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THONG TIN DI ONGCHNG I:

TONG QUAN VE HE THONG GSM

I . LCH S PHAT TRIEN CUA HE THONG THONG TIN DI ONG GSM:ien thoai di ong ra i tnhng nam 1920, khi o ien thoai di ong c s

dung nh la cac phng tien thong tin gia cac n v canh sat My. Dch vu ienthoai di ong mai en au nam 1960 cac dang s dung c va khi o no ch la cacsa oi thch ng cua cac he thong ieu van. Cuoi nhng nam 1980 ngi ta nhan thayrang cac he thong to ong tng t khong the ap ng c nhu cau ngay cang tang vaothe kysau neu nh khong loai bo c cac han che co hu cua he thong nay: (1) phanbo tan so rat han che, dung lng thap; (2) tieng on kho chu va nhieu xay ra khi may

di ong chuyen dch trong moi trng fadinh a tia; (3) khong ap ng c cac dchvu mihap dan oi vi khach hang; (4) khong cho phep giam ang ke gia thanh cuathiet b di ong va c s ha tang; (5) khong am bao tnh bao mat cua cac cuoc goi; (6)khong tng thch gia cac he thong khac nhau, lam cho thue bao khong the s dungc may di ong cua mnh nc khac.

Giai phap duy nhat e loai bo nhng han che tren la phai chuyen sang sdungky thuat thong tin so cho thong tin di ong cung vi cac ky thuat a truy nhap mi.

He thong thong tin di ong s dung ky thuat a truy nhap phan chia theo thigian (TDMA) au tien tren the gii c ra i Chau Au vaco tren goi la GSM .Ban au he thong nay c goi la nhom ac trach di ong (Group Special Mobile)

theo ten goi cua mot nhom c CEPT( Conference Of European Postal AndTelecommunications Administrations Hoi ngh cac c quan quan ly vien thongvabu chnh Chau Au) c ra e nghien cu tieu chuan. Sau o e tien cho viec thngmai hoa GSM c goi la he thong thong tin di ong toan cau (GSM: GlobalSystem for Mobile Communications).

GSM c phat trien t nam 1982 khi cac nc Bac Au gi e ngh en CEPTe quy nh mot dch vu vien thong chung chau Au bang tan 900MHz. Nam 1985 hethong so c quyet nh sdung va thang 5 nam 1986 giai phap TDMA bang hepc chon la.

Viet Nam he thong thong tin di ong so GSM c a vao t nam 1993,

hien nay ang c cong ty VNPT (VMS, GPC), VIETTEL, SPT, EVN khai thac rathieu qua.


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I I . MANG GSM:

Cau truc mot mang te bao n gian gom co:1.Tr am di ong M S: Mobile StationLa mot thiet b oc lap, lam nhiem vu ket noi vi cac thiet b ben ngoai nh

may tnh, Fax. MS bao gom thiet b di ong ME (Mobi le Equipment) va Module nhandang thue bao SIM ( Subcriber Identity Module).

2.Phan he tram goc BSS: Base Station Subsystem

BSS noi vi MS thong qua giao dien vo tuyen va cung noi en NSS. BSS baogom tong ai thu phat tram goc BTS (Base Transceiver Station) va bo ieu khien tramgoc BSC (Base Station Control ler). Mot BSC ieu khien nhieu BTS. Mot bo phanTRAU (Transcoder/Rate Adaption Uni t) thc hien ma hoa va giai ma ong thi ieuchnh toc o cho viec truyen so lieu.

VOICE CIRCUITS

MOBILE TELEPHONESWITING OFFICE

DEDICATED VOICEGRADE CIRCUITS

SWICHES ANDPROCESSOR

CELL SITE

DATA

LINK

DATALINK

VOICELI N

K

CELL #1 CELL #2

MOBILE UNIT


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He thong GSM s dung mo hnh OSI (Open System Interconnection). Co 3giao dien pho bien trong mo hnh OSI: giao dien vo tuyen gia MS va BTS, giao dienA gia MSC va BSC va giao dien A-bis gia BTS va BSC.

Hnh 1.3 BSS = BTS + BSC va cac giao dien.3. Phan he chuyen mach NSS: Network and Switching SubsystemNSS trong GSM la mot mang thong minh. NSS quan ly giao dien gia ngi s

dung mang GSM vi ngi s dung mang vien thong khac, no bao gom:

Trung tam chuyen mach dch vu di ong MSC (Mobi le Service Swi tchingCentre): Co nhiem vu thiet lap cuoc goi en va t thue bao di ong. Mot MSC ieukhien nhieu BSC.

