Đề Cương Thu Phát Vô Tuyến

8/10/2019 Cng Thu Pht V Tuyn

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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 chtn hiu u vo bng gc tng tvo tn hiu trung tn(IF) iu ch.

+ Bbin i nng tn: chuyn i tn hiupht c iu chttrung tn vovo sng v tuyn(RF).

+ Bkhuch i cng sut (PA): khuch i cng sut pht ln trc khi avo anten.

u v tuyn thu bao gm:

+ Bkhuch i tp m nh(LNA) : khuch i tn hiu thu yu nhng gy t tpm.

+ Bbin i htng: chuyn i tn hiu tn sthu v tuyn (RF) vo tn hiu

trung tn (IF).

+ Bgii iu ch: khi phc li tn hiu bng gc pha thu.

+ DSP : bxl tn hiu s.

+ ADC/DAC: bchuyn i tng t/ s.

CU 2:


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Hai nh l ly mu:

+ nh l ly mu Shannon:

-

Tc ly mu phi ln hn 2 ln rng bng khng bmt thng tin:>.-

rng bng tn hiu c thtri rng tmt chiu (DC) n

( ly mu bng

gc, ly mu trn tn) hay tn(ly mu bng thng, ly mu di tn, lymu hi, siu Nyquist).

+ nh l Nyquist:

- Nu :


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

ax

6, 02 1, 76 10 lg

2

s

m

fSNR N dB

f

y, fs l tn sly mu, fmax l tn scc i ca tn hiu tng tu vo. SNRl thuyt bng 6dB thng c ni chnh l xp x ca phng trnh trn khifs=2fmax v bqua 1,76dB.

Thng sthc t:

+ Trong cc ADC thc t, SNR c thc xc nh bng cch o li d (Li d lkt 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 tri c tnh tn hiuu vo, kt qul li d

+ SNR c tnh bng cch chia cng sut bnh phng trung bnh ca tn hiu uvo 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 ccc thnh phn khng mong mun ca tn hiu u ra ADC. cxc nh bng cch sdng 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: Sbit hiu dng l sbit cn thit trong mt ADC l tng cng sut

tp m trung bnh bnh phng trong ADC l tng ny bng cng sut trung bnhbnh phng li d trong ADC thc t.

SFDR: Di ng khng c nhiu gil mt thng shu ch c tcc ADC.Ga su vo ADC l mt tone hm sin. SFDR c thc hin bng cch lyFFT u ra ADC. Sau bin i phu ra ADC c thhin dng cng sutu ra dB phthuc tn s. Khi ny SFDR sl hiu sgia tn hiu u vo hmsin v cng sut nh ca tn hiu ginhiu ln nht trong phu ra ca ADC.

CU 6:

Thut ngv tuyn phn mm c sdng ni vmt my thu pht trong cc thng sthen cht c nh ngha trong phn mm v cc kha cnh c bn


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ca hot ng v tuyn c thc lp cu hnh li bng cch cp nht li phnmm ny.

SDR: V tuyn nh ngha bng phn mm l thut ngc tip nhn ti SDRForum.

MST : u cui a chun ni vmt u cui c khnng hot ng trn mtschun giao din v tuyn khc nhau.

FAR: V tuyn kin trc linh hot chtt ccc kha cnh ca hthng tuyn ulinh hot chkhng chphn bng gc s. FAR thc thu cho php dng phnmm thay i : slng v kiu bin i nng/htn, bng thng blc trung tn(IF), thm ch bng tn cng tc RF.

V tuyn khlp cu hnh: bao gm clp li cu hnh phn mm ln phn sn,chng hn thng qua cc thit bkhlp trnh nh FPGA.

