1 LI M U Ngy nay, th gii thng tin ngy cng pht trin mt cch a dng v phong ph. Nhu cu v thng tin lin lc trong cuc sng cng tng c v s lng v cht lng, i hi cc dch v ca ngnh Vin Thng cng m rng. Trong nhng nm gn y thng tin v tinh trn th gii c nhng bc tin vt bc p ng nhu cu i sng, a con ngi nhanh chng tip cn vi cc tin b khoa hc k thut. S ra i ca nhiu loi phng tin tin tin nh my bay, tu v tr i hi 1 k thut m cc h thng c khng th p ng c l nh v trong khng gian 3 chiu, ng trc s i hi chnh ph M ti tr 1 chng trnh nghin cu h thng nh v trong v tr. Vi mc ch kho st, nghin cu h thng nh v ny. Do em chn ti Nghin cu k thut nh v GPS cho n tt nghip ca mnh. Ni dung ca n gm 3 chng nh sau: Chng 1: Tng quan v h thng thng tin v tinh Chng 2: H thng nh v ton cu GPS Chng 3: Mt s ng dng ph bin ca GPS Chng 1: Gii thiu v s ra i v pht trin ca h thng GPS, cung cp cc khi nim c bn v thng tin v tinh, nh v, c s l thuyt ca php nh v bng v tinh, phng trnh o m, thit lp m hnh ton hc ca php o cng nh cc ngun gy sai s ca php o. Chng 2: Nghin cu v cu trc ca h thng GPS, k thut nh v GPS, cc nguyn tc v phng php o GPS. ng thi nghin cu v phng php A-GPS nhm tng chnh xc, gim thi gian xc nh v tr, gim mc tiu th nng lng v tng nhy ca thit b thu. Chng 3: Tm hiu v mt s ng dng ca GPS c p dng trong i sng hng ngy.

2

CHNG 1: TNG QUAN V H THNG THNG TIN V TINH

1.1. Khi qut chung v cc h thng dn ng v tinh quc t 1.1.1. Khi qut chung Bt u vo nhng thp nin 1960, h thng v tinh c thit lp c ngha quan trng ca vic dn ng trn tri t. H thng c thit k ch yu cho vic xc nh v tr hng ngy ca tu b. Nhng bt u t nn mng cho vic s dng trong qu trnh dn ng cho cc phng tin trn khng. Cc h thng dn ng v tinh dng cung cp thng tin v v tr, tc v thi gian cho cc my thu mi ni trn tri t, trong mi iu kin thi tit. H thng c th xc nh v tr vi sai s t vi trm mt n vi mt v c th gim xung ch cn vi centimet. Tuy nhin, chnh xc cng cao th yu cu my thu GPS cng phc tp hn v gi thnh v th cng tng theo. 1.1.2. H thng dn ng v tuyn (Radio Navigation) H thng dn ng v tuyn, l h thng nh v s dng h ta mt t, nguyn tc nh v da vo nguyn l giao hi hai cnh bng sng radio:

R1 = R2 =Trong :

(X x1 2 Y( y1 ) (X x2 2 Y( y 2 )

2

)2

m

( ) ( )

)

m

- R1: Khong cch t my pht 1 n my thu. - R2: Khong cch t my thu 2 n my thu. - X, Y: Ta my thu. - x1 , x2 , y1 , y2 : Ta cc my pht 1 v 2. Nguyn tc nh v ca h thng dn ng v tuyn da theo nguyn l giao hi hai cnh bng sng radio c th hin nh hnh 1.1.

3

1.1.2.1.

Hnh 1.1: Nguyn l nh v bng giao hi 2 cnh sng Radio Nguyn l hot ng p dng nguyn l tnh ton thi gian truyn sng v tuyn t v tinh n

my thu nh v t trn i tng cn xc nh xc nh khong cch t v tinh n my thu nh v . Ta bit rng tc sng v tuyn trong khng gian gn bng vn tc nh sng (3.108 m/s), nu my thu c th xc nh chnh xc thi gian khi v tinh bt u gi on tin v thi gian my thu nhn c on tin t c th xc nh c khong cch gia my thu v v tinh theo biu thc:R = c.T

(1.1)

vi

R: khong cch th v tinh n my thu. (m) c : Vn tc nh sng. (c= 3.108 m/s)T : Thi gian truyn sng t my pht n my thu. (s)

Nh vy thc hin th phi ng b chnh xc gia v tinh v my thu GPS th my pht v tinh v my thu GPS c cc m nh thi gi ngu nhin ng nht. Mi v tinh s lin tc pht m ng b ca chng mt cch chnh xc, my thu GPS sau khi thu c m ng b pht t v tinh n s thc hin so snh vi m to ra xc nh thi gian truyn sng. Hiu s thi gian nhn vi tc truyn sng s cho ra kt qu khong cch t my thu n v

4 tinh. Hnh 1.3 m t qu trnh so snh m ca v tinh v m ca my thu GPS xc nh thi gian truyn sng. V tinh Hnh 1.2: Qu trnh so snh m ca v tinh v m ca my thu GPS 1.1.2.2 c im ca h thng - Thit b n gin r tin, d thao tc. - Tm hot ng b hn ch, chnh xc khng cao, n ph thuc vo nhiu yu t: + Thi im o, nhit , m ca khng kh nh hng ti qu trnh truyn lan sng in t. + V tr cn xc nh ta , nh hng ca a hnh phc tp ti s lan truyn ca tia sng. tng tm hot ng ca h thng, ngi ta thng lin kt tng cm gm 3 trm n hiu v tuyn thnh tng chui h thng. Khi ph sng ca h thng rng hn mt trm n l, thng vo khong 1000 dm. 1.2. S ra i ca h thng GPS S ra i ca nhiu loi phng tin tin tin nh my bay, tu v tr i hi 1 k thut m cc h thng c khng th p ng c l nh v trong khng gian 3 chiu, ng trc s i hi chnh ph M ti tr 1 chng trnh nghin cu h thng nh v v dn ng trong v tr. Vi B quc phng M l c quan thit k v iu khin h thng nh v ton cu. Trong nhm tham gia iu hnh d n GPS cn phi k n Phd. Ivan Getting v Phd. Bradford Parkinson gp phn ng k trong d n. Thp nin 1920: Ra i h thng dn ng v tuyn u i chin th gii 2: LORAN, h thng dn ng p dng phng php o lch thi gian ca tn hiu sng v tuyn, do Phng th nghim Bc x i hc MIT (MIT Radiation Laboratory). LORAN cng l h thng nh v

5 trong mi iu kin thi tit thc s u tin, nhng hai chiu (v v kinh ). Nm 1957: V tinh Sputnik ca Nga c phng ln v tr. i hc MIT cho rng tn hiu v tuyn in ca v tinh c th tng ln khi chng tip cn tri t v gim i khi ri kh tri t v do vy c th truy theo v tr t mt t Nm 1959 : TRANSIT, h thng dn ng da trn v tinh hot ng u tin, do Phng th nghim vt l ng dng Johns Hopkins pht trin di s ch o ca TS Richard Kirschner. Mc d khi u Transit c ch to h tr cho i tu ngm ca M nhng nhng cng ngh ny c pht trin c ch tr thnh H thng nh v ton cu. V tinh Transit u tin c phng ln v tr vo nm 1959. Nm 1960 : H thng dn ng o hiu thi gian ba chiu (kinh , v v cao longitude, latitude and altitude) u tin do Raytheon Corporation xut theo yu cu ca Air Force lm h thng dn ng s c s dng vi (with a proposed ICBM) c th t ti lu ng bng chy trn mt h thng ng ray. H thng dn ng c trnh by l MOSAIC (Mobile System for Accurate ICBM Control). tng ny b hng khi chng trnh Mobile Minuteman b hy b vo nm 1961 Nm 1963: Tng cng ty Aerospace Corporation thc hin nghin cu v h thng khng gian lm c s cho h thng dn ng cho phng tin chuyn ng nhanh theo ba chiu khng gian. Vic nghin cu ny trc tip dn ti khi nim v h thng nh v ton cu. Khi nim lin quan n vic o thi gian ti ca tn hiu sng v tuyn c pht i t v tinh c v tr chnh xc bit. o thi gian s cho khong cch ti v tr v tinh bit v ln lt c th xc nh c v tr ca ngi s dng. Nm 1963 Air Force bt u h tr nghin cu ca Aerospace, ch nh nghin cu ny bng D n H thng 621B. Khong nm 1972, chng trnh ny biu din hot ng ca mt loi tn hiu xc nh khong cch v tinh mi da trn ting n ngu nhin gi to (PRN, pseudo random noise).

6 Nm 1964 Timation, h thng v tinh hi qun, c pht trin di s ch o ca Roger Easton Phng nghin cu Hi quan (Naval Research Lab, NRL) ci thin ng h c tnh n nh cao, kh nng truyn thi gian, v dn ng 2 chiu. Hot ng ca Timation theo tiu chun thi gian chun v tr cung cp c s quan trng cho h thng nh v ton cu. V tinh Timation u tin c phng ln v tr vo thng 5 nm 1967. Nm1968: B Quc phng M (DoD, Department of Defence, USA) thnh lp mt y ban gi l y ban Th hin V tinh Dn ng (NAVSEC, Navigation Satellite Executive Committee) phi hp n lc ca cc nhm dn ng v tinh (Transit ca Hi qun, Chng trnh Timation, v SECOR ca Qun i, hay cn gi l H thng ng tng quan khong cch chui (Sequential Correlation of Range System). NAVSEC k hp ng mt s nghin cu lm sng t khi nim dn ng v tinh c bn. Nhng nghin cu ny v mt s vn chnh xung quanh khi nim nh la chn tn s sng mang (di L i lp vi di C), thit k cu trc tn hiu, v la chn nh hnh qu o v tinh. Nm 1969-1972 NAVSEC qun l cc tho lun khi nim gia cc nhm dn ng v tinh khc nhau. APL Hi qun ng h nhm Transit m rng, trong khi NRL Hi qun ng h cho Timation m rng, cn Air Force th ng h cho chm sao ng b m rng, tc d n H thng 621B. Thng 4 nm 1973 Th trng B Quc phng quyt nh thit lp mt chng trnh hp tc ba dch v thng nht nhng khi nim khc nhau v nh v v dn ng thnh mt h thng B quc phng hn hp gi l H thng v tinh dn ng quc phng (Defense Navigation Satellite System). Air Force c ch nh lm ngi qun l (iu hnh) chng trnh. H thng mi c pht trin qua vn phng chng trnh kt hp (joint program office), vi s tham gia ca tt c quan chng quc phng. i t Brad Parkinson c ch nh lm ngi ch o vn phng chng trnh kt hp v c t trng trch

7 pht trin kt hp khi nim ban u v h thng dn ng da trn khng gian (space-based navigation system) Thng 8 nm 1973 H thng u tin c trnh by ti Hi ng Thu nhn v Thm nh H thng Quc phng (Defense System Acquisition and Review Council, DSARC) b t chi thng qua. H thng c trnh ln DSARC c gi gn trong H thng 621B ca Air Fore v khng i din cho chng trnh kt hp. Mc d c ngi ng h tng ca h thng dn ng da trn v tinh mi nhng Vn phng Chng trnh Kt hp c thc y khn trng tng qut ha khi nim bao gm xem xt v yu cu tt c cc binh chng quc phng. Ngy 17/12/1973 Mt khi nim mi c trnh ti DSARC v c thng qua thc hin v cp kinh ph l h thng NAVSTAR GPS, nh du khi u cng nhn khi nim ( tng) (Giai on I ca chng trnh GPS). Khi nim mi thc s l mt h thng dn xp (tha hip compromise system) do i t Parkinson thng lng kt hp tt nht gia tt c nhng khi nim v cng ngh dn ng v tinh c sn. Cu hnh h thng c thng qua bao gm 24 v tinh chuyn ng trong nhng qu o nghing chu k 12 gi ng h. Thng 6 nm 1974 Hng Rockwell International c chn lm nh cung cp v tinh cho chng trnh GPS. Ngy 14 thng 7 nm 1974 V tinh NAVSTAR u tin c phng ln v tr. V tinh ny c ch nh l V tinh Cng ngh Dn ng (NTS) s 1, v c bn y l v tnh Timation tn trang li do NRL ng. V tinh th hai (l v tinh cui cng) ca nhm NTS c phng vo nm 1977. Nhng v tinh ny c s dng cho vic xut nh gi khi nim ( tng) v thc hin nhng ng h nguyn t u tin c phng vo trong khng gian (v tr). Nm 1977: Thc hin kim tra thit b ngi s dng Yuma, Arizona. Ngy 22/2/1978: V tinh Block I u tin c phng. Ton b 11 v tinh Block I c phng trong khong thi gian 1978 v 1985 trn Atlas-Centaur.