Chc nang tng tac mang IWF (InterWorking Function): la cong giaotiep gia ngi dung mang GSM vi cac mang ngoai

Thanh ghi nh v thng tru HLR (Home Location Register): cha tat cacac thong tin ve thue bao, va cac thong tin lien quan en v tr hien hanh cua thuebao,

MSC

BSCBTS

BT

S

BTS

GIAO DIEN ABIS

GIAO DIEN A

GIAO DIENVO TUYEN

BSSMS

MSC


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nhng khong chnh xac. HLR co trung tam nhan thc AUC (Authentication Centre) vathanh ghi nhan dang thiet b EIR (Equipment Identi ty Register).

Thanh ghi nh v tam tru VLR (Visitor Location Register): Noi en mothoac nhieu MSC, lu tr cac thong tin hien hanh e cap nhat cho MSC, nh v tr thuebao hien hanh (chnh xac hn trong HLR).

MSC cong (GMSC): e thiet lap cuoc goi, cuoc goi c nh tuyen enGMSC, GMSC se tm ung so thue bao HLR cha so thue bao c goi. GMSC cogiao tiep vi mang ngoai.

Ngoai ra trong mang GSM con co phan hevan hanh OSS (OperationSubSystem). Co 3 vung trong OSS :

(1) Chc nang van hanh mang va duy tr,(2) Quan ly thue bao, bao gom ca viec lap phieu va tnh cc,(3) Quan ly thiet b vo tuyen.

Hnh 1.4 To chc cua OSS.

I I I .MO HNH LP CUA GSM:He thong GSM s dung mo hnh OSI (Open System Interconnection) bao gom 5

lp: Truyen dan TX (Transmission), Quan lytai nguyen vo tuyen RR (Radio Resourcemanagement), Quan ly di ong MM (Mobility Management), Quan ly giao tiep CM(Communication Management), Van hanh, bao dng va duy tr OAM(Operation,Administration and Maintenance).

Lp TX thiet lap mot ket noi gia MS va BTS.

Lp RR bao gom cac giao thc quan ly giao tiep qua giao dien vo tuyen vacung cap mot ng truyen on nh gia MS va BSC.

Lp MM quan ly d lieu thue bao va cac hoat ong xac thc .Lp CM co cac chc nang sau :(1) Thiet lap duy tr va giai phong cuoc goi.(2) Quan ly cac dch vu bosung. Cho phep ngi dung co mot so ieu khien

cuoc goi cua ho trong mang.

Subscriptionmanagementand charging

Network

operationand

maintenance

NSS

NSS

Mobileequipmentmanagement

ME

SIMMS


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(3) Dch vu ban tin ngan SMS (Short Message Service). L ien quan en cacdch vu ban tin ngan iem ti iem. Mot trung tam dch vu ban tin ngan co the ket noinhieu mang GSM.

Hnh 1.5 Mo hnh lp cua GSM.

IV.TRUYEN DAN VO TUYEN:1.Truyen dan tn hieu thoai:

Mot tn hieu thoai tng t 4-KHz c chuyen oi sang tn hieu so64kbps, sauo no c giam xuong con 13kbps trc khi ieu che. ay dung toc o 13kbps thaycho 64kbps e phu hp vi kenh bang hep 13kbps. Mahoa tieng noi thng dung haicach sau:

Kch thch xung eu RPF (Regular Pulse Exci tation): phat xung nhieue mo phong cho tieng noi.

Ma hoa d oan tuyen tnh LPC (Linear Prediction Coding): Phat dangsong tieng noi bang cach dung bo loc vi he so nhan la 8 c phat vi mot khungtieng noi 20ms, dung 260 bi t e bieu dien mot khung 20ms. Co hai cach truyen dan tnheu thoai trong GSM, o la lien tuc va khong lien tuc.

2.Truyen d lieu:Toc o truyen d lieu cao nhat cua GSM la 9600bps va co hai che o truyen

khac nhau la trong suot va khong trong suot.Che o trong suot van hanh theo c che sa sai. Co ba toc o d lieu ap dung

cho che o nay la 2400, 4800 va 9600 bps. Sau khi them cac thong tin bo tr th toc otr thanh 3.6 , 6 va 12 kbps.

OAMCM

MM

RR

Transmission

UserOperator


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MS tm cum FCCH, sau o tm mot cum SCH tren cung mot tan so e at cs ong bo . Tiep theo, MS thu BCCH tren nhieu khe thi gian va chon mot cell rieng trang thai ngh.

b. Kenh chung ng len:Kenh chung ng len duy nhat la kenh truy cap ngau nhien RACH (

Random Access Channel). RACH cho phep MS chon etruy xuat cuoc goi. Co hai toco RACH/F (vi toan toc), va RACH/H (vi ban toc ).

c.Kenh bao hieu:Tat ca cac kenh bao hieu la mot trong nhng kenh vat ly, va ten cua

kenh c da tren chc nang logic cua no. Kenh ieu khien ket noi cham SACCH (Slow Associated Control

Channel): la mot TCH toc o thap dung cho bao hieu ho tr va cac thu tuc khong khancap ma chnh la chuyen giao cuoc goi gia cac cell. No dung vi toc o 1/8.

