chuong 5 - kỹ thuật viễn thông

Chng 3

151

CHNG 5: H THNG V KIN TRC CC H THNG V TUYN5.1. Tm tt vic s dng cc bng tn s

cho vic theo di cc chun v tuyn nm trong di tn s no, trc ht chng ti tm tt li vic s dng cc bng tn s c chun ho. Hnh 5.1.1 gii thiu cc di tn sng in t c s dng trong thng tin v tuyn.

Cc di sng cng nh di tn s v bc sng ca chng c tm tt trong bng sau:Di sngDi tn sBc sng

LF (Low Frequency)30 KHz 300 KHz10 km 1 km

MF (Medium Frequency)300 KHz 3 MHz10O m 10 m

VHF (Very High Frequency)30 MHz 300 MHz10 m 1 m

UHF (Ultra High Frequency)300 MHz 3 GHz1 m 10 cm

SHF (Super High Frequency)3 GHz 30 GHz10 cm 1 cm

EHF (Extremely High Frequency )30 GHz 300 GHz1 cm 1m m

Ngoi ra ngi ta cn dng cc ch ci nh s cc bng tn nh trnh by trong bng 5.1.2.Bng sngDi tn s quy nh (GHz)

L1 2

S2 4

C4 8

X8 12

Ku12 18

K18 - 26.5

Ka26.5 40

Q33-50

U40 60

V50 75

E60 90

W75 110

F90 140

D110 170

G140 220

5.2. Cc chun v tuyn (Wireless Standards)

Trong phn ny s gii thiu cc h thng hay cc chun v tuyn, ch yu tm tt cc thng s k thut ca h thng.5.2.1. Cc h thng thng tin di ng th h th nht (1G)

Cc h thng thng tin di ng th h u tin trn th gii phi ni ti l:

- H thng AMPS (Avanced Mobile Phone Service): H thng dch v in thoi di ng tin tin.- H thng TACS (Total Access Communication System): H thng thng tin truy cp tng th.

- H thng NMT (Nordic Mobile Telephone): H thng thng tin di ng Bc u. H thng AMPS:

Cc thng s k thut chnh ca h thng ny nh sau:

Di tn: Di tn thu: 869-894 MHz.

Di tn pht: 824-849 MHz.

Phng php truy cp knh: FDMA.

Phng php iu ch: iu tn FM.

rng knh v tuyn (ph knh v tuyn): 30 kHz.

S lng knh: 832.Phng php ghp knh: FDD.

H thng TACS: H thng ny c hai loi: ETACS v NTACS

Di tn: Di tn thu: 916 949 MHz. 860 870 MHz.

Di tn pht: 871 904 MHz. 915 925 MHz.

Phng php truy cp knh: FDMA FDMA

Phng php ghp knh: FDD FDD

Phng thc iu ch: FM FM

rng ph ca knh: 25 Hz 12.5 MHz

S lng knh: 1000 400

H thng NMT: Trong c chun: NMT 400 v NMT 900

Di tn: Di tn thu: 463 486 MHz 935 960 MHz

Di tn pht: 453 458 MHz 890 915 MHz

Phng php ghp knh: FDD FDD

Phng php truy cp knh: FDMA FDMA

Phng php iu ch: FM FM

rng ca knh: 25 kHz 12,5 kHz

S lng knh: 200 1999

Cc h thng thng tin di ng th nht khng c ng dng nhiu trn th trung do nhiu hn ch ca chng nh gi ca thit b u cui, ca h thng cao v hn ch v dung lng ph. Hn ch chnh l do s dng phng php iu ch tng t (iu tn: FM: Frequency Modulation) trong h thng hn ch ng k s lng ngi s dng so vi cc h thng dng phng php iu ch s.

5.2.2. Cc h thng thng tin di ng th h th hai (2G)Cc h thng thng tin di ng th h th 2 (2G) c nhiu u im vt tri so vi cc h thng thng tin di ng tng t (anolog) 1G. Cc u im vt tri l vic ng dng cc cng ngh s cho php ci thin cht lng thng tin v tng ng k s lng ngi s dng. Ngoi ra trong h thng 2G, s xut hin ca k thut chuyn giao (hand-over) m ra h thng din thoi t bo (cellular system) , ang v s tip tc c ng dng rng ri trn ton th gii.

H thng hay chun GSMNm 1992, h thng thng tin di ng t bo th h th 2 xut hin Chu u l h thng GSM (Global System for Mobile Communication) hay cn gi l h thng thng tin di ng ton cu. y l h thng thng tin Chu u u tin s dng cc k thut iu ch s. Cu trc mng GSM, vic quy hoch m rng mng s c dy trong cc mn hc v k thut vin thng v thng tin di ng. y ch gii thiu cc thng s k thut c trng c bn ca chun GSM. H thng GSM s dng k thut ghp knh theo tn s FDD (Frequency Division Duplex) v k thut truy cp theo thi gian v tn s (Time Division Multiple Access and Frequency Division Multiple Access). H thng GSM s dng phng thc iu ch GMSK (Gaussian Minimum Shift Keying), b lc s dng l b lc Gaussian. iu ch GMSK ny t b nh hng bi mo phi tuyn, tuy nhin, hiu sut s dng ph hay hiu sut bng thng thp (1 bit/s/Hz). H thng GSM lc u d tnh cho cc ng dng thng tin thoi v truyn s liu tc bit thp (9600 bit/s), v dng cho vic truyn cc bn tin ngn hay cn gi l SMS (Short Message Service) c 1600 k t. Tc bit c s ca h thng sau khi m ho l 279.833 kbit/s nhng h thng s dng phng php a truy cp theo thi gian, do tc bit ny c chia cho 8. Khong thi gian trong cc d liu c nn gi l cc khe thi gian (time slot). H thng ny cho php thng tin gia nhng ngi s dng di ng v c nhiu c im ni tri so vi cc h thng tng t th h th nht. Sau y tm tt cc thng s k thut c trng c bn ca h thng:

Di tn: Di tn thu: 935 960 MHz.

Di tn pht: 890 915 MHz.

Phng php truy cp: TDMA/FDM.

Phng php ghp knh: FDD

Phng thc iu ch: GMSK 1 bit/symbole (1 bit/ 1 k hiu)

M ha thoi: 13 kbit/s.

Tc bit: 270.833 kbit/s.

B lc s dng: B lc Gaussian h s 0,3.

rng ph ca knh: 200 kHz.

S lng knh: 124, mi knh cho 8 ngi s dng.

Vi s tng trng v s lng ngi s dng v c bit l s pht trin ca cc dch v i hi tc cao nh internet tc cao, in thoi hnh trong khi yu cu kt ni khng ch kt ni gia cc thu bao di ng vi nhau m cn kt ni t cc thu bao n cc nh cung cp dch v, cc cng ty trong ln nht l cc nh cung cp dich v internet, cc mng intranet s i hi mt mng thng tin di ng tc cao . Ngoi ra, vi d liu, mng phi p ng c tc tu theo yu cu ca ngi s dng v vic thanh ton cc ph phi c tnh theo s lng thng tin (s lng cc gi tin - packet). Tuy nhin, mng GSM da trn chuyn mch knh nguyn thy kt ni khng th p ng cc dch v i hi tc cao nh trn. tng tc bit, nhiu gii php c a ra cho mng thng tin di ng GSM nh h thng dich v v tuyn gi chung GPRS (General Packet Radio Services) trn nn tng ca GSM hoc h thng EDGE (Enhanced Data Rate for GSM Evolution). Cc h thng ny cn c gi l cc h thng 2G+ hoc 2.5G.

H thng DCS

H thng thng tin di ng t bo th h th 2, h thng DCS (Digital Communication System: H thng thng tin s), xut hin Chu u nm 1993. H thng ny c cc thng s k thut chnh ging nh h thng GSM nhng tn s 1800 MHz. Do mt s nc Chu u ngi ta cn gi chun ny la GSM 1800. Cc thng s k thut c trng nh sau:



Phng php a truy cp: TDMA/FDM.

Phng php ghp knh: FDD.Phng thc iu ch: GMSK.M ha thoi: 13 kbit/s.

Tc bit c s: 270.833 kbit/s.

B lc s dng: Gaussian.

rng knh v tuyn: 200 kHz.

S lng knh: 1600 vi 3 ngi s dng cho 1 knh.

H thng DECT Nm 1993 cng ti Chu u, xut hin h thng in thoi khng dy th h th 2, h thng DECT (Digital European Cordless Telephone: H thng in thoi khng dy s Chu u). H thng ny s dng phng php iu ch tn s GFSK (Gaussian Frequency Shift Keying), b lc s dng l b lc Gaussian c h s 0,5. Cc thng s k thut c trng c tm tt nh sau:

Di tn: 1880 1900 MHz.


Phng php ghp knh: TDD.

Phng thc iu ch: GMSK 1 bit/1 k hiu.


Tc bit c s: 1152 Mbit/s.

B lc s dng: Gaussian.

rng knh v tuyn: 1,728 kHz.

S lng knh: 10 vi 24 ngi s dng cho 1 knh.

H thng IS - 54Cng vo thi im nm 1992 Bc M, h thng in thoi t bo th h th 2 (IS-54 hoc NADC North American Digital Cellular: H thng in thoi v tuyn t bo s Bc M) xut hin. Cng ging nh h thng GSM Chu u, cc bc tin trin tip theo ca h thng IS-54 cng ang c nghin cu v pht trin. H thng NADC s dng phng thc iu ch pha DQPSK. B lc s dng l b lc cosin nng (Raised-Cosine Filter) vi h s truy cp bng hay h s roll-off bng 0,35. Cc thng s k thut chnh ca chun IS-54 nh sau:




Phng php ghp knh: FDD.

Phng thc iu ch: DQPSK 2 bit/1 symbol.


Tc bit c s: 48,6 kbit/s.

B lc s dng: Cosine nng. rng knh v tuyn: 30 kHz.

S lng knh: 832.

H thng IS-95 hay CDMA OneCng nm 1992 Chu M, mt h thng in thoi t bo khc xut hin, l h thng IS-95 hay CDMA one.



Phng php ta truy cp: CDMA/FDM.


Phng thc iu ch: QPSK/OQPSK, 2 bit/1 symbol.

M ha thoi: thay i < 9,6 kbit/s.


S lng knh: 20.

H thng IS-136H thng IS 136 hay cn gi l h thng in thoi di ng s tin tin (Digital Advanced Mobile Phone System) l s pht trin ca h thng tng t AMPS c th s dng bng tn 800 MHz ca chun IS-54 v bng tn 1900 MHz ca h thng PCS. Cc thng s k thut c trng nh sau:



Phng php ta truy cp: TDMA/FDM.

Phng php ghp hnh: FDD.

Phng thc iu ch: DQPSK , 2 bit/1 symbol.




S lng knh: 832.

H thng PDCNm 1994, Nht Bn xut hin mt h thng in thoi t bo th h th 2, h thng PDC (Personal Digital Cellular: H thng in thoi t bo s c nhn). H thng ny s dng phng thc iu ch DQPSK, b lc s dng l b lc cosine nng c h s roll-off bng 0,5.

Di tn: 810 826 MHz.

940 956 MHz.

1777 1801 MHz

1429 1553 MHz

Phng php a truy cp knh: TDMA/FDM.


Phng thc iu ch: DQPSK, 2 bit/1 symbol.



B lc s dng: Cosine nng

rng knh v tuyn: 25 kHz.

S lng knh: 4800.

H thng PHS

y l mt chun khng dy th h th 2 ca Nht Bn xut hin nm 1993. H thng PHS (Personal Handy Phone System: H thng in thoi v tuyn cm tay) s dng iu ch DQPSK, b lc s dng l b lc cosine nng vi h s truy cp bng hay h s roll-off l 0,5.

Di tn: 1895 1918 MHz.

Phng php ta truy cp knh: TDMA/FDM.

Phng php ghp knh: TDD.

Phng thc iu ch: DQPSK, 2 bit/1 symbol.


Tc bit c s: 384 kbit/s.

B lc s dng: Cosin nng.

S lng knh: 300 kHz.

5.2.3. H thng thng tin di ng th h 2.5GNh cp n trong phn 5.2.2, s tng trng v s lng ngi s dng v s pht trin mnh cc dch v a phng tin nh internet, in thoi hi ngh, i hi cc h thng thng tin di ng c tc truyn dn cao. Tuy nhin, h thng thng tin di ng th h th 2 khng cung cp tc bit ln p ng cc yu cu cao ny, do yu cu phi nng cp v pht trin mng GSM hin hu. Ngi ta xut nng cp h thng GSM Chu u ln thnh cc h thng cc dch v v tuyn gi chung GPRS (General Packet Radio Services) v h thng EDGE (Enhanced Data Rate for GSM Evolution). Cc h thng 2.5G ny nh l s st nhp h thng 2G ln h thng thng tin di ng th h th 3 (3G). u im ca cc h thng ny l tn dng c c s vt cht sn c ca mng GSM, ch yu cu thay i rt t c th khai thc c.

