Công nghệ vô tuyến thông minh

7/28/2019 Cng ngh v tuyn thng minh

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NHN XT CA GIO VIN HNG DN

Vi nhu cu ngy cng tng v loi hnh dch v, tc v cht lng truyn dn

v tuyn dn n i hi ph nng cao hiu sut s dng ph tn hin nay. V

tuyn thng minh (Cognitive Radio) l mt cng ngh truy cp ph tn ng ha

hn s ci thin hiu qu s dng ph tn tnh nh hin nay bng cch tm ra

nhng ph tn cha c s dng (h ph) v chia s chng vi nhng ngi s

dng V tuyn thng minh. Tuy nhin, khi s dng ph tn, ngi dng V

tuyn thng minh lun phi m bo khng gy nhiu vi nhng ngi dng

chnh (ngi dng c cp php s dng ph tn ). Vic p dng k thut

ghp knh phn chia theo tn s trc giao OFDM vi kh nng cm nhn v to

dng ph mt cch linh hot v thch ng vo V tuyn thng minh l mt s la

chn y ha hn. n tt nghip Phn b cng sut trong mng V tuyn

thng minh da trn nn tng OFDM ca sinh vin Nguyn Tin Tnh lp

D2007VT3 i su vo nghin cu vic s dng OFDM trong V tuyn thng

m bo ngi dng chnh khng b nh hng nhiu t ngi dng v tuyn

thng minh bng cch xem xt rng buc cng sut cc knh con v cng sut

tng trong h thng OFDM.

Trong thi gian thc hin n, sinh vin Nguyn Tin Tnh th hin c

cch hc tp v nghin cu tch cc, chng v c trch nhim.

ngh Hi ng cho php sinh vin c bo v v cng nhn tt nghip.

im: ..(Bng ch: .) Ngy ... thng ... nm 2011

Gio vin hng dn


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NHN XT CA GIO VIN PHN BIN

im: ..(Bng ch: .) Ngy ... thng ... nm 2011

Gio vin phn bin


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n tt nghip i hc Mc lc

Nguyn Tin Tnh, D2007VT3 ii

MC LC

DANH MC HNH V................................................................................................. v

DANH MC BNG BIU ........................................................................................ vii

CC THUT NGVIT TT ............................................................................... viiiLI NI U ................................................................................................................ 1

CHNG 1. TNG QUAN V TUYN THNG MINH ....................................... 3

1.1. Gii thiu chng............................................................................................. 3

1.2. nh ngha V tuyn thng minh ............................................................... 3

1.3. Hot ng ca v tuyn thng minh .............................................................. 4

1.4. Cc chc nng chnh ca v tuyn thng minh ............................................ 6

1.4.1. Cm nhn ph ............................................................................................. 7

1.4.2. Qun l ph ............................................................................................... 10

1.4.3. Dch chuyn ph ....................................................................................... 11

1.4.4. Chia s ph ................................................................................................ 11

1.5. Kin trc Vt l ca V tuyn thng minh ................................................... 12

1.6. M hnh thc hin V tuyn thng minh ..................................................... 15

1.6.1. V tuyn nh ngha bng phn mm (SDR). ........................................... 15

1.6.2. M hnh thc hin V tuyn thng minh .................................................. 16

1.7. Kt lun chng 1 .......................................................................................... 20

CHNG 2. K THUT GHP KNH PHN CHIA THEO TN S TRC

GIAO (OFDM) ............................................................................................................. 21

2.1. Gii thiu chng........................................................................................... 21

2.2. Khi nim OFDM .......................................................................................... 21

2.3. Nguyn l c bn ca OFDM ........................................................................ 212.4. M hnh h thng OFDM .............................................................................. 24

2.5. Cc k thut iu ch s sdng trong OFDM .......................................... 27

2.5.1. iu ch QPSK......................................................................................... 27

2.5.2. iu ch QAM .......................................................................................... 28

2.6. NC-OFDM ...................................................................................................... 29

2.6.1. Khi nim NC-OFDM............................................................................... 29

2.6.2. Cu trc khung ca NC-OFDM ................................................................ 30

2.6.3. Hiu nng ca NC-OFDM ........................................................................ 33


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Nguyn Tin Tnh, D2007VT3 iii

2.7. u nhc im ca OFDM ........................................................................... 35

2.8. Kt lun chng 2 .......................................................................................... 36

CHNG 3. V TUYN THNG MINH TRN NN OFDM ............................ 38

3.1. Gii thiu chng........................................................................................... 38

3.2. V tuyn thng minhOFDM ..................................................................... 38

3.3. Ti sao OFDM thch hp vi V tuyn thng minh ................................... 40

3.3.1. Khnng nhn bit v cm nhn ph ....................................................... 40

3.3.2. To dng ph ............................................................................................. 41

3.3.3. Thch ng vi mi trng ......................................................................... 43

3.3.4. Cc k thut anten nng cao...................................................................... 43

3.3.5. a truy nhp v cp pht ph tn.............................................................. 443.3.6. Khnng tng tc ................................................................................... 44

3.4. Cc thch thc i vi h thng OFDM thng minh ................................. 45

3.4.1. To dng ph ............................................................................................. 46

3.4.2. Thit k thut ton ct xn hiu qu ......................................................... 46

3.4.3. Bo hiu cc tham s truyn dn............................................................... 47

3.4.4. Sng b ................................................................................................ 47

3.4.5. Nhiu ln nhau .......................................................................................... 47

3.5. OFDM a bng tn ........................................................................................ 50

3.6. Cc chun v cng ngh OFDM thng minh .............................................. 53

3.6.1. WiMAX - IEEE 802.16............................................................................. 53

3.6.2. IEEE 802.22 .............................................................................................. 57

3.6.3. IEEE 802.11 .............................................................................................. 58

3.7. Kt lun chng 3 .......................................................................................... 60

CHNG 4. PHN B CNG SUT TRONG MNG V TUYN THNG

MINH DA TRN NN OFDM ............................................................................... 61

4.1. Gii thiu chng........................................................................................... 61

4.2. M hnh h thng ........................................................................................... 62

4.2.1. H thng v tuyn thng minh v gii hn cng sut nhiu..................... 62

4.2.2. V tuyn thng minhOFDM v rng buc cng sut pht trn mi knh

con ................................................................................................................... 63

4.3. Phn b cng sut cho h thng V tuyn thng minhOFDM khng xt

ti cc sng mang con ln cn. ................................................................................ 65


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Nguyn Tin Tnh, D2007VT3 iv

4.3.1. Phn b cng sut trong cc h thng OFDM thng thng.................... 65

4.3.2. Phn b cng sut trong cc h thng V tuyn thng minh-OFDM....... 66

4.3.3. Thut ton y nc phn chia lp: iu kin cng sut pht tng .... 67

4.4. Phn b cng sut i vi cc h thng V tuyn thng minhOFDM c

xt ti cc sng mang con bn. ................................................................................ 71

4.4.1. Vit li cng thc bi ton phn b cng sut. ......................................... 72

4.4.2. Phn b cng sut trong trng hp hai rng buc bt ng thc tuyn

tnh trng s khc khng......................................................................................... 74

4.4.3. Thut ton phn b cng sut quy cho cc trng hp tng qut........ 76

4.5. Kt qu m phng .......................................................................................... 78

4.6. Kt lun chng 4 .......................................................................................... 81

KT LUN .................................................................................................................. 82

TI LIU THAM KHO ........................................................................................... 84

PH LC ..................................................................................................................... 85

Ph lc 1. Chng minh nh l 1 ................................................................................ 85

Ph lc 2. Chng minh nh l 2 ................................................................................ 88


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n tt nghip i hc Danh mc hnh v

Nguyn Tin Tnh, D2007VT3 v

DANH MC HNH V

Hnh 1.1. Minh ha h ph.............................................................................................. 5

Hnh 1.2. Chu trnh thng minh ....................................................................................... 5

Hnh 1.3. Cc chc nng truyn thng trong mng V tuyn thng minh. .................... 6Hnh 1.4. Phn loi cc k thut cm nhn ph. ............................................................. 7

Hnh 1.5. M hnh nhit nhiu ......................................................................................... 9

Hnh 1.6. Phn loi cc cng ngh chia s ph tn ....................................................... 11

Hnh 1.7. Kin trc vt l ca V tuyn thng minh ..................................................... 13

Hnh 1.8. Cu trc tng qut b thu pht SDR .............................................................. 15

Hnh 1.9. So snh gia V tuyn thng thng, V tuyn c nh ngha bng phn

mm v V tuyn thng minh. ...................................................................................... 16

Hnh 1.10. Quan h gia V tuyn thng minh v SDR ............................................... 17

Hnh 1.11. S khi thc hin V tuyn thng minh da trn SDR. ........................ 18

Hnh 1.12. Kin trc phn lp tng qut cho V tuyn thng minh ............................. 19

Hnh 2.1. a sng mang trc giao (a) v a sng mang thng thng (b) ................... 22

Hnh 2.2. Ph ca mt sng mang con OFDM n l .................................................. 23

Hnh 2.3. Ph ca k hiu OFDM ................................................................................. 23

Hnh 2.4. S khi tng qut ca mt b thu pht OFDM ........................................ 25

Hnh 2.5. Biu tn hiu QPSK .................................................................................. 28

Hnh 2.6. Chm tn hiu M-QAM ................................................................................. 29

Hnh 2.7. Ph tn ca cc sng mang con NC-OFDM ................................................. 30

Hnh 2.8. S tng qut ca mt b thu pht NC-OFDM s dng khi La chn

sng mang con trng. .................................................................................................... 31

Hnh 2.9. Hiu nng BER ca b thu pht NC-OFDM (cc ng lin nt) v MC-CDMA (cc ng gch) i vi mc chim gi (ISO) phthay i. ................... 34

Hnh 3.1. S khi h thng v tuyn thng minh da trn OFDM. ......................... 39

Hnh 3.2. Cm nhn v to dng ph s dng OFDM .................................................. 42

Hnh 3.3. Cc cng ngh v tuyn da trn OFDM ...................................................... 45

Hnh 3.4. Cc thch thc trong h thng V tuyn thng minh v OFDM .................. 46

Hnh 3.5. Mt ph cng sut ca mt sng mang con OFDM ................................. 48

Hnh 3.6. Ca scosin tng vi cc gi tr roll-off () khc nhau. ............................... 49Hnh 3.7. Hiu ng trt (roll-off) trn PSD ca mt sng mang con OFDM n l. . 49


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n tt nghip i hc Danh mc hnh v

Nguyn Tin Tnh, D2007VT3 vi

Hnh 3.8. Lp cc h ph s dng tn hiu SB-OFDM hoc MB-OFDM. ................... 51

Hnh 3.9. Lp cc h ph s dng cc tn hiu SB-OFDM hoc MB-OFDM. ............. 52

Hnh 3.10. Cc bng con ca cc h thng UWB da trn MB-OFDM trong min tn

s. ................................................................................................................................... 53

Hnh 3.11. Minh ha cu trc tn hiu OFDMA s dng trong WiMAX ..................... 55

Hnh 3.12. S pht trin cc chun v cc cng ngh ................................................... 59

Hnh 4.1. M hnh h thng V tuyn thng minh ....................................................... 62

Hnh 4.2. Ph ca SU trong cc h thng V tuyn thng minhOFDM ................... 63

Hnh 4.3. Lc thu pht ca SU trong cc h thng V tuyn thng minhOFDM

....................................................................................................................................... 64

Hnh 4.4. Ti u phn b cng sut trong cc h thng OFDM thng thng. ........... 66

Hnh 4.5. S phn b cng sut ti u vi cc iu kin cng sut pht knh con. ..... 68

Hnh 4.6. Qu trnh y nc phn chia lp ............................................................. 79

Hnh 4.7. Phn b cng sut ti u bi RPA ................................................................ 80

Hnh 4.8. Phn b cng sut ti u bng IPW khng xt ti cc sng mang cnh bn ....