8 Nhng v tinh Block I do Rockwell International xy dng c coi l nhng v tinh mu pht trin c dng kim tra h thng. B mt mt v tinh do phng trt. Ngy 26/4/1980: Phng v tinh GPS u tin thc hin nhng b cm ng H thng pht hin ting n ht nhn hot ng tng hp (Integrated Operational Nucluear Detonation Detection System (IONDS) sensors). Nm 1982: B Quc phng thng qua quyt nh gim s v tinh ca chm v tinh GPS t 24 xung 18 tip theo sau ti cu to li chng trnh chnh do Quyt nh 1979 ca Vn phng Th k B Quc phng gy ra ct gim kinh ph 500 triu la (khong 30%) t ngn sch cho giai on nm ti chnh FY81-FY86. Ngy 14/7/1983 Phng v tinh GPS u tin thc hin h thng d tm ting n ht nhn (NDS) mi hn. Ngy 16/9/1983 Theo (the Soviet downing of Korean Air flight 007), tng thng Reagan ha cho GPS c s dng cho cc my bay dn dng hon ton min ph khi h thng a vo s dng. S kin ny nh du s bt u lan ta cng ngh GPS t qun s sang dn s. Nm 1984: Kho st tr thnh mt th trng GPS thng mi u bng c nng cnh! b cho s v tinh gii hn c sn trong qu trnh pht trin chm v tinh, cc nh kho st chuyn qua s k thut nng cao chnh xc bao gm k thut GPS Vi phn (DGPS) v k thut truy theo pha sng mang (carrier phase tracking). Thng 4 1985 Hp ng thit b ngi s dng chnh u tin c giao cho JPO. Hp ng bao gm vic nghin cu, pht trin cng nh la chn sn xut cc my thu GPS dng cho my bay, tu thy v my thu xch tay (gn nh). Nm 1987: B Quc phng chnh thc yu cu B Giao thng (Department of Transport, DoT) c trch nhim thit lp v cung cp mt vn phng p ng nhu cu ngi s dng dn s v thng tin GPS, d liu v h

9 tr k thut. Thng 2 nm 1989, Coast Guard c trch nhim lm i l hng dn Dch v GPS Dn s (civil GPS service). Thng 3/1988 Th k Air Force thng bo v vic m rng chm GPS ti 21 v tinh cng thm 3 v tinh d phng. Ngy 14/2/1989 V tinh u tin ca cc v tinh Block II c phng t Cape Canaveral AFT, Florida, trn dn phng Delta II (Delta II booster). Phi thuyn con thoi (Space Shuttle) lm b phng theo k hoch cho cc v tinh Block II c Rockwell Intenational ng. Tip theo tai nn Challenger 1986, Vn phng Chng trnh Kt hp (JPO) xem xt li v s dng Delta II lm b phng v tinh GPS. SA (Selective Availabity) v AS (Anti-spoofing). Ngy 21/6/1989 Hng Martine Marietta (sau khi mua xong General Electric Astro Space Division vo nm 1992) c thng hp ng xy dng 20 v tinh b sung (Block IIR). Chic v tinh Block IIR u tin sng sng phng vo cui nm 1996. Nm 1990 Hng Trimble Navigation, nh sn xut bn my thu GPS hng u th gii c thnh lp nm 1978 hon thnh lot sn phm ban u. Ngy 25/3/1990 Do theo K hoch Dn ng V tuyn Lin bang, ln u tin khi ng (kch hot) SA (Selective Availability) lm gim chnh xc dn ng GPS c ch nh. Thng 8/1990 SA c tt i trong chin tranh vnh Ba t (Persian Gulf War). Nhng yu t ng gp vo quyt nh tt SA bao gm vic ph sng ba chiu c gii hn c chm NAVSTAR cung cp trong qu o vo thi gian v s my thu m s chnh xc (Precision (P)-code) trong bn kim k ca DoD. DoD mua hng nghn my thu GPS dn dng ngay sau khng lu dng cho lc lng lin minh trong cuc chin tranh. - H GPS l h thng bao gm cc v tinh bay trn qu o, thu thp thng tin ton cu v c x l bi cc trm iu khin trn mt t. Ngy nay, kh hnh dung rng c mt my bay, mt con tu hay phng tin thm him

10 trn b no li khng lp t thit b nhn tn hiu t v tinh. H GPS l h thng dn ng bng v tinh do Hoa K kim sot v duy tr hot ng. Nhng v tinh tr gi nhiu t USD ny bay pha trn tri t cao 20.200 km (11.900 NM ), vi tc chng 11.200 km/h, c nhim v truyn i cc tn hiu radio tn s thp ti cc thit b thu nhn. T nhng nm u thp k 80, cc nh sn xut ln ch nhiu hn n i tng s dng t nhn. Trn cc xe hi hng sang, nhng thit b tr gip c nhn k thut s PDA (Personal Digital Assistant), c coi l mt trang b tiu chun, th hin gi tr ca ch s hu. - V tinh GPS u tin c phng nm 1978. - Mi v tinh c lm hot ng ti a l 10 nm. - V tinh GPS c trng lng khong 1500 kg v di khong 17 b (5 m) vi cc tm nng lng Mt Tri m (c rng 7 m). - Cng sut pht bng hoc di 50 watts. 1.3. C s ca php nh v bng v tinh xc nh v tr ca mt vt th bng v tinh (nh v im) ta cn s dng v tinh lm cc im tham chiu, ngha l ta cn tnh c khong cch t vt th n cc v tinh ny (Hnh 1.3). y ta bit trc v tr r j ca v tinh th j (pht ra tn hiu) v mun xc nh v tr Ri ca anten th i (thit b thu tn hiu v tinh) do ta cn phi o vector c ly eijIj gia 2 v tr ni trn (eij l vector n v). Khi ty thuc vo cch thc o vector c ly, chng ta c th c nhng k thut nh v v tinh khc nhau v xc nh c v tr ca anten th i theo cng thc sau:Ri = r j eij i j

(1.2)

11

Hnh 1.3: V tr cc vt th c xc nh qua 4 php o Do v tr ca v tinh thay i theo thi gian nn vic d on mt cch chnh xc v tr ca v tinh rj(t) ti mt thi im no l rt kh khn. Nhim v d on qu o hay lch thin vn (ephemeris) ca v tinh i hi phi c kin thc c bit v ng lc hc v tinh m ngi vn hnh h thng cn phi quan tm. Gi s ta b qua sai s ng h my thu trn vt th i v o c c ly t vt th i n v tinh 1 l i1, ngha l vt th i ang nm trn mt mt cu (S 1) c tm l v tinh 1 (C1) v bn knh l i1. Tip theo ta thc hin php o c ly t vt th i n v tinh 2 v nhn c kt qu l i2, iu ny cho chng ta bit rng vt th i khng ch nm trn mt cu (S1) m cn nm trn mt cu (S2) cch v tinh 2 (C2) mt khong cch l i2. Ni cch khc, vt th i s nm trn ng trn (O) do 2 mt cu (S1), (S2) ct nhau to ra. Nu chng ta tip tc o c c ly t vt th i n v tinh 3 l i3 th v tr chnh xc ca n l mt trong hai giao im P1, P2 ca mt cu (S3) vi ng trn (O), nh hnh 1.4. Nh vy, bng cc php o c ly t vt th i n 3 v tinh, ta c th xc nh c 2 v tr c th c ca n trong khng gian. xc nh v tr no l v tr tht ta c th thc hin 1 php o b sung, tuy nhin 1 trong 2 v tr tnh c t php o ny s cho mt kt qu khng ph hp (hoc l rt xa tri t, hoc l chuyn ng vi vn tc v cng ln) v do c th b qua m khng cn phi thc hin php o ny.Ba php o c ly trn cho ta 3 phng trnh c

12 lp vi nhau cn thit xc nh 3 n s. 3 n s ny l ta (x, y, z) ca vt th i trong khng gian 3 chiu. V tinh th j (o c) eijij rj ( bit) Anten th i P (cn tm) Ri Mt t

C (Gc ta ) (Tm tri t) Hnh 1.4: nh v im bng v tinh Khi k n sai s ng h my thu, tt c cc php o c ly ng thi u b lch bi gi tr sai s ny. Do , trong bt k mt tp hp cc php o c ly ng thi no, chng ta cng cn phi xc nh y 4 n s (3 n s v tr, 1 n s thi gian), ngha l cn 4 phng trnh hay 4 php o c ly n v tinh xc nh v tr duy nht ca vt th 1.3.1. Nguyn l o c ly trong php nh v v tinh 1.3.1.1. M gi ngu nhin (Pseudo Random Code - PRC) L thnh phn c bn ca GPS, gm cc m s (digital code) rt phc tp, hay ni cch khc n l mt chui lin tip cc xung nh phn 0 v 1 (hnh 1.5).

Hnh 1.5: M gi ngu nhin PRC Tn hiu ny phc tp gn nh l cc nhiu in t ngu nhin nn c gi l m gi ngu nhin. N c nhim v bo m cho my thu khng ng b ngu nhin vi tn hiu khc. Ngoi ra, do mi v tinh c mt m PRC duy nht ring bit nn iu ny cng bo m rng my thu s khng tnh c bt c tn hiu ca v tinh khc, v vy cc v tinh c th s dng cng tn s m

13 khng lm nhiu ln nhau. Khng nhng vy, vic s dng m PRC ny cn gip cho qu trnh x l v khuch i tn hiu da trn l thuyt thng tin c thc hin d dng hn, gip ti u ha anten thu v tit kim chi ph. 1.3.1.2 Gi c ly L c ly o c gia v tinh v my thu khi k n cc sai s ng h (ng h my thu v v tinh) cng nh cc ngun sai s khc (sai s do lch thin vn, do tng in ly, do tng i lu, ). Cc c ly o c trn hnh 1.8 trn chnh l cc s o gi c ly cn thit xc nh v tr ca vt th i c tnh theo cng thc sau:pri j = i j + c.T

(1.3)

trong prij : gi c ly gia vt th i v v tinh th j

ij : c ly tht gia vt th i v v tinh th jc : vn tc nh sng (3.108 m/s);

T : cc ngun sai s.1.3.1.2. o c ly bng sng xung v sng lin tc Cc h thng o c ly thng dng cc tn hiu xung hoc cc tn hiu sng lin tc. Mi phng php u c nhng u khuyt im ring v u c th s dng trong php o mt chiu hoc hai chiu. H thng nh v v tuyn ton cu l h thng o c ly mt chiu c kh nng s dng c hai loi: sng xung dng trong v sng lin tc. 1.3.1.3. Nguyn l o c ly c bn Bng cch xc nh khong thi gian truyn tn hiu t v tinh n my thu ta c th tnh ton c c ly gia chng nh vo cng thc: C ly = vn tc x thi gian hay = c.t (1.4) Vn y l lm sao tnh ton c thi gian truyn tn hiu gia chng. thc hin iu ny chng ta gi s rng c v tinh v my thu u pht ra cc m PRC ging nhau vo cng mt thi im. Lc ny ti my thu ta

14 nhn c 2 phin bn m khng ng thi, 1 phin bn m ca my thu v 1 phin bn m t v tinh s n tr hn mt khong thi gian do phi tri qua mt qung ng kh xa t v tinh n my thu. Nh vy da vo khong thi gian tr trn ta c th xc nh c c ly mt cch d dng. M nhn c t v tinh

M do my thu to ra thiu ngu nhin trong my thu tng quan (correlator).

