CNG THU PHT V TUYN

1. CHNG 1: TNG QUAN

CU 1:

u v tuyn bao gm u v tuyn pht v u v tuyn thu.

u v tuyn pht bao gm:
+ B iu ch: iu ch tn hiu u vo bng gc tng t vo tn hiu trung tn
(IF) iu ch.
+ B bin i nng tn: chuyn i tn hiu pht c iu ch t trung tn vo
vo sng v tuyn(RF).
+ B khuch i cng sut (PA): khuch i cng sut pht ln trc khi a
vo anten.
u v tuyn thu bao gm:
+ B khuch i tp m nh (LNA) : khuch i tn hiu thu yu nhng gy t tp
m.
+ B bin i h tng: chuyn i tn hiu tn s thu v tuyn (RF) vo tn hiu
trung tn (IF).
+ B gii iu ch: khi phc li tn hiu bng gc pha thu.
+ DSP : b x l tn hiu s.
+ ADC/DAC: b chuyn i tng t/ s.

CU 2:

 Hai nh l ly mu:
+ nh l ly mu Shannon:
-

Tc ly mu phi ln hn 2 ln rng bng khng b mt thng tin: > .

rng bng tn hiu c th tri rng t mt chiu (DC) n ( ly mu bng
gc, ly mu trn tn) hay t n (ly mu bng thng, ly mu di tn, ly
mu hi, siu Nyquist).

+ nh l Nyquist:
Nu : < th s xy ra hin tng xuyn bng. Xuyn bng c s dng t
c li ch trong cc ng dng ly mu di tn.
Phn tch ph ca tn hiu sau ly mu:
-

: ( )
k : s nguyn.
l tc ly mu.

F(f) : ph ca tn hiu tng t cn ly mu.

Hnh 1.2. trang 9

CU 4: T s tn hiu trn tp m lng t, gii thch ti sao fs tng, SNR lng t

tng

Thng s l thuyt:
+ Trc tin, ta gi thit l ch c tp m do li lng t. Gi thit l bin ca tp
m lng t ny l mt bin ngu nhin phn b u trn mt bc lng t, gi thit

u vo dng sin c bin bng FSR ca ADC, th SNR cc i c xc nh nh

sau:

f
SNR 6, 02 N 1, 76 10 lg s dB
2 f max
y, fs l tn s ly mu, fmax l tn s cc i ca tn hiu tng t u vo. SNR
l thuyt bng 6dB thng c ni chnh l xp x ca phng trnh trn khi
fs=2fmax v b qua 1,76dB.
Thng s thc t:
+ Trong cc ADC thc t, SNR c th c xc nh bng cch o li d (Li d l
kt hp ca tp m lng t, tp m ngu nhin v mo phi tuyn).
+ Li d ca ADC c xc nh bng cch ly u ra ADC tr i c tnh tn hiu
u vo, kt qu l li d
+ SNR c tnh bng cch chia cng sut bnh phng trung bnh ca tn hiu u
vo cho cng sut trung bnh bnh phng ca li d.
CU 5:
Li d: l kt hp ca tp m lng t, tp m ngu nhin v mo phi tuyn (
ngha l tt c cc thnh phn khng mong mun ca tn hiu u ra ADC. c
xc nh bng cch s dng u vo dng sin cho ADC sau ly u ra ADC tr
i c tnh tn hiu u vo , tn hiu cn li l li d.
ENOD: S bit hiu dng l s bit cn thit trong mt ADC l tng cng sut
tp m trung bnh bnh phng trong ADC l tng ny bng cng sut trung bnh
bnh phng li d trong ADC thc t.
SFDR: Di ng khng c nhiu gi l mt thng s hu ch c t cc ADC.
Ga s u vo ADC l mt tone hm sin. SFDR c thc hin bng cch ly
FFT u ra ADC. Sau bin i ph u ra ADC c th hin dng cng sut
u ra dB ph thuc tn s. Khi ny SFDR s l hiu s gia tn hiu u vo hm
sin v cng sut nh ca tn hiu gi nhiu ln nht trong ph u ra ca ADC.

CU 6:
Thut ng v tuyn phn mm c s dng ni v mt my thu pht trong
cc thng s then cht c nh ngha trong phn mm v cc kha cnh c bn

ca hot ng v tuyn c th c lp cu hnh li bng cch cp nht li phn

mm ny.
SDR: V tuyn nh ngha bng phn mm l thut ng c tip nhn ti SDR
Forum.
MST : u cui a chun ni v mt u cui c kh nng hot ng trn mt
s chun giao din v tuyn khc nhau.
FAR: V tuyn kin trc linh hot ch tt c cc kha cnh ca h thng tuyn u
linh hot ch khng ch phn bng gc s. FAR thc thu cho php dng phn
mm thay i : s lng v kiu bin i nng/h tn, bng thng b lc trung tn
(IF), thm ch bng tn cng tc RF.
V tuyn kh lp cu hnh: bao gm c lp li cu hnh phn mm ln phn sn,
chng hn thng qua cc thit b kh lp trnh nh FPGA.