....................................................................................................................................... 80


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n tt nghip i hc Danh mc bng biu

Nguyn Tin Tnh, D2007VT3 vii

DANH MC BNG BIU

Bng 1.1. Thng s ca iu ch QPSK ....................................................................... 28

Bng 2.2. So snh cht lng ca h thng MC-CDMA, OFDM v NC-OFDM ........ 33

Bng 3.1. Cc chun v tuyn da trn OFDM ............................................................ 39Bng 3.2. V tuyn thng minh OFDM ........................................................................ 40

Bng 3.1. Cc c tnh anten nng cao ca WiMAX. ................................................... 55

Bng 4.1. Thut ton IPW di iu kin Cng sut pht tng. .................................. 69

Bng 4.3. Thut thut ton phn b cng sut cho bi ton vi hai rng buc bt ng

thc tuyn tnh trng s khc khng. ............................................................................ 76

Bng 4.4. Thut ton RPA cho bi ton vi M+1 rng buc bt ng thc tuyn tnh

trng s khc khng. ...................................................................................................... 76


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n tt nghip i hc Cc thut ngvit tt

Nguyn Tin Tnh, D2007VT3 viii

CC THUT NGVIT TT

Thut ng Tn Ting Anh Ngha Ting Vit

AAS Adaptive Antenna System H thng anten thch ng

AMC Adaptive MIMO Switch Chuyn mch MIMO thch ng

AWGN Additive White Gaussian Noise Nhiu Gauss trng cng

BER Bit Error Rate Tc li bt

BPSK Binary Phase Shift Keying Kha dch pha nh phn

CINR Carrier-to-Interference Noise

Ratio

T s nhiu trn sng mang

CP Cyclic Prefix Tin t vng

CR Cognitive Radio V tuyn thng minh

CSI Channel State Information Thng tin trng thi knh

D/A Digital to Analog Ssang tng t

DFS Dynamic Frequency Selection La chn tn sng

DFT Discrete Fourier Transform Chuyn i Fourier ri rc

DVB Digital Video Broadcasting Truyn hnh s qung b

DVB-T Digital Video Broadcasting

Terrestrial

Truyn hnh s qung b mt t

ETSI European Telecommunications

Standards Institute

Vin cc tiu chun v Vin thng

chu u

FCC Federal Communications

Commission

y ban Truyn thng Lin bang

FDM Frequency Division

Multiplexing

Ghp knh phn chia tn s

FFT Fast Fourier Transform Chuyn i Fourier nhanh

FHDC Frequency Hopping Diversity

Coding

M ha phn tp nhy tn

FRC Federal Radio Commission y ban V tuyn Lin bang

I/Q In-phase and Quadrature-phase Trong pha v pha vung gc


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Nguyn Tin Tnh, D2007VT3 ix

ICI Inter-Carrier Interference Nhiu lin sng mang

IDFT Inverse Discrete Fourier

Transform

Chuyn i Fourier ri rc ngc

IETF Internet Engineering Task Force y ban chuyn trch v InternetIFFT Inverse Fast Fourier Transform Chuyn i Fourier nhanh ngc

IPD Incumbent Profile Detection B pht hin cc thng tin v hot

ng ca thu bao c cp php

IPW Iteractive Partitioned Water-

filling

y nc phn chia lp

ISI Inter-symbol Interference Nhiu lin k t

ITM Interfence Temperature Model M hnh nhit nhiu

ITMA Interfence Temperature Multiple

Access

a truy nhp theo m hnh nhit

nhiu

JRRM Joint Radio Resource

Management

Qun l Ti nguyn V tuyn chung

LAN Local Area Network Mng vng ni ht

MAN Metropolitan Area Network Mng vng trung tm

MC-CDMA Multi-Carrier Code Division

Multiplexing Access

a truy nhp phn chia theo m a

sng mang

MCM Multi-Carrier Modulation iu cha sng mang

MIMO Multiple Input Multiple Output H thng a u vo a u ra

NC-OFDM Non-Contiguous Orthogonal

Frequency DivisionMultiplexing

Ghp knh phn chia theo tn s

trc giao khng lin tc

NTIA National Telecommunication

and Information Administration

C quan qun l Vin thng v

Thng tin Quc gia

OFDM Orthogonal Frequency Division

Multiplexing

Ghp knh phn chia theo tn s

trc giao

OFDMA Orthogonal Frequency Division

Multiple Access

a truy nhp ghp knh phn chia

theo tn s trc giao

P/S Parallel-to-Serial Song song sang ni tip


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Nguyn Tin Tnh, D2007VT3 x

PAPR Peak to Average Power Ratio T s cng sut nh trn cng sut

trung bnh

PSK Phase Shift Keying Kha dch pha

PU Primary User Ngi dng chnhQAM Quadrature Amplitute

Modulation

iu chbin cu phng

QPSK Quadrature Phase Shift Keying Kha dch pha cu phng

RAN Radio Access Network Mng truy nhp V tuyn

RE Radio Equipment Thit b v tuyn

RF Radio Frequency Tn s v tuyn

RPA Recursive Power Allocation Phn b cng sut quy

RS Resource scheduling Lp lch ti nguyn

RSSI Received Signal Strength

Indicator

B ch th mc tn hiu thu

S/P Serial-to-Parallel Ni tip sang song song

SDR Software defined Radio V tuyn nh ngha bng phn

mm

SIR Signal-to-Interfence Ratio T s tn hiu trn nhiu

SM Spatial Multiplexing Ghp knh khng gian

SNR Signal to Noise Ratio T s tn hiu trn nhiu

STC Space-Time Coding M ha khng gian-thi gian

SU Secondary User Ngi dng v tuyn thng minh

TPC Transmit Power Control iu khin cng sut pht

UWB Ultra Wide Band Bng siu rng

WLAN Wireless Local Area Network Mng v tuyn ni ht

WMAN Wireless Metropolitan Area

Networks

Mng v tuyn ni th

WPAN Wireless Personal Area

Networks

Mng v tuyn c nhn


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Nguyn Tin Tnh, D2007VT3 xi

WRAN Wireless Regional Area

Network

Mng v tuyn ni vng

WWRF Wireless World Research Forum Din n nghin cu khng dy th

gii


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n tt nghip i hc Li ni u

Nguyn Tin Tnh, D2007VT3 1

LI NI U

Ngy nay, Cng ngh thng tin v Truyn thng ang pht trin vi tc

chng mt, ko theo l s gia tng khng ngng ca cc ng dng v tuyn v cc

thit b v tuyn mi, i hi phi s dng ngun ti nguyn ph tn tit kim v hiu

quhn. Tri li, vi chnh sch phn b ph tn v tuyn cnh nh hin nay v

vic s dng ph tn cp php li ty thuc vo nhu cu ca ngi dng nn tnh

trng s dng km hiu qu ph tn cp php ang din ra kh ph bin. Nh vy,

chnh sch gn ph tn cnh nh trc y s khng cn ph hp na, cn c mt

cng ngh truy nhp ph tn mi c th tn dng hiu qu cc phn ph tn cha c

s dng. Cng ngh truy nhp ph tn mi ny chnh l V tuyn thng minh (CR -

Cognitive Radio).

Ghp knh phn chia theo tn s trc giao (OFDM) l mt phng thc truyndn ng tin cy cho cc h thng V tuyn thng minh. Th nht, OFDM l mt cng

ngh truyn dn xut sc ang c ng dng trong rt nhiu cng ngh mng v

tuyn hin ti v tng lai. Nn vic p dng OFDM trong V tuyn thng minh s

khin cho qu trnh ng b hot ng gia V tuyn thng minh v cc mng v

tuyn khc trnn ddng hn bao giht. Th hai, vic phn b ti nguyn v tuyn

mt cch linh ng l mt thch thc ln trong cc h thng V tuyn thng minh.

OFDM s cung cp mtphng php rt linh hot trong vic phn b cc ti nguyn

v tuyn trong mi trng ng. N cng m bo vic khng c can nhiu gia cc

knh v tuyn lin k nhau trong h thng. Cng sut cn c phn b hp l ti tt

ccc ngi s dng nhm m bo cho h thng vn hnh mt cch ti u nht, p

ng cc yu cu v cht lng dch v (QoS) cng nh nng cao hiu nng ca ton

b h thng V tuyn thng minh. Do vy, cn c nhng nghin cu ng n v ton

din v vn phn b cng sut trong cc mng v tuyn ni chung v trong V

tuyn thng minh ni ring.

c snh hng v hng dn tn tnh ca c gio ThS. L Tng Hoa, em thc hin n Phn b cng sut trong mng V tuyn thng minh da trn

nn tng OFDM. n bao gm bn chng, c thnh sau:

Chng 1:Tng quan v tuyn thng minh

Gii thiu chung v cu trc v hot ng ca mng V tuyn thng minh.

Trong nu r cc khi nim lin quan v V tuyn thng minh, ng thi phn tch

c im v hot ng ca V tuyn thng minh bao gm cm nhn ph, quyt nh

ph, linh hot ph v chia s ph.

Chng 2: K thut ghp knh phn chia theo tn s trc giao - OFDM


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n tt nghip i hc Li ni u


Trnh by tng quan v k thut ghp knh phn chia theo tn s trc giao. Ni

dung chng bao gm nguyn l truyn dn s dng trong OFDM, m hnh h thng

thu pht OFDM, cc phng php iu ch s dng trong OFDM v gii thiu tng

quan v k thut truyn dn OFDM khng lin tc (NC-OFDM), k thut c p

dng trc tip vo V tuyn thng minh.Chng 3: V tuyn thng minh da trn nn OFDM

Trnh by kin trc ca mng V tuyn thng minh da trn nn tng cng

ngh OFDM - bao gm m hnh h thng v hot ng, cc thch thc cn tn ti v

cc chun p dng.

Chng 4: Phn b cng sut trong mng V tuyn thng minhOFDM

Ni dung chng i su phn tch v vn ti u phn b cng sut trong

mng V tuyn thng minhOFDM. C th ta sa ra cc thut ton phn b cngsut ti u i vi h thng OFDM thng thng, t pht trin chung cho h thng

V tuyn thng minhOFDM.

Di squan tm, gip , ch bo tn tnh trong nghin cu cng nh cung

cp ti liu ca c gio Ths. L Tng Hoa v n lc ca bn thn, n c hon

thnh vi ni dung ng k mc v phm vi nht nh. Tuy nhin, do trnh v

thi gian c hn nn n chc chn khng trnh khi c nhng sai st, knh mong

cc thy c gio v bn c ng gp kin cho ni dung n c hon thin hn

v nh hng cho cc nghin cu tip theo.

Em xin gi li cm n chn thnh nht ti c gio ThS. L Tng Hoa, ngi

trc tip nh hng em la chn n ny ng thi cng l ngi tn tnh

hng dn em trong sut qu trnh thc hin v hon thnh n. Em cng xin gi li

cm n chn thnh ti cc thy c gio trong b mn V tuynkhoa Vin thng I, v

cc bn b gip em trong qu trnh hc tp v lm n.

H ni, ngy 05 thng 12 nm 2011

Ngi lm n

Nguyn Tin Tnh


15/100

n tt nghip i hc Chng 1. Tng quan V tuyn thng minh


CHNG 1. TNG QUAN V TUYN THNG MINH

1.1. Gii thiu chngV tuyn thng minh khng ch l mt cng ngh mi, m n cn l mt s

thay i mang tnh cch mng trong vic s dng ph tn v tuyn. Cng ngh Vtuyn thng minh c thit k nhm nng cao hiu qu s dng ph tn, cc ngi

dng thng minh c khnng s dng ph chia s m khng gy nhiu ti cc ngi

dng c cp php. V tuyn thng minh cho php u cui c th cm nhn, hiu

bit v s dng mt cch linh hot ph tn sn c ti mt thi im nht nh. Chng

ny s cp mt cch tng quan nht v cng ngh V tuyn thng minh, cc khi

nim, c tnh cng nh hot ng ca V tuyn thng minh.

1.2. nh ngha V tuyn thng minhV tuyn thng minh l mt cng ngh cn rt mi m, do nh ngha V

tuyn thng minh c cc c nhn v t chc v v tuyn trn th gii nhn nhn

theo rt nhiu cch khc nhau.

Thut ngV tuyn thng minh ln u tin xut hin trong mt tbo nm

1999, n c Joseph Mitola III nh ngha nh sau: V tuyn thng minh l m hnh

v tuyn sdng nhng suy lun cht cht c mc tiu c th thit lp

trong cc min v tuyn lin quan.

Tuy nhin, trong kho st v V tuyn thng minh ca mt t bo, SimonHaykin nh ngha V tuyn thng minh nh sau: V tuyn thng minh l mt h

thng truyn thng khng dy thng minh c khnng nhn bit vmi trng xung

quanh n t hc hi thch nghi vi sthay i ca mi trng bng cch thay

i cc tham shot ng c th (v d cng sut pht, tn ssng mang, phng

thc iu ch) trong thi gian thc, vi hai c tnh chnh:

- Truyn thng tin cy cao ti mi thi im- Sdng hiu qu phtn sv tuyn

FCC nh ngha V tuyn thng minh da trn nn tng vn hnh ca my

pht nh sau: L mt v tuyn m c ththay i cc tham sca my pht da trn

stng tc vi mi trng m n hot ng.

