te/;. Nhu da trinh bay tran day, de tai chii trgng den SDR ma khong da y den phhn
Cling chuyen dung khac ciia he thong do do da tai khong trinh bay va quan tam den thiet ke do nhay may thu (cac bg khuyech dai, cac bg Igc), phuang phap lay mau va biln d6i D/A hay A/D cung nhu cac chip diau cha bang dai.
Mot trong van da co ban ciia MCM la dong bg khung. Nhiem vu ciia no la phat hien vi tri bat dau ciia 1 khung nham xac djnh chiau dai khung dir lieu. Sau do tran co so chiau dai Cp dugc quy dinh truoc giua ban thu va ban phat ma loai bo Cp trong tung khung da xac dinh doan day dii lieu trong khung. Cuoi cung la day dii lieu trong khung
> r -y / r '
do dugc gian ra nham lap day khoang thai gian trong ma Cp chiam trong khung (chuyan doi toe do dir lieu ~ chuyan doi khoang thoi gian ciia 1 mau du lieu theo ngugc lai voi ban phat). Day la nhiem vu co tinh quyat dinh anh huong Ion dan chat lugng giai diau cha ~ bian doi FFT.
So d6 bg giai dieu cha ciia phan thu dugc miau ta trong hinh 12 duoi day bao gom
2 khoi chinh i) Khoi tien xu li va tach tin hieu dong bo khung, ii) khoi giai dieu che (FFT).
C3QC08_1/peMod
File Edit View Simulation Format Tools Help
D iGs; y a : • -^ - - • ^J' I ^ - • • ¥~Trini L l ] ^ jlOOOO i Normal mm 0 # lr.2 Ready Sig_l CTRL I sig_Q CTRL a Spirt Sync - • 0 > f 3 > ^ 0 -WT^ D e l j y l 100% xn_re xn_Jm start twd_jnv fiwd Inv xn >* we )*_re _md«x index rtd busy uout edone done • M 3 • > f 3 >a > ^ ^ ^ FFT v3 2 1 X^D Re • C D ode45 Vout
Hinh 12: Sa do khoi bo giai dieu che dua tren FFT
Kh6i tifen XLP li va tach xung dong bo
Do CO 2 loai khung (khung phan thue [Re] va khung phan ao [Im]) co chilu
nhau. Chu y r k g DMT chi truyln 1 loai khung [Re] d8 truyan thong ban (Base band) eon OFDM truyk 2 loai khung \[Re] va Q[/m] de cho phq
thong bang dai (Passband). Do do se co hai each xu li va tach tin hieu_( khung khac nhau giua DMT va OFDM. Trong bao cao nay de cap dei khung I/Q cua OFDM do do se co 2 kh6i t i k xu li nhu nhau, song song ra trong hinh 13. , " • .• .
Moi khoi nay bao g6m hai phan, khoi diSu khi^n va khoi tach va hieu. Trong do nhiem vu cua khoi diSu khiSn la tach dugc 2 tin hieu, tin hi bg khung CTRLJ/Q va tin hieu d6ng bg khung tin hieu Sig_I/Q. Nhi?m tin hieu CTRL_I/Q dS diSu khien gian each du lieu trong khung de lap day tr6ng loai bo Cp va diSu k h i k d6ng bg chuySn d6i FFT day du lieu troni do (giai dieu ehl). Trong khi do tin hieu Sig_I/Q dugc su dung de chi ghi lieu trong khung do vao bg nho FIFO ma loai bo (tranh ghi) khoang trong ma Cp chiem da bi loai bo truoc do.