CU 7: Kin trc SDR l tng

Gi thit rng b bin i ADC c c b lc chng xuyn bng bn trong v DAC

c c b lc khi phc tn hiu tng t bn trong. SDR c cc tnh nng chnh
nh sau:
- S iu ch, nh knh v cc giao thc pht v thu tt c u c quyt
nh bng phn mm trong phn h x l s. Cc x l ny c thc hin trong
DSP (b x l tn hiu s).
- B Circulator l tng c s dng phn tch cc tn hiu ng pht v
ng thu. Khi s dng cc gii php da trn b lc s khng xy ra cc hn ch
tn s i vi chc nng phn tch pht thu. Phn t ny c coi rng c trn
phi khng l tng gia n vi anten v tr khng ca b khuch i cng sut.
- Lc xuyn bng v lc khi phc tn hiu r rng nht l cn thit trong kin trc
ny. Tuy nhin y, ADC v DAC c tc ly mu nhiu GHz. Hin nay, lc

cong cng, pht, thu c th t c tc thay i dc trong c my cm tay

v trm gc. Thay i chnh s l chuyn i chng t bng thng vo thng thp.

CU 8: Kin trc SDR BTS (hnh 1.17 v 1.18)

Kin trc ca hu ht cc trm gc v tuyn chuyn dch dn mt kin trc c th

iu ch n mt kin trc c nh ngha rng bng phn mm.
S thay i ny cng vi vic chuyn n cc tiu chun cc giao din s bn
trong BTS vo OBSAI v CPRI thay i tn gc cc m hnh BTS.
M hnh BTS l tng t quan im ca OEM (Original Equipement
Manufactuner) phi bao gm mt s lng nh cc khi c s tiu chun c kh
nng ni tng to nn mt gii php phn cng y . S xut hin ca SDR
khin cho m hnh ny ngy cng c nhiu ngi chp nhn.
Phc ha cc phn t to tn hiu iu ch v truyn dn ca BTS kiu ny c
cho trn hnh. By gi, ta c th nh ngha tng phn t chnh (x l tn hiu s,
my pht c tuyn tnh ha v b lc song cng).

Trong s cc phn t ny, nhiu phn t c OEM thu ngoi sn xut nh

SDP, b lc song cng v c PA

CU 9: Mc ch ca cc chun OBSAI v CPRI (tc s liu cao gia BBU v

RFU, tc s liu thp cho OAM&P)
OBSAI v CPRI l cc hot ng tiu chun ha nhm to ra cc giao din m
BTS. N cung cp mt th trng m cc nh bn my (i tc th 3) c th
cung cp mt khi lng ln cc h thng con BTS cho nhiu khch hng ca
OEM, nh vy gim gi thnh cho khch hng OEM. Cc t chc ny a ra cc
chun lin quan n cc vn sau:
- Giao din tc cao gia bng gc v modul RF ( pht s liu I-Q th hin
dng sng cn pht)
- Tc s liu thp cho iu khin, khai thc, qun tr, bo dng v trang b
(OAM&P)
- Phn phi ng h/ nh thi
- Giao din vi u v tuyn t xa

CU 10: Kin trc BTS mi . Tch ring phn BBU v RFU, ni chung qua OBSAI
hoc CPRI. t RFU gn anten)

Trong trm gc thng thng, cc phn bng gc v RF ca my thu pht thng

c t gn nhau v nhiu khi trong cng mt hp my. B khuch i cng sut
cng thng c t gn v trong nhiu trng hp trn cng mt gi my. V
th gy ra tn hao cng sut ln khi truyn n t PA n anten. khc phc,
ngi ta s dng 3 cu hnh sau y:

Tch ring phn s v phn v tuyn: S xut hin ca cc giao din chun
OBSAI v CPRI cng vi cc my pht thu RF u vo s dn n khng cn t
cc phn s v phn v tuyn gn nhau. My thu pht v tuyn c th c lp t
ti ti tr thun tin gn anten, chng hn trn tng ta nh hay trn nh ct
anten gim yu cu v cng sut v gim c gi thnh vn hnh cng nh v tr
lp t my.
Lp t trn thp anten: Lp t my thu pht RF trc tip trn thp cha cc
anten pht v thu (hnh a). Hin nay, lp t kiu ny kh ph bin cho cc mng
di ng 3G v 4G. N cho php loi b c tn hao ca cp v tuyn (gim 1
na, ~3dB)