Trong khi trgip FCC n lc a ra nh ngha v tuyn thng minh, IEEE

USA a ra nh ngha sau: Mt b pht/thu tn sv tuyn m c thit k

pht hin mt cch thng minh cc phn on ring l ca ph tn ang c s

dng, t c th truy nhp vo cc ph tn cha c s dng mt cch nhanh

chng, linh hot, khng gy nhiu ti cc ngi dng c cp php.


16/100



Da vo mt snh ngha trn ta nhn thy V tuyn thng minh c mt s

c im c bn nh sau:

Squan st: d trc tip hay gin tip, v tuyn thng minh c khnng thuthp c thng tin vmi trng hot ng ca n.

Khnng thch ng: v tuyn thng minh c th thay i cc tham s hotng ca n cho ph hp vi hon cnh.

Tnh thng minh: c kh nng s dng thng tin mt cch linh hot tc mc tiu nh sn.

Ty chng ta c th tin ti mt nh ngha chung nht v V tuyn thng minh

nh sau:

nh ngha: V tuyn thng minh l mt v tuyn c khnngphn tch mi

trng xung quanh n, t thay i cc tham struyn dn ca n sdng phtn sn c mt cch hiu qu.

1.3. Hot ng ca v tuyn thng minhTnh ngha trn ta c th thy v tuyn thng minh c hai c im chnh sau:

- Khnng thng minh: Khnng thng minh ch khnng m cng ngh vtuyn nm bt hoc cm nhn cc thng tin tmi trng v tuyn. Khnng

ny khng chn gin l thc hin gim st cng sut trong mt sbng tn

s quan tm m cn yu cu nhiu cng ngh phc tp nm bt s bin ica mi trng v tuyn theo khng gian v theo thi gian nhm trnh nhiu

nh hng ti nhng ngi dng khc. Thng qua khnng ny, cc phn ph

khng s dng ti mt thi im hoc v tr nht nh c thc xc nh. T

, ta c th la chn c ph tt nht v cc thng s hot ng ph hp

nht..

- Tnh tcu hnh: Tnh t cu hnh cho php V tuyn khnng lp trnh tng theo sthay i ca mi trng v tuyn. c bit, V tuyn thng minh

c thc lp trnh truyn v nhn trn cc tn skhc nhau v s dng

cc cng ngh truy nhp truyn dn khc nhau c phn cng h tr. Mt s

thng s t cu hnh cn ch l: Tn shot ng,iu ch, Cng sut pht,

Cng ngh truyn.

Mc tiu c bn ca V tuyn thng minh l tn dng c ph tn c sn tt

nht thng qua khnng thng minh v tnh t cu hnh. V hu ht ph tn c

gn, nn thch thc quan trng nht l s dng chia s ph tn c cp php m

khng gy nhiu ti qu trnh truyn dn ca nhng ngi dng c cp php khc.V tuyn thng minh cho php s dng nhng vng ph trng theo tng thi im,


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ph ny m ch h ph hay khong trng (xem Hnh 1.1). Nu bng ph ny c

ngi dng chnh (ngi dng cp php) s dng tip th cc ngi dng v tuyn

thng minh phi chuyn n h ph khc hoc nu vn trong cng mt bng th phi

thay i mc cng sut pht hoc s iu ch trnh nhiu.

Cng sutTn s

Thi gianH ph

Ph s dng

Hnh 1.1. Minh ha hph

Hot ng ca V tuyn thng minh c th c m t theo mt chu trnh

thng minh nh Hnh 1.2di y.

Mi trng V tuyn

CM NHNPH

QUN LPH

DCH CHUYN

PH

Tn hiu truyn i Cc tc nhnV tuyn

Thng tin v cch ph

Thng tin

Chuyn giao

Thng tin v cch ph

Cc tc nhn

V tuynCHIA S PH

Lp lch

Thng tin knh

Hnh 1.2. Chu trnh thng minh

Hnh 1.2 l mt chu trnh thng minh n gin nht bao gm cc nhim v chnh ca

mt mng V tuyn thng minh; cc nhim v ny c thc phn loi thnh:

- Cm nhn ph: V tuyn thng minh gim st cc bng ph sn c, nm bt ccthng tin ca chng v sau pht hin ra cc h ph.

- Qun l ph: chim gi phn ph tn tt nht a ra cc k hoch phn bphcho cc ngi dng mt cch hp l.


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- Dch chuyn ph: m bo cc yu cu truyn thng c thng sut v lintc.

- Chia s ph: lp lch ph tn hp l gia cc ngi dng v tuyn thng minhang cng tn ti.

Cc nhim v ny sc phn tch chi tit hn cc phn sau ca chng.

Cc mng V tuyn thng minh cho php cc giao thc truyn thng nhn bit

ph. Tuy nhin, vic s dng ph tn ng gy ra cc nh hng bt li n hiu nng

ca cc giao thc truyn thng thng thng m c pht trin cho cc bng tn

s cnh.

Cc thnh phn trong mng V tuyn thng minh v tc ng gia chng c

minh ha trong Hnh 1.3. Chnh stc ng ny i hi mng V tuyn thng minh

phi c chc nng thit k gia cc lp. c bit, vic cm nhn ph v chia s phphi c kt hp nng cao hiu qu ph. Trong chc nng chia s ph v dch

chuyn ph, cc chc nng lp ng dng, truyn ti, nh tuyn, truy nhp phng

tin v lp vt l c thc hin ng thi.

Chc nng

dch chuyn

ph

Chc nng

qun l

ph

ng dng

Truyn ti

Lp mng

Chia sph

Cm nhnph

Lp vt l

iu khin ng dng

Tn tht, tr chuyn giao

Thng tin nh tuyn

Thng tin

cm nhn

Tr lplin kt

Cc yu cu v QoS

T cu hnh

Thng tin nh tuyn/T cu hnh

Thng tin lp lch/T cu hnh

Thng tin

cm nhn/

T cu hnhQuyt nh chuyn giao, thng tin v ph tn hin ti v tng lai

Lp lin kt d liu

Hnh 1.3. Cc chc nng truyn thng trong mng V tuyn thng minh.

Nh ta thy, chc nng cm nhn ph tn c thc hin ti lp vt l cn chc nng

chia s phc thc hin ch yu ti lp lin kt d liu.

1.4. Cc chc nng chnh ca V tuyn thng minhCc k thut V tuyn thng minh cung cp khnng s dng v chia s ph

theo c hi. Cc k thut truy nhp ph tn ng cho php V tuyn thng minh hotng trong knh tt nht c sn. C thhn, cng ngh V tuyn thng minh cho php


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nhng ngi dng thng minh kh nng: (1) xc nh cc phn ph sn c v pht

hin ra nhng ngi dng chnh khi ngi dng hot ng trong bng cp php

(cm nhn ph), (2) la chn knh tt nht c sn (qun l ph), v (3) ng truy nhp

ti cc knh vi nhng ngi dng khc (chia s ph), v (4) bknh khi pht

hin c ngi dng chnh (dch chuyn ph).1.4.1. Cm nhn ph

Mt yu cu quan trng ca mng V tuyn thng minh l cm nhn cc h

ph. Nh c cp, V tuyn thng minh c thit k c th hiu bit v

nhy cm vi sthay i ca mi trng xung quanh. Chc nng cm nhn ph cho

php V tuyn thng minh thch ng vi mi trng xung quanh bi vic pht hin

cc h ph.

Cch hiu qu nht pht hin cc h ph l pht hin cc ngi dng chnhang truyn nhn d liu trong vng hot ng ca n. Tuy nhin, trn thc t rt kh

cho mt V tuyn thng minh c tho trc tip cc thng s vknh ang s

dng gia my pht v thu ca ngi dng chnh. Do vy,phng php kh thi u

tin l tp trung vo vic pht hin my pht chnh da trn cc quan st cc b ca

cc ngi dng v tuyn thng minh.

Ni chung, cc k thut cm nhn ph c thc phn loi thnh: pht hin

my pht, pht hin cng tc v pht hin da trn nhiu c ch ra trn Hnh 1.4.

Cm nhn ph

Pht hinmy pht

Pht hin theo cch hp tc

Pht hinda trn nhiu

Pht hinda trn

b lc kt hp

Pht hinnng lng

Pht hinda trn

c tnh dng Hnh 1.4. Phn loi cc kthut cm nhn ph.

1.4.1.1. Pht hin my pht (pht hin khng hp tc)V tuyn thng minh phi phn bit gia cc bng tn cha s dng v cc

bng tn c s dng. Bi vy, V tuyn thng minh cn c khnng xc nh

xem tn hiu tmy pht ngi dng chnh c ang tn ti trong mt bng tn c th

hay khng. Phng php pht hin my pht l da trn vic pht hin tn hiu yu t

mt my pht chnh thng qua cc quan st cc b ca cc ngi dng v tuyn thngminh.


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1.4.1.1.1.Pht hin da trn b lc kt hpKhi bit c thng tin tn hiu ngi dng chnh, thphng phppht hin

tt nht trong mi trng nhiu Gauss khng i l b lc kt hp v n cho t s tn

hiu trn nhiu (SNR) ti a. Trong khi u im chnh ca b lc kt hp l yu cu t

thi gian t c li x l cao, th n i hi phi bit trc thng tin v tnhiu ngi dng chnh chng hn nh phng thc iu ch, dng xung, v khun

dng gi. Bi vy, nu cc thng tin ny khng chnh xc th b lc kt hp t ra

khng hiu qu.

1.4.1.1.2.Pht hin da trn nng lngNu my thu khng thc c thng tin hu ch v tn hiu ngi dng

chnh, chng hn nu my thu ch bit c cng sut ca nhiu Gauss ngu nhin, th

b pht hin tt nht trong trng hp ny l pht hin da trn nng lng. onng lng ca tn hiu nhn c, tn hiu u ra ca b lc thng di vi bng

thng W cbnh phng v tch phn qua khong thi gian quan st T. Cui cng,

u ra ca b kt hp c so snh vi mt ngng quyt nh xem c ngi dng

chnh hay khng.

Hiu nng ca pht hin nng lng d bnh hng bi sthay i ca cng

sut nhiu. gii quyt vn ny, mt knh hoa tiu tmy pht chnh c s

dng ci thin chnh xc ca b pht hin da trn nng lng. Mt thiu st

na l b pht hin da trn nng lng khng th phn bit cc loi tn hiu m ch

c thxc nh s c mt ca chng.

1.4.1.1.3.Pht hin da trn c tnh dngMt phng php pht hin khc l pht hin da trn c tnh dng. Cc tn

hiu iu ch thng thng c kt hp vi cc sng mang hnh sin, cc chui

xung, tri ph lp, nhy tn, hoc cc tin t vng. Nhng tn hiu iu ch ny

c m tnh c tnh dng v trung bnh v ttng quan ca chng tun hon theo

chu k. Nhng c tnh ny c pht hin nhphn tch hm tng quan ph. uim chnh ca hm tng quan ph l n phn bit nng lng nhiu vi nng lng

tn hiu iu ch. Bi vy b pht hin c tnh vng tnh c th hot ng tt hn

b pht hin nng lng v n c th tch c nhiu ra tt hn b pht hin da trn

nng lng. Tuy nhin, n yu cu tnh ton phc tp v thi gian quan st s di hn

ng k.

1.4.1.2. Pht hin theo c ch hp tcPht hin theo c ch hp tc lphng php cm nhn ph tn m thng tin t

nhiu ngi dng v tuyn thng minh c kt hp li pht hin ngi dng


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chnh. Pht hin hp tc c thc thc hin theo cphng n tp trung hay phn

tn. Trong phng n tp trung, trm gc ng vai tr thu thp ton b thng tin t

cc ngi dng v tuyn thng minh v pht hin cc h ph. Cn theo phng n

phn tn, n yu cu trao i cc thng tin quan st gia cc ngi dng trong mng

vi nhau.Phng php ny cung cp hiu nng cm nhn chnh xc hn, tuy nhin n to

ra cc nh hng bt li trong cc mng hn ch ti nguyn do cc hot ng b xung

v cc lu lng mo u.

1.4.1.3. Pht hin da trn nhiuGn y mt m hnh o nhiu mi c FCC gii thiu, gi l phng

php nhit nhiu c ch ra trn Hnh 1.5.