[ ^ Q C 0 8 _ l / D e M o d / 5 p H t Sync •
File Edit View Simulation Format Tools Help
Q a ; H ^ i — © ! - ^ ^ -ih 1 i i ^ • - I • -' \^^^ | Normal ;^ 1 1 mm^^ ! i*a C l > Q Ready 5-g. D e l j y Sig_Q Clrt Q cast C o r i ' / e r t l u u p S a m p l e l b d i n d o u t e m p t y ^'^ W g l l re ^"" S.fl I F I F 0 1 *aD cast T4 C o n u e r t 2 u D o w n S a m pi 1 ^ ) b e m p t / > %iM\\ S i a _ Q K Z J M u l t 2 100% bde45
Hinh 13: Sa do khoi tien xu li tin hieu FQ va tach dong bo ciia OFDM
+ Khoi dieu khien: Nhiem vu chii yau ciia khoi nay la xii ki dong bg. Va nhu John G. Proakis chi ra trong | 5 | , tu tuong quan la mot bien phap i mirc do bat dugc tin hieu ma no dugc dich chuyen theo thoi gian, no nl"
ham ciia tong so thai gian dich chuyan. Chinh xac hon tu tuong quan trong khoi diau khian la tuang quan cheo ciia mot tin hieu vai chinh no. Theo |9|, tu tuong quan thuong dugc su dung rat hiiu ich cho viec tim kiam cac mlu lap di lap lai trong mot tin hieu, chahg han nhu xac djnh sir co mat ciia mot tin hieu co tinh chu ky da dugc dau trong on hoac da nhan dang cac tan s6 bi mat trong mot tin hieu bang cac tan so hai hga ba ciia no. Tu tuong quan lian quan dan viec cung cap thong tin va cau tnic cua mot tin hieu trong mian thai gian. Phuong trinh tu tuong quan dugc cho boi:
He thong dong bg va bii tru kanh phu thugc vao each su dung mot phan mo dau huan luyen nhu chi ra trong Hinh 14, Trong cac mang thuong mai nhu Wifi. cac diam truy cap truyan quang ba thong tin huan luyen da dau cuoi (MT) sii dung thue hien dong bg khung, dong bg nhip theo thoi gian, dong bg tan so va uac lugng kanh. Do do giai doan dong bg trong mot MT co tha dugc chia thanh ba phan:
- Phan phat hien: He thong truyan quang ba dii lieu huan luyen da dong bg nhip,
giai doan nay chiia cac mau huan luyen (uoc lugng) da khoi tao bieu tugng OFDM va da bii trii do lech tan so. Nhu da thay trong hinh. 14, phan dii lieu huan luyen c6 2 phan co tan la: A, B va C chiia dii lieu cugc ggi. Phan A dugc sir dung de phat hien khung (dong bg khung), phan B dugc thiat ka da dong bg nhip theo thoi gian va uoc lugng tho do lech tan so song mang (CFO), con phan C dugc sii dung da uac lugng tinh do lech tan so song mang (CFO) va uoc lugng kanh, Ph4n A va ph^n B sau nay dugc diing lam cac thong tin huan luyen tran cac kanh pilot ciia truyen thong dua tran MCM.
Phan A Phan B PhanC
A I Ai Al AJ BI CP C C •
Hinh 14: Thong tin dSng bo OFDM
- D6ng bg khung la giai doan dau tian cua toan bg qua trinh d6ng bg hoa va la giai doan quan trgng nhat vi chi sau khi xac dinh chinh xac mot khung thi mot thiet bi dau cuoi (MT) moi co tha tra thanh mot thanh vian ciia mang truyen dan
MCM. Tin hieu nhan dugc dugc tuong quan vai mot phien ban tra cm
da tim mot dinh trong ph§n A, B va C ciia thong tin huan luyen va thon goi.