Thi tr

Thi tr c xc nh bng cch s dng nguyn l tng quan tn c ly) (Gi

Hnh 1.6: Phng php o gi c ly Gi c ly l tch ca tc nh sng v tr bin i thi gian cn thit so hng mt phin bn m c pht t my thu vi mt phin bn m khc nhn c t v tinh. Trn l thuyt, tr bin i thi gian l tr chnh lch gia thi gian nhn tn hiu (c o bng h thi gian ca my thu) v thi gian pht tn hiu (c o bng h thi gian ca v tinh). Trn thc t, hai h thi gian ny khng ging nhau, mi h tc ng mt sai lch vo tr s . V vy cc s o thi tr sai lch ny c xem l nhng s o gi c ly. 1.3.2. Cc ngun gy sai s trong php o Nh chng ta bit xc nh v tr ca mt vt th, ta cn phi tnh ton c khong cch t n n 4 v tinh da vo php o khong thi gian truyn tn hiu sng in t t cc v tinh n vt th ny. Do chnh xc ca ng h v tinh v ng h my thu l cc thng s rt quan trng nh hng n cc php o c ly cn thit. Ngoi ra, cc yu t khc nh tng in ly, tng i lu, qu o v tinh, n ca my thu, nhiu

15 a ng (multipath)... cng gp phn gy ra cc sai s khng nh trong cc php o c ly ny.Qu o v tinh ng h v tinh Tn hiu truyn t v tinh n my thu b sai s v b tr

28.000km

ng h my thu Nhiu a ng200km 50km

Nhiu my thu

Hnh 1.7: Cc ngun tc ng khc nhau gy ra sai s trong php o c ly 1.3.2.1. ng h v tinh Sng in t truyn i trong khng gian xp x vn tc nh sng (3.108m/s) nn ch cn sai s 1ns s gy ra sai s khong cch 30cm. V vy, ngi ta trang b cho cc v tinh cc ng h nguyn t (Cesium) rt chnh xc. Cc ng h ny tuy c chnh xc cao vn tch ly sai s 1ns sau mi 3 gi, do gii quyt vn ny, chng s c lin tc theo di bi cc trm mt t v c so snh vi h thng ng h iu khin trung tm gm 10 ng h nguyn t khc. Sau khi c tnh ton k lng, sai s v tri ng h v tinh c km vo cc thng ip m v tinh pht i. Khi tnh ton khong cch n cc v tinh, my thu GPS s ly thi gian truyn tn hiu nhn c tr i cc sai s ny xc nh thi gian truyn tn hiu thc s. Mc d cc trung tm iu khin mt t c gng ht sc lin tc theo di hot ng ca cc ng h v tinh, chng vn khng th xc nh cc sai s mt cch chnh xc c. Do cc v tinh vn gy ra sai s ng h tiu biu khong vi nano giy v sai s khong cch khong 1m. 1.3.2.2. ng h my thu

16 Tng t nh ng h v tinh, bt k sai s no trong ng h my thu cng gy ra sai s trong cc php o khong cch. Tuy nhin khng thc t khi trang b cho cc my thu ny cc ng h nguyn t v chng kh nng (khong 20kg), c gi c rt mc (50.000USD) v rt b nh hng bi nhit . Gi s rng, ti mt thi im no , ng h my thu c sai s 1ms v do gy ra sai s khong cch 300.000 m. Nu cc khong cch n tt c cc v tinh c o chnh xc vo cng mt thi im th tt c khong cch ny u b lch 300.000 m. V vy, ta c th xem sai s ng h my thu l mt trong cc n s cn tm v cng l l do m ti sao khi xc nh v tr ta cn thc hin cc php o c ly n 4 v tinh, ngha l cn 4 phng trnh gii ra 4 n s (3 n s v tr x, y, z v 1 n s thi gian l sai s ng h my thu), v t gip ta c th s dng ng h r tin v gn nh hn trong my thu. Ch rng vic xem sai s ng h my thu l 1 n s ch hp l nu ta thc hin cc php o c ly n cc v tinh chnh xc vo cng mt thi im. Nu cc php o ny khng xy ra ng thi th i vi mi php o s c mt sai s ng h khc nhau. Thc hin cc php o ng thi n 4 v tinh, ta khng nhng tnh ton c v tr 3 chiu m cn xc nh c sai s ca ng h my thu vi chnh xc rt cao. Mt ng h tiu biu c tri khong 1000ns mi giy nhng bng phng php trn ta c th iu chnh thi gian my thu t chnh xc bng vi ng h GPS v bin ng h my thu r tin ny tr thnh mt ng h nguyn t c chnh xc cao. My thu hiu chnh ng h ca n mi giy v cung cp mt tn hiu thi chun cho cc ng dng bn ngoi. Nu chng ta t my thu ti mt v tr chnh xc bit th ta ch cn theo di 1 v tinh tnh ton sai s ng h my thu v iu chnh n. Bn v tinh l s lng ti thiu m chng ta cn tnh ton v tr v thi gian. Cng s dng nhiu v tinh th kt qu o nhn c cng chnh xc hn. 1.4. Sai s qu o v tinh Nh tho lun cc phn trn, chnh xc ca v tr cn tnh ton cng ph thuc vo cch xc nh v tr chnh xc ca cc v tinh (c xem l

17 cc im tham chiu). Qu o ca cc v tinh lin tc c theo di t nhiu trm gim st nm xung quanh tri t v thng tin qu o d on c truyn n cc v tinh, t v tinh cung cp cc thng tin ny cho my thu. chnh xc tiu biu ca vic tin on qu o ny vo khong vi mt v do cng s gy ra sai s khong vi mt khi tnh ton v tr. My thu duy tr mt bng nin gim d liu qu o cho tt c cc v tinh v chng cp nht cc bng ny mi gi khi c d liu mi. 1.4.1. Sai s do tng in ly Khi tnh ton khong cch n v tinh, u tin ta o khong thi gian truyn tn hiu t v tinh n my thu v sau nhn khong thi gian ny vi vn tc nh sng. Vn y l vn tc ny thay i ph thuc vo tnh trng ca tng kh quyn. Lp trn ca tng kh quyn gi l tng in ly gm cc ht mang in, gy tc ng lm chm tn hiu m v nhanh tn hiu sng mang. nh hng ca tng in ly nu khng c khc phc c th gy ra sai s php o ln hn 10m. Vi my thu s dng m hnh ton hc tnh ton nh hng ca tng in ly v xc nh gn ng mt cc ht mang in nn c th gim c nh hng ca tng ny khong 50% tuy nhin sai s cn li vn ng k.

hnh 1.8: Sai s do tng in ly

18 Tr nhiu tng kh quyn:

I : l s ca electron trn mt n v Tc ng ca tng in ly i vi tn hiu in t ph thuc vo tn s ca n. Tn s cng cao th nh hng cng t. Do ta c th s dng 2 tn s sng mang khc nhau o tr sai lch gia 2 tn hiu ny v t loi b c nh hng ca tng in ly. chnh l l do ti sao m tt c cc v tinh GPS truyn thng tin bng 2 tn s L1, L2. My thu chnh xc (my thu 2 tn s) ch yu phc v cho qun s theo di c 2 tn hiu L1, L2 v thc hin cc k thut phc tp trch ra cc tn hiu m v sng mang nhm loi b nh hng ca tng in ly. My thu khng chnh xc (my thu n tn) phc v ch yu trong dn s ch theo di 1 tn hiu L1. y l 1 trong nhng c im phn bit chnh gia 2 loi my thu ny. 1.4.2. Sai s do tng i lu Lp thp hn ca tng kh quyn cha ng hi nc c gi l tng i lu, gy tc ng lm chm c tn hiu m ln tn hiu sng mang. Ta khng th loi b nh hng ca tng i lu bng cch s dng h thng 2 tn s.Phng php duy nht loi b nh hng ca tng i lu l tin hnh php o lng hi nc, nhit , p sut ca n v p dng mt m hnh ton hc c th tnh ton tr gy ra bi tng ny. 1.4.3. Nhiu a ng Khi o khong cch n mi v tinh, ta gi s rng tn hiu v tinh c truyn thng t v tinh n anten ca my thu. Nhng trong thc t ngoi tn hiu trc tip ny anten my thu cn nhn c cc tn hiu phn x n t mt t v cc vt th gn anten qua nhiu

19 ng gin tip khc nhau, xen nhiu vo tn hiu trc tip, gy ra sai lch v thi im n ca tn hiu thc s. Nu ng truyn gin tip di hn ng k so vi ng truyn trc tip (ln hn 10m) hai mu tn hiu trn tch ri nhau th nh hng gy ra bi nhiu a ng v c bn c th c khc phc bi cc k thut x l tn hiu. Cc sai s ca my thu My thu c th gy ra vi sai s khi thc hin php o m hay sng mang. Tuy nhin, trong cc my thu cht lng cao cc sai s ny khng ng k, nh hn 1mm i vi php o pha sng mang v vi cm i vi php o pha m.Direct signal

Antenna Antenna image

Reflected signal Ground

Excess of optical path

Hnh 1.9: Nhiu a ng (Bn dch ra ting vit i nh) 1.5. Tng kt chng 1 Trong chng 1 n gii thiu 1 cch tng quan v h thng thng tin v tinh, s ra i v pht trin ca h thng GPS. Trong chng ny cng ch ra c s ca php nh v bng v tinh, cc ngun gy sai s trong php o GPS. y cng l c s nghin cu v cch khc phc cc sai s ny v c nghin cu chng tip theo.

20 CHNG 2: H THNG NH V TON CU GPS 2.1.Cu trc h thng GPS H thng nh v ton cu GPS bao gm 3 b phn cu thnh, l phn khng gian (space segment), phn iu khin (control segment), phn ngi s dng (user segment). Chng ta s ln lt tm hiu c th v tng b phn cu thnh ca h thng v chc nng ca chng.

Hnh 2.1: Cc thnh phn cu to ca h thng GPS 2.1.1. Phn khng gian (Space Segment) 2.1.1.1. Chm v tinh GPS Bao gm 24 v tinh bay trn qu o c cao ng nht 20200 km, chu k 12 gi, phn phi u trn 6 mt phng qu o nghing vi xch o mt gc 55o. Vic b tr ny nhm mc ch ti mi thi im v mi v tr trn tri t u c th quan st c 4 v tinh. Mi v tinh pht 2 tn s sng mang vi tn s cao L1=1575.42 MHz v L2=1227.60 MHz. Loi sng ny pht trn c s dy s ta ngu nhin bao gm cc s 0 v 1. M ny c gi tn l m P (Precise). Bn cnh m P sng cn mang i m C/A (Clear/Acquisition) trong sng L1. M C/A c pht vi 2 tn s 10.23 MHz v 1.023 MHz. Ngoi 2 m trn v tinh cn pht m ph c tn s 50 Hz cha cc thng tin v lch v tinh. Cc v tinh u c trang b ng h nguyn t vi chnh xc cao.