Tn hiu cpphp

Cc c hi micho truy cp ph

Vng phc vnh nht vinh nhiu

Vng phc v tinhiu nn

Nhiu nn

Cng sutti my

thu Gii hn nhitnhiu

Hnh 1.5. M hnh nhit nhiu

M hnh ny ch ra tn hiu ca mt trm v tuyn c thit k hot ng

trong mt di ti cng sut thu gn vi mc nhiu nn. Khi xut hin tn hiu gm

c nhiu th nhiu nn tng ln ti cc im khc nhau trong vng dch v, nh ch ra

bi cc nh pha trn ca nhiu nn ban u. Trong m hnh nhit nhiu cc thu bao

v tuyn thng minh c coi l cc thu bao c quyn u tin hn, cc thu bao khc

v can nhiu chnh l mt ngun nhiu. Ngun nhiu s gii hn dung lng ca

h thng trn tng bng tn c th t h thng v tuyn thng minh s quyt nh

truyn hay khng.

Tuy nhin vn c mt s gii hn trong vic o c nhit nhiu. Phng php

ny xem xt cc nhn t nh phng php iu ch tn hiu khng cp php, cc

anten, khnng pht hin cc knh cp php tch cc, iu khin cng sut v mc

hot ng ca cc ngi dng chnh v ngi dng v tuyn thng minh. Tuy nhinm hnh ny khng xem xt nh hng ca nhiu ngi dng. Hn na, nu ngi


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dng khng c kin thc v v tr gn ngi dng chnh th nhiu khng tho c

c bng phng php ny.

1.4.2. Qun l phTrong mng v tuyn thng minh, cc bng tn phcha s dng sc tri

ra trn mt vng tn s rng bao gm cbng tn cp pht v khng cp pht. Cc

bng tn phcha s dng ny c pht hin thng qua cm nhn ph cho thy cc

c im khc nhau khng chthay i theo thi gian m cn theo cc thng tin bng

tn phnh tn sv bng thng hot ng.

V mng V tuyn thng minh phi quyt nh c bng tn ph tt nht

p ng cc yu cu v QoS trn ton bcc bng tn c sn, nn cc chc nng qun

l ph mi c yu cu xem xt cc c im phng.

Chng ta phn loi cc chc nng ny thnh: cm nhn ph, phn tch ph, vquyt nh ph. Trong , cm nhn phnh cp trn l chc nng thuc lp

vt l, phn tch ph v quyt nh ph thuc chc nng ca cc lp cao hn.

1.4.2.1. Phn tch phTrong mng v tuyn thng minh cc h ph c sn cho thy cc c tnh khc

nhau ca ph bin i theo thi gian. Phn tch ph cho php phn loi cc bng tn

ph khc nhau, t c th la chn c bng tn ph hp vi yu cu ca ngi

dng. thy c cht lng ca cc bng tn ph c th cn phi phn tch ccthng snh mc nhiu, t l li knh, suy hao ng truyn, li lin kt v tuyn, tr

lp lin kt, v thi gian nm gi.

- Nhiu: ccbng tn ph khc nhau thng c cc mc nhiu khc nhau, do cn xc nh cc c im nhiu ca knh. T mc nhiu ti my thu chnh, ta

s suy ra cng sut cho php ca ngi dng t s dng cho vic c tnh

dung lng knh.

- Suy hao ng truyn: khi tn s hot ng tngth suy hao ng truyn cngtng. Do , nu cng sut pht ca ngi dng gi nguyn th phm vi truyn

s gim ti cc tn scao hn. Nu ta tng cng sut pht b li suy hao

ng truyn th stng nhiu i vi cc ngi dng khc.

- Li lin kt v tuyn: da vo s iu ch v mc nhiu ca bng tn ph, tl li ca knh c thay i.

- Tr lp lin kt: xc nh suy hao ng truyn, li lin kt v tuyn, vnhiu th yu cu cc giao thc lp lin kt d liu l khc nhau ti cc bng tn

khc nhau. iu ny dn ti tr truyn dn gi lp lin kt d liu khc nhau.


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- Thi gian nm gi: cc hot ng ca ngi dng chnh c thnh hng ticht lng knh trong cc mng v tuyn thng minh. Thi gian nm gi l

thi gian m ngi dng v tuyn thng minh chim gi mt bng tn c cp

php trc khi b ngt. Hin nhin l thi gian nm gi cng lu th cht lng

cng tt. C thtng thi gian nm gi bng k thut chuyn giao thng k.1.4.2.2. Quyt nh ph

Khi tt ccc bng tn ph sn c, th cn phi la chn c bng tn ph

hp nht vi cc yu cu vQoS v cc c tnh ca ph. Do vy, qun l ph cn

phi bit c cc yu cu v QoS ca ngi dng. Da trn m tc d liu, t

l li chp nhn c, bin gii tr, m hnh truyn dn v bng tn truyn sc

xc nh. Sau da vo cc quy tc quyt nh m s chn la cc bng tn ph hp.

Cc quy tc chn la c xut da trn tnh cng bng v gi tr truyn thng.

1.4.3. Dch chuyn phDch chuyn ph c thc nh ngha l qu trnh mt ngi dng V tuyn

thng minh thay i tn s hot ng ca n. Qu trnh ny c gi l qu trnh

chuyn giao ph.

Trong mng V tuyn thng minh, chuyn giao ph xy ra khi cc iu kin

knh hin thi c biu hin xu i hoc c s trli ca ngi dng chnh. Cc giao

thc i vi cc tng khc nhau ca ngn xp mng phi ph hp vi cc tham s

knh. Mc ch ca vic dch chuyn ph trong v tuyn thng minh l m bo

qu trnh truyn dn xy ra lin tc v cht lng.

1.4.4. Chia s phTrong mng v tuyn thng minh, mt trong nhng thch thc chnh khi s

dng ph tn m l vic chia s ph tn. Khng ging nh cm nhn ph lin quan

chnh ti lp vt l, hay qun l ph lin quan ti cc dch v lp cao hn, cc chc

nng chia s ph tng t vi cc cng ngh phn bti nguyn v a truy nhp a

ngi dng trong lp MAC ca cc h thng truyn thng ang tn ti. Vn chnh

trong vic chia s ph l s cng tn ti ca cc ngi dng v tuyn thng minh v

cc ngi dng chnh v qun l cc bng thng khng lin tc c sn.

Da trn cc tiu chun khc nhau, cc k thut chia s ph c thc phn

loi theo nhiu cch khc nhau.

Cu trc mng

Tp trung Phn tn

Cch cp pht ph tn

Hp tc Khng hp tc

Cng ngh truy nhp ph tn

Overlay Underlay

Hnh 1.6. Phn loi cc cng ngh chia s phtn


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Theo cu trc mng, c th phn thnh chia s ph tp trung v khng tp trung

(phn tn), chia s ph tp trung ngha l ton b cc node trong mng gi thng tin

cm nhn ph ca chng ti n viu khin trung tm, sau n viu khin

trung tm s thit lp lc phn b ph; trong khi chia s phphn tn ngha l

ton b cc node t quyt nh truy nhp ph theo cch ring.Theo cch thc cp pht ph tn, c th phn loi thnh chia s ph hp tc v

khng hp tc, trong chia s ph hp tc mi node chia s kt qu cm nhn ph ca

n vi cc node khc, sau thut ton phn b ph s quyt nh da trn cc thng

tin ny; tri li chia s ph khng hp tc c ngha l cc node t n quyt nh chia s

ph.

Theo cng ngh truy nhp c th phn thnh chia s ph overlay v chia s ph

underlay. Overlay c ngha l ngi dng v tuyn thng minh truy nhp mng thng

qua h phkhng c s dng, thc t th l ghp knh phn chia thi gian gia cc

ngi dng v tuyn thng minh v ngi dng chnh, do nhiu ti ngi dng

chnh l nh nht. Underlay c ngha l mt ngi dng v tuyn thng minh c th

dng cng ngh tri phnh CDMA(a truy nhp phn chia theo m) v UWB (siu

di ng bng rng) chia s cng mt bng tn vi ngi dng cp php, trong

trng hp ny th ngi dng cp php s coi cc ngi dng thng minh nh l

nhiu. Hin nhin, khi ngi dng v tuyn thng minh bit ton b thng tin v h

thng cp php th overlay th hin tt hn underlay, v ngc li.1.5. Kin trc Vt l ca V tuyn thng minh

Kin trc tng quan ca b thu pht V tuyn thng minh c ch ra trn Hnh

1.7(a). Thnh phn chnh ca b thu pht V tuyn thng minh l u cui RF (RF

front-end) v khi xl bng gc. Mi thnh phn c th t cu hnh thng qua mt

bus iu khin thch ng vi mi trng RF bin i theo thi gian. Trong u cui

RF, tn hiu thu c khuch i, trn v chuyn i A/D. Trong khi xl bng gc,

tn hiu c iu ch/gii iu ch, c m ha/gii m. Khi xl bng gc ca Vtuyn thng minh v bn cht cng tng tnh bthu pht ang tn ti. Tuy nhin,

im mi V tuyn thng minh nm u cui RF. V vy, ta s tp trung vo u

cui RF ca V tuyn thng minh.

im mi ca b thu pht V tuyn thng minh l khnng cm nhn bng

rng ca u cui RF. Chc nng ny lin quan ti cc cng ngh phn cng RF nh

anten bng rng, khuch i cng sut, v b lc thch ng. Phn cng RF cho V

tuyn thng minh c khnng iu chnh ti bt k phn no ca di ph tn rng ln.

Cm nhn phcng cho php vic o lng trong thi gian thc cc thng tin ph tmi trng v tuyn.


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Tn s v

tuyn(RF)

B chuyn i

tng t-s(A/D)

X l bng

gc

Tingidng

Tngidng

iu khin(T cu hnh)

Thu

Pht

(a)

u cui v tuyn

X l d liu

AGC A/D

PLL

Anten bng rng

LNA

B lc RF

B khuch itp m nh

VCO

B trn

B lcla chn knh

iu khin li t ng

B chuyn itng t-s

(b)

Hnh 1.7. Kin trc vt l ca V tuyn thng minh(a) B thu pht ca V tuyn thng minh; (b) Kin trc u cui RF/tng tbng

rng.

Ni chung, kin trc u cui bng rng cho V tuyn thng minh c th miu

tnh trn Hnh 1.7(b).

u cui RF ca V tuyn thng minh bao gm cc thnh phn sau:

B lc RF: B lc RF la chn bng mong mun bng cch lc thng di tnhiu RF nhn c.

B khuch i tp m nh (LNA): LNA khuch i tn hiu mong mun trongkhi ng thi gim thiu cc thnh phn tp m.

B trn: Ti b trn, tn hiu nhn c c trn vi tn s RF ni, v cchuyn i thnh tn sbng gc hoc tn s trung tn (IF).


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Bdao ng iu khin bng in p (VCO): VCO to ra tn hiu ti mt tn snht nh vi in p cho trc trn vi tn hiu ti. Qu trnh ny chuyn

i tn hiu ti thnh tn sbng gc hoc tn s trung tn.

Vng kha pha(PLL): PLL m bo rng tn hiu c kha mt tn s nhtnh v c thc s dng to ra cc tn s chnh xc.

B lc la chn knh: B lc la chn knh c s dng la chn knhmong mun v loi b cc knh ln cn. C hai loi b lc la chn knh. My

thu chuyn i trc tip s dng b lc thng thp la chn knh, cn my

thu superheterodyne li s dng b lc thng di.

iu khin li tng(AGC): AGC duy tr li hoc mc cng sut ura ca b khuch i khng i qua mt di rng cc mc tn hiu u vo.

Trong kin trc ny, tn hiu bng rng c nhn thng qua u cui RF, cly mu bi b chuyn i tng t-s (A/D) tc cao, v vic o c c thc

hin pht hin ra tn hiu ca ngi dng chnh. Tuy nhin, y cn tn ti nhiu

hn ch trong vic pht trin u cui ca V tuyn thng minh.

Anten RF bng rng nhn cc tn hiu t cc my pht khc nhau hot ng ti

cc mc cng sut, cc bng thng v cc v tr khc nhau. Kt qu l, u cui RF

phi c khnng pht hin tn hiu yu trong mt di tn sng ln. Tuy nhin, kh

nng ny i hi phi c b chuyn i A/D tc vi GHz vi phn gii cao, m

iu ny th rt kh thc hin.