CU 11: Khi nim khch sn ha BTS hay BTS phn b (t RRU gn ti cc v tr

thun tin v chi ph site r, tp trung cc BBU vo mt HUB; phn tch u im)
Khi nim:
+ Khch sn ha BTS (Hoteling) l khi nim ni ln rng 1 phn thit b trm gc
c t ti cc v tr bn ngoi site trm gc thun tin v gim chi ph. Khi ,
phn ln cc phn t ca mt BTS truyn thng c t ti mt v tr trung tm
(HUB) trong site ca cha mt lng ti thiu cc phn t.
+ Tt c cc phn t mng, cc phn t giao tip, cng nh to tn hiu bng gc,
iu ch, gii iu ch, m ha,u c t ti HUB trung tm. HUB gioa din
trc tip n mng vin thng lin quan v ly ra tt c cc cuc gi t mng ny; to
v thu cc mu s liu cn thit cho pht v thu n/t RRH (u v tuyn t xa)=>
HUB cha ton b tr tu ca trm gc.
Phn tch u im:
- n gin ha bo dng v nng cp: V phn ln thit b trm gc cho nhiu site
s c t trong mt v tr nn ch cn n bo dng mt ln cho tt c cc site
- Gim (hoc loi b hn) cc cabin hoc nh trm cho trm gc
- Gim tiu th ngun: t RRH trn nh thp anten loi b c tn hao cp ng
trc
- Chi ph trin khai thp hn: chi ph PA cng sut thp hn, BTS khng cn c
phng my ti chn thp gim ng k gi xy dng (v c gi thu t site). iu
ha khng kh cng ch cn t ti v tr duy nht (BTS HUB)
- Gi thnh khai thc thp: Khai thc ni chung cng vi vic loi b iu ha
khng kh ti nhiu site t xa dn n gim ng k chi ph khia thc.
- tin cy cao hn

D dng bo dng: t phn ln phn cng BTS ti mt v tr cho php thc hin
bo dng trung tm
D dng trin khai mng: D dng b sung mt site mi

CU 12: Cc phn t ca RRH

RRH-Remote RF Head
y, mt giao din s c b sung h tr khong cch truyn dn xa hn s
vi yu cu ca mt ng dng trm gc thng thng. Giao din ny thng l
quang truyn c xa hn, tuy nhin cng c th s dng cp i dy xon hay
cp ng trc cho cc ng dng trong ta nh hay ngoi tri c khong cch ngn
hn.

CHNG 2
CU 13: Kin trc ca mt my thu n bng i tn:
My thu ngoi sai tng t:

 Gii thch tm tt:

+ T/h RF c lc bi b lc chn bng.
+ Sau c khuch i bi b khuch i tp m thp LNA.
+ Tip tc qua b lc loi b tn s nh . Lu mi tn u tin xut pht t b lc
chn bng.
+ Tn hiu a n b trn ,ti y tn s ca LO tch tn hiu RF thnh IF.
+ Tn hiu IF tip tc c a qua b lc chn bng loi b tn hiu khng mong
mun.
+ Sau t/h IF i qua b khuch i IF tuyn tnh trc khi i vo b gii iu ch ri
n b bin i A/D v DSP to ra tn hiu bng s bng gc.

CU 14: Tn s nh
Nguyn nhn:
+ Tn hiu RF ti u v tuyn thu l:
+
: tn s gc tn hiu hu ch.
: tn s gc tn hiu khng mong mun.
+ Tn hiu b dao ng ni LO

+ 2 tn hiu c a vo b trn c c tnh vo ra phi tuyn:

i=
trong : v=

..

+
(

Kt qu: i= ..+
(

)+

(
)+.

)+

+ B lc trung tn ch cho php thnh phn hiu tn i qua, tng tn b lc.

-

Nu
=
Th
Nu
=
Th
Trong

=2

v
=2
=
=
l tn s trung tn.

v
=

 Thnh phn nhiu sau b trn s lt vo tng trung tn ca my thu cng vi

tn hiu hu ch v b lc trung tn ca my thu khng th loi b n.
Hnh 2.2
Gii php: Nhiu nh ny c th c loi b bng cch dng b lc trc b trn
hoc trong qu trnh bin i t RF vo IF.
CU 15:
Kin trc my thu trung tn IF s.