CU 7: Kin trc SDR l tng

Githit rng bbin i ADC c cblc chng xuyn bng bn trong v DACc cb lc khi phc tn hiu tng tbn trong. SDR c cc tnh nng chnhnh sau:

- S iu ch, nh knh v cc giao thc pht v thu tt cu c quyt

nh bng phn mm trong phn hxl s. Cc xl ny c thc hin trong

DSP (bxl tn hiu s).-

B Circulator l tng c s dng phn tch cc tn hiu ng pht vng thu. Khi sdng cc gii php da trn blc skhng xy ra cc hn chtn si vi chc nng phn tch pht thu. Phn tny c coi rng c trn

phi khng l tng gia n vi anten v trkhng ca bkhuch i cng sut.-

Lc xuyn bng v lc khi phc tn hiu r rng nht l cn thit trong kin trcny. Tuy nhin y, ADC v DAC c tc ly mu nhiu GHz. Hin nay, lc


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cong cng, pht, thu c tht c tc thay i dc trong cmy cm tayv trm gc. Thay i chnh sl chuyn i chng tbng 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 thiu chn 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 bntrong BTS vo OBSAI v CPRI thay i tn gc cc m hnh BTS.

-

M hnh BTS l tng t quan im ca OEM (Original EquipementManufactuner) phi bao gm mt slng nhcc khi c stiu chun c khnng ni tng to nn mt gii php phn cng y . Sxut hin ca SDRkhin cho m hnh ny ngy cng c nhiu ngi chp nhn.

- Phc ha cc phn tto tn hiu iu chv truyn dn ca BTS kiu ny ccho trn hnh. By gi, ta c thnh ngha tng phn tchnh (xl tn hiu s,my pht c tuyn tnh ha v blc song cng).


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-

Tch ring phn s v phn v tuyn: S xut hin ca cc giao din chunOBSAI v CPRI cng vi cc my pht thu RF u vo sdn n khng cn tcc phn sv phn v tuyn gn nhau. My thu pht v tuyn c thc lp tti ti tr thun tin gn anten, chng hn trn tng ta nh hay trn nh ct

anten gim yu cu vcng sut v gim cgi thnh vn hnh cng nh vtrlp t my.-

Lp t trn thp anten: Lp t my thu pht RF trc tip trn thp cha ccanten pht v thu (hnh a). Hin nay, lp t kiu ny kh phbin cho cc mngdi ng 3G v 4G. N cho php loi bc tn hao ca cp v tuyn (gim 1na, ~3dB)

CU 11: Khi nim khch sn ha BTS hay BTS phn b(t RRU gn ti cc v trthun 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 btrm gcc t ti cc vtr 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 ccc phn tmng, cc phn tgiao tip, cng nh to tn hiu bng gc,iu ch, gii iu ch, m ha,u c t ti HUB trung tm. HUB gioa dintrc tip n mng vin thng lin quan v ly ra tt ccc cuc gi tmng ny; to

v thu cc mu sliu cn thit cho pht v thu n/t RRH (u v tuyn t xa)=>HUB cha ton btr tuca trm gc.

Phn tch u im:- n gin ha bo dng v nng cp: V phn ln thit btrm gc cho nhiu site

sc t trong mt vtr nn chcn n bo dng mt ln cho tt ccc site-

Gim (hoc loi bhn) cc cabin hoc nh trm cho trm gc-

Gim tiu thngun: t RRH trn nh thp anten loi bc tn hao cp ngtrc

-

Chi ph trin khai thp hn: chi ph PA cng sut thp hn, BTS khng cn cphng my ti chn thp gim ng kgi xy dng (v cgi thu t site). iuha khng kh cng chcn t ti vtr duy nht (BTS HUB)

-

Gi thnh khai thc thp: Khai thc ni chung cng vi vic loi b iu hakhng kh ti nhiu site t xa dn n gim ng kchi ph khia thc.

-

tin cy cao hn


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-

Ddng bo dng: t phn ln phn cng BTS ti mt vtr cho php thc hinbo dng trung tm

-

Ddng trin khai mng: Ddng bsung mt site mi

CU 12:Cc phn tca RRH

RRH-Remote RF Head

y, mt giao din sc bsung htrkhong cch truyn dn xa hn svi yu cu ca mt ng dng trm gc thng thng. Giao din ny thng lquang truyn c xa hn, tuy nhin cng c thsdng cp i dy xon haycp ng trc cho cc ng dng trong ta nh hay ngoi tri c khong cch ngnhn.

CHNG 2

CU 13:Kin trc ca mt my thu n bng i tn:

My thu ngoi sai tng t:


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Gii thch tm tt:

+ T/h RF c lc bi blc chn bng.