H thng GPRSMt s pht trin u tin ca h thng GSM t c tc bit thch hp vi cc ng dng yu cu tc bit trung bnh l vic da trn nn GSM sn c v thm mt lp trong th tc thng tin cho php vn chuyn cc d liu dng gi vi tc bit khong 115 kbit/s v gi nguyn kiu ( hay mode) chuyn mch cho cc tc bit thp khong chc kbit/s. H thng ny c tn l GPRS. Bng vic s dng li cc tn s, khung truyn dn (trame) v cc c s vt cht sn c ca mng GSM, ch c duy nht c thay i v phn mm trong vic vi t h thng, gii php GPRS s dng l mode thng tin khc nhau:

- Thng tin chuyn mch knh: thng tin ny da trn vic thit lp tm thi mt knh thng tin hai chiu gia cc thit b u cui. Knh thng tin ny l tn ti tht v duy tr trong sut qu trnh truyn tin. Do tn ti mt ng truyn vt l hp thnh bi cc ng truyn dn cho php thit lp mt mch thng tin gia cc ngi s dng. u im chnh ca thng tin chuyn mch knh l thng tin trc tip v thi gian thc. Cc tn hiu truyn dn khng b tr gia cc ngi s dng (khng tnh n tr truyn sng).

- Thng tin chuyn mch gi: kiu thng tin ny da trn vic nhn v gi thng gia cc thit b u cui di dng cc khi tin hay cn gi l cc gi tin. Tn ti hai mode chuyn mch gi:

+ Mode datagram: trong kiu ny, cc gi tin bao gm a ch ngi nhn c truyn i theo ch t tr bi thit b u cui.

+ Mode mch o: mode ny, mng nhn bit thng tin ang tip din v to ra cc mch o thit lp qu trnh trao i d liu. Mng qun l nhp hay tc tuyn tin; hay ni cch khc, tc ti a ca vic nhn cc gi tin ty thuc vo s thu nhn cc gi tin trc din ra nhanh hay chm.

Chun GPRS s dng khung truyn dn TDMA ca chun GSM. Ty theo s lng bit thng tin cn tuyn i, c th mt khe thi gian hoc nhiu khe thi gian c s dng chuyn cc gi tin. Do , kiu chuyn mch knh c s dng truyn thng tin c tc bit thp nh ting ni v kiu chuyn mch gi truyn thng tin tc bit cao hn nh truyn cc gi d liu. GPRS kt hp cc khe thi gian, to ra tc bit cao hn so vi GSM. GPRS cho php tng tc truyn d liu ln 8 ln nu s dng c 8 khe thi gian ca tn s sng mang. Tuy nhin, GPRS vn da vo k thut iu ch GMSK nguyn thy, do , vn hn ch tc truyn tin. GPRS l nn tng IP (Internet Protocol) cho mng GSM v UMTS (Universal Mobile Telecommunication System), do n c s dng cho cc ng dng WAP (Wireless Application Protocol) v Internet.

H thng EDGEMt gii php k thut khc t c tc bit tng thch vi cc ng dng truyn thng a phng tin tc cao l gii php EDGE (Enhanced Data Rate for GSM Evolution). Gii php ny s dng li cc c trng ph ca chun GSM cho php tc bit t ti 384 kbit/s. Chun EDGE cho php t c tc bit ny bng vic kt hp s dng phng thc iu ch pha 8-PSK (8Phase Shift Keying) v s dng hay kt hp nhiu khe thi gian trong qu trnh truyn dn nh trong mng GPRS thay v ch s dng khe thi gian nh trong mng GSM. Bng vic c th s dng li hu ht cc c s vt cht ca mng GSM, gii php ny cho php gim gi thnh u t. Phng thc iu ch 8-PSK; c ngha l trong kt hp 3 bits cho 1 k hiu s tng tc bit ln 3 ln so vi iu ch GMSK ca chun GSM vi cng mt di ph chim dng. Tc bit c s chuyn t 270 kbit/s ln ti 810 kbit/s hoc tc truyn s liu 384 kbit/s cho chun EDGE thay v 9,6 kbit/s cho chun GSM. Tuy nhin hiu sut cng sut ca phng thc iu ch 8-PSK trong mng EDGE ch bng 4/9 ca phng thc iu ch GMSK trong mng GSM. Do cng sut ca my pht EDGE phi ln gp i so vi GSM, iu ny s nh hng ti vic ch to thit b u cui v cc trm thu pht cng sut nh nh Micro BTS, pico BTS. khc phc kh khn v cng sut ca my u cui ngi ta a ra gii php trong my u cui ng ln s pht tn hiu s dng phng thc iu ch GMSK cn trm thu pht v tuyn gc BTS s pht ng xung tn hiu iu ch 8PSK vi l do phn ln cc ng dng tc cao u nm ng xung (nh truy cp internet, ng dng dch v a phng tin), gii php ny nhm hn ch tnh phc tp cho my u cui.

H thng EDGE tuy nhin vn da vo chuyn mch knh v chuyn mch gi v hn ch tc 384 kbit/s nn s kh khn cho vic ng dng cc dch v i hi vic chuyn mch linh ng hn v tc truyn d liu ln hn (khong 2 Mbit/s) trong tng lai. Khi buc phi s dng h thng thng tin di ng th h th 3 hoc th 4

5.2.4. H thng thng tin di ng th h th 3Cc dch v v tuyn di ng th h th 3 mi (3G) khng tng ng vi mt giao din thng tin duy nht v ton cu, m tng ng vi s kt hp cc h thng c nhiu giao din vi nhau. S kt hp ny c gi l IMT 2000 v n kt hp h thng UMTS (Universal Mobile Telephone System), h thng UWC136 v CDMA 2000. M, cc h thng ang trong qu rnh nhin cu v pht trin l h thng CDMA 2000 tng ng vi s tin trin ca h thng IS 95 v h thng UWC136 l mt tin trin ca IS136. Chu u, cc h thng ang c nghin cu v pht trin tng ng vi chun UMTS. Chun UMTS v CDMA 2000 s dng phng php truy cp theo m CDMA, trong khi chun UWC136 da trn phng php truy cp theo thi gian TDMA.

Mc ch ca cc chun ny l cho php cc dch v truyn thng tin a phng tin tc cao (in thoi, d liu v hnh nh) qua mng internet v m ra mt mng thng tin chung trn ton th gii. Cc chun 3G phi tng thch vi cc h thng 2G v 2G+. Do , k thut thng tin s dng bng tn kp hoc a bng s c ng dng.

H thng UMTS

UMTS l mt h thng c la chon cho cc h thng thng tin di ng th h th 3. UMTS c qun l bi lin on vin thng th gii ITU trong khun kh d n IMT-2000 ton cu. Nm 1998, d n UMTS m rng n cc i tc, cc t chc M, Nht v Hn Quc. D n ny c tn l GPP (Third Generation Group Project Partnership). Vin cc tiu chun vin thng Chu u ETSI (European Telecommunicatin Standards Institute) l c quan t chc chun ho cc giao din v tuyn ca h thng UMTS, cng vic thc hin bi nhm 3GPP. Mc ch ca UMTS l pht trin vng ph sng tt nht, tng s lng thu bao, ci tin s hi t gia in thoi c nh v di ng v xc tin vic hon thnh dch v 3G. UTRA (UMTS Terrestrial Radio Access) l giao din v tuyn ca UMTS. UTRA c 2 kiu hay phng thc a truy cp: truy cp theo m bng rng W- CDMA (Wide Band Code Division Multiple Access) dnh cho mode FDD v phng php phn b theo m trong min thi gian TD-CDMA (Time Division Code Division Multiple Access) cho mode TDD. Phng thc iu ch c s dng cho mi knh l QPSK. Ty theo nhu cu s dng ph v tc bit truyn, h s tri ph s thay i cho ph hp. K thut iu ch v tri ph c kt hp gi l HPSK. Cc thng s k thut chnh ca chun UMTS nh sau:

W-CDMA v TD-CDMADi tn: 1920 1980 MHz. 1850 1910 MHz. 2110 2170 MHz. 1930 1990 MHz.

Phng php a truy cp: WCDMA. TDD.Phng php ghp knh: FDD. FDD.Phng thc iu ch: QPSK. QPSK.Tc bit c s trc khi tri ph: 144 kbit/s. 2048 kbit/s. 384 kbit/s. rng ca knh: 5MHz. 20MHz. 10 MHz.

B lc s dng: Cosin nng Cosin nngTc bit d liu thay i ty theo vn tc di chuyn v h thng UMTS hot ng theo phng thc truyn dn khng ng b. Tc d liu thay i v h thng cho php gim cc nh hng ca fading trong knh v tuyn.

5.2.5. Cc mng LAN khng dyMt mng LAN (Local Area Network) l mt c s h tng thng tin kt ni cc thit b tin hc v cho php chia s ti nguyn chung trong mt c ly gii hn vi trm mt. Mt s mng LAN in hnh nh Ethernet, IEEE 802.3, IEEE 802.5 hoc Token-ring, IEEE 802.4 hoc Wireless LAN (WLAN). Mng WLAN c ng dng rt nhiu trong thi gian gn y. WLAN c ng dng nhiu khu vc khc nhau nh trong cc ta nh, trong cc bnh vin, trng hc, . Trong mng WLAN, hai phng thc truyn tin c s dng truyn thng tin: phng thc truyn im-im v phng thc tuyn ng hng (ominidirectional). Hai phng thc truyn thng ny c th hot ng theo kiu h tr nhau ty theo ng dng. Cc vn chnh lin quan n ng dng ca cc mng WLAN l s xut hin cc nhiu (interference). Trong WLAN, k thut tri ph c s dng nhiu. Hai k thut tri ph l: tri ph nhy tn FHSS (Frequency Hopping Spead Spectrum) v k thut tri ph dy trc tip DSSS (Dect Sequence Spead Spectrum). Tuy nhin k thut tri ph dy trc tip c dng nhiu hn trong mng WLAN. Thut ng WLAN bao gm nhiu chun tng ng t chun tc bit thp n chun c tc bit cao (IEEE 802.11, HYPERLAN 1 v HYPERLAN 2).

Chun IEEE 802.11Vin cc tiu chun vin thng Chu u ETSI dnh bng tn t 2.4 GHz n 2.484 GHz cho cc ng dng lin quan n chun ny. Tc d liu trong IEEE 802.11 thng t 1 Mbit/S n 2 Mbit/s. lp vt l, c 2 phng php tri ph l FHSS v DSSS. Bng tn 2.4 GHz n 2.48 GHz c dng chung cho 3 knh chnh. Cng sut pht ti a 1 W ( M), 10 mW ( Nht) v 1 mW ( Php). Cc phng thc iu ch c s dng ph thuc vo tc bit. Vi tc bit t 1 n 2 Mbit/s, phng thc iu ch BPSK hoc QPSK kt hp vi tri ph dy trc tip DSSS; vi tc bit 5.5 Mbit/s hoc 11 Mbit/s, ngi ta s dng phng thc iu ch CCK (Complementary Code Keying), l mt trng hp c bit ca iu ch M trng thi trc giao.

Cc chun HYPERLANChun HYPERLAN (High Performance Radio Local Area Network) l mt h cc chun cho thng tin v tuyn tc cao trong bng tn 5,15 GHz 5,3 GHz v 17,1 GHz 17,3 GHz. Cc chun HYPERLAN m t giao din khng gian v lp vt l cho cc thit b thng tin khng dy. Cc chun ny khng m t tt c cc lp nh trong chun GSM chng hn m n cung cp cc thng s k thut cho 2 lp thp nht trong m hnh OSI, nhng khng m t cc lp cao hn bi v cc chun ny c pht trin cho php ghp ni gia cc mng khc nhau v khng ph thuc vo cc ng dng. Ta c th s dng cc chun HYPERLAN truy cp vo cc mng khc nhau. HYPERLAN phi m bo s tng thch ca cc h thng thng tin khc nhau lp vt l v giao din khng gian. Tn ti 4 chun HYPERLAN: HYPERLAN 1, HYPERLAN 2, Hyperaccess v Hyper-Link.

Cc thng s c trng ca chun Hyperlan 1

- Bng tn s c cp pht nm gia 5.15 GHz v 5.3 GHz. Knh truyn dn phi tp trung vo 1 trong 5 sng mang t F0 n F4 c cc gi tr tham s nh sau:

F0 = 5176,4680 MHz.

F1 = 5199,9974 MHz

F2 = 5223,5268 MHz

F3 = 5242,0562 MHz

F4 = 5270,5856 MHz

Cc tn s F0, F1 v F2 c s dng mt cch ngm nh, cc tn s sng mang khc c th b cm mt s nc.

- Cc phng php iu ch c s dng l GMSK c h s 0,3 cho tc cao v iu ch FSK cho cc tc bit thp.

- Cng sut pht khng vt qu 1 W (30 dBm) v cc b khuych i phi hot ng ch A, B hoc ch C.

- Tc bit l 23,5294 Mbit/s 235 bit/s cho cc tc bit cao v 1,470587 Mbit/s 15 bit/s cho cc tc bit thp.

- ngten s dng l ngten monopole bc x ng hng dng c pha pht v ph thu.

- Gii iu ch cn thit mt b cn bng knh.

- Khong cch gia hai trm c th t ti 50 m trong cc ta nh.Cc c tnh ca chun HYPERLAN 2HYPERLAN 2 c pht trin cho mt c s h tng cung cp vic truy cp khng dy c ly ngn khong 150 m cho cc mng IP, Ethernet, UMTS v cho cc h thng truyn thng a phng tin trong tng lai nh h thng video thi gian thc vi tc bit c th t ti 54 Mbit/s. Chun HYPERLAN 2 ny c thit k cho vic ci thin kt ni tc cao cho cc h thng thng tin di ng v h thng khng dy th h tip theo trong bng tn 5.2 GHz. HYPERLAN 2 cho php truyn dn tc bit cao 54 Mbit/s lp vt l v 25 Mbit/s lp mng. Tc bit cao ny t c nh vic s dng phng php iu ch a sng mang trc giao OFDM. OFDM c bit rt hiu qu trong cc mi trng truyn dn a ng. Khong cch gia hai knh l 20 MHz, cho php mt s lng knh tng i trong mt bng tn tng l 100 MHz. Ngi ta s dng 52 sng mang ph mi knh. Trong s 52 sng mang ph ny, 48 dnh cho vic truyn d liu, 4 sng mang ph cn li c s dng cho vic h tr gii iu ch ng b (coherent demodulation).

