Tn hiu v tinh GPSTn s v iu chMc cng sutHm t tng quan v mt ph cng sutHm tng quan cho & hiu nng CDMAnh dng bn tin GPS

Tng quan v tn hiu GPSV tinh GPS truyn tn hiu nh v trn 2 tn s:Tn s s cp L1 (1.575,42 MHz)Tn s th cp L2 (1.227,6 MHz)Tn hiu c iu ch DSSS bao gm:Sng mangM tri ph PRN (duy nht vi mi v tinh)Bn tin nh vTt c cc v tinh GPS truyn tn hiu CDMA cng mt tn s sng mang.

Tng quan v tn hiu GPS bm tn hiu ca mt v tinh cng trong tm nhn vi nhiu v tinh khc, b thu GPS phi pht lp li bn sao ca:Dy PRN ca v tinh Tn hiu sng mang vi DopplerMy thu 2 tn s cho php o tr tng in ly bi tr ny c quan h vi h s vi sai gia 2 tn s sng mang ca tn hiu o TOA.Trong khi , my thu 1 tn s phi c lng tr tng in ly bng cc tham s m hnh c pht qung b trong bn tin nh v.

1. Tn s v iu ch

1. Tn s v iu chTn s c bn o = 10,23MHzTn s L1 = 154 o Tn s L2 = 120 oC 2 m PRN l m C/A v m PM C/A: tc chp 1,023x106 chips/s (o/10)M P: tc chp 10,23x106 chips/s (o), c mt m ha vi m P => m P(Y)Bn tin nh v c tc 50 bps, c cng modulo 2 vi m tri ph trc khi iu ch.iu ch BPSK c s dng.Pha sng mang c dch 90o trc khi iu ch vi m C/A v data.

(a) Sng mang L1 (pha 0o)(b) Sng mang L1 (pha 90o)(c) P(Y) XOR data(d) C/A XOR data(e) P(Y) XOR data iu ch vi sng mang L1 pha 0o(f) C/A XOR data iu ch vi sng mang L1 pha 90o(g) Tn hiu L1 tng hp

1. Tn s v iu ch

B to m GPS

B to m C/A

B to m PM P ca GPS l dy PRN to bi 4 thanh ghi dch 12-bit X1A, X1B, X2A, X2B.

X2 c a vo thanh ghi dch tr c X2i (s nhp tr tng ng vi PRN ca mi v tinh)M P ca v tinh i s l

1. Tn s v iu ch

1. Tn s v iu chCc a thc sinh ca b to m GPS

1. Tn s v iu chChu k t nhin ca c 2 thanh ghi b ct ngnChu k t nhin: 4095 chipsChu k X1A v X2A: 4092 chipsChu k X1B v X2B: 4093 chipsCc thanh ghi s reset khi sau 4092 hay 4093 chips Thit k nh vy nhm m bo pha vt trc ca thanh ghi X1A vi X1B, tng t vi X2A v X2B.Cng c pha vt trc gia cp thanh ghi X2A/X2B so vi X1A/X1B. S dng b m chia 37 lm cho pha vt trc l 37 chips cho mi chu k gia X1 v X2 v nh vy chu k X2 di hn X1 l 37 chips.

1. Tn s v iu chChi tit pha vt trc nh sau:Chu k X1 c nh ngha l 3750 chu k X1A, tng ng 3750 x 4092 = 15.345.000 chips, ~1,5 giy.Sau 3749 chu k ca X1B, mi chu k 4093 chips, tng ng 3749 x 4093 = 15.344.657 chips. ng b vi X1A, X1B phi dng v ch 343 chips (cho n ht chu k 1,5s)Nh vy, X1 c chu k l 15.345.000 chips.Tng t vi X2A v X2B, ch khc khi kt thc 15.345.000 chips, c 2 thanh ghi cng dng v ch 37 chips ti khi bt u ca tun.Nh vy, cc thanh ghi X2 c chu k 15.345.037 chips, hn 37 chips so vi X1.