+ Chc nng bin i h tn vung gc I/Q c kt hp vo DSP. iu ny gip

t c chnh xc cao v khng c cc dch DC.
+ m bo rng IF bng gc l mt tn s cao c th chn knh nhng
thp c x l bi cc b ADC v DSP. IF c chn xung quanh 10 50MHz ,
tip tc tang khi cng ngh ADC tin b.
Nguyn l hot ng c bn ging cu 14 c s khc nho nh nh va nu
trn.

X l s vi thu IF s.

+ Sau khi ly mu IF gc trong kin trc hnh

2.7 , IF s c to ra. T/hiu s ny c
trn h tng to nn tn hiu bng gc phc
(I v Q).

CU 16: Kin trc my thu a knh IF s.

+ T/hiu IF s (to ra bng cch

ly mu t/h IF bng thng ti tc
ly mu fs) c trn vi b
dao ng vung gc (NCO : b
dao ng iu khin) ti tn s
chnh xc bng fs/4. Bng cch
nhn mu IF s vi cc chui
tun hon [ 1 0 -1 0] i vi
knh thc v [0 -1 0 1 ] i vi
knh o.
+ Sau lung I, Q bng gc
c lc bng b lc FIR(p
ng xung kim hu hn) bng
thng to nn t/h bng gc s
yu cu n cc qu trnh x
l tip theo.

 Nhiu bin i h tng vung gc c thc hin trong min s bng cch s
dng cc b dao ng c iu khin bng s NCO.
S dng lc thng thp cho cc tn hiu I v Q.
Nguyn l hot ng : Nhn hnh phn tch bnh thng.
CU 17: DC offset trong DCR:
Nguyn nhn:
+ Dch DC xut hin ti tm ca knh bng gc trong cc nhanh I v Q v mc dch
ny thng l kh cao so vi tn hiu cn gii iu ch.
+ Tn ti mt s ngun gy ra dch DC nh ngun li DC tnh, v ngun li DC
ng. Ngun li DC tnh xy ra do r tn hiu LO vo ca RF ca b trn v tn hiu
truyn lan phn x t cc phn t u thu ca my thu v quay tr li b trn, ti y
n trn vi chnh thnh phn mt chiu n. Ngun DC ng xy ra do s b tr
khng tng xng cc hiu ng thay i theo thi gian trong mt trng my thu nh
: cc phn x a phng ca LO my thu, s tng nhanh ca cng tn hiu gy
ra do fadinh Rayleigh lm cho mch AGC khng bm kp.
nh hng:
+ Lm gim nhy my thu.
+ Lm gim cp BER
CU 18: Cho mt tn s nhiu fn vo my thu khng i tn, chng minh bng do mo
hi bc 2 thnh phn ny s gy DC offset:
Da vo biu thc:
+ Tn hiu u vo. Lu pha ca tn hiu trong phng trnh 2.10 v 2.12 l :
(
)

+ T/thu c gm thnh phn mong mun v thnh phn 1 chiu v thnh phn
bc 2. Nu t/ u vo l mt nhiu ph lin tc th thnh phn mt chiu s gy ra
dch DC trm trng hn.
CU 19: Cc ng r trong DCR

Cc ng r r tim nng chnh l cc ngun dch DC trong my thu bin i

trc tip:
1) R ti ch v xung quanh cc b trn bin i hn tn chng hn do cch ly
LO-RF khng tt ti b trn. Mc dch DC thng khng i trn ton b
bng cng tc.
2) Cc phn x a phng ca my thu. LO truyn ngc qua tng u my thu
pht x vo khng gian qua anten , phn x t cc vt th gn v quay tr li
my thu.
3) R trc tip vo u my thu. Do pht x LO t hp khi LO sau anten thu
thu li ri pht x trn mch in my thu. Mc dch DC thng thay i trn
bng tn cng tc.
4) R LO vo u vo LNA do pht x t/n cc ng li ca tm mch in.
Trng hp ny mc dch DC cng thng thay i trn bng tn cng tc.
CU 20 + 21: Mt s phng php gim DC offset
Thay i tn s: m bo rng VCO ca b dao ng ni khng lm vic ti
hoc gn tn s ca knh thu. Cc gii php thay i tn s loi r tn hiu
ti tn s thu nh chia tn, nh thang hay dch tn.
Ghp in dung: Ghp in dung trn cc ng I v Q loi b cc dch
DC khng mong mun. i vi h thng CDMA c th s dng gii php ny
m khng lm gim ng k t s tn hiu trn tp m.
Hiu chnh DC: a vo h thng mt lng DC hp l hay sng mang
loi b dch DC. Hot ng hiu chnh c thc hin trc tip da trn cc

qu trnh ly mu gi ngay sau ADC. Ga tr trung bnh c a ln cc b

DAC tc thp. Ga tr u ra b bin i DAC tr i gi tr DC yu cu ti
u ra ca b gii iu ch I/Q. Tuy nhin, hiu chnh DC khng th b tr
thch hp cc dch DC ng.