Trc khi thc hin chuyn i, b chuyn i A/D tc vi GHz cn phi

gim bt di ng ca tn hiu. iu ny c tht c bng cch lc cc tn hiu

mnh. V cc tn hiu mnh c th nm bt cu trong di ph rng ln, nn cn

phi c cc b lc ch V kh chnh (tunable notch filters). Mt cch khc na l s

dng nhiu anten sao cho vic lc tn hiu c thc hin trong min khng gian hn

l trong min tn s. Nhiu anten c th nhn tn hiu mt cch chn lc bng cch s

dng cc cng nghiu khin bp sng.Thch thc ch yu trong kin trc vt l ca V tuyn thng minh l pht hin

chnh xc cc tn hiu yu ca nhng ngi dng chnh qua mt di ph tn rng. Do

vy, vic thc hin u cui RF bng rng v b chuyn i A/D l vn hng u

trong cc mng V tuyn thng minh.

Phn tip theo, chng ta s xem xt m hnh tham kho khi thc hin V tuyn

thng minh da trn V tuyn nh ngha bng phn mm (SDRSoftware Defined

Radio). T thy c skhc nhau c bn nht gia V tuyn thng minh v V

tuyn nh ngha bng phn mm, ng thi thy c cc u im vt tri ca V

tuyn thng minh.


27/100



1.6. M hnh thc hin V tuyn thng minh1.6.1. V tuyn nh ngha bng phn mm (SDR).

Trc khi trnh by kin trc ca V tuyn thng minh, ta si s qua v v

tuyn nh ngha bng phn mm, n c coi l nn tng cho vic thc hin V tuyn

thng minh trong tng lai.

V tuyn nh ngha phn mm l mt h thng truyn thng khng dy c th

cu hnh li, trong cc tham s truyn dn (nh bng tn hot ng,phng thc

iu ch, giao thc ...) c thc iu khin mt cch tng. Chc nng ny c

thc hin bi cc thut ton x l tn hiu c iu khin bng phn mm. SDR l

cha kha thc thi V tuyn thng minh. Da theo vng hot ng ca n th SDR

c th l:

- Mt h thnga bng tn: SDR s h trnhiu bng tn khc nhau c sdung bi mt v tuyn (v d, GSM 900, GSM 1800, GSM 1900).

- Mt h thng a chun: SDR s h tr nhiu chun khc nhau (v d GSM,WCDMA, cdma2000, WiMAX, WiFi). Cc giao din v tuyn khc nhau vi

cng mt chun (v d IEEE 802.11a, 802.11b, 802.11g, 802.11n trong chun

WiFi) cng c thc h trbi SDR.

- Mt h thng h tra dch v: SDR s h trnhiu loi hnh dch v, v dnh thoi t bo hay truy cp Internet khng dy bng rng.

- Mt h thnga knh: SDR c th hot ng truyn/nhn d liu trn nhiubng tn cng lc.

V tuyn nh ngha phn mm s dng cc thit b k thut s kh lp trnh

thc hin x l d liu cn thit truyn v nhn cc thng tin bng tn c sti tn

s v tuyn. Cu trc tng qut ca bthu pht SDR c m tnh Hnh 1.8:

X l d liuX l bng tn

c sA/D

u cui vtuyn

Pht/

Thu

Tn hiu iu khinD liu

vo

D liura

Hnh 1.8. Cu trc tng qut b thu pht SDR

Hu ht cc thnh phn trong cu trc ca SDR (nh b x l tn hiu, b

chuyn i tng t - s, b xl bng tn c s...) u tng t vi v tuyn truyn

thng, ch khc ch l cc thnh phn ny trong SDR c thc iu khin bi cc


28/100



giao thc cc lp cao hn hoc c thc cu hnh li bi cc module v tuyn

thng minh.

Trong v tuyn nh ngha bng phn mm cc c tnh v tn s sng mang,

bng thng tn hiu, iu ch, v truy nhp mng u c nh ngha bng phn

mm. Ngy nay, cc SDR cng c thc hin cc mt m bo mt cn thit; m hasa li trc (FEC); v m ha ngun ting ni, hnh nh, hoc d liu trong phn

mm.

1.6.2. M hnh thc hin V tuyn thng minhNh cp trn SDR l c s thc hin V tuyn thng minh. L do rt

n gin: SDR cung cp mt mt bng v tuyn rt mm do, ta c th lp trnh

v iu khin thch ng bi mt khi gim st trung tm. Cc cng nghin t hin

ti, bao gm ADC, DDC, b tng hp tn s tc cao, phng php ch to vi int, khin cho SDR c th thc hin c vi chi ph rt hp l v kch thc nh

gn. Cc SDR hin ti c th thc hin V tuyn thng minh thc strong tng lai.

Hnh 1.9 so snh v tuyn thng thng, V tuyn c nh ngha bng phn

mm v V tuyn thng minh.

RF iu ch M ha To khung X l

Phn cng Phn mm

V tuynthng thng


Phn cng Phn mm

V tuyn nh nghabng phn mm


Phn cng Phn mm

V tuynthng minh

X l thng minh (cm nhn, quyt nh, chia s)

Hnh 1.9. So snh gia V tuyn thng thng, V tuyn c nh ngha bng phn

mm v V tuyn thng minh.Ts trn, ta c th thy rng, V tuyn thng minh c th thc hin c

hon ton ch da trn nhng thay i cu trc phn mm, ch khng phi thay i

cu trc phn cng bn trong nh cc h thng v tuyn trc y na. pht trin

V tuyn thng minh t SDR, ta ch cn thm vo SDR cc khi xl thng minh nh

DFS, TPC v IPD. im khc bit ch yu ca V tuyn thng minh so vi V tuyn


29/100



c nh ngha bng phn mm (SDR) l khnng thng minh, tng thch ng

nhanh chng vi sthay i ca mi trng v tuyn. Trong khi SDR ch c th thay

i cc quyt nh theo mi trng trong phm vi mt tp cc la chn c cu hnh

sn qua phn mm, th V tuyn thng minh c khnng t cu hnh, tc l n c th

thch ng ngay vi iu kin ca mi trng m khng cn cu hnh trc. Nh vy,V tuyn thng minh thch nghi vi mi trng ph; trong khi SDR li thch nghi vi

mi trng mng, v chng c mt phn chng ln nhau v chc nng.

SDR thch nghi

vi mi trngmng

CR thch nghi

vi mi trngph

Hnh 1.10. Quan h gia V tuyn thng minh v SDR

S khi ca mt V tuyn thng minh da trn cc module SDR c ch ra

trn Hnh 1.11, y c hai khi quan trng nht, mt khi l module my thu bao bi

cc ng gch ngang pha trn, v mt khi l module my pht c bao bi khi

ng gch ngang pha di ca s .

Khi u tin bn tri hnh v lAnten bng rng, khi ny ging nh ci cng

vo V tuyn thng minh, n thc hin iu khin bng tn V tuyn thng minh hot

ng bng tn s RF ca n. Mt V tuyn thng minh c th qut mt bng tn tng

i rng p ng vi sthay i ca mi trng, v do , bng tn tng cng cho

mt V tuyn thng minh nht nh s ph thuc vo cc ng dng v dch v ca n.

Trn hnh v, bng tn tng cng cho anten bng rng c biu th bi

N

i

if1

. Bng

tn tng cng ny phi c chia thnh Nphn, mi phn c gn mt SDR nhtnh hot ng.

Sau anten bng rng, b ghp song cngsiu khin anten chia s vi cc tn

hiu thu v pht c th tch hiu qu cc tn hiu i vo v tn hiu ra ngoi.Khi

la chn tn sngDFS c a vo trnh cc tn hiu radar ca mng IEEE

802.11a hot ng trong bng 5 GHz U-NII, v y DFS lin quan ti qu trnh la

chn tn s tng, nhm t c mt s mc tiu nht nh (nh trnh nhiu c hi

nh hng ti h thng v tuyn vi u tin cao hn) trong V tuyn thng minh.


30/100



Anten

bng rngB ghp

song cng

Cngnhthi

iu khincng sut pht

(TPC)

B tng hpthch ng

Pht hin thu bao c cp php(IPD)

Lachntnsng

(DFS)

T cu hnh

thng tin/

Phi hp

la chn

SDR-1 (f1)

SDR-1 (f2)

SDR-1

(fN)

Nhiu anten

u ra

u vo

Bng tn = fi

Hnh 1.11. S khi thc hin V tuyn thng minh da trn SDR.

C Nkhi SDR hot ng song song trong module my thu Hnh 1.11, v

mi khi sm nhim mt phn bng tn ring. L do s dng nhiu SDR song song,

thay v s dng mt SDR, l lng d liu cn x l trong mi phn bng tn khc

nhau (fi, trong i=1, , N), trc khi thc hin bt k loi quyt nh thng minh

no trong V tuyn thng minh, l rt ln. Mt khc, chng ta cng c th thc hin

mt V tuyn thng minh ch s dng mt khi SDR duy nht. Tuy nhin, trongtrng hp ny, SDR yu cu phi c nng lc xl cao thc hin tt c cc vic

x l d liu trong mt khong thi gian ngn.

Tt c d liu u ra sau sc a n mt khi, khi ny c nhim v

a ra cc quyt nh thng minh. Cc quyt nh ny bao gm vic la chn v kt

hp cc thng tin pht hin c, nhm c c cc thng tin u ra m ta thc

s mun.

Trong Hnh 1.11, module my pht thc hin nhim v gi thng tin.B tnghp thch ng(Adaptive Synthesizer) c nhim v to ra sng mang tham kho chnh

xc thc hin qu trnh iu ch v hot ng bin i nng tn. lm c nh

vy, module my pht cng cn cc thng tin hu ch t khi IPD, khi ny cung cp

biu nh v tn s sng mang hin thi, thi gian biu chng trnh ca my cp

ph, v cc thng tin v cng sut pht, Thng tin ny cn thit xc nh mc

cng sut pht chnh xc m bo vic truyn t V tuyn thng minh khng gy

nhiu vi nhng ngi dng hot ng. Cc chc nng tng t sc thc hin

trong khi Cng nh thi (Timing Gate), khi ny iu khin cc khe thi giantruyn, vic truyn t V tuyn thng minh s ch xy ra khi vng ph trng.


31/100



Kin trc phn lp chung cho s V tuyn thng minh ch ra trong Hnh

1.11 c minh ha trong Hnh 1.12, trong ch c hai lp (vt l v lin kt d liu)

c trnh by chi tit v tt c cc lp cao hn khc l cc ng dng ph thuc v do

ta khng cn quan tm y.

Cc lp cao hn

Giao thc qunl kt ni

Giao thcMAC

Giao thc qunl nhm

Lp con hi t

Ngn xpWWAN

Ngn xpWLAN

Ngn xpWPANLp lin kt d liu

Truyn d liu Qut ph o c knhiu khin cng

sut truynPht hin ngi

dng chnh

Lp Vt l

Cck

nhiukhinnhm

Hnh 1.12. Kin trc phn lp tng qut cho V tuyn thng minh

Qut ph(Spectrum scanning) l mt trong nhng chc nng quan trng nht

lp PHY ca V tuyn thng minh. y, tt c vng ph ca ton bbng tn hotng u c qut. Vic qut ny phi c thc hin lu li cc chu k ca tn s

sng mang, cho php V tuyn thng minh c th tm c ng khe thi gian trong

tn ssng mang ng gi d liu. iu ny si hi khnng xl bng tn ph

rng v sau l thc hin phn tch thi gian, khng gian v ph. V tuyn thng

minh cn trao i cc thng tin cm nhn trong vng n hot ng pht hin ra

nhng ngi dng ang gy nhiu ln nhau mt cch ti u. Vic hp tc gia nhng

ngi dng v tuyn thng minh khc nhau trong cng mt nhm truyn thng s rt

quan trng c tnh chnh xc nhiu.

o lng knh (Channel measurement) phi c s dng xc nh cht

lng ca cc knh qut c chia s vi nhiu ngi dng chnh. Cc thng s

knh ny (nh cng sut pht, tc bt, ) phi c xc nh da trn cc kt qu

o lng knh.

V tuyn thng minh phi c khnng hot ng ti tc truyn d liu, dng

iu ch bin i, cc s m ha knh khc nhau, v truyn cc mc cng sut khc

nhau. H thng MIMO cng c thc s dng trit nhiu khng gian v tngthng lng thng qua vic ghp knh. K thut OFDM cng c thc s dng


32/100



nng cao hiu qubng tn v hiu qu pht hin. Cc chc nng khc ca PHY, nh

TPC v IPD, c cp cc phn trc nn ta s khng trnh by y.