1. Tn s v iu chLu rng, nu trong trng hp khng thc hin reset vo cui mi tun, dy P = XOR(X1, X2) s c di l 15.345.000 x 15.345.037 = 2,3547 x 1014 chips. Tc chip l 10.23 x 106, dy s c chu k l 266,41 ngy hay 38,058 tun.Tuy nhin do ct ngn ti cui tun, mi v tinh ch s dng on m ca 1 tun nn c 38 on ring bit s dng cho mi v tinh.Vy di ca m P ct ngn 7-ngy l 6,1871 x 1012 chips.Tng ng vi m C/A, 37 m c nh ngha v s dng.M P th 38 c dng lm m test cho my thu GPS

2. Mc cng sutMc cng sut tn hiu thu ti thiu ca 3 tn hiu GPS, tnh theo dBW, nh sau:

S dng ng-ten RHCP, phn cc tuyn tnh, tng ch 3-dB

2. Mc cng sut

2. Mc cng sutV d: Tn hiu L1 C/A, cng sut yu cu l:-158.5 3.0 + 184 + 0.5 + 3.4 = 26.8 dbWNu ng-ten v tinh L1 c tng ch ti thiu l 13.4dB trong trng hp gc nhn 14.3o th cng sut my pht ti thiu cho m C/A l

m bo yu cu k thut, cng sut ti thiu a ti ng-ten pht ca v tinh phi t:L1: 32.9WL2: 6.6W

3. Hm t tng quan v mt ph cng sutTnh t tng quan ca cc m PRN trong GPS l c s ca qu trnh gii iu ch.Mt ph cng sut ca m PRN xc nh bng thng yu cu truyn v nhn cc tn hiu tri ph.Cc m PRN c hm tng quan dng tam gic lp li theo chu k, dng ph gn ging dy gi ngu nhin di cc i (Maximum Length sequences).M PRN khng thc s l dy gi ngu nhin di cc i bi v:Tnh tng quan cho ca dy ML khng tt i vi GPSKhong thi gian x l trong my thu GPS rt ngn (1- 5ms) nn lm tng xc sut tm kim sai nh hm tng quan.

3. Hm t tng quan v mt ph cng sutHm t tng quan ca tn hiu GPS C/A nh sau

3. Hm t tng quan v mt ph cng sutHm t tng quan ca m C/A 1023 chips hay 1ms c dng tam gic nh sau:

C nhng thay i nh khong gia hai nh tng quan so vi mc 1/1023 ca dy ML 10-bit.Chnh s thay i ny gy ra s thay i trn ng bao ph dng sinc2(x)

3. Hm t tng quan v mt ph cng sutng bao ph ca dy ML chnh l ng sinc2(x) ch tr thnh phn tn s 0 nh vi m C/A th c thay i nh.

3. Hm t tng quan v mt ph cng sutHm t tng quan ca tn hiu GPS m P nh sau

3. Hm t tng quan v mt ph cng sutM P cng khng phi dy ML.Tuy nhin, do chu k m di, tc chip cao nn hm t tng quan trng l tng hn.

3. Hm t tng quan v mt ph cng sut

3. Hm t tng quan v mt ph cng sutKhi m GPS kt hp vi s liu 50bps c nh hng khng ng k ti hm t tng quan v ph cng sut.Gi thit dy PRN c iu ch BPSK vi sng mang, ph cng sut nh sau:

3. Hm t tng quan v mt ph cng sutPh cng sut ca m L1 P(Y) v C/A t b pht tn hiu GPS

3. Hm t tng quan v mt ph cng sutPh cng sut ca m L2 P(Y) t b pht tn hiu GPS

3. Hm t tng quan v mt ph cng sutPh cng sut ca m L1 C/A t b pht tn hiu GPS

4. Hm tng quan cho v hiu nng CDMAK thut CDMA: iu ch v gii iu ch trong GPS da trn vic s dng PRN khc nhau nhng cng tc chip v tn s sng mang trn mi v tinh.i vi my thu GPS, bm v tinh, bn sao m PRN phi c dch pha tng quan vi PRN pht bi v tinh.Mi m PRN phi tng quan cho cc tiu vi PRN ca v tinh khc vi bt k pha hay dch Doppler no trong 1 chu k m.