21

Hnh 2.2 : Cc qu o ca v tinh trong h thng GPS Cc v tinh NAVSTAR c 2 trng thi: "hot ng khe" (Healthy) v "hot ng khng kho (Unhealthy). Hai trng thi ca v tinh ny c quyt nh do 4 trm iu khin mt t. Chng ta c th s dng tn hiu ca cc v tinh c hai trng thi "hot ng khe" v "hot ng khng khe". 2.1.1.2. Cu trc tn hiu GPS Mi v tinh u truyn hai tn s dng cho cng vic nh v l tn s 1575,42 MHz v tn s 1227,60 NHz. Hai sng mang ny gi l L1 v L2, rt mch lc v c iu ch bi nhng tn hiu khc nhau. M nhiu gii ngu nhin (PRN) th nht c bit di ci tn l m C/A (Coarse/Acquisite-code), bao gm mt chui cc s cng mt v tr mt, c pht i tn s f0/10= 1.023 MHz. Chui ny c lp li sau mi mili giy ng h. M nhiu gii ngu nhin (PRN) th hai, c bit di ci tn l m P (Precise - code), bao gm mt chui cc s cng mt v tr mt khc, c pht i tn s f0 = 10,23 MHz. Chui ny ch lp li sau 267 ngy. Thi gian 267 ngy ny c ct ra lm 38 on 7 ngy. Trong 38 on ny c mt on khng dng n, 5 on dng cho cc trm mt t , theo di cc tu thuyn s dng, gi l trm gi v tinh (Pseudolite), cn li 32 on 7 ngy dnh cho nhng v tinh khc nhau. Bng cch ny P- code rt kh b gii m s dng nu khng c php. M Y (Y-code) l m PRN tng t nh m P, c th dng thay cho m P. Tuy nhin phng trnh to ra m P th c cng b rng ri v khng gi b mt, trong khi phng trnh to ra m Y th gi b mt. V vy, nu m Y c s dng th nhng ngi s dng GPS khng c giy php

22 (ni chung l nhng ngi khng thuc qun i M v ng minh ca h) s khng thu c m P (hoc m Y). Sng mang L1 c iu ch bng c 2 m (M-C/A v M`-P hoc m Y), trong khi sng mang L2 ch bao gm mt M-P hoc m Y. Cc m c iu ch trn sng mang bng cch gin n c thc. Nu m c tr s -1 th phase sng mang i 180 0, cn nu m s c tr s +1 th phase sng mang gi nguyn khng thay i. C hai sng mang u mang thng bo v tinh (Satellite message) cn pht di dng mt dng d liu c thit k tn s thp (50Hz) thng bo ti ngi s dng tnh trng v v tr ca v tinh. Cc d liu ny s c cc my thu gii m v dng vo vic xc nh v tr ca my theo thi gian thc. 2.1.2. Phn iu khin (Control Segment) Phn iu khin l duy tr hot ng ca ton b h thng GPS cng nh hiu chnh tn hiu thng tin ca v tinh h thng GPS. Phn ny bao gm 8 trm mt t trong c 4 trm theo di (Monitor Station): Diego Garcia (n Dng ), Ascension Islend (i Ty Dng ), Kwajalein (Ty Thi Bnh Dng ) v Hawaii (Thi Bnh Dng ); mt trm iu khin trung tm (Master Control Station) v 3 trm hiu chnh s liu (Upload Station). Li trc a t trn 4 trm ny c xc nh bng phng php giao thoa ng y di (VLBI). Trm trung tm lm nhim v tnh ton li ta ca cc v tinh theo s liu ca 4 trm theo di thu c t v tinh. Sau tnh ton cc s liu c gi t trm trung tm ti 3 trm hiu chnh s liu v t gi tip ti cc v tinh. Nh vy trong vng 1 gi cc v tinh u c mt s liu c hiu chnh pht cho cc my thu.

23

Hnh 2.3 : Phn iu khin v tinh trong h thng GPS

Hnh 2.4 : V tr t trm iu khin GPS trn mt t 2.1.3. Phn s dng (User Segment) Phn s dng bao gm cc my thu tn hiu t v tinh trn t lin, my bay v tu thy. Cc my thu ny phn lm 2 loi: my thu 1 tn s v my thu 2 tn s. My thu 1 tn s ch nhn c cc m pht i vi sng mang L1. Cc my thu 2 tn s nhn c c 2 sng mang L1 v L2. Cc my thu 1 tn s pht huy tc dng trong o ta tuyt i vi chnh xc 10 m v ta tng i vi chnh xc t 1 n 5 cm trong khong cch nh hn 50 km. Vi khong cch ln hn 50 km chnh xc s gim i ng k ( chnh xc c dm). o c trn nhng khong cch di n vi nghn km chng ta phi s dng my 2 tn s kh i nh hng ca tng ion trong kh quyn tri t. Ton b phn cng GPS hot ng trong h thng ta WGS-84 vi kch thc elipsoid a=6378137.0 m v =1:29825722.

24

Hnh 2.5 : Phn thit b s dng dn ng GPS 2.1.3.1. Cc b phn ca mt thit b GPS trong phn s dng.

Phn s dng GPS c th c coi gm 3 b phn chnh: * Phn cng * Phn mm * Phn trin khai cng ngh Phn cng bao gm my thu mch in t , cc b dao ng tn s v tuyn RF (Radio Friquency), cc ngten v cc thit b ngoi vi cn thit hot ng my thu. c im chnh yu ca b phn ny l tnh chc chn, c th xch tay, tin cy khi lm vic ngoi tri v d thao tc. Phn mn bao gm nhng chng trnh tnh dng x l d liu c th, chuyn i nhng thng bo GPS thnh nhng thng tin nh v hoc dn ng i hu ch. Nhng chng trnh ny cho php ngi s dng tc ng khi cn c th li dng c nhng u im ca nhiu c tnh nh v GPS. Nhng chng trnh ny c th s dng c trong iu kin ngoi nghip v c thit k sao cho c th cung cp nhng thng bo hu ch v trng thi v s tin b ca h thng ti ngi iu hnh. Ngoi ra trong phn mm cn bao gm nhng chng trnh pht trin tnh c lp ca my thu GPS , c th nh gi c cc nhn t nh tnh sn sng ca v tinh v mc tin cy ca chnh xc. Phn trin khai cng ngh hng ti mi lnh vc lin quan n GPS nh: ci tin thit k my thu, phn tch v m hnh ho hiu ng ca ngten khc

25 nhau, hiu ng truyn sng v s phi hp ca chng trong phn mm x l s liu, pht trin cc h thng lin kt truyn thng mt cch tin cy cho cc hot ng nh v GPS c ly di v ngn khc nhau v theo di cc xu th pht trin trong lnh vc gi c v hiu sut thit b. 2.1.3.2. Nhng b phn chnh ca my thu GPS.

Cc b phn c bn ca mt my thu GPS bao gm: * ngten v b tin khuch i * Phn tn s v tuyn (RF) * B vi x l * u thu hoc b iu khin v th hin * Thit b ghi chp * Ngun nng lng ngten v b tin khuch i : Cc ngten dng cho my thu GPS thuc loi chm sng rng , v vy khng cn phi hng ti ngun tn hiu ging nh cc a ngten v tinh . Cc ngten ny tng i chc chn v c th t trn ba chn hoc lp trn cc phng tin giao thng, vi tr thc s c xc nh l trung tm Phase ca ngten, sau c truyn ln mc trc a. Phn tn s v tuyn : Bao gm cc vi mch in t x l tn hiu v kt hp s ha v gii tch. Mi kiu my thu khc nhau dng nhng k thut x l tn hiu khc nhau i cht, cc phng php ny l : * Tng quan m * Phase v tn s m * Cu phng tn hiu sng mang Phn tn s v tuyn: bao gm cc knh s dng mt trong ba phng php ni trn truy cp cc tn hiu GPS nhn c, s lng cc knh bin i trong khong t 1 n 12 tu theo nhng my thu khc nhau. B iu khin: Cho php ngi iu hnh can thip vo b vi x l. Kck thc v kiu dng ca b iu khin cc loi my thu khc nhau cng khc nhau.

26 Thit b ghi : Ngi ta dng my ghi bng t hoc cc a mm ghi cc tr s quan trc v nhng thng tin hu ch khc c tch ra t nhng tin hiu thu c. Ngun nng lng : Phn ln cc my thu u dng ngun in mt chiu in p thp, ch c mt vi my i hi phi c ngun in xoay chiu. 2.2. c im k thut ca h thng GPS 2.2.1. ng h GPS Trong hu ht cc h thng nh v, thi gian chnh xc l mt thng s v cng quan trng. h thng nh v GPS thi gian chnh xc c to bi ng h nguyn t. ng h nguyn t c chnh xc cao hn ng h quart. tri dt n nh o c l : 1013 s. Trong thc t mi v tinh block1 c ti 4 ng h nguyn t hot ng: + Hai ng h l chun tn s da trn pht x Cacsium. + Hai ng h l chun tn s da trn iu khin kh Rubidium. Ngoi ra cn c nhiu b dao ng quart rt n nh, 4 ng h va h tr cho nhau va gim st ln nhau nhm a ra chnh xc nht. Vic gim st ny cng c s dng nhm tha mn cc yu cu iu chnh ng h trn cc v tinh block2. Cc ng h Rubidium c n nh thp hn mt cht so vi ng h Casium, trong mt khong thi gian di vi mt tc tri dt l: 1012 s. Tt c cc ng h ca h thng GPS c t hot ng tn s 10.23 MHz. Cc m pht v sng mang l mt hm t l vi tn s ng h c s ny. Tuy nhin cc ng h vn b sia lch do chuyn ng, cc ng h khng th t iu chnh c, vic iu chnh ng h do trm trung tm di mt t thc hin. Cc gi tr hiu chnh c pht cho cc v tinh, c trong nhng bn tin d liu (lch v tinh ). Gi GPS c im gc 0 ca thi gian vo m 5/1/1980 v sng ngy 6/1/1980. Trong mt tun c 604800s, gi GPS ly mc l 1,5s , nh vy mt tun theo gi GPS s c 403200 mc. Mi mc chia 1,5s l n v thun tin cho vic tnh ton v lin lc thi gian chnh xc. Thi gian c cng b theo

27 cch thc ny gi l s m Z. Cu trc ca s m Z c 29 bit bao gm 2 phn nh sau: * 19 bit tri ca Z l s m trong tun (TOW-TIME of week ). im mc 0 ca tun c nh vo gia m th 7 v sng ch nht. Phm vi ca s m l t 0 n 43199, mi mc cch nhau 1.5s . * 10 bit cn li ca s Z l s m ch th tun hin ti. N l mt chui s nh phn gm 1024 s, phm vi t 0-1023. im mc 0 ca tun l tun u tin, bt u t m 5/1/1980 v sng 6/1/1980. Khi s m tun n 1023 th tr v 0 li bt u mt chu k tip theo. 2.2.2. Tn s GPS Trong nh v v tinh Navstar-GPS, tn s GPS bao gm cc tn s sau : + Tn s ng h c s 10.23 MHz. + Tn s sng mang. + Tn s chui m. 2.2.2.1. Tn s sng mang GPS y l tn s cc k quan trng, n lin quan ti tn hiu thc t pht t v tinh. H thng Navstar c hai tn s sng mang chnh l L1 v L2. L1 c tn s trung tm l 1575.42 MHz gp 154 ln tn s ng h 10.23MHz v L2 c tn s trung tm l 1227.66MHz gp 120 ln tn s ng h c s. Cc v tinh cn lm vic trn hai tn s sng mang khc na khi thu pht d liu vi trm iu khin di mt t: 1783.74 MHz pht ln v 1227.5 MHz pht xung. 2.2.2.2. Tn s chui m Cc tn hiu dn ng Nadata cng vi thng tin a ch ca ngi s dng c m ha bi mt chui m ngu nhin PRN. Mi ngi s dng s c tng ng mt loi m. H thng GPS s dng 2 loi m PRN chnh l m C/A v m P. M C/A c bo mt km hn m P, hu ht cc my thu u dng m C/A bt v o c ly tng i. M C/A c pht tn s 10.23 MHz cn tn s ca m P l 10.23 MHz. M P thng dng trong vic o c ly xa chnh xc cao v m ha cc bc in qun s. Ngoi ra cn s dng m Y, l m m xy dng da trn m p bng cch m ha m P v c cng tn s vi m P.

