- Ngoai toe dp bit con co mpt thuat ngCr khâ duoL M; I M !•.
7.1.4Phu luc: phan tich phuong sai Allan
d) Bat tay bang phin ciing:
7.1.4Phu luc: phan tich phuong sai Allan
De giai quyet van de sai so, nguoi ta phan loai ngu\en nhan L,U sai i/n liiai^' riiiij-i thong ke va nhieu tat dinh. Viec xu ly nhieu tat dinh de dang hon khi . nniu •, ' - ^ i mpt each dinh luong dugc cac loai nhieu na\ bang \ lee ean ehuan ihiei '^i i )
thong ke thi chimg ta phai su dung bo loc toi uu \ i du nhu ho K>L l\,ilm,i:, - --j
can phai xac dinh dugc cac thong so dac trung cua cac loai nhieu thong ke n,i\ ; ^ ;. pt : nay chung toi su dung phucmg phap phan tich phuang sai Allan de \ae dmh ^ae ih.MiL' s'
nhieu thong ke ciia cam bien 3 chieụ Phuang phap phan tieh mat do pho êMiL: ^uá h^I)
cung dugc su dung nhu mot phuang phap tham khaọ Sir kei hop eua ^a hai ;MI;IM::J pi ,I[
nay tren cimg tap dij lieu thu dugc se cho phep chung ta dac UUHL: hnj , híili ,K :;i "a > u
Phan tich pho mat do cong suat, PSD.
Mat do pho cong suit (PSD) cho hik muc dp nang lugng cho cac ta
cua tin hieu [4]^. Ve mat toari hpc PSD dugc dinh nghia la bicn doi 1 .niner eua dax
q u a n ^ e o chuoi thai gian. 6 day tu tuong quan la gia in irung hmh LỤI if: !io;
chinh no ma dugc lam tre di mot khoang thai gian
PSD CO thu nguyen la donví/Hz va no cho bici "nang kigng trung .MUIM
x(t) dugc phan chia cho cac thanh ph4n tan so ra saọ Mpt dmh nhon trong ÍM) Li
CO mpt tin hieu hinh sin trong du lieụ Nhieu tring dugc mo ta la mot duong ih
song voi true tan so trong d6 thi PSD. Nhieu irSng co cong snat deu doi N." IX e sọ Ve PSD theo thang log-log co the thAy duac cae dironLi dô .ua .,ị . j " ' ''
(hinh 2.1). an so thanh phan !U M n " ! _ n ^ U i a Li I I L : St M I L ' ^ 10' > b u a c goc n^au ^ nhien (gia toẹ
\ van toe goc
\ -^ \ \ nhieu rung hoac mat on dinh offset -1 ^ d U C , ) buac (goc rihueu /..•ail t h. h iu^Tl.]? h . - . van toe) ngau nhuen hoac \ ( ^ ' ^ c nl"ueu crang ,/ gia t o e ) rraniT " i". 2 .hi*"'; n't ' aiz f ^ ) C • 1 V n I 1 ' ' • eae L am
Hinh 1. Cac duong doc dac trung trong PSD vai thang log-log doi \ m du lieu ^ iịi ^ in Phu-ong p h a p phan tich p h u o n g sai Allan
Phuong phap Phuang sai Allan na\' ra doi nam \^)(^(^ de nghui
bp tao dao dpng. Sau do phuang phap nav dugc su dung nga-. cac ung dung khac nhau, de dac trung hoa dugc tinh mat on Jml
dang thay rang CO the ap dung trong viec khao sal hoac mo hmh họ\ eae ^am hu-n .iịtn :MI!;
boi cac cam bien nay thuong chiu tac dpng cua cac loai nhieu troi ngau nhien i nam I wxi 11 Nam 1983, xuat hien cac cong trinh dau tien ve phan tich nhieu dimg phutrng sai Mian ap
d u n g ^ o con quay vi ca lazẹ Do la tien de de phan tieh troi eua eae c^^\^ Ljua\ \ i .>' s,n,
naỵ Nam 1998, IEEE da chinh thirc cong bo phu(Yng sai Mian dm^ si; i , : -
phuong phap danh gia nhieụ Mai tai nam 2003 thi phuong i^iiap nav m.u i,;:] k,,. ' , ^ ;; dung cho cac cam bien vi co dien tu [7].
Chung ta biet rang phucmg phap phan tich pho (PSD) kiiong the dụi \\\ ! IM i:,;;;!.
thong tin toan dien khi danh gia cac nguon nhieụ Phuerng phap Allan \uai phai pumn^L
phap phan tich tren mien thai gian dugc phat trien de phan tieh do ou dmh iren nnc' \'\r. -
Chtjng ta CO the xac dinh cac dac trung cua nhieu ngau nhien lae MMUL: ien m n,/. ; '
xac dinh dugc nguon nhieụ Trong phuang phap Allan neu du heị kh-:v.' M coi la CO nguon goc tu 1 loai nhieu nao do (adsbygoogle = window.adsbygoogle || []).push({});
Co 7 loai nhieu trong cac cam bien quan tinh co the iiir, duoL khi; J n . j ; i : >' ,,;
mat on dinh dp lech, lugng tu hoa va troi van toẹ Ngoai ra con e(^ nhieu hmh sin i 'h . tuong quan theo ham mu (Markov) cung co the dugc xac dmh
Phuorngphdp luan
Gia su rang CO N diem du lieu lien tiep, chu ky la> mau la to i u dọ ia>M. ..K [in..:: ,:.>i: i diem li8n nhau (n<N/2) nhu trong hinh 1, se tam ggi la cac cluster
T = nto T = nto
^ A A
1 2 3 I ^"
to (a- N : )
Hinh 1. Minh hpa cau true du lieu dung trong phuong phap .Allan
ling voi moi cluster la 1 khoang thai gian T=n*tỌ Neu dau ra tuc thai cua ! eam hien quan tinh la Q(t) thi gia tri trung binh cua cluster dugc tinh la:
^AT)=j\it iVii
o d o O chinh la cluster trung binh ciia toe dp dau ra linh ur mau du heu ihu K \ ,I [;,I:- ::• n.