Kenh ieu khien ket noi nhanh FACCH ( Fast Associated Control

Channel): Dung cho viec thiet lap cel l, nhan thc thue bao va yeu cau chuyen giaocuoc goi gia cac cell. Kenh ieu khien oc lap SDCCH (Stand alone Dedicated Control

Channel): Hoat ong vi toc o thap, dung kenh TCH/8. Phuc vu cho viec cap nhat vaqua trnh thiet lap cuoc goi khi mot TCH c ch nh.

Khe vo tuyen c phan phoi en ngi s dung chi khi cuoc goi ac thiet lap xong. Co hai che o la danh rieng va roi. Viec hoat ong che o naola phu thuoc vao ng len hay ng xuong. Trong thuat ng GSM, ng xuong latn hieu phat ra t tram goc en MS va ngc lai cho tn hieu ng len.

Kenh thoai/ d lieu: moi khe thi gian cua kenh thoai cha 260 bi ts

cho moi khoi. Toan bo khoi co 316 bits. Moi khe thi gian kenh d lieu cha 120 hoac240 bits cho moi khoi.

Che o kenh: bi v s qu gia cua pho tan so, nen khong co mot ngidung nao c cap mot kenh danh rieng.

Che o danh rieng: dung TCH trong suot cuoc goi c thiet lap vadung SACCH e cap nhat v tr che o danh rieng. TCH va SACCH la cac kenhdanh rieng cho ca ng len va ng xuong.

Che o ngh: trong luc khong co cuoc goi, th nam kenh ng xuong trang thai roi: FCCH, SCH, BCCH c phat quang ba mot cach eu an; PAGCHva CBCH gi mot ban tin moi 2s. Trong suot che o ngh, MS lang nghe cac kenh

ng xuong, va dung SDCCH eghi nhan mot s lien ket v tr vi mot tram goctng ng trong mang.

VI .PHNG PHAP A TRUY NHAP:GSM las ket hp cua FDMA va TDMA. Tong so kenh trong FDMA la 124,

va moi kenh rong 200KHz. ng len s dung khoang tan so 935 960MHz vang xuong s dung khoang tan so 890 915MHz. TDMA dung moi kenh la200KHz, mot khung co tam khe thi gian, mot khung keo dai trong 4.615ms.


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1.Phng phap FDMA.FDMA la gan cac kenh en tng ngi rieng re. Cac kenh nay c gan da

tren cac yeu cau ma ngi s dung can.Trong suot thi gian cuoc goi tien hanh, khong co mot user nao dung chung

bang tan so o. FDMA co nhng ac iem sau: Kenh FDMA ch phuc vu duy nhat mot thue bao tai mot thi iem. Neu mot kenh FDMA khong c dung, th no trang thai ngh va

khong c dung bi cac user khac e tang kha nang cua he thong. Sau khi a gan mot kenh thoai, tram goc va MS thu va phat mot cach

lien tuc va ong thi.

Hnh 1.6 Cach gan bang tan so cua FDMA.

Bang thong cua kenh FDMA la tng oi nho (khoang 30KHz) khimoi kenh phuc vu duy nhat mot song mang. FDMA thng c ap dung cho he thongbang hep.

Thi gian cua k hieu la ln so vi thi gian tre trung bnh. V vay giaothoa k t ISI thap va khong can s dung Equalizer.

He thong FDMA khong phc tap nh TDMA. FDMA la phng phap truyen dan lien tuc, nen cac bi ts can cho muc

ch nh tuyen la t hn TDMA. FDMA can mot cau truc loc RF chat che giam thieu giao thoa kenh

ke.

Tong so kenh co the hoat ong ong thi trong mot he thong FDMA la:

c

guardtot

B

BBN

2 (1.1)

Btot: Tong so pho c phan phoi.Bguard: Bang bao ve tai canh cua cac kenh .Bc: Bang thong cua moi kenh.

Frequency

Code

Time

Channel1

Channel2

Channel3

Ch

annelN


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2.Phng phap TDMA:He thong TDMA chia pho votuyen ra cac khe thi gian (Time slot) va moi khe

ch cho phep ngi s dung c phat hoac thu.Nh trong hnh 1.7, moi user chiem mot khe thi gian c lap lai mot cach

chu ky, mot kenh c xem nh la mot khe thi gian ma no lap lai moi khung. Motkhung co N khe thi gian. Khong nh he thong FDMA, he thong TDMA truyen dand lieu khong lien tuc va ch s dung cho d lieu so va ieu che so. Viec truyen dan tcac user khac nhau c ket hp lai thanh mot khung lap lai nh hnh 1.8

Hnh 1.7 Phng phap phan chia kenh trong TDMA.

Mot khung bao gom nhieu khe thi gian. Moi khung co bi t m au, bi t thong tinva bit ket thuc.