28 2.2.2.3. Cu trc tn hiu H thng Navstar- GPS s dng k thut a truy nhp m CDMA ( Code Division Mlutiple Access ). Ngi ta s dng k thut tri ph trong vic to nn cu trc d liu Nadata . Mi v tinh h thng GPS pht i hai tn hiu tri ph trc tip DS/SS (direct Sequence/ Spread Spectrum). l tn hiu ng 1(L1) v tn hiu ng 2( L2). Tn hiu L1 mang mt m xc nh c ly chnh xc (m P) v mt m bt o c ly tng i C/A ( Clear or Coarse Acquisition ). Tn hiu L 2 mang mt m xc nh c ly chnh xc cho qun s, tn s L 1 =1575.42 MHz, cn L2=1227.60 MHz. Tn hiu L1 l mt tn hiu QPSK (Quadrature Phase Shift Keying) vi m C/A gn knh I v m rt di v m rt di gn knh Q. Hnh 1.6 trnh by v s khi cu trc tn hiu L1 DS/SS phn pht: Tn hiu DS/SS-QPSK c dng : S(t)=I(t)+Q(t)I = AC (t )D (t ).cos(2 f ct + ) 2Q = AC t1D)t ( +f t ( ).sin(2 ) c

(2.1) (2.2)

(2.3)(2 f t ) c

S ( ) = AC 1t D t ).sin(2 f + c ) AC 2 t D t os t () ( + t ( ) (+ ). c

=

2cos(2f ct + + (t )) C (t )b(t ) (t ) = tan 1 1 Trong : C (t )b(t ) 2 / 4, khiC1(t )b(t ) = 1, C2 (t )b(t ) = 1 3 / 4, khiC1(t )b(t ) = 1, C2 (t )b(t ) = 1 (t ) = 5 / 4, khiC1(t )b(t ) = 1, C2 (t )b(t ) = 1 7 / 4, khiC (t )b(t ) = 1, C (t )b(t ) = 1 2 1

(2.4)

(2.5)

29 (ON NY BN G LI CNG THC NH. PHN CH VIT BN PHI VIT RING RA C DU CCH CH KHNG LIN TH NY)

Q = C t Dt ) in A ( .s (2 1() + f t

)

c

90 09 L1 carrierI =C t Dt) o f t A ( ). 2 ( c + s(2 )

Signal

C/A code

c

Icast data mesge

C 2 ( t ) D( t )

P code

C2 ( )tC1 (t )Hnh 2.6 : S khi cu trc to tn hiu L1

Trong : + Sng mang L1 gm hai thnh phn : + D liu Icast data Messge : D(t) Acos(2f ct + )

A sin(2 f ct + )

30 + M P + M C/A : C1(t ) : C2 ( t )

T y suy ra tn hiu DS/SS- QPSK c th nhn 4 trng thi pha khc nhau : + / 4, + 3 / 4, +5 / 4, +7 / 4. D liu hng hi, lch v tinh c nh dng chun v bn tin s dng chi h thng nh v, d liu ny c tri ph bi hai m C/A v m P c lp nhau trn hai thnh phn ng pha I(t) v thnh phn vung pha Q(t). phn bit c cc v tinh, mi v tinh s dng mt m C/A v mt m P ring khc nhau. M C/A cn c gi l m vng (gold), c chu k 1023 chip, c pht vi tc 1.023 MHz c th lp li mi miligiy mt ln. M P c chu k rt di, n c xy dng trn c s tich ca hai m c di gn nh nhau v c pht vi tn s l 10.23 MHz. M P lp li 280 ngy mt ln, mi mt v tinh s c pht mt on khc nhau ca m ny vi thi gian n nh l mt tun. Tn hiu C/A ngn d bt, cn tn hiu P c tc cao dng o c ly xa chnh xc hn. Thi gian mt chip P vo khong 100ns. C hai tn hiu C/A v P u c iu ch trn mt d liu thng tin pht i vi tc 50bit/svaf lp li tun hon. D liu ny mang thng tin v v tr ca v tinh, mt s thng tin v ci chnh sai s ng h, sai s tng ion. Sau khi bt c m C/A, d liu c gii iu ch. M C/A v thng tin sau gii iu ch cho php ngay lp tc ng b m P. Hnh 2.7 trnh by s khi gii iu ch tn hiu DS/SS-QPSK phn thu s l:S ( ) = C 1 ( ( + + f t A t Dt ).sin ) (2 t

my thu. Nu b qua tp m v gi thit rng tn hiu c tr th tn hiu C 2 ' Dt( c ) Ac +) t( o ). s (2f t ) c'

(2.6)

31

C1( t ) s i n ( 2fc t '

) )

ti + Tb

+

S (t )

C2 (t )

c o s (2fc t ' +

( .)d t

ti

U(t)

Hnh 2.7 : S khi gii iu ch tn hiu Kt qu u ra ca mch tch phn l thnh phn d liu Z i = AD(t ) . Nu bit bn tin l 1 th Zi = AT , nu bt bn tin l -1 th Z i = AT . Cc thnh phn tn s 4 fc c gi tr ftrung bnh bng 0. V th, u ra ca b so snh l +1 (logic1) khi bn tin l +1, v u ra l -1 (logic0) nu bit bn tin l -1. 2.3. iu ch v gii iu ch GPS 2.3.1. iu ch tn hiu GPS Cc m c iu bin trn song mang theo phng thc iu ch BPSK - Vi Tn s sng mang L1 : 1.575,42 Mhz ( bng L ). - Mc cng sut ti thiu : - 160 dBw ti b mt tri t. - M nhiu gi ngu nhin PRN C/A c tn s 1.203 Mhz, chu k 1ms. - Sng mang L1 c iu bin bng c hai m ( m C/A v P hoc Y ). - Sng mang L2 c iu bin bng m P hoc m Y.

32 - Cc m c iu bin trn sng mang theo phng thc iu ch BPSK.

Hnh 2.8: S iu ch (HNH NY CH DCH RA TING VIT) in vn v tinh di dng d liu s tc 50b/s c cng m-un 2 vi m C/A iu ch trn sng mang L1. in vn v tinh s c cc my thu gii m v dng xc nh v tr theo thi gian thc. 2.3.2. Gii iu ch GPS Tn hiu sng mang GPS i n 2 b nhn, 2 b nhn thc hin gii iu ch. Lc vng: lc in p t ng ca b nhn a vo iu chnh tn s v pha ca b dao dng VCO. B nhn th 3 mc ch tm kim sai pha gia sng mang 2 BPSK v sng mang khi phc. Kt qu sai pha s th hin bng in p li.

33

Hnh 2.9: S gii iu ch HNH NY CH DCH RA TING VIT) 2.4. Cc nguyn tc v phng php o GPS 2.4.1. Cc dng i lng o Vic nh v bng GPS c thc hin trn c s s dng hai i lng o c bn, l o khong cch gi theo cc code ta ngu nhin (C/A-code v P-code ) v o pha ca sng ti (L1 v L2 ) 2.4.1.1. o khong cch gi theo C/A-code v P-code Code ta ngu nhin c pht i t v tinh cng vi sng ti. My thu GPS cng to ra code ta ngu nhin ng nh vy. Bng cch so snh code thu c t v tinh v code chnh ca my thu c th xc nh c khong thi gian lan truyn ca tn hiu code, v t y d dng tnh c khong cch t v tinh n my thu ( trung tm ngten ca my thu ). Do c s ng b gia ng h ca v tinh v ca my thu v do c nh hng ca mi trng lan truyn tn hiu, nn khong cch tnh theo khong thi gian o c khng phi l khong cch thc gia v tinh v my thu. chnh l khong cch gi. K hiu: xs , ys , zs :Ta ca v tinh. x, y, z : Ta ca im xt ( my thu). t : Thi gian lan truyn tn hiu t v tinh n im xt.t : Sai s khng ng b gia ng h trn v tinh v my thu.

R: Khong cch gi o c. Khong cch gi o c l :

34

R = c(t + t) = ( xs x)2 +( ys y)2 +( zs z)2Trong : c l tc lan truyn tn hiu.

(2.7)

Trong trng hp s dng C/A-code, k thut o khong thi gian lan truyn tn hiu ch c th m bo chnh xc o khong cch tng ng c 30m. Nu tnh nh hng ca iu kin lan truyn tn hiu, sai s o khong cch theo C/A-code s mc 100m l mc c th chp nhn khch hng dn s c th khai thc. Song k thut x l tn hiu code c pht trin dn mc m bo chnh xc o khong cch ti c 3m, tc l hu nh khng thua km so vi trng hp s dng P-code vn khng c dng cho khch hng i tr. 2.4.1.2. o pha ca sng ti Cc sng ti L1 v L2 c s dng cho vic nh v vi chnh xc cao. Vi mc ch ny ngi ta tin hnh o hiu s pha ca sng ti do my thu nhn c t v tinh v pha ca tn hiu do chnh my thu to ra. Hiu s pha do my thu o c l ( 0< 10 Tt (5->10

Tnh tng thch Tt Tt Trung bnh

Cc vn trin khai LBS trn mng GSM/GPRS

Hu ht cc nh khai thc u cn nhc xem k thut nh v no l tt nht i vi h.Vi tnh n gin v chi ph thp ca cell-ID th n s l s la chn tt nht bt u a dch v LBS vo mng. Cell-ID c trin khai trong mt s mng GSM cho d chnh xc v tr v tnh n nh ca n khng cao v ch h tr s lng dch v rt hn ch. y cng l khong thi gian cc nh khai thc kim chng cng ngh, nhu cu dch v v bc u xy dng m hnh kinh doanh loi dch v ny. Khi s lng thu bao s dng dch v ny tng, ng thi yu cu cung cp nhiu dch v hn th cc k thut nh v c chnh xc cao s c xem xt. Trong a s trng hp ngi ta cn nhc gia E-OTD hay A-GPS. Hnh 2.15 minh ho chi ph trin khai cc k thut nh v trn mng GSM/GPRS.

53Gii php da trn E-OTD

A-GPS u t n 3G Gii php da trn A-GPSA-GPS+Cell ID

Thi gian

Hnh 2.15: Chi ph trin khai E-OTD so vi A-GPS Nu la chn E-OTD cn mt khon chi ph u t ban u rt ln vo LMU, thm ch sau khi u t ln nh vy vn cn trin khai b sung A-GPS nhng ni m cht lng ca E-OTD km h tr cho cc dch v tin tin hn. Hnh 2.16 minh ho s b cc phn t trong mng GSM/GPRS s dng EOTD.

Hnh 2.16: Cc phn t mng GSM/GPRS s dng E-OTD Vi A-GPS th nh khai thc cn t chi ph hn cng nh vic trin khai cng n gin hn so vi E-OTD. Ngoi ra, A-GPS cn tng thch vi tt c cc giao din v tuyn. T cell-ID nh khai thc trin khai A-GPS th khng nhng h ch cn u t mc vn duy tr c mc doanh thu m cn ngay lp tc cho php khch hng s dng dch v c cht lng v tin cy cao hn. nhng ni A-GPS cn c b tr th ngi ta c th dng E-OTD vi s

54 lng rt t LMU. Nh vy A-GPS cho cc ch tiu tt hn vi chi ph thp hn so vi trin khai din rng E-OTD. Nh phn tch trn, E-OTD khng s dng c trong mng WCDMA v k thut OTDOA s dng cho mng WCDMA th li khng dng c trong mng GSM/GPRS. Do , vi nhng nh khai thc GSM/GPRS c d nh tin ln WCDMA rt c th h s la chn A-GPS p ng c tnh tng thch, tnh k tha t ra khi chuyn i. Nh vy, vi nhng u im ni bt ca mnh A-GPS c xem l s la chn s 1 cho cc nh khai thc thng tin di ng. 2.7. Tng kt chng 2 Chng 2 nu ra cu trc, c im k thut ca h thng GPS, cc phng php o GPS. Trong chng ny cng nu c cc k thut nh v thu bao trong mng GSM/GPRS, cc ch tiu nh gi ca cc phng php nh v bng Cell-ID, bng E-OTD, bng A-GPS. So snh c n nh, chnh xc, kh nng m rng .... ca 3 phng php ny. Kt hp cc phng php ny li vi nhau lm tng chnh xc khi nh v cng nh gip cc nh khai thc cung cp a dng cc dch v da trn v tr. V cc ng dng ph bin ca GPS c nu ra chng 3