CU 22: Khng phi hp gia cc nhanh I /Q

Nguyn nhn:
+ Ga thit s khng phi hp bin l
gy ra do s mt phi hp nh sau:
|

, ta c th c tnh sai li
|

+ Ga tr in hnh: = 0.3 ,
th sai li l 1,5.
. Hu qu LO i hi
cc u ra I v Q c sai li bin v pha thp. Yu cu ny kh t c ti tn s
cao.

 Bin php x l:
+ Li bin v pha c 2 thnh phn: tnh (khng thay i theo tn s) v ng. Nu
khng c b tr cc li ny s gy ra tn hiu nh trong bng khng mong mun
hay vecto tn hiu.
+ Trong trng hp tnh c th b tr liox ny bng cch lm mo trc cc tn
hiu I v Q hoc bn trong DSP hay bn ngoi trong phn cng tng t. C hai
dng b tr yu cu c cho trn hnh 2.18:

CU 23: nh ngha tp m 1/f:

Tp m 1/f (tp m nhp nhy) xut hin ngay sau bin i h tn lm gim
cp mnh nhy nht l cc knh bng hp. Thut ng tp m 1/f bt ngun
t mt ph tp m c xc nh nh sau:

 Trong my thu v tuyn c th xc nh c mt tn s

nhp nhy bng sn tp m nhit ca my thu ni tng.

m ti tp m

CU 24: nh hng ca mo bc hai khi c tn hiu nhiu r t my pht:

nh hng: mo bc hay cn gi l IMD2 (mo iu ch giao thoa bc 2 )

trong my thu DCR c th gy ra cc tn hiu chn hoc ph lm gim cp t
s tn hiu trn tp m ca my thu.

 Tn hiu ny ngoi t/h mong mun cn c thnh phn mt chiu v thnh phn
bc 2.
Gii thch tm tt hnh 2.19: R tn hiu pht vo my thu , t/h r ny cng vi
t/h thu ng thi c khuch i LNA v i qua b gii iu ch. Bng gc
ca t/h r v t/h thu c bn ct nhau ti mt mc gi li im ct bc 2 ca my
thu phi tuyn IP2. IP2 l mt thng s quan trng, n cho nh mo tnh phi
tuyn bc hai IMD2 v h tr nh lng nhy ca my thu i vi cc tn
hiu nhiu.
CU 25 : nh ngha IIP2 : C nh ngha ca IP2 ri . IP22 th sch ko vit nh.

CU 27 : My thu s dng c trung tn tng t v trung tn s ( chuyn i xung

trung tn thp c th x l vi b ADC n gin:

 Tn hiu u vo sau khi c lc bng thng v khuch i tp m nh c bin

i trc tip vo bng gc.
Tn hiu bng gc vung gc nhn c sau c lc c lc thng thp
xc nh knh v bng thng con mong mun trc khi bin i nng tn vung
gc n mt trung tn IF ph hp vi b bin i A/D tiu th cng sut thp v
trc n c lc bng bi b lc thng thp bng gc ngay sau bin i h
tn..
Khi ny t/h IF nhn c c th bin i h tn vi chnh xc cao bng b bin
i h tn trong khi x l my thu s.
Kin trc ny cho php la chn IF ph hp cho vic s dng cc ADC cng sut
thp trong cc u cui cm tay. V n ch cn mt ADC duy nht trong khi my
thu bin i trc tip cn 2 ADC.
CU 28: K thut tuyn tnh ha phn hi vi b: My thu a bng i hi di ng cao
hn n bng. tng di ng u vo cn tuyn tnh ha my thu.
K thut tuyn tnh ha my thu bng phn hi c u im:
+ Thc hin n gin v kch thc nh, chi ph thp.
+ C th s dng tuyn tnh ha c c LNA v b trn u thu.
+ nh hng t ln h s tp m h thng.
+ C kh nng ci thin tuyn tnh ln chng no cn hot ng trong cc gii hn
tch khuch i bng thng tr.

 Hot ng :
+ Tn hiu i vo b bin i h tn phi tuyn gm t/h mong mun v t/h li xut hin
ti u ra h thng.
+ Tn hiu li nhn c t hot ng phn hi thi gian thc v ng vai tr l tn
hiu lm mo trc b trn.
+ Qa trnh hnh thnh tn hiu li:
-

T/h u ra h thng c bin i nng tn bi cng b dao ng ni nh b bin

i h tn.
Sau lc nh RF, t/h ny tr i bn sao t/h u vo h thng c iu chnh pha
v bin c t/h li.

