NGHIEN CUtJ, MO PHONG HE XU LY TIN HIEU RA DA DIEU T A N TUYEN TINH
Nguyin Nggc Hung
Khoa Ky thugt Diiu khiin Hgc vien Ky thudt qudn su
0
Torn tdt:
Bdi bdo ndy trinh bdy vi ca .^a thudt todn xir ly tin hi?u ra da vai ky thudt nen xung tuong quan tin hiiu diiu tdn tuyin tinh thuc thi trong cdc ddi ra da cd bdng tdn hep vd trung binh, md nd dimg di phdn biet cdc muc tieu cd sir sai khdc vi cu ly nhd. Thudt todn xir ly ndy dugrc md phdng kiim chirng tren phdn mim Matlab.
Abstract:
This article presents the basic processing radar signal algorithm by linear frequency modulation correlation pulse compression techniques the implementation in narrow and medium band radars, it uses to separate targets having small range resolution. Using Matlab to simulate and verify this processing algorithm.
I. DATVANDE.
• t 0
Do phdn biet cy ly trong ra da cd the dugc cdi thien ddng ke neu chiing ta sir dung xung do rdng rdt nhd. Nhung xung do rdng rdt nho 1dm gidm cdng suat phdt trung binh 1dm dnh hudng tdi che do boat ddng binh thudng ciia ddi ra da ddc biet Id vdi cdc ddi ra da cdnh gidi va da chirc ndng. Tir dd cdng sudt phdt trung binh se dnh hudng tdi ty so tfn/tap (SNR), nen mong mudn tang cdng sudt phdt tmng binh lai cdn tdng do rdng xung, de gidi quyet mdu thudn nay ta cd the sii dung ky thudt nen xung tfn hieu dieu tdn tuyen tfnh. Ky thudt nen xung cho phep cdng sudt phdt trung binh cd the tuong duong vdi cdc xung rdng md khd ndng phdn biet ve cy ly tuong duong vdi cdc xung cd do rdng nhd. Cd nhieu ky thudt nen xung, tuy nhien trong bai bdo nay ta se di nghien ciiu ky thudt nen xung tuong quan tfn hieu dieu tan tuyen tfnh sir dyng trong cdc ddi ra da bang tdn hep vd trung binh.
n . TIN HIEU DIEU TAN TUYEN TINH VA SlT P H A N LTNG CUA BO LQC PHOI HOP.
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a. Tin hiiu diiu tdn tuyin tinh.
De dat dugc tfn hieu gidi rdng ngudi ta siir dung dilu chl pha hoac tan sd, tfn hieu dieu tdn tuyin tfnh (LFM) thudng dugc su dyng ban, day la tfn hieu cd tdn sd thay ddi tuyen tfnh tang hodc gidm trong do rdng xung. Ta ky hieu
<3o rdng xung Id r ,db di tan Id B. ibi
Hinh 1. Cac loai tin hieu LFM. (a) tang tdn so, (b) 2iani tan s6.
Pha tiic thai ciia tfn hieu LFM cd tdn sd tdng hoac giam dugc bilu diln:
^(/) = 2 ; r ( / „ / ± ^ r ) -\^^^\ ^^^
Trong dd /o Id tdn sd tmng tam vd lu = {2nB)lT\h. he sd LFM.
Tan s6 tire thdi cua tfn hieu Id:
litdt • 2 2 Mgt dang tfn hieu LFM cd thi dugc bilu diln.
sAt) = Kect{-)e t . y2f(/o+7'-)
(3) Rec/(-) Id xung vudng cd dg rgng r Phd cua tfn hi?u s(t) dugc tfnh theo dudng bao phiirc cua nd:
- 2
5(fi>) = [ Recti-)e^'^''e-^'^dt = | exp jlTtjUt
2 A
e-"^dt (4)
Ddi biln vd tfnh todn ta dugc :
5(^) = , ,_L , - . - ' - . \{c{x,)^C{x,)yj[s{x,)^S{x,)]]
BT ^
(5)
Trong do x. = . — 1+——
' V 2 I 5 / 2 ' V 2 I 5 / 2 . Vd C
{x) = ]cos\^j 1 1
dv = —+—sin2 7i;x
u
n. 2 \
5(x) = Jsin dv~-+—cos
0 \ ^ J 2 nx
—X'7t vdi X? 1,
'.'. ".:•, 'y t"9>»nn.".«.«'.>»'»<
m m
(8)
'•« - ' - ^
(a) (b) (c) Hinh 2. Mo phong tren Matlab tin hifu LFM, (a) phan thuc, (b) phSn ao, (c) pho.