55 CHNG 3 MT S NG DNG PH BIN CA GPS H thng nh v ton cu (GPS) l h thng hoa tiu cho php nhng ngi s dng n c th nh v cc vt th c th trn tri t vi s tr gip ca mt nhm 24 v tinh. Mc d h thng ny c xy dng phc v mc ch qun s, nhng nhng ngi s dng cho mc ch dn s cng c th tip cn c vi n m khng phi mt chi ph, nhng tnh chnh xc v nh v li b gim i. Nguyn tc c bn ca GPS l s dng cc v tinh mt v tr v khong cch bit lm cc im quy chiu quy ra tam gic cho mt im cha bit ca mt vt th trn tri t. Mt b phn ca mi my thu GPS l mt ra-i- thu cc tn hiu ang pht t cc v tinh. Mi con tu v tr khng ngng chuyn mt dng d liu cha ng cc thng tin v qu o v thi gian chnh xc. My thu GPS tnh ton khong cch ca n tnh t v tinh, da trn c s s khc bit v thi gian gia vic gi v nhn tn hiu v tc hnh trnh i ca tn hiu (thi gian x tc = khong cch). i vi v tr hai chiu (kinh v v ) chnh xc, c nh cc tn hiu cn c t nht 3 v tinh. Vic xc nh v tr 3 chiu (kinh , v v cao) i hi cc tn hiu t t nht l 4 v tinh. my thu cng "nhn thy" nhiu v tinh th v tr xc nh cng chnh xc. Tnh chnh xc cao ca GPS c xc nh bi tng s cc ngun sai s, mt mt ph thuc vo iu kin thit b v iu kin kh quyn, mt khc ph thuc vo phng thc hot ng c gi l "tnh c th s dng c la chn" (S/A). Hn ch ny do vic thoi bin c mc ch v s chnh xc ca tn hiu do Cc quc phng M thc hin trnh vic lm dng cc tn hiu GPS v cc mc ch qun s khng c cp giy php. Kt qu l s chnh xc ca v tr nh v bi GPS bnh thng c th thay i t 20 n 100m. V vy, GPS c coi l mt gii php k thut phc v mc ch iu tra, c th p dng thm vo hoc thay th k thut kho st tri t. Nhng my thu GPS n l t c chnh xc c coi l c hiu qu i vi mc

56 ch lm bn vi t l nh hn 1:50.000, s chnh xc trung bnh 50 m c th tng ng vi s sai lch 1mm trn bn . Tuy nhin lm bn chi tit hn i hi c phin bn GPS tinh vi hn gi l GPS vi phn (DGPS). DGPS da trn nguyn tc ng b ho cc my thu GPS ring l khng ngng tnh c cc v tr cc a im khc nhau. Mt my thu c s dng nh mt trm quy chiu v c thay bng mt v tr trong cc to chnh xc bit. my thu th hai (my lu ng) c dng o nhng v tr cha bit. Nhng v tr c o bng my lu ng s c sa li bng cc dy sai trch o ti trm quy chiu kt hp vi to chnh xc ca trm. Ph thuc vo cc thit b c s dng vic sa cha phi c thc hin vo thi im thc t nu cc my thu u ng b ho s dng truyn qua ra-i-, hoc c th c thc hin sau khi x l, bng cch ti cc d liu c thu thp t c my thu trn my tnh v nhng tnh ton tip theo ca cc v tr c sa xung. Tnh chnh xc ca cc DGPS t t 1 - 5 m vi thit b chun v phc v mc ch lm bn t l 1:5000 c hiu qu. My thu DGPS c bit c th dt chnh xc di 1 mt hoc di 1 cm. 3.1.Thnh lp bn a hnh y bin bng cng ngh GPS 3.1.1. Phng php tch hp d liu GPS v my o su hi m Da vo my thu GPS v my o su hi m c tch hp c vi my tnh bng cc phn mm chuyn dng t xc nh c ta v cao cc im o su. vic xc nh to v su im o c ng b v lin tc ngi ta ni kt my thu GPS v my o su vi my tnh thng qua cc cng ni tip. My o su v my thu GPS phi c cc cng xut d liu theo dng k thut s v trong my tnh cng phi c phn mm chuyn dng c ci sn c th nhn bit c cc thng tin truyn sang t hai thit b trn. Khi khi ng h thng, mi thi im o cc d liu c truyn lin tc t my thu GPS v my o su vo my tnh. My tnh ng thi thu hai tn hiu v tch hp thnh mt c s d liu. C s d liu ny l nhng file cha

57 nhng thng tin v ta , su, thi gian v cc tham s ci t cng nh cc gi tr lin quan thng gi l file th hay file gc lu tr vo a cng ca my tnh. Cc d liu ny cng ng thi c my tnh x l hoc hin th theo yu cu ca ngi dng nh: v tr ng o thit k trc, v tr m phng ca con tu, mt ct su ang o, tc tu, thi gian ng dng ny rt thun li khng ch n thun l kh nng nh v mi ni, vo mi lc trn bin m cn khc phc c hu ht cc nhc nhim ca cng ngh truyn thng, nng cao chnh xc v t nng sut cao. 3.1.2. Qui trnh thnh lp bn a hnh y bin bng cng ngh GPS Trong phng php o su ng dng cng ngh GPS tch hp vi my o su hi m ngoi cc thit b phc v cho vic o su nh tu thuyn, my o GPS, my o su ta cn phi c cc phn mm chuyn dng tch hp v x l cc tr o nhn c. Qui trnh thnh lp bn a hnh y bin thc hin theo s sau (Hnh 3.1) Trn c s tnh nng thc t, chnh xc o c v hiu qu kinh t cao m phng php thnh lp bn a hnh y bin s dng cng ngh GPS v ang c s dng rng ri nhiu nc trn th gii. Vit Nam bc u du nhp v trin khai s dng mt s n v sn xut, qua thc t p dng cho thy u th vt tri so vi cc phng php o su truyn thng. y l mt phng php o tin tin, ng dng cc k thut mi nh DGPS, RTK GPS nn cn c ph bin v ng dng rng ri trong lnh vc o su v mt s lnh vc khc.

58

Hnh 3.1 : Qui trnh thnh lp BH y bin 3.2. ng dng trong lnh vc trc a - a hnh Vi s ra i ca h thng nh v ton cu GPS v c bit l k thut nh v vi sai DGPS nhng ngi lm cng tc trc a a hnh c c mt phng tin o c cha ng nhiu tnh nng u vit ng k so vi phng tin truyn thng, m trc ht l trong lnh vc thng c gi l cng tc khng ch ta . H thng ny cho php t chnh xc cao v v tr tng i gia cc im xt hu nh t ph thuc vo khong cch gia chng, v do vy vic phn cp cc mng li trc a v xy dng chng theo s i t tng qut n chi tit khng cn l vn nguyn tc na. Bn cnh h thng khng i hi thng hng gia cc im o, cn khong thi gian o ti mi im khng qu 2- 3 gi ng h, thm ch l 2-3 pht. C th ni,

59 cng ngh GPS to ra mt cuc cch mng thc s trong lnh vc trc a a hnh v n cn hm cha nhiu kh nng , u th tim n ang c khai thc. Do cng ngh GPS cho php xc nh v tr tng i gia cc im vi chnh xc cao hn hn so vi cng ngh trc a truyn thng, nn vn t ra l phi nh gi mt cch tha ng vai tr cng nh mi quan h ca cc im GPS vi cc mng li khng ch trc a c xy dng. T gc ny ta c mt cch phn chia cp hng i vi mng li trc a quc gia do tc gi Hothem v Williams (M) xut trong th hin r vai tr thc t khch quan ca cc im o GPS. Theo cch ny c hai loi yu cu v chnh xc o c: loi yu cu ph bin v loi yu cu c bit. Loi yu cu ph bin nhm p ng cc mc ch o c ph bin c kt hp vi cc phn hng hin dng cho mng li khng ch trc a, o c cng trnh, o v bn a hnh v bn a chnh. Cc ch tiu v chnh xc c xut tng ng vi chnh xc hin hnh ca chiu di cnh, gc phng v, cao GEOid v cao so vi ellipxoid. Thnh qu o c thuc loi yu cu ph bin s c s l trn c s bnh sai cht ch da vo cc im GPS gn kt vi mng li khng ch khu vc o. Loi yu cu c bit nhm vo cc mc ch o trc a chnh xc cao, chng hn nh quan st chuyn ng ngang ca v tri t, theo di tri ln ca mt t, o c cng trnh chnh xc. Cc kt qu o c thuc loi yu cu c bit c x l c lp, khng ph thuc vo mng li khng ch khu vc o, m ch da vo kt cu ni ti ba chiu ca bn thn mng li GPS. 3.3. ng dng trong lnh vc nghin cu a ng Quan st xc nh bin dng ca v Tri t l khu then cht trong vic nghin cu tm hiu cc qu trnh ng t, chuyn ng ca cc mng kin to, c ch hnh thnh cc dy ni v cc hot ng lp v gn mt t ca v ni la. Quy m ca cc bin dng so hin tng ny gy ra c th c th t t

60 hng chc n hng nghn kilomet, song phn ln cc bin dng ng quan tm thng thy gn ranh gii gia cc mng c t 30 n 300 km. Cc yu cu do vic nghin cu chuyn ng ca v Tri t ra thng khc bit ng k so vi yu cu o c v thnh lp bn ; khng phi l ta tuyt i m l xc nh s thay i v tr, s dch chuyn, bin dng theo thi gian ca i tng nghin cu . V th khi vn l phi tm cch tin hnh o lp trong iu kin cng ging nhau v vi chnh xc cng cao cng tt. chnh xc ca v tr tng i do vic nghin cu chuyn ng ca v Tri t ra thng l c 107 v cao hn (ngha l c vi ba centimet trn khong cch ti 100km). Trc y phng php trc a c xem l phng php duy nht i din cho cc k thut o c trn mt t c th c s dng nghin cu chuyn ng ca v Tri t. Gn y phng php o giao thoa cnh y di (VLBI Very long baseline interferometry) v phng php o khong cch bng tia lade t v tinh (SLR satellite laser ranging) cho php t ti chnh xc vi ba centimet trn khong cch hng nghn kilomet. Song thit b tng ng v i ng k thut i hi chi ph rt cao, nn khng s dng cc phng php ny o c chi tit mc cn thit cho vic nghin cu c ch bin dng ca v Tri t quy m nh thng ng quan tm i vi vng c hot ng a chn mnh. V th, mc d rt c gi tr i vi nghin cu chuyn ng mng trn quy m ton cu cng nh nghin cu bin dng quy m ln trong phm vi tng mng, cc phng php o giao thoa cnh y di v o khong cch bng tai lade t v tinh s khng th p dng mt cch hiu qu v mt kinh t cho cc khong cch di 300km. Vi gi thnh thp, cc php o bng k thut nh v vi sai DGPS hon ton c th p ng c yu cu nghin cu chuyn ng ca v Tri t mc chi tit cao vi khong cch gia cc im xt t vi ba kilomet n hng nghn kilomet. Cc my thu GPS r hn nhiu ln so vi thit b VLBI v

61 SLR, cn i ng k thut c th gim xung cn mt ngi cho mi my thu. Trn thc t GPS c th c xem l cu ni cho khong trng gia cng ngh o tam gic truyn thng vn c hiu qu khong cch ngn vi cng ngh VLBI SLR t ra rt c gi tr khong cch di. Cng ngh GPS cng s c s dng c hiu qu c i vi nhiu bi ton a vt l hin vn ang c p ng bi cc k thut o c trn mt t khong cch t 5km n 30km. Phng php GPS ng vai tr ch yu trong lnh vc nghin cu a ng. Gi thnh ca n thp hn nhiu so vi o thy chun khong cch t vi ba kilomet tr ln, cn chnh xc ri s cao hn khong cch ln hn cng nh iu kin a hnh phc tp. Hiu cao c th c xc nh d dng hn nhiu v ch cn nhm o rt t ngi so vi trng hp o thy chun. 3.4. ng dng nh v GPS trong mt s dng cng tc phc v thm d du kh trn bin. 3.4.1. nh v o a chn trn bin Cng tc a chn trn bin thng c tin hnh theo cc tuyn thng song song theo hai phng vung gc vi nhau. Tu a chn ko tho mt ng cp c bit vi phn chm di nc di t 1000m 2400m. Phn chm c gi su 10 20 m di mt nc do c cu to c bit v c kin tra, iu chnh su bng thit b o su. Trn mi on cp di chng 50m c gn 20 30 u thu chn ng, cc u thu hp thnh nhm. Vi chiu di cp l 2400m c tt c 48 nhm u thu. Nhm gn tu nht c b tr vi gin cch trn 100m so vi tu v gia cn c on cp lm gim nh hng n ca tu. ui cp c ni vi phao ni trn c lp anten raa phn x hay tiu ngm c th quan st nhm xc nh chch ca ton ng cp so vi hng i ca tu. ui ni cn c tc dng d tm li on cp b t trong qu trnh o. Tu a chn ko cp chy lin tc theo thit k, c 25m li li pht ngun chn ng cho cc u thu trn ng cp thu nhn tn hiu phn hi. Cc tuyn a chn thng c to thnh li vung vi dn cch trung bnh l 250m.