+ Sau c khuch i bi bkhuch i tp m thp LNA.

+ Tip tc qua blc loi btn snh . Lu mi tn u tin xut pht tblcchn bng.

+ Tn hiu a n btrn ,ti y tn sca LO tch tn hiu RF thnh IF.

+ Tn hiu IF tip tc c a qua blc chn bng loi btn hiu khng mongmun.

+ Sau t/h IF i qua bkhuch i IF tuyn tnh trc khi i vo bgii iu chrin bbin i A/D v DSP to ra tn hiu bng sbng gc.


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CU 14:Tn snh

Nguyn nhn:

+ Tn hiu RF ti u v tuyn thu l:

+ : tn sgc tn hiu hu ch. : tn sgc tn hiu khng mong mun.

+ Tn hiu bdao ng ni LO

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

i = + + ..trong : v= + +

Kt qu: i= ..+ ( )+ ( )+( ) ()+.

+ Blc trung tn chcho php thnh phn hiu tn i qua, tng tn blc.

-

Nu = + v = 2 - Th - = =

-

Nu = - v = 2 - Th - = - = Trong l tn strung tn.


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+ Sau khi ly mu IF gc trong kin trc hnh2.7 , IF sc to ra. T/hiu sny ctrn htng to nn tn hiu bng gc phc(I v Q).

+ T/hiu IF s(to ra bng cchly mu t/h IF bng thng ti tcly mu fs) c trn vi bdao ng vung gc (NCO : bdao ng iu khin) ti tn schnh xc bng fs/4. Bng cchnhn mu IF svi cc chuitun hon [ 1 0 -1 0] i viknh thc v [0 -1 0 1 ] i viknh o.+ Sau lung I, Q bng gcc lc bng blc FIR(png xung kim hu hn) bngthng to nn t/h bng gc syu cu n cc qu trnh x

l tip theo.

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


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Nhiu bin i htng vung gc c thc hin trong min sbng cch sdng cc bdao ng c iu khin bng sNCO.

Sdng 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 dchny thng l kh cao so vi tn hiu cn gii iu ch.

+ Tn ti mt sngun gy ra dch DC nh ngun li DC tnh, v ngun li DCng. Ngun li DC tnh xy ra do r tn hiu LO vo ca RF ca btrn v tn hiutruyn lan phn xtcc phn tu thu ca my thu v quay trli btrn, ti yn trn vi chnh thnh phn mt chiu n. Ngun DC ng xy ra do sb tr

khng tng xng cc hiu ng thay i theo thi gian trong mt trng my thu nh: cc phn xa phng ca LO my thu, stng nhanh ca cng tn hiu gyra 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 snhiu fn vo my thu khng i tn, chng minh bng do mohi bc 2 thnh phn ny sgy DC offset:

Da vo biu thc:

+ Tn hiu u vo. Lu pha ca tn hiu trong phng trnh 2.10 v 2.12 l :()


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qu trnh ly mu gingay sau ADC. Ga trtrung bnh c a ln cc bDAC tc thp. Ga tru ra bbin i DAC tri gi trDC yu cu tiu ra ca bgii iu chI/Q. Tuy nhin, hiu chnh DC khng thb trthch hp cc dch DC ng.

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

Nguyn nhn:

+ Ga thit skhng phi hp bin l , ta c thc tnh sai ligy ra do smt phi hp nh sau:

| |

+ Ga trin hnh: = 0.3 , th sai li l 1,5.. Hu quLO i hicc u ra I v Q c sai li bin v pha thp. Yu cu ny kh t c ti tn scao.


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Trong my thu v tuyn c thxc nh c mt tn sm ti tp mnhp nhy bng sn tp m nhit ca my thu ni tng.

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

nh hng: mo bc hay cn gi l IMD2 (mo iu chgiao thoa bc 2 )trong my thu DCR c thgy ra cc tn hiu chn hoc ph lm gim cp tstn hiu trn tp m ca my thu.


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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 bgii iu ch. Bng gcca t/h r v t/h thu c bn ct nhau ti mt mc gi li im ct bc 2 ca mythu phi tuyn IP2. IP2 l mt thng squan trng, n cho nh mo tnh phituyn bc hai IMD2 v htrnh lng nhy ca my thu i vi cc tnhiu nhiu.

