MC LCMC LC................................................................................1 LI M U...........................................................................3 TNG QUAN V TNH TON KHP NI......................................4

1.1 Gii thiu.....................................................................................................4 1.2 Mt s quan im v tng lai ca my tnh..............................................51.2.1 Quan im ca Mark Weiser ..................................................................5 1.2.2 Quan im v my tnh v hnh ca Norman (Invisible computer)......7 1.2.3 Mt s quan im v thut ng khc......................................................8

1.3 Tnh ton khp ni v hin thc o.............................................................9 1.4 Mt s nghin cu ban u v tnh ton khp ni ti trung tm Xerox PARC...............................................................................................................10 1.5 Cng ngh Calm........................................................................................12 1.6 Tnh ton khp ni v bi ton nh v......................................................13 1.7 Kt lun.....................................................................................................14CHNG 2............................................................................15 CC PHNG PHP NH V TRONG CC THIT B TRONG NH (INDOOR).............................................................................15

2.1 Gii thiu...................................................................................................15 2.2 Phng php nh v tim cn (proximity sensing)..................................15 2.3 Phng php phn tch cnh (scene analysis)...........................................162.4.1 Giao ng trn (Circular lateration)...................................................17

2.5 Phng php giao gc (angulation)...........................................................18 2.6 Phng php du vn tay trong mng ni b khng dy (WLAN Fingerprint)......................................................................................................19CHNG 3: TN HIU GPS......................................................24

3.1 GII THIU..............................................................................................24 3.2 M BO AN TON THNG TIN TRONG GPS...............................24

3..2.1 Tn hiu GPS...........................................................................................24 3.1.2 Thi gian l mt thng s quan trng....................................................25 3.2.3 GPS nh v th no................................................................................28 3.2.4 DGPS: Differential GPS - GPS vi sai....................................................30KT LUN.............................................................................34 ..........................................................................................34 TI LIU THAM KHO............................................................35

LI M U.Cc h thng tnh ton khp ni v cc dch v lin quan ang ngy cng tr nn ph bin trong thc t, in hnh nht trong s chng l h thng nh v v tinh ton cu GPS. Tuy nhin trong mi trng trong nh (indoor) vn cha xut hin nhiu cc h thng nh v mang tnh thng mi do h thng nh v v tinh khng th hot ng c trong mi trng indoor m nguyn nhn chnh xut pht t hin tng a ng v yu cu gia b pht v thu phi nhn thy nhau trong qu trnh nh v. Vn nh v i tng trong tnh ton khp ni v ang thu ht c s quan tm ca nhiu nh nghin cu khp ni trn th gii. Kt qu l nhiu cng ngh, phng php v h thng nh v mi ra i chng hn nh cc h thng nh v s dng cc cng ngh hng ngoi, siu m, sng v tuyn cng vi cc phng php nh v nh phng php gn k, giao khong cch, giao gc

Mt trong im mu cht ca vn m bo an ninh thng tin trong cc h thng tnh ton khp ni l nh v chnh xc cc thit b truyn thng.

CHNG 1.TNG QUAN V TNH TON KHP NI. 1.1 Gii thiu Cng ngh tin hc tri qua mt s thay i ln ch trong vi thp k qua. u nhng nm 1970 cc my tnh c ln mainframe thng tr trong lnh vc tnh ton trn nguyn tc mt my tnh phc v ng thi nhiu ngi s dng, ti nhng nm 1980 cc my tnh trn dn dn b loi b v thay th bng cc my tnh c nhn v cc my tnh xch tay, im ng lu trong giai on ny l mt my tnh phc v mt ngi s dng, ti nhng nm 1990 vi s pht trin mnh m ca cng ngh in t bn dn, cc cng ngh mng khng dy, gi thnh thit b gim chng ta ang chng kin mt k nguyn mi ca my tnh c nhn, l hin tng nhiu my tnh phc v mt ngi. Thng qua mt thi gian di cc cng ngh tc ng rt ln n cuc sng ca chng ta thay i cch thc chng ta sng, lm vic, gii tr... Ngy nay cng ngh bn dn t ti trnh c th cho php cc nh sn xut to ra c cc chp, v mch bn dn nh gn n mc chng c th c nhng vo cc vt m chng ta s dng hng ngy. Cng ngh cng cho php cc my tnh trn th gii c th kt ni vi nhau mt cch d dng, xo nho khong cch v a l. Hu ht mi ngi khi cp n thut ng my tnh u hnh dung l nhng chic my tnh c nhn hoc cc my tnh bn thng thng. Tuy nhin trong cuc sng hng ngy, rt nhiu ngi li s dng my tnh hoc t nht mt cng ngh my tnh lin quan chng hn nh cc vi x l, vi iu khin trong khi h khng xem nh l nhng my tnh. Cc thit b thng thng nh in thoi di ng, my nghe nhc MP3, tivi, my git thng c gn kn cc cng ngh my tnh. Tuy nhin ngi s dng vn ch coi tivi nh mi chic ti vi thng thng khc m khng h xem chng nh mt loi my tnh no c giao tip c bit v khc nhau. gip hnh dung r dng hn v tng lai ca my tnh sau giai on my tnh c nhn hin nay, chng ta s xem xt mt s quan im ni bt v vn trn.

1.2 Mt s quan im v tng lai ca my tnh 1.2.1 Quan im ca Mark Weiser Mark Weiser (1952-1999) c xem l cha ca tnh ton khp ni, ng l ngi a ra thut ng ubiquitous computing (gi tt l ubicomp) cp ti xu hng l trong tng lai con ngi cng mt lc s khng ch tng tc vi duy nht mt my tnh nh hin nay m thay vo s tng tc vi mt tp hp cc my tnh nh c kt ni mng vi nhau, thng thng chng c tnh v hnh v hin din bn trong trong cc vt dng hay cc i tng m chng ta thy hng ngy. Cng ngh my tnh c nh gi l mt trong nhng cng ngh v i nht mang li nhiu li ch to ln cho con ngi. Tuy nhin Mark Weiser cho rng mc d cc cng ngh tin tin huyn thoi tri qua hng thp k pht trin nhng chng vn cha t ti chn mui. gip nhn r nhn nh ny ng so snh vic pht minh ra my tnh vi vic pht minh ra ch vit. Theo ng ch vit c th coi l v d u tin v cng ngh thng tin: l mt pht minh cho php chng ta lu gi cc ni dung v cc tng cho vic tra cu, c li sau ny, ch vit hin nay c s dng rt ph bin v rng khp mang tnh ton cu do ch vit xut hin khp mi ni trn cc tp ch, t ri, cc bng hiu, nhn hng, trn tng, trn cc phm bm ca cc thit b, cc gi hng v trn bt c th g con ngi c th tng tng ra. iu quan trng nht m chng ta khng ngh n l vic c hoc vit khi chng ta tm hiu cc thng tin v cc bng ch dn, bng hiu, thc n Chng ta xem xt cc thng tin mt cch t nhin thay v tp trung vo vic phn tch nhng t ng h tr nhng g, cch c chng ra sao R rng trong cc tnh hung trn ch vit l mt dng ph bin khp ni v c tnh n, tuy nhin nu cp n my tnh th hin nay chng cha th t n mc nh vy. Khi chng ta s dng my tnh, chng ta thng tp trung vo cc cng c hn l tp trung vo nhim v cn hon thnh. Theo Mark Weiser, Ubicomp khng c ngha l khp ni u c cc my tnh truyn thng m l c cc my tnh c kh nng tnh ton khp mi ni, chng c th c nhng trong mi trng theo cch m chng c th c s dng khi cn n trong khi chng ta khng phi bn tm n s c mt ca chng, my tnh s tr nn rng khp khi chng m thm h tr ngi s dng thay v n li l tm im ca s ch .