62 Cng tc nh v trong trng hp ny phi m bo dn ng cho tu i vo khu vc o va chy theo ng tuyn thit k vi sai lch cho php khng vt qu 10% khong cch n tuyn ln cn ng thi phi xc nh v tr ca im tin hnh quan trc vt l trn tuyn chng hn nh im pht chn ng (im n) vi chnh xc khng thp hn 0.8 mm theo t l bn bo co. T lu nay phng php o a chn thng dng l phng php a chn hai chiu trong cho rng im n v cc im thu tn hiu cng nm trong mt mt phng. Song trn thc t khi tu a chn c th gi c hng i ch chch khi tuyn thit k trong vng 3 -5 m, nhng do nh hng ng k ca dng chy v thy chiu nn cc u thu tn hiu phn x gn trn ng cp khng cng nm trn mt ng thng so vi im n, v c th b gch i trong mt di rng ti vi mt. khc phc tnh trng ny nhm nng cao tin cy ca cc kt qu thm d a chn, ngi ta xy dng phng php chn ng 3 chiu theo mi tu a chn ko theo hai hng u thu (hai ng cp) c mt hay nhiu ngun n xt theo phng vung gc vi thn tu (cng c th ghp nhe th chy song hng). V tr thc t ca im n cng nh ca cc u thu cn c xc nh vi chnh xc cao, chng hn im n phi c sai s dc tuyn khng vt qu 2m, sai s ngang khng qu 3m, nhm u thu gn tu nht phi c sai s dc tuyn v sai s ngang tng ng l 2m v 3.5m; nhm u thu gia cp : 2m v 8m, nhm u thu cui cng 2m v 4m. Ta c th nhn thy yu cu v chnh xc nh v trong cng tc a chn bin l kh cao. Tuy vy, n hon ton c th p ng bi h thng chi tit. My thu GPS s c t trn tu a chn v trn cc phao ni gn ui cc ng cp. Phng php nh v thch hp nht l phng php nh v vi sai DGPS vi b my thu m bo chnh xc c 1m. 3.4.2. nh v khoan trn bin Trong cng tc khoan trn bin cng vic nh v c cc nhim v sau : - Dn ng cho tu a dn khoan ra v tr thit k .

63 - Xc nh chnh xc vi tr ming ging khoan khi bt u khoan. - i vi cc tu khoan, cn phi bo m nh v lin tc cung cp cc s liu iu khin cho tu ng yn tng i ti v tr ban u. - Trong trng hp tu khoan phi ri khi v tr trc khi kt thc khoan, phi nh v li v tr khi tr li khoan tip . - S dng ti liu o lch xc nh v tr thn ging khoan trong lng t v tnh ton ta v tr thn ging khoan gp cc va, tng a cht quan tm . sai lch v tr a tu hoc dn khoan ra hin trng so vi v tr thit k ph thuc vo mc phc tp ca i tng a cht c nghin cu, nhng khng vt qu 1/4 khong cch trung bnh gia hai ng ng su lin nhau trn bn cu trc a cht c ly lm c s cho vic t ging khoan. Ta v tr ming ging khoan c xc nh vi chnh xc ph thuc vo cp, loi ca ging khoan; tuy nhin iu kin s dng thit b nh v hin nay cho php m bo chnh xc cho cc loi v cp ging khoan. chnh xc ny khng c thp hn 8 10 m. p ng cc yu cu nh v khoan trn bin ngi ta s dng phng php nh v vi sai DGPS mc chnh xc mt vi mt. 3.4.3. nh v cc cng trnh trn bin Trong vic xy dng cc cng trnh tm kim, thn d v khai thc du kh trn bin, cng tc nh v c nhim v sau : - m bo nh v cho kho st a cht cng trnh ti khu vc d kin xy dng cc cng trnh nh: ging khoan tm kim thm d, dn khoan khai thc, trm x l du kh, cc ng ng dn du kh, bn rt du kh - a cc thit b, my mc ra v tr thit k, m bo lp t chng theo s thit k. - Xc nh li v tr cc i tng, hng mc cng trnh sau khi lp t chng. - Lp mng li v k hoch quan st dch chuyn, bin dng cc cng trnh nhng ch cn thit v thc hin quan trc v tnh ton dch chuyn, bin dng ca cc cng trnh.

64 Vic a cc cng trnh ra v tr thit k c thc hin bng cch xc nh v tr thit k ny hin trng ri th phao nh du. Sau khi hon tt vic lp t cng trnh, phi xcn nh v tr thc ca chng. chnh xc nh v cng trnh khng c thp hn 1,2mm theo t l bn s dng. Vic quan st dich chuyn bin dng cng trnh trn bin c th i hi chnh xc nh v n c ximet ngoi thc a. R rng p ng cc yu cu nh v cc cng trnh trn bin cn s dng n k thut nh v vi sai DGPS cho kt qu c chnh xc cao. 3.5. ng dng cng ngh nh v ton cu GPS trong bi ton qun l xe bu chnh. Vic ng dng cng ngh GPS trong cc bi ton qun l phng tin giao thng ang tr nn ph bin trn th gii v y l mt dch v mang li gi tr gia tng cao da trn cng ngh vin thng v cng ngh thng tin. i vi ngnh Bu chnh, vic p dng cng ngh GPS trong vic qun l cc phng tin vn chuyn Bu chnh s em li hiu qu cao, ph hp vi cc phng thc qun l tp trung hin i. Bi vit ny cp n vic xy dng phng n qun l xe bu chnh bng cng ngh GPS v thit k thit b thu thp d liu GPS cho xe bu chnh. 3.5.1. bu chnh. Hin nay bi ton qun l xe vn chuyn bu chnh ti cng ty Bu chnh lin tnh v quc t (VPS) thuc Tp on Bu chnh Vin thng (VNPT) ang c thc hin theo quy trnh sau (hnh 3.2) Vi quy trnh qun l trn, mc d hin nay c phng thc tin hc ho, qun l t ng mt phn trong vic tng hp cc phiu hnh trnh trn y. Tuy nhin, phng thc qun l nh trn vn c mt s bt cp nh: Tn nhn cng qun l trung gian, Khng qun l c l trnh v thi gian, nhin liu thc t trong sut qu trnh vn hnh ca 01 xe bu chnh, khng pht hin c nguyn nhn chm tr trong vic vn chuyn bu chnh v khng iu Xy dng phng n ng dng GPS trong bi ton qun l xe

65 hnh, gim st c tng th ton b cc tuyn xe bu chnh ti u ho vic vn chuyn bu chnh.

Hnh 3.2: Quy trnh qun l vn chuyn xe bu chnh ca VNPT Nu s dng cng ngh GPS, cc thng tin v phng tin vn chuyn bu chnh nh: ta hin ti, tc vn chuyn, tuyn ng di chuyn, nhin liu tiu hao s c cp nht v trung tm iu khin, lu tr theo c s d liu (CSDL) v da trn CSDL ny trung tm c th tnhton v nhin liu ca tng phng tin vn chuyn bu chnh, kim tra c s c khi vn chuyn, ti u ho iu hnh cc tuyn bu chnh. 3.5.2 Xy dng phng n qun l xe bu chnh bng GPS Phng n qun l cc phng tin vn chuyn bu chnh bng cng ngh GPS c xut theo 2 phng thc: Qun l trc tuyn (online) v qun l khng trc tuyn (offline). 3.5.2.1 Qun l theo phng thc trc tuyn Qun l theo phng thc trc tuyn ngha l gia trung tm iu hnh v xe bu chnh lin lc trc tuyn, trao i d liu vi nhau. qun l xe vn chuyn xe bu chnh theo phng thc trc tuyn chng ta cn phi c cc phng tin v h thng nh sau:

66

Hnh 3.3: Minh ha phng thc truyn d liu trc tuyn Ti trung tm iu khin: - Mn hnh hin th bn s tng khu vc a l. - My ch v cc my trm ty theo nhu cu qun l vi h thng thng tin qun l GIS (Geographic Information System) bng phn mm MapInfo vi phng thc lp trnh bng ngn ng MapBasic. Ti xe bu chnh: - Modul GPS - Thit b thu thp v truyn d liu GPS thng qua phng thc SMS nh Modem GSM/GPRS. Cc phng thc truyn dn y thng qua mng di ng GSM, cc ID ca tng xe bu chnh c th hin qua cc ID ca SMS nhn v. Nguyn tc hot ng ca h thng: Knh lin lc gia xe bu chnh v trung tm iu khin c th hot ng mt trong s cc ch sau: - Duy tr kt ni lin tc: kt ni lun sn sng phc v vic truyn d liu v v tr v thi gian. - Thit lp kt ni t ng: knh lin lc c t ng thit lp khi mt trong 2

67 bn c d liu cn truyn. - Thit lp kt ni bng tay: ngi iu hnh hoc li xe bu chnh t thc hin cc thao tc khi to lin kt mi khi cn gi i mt thng ip. 3.5.2.2 Qun l theo phng thc khng trc tuyn Qun l khng trc tuyn (offline) c ngha l sau 1 ca lm vic trung tm s cp nht cc d liu v hnh trnh ca xe bu chnh trong ca lm vic lu li v x l t ng phc v cho cng tc qun l. V mt thit b , qun l theo phng thc khng trc tuyn khc vi phng thc qun ltrc tuyn l thit b trn xe bu chnh s khng c modem GSM/GPRS, mch vi x l s thu thp v lu li d liu v v tr ca xe bu chnh v tr d liu v trung tm khi ht ca lm vic. Ti trung tm cng s phi c h thng thng tin x l cc d liu ny phc v cho mc ch qun l. Phng thc khng trc tuyn tuy c r tin v khng cn n modem GSM/GPRS v khng mt cc cc ph lin lc SMS nhng c hn ch l khng qun l trc tuyn n tng xe bu chnh trong khi ang vn chuyn. 3.5.3 Thit k thit b v xy dng chng trnh qun l vn chuyn bu chnh bng cng ngh GPS. Hin nay, ti Khoa k thut in t 1 thuc Hc vin Cng ngh BCVT bc u xy dng c h thng thng tin qun l v thit b thu thp d liu t GPS t trn xe bu chnh phc v cho cc phng thc qun l trn. Thit b t trn xe bu chnh do chng ti thit k s tch hp modul GPS v mch vi x l vi yu cu gn nh chnh xc. 3.5.3.1 Modul GPS xy dng thit b t trn xe bu chnh ta s s dng modul GPS c nhim v nhn cc tn hiu t v tinh, x l tn hiu a ra kt qu bao gm cc thng tin sau: - Ta kinh tuyn, v tuyn ca xe v chiu cao so mt nc bin. - Thi gian hin ti theo gi GMT. - Tc v hng chuyn ng ca xe.