' \ \ 0
b. Bg lgc phdi hgp tin hiiu diiu tdn tuyin tinh.
Ta se xem xet phdn ung cua bd lgc phdi hgp tdi tin hieu LFM bang mdt vi du bdm sat
Y r Y y2'r(/o'+fr)
myc tieu cd van tdc vcua dai ra da. Tfn hieu tmySn la: 5,(f) = Reef (9)
Khi do tfn hieu nhdn dugc la: .v,,(t) = s, (t- A(0) vdi A(0 = /^ - — (/-/„) (10) c
Trong dd t^ la thdi giun tuong iing vdi gia trj khdi tao ciia cu ly muc tieu, c la van tdc dnh sdng. Ta cd:
f
s,it) = s, t-to-\- — (?-/(,) =5,(/(r-fo)) vdi / = I + 2 - I d h e s d t y l e .
\ c J c
Tir do tfn hieu nhdn cd the dugc viet dudi dang.
s (t) = e'^'''-''^" Re erf ^^^~^°^ \gn''U(r-\v.i-i^)^]'viY-(i-ta)-
(11)
(12) Djch tdn Ddple do myc tieu di chuyen dugc tfnh bdng f^ = — f^ md ; ' - l = 2v//c nen 2v
e
/rf = ( y - l ) / o . sir dyng gdn dung ;/ = 1 ta dugc s^(t) = e^-''^'^'"»'5(r -/„) (13)
trong do s{t-t^) = e-'-''^'^s,{t-t^) (14)
am
Ddc tfnh bg lgc phdi hgp dugc tfnh bdng tfnh chap: s^(t) = \ h(u)s^(t-u)du (15) Ddc tfnh xung h(u) ciia bd lgc phdi hgp bdng s'(-t) [1] nen:
oo oo
5o{t)= I s\-u)s^(t-u)du= j s\u)e'-'^-'"*"-''''s(t-hu-t^)du (16)
Ddi biln t =t-hu vadat /„ = 0 tadugc:5o(/;/J= f s(t')s\i-t)e'-'^''di (17) nhu vay ddu ra bd lgc la hdm cua cd thdi gian va tdn sd Ddp le. r t
0 -y \ 0
c. Ham bdt dinh cho tin hiiu diiu tdn tuyin tinh.
0
Ham bat djnh ra da cho tfn hieu s(t) dugc djnh nghTa Id binh phuang md dun cua hdm tuang quan hai chilu, ky hieu jzC^J/rf)]' '•
k(r,/jf =
\sit)s\t-T)e^^''^''dt s(t) Id hinh bao phiic cua tfn hieu. (18) Ta xem xet dudng bao pbiic cua tfn hieu dieu tdn tuyen ti'nh:1 ( t \ ^
s(t) = -j=Rect — e^"'" T Id do rgng xung nen. (19) Ddu tien ta xem xet khi 0 < r < r liic ndy tfch phdn gidi ban tir -T 12 den (r /2) - r khi do ta cd:
Z(j\fa) = —\ Reer 1 r
T •'
O^
Ree/\T ) \ T J
gP.m-^-jm>-ry^j2nf,,,^^j (20)
-JTtflT 2
Nen: /M''f,i) = f ../-^n/""^./,;) dt (21)
Cuoi cung ta dugc: Zi^\f^) = e i^rf,! (
Sin ^^'(M + fri)
( \ \
\ T^\
1 r
0<T<T (22) 7tr{in + f,)
\ ^ ' .
Tfnh tuong ty cho tmdng hgp - r < r < 0 hoac cd thi suy ra tir tfnh ddi xirng qua tdm cua ham bdt dinh tire la \x(r, f, )| = \X{-T\ -f,)| khi dd ta cd tbi tim dugc cdng thOrc tdng qudt cho 2 tmdng hgp.
[nvip^fAl-^
j'"i„
Xir\f,,) = -
'i-ai
'^ ;rr'(// + /„)fl-W
M^r (23)
Nen hdm bdt dinh Id: • \x(r;f„)\' =
X
sin ^'(/" + / / )
w
TtT
(^ + /J 'l-tl'
(24)
">».,»• J*:**; ^y-rf".''-'' •' -»• ••:'•••
A , it/. J i'v ; « . I
f ,a, • " -2 '• r i O M ' i
i :
;7a
. 1 ^ " % ^
.1 4 « « • 44 4J 0 a f B« • • • •
(a) (b) Hinh 3. (a) vat thi bdt djnh tin hieu LFM; (b) ham bat dinh tin hif u LFM.