Mt v d khc c Mark Weiser la chn nhn mnh quan im trn l nhng chic ng c in, khong hn mt th k trc y khi cc m t in tr thnh mt cng ngh cch tn to ln, n l thnh phn c bn trong cc phn xng. Mt chic m t in thng qua c cu truyn ng thch hp s cung cp nng lng cho hng t cc my mc v thit b. Ngy nay thay vo cc m t in tr nn c gi thnh rt r, r n mc mi cng c ph bin (chng hn nh khoan, ca, qut, my ht bi) hu nh u c t nht mt chic m t bn trong. Trong mt chic xe hi thng thng, ng quan st thy c ti hn 20 m t in, mt vi trong s chng c kch hot bng mt ng tc n gin v ngi li xe hu nh khng quan tm n vic cc m t in hot ng chi tit nh th no. y l mt v d khc v cng ngh c tnh n ph bin pha sau hu trng.

Hnh 1-1 Xu hng pht trin ca tnh ton khp ni (ngun http://www.ubiq.com). Hnh 1-1 cho l tin on ca Mark Weiser v xu hng pht trin ca my tnh trong tng lai c ng a ra trong mt ti liu nm 1996, cho ti thi im ny cc mc thi gian do ng a ra c l hi sm nu nhn li thc t trin khai ca tnh ton khp ni hin nay, tuy vy xu hng m ng quan nim ang ngy cng c cng c. Trong bi vit My tnh ca th k 21 [9] Mark Weiser a ra nhng nhn nh ca mnh v my tnh trong th k 21, theo ng con ngi v my tnh c hp nht nh l mt thc th thng nht. ng m t Cc cng ngh c bn s bin mt. Chng lin kt vi nhau thnh kt cu ca cuc sng hng ngy

cho ti khi khng th phn bit c vi nhau. V bn cht, quan im ca ng l trong tng lai, s tn ti cc thit b tnh ton khp ni trong mi trng thc m ngi s dng hu nh khng cm nhn c s hin din ca chng. y chng ta phi lu qu trnh tng tc vi my tnh c nhn vn c chp nhn rng ri bi b phn ln ngi s dng. Cc my tnh c nhn ang dnh c nhiu vai tr quan trng nhng chng cha thc s mang li cch thc tnh ton trn vn, khng phi l thnh phn n trong cuc sng hng ngy ca chng ta. Mt cng ngh no mun tr nn rng khp n phi b trit tiu trong mt bi cnh no v ng thi n phi c lin kt trong cc hot ng t nhin ca con ngi. 1.2.2 Quan im v my tnh v hnh ca Norman (Invisible computer). Trong cun sch The invisible computer [8] vit nm 1998, Don Norman pht trin quan im ca Mark Weiser v cc my tnh v hnh, thm d kh nng hin thc ha vic tch hp cc thit b tnh ton dn dn vo cc sn phm thng mi. Trong v d u tin c cp trong cun sch Norman quay li v d v trng hp chic ng c in m Mark Weiser cp v ch ra cc tnh hung s dng chng mt cch ph bin, ng ly v d trong mt catalogue qung co t nm 1918 trong cp v cng dng ca cc ng c in c th ng dng trong gia nh, theo qung co th chic ng c c th c th kt hp linh hot vi mt danh sch v tn cc vt dng khc nhau gip ngi ch s dng c th thc thi c hng lot cc cng vic ph bin trong gia nh chng hn nh chng c th ng vai tr quan trng trong cc my ht bi, qut in, my nh trng, my khu Ngy ny ta thy s khng cn ph hp khi tho ng c ca my khu gn n vo chic my nh trng hay thay th cho mt chic qut in hng, thay vo s l iu t nhin hn khi mi vt dng bao gm cc ng c nu cn thit v cc ng c ny c kch c v cng sut ph hp c gn c nh vo vt dng v tht kh c th hnh dung khi ch cch y mt vi thp k chng ta c th b thuyt phc bi vic mua mt chic ng c in a nng nh trn, gi y chng my ai quan tm n nhng chic ng c , iu m hu ht chng ta thc s quan tm l tnh nng ca cc vt dng ch khng phi l nhng chic ng c trn. Vi my tnh ngy nay theo ng chng ta cng ang gp

tnh hung tng t, cc h gia nh c thuyt phc mua nhng chic my tnh c nhn nhm phc v cho nhiu mc ch khc nhau trong cuc sng hng ngy chng hn nh duyt web, vit th, son tho vn bn, qun l ti chnh, xem phim nghe nhc tt c nhng thao tc v giao tip vi my tnh thc thi nhng cng vic c thc hin thng qua cc thit b vo ra thng thng nh chut, bn phm, chic my tnh c nhn c Norman so snh nh mt con dao a dng ca mt qun nhn do Thy S sn xut, n c th c s dng thc hin cng vic ca nhiu cng c khc nhau, tuy nhin khng ging nh bt k mt cng c c nhn chuyn dng no, do c qu nhiu mc ch cng dng nn chng thng kh s dng v bo dng ng thi kh m bo c cht lng cao trong hu ht cc trng hp s dng ng cho rng mi cng vic s c hon thnh v h tr tt hn nu ta s dng cc cng c c thit k chuyn bit cho mc ch . ng cng cho rng tn dng kh nng chia s d liu vi nhau cc vt dng ny cn c kh nng gi nhn thng tin vi nhau thng qua cc lin kt mng. 1.2.3 Mt s quan im v thut ng khc Ngoi hai quan im tiu biu nu trn cn c mt s quan im khc v tng lai ca my tnh chng hn nh: +Tnh ton t tr (Autonomic computing) do Horn xut nm 2000, cp n vic xy dng cc h thng c th t gim st, t sa cha v t cu hnh. Tnh ton t tr lin quan ti cc h thng tnh ton khp ni v c th tn dng thng tin v mi trng ca h thng v nhng ngi s dng hot ng hoc ra quyt nh. +Pervasive computing cp ti vn v my tnh hay cc thit b tnh ton xut hin rng khp trong cuc sng hng ngy. Pervasive computing c th xem nh l s kt hp ca my tnh di ng (loi my tnh c eo bn ngi hoc c c ngi s dng mang theo) v cc my tnh nhng trong mi trng c nh do chng cng c th c hiu nh l tnh ton khp ni. Ngoi ra cn mt s quan im vi cc tn gi khc nh Disappearingcomputer, Proactive computing, Ambient intelligence, Sentient computing, Embedded Computing sau chng l nhiu vn cng ngh ang c nghin cu pht trin, v bn cht chng lin quan n vic m t tng tc trong tng lai