Trong TDMA bit m au cha thong tin ve a ch va ong bo ma ca tram gocva MS dung e nhan dang. Cac ac iem cua TDMA:

TDMA chia mot tan so song mang n cho mot user. So khe thi giantrong moi khung phu thuoc vao nhieu he so nh ky thuat ieu che, bang thong

Truyen dan d lieu he thong TDMA la khong lien tuc nhng dien ratheo cum.

Qua trnh x l chuyen giao cuoc goi gia cac cell la n gian, MS co

the lang nghe t cac tram goc khac trong suot thi gian ngh. TDMA dung cac khe thi gian khac nhau cho phat va thu, v vaytruyen song cong c yeu cau.

Viec can bang thch ng luon can thiet trong he thong TDMA, bi vtoc o truyen dan trong TDMA ln hn so vi FDMA.

Trong TDMA thi gian bao ve nen c toi thieu. Qua trnh ong bo khung oi hoi rat chat che.

Frequency

Code

Time

Channel 1

Channel 2

Channel N

Timesl

ots


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Tong so kenh trong he thong TDMA:

c

guardtot

B

BBmN

)2( (1.2)

m: la so user cc ai trong mot kenh vo tuyen.

Hnh 1.8 Cau truc khung cua TDMA.3.Hang so thi gian tr e gia ng len va ng xuong:Viec anh so cac khe cua cac khe ng len la lay khe thi gian ng xuong

bang cach lam tre ba khe. Trong trng hp nay, MS se khong phat va thu ong thibi v hai khe nay la khac nhau ve vat ly. Tretruyen dan khi MS xa tram goc.

4.Cac loai khe thi gian khac:Moi cell cung cap mot xung clock chuan cho cac khe thi gian. Moi khe thi

gian c anh so TN (Time Slot Number) ma no c biet bi tram goc va MS. TN

c lap lai mot cach chu ky.5. Cum va chuoi hng dan: TDMA, tn hieu c phat dang cum. Chu k cua cum mang bien o tn

hieu phat bat au t gia tr 0 cho en gia tr chuan cua no. Mot goi bits c phat bitn hieu ieu che. Sau o bien o giam ve 0. Cum nay dien ra tai MS phat hoac taiBTS neu cum ke khong c phat.

Trong mot cum co cac bit uoi va cum hng dan. Cac bits uoi gom co ba bitstai iem bat au va ket thuc cua moi cum, no nham cung cap thi gian bao ve.

Chuoi hng dan la chuoi c biet may thu, no hng dan cho bo Equal izer.Co cac loai cum sau ay:

(1). Cum bnh thng dung trong TCHFlag Flag

3 57 1 26 1 57 3Tail Information Training sequence Information Tail

(2). Cum truy xuat dung RACH hng ng len.

Preamble Tail bitsInformation Message

Slot 1 Slot 2 Slot 3 Slot N

Trail bitsSync bits Guard bitsInformation Data

Mot khung TDMA


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Flag

7 41 1 35 3Tail Training sequence Information Tail

(3). Cum F va S. Cum F c dung FCCH va co nh dang n gian. Tat ca co148 bi ts zero, a ra mot dang song thuan sine. 5 cum S trong moi 51x8 chu ky BPc dung SCH. Mot cum S nh sau:

Flag Flag3 38 1 64 1 38 3

Tai l Information Training sequence Information Tai lVII . THU TUC VAN HANH CUA M ANG:

Thu tuc van hanh cua he thong c chia ra bon phan vamot thu tuchandoff.

1. MS khong khi ong:Khi mot thue bao khong trang thai goi, no se quet 21 kenh thiet lap trentong so 416 kenh. Sau o no chon mot kenh manh nhat va khoa kenh nay. Sau 60squa trnh t nh v c lap lai.

2. Cuoc goi khi ong t MS:Thue bao bam so can goi, kiem tra xem so can goi co ung hay khong, bam

nut send . Mot yeu cau cho dch vu c gi bang cach chon mot kenh thiet lap atc t qua trnh t nh v. Tram goc thu tn hieu nay, va no chon mot hng Antentoi u cho kenh thoai dung. Tai thi iem nay, tram goc cung ong thi mot yeu cauen trung tam chuyem mach di ong MTSO ( Mobile Telephone Switching Office) vi

mot toc o d lieu cao. MTSO chon mot kenh thoai thch hp cho cuoc goi, va tramgoc thong qua nh hng Anten e ket noi vi MS.

3. Cuoc goi khi ong t mang:Thue bao A muon goi cho thue bao B, no se quay so cua thue bao B. Trung

tam vung se nhan dang so nay va gi thang en MTSO. en lc MTSO se gi motban tin tm goi da tren so thue bao nay en cac tram goc va tai ay tien hanh giaithuat tm kiem. Moi tram goc phat mot ban tin tm goi tren kenh thiet lap cua no. MSnhan dang c so nay tren mot kenh thiet lap manh nhat , khoa o va ap ng vetram goc. MS theo cac lenh e c danh rieng kenh thoai vacuoc goi a san sang.