4. Hm tng quan cho v hiu nng CDMAHm tng quan cho l tng ca m GPS c nh ngha nh sau:

Phng trnh trn cho thy dng sng PRN ca v tinh i khng tng quan vi bt k PRN ca v tinh khc vi dch pha bt k.Thc t, iu ny l khng th bi khng th c mt v tinh t c t tng quan zero ngoi khong thi gian tng quan ca n.

4. Hm tng quan cho v hiu nng CDMAK thut CDMA ch kh thi khi tng quan cho gia tt c cc PRN t c mc nht nh.Vi m P(Y), di m 6,1871x1012 chips (1-week period)Tc chip 10,23Mchip/sNn mc tng quan cho l -127dB so vi nh tng quan.Vi m C/A di m 1023 chips (1-ms period)Tc chip 1,023Mchip/sNn mc tng quan cho ch khong -24dB so vi nh tng quan khi Doppler = 0 gia 2 m bt k, trng hp xu nht c th l -21.1dB.

4. Hm tng quan cho v hiu nng CDMA

4. Hm tng quan cho v hiu nng CDMA

5. nh dng bn tin nh vC m P(Y) v m C/A u c iu ch vi dng s liu 50bps.S liu ny cung cp cho NSD thng tin cn thit tnh ton chnh xc v tr ca mi v tinh trong tm nhn v thi gian truyn ca mi tn hiu nh v.Bn tin nh v c truyn trong 5 khung con, mi khung con 300 bits bao gm 10 t m 30-bit.6 bit cui ca mi t m dng cho kim tra chn l (parity check vi m Hamming) my thu NSD c th pht hin li bit khi gii iu ch.

5. nh dng bn tin nh vMi 5 khung con c truyn bt u t khung 1.Khung con 4 v 5 bao gm 25 trang (page).Bit 1-60 ca mi khung con l s liu telemetry (TLM) v HOW (Handover word).TLM = 10001011 (8-bit) => fixed preamble my thu NSD xc nh u khung con.TLM cng bao gm 14 bits s liu dng cho NSD c y quyn.

5. nh dng bn tin nh vHOW : cho php my thu NSD chuyn giao t bm m C/A sang bm m P(Y), cung cp GPS time-of-week (TOW) di dng modulo 6 giy tng ng vi ranh gii ca khung tip theo.HOW cng cung cp 2 bit c1 ch th kch hot antispoofing1 dng cho cnh bo (cht lng tn hiu rt ti)

5. nh dng bn tin nh vKhung con 1 cung cp s tun GPS, l s ca tun modulo 1024, tnh t January 5, 1980, ln chuyn u tin l August 22, 1999, ln chuyn tip theo l April 2019.Khung con 1 cha thng tin hiu chnh ng h v tinh: af0, af1, af2 v thi gian ca ng h toc. Cc tham s ny quan trng trong o chnh xc khong cch bi n cho php ng b thi gian gia tn hiu truyn t v tinh v thi gian h thng.Khung con 2 v 3 cung cp thng tin v qu o v tinh (cc thnh phn Keplerian), cho php xc nh chnh xc v tr ca v tinh. Cc thng tin ny cp nht mi 4 gi.

5. nh dng bn tin nh vTrang 2-5 v 7-10 ca khung con 4, trang 1-24 ca khung con 5 cha thng tin almanac cho php my thu NSD xc nh tng i v tr v tinh. Cc thng tin ny h tr nhn bit tn hiu.Trang 13 ca khung con 4 cha cc tham s hiu chnh o khong cch.Trang 18 ca khung con 4 cha thng tin hiu chnh li tng in ly cho my thu n tn v thng s v quan h thi gian UTC v thi gian GPS.Trang 25 ca khung con 4 v 5 cung cp thng tin v cu hnh v trng thi (sc khe) ca cc v tinh t 1-32.C mt s trang ca khung con 4-5 d phng.

