xay dung he thong radar su dung he thong phat thanh truyen hinh viet nam.pdf

7/27/2019 Xay dung he thong radar su dung he thong phat thanh truyen hinh Viet Nam.pdf

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Nghin cu xy dng h thng radar th ng s dng tn hiu phtthanh truyn hnh ti Vit Nam

Lng Xun Trng

Chuyn ngnh Thng tin v tuynNgnh K thut in t

Khoa Cng ngh in t - Vin [email protected]

Trn Minh TunVin Chinlc Thng tin v Truyn thng

B Thng tin v Truyn [email protected]

T kha Radar; radar th dng; radar th ng hai v tr; hm nh gi m m; phng trnh radar.

I. TNGQUANVRADARGii thiu mt cch tng quan v radar.

Radar (Radio Angle Detection and Ranging)Radar l tn vit tt ca thut ng ting Anh chh thng thit b ra i nhm mc ch nhn dngv tr mc tiu nh vo hin tng phn x sng

in t.Mt s khi nim c bn: i ra a thu, i

pht.

Di tn s hotng: T bng V,U,L,S

Cng sut pht sng c th ln n hng triuWatt.

Radar c phn loi theo phng thc hotng hoc ng dng. Mt s tn gi cc loiradar thng gp: radar xung, radar theo di,radar thi tit, radar hnh nh

Cc yu t nh hng nhiu n n hotng ca radar: a hnh, can nhiu tn s vtuyn in

ng dng radar: Radar gim st, theo di, dnng, iu khin v kh (dn s), radar khtng thy vn (dn s).[1]

II. CSLTHUYTTrnh by cc c s l thuyt quan trng lin

quan n hot ng ca h thng radar. Bao gm: - Tnh cht lan truyn sng in t trong

khng gian t do:o Sng in t truyn qua mi trng ngnht,v ng hng th truyn thng. Vn tctruyn bng vn tc nh sng (3.108 m/s).o Suy hao nng lng ca sng in t khitruyn qua khng gian t do l:

4L ( ) 20log( )F

rdB

(1)

o Ngoi ra cn phi k n hin tng phnx, nhiu x - chng l cc yu t nh hngtrc tip ti hot ng ca radar.

- Hiu ng Doppler:o Hiu ng Doppler l hin tng khi sng tngun pht khi truyn i v phn x bi mctiu ang chuyn ng (so vi ngun pht) thtn s ca sng phn x b thay i, s thayi c gi l dch tn Doppler. Dch tnDoppler c th lm tng hoc gim tn s sngphn x so vi sng ti ph thuc vo gc tica sng, vn tc chuyn ng ca mc tiu vtn s ban u ca sng c truyn i.o Cng thc tnh trng hp tng qut. Giibi ton tnh dch tn Doppler trong kthut radar. Trng hp 1, mc tiu chuynng, i thu i pht ng c nh. Trnghp 2, i pht, i thu chuyn ng, mc tiukhng chuyn ng.- L thuyt anten:o th bc x (gin ) ca anten.o Anten c mt phn x, anten parabol.o Anten mngo Bi ton nh hng sng n.- Mt s lnh vc quan trng khc: Siu cao

tn, x l s tn hiu, k thut my tnh

III. RADARTHNG- Gii thiu radar th ng


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o Lch s ra i ca nhng h thng radar thng u tin vo nhng nm trong chintranh th gii ln 2.

o Khi nim radar th ng (passive radar) cth hiu mt cch gn chnh xc l: Radar thng (Passive radar) l dng radar pht hin

vo theo di mc tiu bng cch thu cc tnhiu b phn x bi mc tiu. Cc ngun phttn hiu l cc ngun pht x c sn trong nhtn hiu qung b pht thanh truyn hnh, tnhiu ca cc h thng vin thng.

o Dng tiu biu ca radar th ng c s nh hnh 1 c gi l radar th ng hai v tr(bistatic passive radar), l dng nghin cu chyu trong lun vn.