4. Ket thuc cuoc goi:Khi MS tat may phat, mot tn hieu ac biet (tn hieu n tone) c phat

en cac tram goc va hai ben cung giai phong cuoc goi. MS tiep tuc kiem tra tm goithong qua kenh thiet lap manh nhat.

5. Thu tuc handof f:Trong luc cuoc goi dien ra, hai thue bao cung tren mot kenh thoai. Khi

mot MS di chuyen ra khoi vung phu song cua tram goc cha no th tn hieu thu tr nenyeu. e cuoc goi khong b ngat, tram goc hien hanh se yeu cau mot thu tuc chuyen


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giao cuoc goi en mot kenh tan so mi mot tram goc mi ma khong gay ra ngat cuocgoi hoac bat au mot cuoc goi mi.

VII I . QUAN LY VO TUYEN:1. Quan ly tai nguyen vo tuyen RR (Radio Resoucr e management):Trong mang vo tuyen, kenh vo tuyen c phan phoi cho viec thiet lap,

chuyen giao va giai phong cuoc goi tren mot nh hng cuoc goi. Co ba chc nangquan ly la nh v, chuyen giao va di ong. Viec thc hien chc nang RR yeu cau motso giao thc gia MS va mang.

a. Giao thc ng truyen:Viec trao oi thong tin bao hieu phai c gi va hieu bi moi thiet b ho

tr bao hieu. Hau het cac chc nang trao oi thong tin c phan phoi en cac thiet bkhac nhau. Co ba loai giao thc e cung cap cho viec trao oi thong tin.

Giao thc ng truyen vo tuyen RLP (Radio L ink Protocol) actrng trong GSM la LAPDm.

LAPD la giao thc ng truyen thch ng vi kenh D cua ISDN. Phan chuyen ban tin MTP (Message Transfer Part) la giao thcdung cho mang bao hieu so 7.

Toc o ban tin bao hieu cua giao thc ng truyen vo tuyen la 22.8kbps.Toc o ban tin bao hieu cac giao thc ng truyen khac la 64kbps.

b. Giao dien lien ket vi giao t hc ng tr uyen:

Giao dien GiaoMS BTS LAPDmBTS BSC LAPD

BSC MSC MTP( Giao thc SS7)MSC/VLR/HLR mang SS7 MTP( Giao thc SS7)MSC MSC ( bao hieu l ien quan ti cuocgoi)

TUP( Telephone User Part)

BSC chuyen tiep ( bao hieu l ien quan ticuoc goi)

ISUP ( ISDN User Part)BSS MAP (MAP/B)

MSC MSC MAP (Mobility Application Part)


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Hnh 1.9 Cac giao thc t MAP/C en MAP/I

2. Quan l di ong M M: Mobility ManegementCac tn hieu khong lien quan en cuoc goi tng ng vi giao thc trong MSC

ma no khac so vi MSC hoac HLR khac va c nhom lai thanh MAP. Chung ta cothephan biet chung bang MAP/X, ay X co the la B, C, D hoac E.

MAP/B: giao thc gia BSC va MSC chuyen tiep.MAP/C: giao thc gia GMSC va mot HLR.MAP/D: giao thc gia MSC/HLR khac va HLR.MAP/E: giao thc gia cac MSC.Ngi dung he thong Cellular yeu cau quan l di ong cho cac hoat ong cap

nhat v tr, chuyen giao va di ong. Mot hoat ong chuyen giao xay ra khi mot kenhthoai thay oi khi mot MS i vao mot cell khac trong luc cuoc goi ang dien ra. Diong lakha nang khi ong cuoc goi trong he thong mang nay va phan phoi no enhe thong cac mang khac bang cach dung MM va quan l cap nhat v tr.

a. Quan l cap nhat v tr :

Thue bao luon c l ien ket vi mang di ong mat at PLMN (Publ icLand Mobile Network) thng tru cua no. Khi di chuyen no se lien ket vi mangPLMN tam tru. Chung ta co the nhan dang cuoc goi t PLMN tam tru t v tr cua MS.

Trong qua trnh x l chon la PLMN, MM thng tm cel l trongPLMN thng tru. Neu khong co dch vu hien hanh, user co the chon che ot ong(tm kiem mang ) hoac che o thao tac bang tay (tm kiem user) e tm c PLMNphu hp. Trong trng hp dch vu gii han, MM tiep tuc kiem tra ch 30 song mang

(B)

(B)

MSC

VLR

EIR

HLR

GMSC

MS

MAP/F

MAP/I

MAP/D

MAP/CMAP/GMAP/E

MAP/C

SMS - gateway

MAP/H

VLR

MSC


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manh nhat. Dch vu gii han luon quan tam en vung phu song tai bien gii cua cacquoc gia lan can.

b. Chon la cell :Viec chon la cel l tot nhat t 1 MS phu thuoc vao 3 yeu to.