CU 25 : nh ngha IIP2 : C nh ngha ca IP2 ri . IP22 th sch ko vit nh.

CU 27 : My thu sdng ctrung tn tng tv trung tn s( chuyn i xungtrung tn thp c thxl vi bADC n gin:


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Tn hiu u vo sau khi c lc bng thng v khuch i tp m nhc 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 vunggc n mt trung tn IF ph hp vi bbin i A/D tiu thcng sut thp vtrc n c lc bng bi blc thng thp bng gc ngay sau bin i htn..

Khi ny t/h IF nhn c c thbin i htn vi chnh xc cao bng bbin

i htn trong khi xl my thu s. Kin trc ny cho php la chn IF ph hp cho vic sdng cc ADC cng sutthp trong cc u cui cm tay. V n chcn mt ADC duy nht trong khi mythu bin i trc tip cn 2 ADC.

CU 28: Kthut tuyn tnh ha phn hi vi b: My thu a bng i hi di ng caohn n bng. tng di ng u vo cn tuyn tnh ha my thu.

Kthut tuyn tnh ha my thu bng phn hi c u im:

+ Thc hin n gin v kch thc nh, chi ph thp.

+ C thsdng tuyn tnh ha ccLNA v btrn u thu.

+ nh hng t ln hstp m hthng.

+ C khnng ci thin tuyn tnh ln chng no cn hot ng trong cc gii hntch khuch ibng thng tr.


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Hot ng :

+ Tn hiu i vo bbin i htn phi tuyn gm t/h mong mun v t/h li xut hinti u ra hthng.

+ Tn hiu li nhn c thot ng phn hi thi gian thc v ng vai tr l tnhiu lm mo trc btrn.

+ Qa trnh hnh thnh tn hiu li:

- T/h u ra hthng c bin i nng tn bi cng bdao ng ni nh bbin

i htn.- Sau lc nh RF, t/h ny tri bn sao t/h u vo hthng c iu chnh phav bin c t/h li.

+ T.h li ny c iu chnh ln v pha sau cng vi t/h u vo to nn uvo RF ca btrn nng tn nh hnh v.

CU 29:Kthut tuyn tnh ha sa mo thun:


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


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Tn hiu vung gc I v Q c to ra bi DSP. Cc tn hiu I v Q c a ncc bDAC. V cc tn hiu I v Q c tc bng tc u vo nn cc bDAC chcn hot ng ti tc ly mu bng tc Nyquist ca bng thngknh.

Cc btrn v bphn chia vung gc ca bdao ng ni c thsn xut rirc. Dao ng ni c to ra theo hai phng php chnh. 1 l nhn tn sau chia tn, trong trc ht bdao ng to ra tn s gp 2 ln LO sau chia 2tn sny. 2 l sdng blc dch pha 90obng rng.

Cu 32:My pht b trli vung gc:

Cc knh I v Q c thkhng phi hp vi nhau v bin v pha.Trong trng hpcc thnh phn tnh c thb trsai li ny bng cch lm mo trc cc tn hiuI v Q.

C thtng ha qu trnh b trbng mch phn hi to ra tn hiu li chnhsa mt phi hp. ADC phi c khnng ly mu nhanh cho u vo IF. Tc

ly mu t nht phi gp oi tc ly mu ca bFAC v thng th hn gpi mt cht.

CU 33:Kin trc my pht sdng u ra IF sv blc ni suy

Kthut ni suy hot ng trn nguyn tc tng tc ly mu hiu dng vi ccdng sng u vo bng cch tng hp cc mu bsung vo gia cc mu gc.


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Mu mi ny c xy dng da trn gi trtrung bnh c nh trng scacc mu gc.

Nguyn tc:

+ u ra ca cc xl ni suy by gic cp cho mt bbin i nng tn vunggc sdng NCO lm tn hiu dao ng ni.