Mt trong nhng c im ca lp vt l l kh nng s dng cc phng thc iu ch khc nhau trn cc sng mang ca OFDM v vic m ha cho php m bo cht lng truyn dn v tuyn tt nht. Cc phng php iu ch l: BPSK, QPSK, 16 QAM v mt cch ty chn, 64 QAM.

Cc d liu truyn qua HYPERLAN 2 chu s ghp knh theo thi gian v s kt ni nh hng theo ng xung. Mt thit b u cui thu bao di ng lin lc vi mt im tuy cp c nh AP (Access Point) bi giao din khng gian. Vic truy cp vo mng s c thc hin ti cc im truy cp. Ngoi ra, trong HYPERLAN 2 khng cn thit thit lp mt s quy hoch cc tn s nh trong cc mng t bo nh GSM. Cc im truy cp tng ng vi cc trm thu pht v tuyn gc (BTS) trong mng GSM c 1 hm tch hp cho php s dng cc tn s mt cch t ng trong mt vng ph sng. Hm ny gi l hm la chn tn s linh hot DFS (Dynamic Frequency Selection). Hm DFS hot ng theo phng thc sau: im truy cp nghe cc im truy cp k bn cng nh tt c cc ngun ti nguyn v tuyn trong mi trng ln cn v duyt li tt c cc knh s dng bi cc im truy cp khc. im truy cp la chon mt knh sn sng c cc nhiu vi mi trng nh nht. Ngoi ra, trong HYPERLAN 2 cn c hm chuyn giao (Handover) cung cp kh nng di chuyn cho cc thit b u cui. Cc thit b u cui c kt ni n cc im truy cp c t s tn hiu-tp m cao nht. Khi ngi s dng di chuyn, cc kt ni c thit lp c di sang cc im truy cp c tnh nng truyn dn tt nht. Thit b u cui di ng gi nguyn kt ni vi mng nu nh chng vn nm trong vung ph sng ny.

Bluetooth v Home RFNhiu h thng truyn dn v tuyn c ly ngn vn ang c nghin cu v pht trin kt ni cc thit b khc nhau trong mt c ly t vi mt n vi chc hoc vi trm mt. y ch gii thiu s lc h thng Bluetooth v Home RF. Hai h thng ny hot ng trong bng tn ISM xung quanh tn s 2.4 GHz.

Home RF c dng trong cc ta nh v dnh cho cc tuyn c c ly thng tin ti a khong 300m vi cng sut pht 100 mW. Cn Bluetooth dnh cho thng tin gia cc thit b thng dng bng hng ngoi. Khong cch truyn d tnh khong vi chc mt vi cng sut pht 1 mW. Hai h thng s dng mt k thut nhy tn gim nhiu bi cc l vi sng.

Cc thng s k thut chnh lp vt l ca Bluetooth v Home RF nh sau:BluetoothHome RF

Di tn2402 2480 MHz

(Di tn c th thay i ty tng nc)2404 2478 MHz

Phng php truy cp/ghp knhTDMA/TDDTDMA/TDD

Phng php iu chGFSK2-FSK hoc 4-FSK

Tc bit c s cho cc burst1 Mbit/s1 hoc 2 Mbit/s

Khong cch gia cc knh1 MHz1 MHz

M ha thoi64 kbit/s32 kbit/s

Tc bit d liu721 Kbit/s800 hoc 1600 Kbit/s

Cng sut pht1 hoc 100 mW100 hoc 1 mW

5.2.6. Mch vng v tuyn ni ht WLL (Wireless Local Loop)Mch vng v tuyn ni ht l cc mng v tuyn c nh cung cp vic truy cp v tuyn cho cc mng vin thng cng cng. u im ca mng WLL l da trn s tin tch, s linh hot v s pht trin mng mt cch nhanh chng. Cc h thng v tuyn bng tn rng c th cung cp cc tc bit a dng v cho nhiu ngi s dng ng thi. Vic s dng bng tn thp gia 1,9 GHz v 3,4 GHz cho php cung cp dch v tc bit thp (N ln 64 Kbit/s). cung cp dch v tc bit c 2 Mbit/s cn tng tn s trong bng ln 10,5 GHz hoc 26 GHz. truy cp vi tc bit c Gbit/s cn thit di tn rng hn t 28 GHz ti 40 GHz, thm ch 60 GHz.

Cng ngh c la chn cho mch vng v tuyn ni ht l h thng phn b a im ni ht LMDS (Local Multipoint Distribution System). LMDS l s m rng tng i gn y ca h thng phn b a im a knh MMDS (Microwave or Multichannel Multipoint Distribution System).

H thng MMDSMMDS l mt h thng pht v tuyn truyn hnh, do phng thc truyn dn l bn sng cng v ch cung cp ng truyn xung hng thu bao. H thng ny s dng mt bng tn s kh hp 200 MHz t 2,4 GHz n 2,6 GHz. Hn ch ny gim dung lng truyn dn s knh truyn hnh. i vi tn hiu truyn hnh bng thng 6 MHz, ch c 33 knh c th c pht.

Cc tn s c s dng trong mng MMDS cho php ph sng cc vng vi bn knh t 50 n 60 km. Ngoi ra, cc tn s ny t b nh hng bi cc hin tng suy gim gy ra bi cc phn t nc v do m bo s hot ng ca h thng MMDS trong iu kin thi tit xu. Cc phng thc iu ch s dng trong MMDS l QPSK, 16 QAM hoc 64 QAM. B khuych i cng sut m bo cng sut ra t 1 n 100 mW.

H thng LMDSLMDS l mt h thng thng tin v tuyn bng rng im a im c tn s hot ng di 20 GHz ph thc vo mi nc. H thng ny cho php thng tin song bin (2 bin) ting ni, d liu, internet v video. Cc ch vit tt trong LMDS bao hm ngha v cc ng dng ca h thng:

L (Local): h thng LMDS l mt h thng ni ht v tn s s dng, khong cch hay c ly truyn sng b hn ch c chc km.

M (Multipoint): LMDS l mt h thng thng tin trong cc tn hiu c pht t trm thu pht v tuyn ti nhiu ngi s dng, trong khi hng ngc li l phng thc truyn dn im im.

D (Distribution): H thng ny cho php truyn dn cc tn hiu c th ng thi l thoi, d liu, internet hoc hnh nh.

Mc d cc phng php iu ch 16 QAM v 64 QAM c d kin, nhng phng php iu ch QPSK c u tin hn c. Cc tc bit truyn thay i t 64 Mbit/s n 8 Mbit/s v c ly thng tin trung bnh t 5 km n 6 km.

5.3. Mt s vn c bn trong thit k cc h thng v tuynKhi phn tch v thit k h thng my thupht v tuyn (transceiver), mt h cc tham s sau cn c quan tm v tnh ton: cc tham s tyn tnh, cc tham s v tp m v cc tham s v cng sut hay cc tham s phi tuyn. T hp cc tham s ny cho ta bit s nh hng ca tn hiu v tp m i vi tnh nng ca h thng.

Hnh v 5.3.1 di y trnh by s khi ca mt h thng v tuyn.

S suy hao ca tnh hiu v tuyn trong knh v cc vn v knh v tuyn c trnh by chng 2. Chi tit chc nng v nguyn l hot ng ca cc khi trong my pht v my thu s c trnh by cc phn tip theo ca chng ny. Trong phn ny, ta gi thit my pht nh mt ngun pht tn hiu l tng. Hn ch ch yu khi tn hiu thu yu l mc tp m nhit thu bi ngten v to ra chnh trong my thu. Ngi ta nh ngha ba thng s c trng cho hin tng ny: h s tp m ca my thu, nhit tp m h thng v nhy my thu. Trong trng hp tn hiu thu v nhiu mnh hn ch l do my thu c cc phn t phi tuyn nh cc b khuych i, cc b trn tn, b chuyn i tng t s. B trn tn trong my thu s tao ra cc tn s mi c th hoc trong bng tn s dng v do s lm suy gim t s tn hiu-tp m v do gim nhy my thu.

5.3.1. Nhit tp m h thng v h s tp mTa nh ngha nhit i tp m ca h thng u vo ca my thu nh trong hnh v sau:

Tp m y c coi nh l tp m trng Gaussian c c trng bi qu trnh ngu nhin Gaussian c tr trung bnh bng khng v c mt ph cng sut bng N0/2 (W.Hz-1). Gi s tp cc tp m (tp m kh quyn, mt tri, thin h) thu bi ngten l tp m nhit, thm ch mt ph cng sut ca chng khng phi l mt hng s khng i. Tp m ny nh hng n tn hiu theo cch cng (AWGN: Additive White Gaussian Noise). Lin quan n ngten ta c:

vi k = 1,38 . 10-23J.K-1 l hng s Boltzmann Ta l nhit tp m ngten (K: Kelvin)

Trong trng hp ngten v my thu c phi hp tr khng trong mt bng thng hiu dng ca tp m, B. Cng sut ti my thu s l:

Tp m nn c nh ngha bi cng sut ny. i vi mt ngun tp m nhit chun 290K, cng sut tp m nn biu din theo n v dBm s l:

Trong mt h thng gm mt ngten v mt my thu c khuych i cng sut G, tp m ca my thu v bng thng hiu dng tp m B (Hnh 5.3.3), cng sut tp m nn u ra my thu s l:

: tp m ca chnh my thu.

Vi c gi l nhit tp m hiu dng.

c gi l nhit tp m ca h thng chun ha u vo my thu.

Mt tham s khc xc nh mc tp m gy ra trong 1 bn cc (mi tng trong my thu c th coi l mt bn cc) l h s tp m F. H s tp m F c xc nh l t s gia cng sut u ra v cng sut tp m u ra ca bn cc phn hi khng nhiu vi gi thit rng ngun tp m u vo c nhit tp m chun (thng ly 290 K). H s tp m F cng c th c xem nh l s suy gim t s tn hiutp m (S/N) gia u vo v u ra ca bn cc.

Hay Trong trng hp mt my thu gm n tng (mi tng coi l 1 bn cc) mc ni tip nh hnh 5.3.4, c th d dng ch ra rng h s tp m ca h thng c tnh theo cng thc Friis:

: h s khuych i ca tng th i ().

: nhit tp m hiu dng ca tng th i.

: h s tp m ca tng th i.

Do nhit tp m hiu dng c th vit di dng:

Ngoi ra, d dng ch ra rng h s tp m ca mt bn cc suy gim bng chnh h s suy gim L :

Khi thit k cc mc siu cao tn tch hp, kh c th thc hin v tnh ton vi cc tng phi hp tr khng . Khi ngi ta thng tnh ton da trn dng in v in p nh biu din theo hnh 5.3.5:

Trng hp ny, bn cc c ngun tp m ni ti v c ni vi mt in tr ca ngun pht tp m tng ng . H s tp m khi c tnh [Raz98]:Do , h s tp m ph thuc duy nht vo tr khng ca ngun hay ngi ta thng ni l chun ha theo tr khng ngun .

Trng hp h thng tng mc ni tip (Hnh 5.3.6), tng t nh cng thc Friis, ngi ta xc nh h s tp m ca h thng nh sau:

Tng qut ha, cho h thng gm M tng mc ni tip v gia cc tng phi hp tr khng , h s tp m c tnh theo:

y, tt c cc h s tp m ca cc tng c chun ha theo ngun pht v i din cho khuych i in p ca bn cc khng ti.

5.3.2. nhy thu nhy ca my thu l cng sut ti thiu u vo my thu cho php t mt mc t s sng mang-tp m (C/N) nht nh u vo b gii iu ch hoc t s tn hin-tp m (S/N hay SNR: Signal-to-Noise Ratio) u ra vi mt mc t s li bit BER (Bit Error Rate) khi phng thc iu ch c la chn. Hay ni cch khc nhy ca my thu c xc nh l mc tn hiu thu nh nht m h thng c th thu c vi mt t s tn hiu- nhiu chp nhn c.

tnh ton nhy thu, theo nh ngha h s tp m, ta c:

Trong : SNRin: t s tn hiu- tp m u vo.

SNRout: t s tn hiu- tp m u ra.

Psig.: cng sut tn hiu vo trn 1 n v bng thng (1 Hz).

PRS: cng sut tp m gy ra bi in tr ngun trn 1 Hz. nhit phng, PRS c tnh nh sau:

Do :

Khi xt trn ton b bng thng B, ta c:

Phng trnh PT (5.3.17) d on nhy thu l mc tn hiu ti thiu a vo my thu m vn m bo u ra mt t s tn hiu-tp m nht nh.

Biu din bng n v dBm, ta c:

y, l cng sut tn hiu u vo ti thiu t c t s v l bng thng (Hz).

