct t altitud is shwn in Fig. 6. h D dcrass with incras in altitud fr bth th mdls. h D is bsrvd high at th surfac f th arth, fr Hpfild mdl (13 m) as wll as fr EGNOS mdl (13. m). h D gradually dcrass and bcms 0 m fr bth th mdls nar 40 km altitud. 6.3 Estimatin f trpsphric dlay in GPS signals using balln data h balln data is cllctd frm a suthrn rgin f India frm surfac f arth t 3 km altitud. It is incrpratd by GPS mdls t stimat th trpsphric tim dlay fficintly. h D is stimatd with rspct t lvatin angl and altitud. Estimatin f D with rspct t lvatin angl is shwn in Fig. 7. As th lvatin angl incrass, D xpnntially dcrass. Whn lvatin is 5, th trpsphric dlay is fund t b maximum fr Hpfild mdl (4 m) as wll as fr EGNOS mdl (13.5 m). h D rducs t apprximatly.5 m fr Hpfild mdl and 1.5 m fr EGNOS mdl, whn Fig. 5 Estimatin f trpsphric dlay with rspct t lvatin angl Fig 4 Intrplatin f partial prssur du t watr vapur with rspct t altitud Fig. 6 Estimatin f trpsphric dlay with rspct t altitud

6 164 INDIAN J RADIO & SPACE PHYS, JUNE 013 lvatin incrass t 90. h maximum diffrnc (10 m) in D is bsrvd btwn pints A and B, i.. at 5 lvatin angl. h stimatin f D with rspct t altitud is shwn in Fig. 8. h D is high at th surfac f th arth, fr Hpfild mdl (1.88 m) as wll as fr EGNOS mdl (1.96 m). his is bcaus th trpsphric layr is th thickst fr GPS signals at th surfac f arth. As th altitud incrass, thr is a sharp dcras in D till 16 kms altitud fr bth th mdls. hn, th D gradually dcrass furthr and bcms apprximatly 0 mb at 3 km altitud. Maximum diffrnc (i.. 6 m) btwn bth th mdls is bsrvd at pints A (10 km fr EGNOS) and B (1 km fr Hpfild). h curvs intrsct at pint C, whn thy rach 17 km altitud, and th D is bsrvd as m. abl 3 shws th cmparisn f GPS trpsphric rrr crrctin mdls. At th surfac f arth, th D is bsrvd maximum fr Hpfild mdl (1.88 m) as wll as fr EGNOS mdl (1.96 m) at 0 km altitud. h D bcms apprximatly 0 m fr bth th mdls at 3 km altitud. 6.4 Effct f trpsphric rrr n GPS usr psitin h psitin f a GPS rcivr can b dtrmind by calculating psud rangs frm a minimum f fur GPS satllits. h rangs masurd d nt rprsnt th tru rangs bcaus th signal cming frm a GPS satllit will b affctd by varius rrrs. Aftr making ncssary crrctins t th bsrvd psud rangs, th rcivr psitin and th rcivr clck bias with GPS tim can b dtrmind by using th ppular algrithm knwn as Bancrft Algrithm 14. Fr th analysis, GPS data is cllctd by DL4 plus dual channl GPS rcivr kpt at Osmania Univrsity fr a particular day (19 January 008). Figur 9 shws th variatins in usr psitin rrr, with and withut incrprating trpsphric crrctins, with rspct t lcal tim. Cmparativly, rrr in th usr psitin is fund t b mr whn trpsphric rrr crrctin is nt incrpratd. abl 4 shws th minimum, maximum and man valus f th usr psitin with and withut incrprating trpsphric rrr crrctin. h man valu f usr psitin bfr incrprating trpsphric rrr crrctin was 9.37 m and aftr intrducing th trpsphric rrr crrctin it rducd t 8.47 m apprximatly. abl 3 Cmparisn f trpsphric rrr crrctin mdls usd fr GPS signals Mdl Min D, m Max D, m Man D, m Hpfild EGNOS abl 4 Errr in usr psitin with and withut incrprating trpsphric crrctin Fig. 7 Estimatin f trpsphric dlay with rspct t lvatin angl Errr in usr psitin Withut trpsphric crrctin, m With trpsphric crrctin, m Minimum Maxmum Man Fig.8 Estimatin f trpsphric dlay with rspct t altitud Fig. 9 Errr in usr psitin with and withut incrprating trpsphric crrctin