Lp lin kt d liu gm ba khi chnh, bao gm Giao thc qun l nhm, Giao

thc iu khin truy nhp phng tin (MAC), v Giao thc qun l kt ni. Gi s

rng bt k mt ngi dng thng minh no cng u thuc mt nhm ngi dngthng minh cp nht nh. Giao thc qun l nhm sc s dng phi hp tt c

nhng ngi dng thng minh trong cng mt nhm. Bt k ngi dng mi no cng

c th ly thng tin cn thit v nhm khi tham gia vo mt nhm nht nh. Giao thc

lin kt d liu c s dng la chn mt knh ph hp to ra kt ni truyn

thng. La chn ny nn c thc hin da trn cc thng tin ly c t vic qut

ph v IPD. Mt khi kt ni th cp (secondary link) c thit lp, cc giao thc lin

kt d liu c trch nhim duy tr kt ni. Giao thc MAC hot ng da trn cc

thng tin t c tPHY, nh qut ph v IPD Giao thc MAC quyt nh

cch thc truy nhp vo knh, ph thuc vo kiu knh chia s hot ng bi ngi

dng chnh.

Lp con hi t (Convergence Sublayer) trong lp lin kt d liu cung cp mt k

thut phi hp trong V tuyn thng minh hot ng trong cc mi trng khng

dy khc nhau, nh WWAN, WLAN, v WPAN,

1.7. Kt lun chng 1Sra i v pht trin ca V tuyn thng minh gii quyt c nhng hn

ch trong s dng ph tn hin nay. Cng ngh truy nhp ph tn ng cho php V

tuyn thng minh hot ng tt nht trong knh c sn. Chng 1 trnh by tng

quan v Cng ngh V tuyn thng minh gm nh ngha, cc nhim v chnh nh:

- Cm nhn ph: xc nh cc phn ph sn c v pht hin ra ngi dng ccp php khi ngi dng hot ng trong bng cp php.

- Quyt nh ph: la chn knh tt nht c sn.- Chia s ph: ng truy nhp ti cc knh vi nhng ngi dng khc.- Dch chuyn ph: bknh khi pht hin c ngi dng c cp php

hoc iu kin knh xu.

Ngoi ra, Chng 1 cng trnh by hot ng ca V tuyn thng minh thng

qua chu trnh thng minh, kin trc ngn xp cng nh kin trc vt l ca V tuyn

thng minh.


33/100

n tt nghip i hc Chng 2. Kthut ghp knh OFDM


CHNG 2. K THUT GHP KNH PHN CHIA THEO

TN S TRC GIAO (OFDM)

2.1. Gii thiu chngPhng thc truyn d liu bng cch chia nh ra thnh nhiu lung bit v s

dng chng iu ch nhiu sng mang c s dng cch y hn 30 nm.

Ghp knh phn chia theo tn s trc giaoOFDM (Orthogonal Frequency Division

Multiplexing) l mt trng hp c bit ca truyn dn a sng mang, tc l chia nh

mt lung d liu tc cao thnh nhiu lung d liu tc thp hn c truyn

ng thi trn cng mt knh truyn. OFDM l mt phng thc iu ch l tng

cho cc knh c p tuyn tn s khng bng phng.

Chng ny s gii thiu v khi nim, cc nguyn l c bn, v cc k thut

iu ch s dng trong OFDM. c bit, ta cng s phn tch k v k thut truyn

dn OFDM khng lin tc (NC-OFDM) m c ng dng chnh trong V tuyn

thng minh. ng thi phn tch v so snh hiu nng ca NC-OFDM vi cc phng

thc truyn dn khc. Cui chng s cp ti mt vi u nhc im ca h thng

OFDM.

2.2. Khi nim OFDMOFDM l k thut ghp knh phn chia theo tn s trc giao. OFDM phn ton

bbng tn thnh nhiu knh bng hp, mi knh c mt sng mang. Cc sng mang

ny trc giao vi cc sng mang khc c ngha l c mt s nguyn ln lp trn mt

chu k k hiu. V vy, ph ca mi sng mang bng khng ti tn s trung tm ca

tn s sng mang khc trong h thng. Kt qu l khng c nhiu gia cc sng mang

con.

2.3. Nguyn l c bn ca OFDMNguyn l c bn ca h thng OFDM l phn chia lung d liu tc cao

(Bng thng W) thnh N lung d liu tc thp v sau truyn chng ng thiqua nhiu sng mang con. Mt gi tr ln ca N to ra bng thng n l (W/N) ca

cc sng mang con hp hn bng thng nht qun ca knh (Bc). Cc sng mang n

l ch c fading phng v iu ny c thcb p cho vic s dng mt b cn

bng phn nhnh n l min tn sthng thng. S la chn sng mang con n l

sao cho chng trc giao vi nhau cho php cc sng mang con c th chng ln ln

nhau bi v tnh trc giao m bo s ring r ca cc sng mang con ti u cui my

thu. Phng php ny em li hiu qu ph tn tt hn so vi cc h thng FDM

khng cho php chng ln ph gia cc sng mang con.


34/100



Ch. 1 Ch. 10

Tn s(a)

Tn s(b)

Tit kim bng thng

Bng tnbo v

Hnh 2.1. a sng mang trc giao (a) v a sng mang thng thng (b)Hiu qu ph tn ca mt h thng OFDM c chra trong Hnh 2.1, trong

minh ha s khc nhau gia k thut a sng mang khng chng ln thng thng

(nh FDMA) v k thut iu cha sng mang chng ln (nh DMT, OFDM, ).

Nh ch ra trong Hnh 2.1 vic s dng k thut iu cha sng mang chng ln c

tht c hiu qu ph tn cao hn. Tuy nhin, vic chp nhn cc li ch ca k

thut a sng mang chng ln ng ngha vi yu cu phi gim xuyn nhiu gia

chng, l l do ta s dng tnh trc giao gia cc sng mang con iu ch.

Thut ngtrc giao ch mt quan h ton hc c bit gia cc tn s ca cc

sng mang con trong cc h thng OFDM c s. Trong h thng ghp knh phn chia

theo tn sthng thng, cc sng mang c tch bit v mt khng gian sao cho cc

tn hiu c thc thu bng cch s dng cc b lc v cc b gii iu ch thng

thng. Trong cc my thu nh vy, cc bng tn bo vc t gia cc sng mang

con khc nhau trong min thi gian, dn ti s lng ph hiu qu ph tn. Tuy nhin,

c th sp xp cc sng mang con trong mt h thng OFDM sao cho cc cnh bn

ca ph chng ln ln nhau v cc tn hiu vn nhn c m khng c nhiu sngmang ln cn. My thu OFDM v th c thc cu trc nh mt tp cc b gii iu

ch, chuyn mi sng mang xung bDC v sau ly tch phn trong mt chu k k

hiu khi phc d liu c pht. Nhng sng mang con ny c thc to ra c

lp tuyn tnh (v d trc giao) nu khong cch sng mang l bi s ca 1/T (T l chu

k k hiu).

Tnh trc giao ca cc sng mang con c duy tr c trong trng hp knh

phn tn bng cch s dng tin t vng (CP). CP l phn cui cng ca mt h thng

OFDM.


35/100



-5 -4 -3 -2 -1 0 1 2 3 4 5

1.0

0.8

0.6

0.4

0

0.2

-0.2

-0.4-6-7 6 7

Hnh 2.2. Phca mt sng mang con OFDM n l

-5 -4 -3 -2 -1 0 1 2 3 4 5

1.0

0.8

0.6

0.4

0

0.2

-0.2

-0.4

-6-7 6 7

0

Hnh 2.3 Phca k hiu OFDM

Hnh 2.2 m t ph ca mt sng mang n l v Hnh 2.3 m t ph ca mt

k hiu OFDM. Tn hiu OFDM c ghp knh bi cc ph ring l vi mt khong

cch tn stng ng vi bng thng truyn dn ca mi sng mang con nh trn

Hnh 2.2. Hnh 2.3 ch ra ti tn s trung tm ca mi sng mang con khng c xuyn

nhiu t cc knh khc. Bi vy, nu my thu hot ng tng quan vi tn s trung

tm ca mi sng mang con, n c th khi phc li d liu truyn m khng b nhiu.Thm vo , vic s dng k thut a sng mang da trn DFT, ghp knh phn chia


36/100



theo tn sc thc hin bi vic xl bng gc n gin hn x l thng di tn

km.

2.4. M hnh h thng OFDMMt vn quan trng trong h thng OFDM l vic ng dng bin i

Fourier (FT-Fourier Transform) vo iu ch v gii iu ch tn hiu. K thut ny

phn chia tn hiu ra thnh tng khi N s phc. S dng bin i Fourier nhanh

ngc IFFT (Inverse Fast Fourier Transform) cho mi khi v truyn ni tip. Ti pha

thu, bn tin gi i c phc hi li nh bin i Fourier nhanh FFT (Fast Fourier

Transform) cc khi tn hiu ly mu thu c. FFT l mt dng bin i Fourier ri

rc (DFT) nhng cho hiu qu tnh ton cao hn nn c dng trong cc h thng

thc t. K thut iu ch OFDM kt hp vi cc phng php m ha (coding) v

ghp xen (interleaving) thch hp cho php truyn d liu tc cao qua knh vtuyn vi tin cy cao.

Mt lc khi tng qut ca mt h thng thu pht OFDM im-im n

gin c chra nh Hnh 2.4 di y. Nguyn l c bn ca OFDM l chia lung

d liu tc cao t mt ngun d liu thnh N lung d liu tc thp hn. Cc

lung ny sau c iu ch mt cch c lp s dng MPSK (M-ary Phase Shift

Keying) hoc MQAM (M-ary Quadrature Amplitude Modulation). Cc lung ny

c truyn ng thi qua N sng mang con trc giao s dng b chuyn i ni tip

song song (S/P). Cc d liu qua cc sng mang con ny c tng hp li thnh

mt k hiu OFDM. Theo nh ngha ton hc, nu , k = 0, 1, 2, , N 1, l cck tu vo phc ca sng mang con th k ti thi im th m, N l s sng mang

con, v T l khong thi gian k hiu, th mt k hiu OFDM bt u ti trongk hiu bng tn c sdng phc c thc vit thnh:

(2.1)

trong , Tn hiu OFDM bng tn c s phc c nh ngha trong cng thc (2.1)

tng ng vi bin i Fourier ngc ca N k hiu u vo M-PSK (hoc M-

QAM). Tng ng ri rc trong min thi gian l bin i Fourier ri rc ngc

(IDFT). Bi vy, IDFT v bin i Fourier ri rc (DFT) c s dng cho iu ch

v gii iu ch cc chm sao d liu trn cc sng mang con trc giao.


37/100



B iuch MPSK

(hocMQAM)

S/P

Xl

trn

mintns

IFFT

X ltrn

minthigian

P/SCP

B iuch MPSK

(hocMQAM)

P/S

X ltrn

mintns

Bcn

bngFFT

Xl

trn

minthigian

LoiCP

S/P

x(n) Xm(n)

Xm.0

Xm,1

Xm,N-1

Ym,0

Ym,1

Ym,N-1

s(n)

(a) My pht

(b) My thu

r(n) x(n)

Xm(n)

(OC1)

(OC2)

(OC1)

(OC2)

^

^

Hnh 2.4. S khi tng qut ca mt b thu pht OFDM

Cc thut ton x l tn hiu ny thay th cc biu ch v gii iu ch trong pha v

pha vung gc (I/Q). Cc mu ri rc ca k hiu OFDM c cho bi:

(2.2)Khong bo v cho mi k hiu OFDM c chn ln hn tri tr knh mong

mun cc thnh phn a ng t mt k hiu khng th gy nhiu ti k hiu tip

theo. Khong bo v khng cn cha bt k tn hiu c bit no, nhng s mrng

theo chu k ca tn hiu OFDM trong khong bo vm bo rng cc bn sao tr ca

k hiu lun lun c mt s nguyn chu k vi khong FFT. iu ny c duy tr

cho ti khi tr nhhn khong bo v (v dnh tin t vng (CP)-l mt s lp li

ca mt on cui ca khi s liu v c gn ti u ca on ti s liu) v nh

hng ca knh phn tn theo thi gian bng vi mt vng cyclic. Da vo cc c

tnh ca vng cyclic, nhiu lin k t (ISI) c thc loi b bng phng php cn

bng n gin. Trngi duy nht i vi nguyn l ny l s gim hiu nng ca cc


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truyn dn OFDM. Tip sau b chuyn i song song-ni tip (P/S), tn hiu OFDM

bng gcs(n)c ly mu ln cao v a qua b chuyn i s-tng t(D/A)

chuyn tn hiu s thnh tn hiu tng t. Tn hiu OFDM bng gc sau c lc

thng thp, nng tn ti tn s trung tm mong mun bng cch s dng mt b trn

v mt b to dao ng ni (LO), v c khuch i bi b khuch i cng sut(PA).