Vy:

Ba thnh phn u tin v phi ca phng trnh PT (5.3.19) l tng ca tp m tch hp ca h thng v thng gi l tp m nn. Ngoi ra ta cn thy phng trnh PT (5.3.19) khng ph thuc vo khuych i ca h thng v l mt hm ca bng thng hiu dng ca tp m my thu. B c tnh ton t c trng tuyn ca b lc trung tn (b lc c bng thng hp nht trc khi gii iu ch).

Khi nhit ca ngun tp m khng phi l T0 (v d nh nhit tp m ngten khc T0), nhy thu c trn nhit tp m ca h thng TS.5.3.3. Cc hin tng phi tuyn v cc tham s c trng tng ng5.3.3.1. Cc hin tng phi tuynMt h thng l tuyn tnh nu u ra ca n c th c biu din l mt s kt hp tuyn tnh ca cc p ng xung ca cc u vo.

V d: l 2 u vo

l 2 u ra tng ng.

Khi , nu u vo l: th u ra tng ng s l . Trong a, b l cc hng s.

Bt k h thng no khng tha mn iu kin ny l h thng phi tuyn.

Nh s trnh by trong cc phn sau, my pht v my thu v tuyn c cha cc phn t tuyn tnh v phi tuyn. Cc phn t phi tuyn s gy ra cc hin tng lm suy gim cc tnh nng ca h thng hoc s thay i cc tham s no ca h thng ( khuych i ca my thu) hoc to ra cc thnh phn tn hiu k sinh nh cc hi . Hin tng ny xy ra trong cc phn t tch cc nh transistor, diode; trong cc thit b tch cc nh b chuyn mch, b trn tn, b khuych i; hoc trong cc vt liu t ferrit Ngoi ra, hin tng phi tuyn cng c th gp phi trong cc thit b tuyn tnh do vic gii hn bng tn lm cho cc tn hiu b mo. y ta ch cp n mt s thng s chnh v cc php tnh thc hin p dng cho my pht, my thu v trong bt k h thng phi tuyn no.

Ngi ta thng s dng hm truyn t bng in p ca cc h thng phi tuyn bc 3 v b qua cc bc cao hn cho vic tnh ton c n gin:

Trong : Vout(t) l in p u ra ca h thng phi tuyn.

Vin(t) l in p u vo.

l i din cho b khuych i tuyn tnh in p ca h thng.

5.3.3.1.1. Hi (Harmonic)Nu mt tn hiu hnh sin a vo mt phn t hoc mt h thng phi tuyn, u ra ca h thng thng xut hin cc thnh phn tn s l s nguyn ln ca tn s u vo. Gi s tn hiu u vo:

Khi tn hiu u ra:

Trong biu thc PT (5.3.22), thnh phn c cng tn s vi tn hiu vo c gi l thnh phn c bn (fundamental) v cc thnh phn bc cao hn gi l cc hi (harmonics).

Cng t biu thc PT (5.3.22) ta thy bin ca hi bc n t l vi An v cc i lng khc t l vi Am (m > n). Vi gi tr A nh, ta c th coi hi bc n t l vi An.

5.3.3.1.2. im nn 1 dB Mt trong nhng thng s c trng cn thit trong mt mch hay trong mt h thng phi tuyn, l mo bin gy ra bi c tnh truyn t khng tuyn tnh. Trong hu ht cc mch hoc cc h thng, tn hiu u ra c th b bo ha ty theo mc bin tn hiu u vo.

T biu thc PT (5.3.22) ta thy rng thnh phn chnh ca tn hiu u ra c bin . V ta thy: Thng v c khuych i gim khi cng sut u vo tng. Ngi ta gi hin tng ny l nn khuych i (gain compression) hoc s bo ha ca cng sut u ra, do ngi ta nh ngha cng sut nn 1 dB u ra.

khuych i tn hiu tn s c bn c tnh bi:

khuych i tuyn tnh (n v dB) c nh ngha bi:

khuych i nn 1 dB c xc nh bi:

Vy im nn 1 dB c xc nh l mc tn hiu u vo gy ra khuych i truyn tnh hay khuych i tn hiu nh gim 1 dB (Hnh 5.3.7).

5.3.3.2.im chn bc 3 - IP3 (Third Intercept Point)By gi cng vi phn t hoc h thng phi tuyn trn, nhng tn hiu y vo l t hp ca hai sng mang hnh sin: Khi u ra ca h thng, ta c:

Bng cch sp xp li PT (5.3.28), ta thy bin ca tn hiu vi tn s u ra l: Trong trng hp ny ta c th xem nh mt tn hiu nhiu tn s bin A2 ln c th lm suy gim tn hiu hu ch bng vic lm gim khuych i.

Cng t biu thc PT(5.3.28) ta cn thy s xut hin cc thnh phn khng phi l cc hi (harmonics). Gi s ta khng cp n cc thnh phn mt chiu v cc hi, ch quan tm n thnh phn c bn (hay thnh phn chnh) v cc thnh phn cn li (cc thnh phn ny gi l thnh phn bin iu (intermodulation), hay vit tt l IM). Ta c:

Cc thnh phn c bn tn s v :

EMBED Equation.3

Cc thnh phn IM:

tn s: :

tn s: :

tn s: :

Ta thy cc thnh phn tn s v c th gn bng hoc trng vi thnh phn tn s c bn v gy mo tn hiu khi s khc nhau v tn s gia v nh. Minh ha nh trong hnh v 5.3.8.

T hnh v ta quan st thy rng, vi hai nhiu tn s v cch tn s ca tn hiu thu ln lt l v , sau khi qua phn t hoc h thng phi tuyn xut hin thnh phn tn s (IM3) trong bng tn ca tn hiu thu.

IP3 i vi mt phn t phi tuynHin tng bin iu IM l mt trong nhng nguyn nhn chnh lm hn ch cc tnh nng ca mt my thu v tuyn. nh hng n, ngi ta nh ngha mt i lng gi l im chn phi tuyn bc 3 (IP3).

Khi u vo phn t phi tuyn l hai nhiu c cng bin (A1= A2=A). T cc biu thc PT (5.3.30) v PT (5.3.31) ta nhn thy rng, khi bin A ca tn hiu vo tng, bin ca tn hiu tn s c bn u ra cng tng theo t l thun vi A, trong khi bin ca cc IM tng t l vi A3.

im IP3 u vo h thng IPP3(IIP3: Input IP3) c xc nh l mc tn hiu u vo to ra u ra h thng cc mc tn hiu tng ng i vi thnh phn tn s c bn v thnh phn bc 3. By gi ta tm mi lin h gia IP3 v cc h s trong hm tuyn t ca phn t hay h thng phi tuyn.

Vi gi thit A1= A2=A, vit li biu thc PT (5.3.28) ta c:

Gi thit rng:

Khi bin tn hiu vo u ra cc thnh phn tn hiu tn s v tn s , c cng bin b l:

y, l IP3 u vo. Do :

im IP3 l im tng tng v hin tng nn hoc bo ha lun t xy ra trc khi ngi ta c th t ti. iu ny khng cho php tha mn gi thitPT (5.3.33). Phng php o hu hiu nht l o cc c tnh ca hnh trn (hnh 5.3.9) vi tn hiu c bin nh sau thc hin vic ni suy tuyn tnh.

Nu nh ta bit IP3 u vo hoc u ra (s khc nhau chnh l khuych i), ta c th tnh c bin ca cc thnh phn IM3.

Gi l bin ca hai tn hiu u vo

l bin ca cc thnh phn tn s c bn u ra.

l bin cc tnh phn IM3 u ra.

Khi :

Kt hp phng trnh PT (5.3.34) v PT (5.3.36) ta c:

V vy:

Nu biu din theo cng sut, ta c:

Hoc:

Vi .

Tm li, mi lin quan gia IP3 v bin cc thnh phn IM3 nh sau:

Mi lin h ny c th c biu din theo hnh sau:

Thng thng, IP3 c xc nh u vo ca my thu cho vic so snh vi bin ca tn hiu thu c d dng, trong khi i vi my pht IP3 c xc nh u ra m bo vic so snh gia thnh phn mo v bin tn hiu pht.

IP3 vi nhiu phn t phi tuyn mc ni tipTrong mt h thng c th c hai hay nhiu phn t phi tuyn mc ni tip. Hnh 5.3.11 minh ha mt h thng gm hai phn t phi tuyn mc ni tip.Sau y ra s tm mi lin h gia IP3 tng v IP3 ca tng tng hay tng phn t.

Gi thit tn hiu c a vo h thng trn.

u ra ca tng 1 ta c:

u ra ca tng th 2 ta c:

Khi ch xt n cc thnh phn bc 1 v bc 3 ta c:T biu thc trn ta tnh c IP3 u vo:

Du ca mu s ca biu thc PT (5.3.45) c th dng hoc m, do ta c th la chn cc gi tr v du ca cc thnh phn mu s s cho mt gi tr IP3 ln. Tuy nhin thc t khng d dng la chn cc gi tr trn. Ta xt trng hp xu nht l ba thnh phn di mu s u ly gi tr tuyt i, khi bnh phng v nghch o PT(5.3.45) ta c:

Trong v tng ng l cc IP3 u vo ca tng th nht v tng th 2.Thnh phn l kt qu ca vic trn gia thnh phn tn hiu c bin cc tn s vi cc thnh phn tn hiu c bin cc tn s v .

Cng t kt qu trn ta thy, khi tng, gi tr gim bi tng th nht c khuych i ln dn n tn hiu u vo tng th hai cng ln v do thnh phn IM3 ln hn.

Trong mt my thu, do vic s dng cc b lc, cc thnh phn tn hiu tn s v b suy gim, do ta c th loi b thnh phn th 2 trong biu thc trn, v ta c:Tng qut ho cng thc trn i vi mt h thng c trn 2 phn t phi tuyn mc ni tip, ta c:

l IP3 u vo cho tng th 3.

tnh IP3 theo dBm i vi h thng gm 2 phn t phi tuyn mc ni tip, ngi ta c th s dng cng thc Norton [Bau02]:.

i vi h thng gm hn 2 tng mc ni tip, ta ch vic tnh cho 2 tng u ri kt qu li tnh cho tng tip theo v c lin tc cho n ht.

5.3.3.3. Di ng SFDR (Spurious Free Dynamic Range)

Di ng c xc nh l t s gia mc tn hiu u vo ti a m h thng chp nhn c v mc tn hiu nh nht cho php t c t s tn hiu-tp m mong mun u vo ca b gii iu ch. Trong thng tin v tuyn, mc tn hiu ti a c tnh t cc c tnh bin iu v mc tn hiu nh nht c xc nh t nhy thu.

y mc tn hiu ln nht c xc nh nh l mc tn hiu u vo trong mt qu trnh th nghim 2 sng mang, v trong qu trnh ny mc tn hiu tn s khng vt qu tp m nn nh hnh v (Hnh 5.3.12).

T phng trnh PT (5.3.39), ta c th vit li mi lin h gia IP3 v IM3 nh sau:

y l cng sut u ra ca cc thnh phn IM3.

Do , ta c th biu din cc i lng u vo nh sau:

Trong : G(dB) l khuych i ca h thng.

l cng sut u vo chun ca cc thnh phn IM3.

Do :

Mc u vo ti a cho bin cc thnh phn IM3 quy v u vo, , bng vi mc tp m nn quy v u vo l:

Mc tn hiu u vo nh nht c coi nh l nhy thu l

Di ng SFDR l s khc nhau gia v , do :Ta thy rng di ng SFDR lin quan n nhiu tham s v thit lp mt lin h n gin gia h s tp m, IP3 v bng thng ca tp m cng nh t s tn hiu- tp m ti thiu yu cu u vo ca b gii iu ch.

5.4. Kin trc cc h thng v tuyn5.4.1. H thng pht v tuyn5.4.1.1. Gii thiu chungMy pht v tuyn thc hin vic iu ch, nng tn v khuych i tn hiu trc khi a ra ngten pht i vi iu kin khng c gy mo tn hiu. Trong mt s trng hp, iu ch v nng tn c th kt hp lm mt. Trong h thng pht, cht lng ca tn hiu pht c kim chng bi nhiu yu t sau:

- Cht lng iu ch: Cht lng iu ch c c lng theo pha hoc/v bin ty theo cc chun. Trong h thng GSM, ch duy nht sai s v pha c c lng v khng ch, trong khi trong h thng EDGE, vic c lng c thc hin cho c bin v pha tng qua vic o EVM (Error Vector Measurement).

- Ph ca tn hiu pht: Ph ca tn hiu pht c xc nh bi rng ph nh trong h thng GSM, HYPERLAN 2, hoc c kim sot bi cc gi tr v t s cng sut cn ACPR(Adjacent Channel Power Ration) hoc t s cng sut r r knh lnh cn ACPR (Adjacent Channel Leakage Power Ration) nh trong h thng UMTS.

- Cht lng ca tn hiu pht cn lin quan n cc tn hiu pht k sinh.

- Ngoi ra, i vi vc h thng s dng phng php truy cp theo thi gian, cht lng pht cn lin quan n cc tham s trung gian lin quan n chuyn mch.

Ngoi cht lng ca tn hiu pht, hiu sut ca my pht cng l mt vn quan trng trong vic la chn kin trc my pht. i vi cc h thng s dng cc phng php iu ch c ng bao tn hiu khng i, l tng l s dng cc b khuych i c hiu sut cng cao cng tt, cn trong trng hp h thng s dng phng php iu ch c ng bao thay i, nn s dng b khuych i rt tuyn tnh.