+ T.h li ny c iu chnh ln v pha sau cng vi t/h u vo to nn u

vo RF ca b trn nng tn nh hnh v.
CU 29: K thut tuyn tnh ha sa mo thun:

 Tuyn tnh ha LNA bng sa mo thun: Cu hnh h thng tuyn tnh ha sa

mo thun s dng cho b khuch i tp m n c im ct cao c cho trn
hnh 2.43.
Mch b tr trn hnh k hiu cho cc b iu khin pha/ ln (hay cc b iu
ch vecto c s dng loi b ti u nng lng tn hiu chnh trong tn hiu
li v nng lng tn hiu li ( mo v tp m ca tn hiu chnh)
Nguyn l hot ng : Phn tch bnh thng, cc b tr ng b tn hiu chnh
v tn hiu lm mo thun.
CU 30: K thut to phi tuyn ni tng:
K thut ny thc hin lm mo trc hoc lm mo sau tn hiu u vo b tr
mo phi tuyn ca cc phn t my thu.

Cu 31: Kin trc my pht vi b bin i nng tn tng t:

 Tn hiu vung gc I v Q c to ra bi DSP. Cc tn hiu I v Q c a n

cc b DAC. V cc tn hiu I v Q c tc bng tc u vo nn cc b
DAC ch cn hot ng ti tc ly mu bng tc Nyquist ca bng thng
knh.
Cc b trn v b phn chia vung gc ca b dao ng ni c th sn xut ri
rc. Dao ng ni c to ra theo hai phng php chnh. 1 l nhn tn sau
chia tn, trong trc ht b dao ng to ra tn s gp 2 ln LO sau chia 2
tn s ny. 2 l s dng b lc dch pha 90o bng rng.

Cu 32: My pht b tr li vung gc:

Cc knh I v Q c th khng phi hp vi nhau v bin v pha.Trong trng hp

cc thnh phn tnh c th b tr sai li ny bng cch lm mo trc cc tn hiu
I v Q.
C th t ng ha qu trnh b tr bng mch phn hi to ra tn hiu li chnh
sa mt phi hp. ADC phi c kh nng ly mu nhanh cho u vo IF. Tc
ly mu t nht phi gp oi tc ly mu ca b FAC v thng th hn gp
i mt cht.

CU 33: Kin trc my pht s dng u ra IF s v b lc ni suy

K thut ni suy hot ng trn nguyn tc tng tc ly mu hiu dng vi cc
dng sng u vo bng cch tng hp cc mu b sung vo gia cc mu gc.

Mu mi ny c xy dng da trn gi tr trung bnh c nh trng s ca

cc mu gc.

Nguyn tc:
+ u ra ca cc x l ni suy by gi c cp cho mt b bin i nng tn vung
gc s dng NCO lm tn hiu dao ng ni.
+ u ra ca b bin i nng tn c cp cho mt b DAC u ra IF v nu DAC
ny c ly mu qu tn th tc ly mu c th ln ti vi tram MHs
+ u ra DAC cha bng mong mun cng vi cc hi v sn phm xuyn bng. Cc
thnh phn gy nhiu ny c lc bi b lc bng thng (b lc SAW). Sau IF
c chuyn vo RF bng cch bin i nng tn.
Li im: S dng DAC hin i nhn c u ra ti mt tn s IF kh dng
(nhiu chc MHz). V th c th x l bin i nng tn vung gc trong min tn
s v loi b nh cng nh trit r LO hon ho.
Cu 34: B tch pha 900 s dng b lc thng cao v thng thp

Cu 35: nh ngha cc thng s hiu nng my thu

Tn hao ghp ti thiu: L tn hao ng truyn ti thiu (bao gm c h s
khuch i v tn hao cp) gia conecter anten ca thit b pht v thit b thu.
Cch ly anten: m bo ng tn ti hai h thng m khng gy nhiu nguy
hi. Cch ly anten c nh ngha l tn hao ng truyn t EAC my ht gy
nhiu n EAC my thu b tc ng. Cc yu cu cash ly rt ra t tiu ch pht x
gi/pht x ngoi bng, sn phm iu ch giao thoa v tng cong sut sng mang
gy nhiu b suy hao.