- Tu tu'ong quan la giai doan truyen dii lieu cugc ggi co nhiem vu thee
bg khung, d6ng bg nhip thai gian, d6ng bg tan so va uac lugng do U
song mang b^ng each tuong quan cheo tin hieu nhan dugc voi phian b; chinh no. Da tuong quan cheo thi can phai co mot bg nhan, mot bg cgi bgnho 128-16bitRAM
Xii li so tin hieu (DSP) sii dung giai thuat CORDIC (Coordinate
Digital Computer - Tinh toan quay tga do so) de thue hien phep tinh
quan tren FPGA. CORDIC la mot thuat toan don gian va hieu qua da tinl ham lugng giac va cac ham hyperbolic. Tat ca cac ham lugng giac c6 tinh hoac tao ra tu chiic nang quay vector. Quay vector cQng co tha dugi chuyen doi tii cue hinh chii nhat nay sang cue hinh chii nhat kia va xay c cac bian doi nhu DFT va DCT [8|. Cac thuat toan CORDIC cung cap mc phap lap di lap lai ciia phep quay vector thue hien bai thay doi goc tiiy y cac phep dich va phep toan cong. Giai thuat co ten Voider |2, 6| chi phuong trinh (ii) va (iii)
Cac phuang trinh co ban CORDIC la:
X(i+J) = X(i)Cos(p - Y(i)Sin(p (ii) Y(i+1) = Y(i)Cos(p + X(i)Sin(p (iii) X(i+1) = Cos(p (X(i) - Y(i)Tan(p) (iv)
Y(i^l) = Coscp (Y(i) + X(i)Tan(p) (v)
Neu cac goc quay han cha da tanip = ± 2e" thi so cac phep toan n
giam boi toan tii dich don gian. Phuong trinh (iv) va (v) bay gio co tha hien cho moi lan lap la:
X(i+l)=K,[X(i)-Y(i).d,2.e'] Y(i^l)-K,[Y(i)-X(i).d,.2.e']
Trong do K, = Cos (tan'' l.e") - 0.60725 va r/, = ±7
Dai lugng thii ba
X...in XI X2^*f-Y1 ^n. ;: J -- X2 ''29-^5^2 stirf X 4 = > 3 'I'lr^'P tV> srift 3 X5:^X4-*.Je»4>.:^V4 [xJ^ I ihfi :x <:,+•.2i?>^-:.\Y6 [ZlfJCZ] X/-yji-r<.2s-i;>.<i\(^ fjf\ VI • C j n i •vrs = Y? ;*'?.t>f\}f) :<: 1 ' V.1 ^ V3. ^^MpJX^ I .,.,„^iitt Y5-Y4-iO^>ii-JXi yiiti
YV) • y^/';!fj7ii :sx'i
i inn I Y / = Vt.l-it-S',e):p-4.<>J Y / = Vt.l-it-S',e):p-4.<>J \ r-^ -.90 ^1 z;\ - z?.».' -tr' ^1 Z - ^ . ' ;•(', 1 / i , 'KI 4=. IQ Z5=:2i*^-. i : £'i .^ /!' LI 27 --Z6*'. -I
Hinh 15: Kien true Cordic xu li tucxng quan
Vi vay, da dat dugc mot goc mong dgi, mot loat cac yau cau lap dugc thue hien va trong thiat ka nay, so lan lap lai la 5 va trong moi lan lap lai cac gia tri moi ciia x, y va z phu thugc vao cac gia tri truoc day . Theo | 5 | , bg vi xu ly CORDIC CO the dugc cau hinh da lam tron, hyperbolic va phep quay tuyan tinh cho ca cha do vectoring va cha do quay. Cha do vectoring tron dugc sii dung da tinh toan uoc lugng tho do lech tan so (CFO) va uoc lugng tinh CFO. Cha do quay tron dugc sii dung da hieu chinh tho CFO theo chuoi dii lieu huan luyen va hieu chinh cac dii lieu biau tugng OFDM thu dugc tai phan C. Cha do vectoring tuyen tinh dugc sir dung da tinh toan trong giai doan uac lugng kanh. Nhu vay
viec ap dung cac thuat toan CORDIC cho OFDM la mot trong nhiing yeu cau
quan trong da uoc lugng kanh, bu trii tan so va uoc lugng do lech tan so.
Hinh. 15 mo ta kien triic CORDIC hoan toan duomg ong lap di lap lai. Cac kien triic CORDIC lap di lap lai co tha dugc lay don gian bang each sao chep moi cua cac phuong trinh khac biet ba tha hien trong phuong trinh (ii-vii). Ham quylt
dinh di, dugc dilu khian boi dau ciia thanh ghi ''y " hoac " z " tuy thugc vao viec
tri chinh xac hon. De tai da tao CORDIC duong ong xu ly nhanh viet b
dk thue hien chiic nang xii li tuang quan va dugc kiem chiing nha su g
ham CORDIC c6 sin trong Ip_core Xillinx Blockset.
RQC08_1A-./5plit Sync/control *
Fie Edt View simulation Format Tods Help
e i '^^ -y -1 I - V B 10000 Normal \Sm 0 ^^*J^ ft © n a ^
On
[Ready
L>n^ ^ b )