Ngi ta c th chia hai kiu kin trc my pht, l:

My pht trc tip hay cn gi l my pht khng qua trung tn.

My pht 2 tng hay my pht c trung tn.

5.4.1.2. My pht trc tip khng qua trung tnHnh 5.4.1 gii thiu s khi chc nng ca mt my pht trc tip.

Pha pht, tn hiu c th l ting ni, d liu trc ht c m ha v sp xp gim ti thiu giao thoa gia cc k hiu v hn ch b rng bng thng bi mt khi x l tn hiu s DSP (Digital Signal Processing). Sau khi qua b chuyn i s tng t DAC (Digital-to-Analog Converter) v b lc thng thp LPF (Low Pass Filter), cc tn hiu bng tn c bn I v Q a n u vo ca 2 b trn tn cho php thc hin iu ch I/Q. Hai nhnh c nhn vi hai tn hiu trc giao n t b dao ng ni ( y l mc vng kha pha PLL: Phase Locked Loop). Sau b iu ch tn hiu c lc bi b lc thng di BPF (Band Pass Filter) v a n b khuych i cng sut PA (Power Amplifier) sau c lc li lo b cc hi bc cao gy ra do s phi tuyn ca b khuych i cng sut trc khi a ti h thng phi hp tr khng Match(Matching) a ra ngten pht i.Trong cu trc ny, tn s ca tn hiu cao tn pht bng vi tn s ca b dao ng ni trong b iu ch, do my pht ny c tn l my pht trc tip.

Kin trc my pht ny hin nhin c t phn t so vi kin trc my pht c trung tn (s khi chc nng s c trnh by sau). Gii php ny do l mt thun li cho cc ng dng cng cng bi v n cho php gim c mt b trn, mt t hp tn s v do s tiu hao nng lg t hn. Tuy nhin, kin trc ny cng c hai nhc im l: s nh hng gia b khuych i cng sut v b dao ng iu khin bng in p VCO (Voltage Control Oscillator) trong b t hp tn s; v cc vn tp m pht k sinh.

Thng trong hu ht cc kin trc my pht b khuych i cng sut gy nhiu ti tn s u ra ca b t hp tn s PLL do s h cm gia b khuych i cng sut v b b to dao ng bng in p VCO trong b t hp tn s PLL s gy ra nhiu ti tn s u ra ca b t hp tn s.Tn hiu sau khi c khuych i mt phn b phn hi v a ti VCO bi v u ra ca b PA l tn hiu iu ch c cng sut cao v c cng tn s vi tn s ca PLL. B dao ng ni b nh hng bi pha ca tn hiu pht. Trong trng hp h thng s dng cc phng php iu ch pha, b dao ng ni c xu hng sao chp li pha ca tn hiu pht, do s gy ra mt s sai pha ca b t hp tn s. Sai pha ny s lin quan n tp m pha (phase noise) i vi tn hiu iu ch sau khi nng tn. Hnh 5.4.3 minh ho s nh hng ca tn hiu pht do sai pha trong b to dao ng ni gy ra. Kt qu s lm mo lc chm sao (constellation diagram) ca tn hiu pht. Vn gy nhiu gia b PA ti b VCO cn nghim trng hn trong tng hp b PA c iu khin chuyn mch nh trong cc h thng truy cp ghp knh min thi gian hoc tit kim nng lng. Tuy nhin vn ny c th gim hoc trnh c nu nh tn s u ra ca b PA phi nh hn hoc ln hn tn s ca b dao ng ni. iu ny c thc hin bng cch lm lch tn s ca b dao ng ni bng cch cng thm hoc tr i tn s u ra ca mt b to dao ng ni khc.5.4.1.3. Kin trc my pht c trung tn (my pht 2 tng)Mt gii php khc gii quyt vn nhiu gia b khuych i cng sut v b to dao ng ni l trn tn hiu bng tn c bn theo hai hoc nhiu tng cho ph ca tn hiu u ra b PA khc xa vi cc tn s ca cc b dao ng ni. Hnh 5.4.4 gii thiu s khi chc nng ca my pht 2 tng.

B iu ch I-Q chuyn tn hiu bng tn c bn (BF: Base Frequency) ln tn s trung gian hay cn gi l trung tn (IF: Intermedia Frequency) f1, sau qua b lc thng di th nht BPF1 v c a n khi nng tn th 2, f2. Tn hiu iu ch sau khi nng tn ny v sau khi qua b lc thng di th 2 BPF2 c tn s l f1 + f2. B lc thng di th nht BPF1 loi b cc hi ca tn hiu tn s trung tn, trong khi b lc thng di th 2 loi b tn hiu tn s f1 - f2.Tng u tin thc hin vic iu ch v nng tn ln tn s trung tn IF. Tn s trung tn thp hn tn s cao tn pht, do my pht hai tng c nhng u im so vi my pht trc tip nh sau:- S mt cn bng v bin v pha gia hai tn hiu I v Q nh hn nhiu so vi my pht trc tip, do giao thoa gia hai tn hiu I v Q nh.

- B lc knh c th c s dng trung tn thay v cao tn hn ch tp m v cc tn hiu k sinh pht trong cc knh ln cn.

Kh khn gp phi trong kiu my pht ny l vic thit k b lc thng di th hai. B lc ny phi loi b cc bng tn khng mong mun vi mt h s lc cao. Tht vy trong cu trc ny, tn s nh pht sinh sau b trn tn th hai nh minh ho trong hnh 5.4.5 bt buc phi c lc khng gy nhiu cc h thng khc. Yu cu b lc ny phi c h s phm cht rt cao nu nh tn s nh ny qu gn vi tn s sng mang trong trng hp tn s trung tn nh. Vic la chn tn s trung tn rt quan trng cho vic thit k b lc tn s nh, c bit trong cc h thng s dng phng php a truy cp theo tn s.

5.4.2. Kin trc my thu5.4.2.1. Gii thiu chung

Vai tr ca my thu l nhn t ngten mt tn hiu iu ch cao tn sau h tn v lc trc khi a vo b gii iu ch tn hiu. Hnh 5.4.6 gii thiu s khi chc nng ca mt my thu s. Tn hiu iu ch cao tn thu bi ngten c a qua b lc thng di BPF, b khuych i tp m thp LNA (Low Noise Amplifier), sau li c lc v c h tn ln th nht xung trung tn thng qua b trn tn v b to dao ng ni th nht PLL1. Tn hiu trung tn c tch ra hai nhnh v a vo b gii iu ch I/Q. Tn hiu bng tn c bn sau b gii iu ch I/Q c khuych i v chuyn i t tng t sang s nh b chuyn i tng t-s ADC (Analog-to-Digital Converter). Sau vic lc, khuych ai v khi phc li tn hiu pht ban u tn s c bn c thc hin thng qua b x l tn hiu s DSP.

Tu theo tng h thng v tu theo yu cu v cc tnh nng, iu ch c th l iu ch s, cn thit to ra nhnh I v nhnh Q, hoc iu ch tng t. in hnh, cc h thng GSM v DECT s dng iu ch GMSK nhng trong GSM iu ch l s trong khi trong mng DECT l tng t. Cc tnh nng ca my thu s c nh gi bng t s li bt BER (Bit Error Rate). My thu khng ch thu tn hiu hu ch m cn thu c nhiu gy ra bi chnh h thng hoc bi cc h thng ln cn nh minh ho trong hnh 5.4.7 di y.

Ta thy cng tn ti nhiu tn hiu:

- Cc tn hiu c cng sut mnh. Trong h thng thng tin v tuyn chng thng l cc tn hiu hnh sin v thng xut hin hoc trong hoc ngoi bng tn thu.

- Tn hiu ca cc knh ln cn, y c th l cc tn hiu ca h thng ang xt nhng nhng tng ng vi cc knh s dng khc.

- Tn hiu ng knh, l cc tn hiu iu ch n t h thng ang xt nhng ti v chng ln ln tn hiu hu ch.

My thu do phi lc tt cc tn hiu ny cho b gii iu ch c th duy tr tnh nng yu cu. Bt k my thu no, b lc u tin hay cn gi l b lc chon la trc c vai tr hn ch bng tn thu u vo my thu nm trong bng tn thu ca h thng. V d trong h thng GSM l t 925 MHz n 960 MHz. Cht lng ca b lc ny s quyt nh mc lc cc nhiu ngoi bng. Cc b lc khc s c tnh ton v thit k theo chc nng lc cc tn hiu hu ch v theo mc cc nhiu trong bng tn thu.

Khi my thu hot ng, bn thn n cng c th gy ra cc nhiu, cc nhiu ny s c a ti ngten nh ch ra trong hnh v5.4.8.

Trong tt c cc chun v tuyn, cc tn hiu pht k sinh c kim sot n khng gy nhiu cc h thng khc. Ngun chnh gy ra cc nhiu k sinh ny n t b dao ng ni. Cc nhiu k sinh khc l cc tn hiu c tn s l bi ln ca xung ng h s dng. Cc nhiu s lm gim nhy ca my thu. Do my thu phi lc c knh mong mun v loi b cc nhiu ln cn. Tuy nhin nhiu khi thc hin khng n gin do yu cu cc b lc c h s phm cht rt cao trong khi li khng mun suy hao ln. Thng ta phi dung ho gia hai tiu ch l vic loi b cc nhiu ngoi bng bng cch tng h s phm cht ca b lc v suy hao trong bng. Ngoi ra cn phn bit gia bng tn v knh. Bng tn bao gm ton b di tn m mt chun hay h thng no c cp php. V d my thu GSM c bng tn 935 MHz - 960 MHz. Trong khi knh cp n bng thng ca tn hiu ca duy nht mt ngi s dng trong h thng. V d trong GSM, knh c b rng 200 kHz. Do cn ch phn bit la chn bng tn v la chn knh. La chn bng tn l thc hin vic loi b cc nhiu ngoi bng v la chn knh l loi b cc nhiu ngoi knh (thng vn trong bng). Thng b loc thng di u tin dng lc bng tn cn la chn knh s do cc khi tip theo trong my thu thc hin.

Nh trnh by trong hnh v (hnh5.4.9), hm truyn t ca b lc thng di u tin c bng thng hu hn, c th xut hin cc nhiu ti cc tn s m nhiu ny ch b suy gim khng ng k. Sau b lc thng di u tin vn c th tn ti cc nhiu trong bng, cc nhiu ny s tng do s mo phi tuyn ca cc tng tip theo nh b khuch i tp m thp, b trn tn nh trnh by phn trc.

Mt im quan trng khc khi thit k my thu pht v tuyn l di ng ca tn hiu. Cng vi fading a ng v suy gim ng truyn, di ng yu cu ca tn hiu thu thng ln hn 100 dB.

Cc kiu kin trc my thu vn ang c nghin cu v thit k nhm tng tnh nng cng nh cc thng s k thut, cc ch tiu kinh t khc. Tnh n thi im ny, theo hiu bit ca tc gi, c th phn loi cc kin trc my thu nh sau:

My thu to phch hay my thu heterodyne (Heterodyne receiver). My thu loi b tn s nh (Image-reject receiver).

My thu gii iu ch tn hiu trc tip hay my thu homodyne (Homodyne receiver).

My thu trung tn s (Digital IF receiver).

My thu Subsampling (Subsampling receiver)

Sau y ta s cp n cc loi my thu ny.

5.4.2.2.My thu Heterodyne

Tn hiu thu t ngten thu qua b lc bng thng v khuych i tp m thp LNA c chuyn xung tn s trung tn trung tn lc sau tip tc c h xung tn s c bn v tch thnh hai tn hiu trc giao I v Q. Cc tn hiu I v Q c a qua b lc thng thp loi b thnh phn tn s cao, sau c ly mu chuyn i t tn hiu tng t sang tn hiu s nh hai b chuyn i tng t-s ADC. Cc tn hiu l cc mu ri rc c a ti khi x l tn hiu s thc hin cc chc nng x l mong mun nh khi phc d liu, lc .Kin trc my thu ny c s dng nhiu v n c nhiu u im v mt k thut. Tuy nhin kin trc my thu ny gp phi vn v vic loi b tn s nh. Tht vy tn s nh c mt u vo ca b trn tn th nht c trn vi tn s ca b dao ng ni th nht cng cho ra mt tn hiu c cng vi tn s trung tn. Do cn phi loi b tn s nh ny trc khi a qua b trn tn. Nh trong hnh v, mt b lc thng di la chn trc v mt b lc tn s nh thng c s dng trc v sau b khuych i tp m thp. Thng thng cc b lc ny l cc b lc sng m b mt c kch thc ln v gi thnh cao v kh tch hp, do s tng kch thc cng nh gi thnh ca h thng. Ngoi ra, cc b lc ny thng khng c cng tr khng vi b khuych i tp m thp, do cn thm cc phn t th ng thc hin vic phi hp tr khng. Do vy, ngi ta cn tm cc gii php loi b tn s nh m khng dung cc b lc ny. 5.4.2.3. My thu loi b tn s nh

Nh trnh by phn trc, trong my thu heterodyne, vic la chn v s dng cc b lc tn s nh cng phi dung ho cc thng s. iu ny khch l cc nh thit k tm ra nhng k thut khc loi b tn s nh. Sau y ta s kho st hai kin trc my thu kiu ny. Kin trc my thu Hartley

Nguyn l ca my thu Hartley da trn vic gii iu ch tn hiu I v Q. Nh trnh by trong hnh v trn, tn hiu cao tn RF u vo c trn vi hai tn hiu cu phng ca b dao ng ni LO. Mi nhnh sau c lc bi b lc thng thp, sau mt trong hai nhnh ( y l nhnh Q) c di pha 90 trc khi chng c a qua b cng.