gia con ngi vi my tnh nhng nhn chung chng tng i gn gi vi thut ng tnh ton khp ni Ubiquitous Computing. 1.3 Tnh ton khp ni v hin thc o. i nghch vi tnh ton khp ni, theo Mark Weiser l hin thc o (Virtual reality), trong hin thc o th gii thc c mang vo my tnh trong khi tnh ton khp ni li mang my tnh vo th gii thc. Theo ng hin thc o da trn cc m hnh phc tp ca th gii ang tn ti hoc th gii tng tng. M hnh ny khng ch n thun tn ti trong khng gian ba chiu m chng cn bao gm nhiu m t tnh v ng c m hnh ha, hin thc o tp trung cc cng c phc tp m phng th gii hn l n mnh trong th gii m chng tn ti, trong th gii con ngi c t trong mi trng do my tnh to ra, ngc li trong tnh ton khp ni con ngi sng trong th gii thc v vn tn dng c nhng kh nng to ln ca my tnh. Chng hn trong mt s d n ngi s dng c eo mt loi knh c bit trong cc cnh nhn to, eo gng tay hay thm ch mc mt b c bit c th cm nhn c nhng hiu ng khin ngi s dng c th di chuyn v tng tc vi cc i tng o Khi phc tp ca cc m hnh tng ln, ngy cng nhiu kha cnh ca th gii thc c m phng trong hin thc o, cui cng hu ht mi th xut hin trong th gii o thm ch l con ngi tr thnh vai tr ph i vi my tnh.

Hnh 1-2. So snh ca Mark Weiser v hin thc o v tnh ton khp ni (Ngun http://www.ubiq.com) Mc d hin thc o c th t c mc ch ring trong vic cho php con ngi khm ph, hc tp, tm hiu mt lnh vc no m bnh thng con ngi khng th c iu kin hoc kh nng tip cn chng hn nh pha bn trong cc ,

b mt ca cc hnh tinh no , mng thng tin ca cc c s d liu phc hp Tuy nhin Mark Weiser vn ph nh vai tr trung tm ca my tnh trong hin thc o ng thi xut m hnh tnh ton khp ni nhm o ngc vai tr trn, trong loi b vai tr trung tm ca my tnh bng cch nhng chng vo mi trng hoc trong cc i tng vt l, trong cc cn phng c thit k sao cho con ngi tr thnh trung tm Trong tnh hung ny, ng s dng thut ng cm xc o (embodied virtuality) thay th cho cm t Ubbiquitous computing (tnh ton khp ni). Hnh 1-2 do Mark Weiser a ra nhm m t r hn quan im ca ng v s i lp gia tnh ton khp ni v hin thc o. 1.4 Mt s nghin cu ban u v tnh ton khp ni ti trung tm Xerox PARC. Cc nghin cu v tnh ton khp ni ti trung tm Xerox PARC ni Mark Weiser lm vic c xem nh l nn mng trong vic thm d v quan im v hnh ca my tnh v pht trin mt s thit b my tnh di t duy hon ton mi, cc thit b my tnh ny khng nht thit phi gm cc b phn nh hp my, mn hnh, bn phm... ging cc my tnh truyn thng. in hnh trong s cc thit b ny l cc thit b kch thc t rt nh nh thit b Tab, kch thc trung bnh Pad n thit b c kch thc ln Board c th nghim ti phng th nghim ca trung tm Xerox PARC trong khong thi gian t 1988 n 1994 di s gim st ca Mark Weiser. Ngun cm hng to ra cc thit b kch thc phong ph nh vy xut pht t vic quan st cc vt c kch thc khc nhau xung quanh trong cuc sng hng ngy m chng ta thng bt gp chng hn nh t nhng mu giy nhc vic nh, cc cun sch, my tnh xch tay n cc bng hiu, bng vit, mn hnh kch thc ln... y c xem nh l nhng n lc u tin c th a cng ngh my tnh ho dn vo mi trng ging nh cch m chng ta vit, cc nh nghin cu ca trung tm Xerox PARC nhm n vic thay th cc my tnh bn ang ng vai tr trung tm bng cc thit b c thit k chuyn dng hn. Cc thit b Tab lc l cc thit b c kch thc rt nh c mt mu giy c th t gn trong lng bn tay nng khong 200g, thit b ny bao gm mt mn hnh hin th n sc, 3 nt bm v mt chic loa nh, cc phm bm c thit k sao cho c ngi thun tay tri hoc tay phi u c th d dng s dng, c th

nhp liu thng qua vic s dng cc bt in t. Thit b ny giao tip vi mt b thu pht t trong phng bng tia hng ngoi vi tc truyn l 19.2 Kbaud. Chc nng ca Tab tng t nh nhng t giy ghi ch v sau khi kt ni vi cc thit b thu pht trong khu vc vn phng lm vic, cc Tab c th pht hin v cung cp mt s ng dng cho ngi s dng. Thay v c nhiu ca s c m trn my tnh bn, ni dung ca mi ca s c th c chuyn vo mt Tab. Mt ng dng khc ca Tab l nt d bo, trong n c th np thng tin d bo thi tit mi nht t mng internet v nt email c th cho php ngi s dng duyt qua, tr li hoc lu tr email... cng nhiu ng dng khc m cc Tab c th cung cp chng hn nh trong vic gim st, a ra cnh bo v cc dch v khc nhau da vo thng tin v tr ca ngi s dng

Hnh

1-3

Thit

b

Tab

ca

hng

Xerox

Parc

(

ngun

httpBB://www.ubiq.com) Thit b ParcPad c mn hnh hin th 640x480 pixel, s dng bt in t nhp d liu, chng c coi nh l nhng thit b my tnh cm ng u tin trn th gii, s dng cc cng ngh truyn thng gm hng ngoi tc 19.2 kb/s, sng radio tc 240 kb/s v kt ni c dy vi tc 1Mb/s. Mc ch thit k ban u ca thit b ParcPad l s dng nh chc nng ca giy v bt vit (mt vt dng c loi ngi s dng rt ph bin hin nay), chng l mt dng my tnh tm thi, khng c kh nng mang theo bn ngi, thay vo ngi s dng s bt gp n ti nhiu ni v c th t do s dng chng khi cn.

Hnh 1-4 Mt loi thit b ParcPad ca hng Xerox Parc (ngun http://www.ubiq.com) Cc Board c mn hnh hin th khong 1x1m v mc ch ca n l hin th cc thng ip, cc on video nhm phc v mt cng ng ngi s dng y ta cng cn lu l kh nng ca cc thit b ny khng phi do mnh n mang li m do s kt hp tng tc gia nhiu thit b khc nhau. 1.5 Cng ngh Calm Mark Weiser v Seely Brown s dng thut ng cng ngh calm (calm technology) m t mt kha cnh quan trng khc trong lnh vc ubicomp: Thc t l my tnh khng cn gi v tr c tn trong trung tm s ch ca ngi s dng. Trong nhiu trng hp cc cng vic tnh ton c th hon ton din ra sau hu trng v to ra tc ng ti nhn thc bn ngoi ca ngi s dng theo cch khim tn. minh ha cho vn ny, cc tc gi a ra mt v d v si dy Dangling.