68 - S v tinh nhn c tn hiu. Cc thng s trn c th hin di dng cc bn tin c nh dng chun NMEA-183 trn ton th gii vi cc khung bn tin theo vi x l chun. Modul GPS s tr v bn tin nh sau: $GPRMC, 161229.487, A, 3723.2475, N, 12158.3416, W, 0.13, 309.62, 120598, *10 Sau y l din gii ca bn tin Bng 3.1: Din gii ca bn tin Modul GPS tr v Tn Message ID Thi gian (UTC Time) Tnh trng V (Latitude) Ch dn Nam Bc (N/S Indicator) Kinh (Longitude) Ch dn ng Ty (E/W Indicator) Tc trn mt t Hng bm trn mt t Ngy thng Kim tra (Checksum) V d $GPRMC 161229.487 A 3723.2475 N 12158.3416 W 0.13 309.62 120598 *10 Knots n v M t Giao thc header RMC (RMC protocol header) Gi pht giy (% giy) hhmmss.sss A: d liu hp l; V: d liu khng hp l. ddmm.mmmm N = Bc hoc S=Nam N=north or S=south dddmm.mmmm E=ng hoc W=Ty E=east or W=west ng (True) ddmmyy Kim tra m truyn tin Kt thc bn tin

3.5.3.2

Mch vi x l thu thp d liu GPS

Mch vi x l s c thit k x l cc d liu thu thp t modul GPS v lu tr cc d liu theo mc ch s dng. Trn mch vi x l s c modul

69 truyn d liu thng qua cng COM, mch vi xl ny s dng ngun 12V trn xe bu chnh.

Hnh 3.4: S khi ca mch vi x l trn xe bu chnh y s s dng h vi iu khin c kh nng lp trnh c PSoC (Programable Systems on Chip) thc hin vic lu tr v truyn d liu v thi gian v to thu nhn c t modul GPS, cc bn tin ny c PSoC gia cng v truyn v trung tm theo phng thc truyn SMS thng qua modem GSM/GPRS. Hon ton cc d liu t trn xe bu chnh c th hin th ngay trn xe bu chnh cho ngi lixe bit v l trnh, thi gian v c th nhn mt s lnh trc tuyn t trung tm iu khin cng nh bit v cc xe trong i xe ca mnh.

Hnh 3.5: Thit b t trn xe bu chnh 3.5.3.3 H thng qun l ca trung tm iu khin

70 H thng qun l ti trung tm iu khin c chc nng cp nht cc d liu nhn c t thit b thu thp GPS t trn xe bu chnh, tch hp vi bn s lm nhim v: - Cp nht, hin th trc tuyn cc xe bu chnh cn gim st trn mn hnh ch huy. - Thng bo v tnh trng l trnh cc xe bu chnh. - a ra cc thng bo v nhin liu, thi gian vn hnh ca tng xe. - Gim st c cc s c ca cc xe. 3.5.3.4 H thng qun l d liu trn xe bu chnh

Vi cc thit b v h thng thng tin qun l trn, quy trnh qun l xe bu chnh s c th hin nh sau: Qun l theo phng thc trc tuyn. - Cc xe bu chnh s xut pht t gara, kch hot thit b thu thp GPS hot ng. - Trong sut qu trnh vn chuyn cc d liu GPS trn xe bu chnh c gi lin tc v trung tm theo phng thc nhn tin SMS vi tn sut gi tin do chng ta quy nh. - Trung tm nhn d liu v hin th trn mn hnh ch huy bng h thng thng tin qun l GIS. Khi cn trung tm c th yu cu 1 s thng tin t xe bu chnh. - Cp nht cc d liu gi v lu thnh cc file qun l ti trung tm.

71 Hnh 3.6: Chng trnh qun l d liu trn xe bu chnh Qun l theo phng thc khng trc tuyn. - Cc xe bu chnh s xut pht t gara, kch hot thit b thu thp GPS hot ng. - Trong sut qu trnh vn chuyn cc d liu GPS trn xe bu chnh c lu li b nh trong mch vi x l trn xe. - Khi ht ca lm vic, khi xe bu chnh tr v gara, ti gara s c thit b thu thp d liu truyn v trung tm ch huy, trung tm nhn d liu v hin th trn mn hnh gim st bng h thng thng tin qun l GIS. - Cp nht cc d liu gi v lu thnh cc file qun l ti trung tm. 3.6 Dch v da trn v tr thu bao cho mng GSM/GPRS 3.6.2 Gii thiu Cng ngh GIS (Geographic Information Systems) v cc k thut nh v ang m rng cc ng dng truyn thng sang cc ng dng da trn v tr. Thng qua vic tch hp cc cng ngh ny vo thit b di ng cho php cc nh khai thc cung cp rt nhiu cc ng dng khc nhau cho khch hng khi xc nh c v tr ca h. Chng c gi l cc dch v da trn v tr thu bao LBS (Location Based Services). Hu ht cc d bo trn th gii u cho rng y l mt loi dch v c tim nng to ln, t c tnh ca hai nghin cu v th trng mi nht cho thy th trng v dch v LBS s c doanh thu t 7 n 8 triu USD trong vng 4 nm ti. V vy cc nh khai thc dch v di ng rt quan tm n cc vn kinh t, k thut khi trin khai dch v ny trn mng ca h. Bi bo ny s gii thiu cc loi dch v v cc vn k thut lin quan khi trin khai trn mng GSM/GPRS. 3.6.3 Cc dch v da trn v tr Vic xc nh c v tr thu bao cho php cc nh khai thc cung cp cho khch hng nhng dch v m h mong mun v cng l c hi ln cung cp thm cc dch v mi. Dch v da trn v tr LBS c th chia lm 4 loi chnh:

72 + Dch v thng tin da trn v tr (Location based information services) + Tnh cc theo v tr a l (Location sensitive billing) + Cc dch v khn cp (Emergency services) + Dch v d tm (Tracking) 3.6.3.1 Dch v thng tin da trn v tr Loi dch v ny gm nhiu ng dng c cc thng tin c la chn v chuyn ti n ngi s dng u cui da vo v tr ca h. Chng hn, mt khch hng c u cui h tr WAP (Wireless Access Protocol) c th s tm ra 1 nh hng thch hp. ng dng LBS s tng tc vi cc thnh phn khc trong mng xc nh c v tr ca khch hng ny v cung cp danh sch cc nh hng gn h nht. Cc loi dch v khc nhau yu cu chnh xc v v tr ca thu bao cng khc nhau v tu thuc vo loi thng tin cung cp. V d, dch v dn ng yu cu chnh xc cao cn dch v cung cp thng tin thi tit th ch cn chnh xc tng i. 3.6.3.2 Tnh cc theo v tr a l Loi ng dng ny cung cp kh nng c tnh cc u i. Thng qua dch v tnh cc theo v tr a l, khch hng c th thit lp cc vng dnh ring chng hn vng lm vic hoc vng c tr. Khch hng s tho thun vi nh cung cp v gi cc h c th t c tc d liu khng thay i khi thuc vng c tr v cc tc cao hn vng lm vic. Loi hnh dch v ny c th c bit hu ch khi s dng cng vi cc ng dng di ng khc nh dch v thu bao tr trc. 3.6.3.3 Dch v khn cp Khch hng c th gi cc dch v khn cp t my di ng ca h, dch v ny s xc nh v tr cng nh cc thng tin c nhn lin quan nh tnh trng sc kho, nhm mu.. v thng bo vi thi gian ngn nht cho cnh st, cu thng, cha chy gn nht. 3.6.3.4 Dch v d tm

73 Nhng dch v ny bao gm c cc ng dng cho c nhn v tp th v chnh xc ca n cng i hi rt cao. C ba loi dch v d tm ch yu: Qun l nhn lc/Qun l cc phng tin: ng dng cho cc cng ty taxi, vn ti Dch v ny gip h bit c nhn vin h/cc my mc thit b ang u c th iu hnh mt cch hiu qu nht. D tm hin vt: dng cho c cc t chc hay c nhn mun m bo mt vt g gi tr c th tm c nu nh b nh cp. Dch v tm ngi: Dch v ny cho php b m bit c con ci h hin ang u, hoc bn b tm kim nhau v.v... 3.7 Tng kt chng 3 Chng 3 cho chng ta thy c cc ng dng rt ph bin v hu ch ca h thng GPS. Cng ngh GPS gip chng ta thnh lp bn a hnh y bin, ng dng trong cc lnh vc trc a, a hnh v mt s cng tc phc v thm d du kh trn bin. Cc ng dng v GPS c s dng trong i sng hng ngy nh qun l xe bu chnh, cc dch v da trn v tr thu bao cho mng GSM/GPRS nh tnh cc theo v tr a l, dch v khn cp, dch v d tm.... Cc dch v ny ngy cng c pht trin mnh m v gip ch chng ta rt nhiu trong cuc sng hin i.

74 KT LUN Vic nghin cu h thng v tinh dn ng GPS v cc ng dng ca n l rt cn thit trong thi bui hin nay. Tuy vn ny cn kh mi so vi nc ta nhng c s dng nhiu cc nc pht trin, v th m trong nhng nm ti chng ta cn y mnh nghin cu v h thng GPS c th c thm nhiu ng dng na phc v cho i sng hng ngy. n i su nghin cu v k thut nh v GPS, cc ng dng ca n v t c nhng kt qu sau: n nu bt c kh nng ng dng ca h thng GPS ang c ng dng trn ton cu. n phn tch v cu trc, cc c im k thut ca h thng GPS, cc nguyn tc v phng php o GPS. n nghin cu v cc k thut nh v thu bao trong mng GSM/GPRS. Hn na, n nghin cu v phng php A-GPS c nhiu u im hn so vi GPS nh tng chnh xc, gim thi gian xc nh v tr, tng nhy ca thit b.... Cc thit b di ng hin nay yu cu phi nh gn, tiu th nng lng thp, kh nng di ng cao v thi gian xc nh c v tr cng nhanh cng tt. V vy m phng php A-GPS khc phc c rt tt cc vn ny. Do thi gian lm n c hn v nhng hn ch khng trnh khi ca vic hiu bit cc vn ch yu da trn l thuyt l chnh nn n tt nghip ca em chc chn khng trnh khi nhng thiu st. Em rt mong c c nhng kin nh gi, gp ca cc thy v cc bn n thm hon thin. Cui cng em xin gi li cm n su sc n cc thy c trong khoa V tuyn in t - HVKTQS, c bit l Thy TS. Phm Xun Ngha hng dn nhit tnh, ch bo gip em hon thnh n ny. Em xin trn thnh cm n!

75 TI LIU THAM KHO 1. Ting Vit [1] TS. Nguyn Phm Anh Dng (1995), Thng tin v tinh, nh xut bn H Ni. [] TS. Nguyn Vn Tun, Gio trnh thng tin vi ba-v tinh. Ti bn nm 2004. [2] Trn Ngc Sn, (2008), Cc phng php nh v trong mng GSM, Tp ch Cng ngh thng tin & Truyn thng . [4] KS. Trn Anh T, TS. Chu Ngc Anh, KS. Lng L, KS.Bi Vn Ph, Dch v da trn v tr thu bao cho mng GSM/GPRS, Tp ch Cng ngh thng tin & Truyn thng. 2. Ting Anh FRANKVIQUEZ,ANNALEE,DRAGON,TIM ARCHDEACON, Location

Based Services, A Strategic Analysis of Wireless Technologies, Markets, and Trends; Allied Business Intelligence 1Q, 2001 ALLEN NOGEE, Ready or Not, Mobile Location Technology is Here!;

Cahners In-Stat Group March 2001 - Mobinder S. Grewal, Lawrence R, Weill, and Angus P. Andrews Global Positioning System.Nm 2005. [12] J.Borkowski, JarnonNiemela and Jukka Lempiainen, Cellular location techniques supporting AGPS positining, Institute of Communication Engineering, Tampere University of technology. V NGUYN TC LM TI LIU THAM KHO, BN PHI SON:

76 - TING VIT BN SON THEO TH T: TN TC GI (TH T THEO ABC), NM XUT BN TN TI LIU THAM KHO, NH XUT BN. - TING ANH TH TN TING ANH (H XP THEO ABC), NM XUT BN, TN TI LIU, NH XUT BN. BN PHI NH S V CH THCH N THEO NG S NH TRONG TI LIU THAM KHO. TI NH MU CHO BN HAI CI TING VIT V 1 CI TING ANH BN LM MU. BN SA I RI C G GI IN CHO TI NH. PHN N TI THY BN CHA CH THCH TI LIU THAM KHO T NO.