 Sn tp m my thu: Trong my thu lun tn ti mt sn tp m c s. Tp m

ny ph thuc bng thng v nhit ca my thu. Mc tp m ny c gi l
sn tp m v lun c t l bin thp ca hiu nng my thu.
T s d knh ln cn(ACLR): L suy hao cng sut pht r r vo cc knh ln
cn tnh bng t s gia cng sut pht trung bnh c tm ti tn s knh c n
nh trn cng sut trung bnh c tm ti tn s knh ln cn v c o bng dBc.
T s ny ph thuc vo dch tn so vi tn s trung tm ca knh c n nh
nhy my thu: L s gim cp cp v nhy my thu do tng tp m so vi
sn tp m gy ra bi nhiu pht x gi/OOB hay IMP.
T s nhiu knh ln cn(ACIR): L t s tng cng sut pht t mt ngun vi
tng sng sut nhiu tc ng ln my thu nn nhn sdo cc khim khuyt va
my pht v my thu . y l s o ton b nhiu gay ra bi mt my pht i vi
mt my thu knh ln cn do s khng hon thin ca cc b lc ca my pht
lc pht x OOB v cc b lc my thu lc lm suy gim tn hiu knh ln cn.
ACIR

1
1
1

ACLR ACS

CU36: Phng n BTS phn b (DBS), so snh gii php sd RF over Fiber v u ra
s.

Cc n v v tuyn t xa RRU c coi l cc phn t pht v thu cc tn hiu

v tuyn.
Cc n v bng gc BBU c coi l cc phn t x l v pht cc tn hiu bng
gc t/n RRC.
Thit k DBS phn b chop php cc nh khai thc di ng trin khai cc RRU v
h thng ngun tch ring so vi BBU.

 RRU v BBU c kt ni vi nhau bng cp quang n mode do khch hng

cung cp trn khong cch 10Km hoc xa hn.
Trm gc UMTS(nt B) gm mt n v bng gc BBU v nhiu n v v tuyn
t xa ni vi nhau bng si quang n mode.
Kin trc phn b ny gip gim ng k cng sut tiu th BTS nh gim tn hao
cng sut trong cp ng trc v tng c ly thng tin, gim ng k gi thnh trin
khai mng WCDMA/HSPA UMTS. Cung cp n v gn, r tin cho cc mng
nh v cho php linh hot khi lp rp, tng dung lng vng ph m t chim
khng gian nht , cho php iu khin phn mm t xa
SO SNH RF over Fiber v u ra s

RF over Fiber: Trong gii php ny tn hiu v tuyn t thit b trong nh c

truyn ln RRU t ti anten bng ng cp quang . Cn c :
+1_ thit b b sung ring.
+ 2_ chuyn i nhiu ln tn s v tuyn.
+ 3_ qun l ring.
u ra s: Trong gii php ny tnn hiu bng gc c a ln khi RRU t ti
thp anten bng ng cp quang. Truyn tn hiu bng gc trn si quang cho
php:
+ 1_ pht thu trc tip cc tn hiu bng gc trn si quang.
+ 2_khng cn b bin i tn s vo tuyn vo quang.
+ 3_s dng cng h thng khai thc v bo dng nh BTS.
+ 4_s dng chung c s h tng cho cc ng dng khc.
+ 5_ty chn pht trin sng mang trong ton
Cu 37: Cu hnh khch sn ha NodeB vi BBU tp trung

 Mng truyn dn c thit k trn cc ng ring im n im, c th s

dng mt hoc hai si quang cho mt RRU, trong mt RRU c th h tr 3 on
.

Cu 38: Cu trc tng qut ca mt h thng anten phi

Tn hiu v tuyn t u ra ca b lc tr khng 50 c truyn dn anten bng

mt ng truyn dn bao gm 2 cp nhy v cc phido. Cp nhy mm d un v
c kch thc ph hp d dng u ni vi cc connecter ca b lc v anten
cn cp phdo thng c kch thc to hn vi suy hao ng truyn nh m
bo truyn dn sng in t tt nht.
Cu 39: Phn x trong h thng phi v cc thng s nh gi:

 m bo truyn dn sng in t tt nht t phn v tuyn ca trm gc n

anten cn m bo phi hp tr khng gia cc phn t truyn dn vi cc u v
tuyn v anten.
S khc nhau gia tr khng ti v ng tuyn dn s dn n mt phi khng
dn n hin tng phn x sng trong mt phn sng s phn x ngc t ti
v ngun cp sng , sng phn x s giao thoa vi sng i thng v ti ni n ng
pha vi sng i thng bin in p tng ta c im bng sng cn li ni n
ngc pha ta c vi sng i thng bin in p s gim ta c im nt
sng.
Phn x trong h thng fido s dn ti nh hng l: tn hao cng sut. thay
i ch lm vic ca c linh kin in t trong phn v tuyn ca BTS.
Cc thng s nh gi:
H s phn x cng sut Pr2

Pr
vi 0 Pr2 1 , Pf , Pr l cng sut ca sng i
Pf

thng v sng phn x tng ng.