Hnh 1: H thng radar th ng hai v tr

- thit k mt h thng radar th ngngi ta nghin cu hai phn c bn sau:

o Nghin cu dng tn hiu s dng. Cng cton hc chnh c dng l hm nh gi m m (Ambiguity function)

o Bi ton xy dng m hnh, tnh ton vngph sng, khong cch i thu vi ngunpht.Cc tham s cn tnh ton l: T s SNR,phng trnh radar v hng s radar th ngK, tnh ton vng ph sng v v tr t iradar thu.

- c im mt s dng tn hiu c nghincu s dng cho radar th ng:

o Tn hiu FM c quy hoch trong bngtn VHF 88-108 MHz. Qu trnh iu ch liu ch FM bng thng rng. (Vi mt knhtruyn c bng thng B khong 50 kHz tngng vi phn gii khong c/2B = 3000 m).

o Cc tn hiu truyn hnh tng t c quyhoch trong c bng tn VHF (on bng tnt 174MHz - 216 MHz) v bng UHF (onbng tn t 470-806 MHz ). Bng thng cacc iu ch video tng t thng c 5,5 6,5MHz (tng ng vi phn gii khong

c/2B = 30 m).o Mt s dng tn hiu khc nh Truynthanh s, truyn hnh s, truyn hnh v tinh,HF, tn hiu in thoi ca trm BTS

- Hm nh gi m m (AF)o Hm m AF l mt cng c nghin cuv nh gi kh nng hot ng ca radar theocc dng sng radar s dng. Biu dinton hc ca hm AF c dng [9]:

22 * 2| ( , ) | | ( ) ( ) |dj f tdf s t s t e dt

(2)

o Trong vai tr nghin cu dng tn hiu, hmAF c s dng nh gi phn gii vkhong cch v tn s ca radar i vi midng tn hiu s dng.

Hnh 2: Biu din ca hm AF i vi tn hiuu vo l tn hiu FM v DVB-T


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o Tnh cht quan trng rt ra c khi nghincu hm AF i vi cc tn hiu s dng choh thng radar l: Khi bng thng ca tnhiu cng ln th phn gii khong cchcng chnh xc. Ngc li khi thi gian kodi xung cng di th phn gii Doppler

cng chnh xc..- Bi ton xy dng m hnh radar th ng

Gi PT l cng sut ca i pht, PR l cngsut tn hiu phn x thu c ti my thu, RR,RT l khong cch t mc tiu n radar vngun pht, G l tng ch anten, Li, Fi l ccyu t suy hao khng gian truyn sng . Khi phng trnh radarc biu din nh sau:

2 2 2

3 2 2(4 )

T T R B T R

RT R T R

P G G F F P

L L R R

(4)

T s S/N c tnh nh sau: 2 2 2

3 2 2(4 )T T R B T R

s n T R T R

P G G F F S

N kT B L L R R

(5)

K gi l hng s radar c tnh nh sau:2 2 2

3K

(4 )T T R B T R

s n T R

P G G F F

kT B L L

(6)

Vit li cng thc S/N trong h ta Cc nhhnh 4, L c gi l di ng c s, sdng bin i Cassini cho ta kt qu nh sau:

Hnh 4: Biu din radar th ng hai v tr trongh ta Cc

22 2 2 2 2( ) cos

4

KSNR

Lr r L

(7)

Gii phng trnh 7 cho ta kt qu nh hnh:

Hnh 3: Biu din vng ph ca radar th nghai v tr theo gi tr SNR

Trong hnh 3 mi elip th hin vng ph i vimi gi tr SNR ca h thng radar

Din tch vng ph s c tnh nh sau:

4 8

1 2 4

1 31 ( )( ) ( )( )

64 16384B

L LA

(8)

Bi ton xy dng m hnh h thng radar th

ng cn xc nh c 3 yu t quan trng:

+ T s SNR

+ V tr t radar ( di ng c s)