Gi thit tn hiu thu c dng:

u ra ca b trn tn v sau lc loi b thnh phn tn s ta c:

Nu nh u vo b trn tn, ta c mt tn hiu tn s nh c dng:

Vi , u ra ca b trn ta c:

nhnh Q thc hin vic di pha tn hiu 90, do tn hiu u ra b di pha (im A) s l:

Tng t nhnh I:

Thc hin vic cng hai tn hiu QA v IB, tn hiu u ra im C c dng:

Ta thy tn s nh b loi b bi cu trc ny. Tuy nhin nhc im ca cu trc Hartley l s nh hng ca vic khng cn bng gia hai nhnh I v Q. Sai s v bin A v v pha gia hai nhnh I v Q lm cho vic loi b tn s nh nh trnh by trn l khng hon thin v tn hiu tn s nh cn tn ti s lm nh hng n tn hiu hu ch trung tn.

V d i vi nhnh I, tn hiu t b to dao ng ni nh sau:

Do tn hiu trn nhnh I u ra ca b lc thng thp tr thnh:

Tng t nh trn, tn hiu trung tn sau khi cng hai nhnh l:

T phng trnh ny, ngi ta nh ngha s loi b tn hiu tn s nh. u vo, ta c t s tn hiu v tn hiu tn s nh xc nh theo tham s cng sut nh sau:

u ra, t phng trnh trn ta c th tnh c t s cng sut:

T ngi ta nh ngha t s loi b tn hiu tn s nh IRR (Image Reject Ratio) nh sau:

t , c trng cho s sai lch bin tng i, ta c:

T phng trnh trn ta thy, vi mt b trn c li pha 2 v li bin 0.5 dB gia hai nhnh I v Q, t s IRR s l -19.4 dB.

Kin trc my thu Weaver

Kin trc Weaver l mt kin trc khc cho php thc hin vic dch chuyn tn s l tn hiu hu ch khng b suy gim bi tn hiu tn s nh. Vic khi phc tn hiu c thc hin bng tn c bn v cho php loi b tn s nh bi v s di pha 90 c thc hin khng phi bng b di pha m bng s dch chuyn tn ln th hai. S kin trc my thu Weaver c trnh by trong hnh 5.4.12.Kin trc ny cng gp phi cc nhc im nh trong kin trc Hartley v phng din loai b tn s nh v ch thch hp vi cc h thng khng yu cu ti to li tn hiu cu phng I v Q.

5.4.2.4. My thu gii iu ch tn hiu trc tip hay my thu homodyne

My thu homodyne i khi cn c gi l my thu trung tn bng khng. Trong kin trc ny, tn hiu cao tn c chuyn thng xung tn s c bn BF m khng qua tn s trung gian hay trung tn. Hnh 5.4.13 gii thiu s khi chc nng ca my thu gii iu ch tn hiu trc tip.

Tn hiu iu ch cao tn c a qua b lc thng di v b khuych i tp m thp sau a n b gii iu ch cu phng cho php khi phc tn hiu I v Q. Trong b gii iu ch cu phng ny, tn s ca b dao ng ni c iu chnh bng vi tn s ca tn hiu thu , do .

My thu homodyne c nhng u im sau:

- Khng cn b lc tn s nh c gi thnh rt t, kch thc ln v kh tch hp, do my thu ny c kch thc gn nh, t thnh phn cu thnh (mt tng dao ng ni so vi hai hay nhiu tng trong cu trc heterodyne trnh by phn trc). Cng do loi b c b lc tn s nh nn my thu ny c kh nng tch hp cao v tiu th nng lng t hn.

- My thu homodyne n gin trong vic thit k. Hin ti ngi ta c th thit k cc b di pha 90, b trn tn, b chia cng sut bng rng, do rt d dng thit k my thu bng rng , nhiu bng vi kin trc ny.

Mc d c cc u im k trn, my thu homodyne cng tn ti mt s nhc im sau: Vn thnh phn mt chiu u ra b gii iu ch cu phng (ngi ta cn gi l vn DC-offset)

Vn mo bc chn (Even-Order Distorsion)

Vn mt cn bng gia hai nhnh I v Q (I/Q mismatch).

Sau y ta s trnh by c th tng vn trn i vi kin trc my thu ny bng vic xem xt nh hng ca chng i vi cht lng ca my thu thng qua t s li bit BER. Vn DC-Offset

Nhc im chnh ca my thu homodyne l nhy thu gim do vic xut hin in p mt chiu u ra ca b gii iu ch cu phng. Thnh phn in p mt chiu s nh hng ti tn hiu hu ch. in p ny s c khuych i bi cc tng tip theo sau b gii iu ch cu phng. Tn hiu ny sau khi c khuych i s gy ra s bo ho cc tng khuych ai tip theo v b chuyn i tng t -s ADC. Tn hiu I v Q sau b gii iu ch s rt d b nh hng bi thnh phn in p mt chiu ny.

C nhiu nguyn nhn gy ra thnh phn in p mt chiu ny nh c minh ho trong hnh di y. Hnh 5.4.14 ch minh ho cho tn hiu I, nhng cng tng t cho tn hiu Q.

Nguyn nhn u tin la do s cch ly khng tt gia b dao ng ni LO (Local Oscillator) v b trn tn cng nh b khuych i tp m thp LNA. Tn hiu t b dao ng ni mt phn b r sang b trn tn v LNA. Tn hiu ny c pht i bi ngten v b phn x tr li bi cc chng ngi vt gn ngten (v d u v c th ngi khi nghe in di ng), tn hiu phn x ny li c thu bi ngten v t trn vi chnh tn hiu LO do lm xut hin thnh phn mt chiu u ra b lc thng thp. Thnh phn mt chiu ny l khng mong mun v n cn lm lch lc chm sao (constellation diagam) nh minh ho trong hnh v di y cho trng hp tn hiu iu ch QPSK.

V do s lm tng t s li bit. Hnh 5.4.16 ch ra s nh hng ca thnh phn ny ti t s li bit ca iu ch QPSK khi c mt ca tp m Gaussian trng cng AWGN (Additive White Gaussian Noise) v DC-offset.

Ta nhn thy rng i vi BER =10-3, t s tn hiu-nhiu gim 4 dB vi thnh phn in p mt chiu chim 45% bin ca tn hiu hu ch.

Nguyn nhn th hai gy ra DC-offset l s xut hin ca cc tn hiu k sinh hay nhiu u vo angten. Cc nhiu ny c khuych i nh b LNA v r sang u vo LO ca b trn tn. i vi cc my thu heterodyne, in p mt chiu to bi b trn tn u tin c lc bi b lc thng di. in p mt chiu tao ra bi b trn tn th hai c nh hng t hn nhiu so vi my thu homodyne.

S thay i ca knh v tuyn hoc mi trng truyn song gn angten thu (v d s di chuyn ca ngi s dng) s gy ra s phn x thay i theo thi gian ca tn hiu r t b LO, do s to ra mt in p mt chiu c bin thay i theo thi gian. Do cn c bin php loi b hoc b thnh phn in p mt chiu ny. y l mt vn , ang v s c nghin cu v l thch thc i vi cc nh nghin cu tu theo tng ng dng c th. y ch trnh by s lc mt s bin php c nghin cu v trin khai.

Gii php 1: Gii php u tin loi b DC-offset l to ta mt t in k sinh mc ni tip hai u ra b gii iu ch I/Q. S c mt ca t in ny tng ng vi mt b lc thng di. Gii php ny rt n gin nhng cng tn ti mt s nhc im sau:- B lc thng di s lm suy gim tn hiu I v Q trong trng hp phng php iu ch s dng c nng lng ph tp trung xung quanh thnh phn mt chiu.

- Gi tr ca t in u ra l c nh, do gii php ny khng loi b c ht thnh phn in p mt chiu thay i theo thi gian. Gii php ny c s dng cho cc h thng s dng phng php iu ch n-FSK nh trong cc h thng nhn tin.Gii php 2: Mt gii php khc hiu qu hn l da vo qu trnh x l tn hiu bng tn c bn bng vic c lng gi trin trung bnh ca cc in p mt chiu sau tn hiu I v Q thu c tr i i lng trung bnh ny. Gii php 3: Mt gii php khc trnh khi vn DC-offset l s dng b dao ng ni c tn s gp hai ln sau a qua b chia hai. Trong trng hp ny ngi ta c th tng s cch ly gia LO v b trn tn, do s hn ch s xut hin ca DC-offset. Tuy nhin gii php ny s tng gi thnh h thng do vic s dung b LO c tn s cao.Gii php 4: Mt gii php na cng c th p dng l s dng my thu hon ton s. Khi tn hiu cao tn iu ch c ly mu trc tip khng thng qua cc tng tip theo. Do vi gii php s ny khng tn ti cc nhc im gy ra bi cc phn t tng t. Tuy nhin trong my thu hon ton s ny, yu cu b chuyn i tng t-s c tc rt cao. S pht trin ca cng ngh CMOS s cho php thc hin c iu ny [Ben01]. Ngoi ra cn c th p dng cc gii php gim tn s ly mu ca cc b ADC m vn m bo khi phc c thng tin [Yem06a].

Gii php 5: Mt gii php khc tn dng cc u im ca my thu gii iu ch tn hiu trc tip v trnh c nhc im ca vic xut hin DC-offset l thc hin h tn nhng khng v tn s bng tn c bn bng khng m l xp x bng khng. Gi tr tn s bng tn c bn ny phi tng i nh vic dng b chuyn i tng t-s c thun li. Bt k vi phng php iu ch no, ta hon ton c th lc tn hiu bi mt b lc thng cao m khng lm suy gim tn hiu. Vic la chn tn s ny phi m bo sao cho cc knh ln cn khng trng vi tn s nh ca tn hiu.

Vn Even-Oder DistorsionVn suy gim mode bc chn sy ra khi c nhiu knh ln cn.

Tn hiu thu u vo ngten gm tn hiu hu ch c tn s f0 v nhiu c cng sut ln tn s sng mang fadj. Nhiu knh ln cn ny c biu din di dang sau:

Do my thu s cch ly km gia cng RF v LO dn n s r tn hiu RF sang cng LO ca b to dao ng ni v hin tng phi tuyn trong b khuych i tp m thp i vi tn hiu mnh s gy ra IM2 v IM3, nhiu knh ln cn s t trn vi chnh n lm xut hin mt thnh phn tn s c bn u ra b gii iu ch I/Q:

Do tn hiu hu ch u ra bng tn c bn v tn hiu sdits.(t) chng ln nhau v khng th loi b tn hiu sdist.(t) bng phng php lc.

Ngoi ra, cng vo ca b trn tn cng chu nh hng bi hin tng tng t. Do khi thit k b trn tn yu t ny cn phi c bit quan tm v tn hiu ti b trn tn c khuych i bi LNA v c th to ra mo ng k. Mo bc 2 c th c xc nh bng im chn IP2 tng t nh khi nim IP3 nh trnh by trong phn trc.

Mt s nh nghin cu tm cch gii quyt vn IM2. V d gio s ngi c, M. Faulkner, xut mt gii php nh sau [Fau01]:

S ny cn c thc hin cho c hai nhnh I v Q. Gii php ny da trn vic c lng tn hiu nhiu sdist.(t): mt b lc thng cao loi b cc tn hiu tn s c bn, do u ra b lc ny (im A) ta c nhiu ca knh ln cn tn s fadj(t). Mt b trn cu phng cho php to ra mt tn hiu tn s c bn sdist(t) t l vi sdist(t); mt b khuych i c khuych i iu chnh c v mt b tr cho php vic loi b IM2 bng cch iu chnh:

y g l khuych i iu chnh c.

Mt b lc thng thp loi b thnh phn nhiu tn s fadj v 2fadj ,do ta thu c tn hiu hu ch u ra. Phng php ny cho php ci thin vic loi b nhiu knh ln cn 11 dB.

Phng php loi b IM2 vn ang l vn m cc nh nghin cu quan tm. Vn I/Q mismatch

Nh trinh by trong hnh 5.4.19, my thu homodyne s dng b gii iu ch cu phng trong yu cu dch pha tn hiu RF hoc LO 90. Nhng thc t lun sy ra sai pha, s khc pha ca tn hiu LO sau khi qua b di pha khng phi l 90. Ngoi ra, bin ca tn hiu I v Q cng khng bng nhau. S sai pha v khc nhau v bin ca tn hiu I v Q s nh hng n lc chm sao ca tn hiu, do s tng t s li bit.

Nu tn hiu thu c dng:

vi a = b = -1 hoc a = b = 1.Gi thit tn hiu I v Q ca b to dao ng ni LO nh sau:

H s 2 trong hai biu thc trn lm cho kt qu n gin hn. v sai bin v sai pha.

Bng vic nhn tn hiu thu trong biu thc PT (5.4.19) vi tn hiu I v Q ca b to dao ng ni trong biu thc PT (5.4.20) v PT (5.4.21) v sau khi qua b lc thng thp loi b thnh phn cao tn, tn hiu thu bng tn c bn nh sau:

S khng cn i v bin v pha gia tn hiu I v Q ca b gii iu ch do s khng l tng ca cc phn t gy nn. Hnh 5.4.20 minh ho s nh hng ca s mt cn bng ny ln lc chm sao tn hiu QPSK i vi mt gi tr v c inh.