7 AHMED t al.: ROPOSPHERIC ERROR CORRECION IN ASSISED GPS SIGNALS Estimatin f trpsphric dlay in cllular signals using intrplatd mtrlgical data stimat th trpsphric tim dlay in cllular signals, RCA and LC mdls ar implmntd and analyzd. h LC mdl is basd n th wll knwn Lngth Basd rpsphric (LB) mdl. Hnc, LB mdl is als implmntd. Hydrabad ME data (abl ), which is intrplatd fr varius altituds is usd by ths mdls t stimat th D. h stimatin f D with rspct t lvatin angl is shwn in Fig. 10. It is bsrvd that th D is minimum whn th lvatin angl, is maximum and th dlay is maximum whn th lvatin angl is minimum. At 5 lvatin angl, th maximum dlay is bsrvd fr RCA mdl (7.5 m) and fr LC mdl (1.4 m). h maximum D diffrnc (6 m) is bsrvd btwn pint A and B at 5 lvatin angl fr bth th mdls. In cllular systm, with rspct t arth surfac, th D gradually incrass with incras in altitud upt th nd f trpsphr, i.. 14 km. h D bcms maximum abv th trpsphric layr bcaus th signals rcivd by th mbil usr ar transmittd frm bas statin, which is lcatd within th trpsphr at fixd hight. Estimatin f D with rspct t altitud is shwn in Fig. 11. h maximum D is bsrvd fr th LC Fig. 10 Estimatin f trpsphric dlay with rspct t lvatin angl Fig. 11 Estimatin f trpsphric dlay with rspct t altitud mdl (11.41 m) as wll as fr RCA mdl (9.08 m) at an altitud f 14 km, i.. nd f trpsphr. h dlay is minimum (0 m) at th arth surfac, i.. at 0 km altitud. At 7 km altitud, th maximum D diffrnc (.3 m) is bsrvd btwn pint A and B. h tw curvs intrsct at pint C at 11 km altitud whr th D is ntd as 9 m. abl 5 shws th cmparisn f trpsphric rrr crrctin mdls fr cllular signals. h maximum D is fund fr RCA (9.08 m) and LC (11.4 m) mdls at 14 km altitud. h D is ngligibl (0 m) at arth surfac fr bth th mdls. At 7 km altitud th maximum D diffrnc is bsrvd fr RCA (4.3 m) and LC (7 m) mdls. 6.6 rpsphric ffct n cllular signals in ral tim scnari A standaln GSM mdul (rprsnting cll phn) is kpt at th Rsarch and raining Unit fr Navigatinal Elctrnics (NERU), Osmania Univrsity, Hydrabad. It rcivs signals frm narst bas statins. GSM data sht prvids th psitin f th bas statins in gdtic crdinat systm alng with th cd and nam f th bas statin. GPS rcivr (Nvatl DL4 plus) is als muntd at NERU alng with GSM mdul t dtrmin usr psitin. Frm th GSM and GPS data, th slp distancs and th lvatin angls btwn th usr and th bas statins ar calculatd (abl 6). As th usr mvs frm n cll t anthr cll, th lvatin angl als changs, which rsults in th trpsphric dlay (D) chang. D with rspct t lvatin angl is stimatd. Frm Fig. 1, it can b bsrvd that th D rducs as th lvatin angl incrass. Whn lvatin is 1.5, D is apprximatly abl 5 Cmparisn f trpsphric rrr crrctin mdls usd fr cllular signals RCA mdl LC mdl Altitud, km D, m abl 6 Dtails f bas statins and rspctiv trpsphric dlay Bas statins Lcatin El, dg Slant distanc, km BS1 Ambr Nagar BS O U BS3 Vidya Nagar BS4 Zamistanpur BS5 Padmara Nagar BS6 Ramnagar BS7 Biguda BS8 Warsiguda BS9 Parsigutta