Nh ch ra trn Hnh 2.4, my thu hot ng ngc li so vi my pht, trn

tn hiu RF thnh tn hiu bng gc cho xl. Sau , tn hiu c lc thng thp,

c chuyn i thnh tn hiu s s dng b chuyn i tng t-s (A/D), v ly

mu gim xung. Lung tn hiu ni tip ly mu theo thi gian ny c chuyn i

thnh cc lung song song vi mt b chuyn i S/P v tin tvng c loi b t

tn hiu tng hp nhn c, rm,n. Sau , DFT c s dng chuyn i d liu

min thi gian sang min tn s:

(2.3)

Cc lung song song ny sau c gii iu ch thnh d liu sv c kt

hp vi nhau s dng b chuyn i P/S thnh lung bt ni tip, cui cng c phn

pht ti b gp d liu.

Ti my thu, pht hiu khung l mt nhim v quan trng. Hn na, sng bv nh thi tn sc yu cu trc khi k hiu OFDM c thc gii iu ch

ng. Sc tnh v cn bng knh mt cch ph hp cng sc yu cu ty theo

cc i hi v BER ca h thng truyn thng. Mt on bit c gi trc mi

khung OFDM cho php my thu ng bv c tnh knh.

Da vo tng ca cc sng mang ti my pht, tn hiu OFDM tng hp trong

min thi gian c th th hin cc s bin i ln, m c c trng bi mt PAPR

ln. Khi xy ra PAPR cao, b chuyn i D/A v PA ca my pht phi c di ngln trnh s ct xn bin , dn n tng tiu th cng sut v gi thnh thit b

ca my pht. C th gim PAPR ca tn hiu OFDM bng cch sa i cc c trng

tn hiu trong min thi gian hoc min tn s, thng tin c pht ti my thu thng

qua knh iu khin (OC1) (nu cn thit). Thng tin ny s cho php my thu o

ngc cc thay i ti pha my pht gii iu chchnh xc cc thng tin pht.

Tng t, nu tn hiu OFDM c thay i trong min thi gian, th thng tin c

truyn ti my thu thng qua knh iu khin (OC2) (nu cn thit) nh ch ra trn

Hnh 2.4.


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2.5. Cc k thut iu ch s sdng trong OFDM2.5.1. iu ch QPSK

y l mt trong nhng phng php iu ch thng dng nht trong truyn

dn. Cng thc cho sng mang c iu ch PSK bn mc nh sau:

2cos[2 ( ) ] 0

( )

0 0;

i

Et t t T

S t T

t t T

(2.13)

Vi l pha ban u ta cho bng 0, ( ) (2 1)4

t i

Trong : i = 1, 2, 3, 4 tng ng l cc k t c pht i l 00, 01, 11, 10

T= 2.Tb (Tb l thi gian ca mt bit, Tl thi gian ca mt k t)

El nng lng ca tn hiu pht trn mt k t.

Khai trins(t)ta c :

2 2cos[(2 1) ]cos(2 ) sin[(2 1) sin(2 ) (0 )

( ) 4 4

0 ( 0; )

c c

i

E Ei f t i f t t T

S t T T

t t T

(2.14)

Chn cc hm nng lng trc chun nh sau:

12( ) sin[2 ]; 0ct f t t T T

(2.15)

2

2( ) sin[2 ]; 0

c bt f t t T T

(2.16)

Khi :

1 2( ) ( ) sin[(2 1) ] ( ) cos[(2 1) ]4 4

iS t t E i t E i

(2,17)

Vy bn im bn tin ng vi cc vector c xc nh nh sau :

1

2

sin[(2 1) ]4

( 1, 2,3, 4)

cos[(2 1) ]4

ii

i

E iS

S iS

E i

(2.18)

Quan h ca cp bit iu ch v to ca cc im tn hiu iu ch QPSK

trong khng gian tn hiu c cho bng sau:


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Bng 1.1. Thng sca iu chQPSK

Cp bit voPha ca tn hiu

QPSK

im tn hiu

Si

Tocc im bn tin

1 2

00 4/ S1 2/E 2/E

01 4/3 S2 2/E 2/E

11 4/5 S3 2/E 2/E

10 4/7 S4 2/E 2/E

Ta thy mt tn hiu PSK bn mc c c trng bi mt vector tn hiu hai chiu v

bn im bn tin nh hnh v:

Hnh 2.5. Biu tn hiu QPSK

2.5.2. iu ch QAM h thng iu ch PSK, cc thnh phn ng pha v vung pha c kt hp

vi nhau sao cho to thnh mt tn hiu ng bao khng i. Tuy nhin, nu loi b

iu ny v cho cc thnh phn ng pha v vung pha c thc lp vi nhau thta c mt s iu ch mi gi l iu bin cu phng QAM (Quadrature

Amplitude Modulation: iu chbin vung gc). s iu ch ny, sng

mang c iu ch cbin ln pha. iu chQAM c u im l tng dung lng

ng truyn dn s.

Dng tng qut ca iu ch QAM m mc (m - QAM) c xc nh nh sau:

0 01

2 2( ) cos(2 ) sin(2 ) (0 )i c i c

E ES t a f t b f t t T

T T

(2.19)

Trong :E0l nng lng ca tn hiu cbin thp nht.


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ai, bi: l cp snguyn c lp c chn tu theo v tr bn tin.

QPSK

16-QAM

64-QAM

Hnh 2.6. Chm tn hiu M-QAM

Tn hiu sng mang gm hai thnh phn vung gc c iu ch bi mt tp

hp bn tin tn hiu ri rc v thc tn l iu chbin vung gc.

C th phn tch Si(t) thnh cp hm c s:

1

2

2( ) sin(2 ) (0 )

2( ) sin(2 ) (0 )

i c

i c

t b f t t T T

t a f t t T T

(2.20)

2.6. NC-OFDM2.6.1. Khi nim NC-OFDM

Nh cp trc, phng php iu cha sng mang (MCM) rt thch

hp cho truyn dn d liu tc cao, nhvo khnng x l hiu qu mo trong

knh chn lc tn s. Hn na, cc k thut MCM chng hn nh OFDM c th cung

cp vic s dng ph tn nhanh cn thit, khi cc phn ca ph tn cp php ch b

chim gi bi cc ngi dng cp php v ngi dng khng cp php. iu ny t

c bng cch loi b cc sng mang m c khnng s gy nhiu vi cc ngi

dng khc. Dng tn hiu OFDM m trong vic la chn cc sng mang mt cch

khng lin tc t c tc d liu cao c gi l NC-OFDM.

Nh vy, NC-OFDM c thc nh ngha nh sau: NC-OFDM l kthut

truyn dn a sng mang da trn nn ca OFDM trong vic sdng cc sng

mang con cho truyn dn c la chn hp l m bo khng gy nhiu ti ccngi dng khc v tng dung lng ca h thng.


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Hnh 2.7 m t ph tn ca NC-OFDM 16 sng mang con vi 9 hot ng v 9

khng hot ng, trong cc sng mang con chng ln trc giao vi nhau.

Sng mang con hot ng Sng mang con tt

f0 f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14 f15 f16f

Hnh 2.7. Phtn ca cc sng mang con NC-OFDM

Cc sng mang con tng ng vi phang bngi dng chnh chim gi, c xc

nh tcc phng php cm nhn ph tn, s b tt. Trong cc phn tip theo ca

chng, chng ta s xem xt tng quan v cu trc khung lm vic ca NC-OFDM,hiu qu thc hin ca cc b thu pht NC-OFDM, v phn tch hiu nng ca h

thng.

2.6.2. Cu trc khung ca NC-OFDMS tng qut ca mt b thu pht NC-OFDM c chra nh Hnh 2.8. Xt

trong trng hp tng qut nht khng c tn hao, lung d liu tc caox(n)c

iu ch s dng M-ary PSK hoc M-ary QAM. D liu sau iu chc chia thnh

N lung c tc thp hn s dng b chuyn i S/P. y, cc sng mang controng b thu pht NC-OFDM khng cn phi hot ng tt ccng lc nh trong cc

truyn dn OFDM thng thng. Hn na, cc sng mang tch cc c t trong cc

bng ph khng b chim gi, c xc nh bi cc k thut cm nhn ph tn ng

v cc k thut c tnh knh. Sau cc lung d liu ny c iu ch ti cc tn

s trung tm sng mang con khc nhau s dng bin i Fourier nhanh ngc (IFFT).

Hnh bao ca tn hiu NC-OFDM bng tn c sdng phc, bao gm N sng mang

con lin tc trong khong thi gian [0,T] ti thi im thm, c cho bi cng thc

sau:

(2.21)

Trong , l k hiu ca sng mang con thk, Tl thi gian k hiu OFDM, v . K hiu sng mang con khng hot ng thklXm,k = 0. Cc mu ri rcca tn hiu NC-OFDM c cho bi:

(2.22)


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B iuch MPSK

S/P IFFT P/SCP

B giiiu chMPSK

P/S

Bcn

bngFFT

LoiCP

S/P

x(n) Xm(n)

Xm.0

Xm,1

Xm,N-1

Ym,0

Ym,1

Ym,N-1

s(n)

(a) My pht NC-OFDM

(b) My thu NC-OFDM

r(n) x(n)

Xm(n)

Thng tin Tt/M sng mang con

La chn sng mangcon trng

Thng tin Tt/M sng mang con

T cc php ocm nhn ph tn

Hnh 2.8. S tng qut ca mt b thu pht NC-OFDM sdng khi La chn

sng mang con trng.

My thu hot ng ngc so vi my pht, trn tn hiu RF thnh bng tn c

s x l, r(n).Sau , tn hiu c chuyn i thnh cc lung song song s dngb chuyn i S/P, CP c loi b, v k thut FFT c p dng chuyn d liu

t min thi gian sang min tn s. Sau khi b mo gy ra bi knh s dng cc k

thut cn bng, d liu trong cc sng mang con tch cc c ghp knh s dng b

chuyn i P/S, v c gii iu ch thnh tn hiu ti cu trc ca u vo tc

cao gc, .Khi la chn sng mang con trng ti my pht NC-OFDM hot ng theo

chu k chn lc thng tin v ph chim gi tcc php o cm nhn ph. Sau ,

cc sng mang con ng vi cc truyn dn ngi dng hin thi c tt i ti my

pht trnh nhiu ti cc ngi dng cp php chnh. Thng tin ny c th c


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truyn ti my thu thng qua knh iu khin trc khi xy ra bt k mt qu trnh

truyn dn d liu no, do d liu trn cc sng mang con tch cc c iu ch

mt cch ng n.

Vc bn th s to v nhn tn hiu NC-OFDM kh ging vi tn hiu OFDM.

Tuy nhin, vi tnh trng thiu ph tn lin tc ang tng ln, th cc k thut NC-OFDM a ra u th rt quan trng, v dnh n c th h trhiu qu v phn pht

ph tn ng cho cc truyn dn tc d liu cao. Di y l mt s lnh vc

nghin cu pht trin v thc thi h thng NC-OFDM:

c tnh hiu nng: NC-OFDM thch ng nhanh vi vic s dng ph tn,in vo cc khong trng ph sn c mt truyn dn bng thng ri rc

chim gi bi cc ngi dng khc (hin ti hoc cp php) trong khi khng

gy ra li. V cng sut ca cc sng mang con trng c thc phn phi liti cc sng mang con hot ng ci thin t s tn hiu trn nhiu (SNR)

trong cc h thng NC-OFDM, nn hiu nng tc li bt ca chng (BER) c

thc ci thin khi so snh vi h thng OFDM thng thng.

Vn t scng sut nh trn cng sut trung bnh: mt tn hiu OFDM ltng ca cc tn hiu c lp c iu ch trn mt vi sng mang con trc

giao bng thng ging nhau. Bi vy, khi kt hp chng li, tn hiu OFDM c

th to ra cc nh cng sut ln, trong khi cng sut trung bnh vn gimc

thp. L mt bin i ca OFDM, cc tn hiu NC-OFDM cng gp phi vn tng t. Khi xy ra hin tng PAPR cao, b chuyn i D/A v b khuch

i cng sut ca my pht s yu cu di ng ln trnh hin tng ct xn

bin , do tng cng sut tiu th v gi thnh thit b b thu pht. Bi vy,

cn thit phi nghin cu gim PAPR ca tn hiu OFDM v NC-OFDM.