Hnh 1-5. M phng dung lng mng thng qua si dy Dangling (ngun http://nano.xerox.com). Dangling l mt si cp nha mu c treo vo mt chic m t nh gn vi thit b phn cng mng v c giu trong mt gc phng, khi c cc gi tin truyn qua mng s lm cho ng c pht ra cc xung iu ny s lm cho si dy s b rung theo. Khi mng bn, si dy s rung lin tc, khi mng khng b nghn, si dy ch rung mt vi giy. R rng si dy Dangling ny cho ta thng tin th v hn nu so snh chng vi mt chng trnh gim st cc gi tin, n khng cn i hi s ch ca ngi s dng v ta hon ton c th ty trong vic lu n trng thi ca n ra sao. Nh vy v bn cht c th xem nh mc ch ca cng ngh calm l nhm n vic tm cch gim bt s tp trung ca ngi s dng i vi cc thng tin lm con ngi d qu ti thng qua bin php no cho php ngi s dng la chn thng tin no l thit yu, thng tin no mang tnh ph tr t dnh s quan tm khc nhau cho chng. 1.6 Tnh ton khp ni v bi ton nh v. Trong tnh ton khp ni chng ta cn phi gii quyt nhiu vn phc tp khc nhau chng hn nh cc vn v mt cng ngh, cng sut tiu th, tnh bo mt Mt trong nhng bi ton quan trng m chng ta cn gii quyt l vn v xc nh v tr ca cc i tng hay cn gi l bi ton nh v. Cc h thng nh v trong mi trng bn ngoi (outdoor), chng hn nh GPS c trin khai ht sc rng ri v mang li nhiu li ch thit thc trong nhiu ng dng. Vi mi trng trong nh (indoor) c nhiu cng ngh v phng php khc nhau c khai thc s dng trong cc h thng nh v, tuy nhin phn ln trong s chng c gi thnh tng i cao v ang trong qu trnh nghin cu hon thin. xc nh c v tr ca mt i tng trong mi trng indoor thng chng ta phi kt hp nhiu vn cng ngh, phng php vi nhau, y l nhng cng vic tng i phc tp v mt cng ngh v k thut. Trong cc chng sau ca lun vn chng ta s i vo tm hiu cc vn lin quan n nh v c bit l trong mi trng indoor t gip chng ta hiu v c ci nhn tng th v cch thc trin khai, nghin cu v cc h thng nh v trong tnh ton khp ni.

1.7 Kt lun. Tnh ton khp ni l quan im v th h my tnh k tip trong con ngi v my tnh c xem nh s hp nht vi nhau. Tt c cc hnh ng t nhin ca con ngi u c tng cng trong kha cnh tnh ton. Nng lc tnh ton ny thng c nhng vi cc hot ng ca con ngi theo cch m cc thit b tnh ton v hnh trong bi cnh no . N i ngc li vi khi nim v cch tng tc vi my tnh m hin nay chng ta ang tin hnh. Thch thc ln nht m chng ta phi i mt trong vic hin thc ho khi nim tnh ton khp ni l s kt hp ca nhiu cng ngh lin quan. Cc cng ngh lin quan bao gm phn cng, phn mm, cm bin thc, lin kt vi ngi s dng v trin khai, tnh t l, an ton v ring t. Tnh ton khp ni l mt lnh vc phong ph cho cc nh nghin cu trong cc quy tc cha c vch ra v bin gii cha c nh hnh mt cch y .

CHNG 2 CC PHNG PHP NH V TRONG CC THIT B TRONG NH (INDOOR). 2.1 Gii thiu Cc phng php nh v trong tnh ton khp ni v c bn c th c phn loi thnh: phng php phn tch cnh, phng php tim cn mt s phng php hnh hc nh giao giao ng trn, giao gc, giao hyperbolic t c chnh xc cao hn, mt s h thng nh v thng kt hp s dng cc phng php trn. Trong chng ny chng ta s i su vo tm hiu cc phng . 2.2 Phng php nh v tim cn (proximity sensing). y l phng php n gin v c s dng rng ri nht hin nay xc nh v tr ca mt thc th, phng php ny da vo khong gii hn trong vng ph sng (v tuyn, hng ngoi hoc sng siu m) ca mt trm thu pht c s (Base Station BS). T v tr ca thc th cn nh v c xc nh qua cc to lin quan ca trm thu pht c s. Nguyn tc hot ng ca phng php tim cn c m t trong hnh 2-1. Hnh 2-1 (a) l mt v d v trng hp s dng phng php nh v tim cn thng qua ng ten v hng, hnh 2-1 (b) l v d khc v vic s dng phng php nh v tim cn thng qua ng ten qut. Cc trm thu pht c s ( bit trc v tr) s gi hoc nhn cc tn hiu iu khin ti cc thit b u cui, nu qu trnh gi nhn thnh cng th c th kt lun thit b u cui ang trong phm vi ph sng ca mnh.

Hnh 2-1 Nguyn tc hot ng ca phng php nh v tim cn. 2.3 Phng php phn tch cnh (scene analysis) Phng php phn tch cnh thc ra ch l mt trng hp ring ca phng php phn tch mu (pattern Matching). Phng php phn tch cnh c th phn thnh hai loi chnh l phn tch cnh tnh v phn tch cnh ng. Trong phn tch cnh tnh, v tr ca mt i tng c th c xc nh bng cch so snh nh chp ca mt cnh to ra t i tng quan st vi mt s nh n gin c ghi li t trc (cc nh ny c th c chp t cc v tr khc nhau v c cc ta cn quan tm c xc nh), trong cc i tng hoc l chnh n, hoc l mt i tng no tn ti trong cnh. Trong trng hp ca phn tch cc cnh ng, v tr i tng cn xc nh cc im khc nhau trong cc nh c chp thnh cng t mt cnh no . Mt v d v vic s dng phng php phn tch cnh c m t trong hnh 2-2, trong hnh dng ng chn tri c suy ra t mt cnh c nh c th c s dng tra cu v tr t mt c s d liu xy dng sn hoc tnh ton s chuyn ng ca cc phng tin giao thng trong cc camera gim st.

Hnh 2-2 Mt v d v phng php phn tch cnh. 2.4 Phng php giao khong cch (Lateration) Vi phng php giao khong cch, cc kt qu xc nh c s hoc l khong cch hoc s chnh lch v khong cch gia i tng cn xc nh v tr ti t nht 3 trm thu pht c s. C hai thng tin trn sau to thnh mt h phng trnh gm n cng thc khng tuyn tnh, gii phng trnh ny ta xc nh

c v tr ca i tng, trong n l s trm c s. Vi n=3, phng php giao khong cch c gi php c tam gic (trilateration). Nu nh v da trn vic xc nh cc khong cch, v tr ca cc i tng lc ny s c tnh ton bng phng php giao ng trn (circular lateration), trong khi nu nh v da trn s chnh lch khong cch th v tr ca i tng s xc nh thng qua phng php giao hyperbol (hyperbolic lateration). y chng ta cng cn phi lu vn l lm cch no xc nh cc khong cch v chnh lch khong cch mt cch r rng. 2.4.1 Giao ng trn (Circular lateration). Trong phng php giao ng trn, trc ht chng ta gi thit bit trc cc khong cch ri gia i tng v cc trm thu pht c s i (i = 1, . . . , n). Trong khng gian hai chiu chng c m t trong hnh 2-3. Nu ch c mt trm thu pht c s, v tr ca i tng s b gii hn trn ng trn c tm l trm BS v bn knh chnh l khong cch t i tng n BS (xem hnh 2-3 (a)). Nu c thm mt trm thu pht th 2 th v tr ca i tng c gii hn ch cn hai kh nng l hai v tr giao nhau ca vng trn ban u v vng trn mi (xem hnh 2-3 (b)). Tng t nh vy nu c thm BS th 3 chng ta s xc nh c chnh xc v tr ca i tng chnh l im giao nhau ca ba ng trn tng ng vi tm l v tr ca ba BS, c bn knh tng ng vi khong cch t i tng n ba BS (xem hnh 2-3 (c)).