+ Hnh dng v din tch vng ph

o Cc yu t nh gi cht lng ca hotng radar: phn di khong cch, phndi tn s, xc sut pht hin, xc sut bogi.[3][7]

o Bi ton:i FM Truyn hnh

DVB-T

Tn s 102,7MHz 514MHz

Cngsut

20KW 10KW

iuch

FM OFDM

Bngthng

300KHz 8MHz


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Cc gi thit:

li anten pht : 15 dB

li anten thu : 15 dB

Din tch phn x hiu dng RCS : 10 m2

H s truyn lan trn ng pht :1dB

H s truyn lan trn ng thu : 1dBTng nhit tp m my thu : 2900K

Bng thng tp m : 180KHz

Suy hao pht :1dB

Suy hao thu :1dB

T s SNR = 15

Kt qu tnh ton:

FM DVB-T

phndi khong

cch

Hng trmmt

Vi chc mt

SNR 15 15

Hng s K 1343.1019 5362.1017

ding c

s L

60Km 30Km

RTRR 1542Km2 274,5Km2

IV.NGHINCUXYDNGHTHNGRADARTHNGTIVITNAM

Xy dng tiu chun xy dng mt hthng radar th ng s dng tn hiu cc ngunpht tn hiu pht thanh, truyn hnh. Phn tchhin trng pht thanh truyn hnh ti Vit Nam

hin nay v xu hng pht trin. nh gi khnng xy dng h thng radar th ng ti VitNam.

- iu kin mt ngun pht c th sdng cho mt h thng radar th ng:

Thi gian pht sng lin tcCng sut lnBng thng ph hpV tr ph hpTn s nm trong on bng tn c quyhoch ph hp nhm trnh can nhiu do vics dng li tn s trong khu vc.

- Hin trng ph sng pht thanh, truyn hnhti Vit Nam:

Vit Nam c h thng pht thanh, truynhnh dy c vi nhiu loi hnh.

Truyn hnh tng t v pht thanh FM triu trn 63 tnh thnh vi mt ph snggn 100% din tch t lin.

H thng truyn hnh s mt t kh phttrin (nh cung cp VTC, AVG).

- Kh nng xy dng h thng radar th ngti Vit Nam:

Vit Nam c nhiu i pht quc gia, quym ln, hot ng lin tc v vng ph sngrng. Cc i pht ny cn c u im cquy hoch ring knh tn s do trnh ccc can nhiu khng mong mun t i khc.

C s h tng pht thanh truyn hnh hinnay hon toan cho php Vit Nam trin khaicc h thng radar th ng. c bit ti cckhu vc ng bng, khu tp chung ng dnc, vng kinh t trng im, vng ca bin.

V.

KTLUNLun vn t c nhng kt qu nghin cu

v h thng radar th ng v bi ton xy dngh thng radar th ng s dng ngun pht tnhiu pht thanh truyn hnh.

Lun vn xut m hnh th nghim thct v nh gi tim nng trin khai h thng radar


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ny trn lnh th Vit Nam da trn nhng khost tin hnh.

TILIUTHAMKHO

[1]Merrill Skolnic.Radar Handbook . Mc Graw-Hill, 2008.

[2]H.D Griffiths. Passive Bistatic Radar.RTO-EN-SET-133

[3]Benson Chan.Reciever site optimisation forpassive coherent location radar system.CapeTown, 2008.

[4]Nicholas J. Willis. Bistatic Radar.ScietechPublishing INC, 2005.

[5]John W.Franklin.Passive Bistatic Radar.www.cse.unt.edu, 2010.

[6]H.D Griffiths. Bistatic and Multistatic Radar.IEE Military Radar Seminar, Shrivenham,2004.

[7]Amerigo Capria, Michele Conti, Dario Petri,Macro Martorella, Fabrizio Berizzi, EnzoDalle Mese, Rocco Soleti, Vincenzo Carulli,Ship Detection with DVB-T software defined

passive radar,ieee.uniparthenope.it, 2010.

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