S lch chm sao do li pha gy nn s to ra li khi quyt nh cc k hiu thu, do s tng t s li bit. Hnh 5.4.21 ch ra s nh hng ny ti BER [Man02]:

y l kt qu phn tch v m phng i vi cc gi tr li bin v pha khc nhau cho 106 bit. Ta nhn thy rng t s BER ca tn hiu iu ch QPSK vi s c mt ca ca tp m AWGN v hin tng I/Q mismatch nh sau:- Vi BER=10-3: t s tn hiu-tp m gim 2 dB i vi trng hp sai bin giu I v Q l 60%

- Vi BER=10-3: t s tn hiu-tp m gim 4 dB vi trng hp sai pha gia I v Q l 15%.

Tm li I/Q mismatch lm suy gim cht lng iu ch s. Do cn thit phi tm cc phng php gii quyt vn ny v y vn ang l mt ch nghin cu hin ti ca cc nh khoa hc. Trong [Cav93] J.K. Cavers xut mt phng php b khc phc v sa li do I/Q mismatch gy ra. Phng php ny da trn vic c lng s khng cn bng v bin v v pha bng cch tnh s tng quan gia cc chui bit I v Q nhn c.

Thc t ta cn phi duy tr I/Q mismatch v bin nh hn 1 dB v li pha nh hn 5, nhng cc gii hn ny cn tu thuc vo phng php iu ch.

Trong cc my thu heterodyne, b gii iu ch I/Q c thc hin tn cui cng, cc yu cu v I/Q mismatch s nh nhng hn v cc l do sau:

Th nht, tn s b gii iu ch I/Q thng c gi tr nh hn so vi trng hp trong my thu homodyne, do hai nhnh I v Q s t b nh hng hn vi vn I/Q mismatch. Ngoi ra, trong thit k IC, tn s thp cho php s dng nhiu thit b v gii php ci thin vic phi hp tr khng.

Th hai, trong my thu heterodyne, tn hiu c khuych i rt ln trc khi tch lm hai nhnh I v Q, do ch yu cu mt hoc hai tng sau . Nhng ngc li, mi knh ca my thu homodyne thc hin vi tng khuych i v lc, mi mt tng s gy ra vic mt phi hp. Ngoi ra, trong my thu heterodyne, ta cng c th thc hin vic tch hai nhnh I v Q trong min s trnh cc vn v IQ mismatch trong khi iu ny khng th thc hin c vi my thu homodyne. Vn IQ mismatch c th c khc phc bng cc phng php x l tn hiu chnh sa li cc im trong lc chm sao.5.4.2.5. My thu trung tn s

Kin trc my thu trung tn s thc ra xut pht t kin trc my thu heterodyne tn hiu RF c h xung trung tn v c ly mu trc tip thng qua b chuyn i tng t-s, cc nhim v khc nh lc, h tn c thc hin trong min s. Hnh sau gii thiu s khi chc nng my thu trung tn s.

Trong my thu ny, u tin tn hiu tn s trung tn c ly mu sau vic ti to li tn hiu I v Q bng cch trn tn, lc, khuych i c thc hin trong min s bng phng php x l tn hiu s. Vic p dng x l tn hiu trong min s s trnh c vn IQ mismatch. Vn chnh i vi kin trc my thu kiu ny l yu cu i vi b chuyn i tng t-s ADC. Bi v bin ca tn hiu trung tn thng khng vt qu vi trm mV, tp m lng t v tp m nhit ca b ADC do phi khng vt qu vi chc mV. Do nu nh b lc thng di trung tn u tin khng loi b ht cc nhiu ca knh ln cn, s phi tuyn ca b ADC phi nh gim nh hng ti thiu ti tn hiu. Ngoi ra, di ng ca b ADC cng phi ln thch ng vi vic thay i v bin ca tn hiu thu do suy hao truyn dn v fading a ng. B ADC phi t c bng tn u vo tng ng vi gi tr ca tn s trung tn trong khi phi tiu th cng sut va phi.

Cc yu cu trn lm cho vic thc hin tiu chun Nyquist tn kh khn bi v thng thng tn s trung tn khong 100 MHz, s yu cu tn s ly mu ca b ADC t nht vi trm MHz v yu cu v s tuyn tnh, v tp m nn v di ng, cn thit mt b ADC ti thiu khong 14 bit. Hn ch ca b ADC c th c khc phc bng cch ly mu tn hiu trung tn vi tc nh hn tn s trung tn. nh trnh by trong Hnh 5.4.23.

Ta thy rng, ph ca tn hiu c ly mu v h tn tp trung tn s fIF-fs. Do khi trn tn, lc tip theo cho php chuyn ph xung tn s c bn.

My thu trung tn s hin ti cha c s dng trong cc thit b u cui di ng bi v do s hn ch hin ti ca cc b ADC. Tuy nhin, cng vi s pht trin ca cng ngh vi in t, ngy nay ngi ta c th ch to cc b ADC c tn s ly mu c GHz. Do kin trc my thu trung tn s, thm ch my thu hon ton s m tn hiu cao tn RF c ly mu trc tip khng qua khi h tn no s c tim nng pht trin v ng dng trong tng lai rt gn v cng ang l ch nghin cu c nhiu ngi quan tm [Yem06, Juo03].

5.4.2.6. My thu Sub-sampling

Trong kin trc my thu ny, tn hiu cao tn RF u vo c th c ly mu vi nhp thp hn bi v cc tn hiu bng hp ch c mt thay i nh t mt chu k sng mang ti cc chu k tip theo. tng trong kin trc my thu ny nh sau: mt tn hiu tn s sng mang c bng thng B c th c chuyn xung bng tn thp hn nu nh n c ly mu vi nhp ly mu ln hn 2B.

Nh minh ho trong hnh 5.4.24, qu trnh ny to ra s lp li ph m khng b chng ln. Nh c s gim nhiu v tc chuyn i, vic thit k b to dao ng ni hoc b t hp tn s n gin hn rt nhiu. Ngoi ra, so snh vi b trn tn RF, bn thn mch ly mu cng c nhiu u im.

Tuy nhin kin trc my thu kiu ny c mt nhc im rt quan trng l s chng ln v tch t tp m. iu ny c th c l gii nh sau: bng thng ca b ly mu t nht l bng tn s ca tn hiu cao tn u vo, do tp m trong bng rt ln.

Bi tp chng 5Bi tp 5.1Cho mt h thng gm ba tng mc ni tip (hnh v) vi cc tham s sau:

Tng 1 l b lc thng di c h s khuych i: G = -3 dB.

Tng 2 l b khuych i tp m thp c khuych i G = 20 dB v u ra l 20 dBm.

Tng 3 c khuych i G = -7 dB v u ra l 15 dBm.

Tnh IP3 u ra v IP3 u vo ca ton b h thng.

Bi tp 5.2

Mt my thu c IP3 u ra l 10 dBm, h s tp m 6 dB v bng thng ca tp m 10 kHz. Tnh di ng SFDR ca my thu nu yu cu t s tn hiu-tp m u vo ca b gii iu ch ti thiu l 12 dB.Bi tp 5.3Mt my thu c bng thng 30 kHz c ni vi ngten thng qua cp ng trc. H s tp m ca my thu l 6 dB, suy hao cp ng trc l 3 dB, nhit tp m hiu dung ca ngten l 290 K.1. Tnh nhit tp m hiu dng ca h thng, gi thit T0 = 300K.

2. Tnh cng sut tn hiu yu cu u vo ngten c t s tn hiu-tp m l 30 dB cng vi gi thit T0 = 300K.

Bi tp 5.4Hai my thu c biu din theo hnh sau:Gi thit t s tn hiu-tp m u vo ca hai my thu trn l 16.5 dB. My thu no trong hai my trn m bo t s tn hiu-tp m u ra cao hn ?. C nhn xt g t kt qu trn?Bi tp 5.5

Mt my thu c b tin khuych i ni vi b khuych i thng qua mt cp nh hnh sau:

Tnh khuych i ti thiu ca b tin khuych i bit rng h s tp m tng ca my thu khng vt qu 9 dB.Bi tp 5.6Mt my thu c tn m u vo c h s tp m 10 dB v suy gim 6 dB, tng tip theo c khuych i rt ln v h s tp m 2 dB. u vo my thu, nhit tp m tng ng l 7C v t s tn hiu-tp m l 105. Gi thit rng cc tng ny l tuyn tnh phi hp tr khng v c cng bng thng v cc h s tp m c tnh so vi nhit 290K.

1. Tnh t s tn hiu-tp m u ra ca my thu.

2. m bo t s tn hiu-tp m u ra ca my thu ti thiu 40 dB, ngi ta thm vo tng tin khuych i. Nu yu cu h s tp m ca tng tin khuych i nh hn 9 dB, tnh h s khuych i ca tng ny.

Bi tp 5.7Mt my thu c s v cc tham s sau:

Tng phi hp tr khng u vo c suy hao 4 dB v nhit tp m 100 K. Ba tng tip theo u c khuych i mi tng l 10 dB v h s tp m mi tng 3 dB (nh minh ha theo hnh trn). Tnh nhit tp m tng ng ca h thng khi h thng trn c ni vi angten c nhit tp m Ta = 50 K. Gi thit rng cc tng ny u phi hp tr khng v nhit 290 K.

Bi tp 5.8Mt my thu c h s tp m FR = 6 dB c ni vi ngten, c nhit tp m l 290 K, qua cp ng trc c suy hao L = 20 dB (nh hnh v).

Ngi ta d tnh thm b khuych i c khuych i GA = 20 dB v h s tp m FA = 6 dB vo pha u trn (gn vi ngten) hoc pha u di (gn my thu) ca cp. Tnh h s tp m ca ton h thng trong 3 trng hp: khng c b khuych i, b khuych i t u trn ca cp v b khuych i t u di ca cp. Nhn xt g v kt qu tnh c ?.

EMBED Equation.3

Hnh 5.3.7: im nn 1 dB

PT (5.3.27)

EMBED Equation.3

EMBED Equation.3

PT (5.3.26)

EMBED Equation.3

PT (5.3.25)

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

nu

nu

BPF

PA

BPF

LO2

Amp.

Amp.

EMBED Equation.3

PT (5.3.24)

PT (5.3.23)

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

PT (5.3.22)

EMBED Equation.3

PT (5.3.21)

EMBED Equation.3

EMBED Equation.3

PT (5.3.20)

EMBED Equation.3

PT (5.3.19)

PT (5.3.18)

EMBED Equation.3

PT (5.3.17)

EMBED Equation.3

EMBED Equation.3

LPF

LPF

Mixer

BPF

LO1

BPF

EMBED Equation.3

PT (5.3.16)

PT (5.3.15)

PT (5.3.14)

EMBED Equation.3

Hinh 5.3.6: M hnh ha ca hai bn cc mc ni tip tnh ton tp m

EMBED Equation.3

LNA

BPF

PT (5.3.12)

EMBED Equation.3

PT (5.3.13)

Hnh 5.3.5: M hnh ha tp m ca bn cc tnh ton tp m da trn in p

DSP

PT (5.3.11)

EMBED Equation.3

EMBED Equation.3

PT (5.3.10)

PT (5.3.9)

EMBED Equation.3

Hnh 5.3.4: H s tp m ca my thu gm n tng mc ni tip

PT (5.3.8)

EMBED Equation.3

PT (5.3.7)

EMBED Equation.3

EMBED Equation.3

PT (5.3.6)

PT (5.3.5)

Hnh 5.3.3: Ngun tp m ngten v my thu

EMBED Equation.3

PT (5.3.4)

EMBED Equation.3

PT (5.3.3)

EMBED Equation.3

PT (5.3.2)

EMBED Equation.3

PT (5.3.1)

Hnh 5.3.2: Mt phng chun cho vic nh ngha cc tham s ca tp m

ADC

Hnh 5.3.1: V d s khi ca mt h thng v tuyn

90

Knh

My pht

Hnh 5.1.1: Cc di sng in t c s dng trong thng tin v tuyn

ADC

Bng 5.1.1: Cc di sng in t c s dng trong thng tin v tuyn

Bng 5.1.2: Cc bng sng s dng trong thng tin v tuyn

Mixer

LO

My thu

Mt phng chun u vo

My thu

My thu

Mt phng chun u vo

Z0

Ngun tp m Ta

Z0

Ts

G, EMBED Equation.3 , B

EMBED Equation.3

Tng 1

u vo

chun ho

Z0

Ngun tp m Ta

EMBED Equation.3

Tng 2

Tng n

EMBED Equation.3

EMBED Equation.3

Vin

Rs

Zin

Bn cc khng nhiu

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

Rs

EMBED Equation.3

EMBED Equation.3

Bn cc khng nhiu

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

Tng 1

EMBED Equation.3

EMBED Equation.3

Bn cc khng nhiu

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

Tng 2

EMBED Equation.3

EMBED Equation.3

RL

Pout

1dBm

Pin

Phn t hay h thng phi tuyn

T hiu hu ch

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

T hiu hu ch

EMBED Equation.3

Pout (dB)

OIP3

Thnh phn c bn

Thnh phn bc 3

IM3

1 1

Pin(dB)

1 3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

Tng 2

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

Tng 1

Cng sut c quy v u vo

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

SFDR

Pin,max

nhy thu

Tp m quy v u vo

PLL

BPF

PA

BPF

Match

90

DSP

DAC

DAC

Quadrature

LPF

LPF

BPF

PA

BPF

Match

90

Quadrature

I

Q

VCO

I

Q

I

Q

PA

BPF

90

Quadrature

I=cos()

Q=sin()

LO

f0

f

Cng sut u ra

Sai pha

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

PA

BPF1

Match

90

DSP

DAC

DAC

Quadrature

LPF

LPF

BPF2

PLL1

PLL2

I

Q

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

Hnh 5.4.6: S khi chc nng ca my thu s

ADC

DSP

BPF

LNA

BPF

RF

BPF

Mixer

LPF

Amp.