(1) Mc o thu cua tn hieu thu tai MS.(2) Cong suat phat cc ai cua MS.(3) Hai he so p1 va p2 ac trng cua cell. ay la chuan C1.

C1 = A Max(B,0)A = Trung bnh mc thu p1B = p2 cong suat RF ln nhat cua MSP1 = mot gia tr gia 110 va 48dBmP2 = mot gia tr gia 13 va 43dBm

Ca hai gia tr p1 va p2 c phat quang bat cac cell.Cong suat ln nhat cua MS = 29 en 43dBm.

Thuat giai chon cell: Mot SIM phai c chen vao C1 ln nhat c chon bang cach at c C1 t cell tng ng ; C1 phai

ln hn 0. Tat ca cac cell phai khong can tr dch vu.

c. Hoat ong nhan thc:Hoat ong nhan thc bao ve mang chong lai s truy xuat bat hp phap.Giai oan 1: Mot ma so nhan dang thue bao ca nhan PIN (Personnal

Identification Number ) bao ve SIM. PIN c kiem tra bi SIM tai cho, sau o SIMkhong bao gi c gi ra ng truyen vo tuyen.

Hnh 1.10 Qua trnh tnh toan nhan thc.

Giai oan 2: Mang GSM tien hanh mot cuoc kiem tra bang cach gi mot songau nhien RAND. Mot so RAND 128 bits c gi t mang en MS va no tron vi heso bao mat cua MS la K I, thong qua mot giai thuat x l la A3, no a ra mot


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SRES(Signed Result). Dai 32 bi ts. Sau o SRES c gi en mang t MS e chngthc.

d. Ma hoa:

Ma hoa e chong lai viec nghe len. MS dung RAND thu c t mangva tron vi K I thong qua mot giai thuat khac la A8 va phat ra Kc (64 bi ts). Chuoi matma c phat ra t Kc.

So khung va Kc di chuyen en giai thuat mat ma A5 va phat ra S2 (114bi ts), chung c a vao cong EX-OR ma au vao la chuoi bi ts kiem tra 114 bi ts vachuoi mat ma S2 nh hnh 1.11.

e. Hoat ong nhan thc thue bao hoat ong bao mat:SIM (pha MS) va AUC ( pha mang) la ni cha khoa K I cua thue bao.

Khoa K I khong bao gi c phat ra khong gian. Ca hai eu tnh toan A3 va A8.

3. Quan ly giao t iep CM: Communication ManagementLp CM cung cap cac dch vu vien thong nh thoai, fax va d lieu cho

ngi s dung thong qua lp RR va MM nh trnh bay trong hnh 1.12Ngi dung GSM bao gom may goi va may b goi. Chc nang quan l

cua CM la ieu khien cuoc goi, quan l dch vu va dch vu ban tin ngan.

a. ieu khien cuoc goi CC: Call Control


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CC quan ly hau het cac dch vu hung mach ( nh thoai, d lieu) thongqua MSC/VLR, GMSC, IWF va HLR. Chc nang cua CC la thiet lap, duy tr va giaiphong cuoc goi. e thiet lap cuoc goi, so cua MS phai c gan. MS/ISDN la so ISDNcua MS. So di ong MS (MSRN) la so nh tuyen, mot so khac co the cho phep thuebao GMS hoac nhan dang thue bao quoc te IMSI (International Mobi le SubscriberIdentity) va cung cap bi MS e truy xuat vao mang quoc te.

b. Chuyen giao: Handoff hay HandoverThuat giai chuyen giao cua GSM khong c xay dng thanh mot

chuan. o la ac trng cua chuyen giao ho tr di ong MAHO (Mobile AssistanceHandover). MS quet cac song mang vo tuyen theo ch dan cua BTS. No theo doi cackhe thi gian, cac khe nay khong c gan e no thu tn hieu. Trong thng hp nay,theo yeu cau cua BTS, cng o tn hieu cua mot song mang vo tuyen ac trng co trong mot khung thi gian, so o o c gi thang ve BTS e ho tr qua trnh x lychuyen giao. Qua trnh c goi la MAHO. MSC dung hai thong tin e quyet nh cho

viec chuyen giao. Hai thong tin nay la:(1) Cng o ma MS thu c tai cac BTS lan can.(2) Cng o tn hieu ma BTS thu c tai MS.

c. Quan ly cac dch vu bo sung SSM: Supplementary Service ManagementCC cung cap cac dch vu bo sung nh ch cuoc goi, nh hng cuoc goi, va

tra li t ong. SSM la dch vu quan ly iem en iem. Mot trung tam dch vu SSM(SSM SC ) co the noi vi nhieu mang GSM. SSM bao gom hai chc nang:

(1) Ket thuc t ong ban tin ngan;(2) Khi ong t ong ban tin ngan.4. Quan ly mang NM: Network Management

Mot trung tam MS giam sat cac hoat ong sau:(1) Quan ly va giam sat thue bao;(2) Lap phieu va tnh cc ;(3) Duy tr;(4) Giam sat hoat ong cua thue bao e cung cap ma nhan dang cho ME vi so

nhan dang thiet b di ong quoc te IMEI (International Mobile Equipment Identity).(5) Trong mang quan ly vien thong GSM (TMN), tat ca cac may van hanh va

duy tr tao thanh mot mang ma chung c ket noi en tat ca cac may ieu khien lulng. GSM Q3 la mot giao thc quan ly mang cho chc nang van hanh he thong vamay ieu khien lu lng.

IX.QUY HOACH CELL:X. NHIEU TRONG HE THONG:

1. Nhieu ngoai:Nhieu ngoai la loai nhieu ben ngoai cac thiet b va mach ien. Co ba loai

nhieu ngoai : Nhieu kh quyen, nhieu ben ngoai trai at va nhieu nhan tao.a. Nhieu kh quyen.


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Nhieu kh quyen la at tnh ien t nhien cua kh quyen trai at. Nhieu khquyen thng c goi la nhieu tnh ien va anh hng cua no la xuat hien tieng laoxao thng nghe cac loa khi khong co tn hieu. Tnh ien thng dang ap ngxung ma s phan tan nang lng trai rong tren tan so cua no. Bien o nang lng t lenghch vi tan so cua no.

(a) (b)

Hnh 1.13 Anh hng cua nhieu len tn hieu.(a) Tn hieu khong nhieu.(b) Tn hieu co nhieu.

b. Nhieu ngoai t r ai at:Nhieu ngoai trai at bao gom cac tn hieu ien bat au t ben ngoai bau kh

quyen cua trai at. No c chia lam hai loai la nhieu mat tri va nhieu vu tru.

Nhieu mat tri: c phat ra t sc nong cua mat tri. Nhieu vu tru: la nguon nhieu c phan phoi mot cach lien tuc qua dayngan ha, cng o nhieu tng oi nho.

c. Nhieu nhan tao:La loai nhieu sinh ra do hoat ong cua con ngi. No co cng o manh

trong vung thanh th va cong nghiep, nen co luc c goi la nhieu cong nghiep.2. Nhieu noi:

La loai giao thoa ien ma c phat ra t ben trong mot thiet b hoac machien.

a. Nhieu nhiet:

Sinh ra do s di chuyen nhanh va ngau nhien cua electron ben trong vatdan do s di chuyen nhiet. S chuyen ong cua electron tang len khi nhiet o tang.

Cong suat nhieu nhiet:N = KTB (1.11)

K: hang so Boltzmann (1.38.10-23J/0K)B: bang thongT: nhiet o tuyet oi (0K)

t

V

t

V


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b. Nhieu shot :Gay ra bi en mot cach ngau nhien cua song mang tai phan t au ra cua

thiet b ien t nh la diode, FET, BJT.c. Nhieu thi gian vt:

Mot so thay oi cua chuoi song mang khi chung i t au vao en au racua mot thiet b sinh ra mot dang tn hieu khong hp le, bien thien ngau nhien goi lanhieu thi gian vt.

3. ien ap nhieu:Mo hnh tng ng cho nguon nhieu ien tr:

RI : la ien tr noi.RN : la ien tr tai.VN : la nguon ien ap nhieu.

Khi RN = RI, ien ap2

N

R

VV , khi o cong suat nhieu tren tai R la:

R

V

R

V

KTBN NN

4

2 2

2

(1.12)

RKTBVN 42 (1.13)

RKTBVN 4 (1.14)

4. Meo hai:Meo hai la khi cac hai khong mong muon cua mot tn hieu c sinh ra khi

cho tn hieu goc i qua mot bo khuech ai phi tuyen. Meo hai tong cong c tnh:

100.%lfundementa

higher

V

VTHD (1.14)

%THD : meo hai tong cong phan tram.22

3

2

2 ... nhigher VVVV

V fundemental = ien ap hieu dung cua hai bac mot.5. Meo qua ieu che:Meo qua ieu che sinh ra cac tn hieu ma tan so la tong hoac hieu cua cac

tan so cua cac tn hieu goc au vao khi chung c tron vao mot thiet b phi tuyen. Tanso tong va hieu goi la tch cheo (Cross Product):

Cross Product = mf1 nf2 (1.15)f1, f2 la cac tan so c ban .


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n,m la cac so nguyen dng t 1 en vo cung.6. Ty so cong suat tn hieu t r en nhieu:

La ty so mc cong suat tn hieu tren mc cong suat nhieu.

N

S

P

P

N

S (1.16)

PS : cong suat tn hieu (W).PN : cong suat nhieu (W).