Hnh 2-3 phng php giao ng trn trong khng gian hai chiu 2.4.2 Giao Hyperbolic

Phng php giao hyperbol l phng php nh v bng cch tnh ton chnh lch thi gian n TDOA (Time Difference Of Arrival) ca mt tn hiu c truyn t i tng cn nh v ti ba hay nhiu b thu. y chng ta cn phn bit phng php giao hyperbol vi phng php giao ng trn khong cch l phng php giao hyperbol s dng cc kt qu o tuyt i ca thi gian n t cc v tr khc nhau. Phng php giao hyperbol c s dng ph bin trong cc ng dng cho dn dng v qun s nh v my bay, xe c gii hoc cc trm pht. Nu mt xung c pht t mt im, n s c thi truyn khc nhau n hai im khc nhau trong khng gian, thi gian khc nhau ny xut pht t nguyn nhn do khong cch t cc im thu n im pht khc nhau. Trn thc t, nu bit trc v tr ca hai im thu ta c th xc nh c v s cc im pht sao cho kt qu o thi gian n TDOA ging nhau. Nu bit trc v tr hai b thu v TDOA, tp hp cc v tr pht tho mn iu kin trn s nm trn mt trong hai na ca hnh hyperboloid. (xem hnh v 2-6)

Hnh 2-6 Tp hp cc im c cng TDoA ti hai trm thu s nm trn hai na ca hnh hyperboloid

2.5 Phng php giao gc (angulation) Phng php giao gc l phng php nh v i tng t cc to bit ca mt s trm thu pht c s tuy nhin i ngc vi phng php giao khong

cch trong l s dng cc khong cch o c xc nh to , phng php giao gc s dng cc gc gia i tng v cc trm BS lm c s xc nh v tr. xc nh c cc gc ny cc trm thu pht c s hoc cc thit b u cui cn phi c trang b cc loi ng ten mng (array antena) v tu thuc vo cu trc nh v da trn c s mng hay cu trc da trn thit b. Do vn phc tp trong thit k v gim gi thnh, trong hu ht cc h thng s dng phng php giao gc hin nay cc ng ten mng c s dng ch yu pha trm thu pht c s. Nguyn tc c bn ca phng php giao gc c m t trong hnh 2-9. Gc ti ca tn hiu iu khin c o ti trm BS do chng hn ch v tr ca i tng dc theo mt ng thng giao nhau gia i tng v v tr BS. Nu mt gc ti trm BS th hai c xc nh, ng thng khc s c xc nh v giao nhau gia hai ng thng trn chnh l v tr ca i tng. Nh vy theo l thuyt c th xc nh c v tr ca i tng ta ch cn xc nh c gc tng ng gia i tng v hai trm BS l .

2 1 (X2,Y2)Trm thu pht c s

(X1,Y1) Thit b u cui Hnh 2-9 Xc nh v tr i tng qua phng giao gc. 2.6 Phng php du vn tay trong mng ni b khng dy (WLAN Fingerprint) Phng php du vn tay trong mng ni b khng dy (gi tt l WLAN Fingerprinting) l phng php c s dng ht sc ph bin hin nay trong cc h thng nh v s dng cng ngh WLAN, y cng l mt hng nghin cu nh v ang c rt nhiu cc trung tm nghin cu quan tm. Trong phn ny chng ta s tm hiu chi tit v phng php ny. V bn cht phng php Fingerprinting c chia thnh hai giai on: giai on off-line l giai on trong h thng s ghi li cc mu thng s thu c

ca cng tn hiu t tp hp cc im tham chiu hu hn xc nh trc sau lu tr chng trong mt c s d liu tin cho vic nh x v nh gi sau ny. V d trong mt phng php n gin c s d liu ny c th cha cc bn ghi c dng (p, RSS1, . . . , RSSn), trong p biu th im tham chiu v RSSi vi i = 1, . . . , n biu th gi tr RSS ca AP th i. Tuy nhin RSS ph thuc rt nhiu vo vic gia b thu v pht c th nhn thy nhau hay khng (line-of-sight) v hng ca i tng ti mt v tr, do hu ht cc bn ghi RSS trong c s d liu c cha thm thng tin v mt s hng ca i tng (chng hn nh hng ng, Ty, Nam, Bc hoc biu th qua cc o 00,900,1800,2700 ) ti mi im tham chiu, kt qu l thng tin trong bn ghi c s d liu s c dng (p, d, RSS1, . . . , RSSn). Bng 2.1 cho ta mt v d v mt c s d liu c to ra theo cch ny. BNG 2.1: V D V MT C S D LIU CHA CC THNG TIN C XC NH TRC TRONG PHNG PHP FINGERPRINTING. V tr P1 0O 90O 180O 270O P2 0O 90O 180 270 P3 0O 90O 180O 270OO O

Hng RSS[dbm] 00-15-F2-52-42-1D -21 -23 -25 -19 -33 -30 -29 -35 -51 -53 -56 -50

RSS[dbm] 01-36-E4-89-45-1A -75 -76 -71 -79 -66 -69 -65 -64 -41 -43 -46 -40

RSS[dbm] 0A-CA-56-21-407C -81 -83 -85 -80 -78 -72 -76 -79 -16 -14 -18 -17

Cc im tham chiu c th c xc nh theo mt nguyn tc nht nh chng hn nh cch u nhau trong trong khng gian tu theo chnh xc yu cu

hoc cu trc ca to nh. V d nh trong hnh 2-11 cc im tham chiu c th c xc nh theo gi tr trung bnh da theo to Cc, da theo s phng hoc mt h thng tham chiu no . Giai on off-line cn c gi l giai on giai on hc (training) hoc giai on giai on xc nh (calibration ). Trong giai on trc tuyn (on-line) hay cn gi l giai on thi gian thc, cc mu RSS tng ng vi v tr thc th c lu li sau c so snh vi cc trng RSS ca cc bn ghi c lu tr trong c s d liu. V tr ca i tng sau c xc nh bng cch so snh gi tr o c vi gi tr gn nht trong c s d liu theo cc phng php v thut ton khc nhau.