+ u ra ca bbin i nng tn c cp cho mt bDAC u ra IF v nu DACny c ly mu qu tn th tc ly mu c thln ti vi tram MHs

+ u ra DAC cha bng mong mun cng vi cc hi v sn phm xuyn bng. Ccthnh phn gy nhiu ny c lc bi blc bng thng (blc SAW). Sau IF

c chuyn vo RF bng cch bin i nng tn. Li im: Sdng DAC hin i nhn c u ra ti mt tn sIF khdng

(nhiu chc MHz). V thc thxl bin i nng tn vung gc trong min tnsv loi bnh cng nh trit r LO hon ho.

Cu 34: Btch pha 900sdng blc 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 chskhuch i v tn hao cp) gia conecter anten ca thit bpht v thit bthu.

Cch ly anten: m bo ng tn ti hai hthng m khng gy nhiu nguyhi. Cch ly anten c nh ngha l tn hao ng truyn tEAC my ht gynhiu n EAC my thu btc ng. Cc yu cu cash ly rt ra ttiu ch pht xgi/pht xngoi bng, sn phm iu chgiao thoa v tng cong sut sng manggy nhiu bsuy hao.


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Sn tp m my thu: Trong my thu lun tn ti mt sn tp m c s. Tp mny phthuc bng thng v nhit ca my thu. Mc tp m ny c gi lsn tp m v lun c t l bin thp ca hiu nng my thu.

Tsd knh ln cn(ACLR): L suy hao cng sut pht r rvo cc knh lncn tnh bng tsgia cng sut pht trung bnh c tm ti tn sknh c nnh trn cng sut trung bnh c tm ti tn sknh ln cn v c o bng dBc.Tsny phthuc vo dch tn so vi tn strung tm ca knh c n nh

nhy my thu: L sgim cp cp vnhy my thu do tng tp m so visn tp m gy ra bi nhiu pht xgi/OOB hay IMP.

Tsnhiu knh ln cn(ACIR): L tstng cng sut pht tmt ngun vitng sng sut nhiu tc ng ln my thu nn nhn sdo cc khim khuyt vamy pht v my thu . y l so ton b nhiu gay ra bi mt my pht i vimt my thu knh ln cn do skhng hon thin ca cc blc ca my pht lc pht xOOB v cc blc my thu lc lm suy gim tn hiu knh ln cn.

11 1

ACS

ACIR

ACLR

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

Cc n vv tuyn t xa RRU c coi l cc phn tpht v thu cc tn hiuv tuyn.

Cc n vbng gc BBU c coi l cc phn txl v pht cc tn hiu bnggc t/n RRC.

Thit kDBS phn bchop php cc nh khai thc di ng trin khai cc RRU vhthng ngun tch ring so vi BBU.


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RRU v BBU c kt ni vi nhau bng cp quang n mode do khch hngcung cp trn khong cch 10Km hoc xa hn.

Trm gc UMTS(nt B) gm mt n vbng gc BBU v nhiu n vv tuynt xa ni vi nhau bng si quang n mode.

Kin trc phn bny gip gim ng kcng sut tiu thBTS nhgim tn haocng sut trong cp ng trc v tng cly thng tin, gim ng kgi thnh trinkhai mng WCDMA/HSPA UMTS. Cung cp n vgn, rtin cho cc mngnhv cho php linh hot khi lp rp, tng dung lng vng phm t chimkhng gian nht , cho php iu khin phn mm txa

SO SNH RF over Fiber v u ra s

RF over Fiber: Trong gii php ny tn hiu v tuyn tthit btrong nh ctruyn ln RRU t ti anten bng ng cp quang . Cn c :+1_ thit bbsung ring.+ 2_ chuyn i nhiu ln tn sv tuyn.+ 3_ qun l ring.

u ra s: Trong gii php ny tnn hiu bng gc c a ln khi RRU t tithp 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 bbin i tn svo tuyn vo quang.+ 3_sdng cng hthng khai thc v bo dng nh BTS.+ 4_sdng chung c shtng 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


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Mng truyn dn c thit ktrn cc ng ring im n im, c thsdng mt hoc hai si quang cho mt RRU, trong mt RRU c thhtr3 on.

Cu 38:Cu trc tng qut ca mt hthng anten phi

Tn hiu v tuyn tu ra ca blc trkhng 50 c truyn dn anten bng

mt ng truyn dn bao gm 2 cp nhy v cc phido. Cp nhy mm dun vc kch thc ph hp ddng u ni vi cc connecter ca blc v antencn cp phdo thng c kch thc to hn vi suy hao ng truyn nh m

bo truyn dn sng in ttt nht.