Cc tn hiu GPS miCc tn hiu GPS

Cc tn hiu mi (modernized)B sung thm:Hai tn hiu dn s mi: L2C v L5Tn hiu qun s mi: m M

Cc tn hiu GPS miTn hiu dn s L2C: pht qung b bi v tinh th h Block IIR-M v IIFTn hiu L2C c ph cng sut tng t m C/A, bng thng 2,046MHz, mc tn hiu ti thiu my thu l -160dBW, Tuy nhin L2C c nhiu im khc bit.L2C s dng 2 PRN cho mi v tinh;M PRN th nht gi l CM (civil moderate) c chu k 10230 chips;M PRN th 2 gi l CL (civil long) di hn nhiu CM vi chu k 767250 chips

Cc tn hiu GPS miTo tn hiu L2C bng c s

Cc tn hiu GPS miCch to tn hiu L2CM CM c iu ch vi dng s liu 50-baud (25 bps & m 7 FEC t s 1:2) => nhm d dng hn trong gii iu ch tn hiu trong mi trng khng thun li.M CM c s liu ghp knh vi m CL (khng c s liu) lm tng kh nng bm tn hiu GPS => y l im ni bt ca tn hiu GPS mi.Ghp knh m CM v CL:2 x 511.5 k-chip/s = 1.023 Mchip/sTo ra tn hiu c ph ging m C/A nhng c di m ln hn nn kh nng chng nhiu tt hn.

Cc tn hiu GPS miTo m CM v CL

S dng thanh ghi dch hi tip tuyn tnh 27 khu, mi khu 1-bit.M c pht vi gi tr khi to khc nhau tng ng vi mi v tinh Thanh ghi reset c sau 10230 chips cho m CM v 767250 chips cho CL.

Cc tn hiu GPS miTn hiu L5: pht qung b bi v tinh Block IIF, mc tn hiu thu khong -154,9dBWiu ch QPSK kt hp 2 thnh phn I5(in-phase) v Q5(quadraphase);I5 c iu ch vi s liu 50bps, s liu ny c m ha FEC ging nh vi L2C, nn tc symbol l 100 baud;M PRN tc 10,023MHz c s dng c cho I5 v Q5, dn n chu k m l 1ms;

To tn hiu L5

Cc tn hiu GPS miM ng b Neuman-Hofman (NH) c iu ch I5 v Q5 ln tc 1-kbaud.Vi I5, m NH 10-symbol (0000110101) c pht trong thi gian 10ms v lp li;Vi Q5, m NH 20-symbol (00000100110101001110) c s dng;C mi 1ms, bit ca m NH c cng modulo-2 vi chip ca m PRN

To m PRN I5 v Q5

Cc tn hiu GPS miTn hiu qun s M M: Pht qung b bi v tinh th h Block IIR-M, mc tn hiu khong -158dBW trn L1. T th h Block III tr i, tn hiu m M s c pht cng sut cao hn mt s vng a l gii hn, mc cng sut vo khong -138dBW.c thit k dng ring cho qun s, nhm thay th m P(Y). Trong qu trnh chuyn i, my thu qun s c th dng kt hp m P(Y), m M v m C/A. Thit b thu nh vy gi l YMCA.

M Code tng cng bo mt v c ph tch bit hn khi tn hiu dn dng trnh b nhiu, tng kh nng chng nhiu.M Code c tng cng hiu qu bm tn hiu v gii iu ch s liu so vi m C/A v m P(Y).Tn hiu M Code dng iu ch BOC (Binary Offset Carrier) phn tch ph.Tn hiu M Code dng BOCs(10,5).Cc tn hiu GPS mi

Tn hiu M Code dng BOCs(10,5): 10 x 1,023MHz: tn s sng mang ph5 x 1,023Mhz: tc chip ca b pht m M CodeCc tn hiu GPS mi

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