Hnh 2-11 V d v mt mi trng p dng phng php fingerprinting. Phng php Fingerprint c th c trin khai thng qua ba m hnh: m hnh c s tr gip ca thit b u cui (terminal assisted), m hnh da trn thit b u cui (terminal based) v m hnh da trn kt ni mng (network based) (xem hnh 2-12). Vi m hnh c s tr gip ca thit b u cui v m hnh da trn thit b u cui, c s d liu c xc nh t cc php o hng v ti cc im tham chiu khc nhau trong giai on off-line. Vi mc tiu mt thit b u cui s thu cc tn hiu iu khin c pht bi cc im truy nhp trong khu vc cn nh v theo cc hng khc nhau v lu li cc gi tr RSS tng ng. Th tc trong giai on thi gian thc sau s c trin khai theo trnh t: Thit b u cui ghi li cc mu RSS ging nh trong qu trnh off-line tuy nhin ch theo hng ca ngi s dng. Trong m hnh c s tr gip ca thit b u cui, nh k thit b u cui s gi cc kt qu o ti my ch trong h thng (xem hnh 212(a)). My ch ny duy tr c s d liu v sau thc hin i snh cc mu RSS

xc nh v tr i tng. Trong m hnh da trn thit b u cui, c s d liu c duy tr trong cc thit b u cui v vic i snh c so snh din ra cc b trong thit b u cui (Hnh 2-12(b)).

Hnh 2-12 Cc m hnh hot ng ca fingerprinting Vi m hnh da trn kt ni mng, c s d liu c to ra t cc php o xc nh RSS theo hng truyn ln. Trong giai on off-line, cc thit b u cui nh k pht cc tn hiu iu khin t mt vi hng khc nhau ti mi im tham chiu. Cc im truy cp AP trong khu vc nh v thu nhn cc tn hiu iu khin ny v lu tr li cc thng tin RSS tng ng. Nhng kt qu o c sau c tp trung li trong c s d liu. Trong giai on thi gian thc, cc thit b u cui nh k phi pht cc tn hiu iu khin ti cc AP xung quanh, sau cc AP s chuyn tip cc kt qu c ti my ch phc v mc ch i snh (hnh 2-12(c)). Mt trong nhng vn phc tp nht ca fingerprinting l vn tp hp s liu trong giai on off-line. Vic xc nh cc to ti nhng im xc nh trc trong ton b khu vc cn trin khai h thng nh v l mt qu trnh tn nhiu thi gian v cng sc. Thm ch qu trnh ny phi trin khai li khi c s thay i lin quan n AP, v d nh khi ci t thm mt AP mi hoc khi mt AP c c thay th hoc di chuyn. Mt cch khc xc nh c s d liu l xy dng t cc m hnh ton hc tnh ton thng qua vic xem xt v tr ca cc AP, cng tn hiu truyn ca chng, suy hao trong khng gian t do v phn x hoc hp th do cc vt chn nh cc bc tng hoc vt trong khu vc nh v. Theo cch ny c th dn n phng thc thun li v nhanh chng c th to ra mt c s d liu nhm cp nht cho mt mng li cc im tham chiu bt c khi no cu hnh ca cc AP thay i m khng cn phi tin hnh o xc nh

li s liu. Trong tin trnh thi gian thc, qu trnh i snh gia gi tr thu thp c v cc mu RSS trong c s d liu din ra theo tng giai on, mt trong nhng phng php ph bin thng c p dng l tnh ton khong cch clit , trong (RSSo,1, . . . , RSS o,n) l cc mu RSS thu c v (RSSr,1, . . . , RSSr,n) l cc mu lu tr trong c s d liu ti cc im tham chiu. T tt c cc im tham chiu lu tr trong c s d liu, nhng v tr no c khong cch clit nh nht s c xem nh v tr ca i tng. Phng php ny cn c gi l lng ging gn nht trong khng gian tn hiu (Nearest Neighbor in Signal Space NNSS) do Bahl v Padmanabhan a ra nm 2000. Mt hn ch ca phng php trn l vi mi v tr c nh ta phi xc nh li ton b c s d liu v vic i snh ch da trn cc mu RSS trung bnh. Phng php sau c th nh hng nghim trng n chnh xc ca h thng nu cng tn hiu thu RSS c s bin ng ln xy ra do mt s l do nht nh, mt s phng php phc tp hn chng hn nh thay v vic lu li cc gi tr trung bnh chng li lu gi cc m t cc bin i ca cng tn hiu c to ra trong tin trnh off-line thng qua cc phn b xc sut sau ny ch cn cn c vo phn b xc sut xy dng li c s d liu.

CHNG 3: TN HIU GPS 3.1 GII THIU S ra i ca nhng phng tin vn chuyn nh my bay, v nhng con tu v tr i hi iu khin nhng thit b trong khng gian ba chiu. Nhng phng php dn ng v nhng h thng dn ng v tuyn in ch dng cho vic dn dt cc tu thy tr thnh li thi v khng ph hp vi vic iu khin cc thit b chuyn ng trong khng gian ba chiu (6 bc t do) v nhng h thng ng thi ch xc nh c v tr theo 2 chiu khng gian. Trc nhng i hi v k thut nhiu nh khoa hc c chnh ph M ti tr thc hin nghin cu h thng dn ng da trn v tr. GPS l g ? GPS ( Global Positioning System H thng nh v ton cu ): l mt mng li cc v tinh lin tc gi cc tn hiu, qua cc my thu GPS c th xc nh c v tr ca mnh.

3.2 M BO AN TON THNG TIN TRONG GPS 3..2.1 Tn hiu GPS Cc v tinh GPS pht hai tn hiu v tuyn cng sut thp gii L1 v L2. (Gii L l phn sng cc ngn ca ph in t tri rng t 0,39 ti 1,55 GHz). GPS dn s dng tn s L1 1575.42 MHz trong gii UHF. Tn hiu truyn trc th, c ngha

l chng s xuyn qua my, thu tinh v nha nhng khng qua phn ln cc i tng cng nh ni v nh. L1 cha hai m "gi ngu nhin"(pseudo random), l m Protected (P) v m Coarse/Acquisition (C/A). Mi mt v tinh c mt m truyn dn nht nh, cho php my thu GPS nhn dng c tn hiu. Mc ch ca cc m tn hiu ny l tnh ton khong cch t v tinh n my thu GPS. Tn hiu GPS cha ba mu thng tin khc nhau m gi ngu nhin, d liu thin vn (almanac data) v d liu lch (Ephemeris data). M gi ngu nhin n gin ch l m nh danh xc nh c qu v tinh no l pht thng tin no. C th nhn s hiu ca cc qu v tinh trn trang v tinh ca my thu Garmin bit n nhn c tn hiu ca qu no. D liu thin vn cho my thu GPS bit qu v tinh u trn qu o mi thi im trong ngy. Mi qu v tinh pht d liu thin vn ch ra thng tin qu o cho v tinh v mi v tinh khc trong h thng. D liu lch c pht u n bi mi qu v tinh, cha thng tin quan trng v trng thi ca v tinh (lnh mnh hay khng), ngy gi hin ti. V v tinh c th i chch khi qu o cht t, nn trm iu khin mt t s lu gi cc thng tin v qu o, cao, v tr v tc ca v tinh. Nhng thng tin ny c chuyn v trung tm iu khin, y, n s c x l v gi ln v tinh hiu chnh n. Nhng thng tin chnh xc sau khi c x l ( thng theo tn sut 4-6 gi /ln ) c gi l ephemeris s c gi theo tn hiu v tinh n my thu. Hai thng tin tng hp l almanac data v ephemeris data ny s cho chnh xc v tr ca v tinh. 3.1.2 Thi gian l mt thng s quan trng. Mc d my thu GPS bit chnh xc v tr v tinh nhng n cn bit khong cch ti v tinh . Tht n gin, ta c:

Qung ng (khong cch) = vn tc x thi gian. Hi b chng ta cng c th chi mt tr chi nh th ny tnh xem chng ta cch m my ma bao xa. Chng ta nhn thy nh chp, bt u m giy v khi nghe thy ting st n, chng ta s bit c my giy m thanh truyn n tai chng ta, t s nhn vi vn tc chuyn ng ca m thanh ra c khong cch. S dng nguyn tc tng t, my thu GPS o c qung ng ti v tinh. Vn tc sng l 300.000 m/giy, c th b tr i mt cht do nhiu khi truyn qua kh quyn. By gi, GPS cn tnh ton thi gian ca cng thc trn. Vo mt thi im no , gi s vo lc 0 gi, mt v tinh bt u truyn mt chui tn hiu di, c gi l m ngu nhin gi. My thu cng bt u to ra chui m ging ht vo cng thi im. Khi tn hiu t v tinh truyn n my thu, chui tn hiu s b tr mt cht so vi chui do my thu to ra. Chiu di khong thi gian tr ny chnh l thi gian truyn ca tn hiu t v tinh. My thu nhn thi gian ny vi tc nh sng xc nh qung ng truyn tn hiu. Gi s rng tn hiu truyn trn ng thng, y chnh l khong cch t v tinh n my thu. thc hin php o ny, chng ta phi chc chn l ng h trn v tinh v trong my thu phi ng b vi nhau. Mt sai s 1 giy s dn n sai s l 300 ngn mt, qu nhiu phi khng cc bn. Do , chnh cc ti thiu cho cc my thu phi l c nano giy (10-9). c chnh xc nh vy, phi trang b ng h nguyn t cho khng ch cc v tinh m cn my thu ca bn na. Nhng ng h nguyn t th li t, khong 50 n 100 ngn . iu th qu t cho ngi dng. My thu GPS ch c ng h quartz ( thch anh ) loi ging nh ng h in t eo tay. Cc ng h quartz ny c iu chnh lin tc da vo tn hiu c truyn i t cc v tinh.Trn l thuyt th 4 mt cu phi giao nhau ti 1 im. Nhng do sai s ng h quartz r tin, 4 mt cu khng cho 1 giao im duy nht. Bit rng sai s ny gy ra bi ng h trn my thu l nh nhau t,

my thu c th d dng loi tr sai s ny bng cch tnh ton ra lng hiu chnh cn thit 4 mt cu giao nhau ti mt im. Da vo , my thu t ng iu chnh ng h cho ng b vi ng h nguyn t trn v tinh. Nh m ng h trn my thu c chnh xc gn nh tng ng vi ng h nguyn t. Vy l chuyn o khong cch c gii quyt n tho bng cng thc n gin trn : qung ng = vn tc x thi gian. Bit khong cch ri, chng ta cn phi bit v tr chnh xc ca cc v tinh trn qu o. iu ny cng khng kh lm v cc v tinh chuyn ng trn cc qu o bit trc v c th d on c.Trong b nh ca mi my thu u c cha mt bng tra v tr tnh ton ca tt c cc v tinh vo bt k thi im no gi l Almanac. Lc ht ca mt trng, mt tri c nh hng nht nh lm thay i qu o ca cc v tinh mt cht xu nhng b quc phng M lin tc theo di v tr chnh xc ca cc v tinh v truyn thng s hiu chnh n cc my thu thng qua tn hiu t v tinh. Vy l c hai vn khong cch v v tr gii quyt xong, v h thng c bn hot ng tt, tuy nhin, ngi ta nhn thy h thng c nhiu sai s. Nguyn nhn u tin l do vic gi s rng cc tn hiu v tinh c truyn theo ng thng n cc my thu vi vn tc khng i. Trong thc t, bu kh quyn tri t t nhiu lm chm tc truyn, c bit l khi sng in t i qua cc tng in ly v i lu. Do tnh cht ca cc tng ny khc nhau ti cc v tr khc nhau trn tri t nn tr ny ph thuc vo v tr ca my thu trn mt t, iu c ngha l kh c th loi tr sai s ny. Gn y ngi ta to ra cc m hnh ton hc m phng tnh cht ca bu kh quyn tri t gim thiu sai s ny. Ngoi ra, khi tn hiu phn x t cc vt th ln nh cc to nh cao tng, cng to cho my thu mt sai s nh l n t mt khong cch xa hn. Thnh thong, tn hiu t cc v tinh cng c sai s. B quc phng M cng thm vo sai s nhn to c gi mt cch vn hoa l Selective Availability hay SA. Chng ta thy chc nng c bn nht ca my thu GPS l thu nhn thng tin t ti thiu 4 v tinh, phi hp cc thng tin ny vi thng tin c cha trong Almanac tnh ton ra v tr ca my thu trn mt t.

V tinh cng nhiu th chnh xc cng cao. GPS cn bt c sng ca t nht l 3 v tinh nhng ti a c th ti 12. 3.2.3 GPS nh v th no. Cng vic ca mt my thu GPS l xc nh v tr ca 4 v tinh hay hn na, tnh ton khong cch t cc v tinh v s dng cc thng tin xc nh v tr ca chnh n. Qu trnh ny da trn mt nguyn l ton hc n gin.

Gi s bn mt ni no Vit Nam v bn hon ton khng bit mnh u v mt l do no . Bn gp mt ngi dn a phng v hi mt cch thn thin: Lm n cho ti bit ti ang u ? . Anh ta tr li: Bn ang cch H Ni 45km , y l mt s tht th v nhng cha c ch. Bn c th bt k u trn vng trn c tm l H Ni bn knh 45 km. Bn hi mt ngi khc v anh ta cho bit bn cch Hi Phng 40 km. By gi th kh hn. Nu bn tng hp hai thng tin bn s c hai vng trn giao nhau. V tr ca bn l mt trong hai giao im ca hai ng trn. Ngi th ba cho bn bit v tr ca bn cch Nam nh 30km. By gi th bn bit mnh u v ba ng trn ny giao nhau ti mt im l ni bn ang ng. Nu bit ta chnh xc ca H Ni, Hi Phng, Nam nh my thu GPS s tnh ra ta ca bn.