Cu 39:Phn xtrong hthng phi v cc thng snh gi:


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m bo truyn dn sng in ttt nht tphn v tuyn ca trm gc nanten cn m bo phi hp trkhng gia cc phn ttruyn dn vi cc u vtuyn v anten.

Skhc nhau gia trkhng ti v ng tuyn dn sdn n mt phi khngdn n hin tng phn xsng trong mt phn sng sphn xngc ttivngun cp sng , sng phn xsgiao 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 nngc pha ta c vi sng i thng bin in p sgim ta c im ntsng.

Phn xtrong hthng fido sdn ti nh hng l: tn hao cng sut. thayi chlm vic ca c linh kin in ttrong phn v tuyn ca BTS.

Cc thng snh gi:

Hsphn x cng sut

2 r

rf

PP

P

vi20 1

rP

, Pf, Pr l cng sut ca sng ithng v sng phn xtng ng.

Hsphn xin p: rrf

UP

U vi 0 1rP , Uf , Url in p ca sng i thng

v sng phn xtng ng. Tn hao phn hi: 210lg 20(lg lg ),r r f r P U U dB trong Pf, Prl sng sut

sng i thng v phn xtng ng. Uf , Url in p ca sng i thng v sngphn xtng ng.

Tssng ng in p: axmin

f rm

f r

U UUVSWR

U U U

Tn hao mt phi khng: 221

10lg 10 lg 10 lg 11

r r r

r

L L PP

Cu 40: Phn cc anten v anten phn cc cho

KN:


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Phn cc sng in tl 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 tt song song vi mt t), ng(chn tt vunggc vi mt t) v cho(chn tt nghing gc 45 so vi mt t)

Anten phn cc cho_Xpol c to ra bng cc chn tt nghing 45oso

vi trc ng. hai chn tto nn ng phn cc trc giao v tn hiu pht xca chng sc lp vi nhau do c sdng cho phn tp thu hoc phtvi 2 ng thu pht c lp. tsphn cc cho (CPR)c dng nhgi tnh phn cc ca hai ng ni trn.

10lg 10lgco pol cross pol CPR dB g g

.

Cu 41: Anten lng bng


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Anten lng bng da trn hai anten Xpol (Xxpol) l mt hthng anten bao gmmt anten Xpol vi cc kch thc chn tln hn cho bng tn thp v mt hthng anten Xpol c kch thc nhhn cho bng tn cao. C thphn loi theosu vo nh sau:

+ 4 u vo: cn 4 cp phido 4 cp nhy u ni (hnh a)

+ 2 u vo: Chcn 2 cp phi v hai cp nhy cho u ni nhng phi c thmblc song cng (bkt hp) gn trm gc phn tch hai bng tn (hnh b)

u im ca anten lng bng:-

Chcn mt anten cho nhiu bng tn-

Kch thc ging nh cc anten 900MHz-

m bo hiu nng do 4 hthng hot ng c lp- Cc blc tch hp cho php n gin ha nng cp 900/1800MHz-

Ti sdng cc ng cp phi hin c

-

Cc anten Xpol c thc lp t xung quanh ct anten vi khong cch tithu; cch ly gia cc ca tt hn 30dB.

Cu 42: Cc s kt hp phn tp thu.


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-

Sdng blc song cng phn chia tn hiu pht thu tmt anten (hnh a)-

Dng bchia tn hiu thu phn phi tn hiu thu tmt anten n nhiu mythu (hnh b)

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Cc s ny cho php gim santen t9 xung 6, nhng khng cho php gim

khong cch gia hai anten phn tpCu 44: Tnh ton cch ly yu cu gia 2 anten A v B khi pht xnhiu gitmtanten vo anten thhai bng -40dBm, tha sgim cp tp m Dleak=0.5dB, hstp m my thu NF=6dB (tnh tp m nhit my thu Nt=10lg(kTNFB) viB=3.84MHx, sdng phng trnh 9.12 tnh cng sut tp m r cho php Nleak[dB], trnhiu gicho tp m r.

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