H s phn x in p: Pr

Ur
vi 0 Pr 1 , Uf , Ur l in p ca sng i thng
Uf

v sng phn x tng ng.

Tn hao phn hi: r 10lg Pr2 20(lgU f lgUr ), dB trong Pf , Pr l sng sut
sng i thng v phn x tng ng. Uf , Ur l in p ca sng i thng v sng
phn x tng ng.
T s sng ng in p: VSWR

U max U f U r

U min U f U r

1
10lg 1 Pr2
2
1

Tn hao mt phi khng: Lr 10lg Lr 10lg

Cu 40: Phn cc anten v anten phn cc cho
KN:

 Phn cc sng in t l phng dao ng ca vecto ng in trng E .

Mt phng phn cc l mt phng cha vecto E v vc t truyn sng K. C
phn cc ngang (chn t t song song vi mt t), ng(chn t t vung
gc vi mt t) v cho(chn t t nghing gc 45 so vi mt t)
Anten phn cc cho_Xpol c to ra bng cc chn t t nghing 45o so
vi trc ng. hai chn t to nn ng phn cc trc giao v tn hiu pht x
ca chng s c lp vi nhau do c s dng cho phn tp thu hoc pht
vi 2 ng thu pht c lp. t s phn cc cho (CPR)c dng nh
gi tnh phn cc ca hai ng ni trn.
CPR dB 10lg gco pol 10lg gcross pol
.

Cu 41: Anten lng bng

 Anten lng bng da trn hai anten Xpol (Xxpol) l mt h thng anten bao gm
mt anten Xpol vi cc kch thc chn t ln hn cho bng tn thp v mt h
thng anten Xpol c kch thc nh hn cho bng tn cao. C th phn loi theo
s u vo nh sau:
+ 4 u vo: cn 4 cp phido 4 cp nhy u ni (hnh a)
+ 2 u vo: Ch cn 2 cp phi v hai cp nhy cho u ni nhng phi c thm
b lc song cng (b kt hp) gn trm gc phn tch hai bng tn (hnh b)

u im ca anten lng bng:

Ch cn mt anten cho nhiu bng tn
Kch thc ging nh cc anten 900MHz
m bo hiu nng do 4 h thng hot ng c lp
Cc b lc tch hp cho php n gin ha nng cp 900/1800MHz
Ti s dng cc ng cp phi hin c
Cc anten Xpol c th c lp t xung quanh ct anten vi khong cch ti
thu; cch ly gia cc ca tt hn 30dB.

Cu 42: Cc s kt hp phn tp thu.

 Trong my thu phn tp khng gian, cc tn hiu thu t hai anten c lp c kt

hp vi nhau c mt tn hiu tt hn. Tn ti hai s kt hp tn hiu thu:
- Kt hp chn la (hnh a)
- Kt hp cc i (hnh b)
Trong s a, chuyn mch c thc hin gia hai tn hiu thu n t hai anten
chn tn hiu thu tt nht da trn t s tn hiu trn tp m ca cc nhnh thu
ny. S ny cho li phn tp t 3 n 4dB
Trong s b, c hai tn hiu thu n t hai anten c nh trng s (khuch i)
theo t s tn hiu trn tp m tng ng ca tng nhnh, sau , c kt hp
ng pha nh nhau c t s tn hiu trn tp m ln nht. S ny cho
li phn tp t 6 n 7dB.
Cu 43: Cc cu trc h thng anten phn tp khng gian

gim bt s lng anten cho phn tp thu, cc bin php phn tp khng
gian sau y uc s dng:

S dng b lc song cng phn chia tn hiu pht thu t mt anten (hnh a)
Dng b chia tn hiu thu phn phi tn hiu thu t mt anten n nhiu my
thu (hnh b)
Cc s ny cho php gim s anten t 9 xung 6, nhng khng cho php gim
khong cch gia hai anten phn tp

Cu 44: Tnh ton cch ly yu cu gia 2 anten A v B khi pht x nhiu gi t mt

anten vo anten th hai bng -40dBm, tha s gim cp tp m Dleak=0.5dB, h s
tp m my thu NF=6dB (tnh tp m nhit my thu Nt=10lg(kTNFB) vi
B=3.84MHx, s dng phng trnh 9.12 tnh cng sut tp m r cho php Nleak
[dB], tr nhiu gi cho tp m r.