By gi, bn hy thay i 3 im H Ni, Hi Phng, Nam nh bng 3 v tinh bay tt m trn tri: chng ta bit V tr, tn ca v tinh Khong cch t v tinh n v tr bn ng

Nh vy, v tr ca bn l im giao nhau gia cc mt cu c bn knh t v tr ca bn ti cc v tinh ni trn. Th l GPS tnh c v tr ca bn: Nu bn bit rng mnh ang cch v tinh A 20 km, bn c th bt k ni no trn mt mt cu khng l c bn knh 20 km. Nu bn bit thm rng bn ang cch v tinh B 30 km, giao tuyn ca hai mt cu ny l mt ng trn V. V nu bn bit thm mt khong cch na n v tinh C, bn s c thm mt mt cu, mt cu ny giao vi ng trn V ti hai im. Tri t chnh l mt cu th t, mt trong hai giao im s nm trn mt t, im th hai nm l lng u trong khng gian v d dng b loi. Vi vic gi s tri t l mt mt cu, ta b qua cao ca bn ri. Do vy c c tung , honh v cao , bn cn thm mt v tinh th t na.

3.2.4 DGPS: Differential GPS - GPS vi sai.

V v tinh bay trn tri c th c nhng sai s nn ngi ta t nhng trm mt t hiu chnh sai s ny. Trm mt t cng ging v tinh trn tri, nhng v tr ca n chnh xc v sng pht trong khu vc ca n c th khe hn. M c nhng trm cng cng truyn h s hiu chnh min ph !!! Lc lng tun duyn M v cc c quan khc ca chnh ph M thit lp cc trm pht khp ni, c bit l chung quanh cc cng v tuyn giao thng thu. Cc tn hiu ny cng c truyn trn di tn 300kHz l di tn dn ng hng hi M. Bt k ai trong vng ph sng cng c th tn dng c thng tin hiu chnh ny ci thin c chnh xc ca vic nh v bng GPS. Hu ht cc tu thuyn u c trang b radio thu tn hiu dn ng ri nn vic thu thm tn hiu DGPS cng khng kh lm. My thu GPS by gi thng c thit k c th chp nhn hiu chnh, mt s khc c trang b c my thu tn hiu hiu chnh. chnh xc t h thng ny c th t 1-5 mt. S DGPS

Bn cc trm pht DGPS v phm vi ph sng M

V Nht Bn

USCG l tn vit tt ca Lc lng tun duyn M, nhng ngi xy dng, lp t, vn hnh v pht trin mng li thu pht DGPS trn ton lnh th M. H DGPS ca h c gi l USCG DGPS. WAAS Wide Area Augmentation System C quan qun tr hng khng Lin bang ca M (Federal Aviation Administration - FAA) cng u c km. H mun c mt mng li DGPS bao trm ton b lc a, v c th gii nu c th. FAA a ra mt k hoch

y tham vng gi l "Wide Area Augmentation System" hay "WAAS," v n chnh l mt h DGPS xuyn lc a. tng ny c pht trin t mt vi yu cu v tnh ton vn ca h thng hay "system integrity". D rng GPS l mt h thng c tin cy cao nhng thnh thong mt v tinh b trc trc c th pht i nhng thng tin khng chnh xc. Cc trm iu hnh mt t theo di cc v tinh v truyn mt thng ip h thng thng bo vi cc my thu hy lm l tn hiu t v tinh hng cho n khi c thng bo mi. Bt hnh thay qu trnh ny c th ko di vi pht v c th l qu tr i vi nhng chic my bay ang h cnh.

V th FAA c mt tng rng h c th gy dng mt h thng ring ca mnh c kh nng p ng nhanh hn. Khng nhng th, nh v chnh xc v tc thi cn gip cho FAA thu hp hnh lang bay m vn bo m an ton, trnh c cc s c m nhau ca my bay. FAA cn m ti vic hon thin cc thit b ct cnh v h cnh cho chnh xc hn, thm ch thay th cc h thng dn ng khng lu hin hu na. Nhng m, lm sao ? FAA cho rng h c th phng ln vi v tinh a tnh l lng trn u u vi nhim v truyn thng tin cho cc my bay tc th nu c s c. D nhin l nu thng tin c truyn trn cng tn s GPS th my thu GPS trn my bay c th thu m khng cn phi sm thm mt my thu ring. N s cung cp cc thng tin nh v lun th. Nu c vy th s lng v tinh trong tm nhn cng tng ln. FAA d tr cn khong 24 trm nm ri rc trn khp nc M l thu thp thng tin trn ton lnh th. Nhng trc ht, phi bt u t cc trm gn cc phi trng chnh trc, vy l Local Area Augmentation Systems" ra i.

Vi LAAS aircraft c th dng GPS h cnh trong iu kin tm nhn bng zero (hng bit FAA ni thit hay ni chi). Tuy nhin, c mt s hn ch bn cng nn bit. u tin l WAAS cha xy dng xong, v tinh cha phng s. WAAS c thit k cho hng khng c s dng v tinh a tnh, m chc cc bn cng bit, qu o v tinh a tnh phi nm trn mt phng xch o, v vy nu my thu gn 2 cc th kh nhn thy cc v tinh ny. Cng nh GPS, sng t v tinh a tnh cng b ni non, nh ca, vv che khut. Waas cho sai s t 3-5 mt v 3-7 m theo chiu cao v Vit nam hin nay cha c Waas. Ngoi ra do hin nay vic trin khai cc h thng WLAN trong cc c quan, x nghip trng hc ngy cng tr nn ph bin nn y cng s l mt thun li c th xy dng v trin khai cc h thng nh v da trn cc phng php Fingerprint v cng ngh WLAN m khng pht sinh thm nhiu chi ph.

KT LUN

Vn m bo an ninh thng tin trong h thng tnh ton khp ni lien quan cht ch n vn nh v cc thit b truyn thng trong h thng. C nh v thit b kt ni c chnh xc th mi c th m bo thng tin c truyn chnh xc. Do tiu lun ny ch yu tm hiu cch thc nh v trong h thng tnh ton khp ni, in hnh l h thng nh v ton cu GPS, v truyn thng trong mi trng trong nh.

TI LIU THAM KHO.[1] Axel Kupper (2005), Location-Based Services Fundamentals and operation, John Wiley & Sons. Ltd, England. [2] Frank Stajano(2002), Security for Ubiquitous Computing, John Wiley & Sons. Ltd, England. [3] Jeffrey Hightower and Gaetano Borriello (2001), A survey and taxonomy of location sensing systems for ubiquitous computing, UW CSE 01-08-03, Department of Computer Science and Engineering, University of Washington, Seattle, WA. [4] Jeffrey Hightower and G. Borrielo (2001), Location Sensing Techniques, University of Washington, Computer Science and Engineering, Technical Report UW-CSE-01-07-01. [5] Jeffrey Hightower and Gaetano Borriello (2001), Location systems for ubiquitous computing, IEEE Computer, 34(8), pp. 57-66. [6] Jeffrey Hightower and Gaetano Borriello (2001), Location Systems for Ubiquitous Computing, IEEE computer, pp. 57-66. [7] Joshua A Tauber (2002), Indoor location systems for pervasive computing, Technical report, Theory of Computation Group Massachusetts Institute of Technology. [8] Norman, D. A (1998), The Invisible Computer. Cambridge, MA: MIT Press [9] Mark Weiser (2002), "The Computer for the 21st Century", IEEE Pervasive Computing, pp. 19-25. [10] Mark Weiser (1993), Some computer science issues in ubiquitous computing, CACM, 36(7), pp. 74-83.