8 166 INDIAN J RADIO & SPACE PHYS, JUNE 013 maximum D is fund at 14 km altitud fr RCA mdl (9.08 m) and LC mdl (11.41 m) and D is ngligibl at arth surfac. In ral tim scnari, D is stimatd with rspct t lvatin angl as wll as slant distanc btwn th usr and bas statin. h maximum D is bsrvd as 0.7 m fr th RCA mdl and 0.4 m fr LC mdl whn th lvatin angl was 1.5. h bhaviur f ths tw mdls is fund t b similar. Fig. 1 rpsphric dlay with rspct t lvatin angl Fig. 13 rpsphric dlay with rspct t slant distanc 0.7 m fr RCA mdl and 0.4 m fr LC mdl. h D rducs t arund 0. m fr RCA mdl and 0.05 m fr LC mdl whn lvatin incrass t 5.5. h slp distanc btwn th bas statin and th usr changs cntinuusly as usr mvs and th rsultant trpsphric ffct is shwn in Fig. 13. h D incrass, whn thr is an incras in slp distanc fr bth th mdls. h maximum D is bsrvd fr th RCA mdl (0.7 m) as wll as fr LC mdl (0.4 m) whn th slp distanc is incrasd t 50 m. h D is minimum fr RCA (0. m) mdl as wll as fr LC (0.05 m) mdl, whn th slp distanc is rducd t 600 m. 7 Cnclusins In this papr, an attmpt is mad t stimat th trpsphric tim dlay by implmnting Hpfild and EGNOS mdl fr GPS signals and RCA and LC mdls fr cllular signals. Intrplatin f mtrlgical paramtrs fr thr diffrnt citis and cmparisn with balln data is prfrmd. Maximum D is fund fr Hpfild (1.88 m) and EGNOS mdl (1.96 m) at th surfac f arth and th D bcms 0 m at 3 km altitud. Similarly, Acknwldgmnt h prsnt wrk has bn carrid ut undr th prjct ntitld, Invstigatin f Atmsphric Effcts n Futur Grund Basd Augmntatin fr GPS Systm spnsrd by Dpartmnt f Scinc and chnlgy, Nw Dlhi, India, vid sanctin lttr N: SR/S4/AS:53/010, datd:1th July 010. Rfrncs 1 L W C Y, Mbil cmmunicatin nginring: hry and applicatins, nd ditin, (McGraw Hill, Nw Dlhi), Agarwal D P & Qing-An-Zng, Intrductin t wirlss and mbil systms, nd ditin (Glbal Enginring, Christpr, USA), Misra Pratap & Michal, GPS prfrmanc in navigatin, Prc IEEE (USA), 87 (1999) pp layr. 5 Ashraf Farha & rry Mr, High spatial variatin trpsphric mdl (Univrsity f Nttingham, ION GPS/GNSS, UK), Sptmbr Hpfild H, w-quartic trpsphric rfractivity prfil fr crrcting satllit data, J Gphys Rs (USA), 74 (18) (1969) pp Pnna N t al., Assssmnt f EGNOS trpsphric crrctin mdl, J Navig (UK), 54 (1) (001) pp RCA, GNSS basd prcisin apprach Lcal Ara Augmntatin Systm (LAAS), Signal-in-Spac Intrfac Cntrl Dcumnt (ICD), RCA/DO-46A, (Radi chnical Cmmissin fr Arnautics, Amrican Institut f Arnautics & Astrnautics, Rstn, VA), Mazhr Chudaray, Bruc Harvy & Chris Rizs, rppshric crrctin fr Lcata whn knwn pint ambiguity rslutin tchniqu is usd in static survy-is rquird?, Papr prsntd at IGNSS sympsium, Australia, Sultana Quddusa, Invstigatins n th nhancmnt f DOP du t Augmntatin f GNSS with psudlits, Ph D hsis, Jawaharlal Nhru chnlgical Univrsity Hydrabad (JNUH), Hydrabad, MOPS, Minimum Opratinal Prfrmanc Standards fr Glbal Psitining Systm/Wid Ara Augmntatin Systm Airbrn Equipmnt, Dcumnt N.RCA/DO-9A, Jun 8, 1998, (RCA SC-159, Amrican Institut f Arnautics & Astrnautics, Rstn, VA), Bancrft S, An algbraic slutin f th GPS quatins, IEEE rans Arsp Elctrn Syst (USA), 1 (1985) pp