Tir hdm bat djnh ta thdy neu sir dyng xung cd dg rgng Idn nhung dugc dieu che vdi dp di tan Idn ta cd the ddng thdi ddm bdo do chi'nh xdc cao cd do cy ly va do tdc do. Ddy la mgt
0 . t ^ 0 ' • '
dac tfnh ddc sac cua dang tin hieu dieu tan tuyen tfnh [2].
III. THUAT T O A N XU" LY N 6 N XUNG TU'ONG QUAN TIN HIEU DIEU T A N TUYEN TINH.
Nen xung LFM dugc thyc hien bdng viec dieu che tdn sd ciia tfn hieu phdt trong mgt xung rgng va sir dyng bg lgc phdi hgp cua mdy thu de nen tfn hieu nhdn dugc. Tfn hieu ddu ra cua bd lgc phdi hgp dugc nen bdi he sd ^ = Br trong dd r Id do rdng xung B Id gidi thdng bd lgc. Khi dd ta cd thi dat dugc he sd nen xung Idn.
Hinh 4 chi ra qud trinh nen xung dilu tdn tuyin tfnh. Hinh (a) chi ra dudng bao la mdt xung rdng,
1
^ t - i ,
•-»lLocPh4iho|>
tH
i J )
hinh (b) chi ra viec dieu tdn vdi tdn so tdng trong gidi B = f_- f, hinh (c) chi ra ddc tfnh giir tre ciia bg lgc phdi hgp, hinh (d) chi ra dudng bao ciia xung da nen, cuoi cung hinh (e) chi ra dang tfn hif u ddu vdo, dau ra ciia bg lgc phoi hgp.
Ciia so ciia may thu dugc djnh nghia la khodng giii'a cua cy ly Idn nhdt va nho nhdt cua myc tieu ma dai ra da phat hien dugc, tfn hieu trd ve tir tdt cd cac muc tieu ndm trong cira sd may thu dugc lya chgn vd cho c^ua mach lgc phdi hgp de thirc hien viec nen xung. Do sy phdt trien Idn manh' ciia may tfnh so nen cdc bg xir ly tuong quan thudng dugc thyc hien bdng mach sd sir dyng FFT. Thyc thi sd ndy thudng dugc ggi la xOr ly tfnh tfch chap nhanh (FCP) CO the dugc dung trong cdc bdng tdn co sd.
Tin hi?u dau \ 60
CZO FFT
Bp nhcf &}c tinh xung
Tr^n
^ FFT
Hinh 4. Nen xung tfn hieu LFM
I in ni^u dku ra
Hinh 5. So* do xir ly tuong quan tin hif u LFM.
Bg lgc phdi hgp Id mgt he nghjch ddo thdi gian tuyin tfnh, ddu ra ctia nd cd thi dugc tfnh
bdi tfch chap giira ddu vdo vd ddc tfnh xung cua nd: y(t) = s(t) • h(t) (25) s{t) Id tfn hieu ddu vdo, h(t) Id ddc tfnh xung cua bd lgc, • Id todn tu tfnh tfch chap. Tir
tfnh chdt cua biln ddi Fourier: FFT{s{t)»h{t)} = S{f).H{f) (26) Vd khi cd hai tfn hieu dugc Idy mdu hgp ly thi tfn hieu nen cd the dugc tfnh tir:
y{t) = FFT-'{S{f).H{f)} (27) Xem xet mdt be thdng ra da thyc hien xir ly tuong quan (d ddy la dimg bd lgc phdi hgp)
cd ciia sd mdy thu dugc tfnh bdng: R^^^. = R^^ - /?^„. Trong do R^^, /?^„ la cy ly Idn nhat va nhd nhdt ma ddi ra da cd the phdt hien dugc, R„,.\a giai ban cy ly phdt hien dugc myc tieu.
Tfn hieu phat dang phiic la:
•(r) = exp j27r f,t+^t'
V V ^
0 < r < r (28)
T la do rdng xung, /J = B/T ,wa 5 Id do rdng bdng tdn.