Hiu quiu chv gii iu ch: nh chng ta thy cc phn trc, bthu pht OFDM c s dng cc khi IFFT v FFT. Thut ton FFT lm cho

iu ch v gii iu ch cc sng mang con hiu qucao hn lin quan ti

phn cng v s phc tp trong tnh ton. Tuy nhin, mt b thu pht NC-

OFDM c th c mt vi sng mang con khng c kch hot trnh nhiu

ti cc truyn dn ngi dng hin thi. Cc sng mang con khng hot ng

ny s c gi tr 0 khi vo cc khi IFFT v FFT. Do vy, cc ti nguyn phn

cng ca FFT khng cn x l qu ti v cc tnh ton vi u vo 0 l khng

cn thit.

K thut NC-OFDM a ra cch thc s dng cc sng mang con khng lin

tc rt linh hot i vi cc truyn thng d liu tc cao cho php bi V tuynthng minh.


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2.6.3. Hiu nng ca NC-OFDMVic la chn k thut truyn dn lp vt l l mt quyt nh rt quan trng

khi thc thi V tuyn thng minh. t c tc cn thit cho truyn dn vi

bng tn cp php chim gi bi nhng ngi dng chnh, cc b thu pht da trn a

sng mang l s chn la ph hp nht. Bn cnh khnng v hiu cc sng mangcon c th gy nhiu vi ngi dng khc th cc bthu pht a sng mang cng c

th cung cp tc d liu cao ti mc li c th chp nhn c. Mc d c mt

vi b thu pht a sng mang ang c thc thi nhng ph bin nht l OFDM v

CDMA a sng mang (MC-CDMA). K thut NC-OFDM t c tc d liu cao

thng qua vic la chn s dng mt s lng ln sng mang con khng lin tc,

trong khi ng thi trnh nhiu ti cc truyn dn ngi dng chnh bng cch v hiu

cc sng mang con ln cn ca n.

Trong phn ny chng ta si phn tch hiu nng ca NC-OFDM th hin qua

xc sut li ca bthu pht, ng thi so snh NC-OFDM vi MC-CDMA.

hiu c cc u im cng nh nhc im khi thc thi NC-OFDM trong

V tuyn thng minh, u tin chng ta so snh cht lng ca k thut ny vi MC-

CDMA v OFDM thng thng. Bng 2.2 th hin s so snh ny.

Bng 2.2. So snh cht lng ca h thng MC-CDMA, OFDM v NC-OFDM

Cc c tnh MC-CDMA OFDM NC-OFDMSng b Linh hot ph Thng lng Mo u Schu li N/A PAPR

(Trong thhin b thu pht vi hiu nng tt nht)

Mt vi k thut iu ch da trn DFT rt nhy cm vi dch tn s v dch

thi. Tuy nhin, tn ti mt s k thut ng b s dng cc sng mang con hoa tiu

khong cch u nhau trong min tn s. Mc d OFDM thng thng c th tn dng

cc sng mang con hoa tiu v bng thng truyn dn ca n lin tc, nhng c NC-

OFDM v MC-CDMA khng th s dng cc sng mang con hoa tiu ny, v chng

c th c t trong ph b chim gi v b v hiu. Kt qu l gii php ny


46/100



khng p dng c vi hai k thut ny, do phi cn ti nhiu bin php phc tp

trong vic ng b ha.

(a) Knh AWGN

(b) Knh Rayleigh ba ng.Hnh 2.9. Hiu nng BER ca b thu pht NC-OFDM (cc ng lin nt) v MC-

CDMA (cc ng gch) i vi mc chim gi(ISO) phthay i.

C NC-OFDM v MC-CDMA u rt linh hot trong vic s dng ph tn,

in y cc khong ph c sn trong bng thng truyn dn ring rc chim

gi bi cc ngi dng khc (ngi dng ng thi v ngi dng khng cp phpkhc). Tt c khnng m OFDM thng thng c th lm l truyn trong phn ln


47/100



nht cha b chim gi, nu bng thng truyn dn ca n khp vi khong trng u

tin. Tuy nhin, s linh hot phi vi NC-OFDM v MC-CDMA dn ti tng mo

u truyn dn, trong trng thi hot ng ca mi sng mang con phi c chia

s gia my pht v my thu. Hn na, nu ph b chim githay i nhanh th yu

cu phi cp nht thng xuyn.V NC-OFDM da trn nn OFDM thng thng, nn cng bnh hng bi

PAPR, trong khi vn ny li t xy ra trong h thng MC-CDMA do n s dng

k thut tri ph trong min tn s. Mc d PAPR nh hng trong h thng NC-

OFDM nhng c mt vi k thut c thc p dng gim PAPR ca b thu pht.

Vi vic v hiu cc sng mang con trong vng ln cn cc ph chim gi,

NC-OFDM c th hon thnh nhim v ny m khng lm gim khnng chu li v

cc sng mang con c lp tng i vi nhau. Tuy nhin, cc sng mang con ca bthu pht MC-CDMA khng c lp nhvo tri ph trong min tn s. Kt qu l kh

nng chu li ca h thng MC-CDMA gim khi cc sng mang con b trng.

Hnh 2.9 (a) l kt qu phn tch hiu nng xc sut li bt (BER) ca b thu

pht NC-OFDM v b thu pht MC-OFDM hot ng trong knh AWGN vi t l

sng mang con b v hiu l khc nhau. Khi cc sng mang con b v hiu l 0% th c

hai b thu pht c cng hiu nng khi hot ng trong knh AWGN. Khi phn trm

sng mang con b v hiu tng ln th hiu nng ca hai b thu pht bt u khc nhau.

Hiu nng ca b thu pht NC-OFDM tng nh so vi ng 0%, cn hiu nng cab thu pht MC-CDMA gim nhanh theo stng ca cc sng mang con b v hiu.

Hnh 2.9 (b) ta thy, trong knh Rayleigh ba ng th hiu nng ca hai b

thu pht khng khc nhau nhiu. Nhng nhn chung th hiu nng ca cc b thu pht

NC-OFDM tt hn so vi cc b thu pht MC-CDMA.

2.7. u nhc im ca OFDMT nhng c im phn tch trong chng ny, ta c th rt ra mt vi u

v nhc im ca OFDM.

u im:

S dng bng tn hiu qu. H thng OFDM c th loi b hon ton nhiu gia cc k hiu ISI v gia

cc sng mang ICI bng cch chn thm khong bo v.

Ph hp vi cc h thng truyn dn bng rng, do nh hng ca ca phntp v tn s i vi cht lng h thng c gim nhiu so vi h thng

truyn dn n sng mang.


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S dng vic m ha knh thch hp h thng OFDM c th khi phc licc k hiu b mt do hin tng chn la tn s.

t b nh hng vi khong thi gian ly mu hn so vi h thng n sngmang.

H thng c cu trc thu n gin. Nhc im:

ng bao bin ca tn hiu pht khng bng phng. iu ny gy ramo phi tuyn cc b khuch i cng sut pha pht v thu.

S dng khong bo v trnh c nhiu phn tp a ng nhng li gimi mt phn hiu sut ng truyn, do bn thn khong bo v khng

mang thng tin.

Do yu cu v trc giao gia cc sng mang ph, h thng OFDM rt nhycm vi hiu ng Doppler cng nh s dch tn v dch thi gian do sai s

ng b.

2.8. Kt lun chng 2Chng 2 cp mt cch tng qut v k thut ghp knh phn chia theo

tn s trc giao (OFDM), mt trng hp c bit ca truyn dn a sng mang,

nguyn l c bn l chia nh mt lung d liu tc cao thnh nhiu lung d liu

tc thp hn sau truyn ng thi trn cng mt knh truyn, cc sng mang conny l trc giao vi nhau nhm m bo trnh nhiu gia cc sng mang v tng tc

ca ton b h thng. OFDM p dng bin i Fourier vo vic iu ch v gii

iu ch tn hiu. Bin i Fourier nhanh (FFT) v bin i Fourier nhanh ngc

(IFFT) c ng dng vo h thng OFDM lm tng tc v hiu nng tng th ca

h thng ln ng k. ng thi OFDM cng s dng cc phng php iu chnh

M-PSK v M-QAM t c hiu nng mong mun. OFDM a ra mt vi u

im trong truyn dn nh: cho php d liu tc cao c truyn song song vi tc

thp trn cc bng hp, khnng cho hiu sut ph cao, khnng chng li fading

chn lc tn s, khnng loi tr nhiu xung, v khnng xl fadinh a ng v

fadinh chn lc tn s mnh m.

Bn cnh , Chng 2 cng gii thiu k thut truyn dn OFDM khng

lin tc NC-OFDM, NC-OFDM l mt k thut da trn OFDM trong n c kh

nng v hiu (tt) mt s sng mang con nht nh trnh gy nhiu nh hng ti

cc ngi dng hin thi v gim c cc x l khng cn thit cho phn cng.

Chnh u im ny khin cho NC-OFDM c ng dng trong cc h thng Vtuyn thng minh. Ngoi ra, ta cng phn tch v so snh c hiu nng ca h


49/100



thng NC-OFDM so vi cc h thng OFDM thng thng v h thng MC-CDMA,

t thy r c cc u th ca NC-OFDM trong mi trng truy nhp ph tn ng

c s bin i ca t l sng mang con b tt.

Chng sau ta si tm hiu chi tit hn v h thng V tuyn thng minh ng

dng nn tng k thut truyn dn OFDM.


50/100

n tt nghip i hc Chng 3. V tuyn thng minh trn nn OFDM


CHNG 3. V TUYN THNG MINH TRN NN OFDM

3.1. Gii thiu chngNh cp trong Chng 2, OFDM l cng ngh v ang c ng dng

rng ri trong cc h thng truyn thng khng dy hin ti v n c tim nng c thp ng trc tip cc yu cu ca V tuyn thng minh hoc vi mt vi thay i nh.

OFDM c s dng thnh cng trong nhiu cng ngh khng dy nh WLAN,

WMAN, v DVB Tip theo, ta s tho lun vng dng ca OFDM v c th l

NC-OFDM trong vic thc thi V tuyn thng minh. Ta cng sa ra cc u th ca

OFDM so vi cc cng nghkhc v ng thi cng ch ra cc thch thc cn tn ti

trong h thng V tuyn thng minhOFDM.

3.2. V tuyn thng minhOFDMng dng ca OFDM vo V tuyn thng minh em li nhiu xu hng cng

nh nhiu thch thc mi trong vic thit k h thng. M hnh V tuyn thng minh

trn nn OFDM c minh ha nh trong Hnh 3.1. Phn my thng minh chu trch

nhim to cc quyt nh thng minh v cu hnh cc tham s v tuyn cngnh cc

tham s tng vt l (PHY). Cc c hi phc nhn dng bi n v quyt nh da

trn thng tin t bmy chnh sch cng nh d liu cm nhn ph cc b v mng.

B my chnh sch cung cp thng tin lin quan ti cc chnh sch hin ti ti

b my thng minh xem xt da trn v tr ca h thng. iu ny m bo v

tuyn thng minh s khng s dng bt hp php cc dng sng hoc bt k chnh

sch no vi phm. Mt khc, n v cm nhn ph tn cc b x l thng tin ph tn

v xc nh cc ngi dng cp php ang truy nhp ph, cc c t tn hiu cng nh

bng thng hay mc cng sut ca chng v cc c hi ph pht hin c c th

c khai thc bi V tuyn thng minh.

Khi cc thng tin yu cu c, n v quyt nh c th to mt quyt nh

hnh ng tt nht cho h thng. Quyt nh bao gm vic la chn m ha knh,phng thc iu ch, cc tn s hot ng, v bng thng ph hp. Ti giai on ny,

cng ngh OFDM t ra hiu quhn so vi cc cng ngh truyn dn khc vi cc c

tnh thch ng v mm do ca n. Ch cn thay i cc tham s ca OFDM (Bng 3.1

ch ra mt vi tham s v d) v cc tham s v tuyn, h thng thng minh c th lin

lc vi nhiu cng ngh truy nhp v tuyn khc trong mi trng, hoc n c th ti

u s truyn dn da vo cc c im ca mi trng.

Mch v tuyn c chia thnh mt phn s (IF s, ADC, v DAC s) v mt

phn tng t (v tuyn tng tiu chnh c bng phn mm). C hai phn u


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n tt nghip i hc Chng 3. V tuyn thng minh trn nn OFDM


c th cu hnh li bi bmy thng minh tng s linh hot ca h thng. iu ny

bao gm vic iu khin tn s hot ng, bng thng, cc b lc, v cc b trn.

Ngay c cc tham santen (nh s anten, to bp) cng c thc cu hnh ci

thin hiu nng ca h

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