90

PLL2

BPF

Amp.

ADC

LPF

Amp.

BPF

Amp.

PLL1

IF

BPF

LNA

Mixer

LO

Tn hiu

pht k sinh

BPF

LNA

Bng tn thu

Nhiu

Tn hiu hu ch

f

f

ADC

DSP

BPF

LNA

BPF

BPF

Mixer

LPF

ADC

LPF

LO1

LO2

I/Q

Demod

I

Q

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

90

BPF

LNA

LPF

LPF

LO

EMBED Equation.3

90

A

f

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

I

EMBED Equation.3

EMBED Equation.3

Q

EMBED Equation.3

Q

j EMBED Equation.3

RF input

EMBED Equation.3

EMBED Equation.3

f

Hnh 5.4.13: S khi chc nng ca my thu Homodyne

90

ADC

ADC

DSP

BPF

LNA

LPF

LPF

Amp.

Amp.

LO

EMBED Equation.3

0 Hz

f

f

EMBED Equation.3

EMBED Equation.3

BPF

LNA

Mixer

LO

LPF

Amp.

EMBED Equation.3

I

Q

EMBED Equation.3

EMBED Equation.3

BPF

LNA

Mixer

LO

LPF

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

BPF

LNA

Mixer

LO

LPF

+

-

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

g

A

90

BPF

LNA

LPF

LPF

LO

EMBED Equation.3

EMBED Equation.3

Li pha v bin

Li pha v bin

I

Q

L tng

I

Q

L tng

ADC

DSP

BPF

LNA

BPF

BPF

Mixer

LO1

Amp.

ADC

BPF

LNA

BPF

BPF

Mixer

PLL

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

f

EMBED Equation.3

0

f

EMBED Equation.3

0

EMBED Equation.3

f/ EMBED Equation.3

Ph ca tn hiu

cao tn

Tn hiu ly mu

Ph ca tn hiu

u ra b ly mu

f/ EMBED Equation.3

f/ EMBED Equation.3

0

BPF

LNA

LO

G = - 3 dB

EMBED Equation.3

G = 20 dB

EMBED Equation.3

G = -7 dB

EMBED Equation.3

ng dn sng

Suy hao L1 = 0.033 dB

G2 = 10 dB

T2 = 8 K

G3 = 30 dB

F3 = 7 dB

G4 = 30 dB

F4 = 12.9

G5 = 30 dB

F5 = 10

My thu 1:

ng dn sng

T1 = 290 K

G2 = 20 dB

T2 = 106 K

G3 = 20 dB

T3 = 1000 K

G4 = 30 dB

F4 = 12.9 dB

G5 = 30 dB

F5 = 10

My thu 2:

Tin khuych i

Khuych i

Cp

L2 = 8 dB

F1 = 6 dB

F3 = 13 dB

Phi hp tr khng

G2=10 dB

F2=3 dB

L1=4 dB

T1=100 K

G3=10 dB

F3=3 dB

G4=10 dB

F4=3 dB

Tng 1

Tng 2

Tng 3

Tng 4

My thu FR = 6 dB

L=20 dB

EMBED Equation.3

EMBED Equation.3

PT (5.3.28)

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

PT (5.3.30)

EMBED Equation.3

EMBED Equation.3

PT (5.3.31)

EMBED Equation.3

PT (5.3.29)

EMBED Equation.3

EMBED Equation.3

Hnh 5.3.8: Gy mo tn hiu bi IM3

Hnh 5.3.9: Xc nh IP3 bng th

PT (5.3.32)

IIP3

EMBED Equation.3

EMBED Equation.3

PT (5.3.33)

PT (5.3.34)

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

PT (5.3.35)

PT (5.3.36)

PT (5.3.37)

EMBED Equation.3

PT (5.3.38)

EMBED Equation.3

PT (5.3.39)

EMBED Equation.3

PT (5.3.40)

EMBED Equation.3

EMBED Equation.3

PT (5.3.41)

Hnh 5.3.10: Mi lin h gia IP3 v IM3

EMBED Equation.3

Hnh 5.3.11: H thng gm hai tng phi tuyn mc ni tip

PT (5.3.50)

EMBED Equation.3

PT (5.3.49)

EMBED Equation.3

EMBED Equation.3

PT (5.3.48)

EMBED Equation.3

PT (5.3.46)

EMBED Equation.3

EMBED Equation.3

PT (5.3.45)

PT (5.3.44)

PT (5.3.43)

EMBED Equation.3

PT (5.3.42)

Hnh 5.3.12: nh ngha di ng SFDR

EMBED Equation.3

PT (5.3.51)

EMBED Equation.3

PT (5.3.52)

PT (5.3.53)

PT (5.3.54)

PT (5.3.55)

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

Hnh 5.4.1: Kin trc my pht trc tip

Hnh 5.4.2: nh hng ca b khuych i cng sut (PA) ti b to dao ng iu khin bng in p (VCO)

Hnh 5.4.3: nh hng ca tn hiu pht do sai pha trong b to dao ng n gy ra

Hnh 5.4.4: S khi chc nng my pht 2 tng

Hnh 5.4.8: Tn hiu pht k sinh trong my thu

Hnh 5.4.9: La chn bng tn trong my thu

Hnh 5.4.10: Kin trc my thu Heterodyne

Hnh 5.4.11: Kin trc my thu Hartley

Hnh 5.4.14: Cc nguyn nhn gy ra DC-offset

Hnh 5.4.15: S lch lc chm sao gy ra bi thnh phn in p mt chiu trong trng hp tn hiu iu ch QPSK

Hnh 5.4.16: nh hng ca DC-offset ti BER i vi tn hiu iu ch QPSK

thc hin vi 106 bits vi cc gi tr DC-offset khc nhau[Man02].

(o): Khng c DC-offset; (): 15 % ; (x): 30 %; (): 45 %

Hnh 5.4.17: Vn mo do mode bc chn (Even-order distorsion)

Hnh 5.4.18: Phng php loi b IM2 i vi tn hiu nhnh I hoc nhnh Q

Hnh 5.4.19: Li bin v pha trong my thu homodyne

Hnh 5.4.20: Hin tng I/Q mismatch do li bin (hnh tri)

v do li pha (hnh phi)

Hnh 5.4.21: nh hng ca I/Q mismatch v bin (hnh tri) v pha (hnh phi)

i vi BER vi phng thc iu ch QPSK thc hin vi 106 bits vi cc gi tr li bin v pha khc nhau[Man02].

(o): Khng c li bin (o): Khng c li pha

(): 20 % (): 5 %

(x): 40 % (x): 10 %

(): 60 % (): 15 %

Hnh 5.4.22: S khi chc nng my thu trung tn s

Hnh 5.4.23: S khi chc nng v ph ca my thu trung tn s

vi tn s ly mu thp

Hnh 5.4.24: Biu din qu trnh sub-sampling l tng trong min tn s

PT (5.3.47)

PT (5.4.1)

EMBED Equation.3

lc

EMBED Equation.3

EMBED Equation.3

PT (5.4.2)

lc

EMBED Equation.3

EMBED Equation.3

PT (5.4.3)

PT (5.4.4)

PT (5.4.5)

PT (5.4.6)

PT (5.4.7)

PT (5.4.8)

PT (5.4.9)

PT (5.4.10)

PT (5.4.11)

PT (5.4.12)

PT (5.4.13)

PT (5.4.14)

PT (5.4.15)

PT (5.4.16)

PT (5.4.17)

PT (5.4.18)

PT (5.4.19)

PT (5.4.20)

PT (5.4.21)

PT (5.4.22)

PT (5.4.23)

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

Cc knh ln cn

EMBED Equation.3

EMBED Equation.3

Hnh 5.4.5: Vn tn s nh sau b trn tn th hai

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

My thu

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

Tn hiu hu ch

Cc tn hiu kho

Hnh 5.4.7: Cc tn hiu ti my thu

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

C

EMBED Equation.3

Hnh 5.4.12: Kin trc my thu Weaver

I

EMBED Equation.3

+

_

PLL2

EMBED Equation.3

EMBED Equation.3

90

PLL1

EMBED Equation.3

EMBED Equation.3

Q

EMBED Equation.3

f

EMBED Equation.3

EMBED Equation.3

RF input

Q

I

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

EMBED Equation.3

f

LPF

LPF

LNA

BPF

90

_1218491602.unknown

_1218803070.unknown

_1219042449.unknown

_1219043349.unknown

_1219044384.unknown

_1219045675.unknown

_1219045928.unknown

_1219046441.unknown

_1219051195.unknown

_1219045931.unknown

_1219045935.unknown

_1219045784.unknown

_1219045808.unknown

_1219045716.unknown

_1219045762.unknown

_1219044453.unknown

_1219045399.unknown

_1219045537.unknown

_1219045660.unknown

_1219045160.unknown

_1219044418.unknown

_1219044441.unknown

_1219044406.unknown

_1219043638.unknown

_1219044184.unknown

_1219043359.unknown

_1219042732.unknown

_1219043195.unknown

_1219043328.unknown

_1219042766.unknown

_1219042775.unknown

_1219042795.unknown

_1219042744.unknown

_1219042756.unknown

_1219042479.unknown

_1219042721.unknown

_1219042451.unknown

_1218865607.unknown

_1218866564.unknown

_1218867002.unknown

_1218867230.unknown

_1218873579.unknown

_1218883329.unknown

_1218883333.unknown

_1218887056.unknown

_1218887287.unknown

_1218887288.unknown

_1218886810.unknown

_1218886911.unknown

_1218886989.unknown

_1218884318.unknown

_1218883331.unknown

_1218883332.unknown

_1218883330.unknown

_1218883327.unknown

_1218883328.unknown

_1218873652.unknown

_1218867351.unknown

_1218873161.unknown

_1218873226.unknown

_1218873390.unknown

_1218867362.unknown

_1218871370.unknown

_1218867251.unknown

_1218867074.unknown

_1218867190.unknown

_1218867036.unknown

_1218866743.unknown

_1218866852.unknown

_1218866895.unknown

_1218866815.unknown

_1218866652.unknown

_1218866688.unknown

_1218866574.unknown

_1218866349.unknown

_1218866451.unknown

_1218866499.unknown

_1218866362.unknown

_1218865790.unknown

_1218866305.unknown

_1218865779.unknown

_1218807417.unknown

_1218807701.unknown

_1218865390.unknown

_1218865588.unknown

_1218807786.unknown

_1218807567.unknown

_1218807654.unknown

_1218807474.unknown

_1218806146.unknown

_1218806363.unknown

_1218807321.unknown

_1218806183.unknown

_1218806287.unknown

_1218803774.unknown

_1218805095.unknown

_1218806134.unknown

_1218806044.unknown

_1218805066.unknown

_1218803733.unknown

_1218803204.unknown

_1218668574.unknown

_1218799033.unknown

_1218801825.unknown

_1218802752.unknown

_1218802880.unknown

_1218801897.unknown

_1218799612.unknown

_1218799677.unknown

_1218801398.unknown

_1218801793.unknown

_1218799644.unknown

_1218799325.unknown

_1218799457.unknown

_1218799218.unknown

_1218670150.unknown

_1218670668.unknown

_1218798438.unknown

_1218798476.unknown

_1218798525.unknown

_1218672030.unknown

_1218670546.unknown

_1218669924.unknown

_1218670136.unknown

_1218669779.unknown

_1218668596.unknown

_1218644758.unknown

_1218667141.unknown

_1218668480.unknown

_1218668563.unknown

_1218667762.unknown

_1218666150.unknown

_1218666866.unknown

_1218667014.unknown

_1218666673.unknown

_1218666743.unknown

_1218666549.unknown

_1218649266.unknown

_1218665900.unknown

_1218649181.unknown

_1218649207.unknown

_1218649041.unknown

_1218644759.unknown

_1218536688.unknown

_1218643625.unknown

_1218644212.unknown

_1218644384.unknown

_1218644073.unknown

_1218537345.unknown

_1218540583.unknown

_1218643406.unknown

_1218643541.unknown

_1218544201.unknown

_1218551823.unknown

_1218551876.unknown

_1218551556.unknown

_1218544187.unknown

_1218537960.unknown

_1218540564.unknown

_1218537853.unknown

_1218537930.unknown

_1218537772.unknown

_1218537288.unknown

_1218537014.unknown

_1218536934.unknown

_1218493907.unknown

_1218496583.unknown

_1218497111.unknown

_1218499528.unknown

_1218532535.unknown

_1218534958.unknown

_1218535039.unknown

_1218536637.unknown

_1218534897.unknown

_1218534957.unknown

_1218534633.unknown

_1218532400.unknown

_1218499354.unknown

_1218499433.unknown

_1218498926.unknown

_1218497172.unknown

_1218497110.unknown

_1218494826.unknown

_1218496048.unknown

_1218496504.unknown

_1218494846.unknown

_1218494476.unknown

_1218494542.unknown

chuong 5 - kỹ thuật viễn thông

Documents