Tfn hieu mdy thu ra da nhdn dugc cua muc tieu d cy ly R^ la:
f f U 2' 5,(0 = fl,exp j27r fo(t-T,)+^{t-T,)
\ \ 2 ,
(29)
0 0
a, la he sd ty le dugc tfnh tir dien tfch phdn xa hieu dyng myc tieu, khuyech dai anten, sy suy gidm tfn hieu theo cy ly. Thdi gian giii tri r, dugc tfnh theo: r, =2RJc (30)
Budc xu ly ddu tien Id loai bd tdn sd /Q thyc hien bdng bd trgn tfn hieu s^(t) vdi tfn hieu tham chieu cd pha Id 2;r/o/ vd qua lgc thdng thdp ta dugc tfn hieu sau:
i/f(t) = 2n{-f,T,+^{t-T,f^
Tdn sd tlie thdi Id : / (r) = 1 d 'Bf 2ndt ^' ^^ '' T t-
2R,'
c J
(31) (32) Tiep theo ta cdn quan tdm den so mdu N dugc lya chgn sao cho ddm bdo sy nguyen ven
' \ "* ^ 0 0 mm • t
ve phd cua tfn hieu, khi dd tdn sd Idy mau fdugc xdc djnh theo tieu chudn Nyquist la:
./; > IB nen thdi gian Idy mdu la: At<l/2B Tu phuang trinh (32) chi ra do phdn gidi tdn si cua'pFTIa: A/- = l / r [1].
Nen so mdu nho nhdt theo yeu cdu Id: A^ = _ L _ = £ - Suy ra /V > 2BT . Nhu vay cd tdt AAA/ Ar
cd 2BT mdu thuc hodc Br mdu phirc dl md td mgt tfn hieu dilu tdn tuyin tfnh dugc dieu chl trong xung cd dg rgng r vdi dg di tdn B. Vf dy tfn hieu LFM cd T = 20//5 vd B = 5MHz yeu cau 200 mau thyc dk md td. D I thuc thi tot ban ph6p FFT thi sd mau thudng dugc xac djnh theo: N^^^ = 2'" > N vdi m Id so nguyen.
Budc cuoi ciing la xir ly FCP gom: (1) lay FFT cua day mau; (2) trgn day miln tdn so cua tfn hieu vdi FFT cua ddc tfnh xung bg lgc phdi hgp; (3) thyc tbi phep tfnh ddo FFT ciia day hdn hgp cdc mien tdn so
dugc nen xung theo mien thdi gian. Tuy nhien ciing phdi tfnh din hi?u chinh bii, khuylch dai anten, vd suy gidm tfn hieu theo cy ly.
Bay gid ta x6t cdc myc tieu cd cu ly Id R^, /?,,...
diu thugc cira so mdy thu, theo tfnh chdt xep chdng ta cd tfn hieu thu dugc Id:
ifr{t) = Y^2J-f,T,+^{t-Tf
vdi r, =2/?./e, z = l,2,...,/
Mdt vf dy vdi cdc tham sd nhu bdng ben thyc hien md phdng tren Matlab ta thay khi khdng cd nen xung thi tfn hieu cua 3 myc tieu bi chdng len nhau vd khdng phan biet dugc, khi sii dyng ky thudt nen xung tuong quan thi cdc myc tieu cd the phan biet ro rang tu dd ta thay dugc uu diem ndi bat cua xu ly tfn hieu ra da theo ky thuat nen xung tuang quan tin hieu dieu tan tuyen tfnh.
Sd myc tieu ndm trong cira sd mdy thu Dg rgng cira sd mdy thu
Dg rgng xung chua ndn Dg rgng ddi tdn
Cy ly myc tieu ndm trong cua sd mdy thu Dien tfnh phdn x? hieu dyng ciia myc tieu Loai cira sd
3 200m 0.005m lOOedHz [I0 75 120]m
[1 2 i K 2
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J , C O V
^ ri
" « • » • * • •
• • I . I
. . . . > ^ ^
' 'f^'
• '0*
! :
,.- . \ ...j .-i... -
•
I -0 'i 0 0 4 \ 14
.10* Thai 9«M ^m cMm
i . .
i - t 'i'l '••
GO ao toe 133 I « i«0 ISO 3)0(a) (b) (c)
Hinh 6. (a) ph4n thyc va phi ciia dac tinh qua dg bg lgc phoi hgp;
(b) tin hieu khi khong dugc nen; (c) tin hieu dugc xir ly nen xung tinmg quan.
IV. KET LUAN
Bdi bdo da gidi quylt dugc vdn dk quan trgng trong xir ly tfn hieu ra da, xay dung thudt todn phan biet cdc muc tieu bay theo tip vdi so lugng Idn. Day la Igi the Idn nhdt ciia ky thuat nen xung tuang quan tfn hieu dilu tdn tuyen tfnh iing dyng trong thiet ke cdc dai ra da the he mdi.
Ket qud kiem chirng tren Matlab cho thdy tfnh dung ddn cua thudt todn xii ly.
TAI LIfU THAM K H A O :
[1] Bassem R.M, Ph.D: Matlab Simulation for Radar System Design, the university of Mississippi Oxford, 2004.
[2] PGS.TS Nguyin Diic Luyen: Ca sd thong ke ciia Ra da, Hgc vien ky thudt qudn su, 2003.