N

S: c tnh bang dB th

N

S

P

PdB

N

Slog10)( (1.17)

Neu tnh S/N qua ien ap th :

N

S

V

VdB

N

Slog20)( (1.18)

VS : ien ap tn hieu (V).VN : ien ap nhieu (V).

7. Noise figure va Noise factor :Noise factor (F) va Noise f igure (NF) la he so dat trng dung e cho thay ty

so tn hieu tren nhieu suy giam bao nhieu khi noi qua mot mach hoac mot day mach.

Noise factor la ty le cuaINN

S

vaOUTN

S

:

rationoisetosignalOutputrationoisetosignalInputF

____

(1.19)

Noise figure la Noise factor bieu dien dB:NF = 10logF (1.20)

Noise factor va Noise figure cua mach ghep casecaded:

1121

3

1

21

...

1....

11

n

n

TAA

F

AA

F

A

FFF (1.21)

FT : Noise factor tong.F1: Noise factor cua mach 1.Fn : Noise factor cua mach n.A1 : o li cua mach 1.An : o li cua mach n.Va Noise f igure tong cua mach c tnh.

NFT(dB) = 10logFT. (1.22).


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CHNG I I :KY THUAT IEU CHE SO TRONG MANG

IEN THOAI DI ONG

I .KY THUAT IEU CHE BPSK:1. ieu che BPSK:

Tn hieu ieu che BPSK co bien o khong oi va pha thay oi theo hai gia trnh phan au vao la 0 va 1.

Song mang hnh sine:SC = AC.cos(2fCt) (2.1)

Gia s ban au pha bang 0.Chuoi d lieu nh phan au vao la d(t), bieu dien di dang RNZ vi bit 1 la

+1V va bit 0 la1V.Tn hieu ieu che BPSK la:

)2cos(.2

)( tfT

EtS C

b

bBPSK (d(t) = 1) (2.2)

hoac :

)2cos(.2

)( tfT

EtS C

b

bBPSK (d(t) = 0) (2.3)

vi Tb: la chu ky bi t.

bCb TAE2

2

1

: la nang lng cua mot bit.T (2.2) va (2.3), ta ket hp lai tng ng dang cua cua tn hieu BPSK la:

)2cos(.2

)()( tfT

EtdtS

C

b

bBPSK (2.4)

Hnh 2.1 S o ieu che BPSK2. Pho va bang thong cua t n hieu BPSK :

Tn hieu BPSK co the bieu dien di dang hnh bao phc:

d(t)

Cos(2fCt)

SBPSK(t)


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SBPSK(t) = RegBPSK(t).exp(j2fCt)(2.5)

Vi gBPSK(t) la hnh bao phc cua tn hieu c cho bi:

)(.

2

)( tdT

E

tgb

b

BPSK (2.6)

Mat o pho cong suat PSD (Power Spectral Density) cua hnh bao phc la:2

0

sin2)(

b

bg

fT

fTEfP

BPSK

(2.7)

PSD cua tn hieu BPSK c tnh bang cach dch PSD cua hnh bao phc lentan so song mang tng ng:

22

)

)(

)(sin

)(

(sin

2

)(

bC

bC

bC

bCb

BPSK

Tff

Tff

Tff

TffEfP

(2.8)

Bang thong cua tn hieu BPSK c xap x khi no cha 90% nang lng cua tnhieu:

b

bT

RBW6.1

6.1 (2.9)

o th xac suat loi bi t trong ieu che BPSK vi moi trng nhieu trang.

Pe

)(0

dBN

Eb


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3.Thu tn hieu BPSK:Tn hieu BPSK tai may thu:

)2cos(.2

)()( tfT

EtdtS C

b

b

BPSK (2.10)

: la o lech pha cua tn hieu tng ng vi thi gian tre trong kenh truyen, no phuthuoc vao khoang cach gia may phat va may thu va o dch pha sinhra do bo khuechai at trc bo giai ieu che cua may thu.

Yeu cau may thu la phai khoi phuc lai ung chuoi d lieu d(t). Ky thuat giaiieu che ket hp hay ong bo BPSK oi hoi phai co s ong boro rang ve pha vatan so cua song mang tao ra tai may thu. S o khoi cua mot may thu BPSK c trnhbay nh hnh 2.2:

Tn hieu BPSK sau khi i qua mach bnh phng la:

)2(2cos12

12)()2(cos.

2).( 2 tf

T

Etdf

T

Etd C

b

b

C

b

b (2.11)

Sau khi i qua mach loc bang thong va chia hai th tn hieu tai au ra cua khoiphuc song mang la:

Hnh 2.2 S o may thu BPSKSC

= cos(2fC + ) (2.12)Tn hieu SC

va BPSK c a en bonhan va tn hieu au ra cua bo nhan la:

tfT

Etdtf

T

Etdtf

C

b

b

C

b

b

C 22cos2

1

2

1.

2).(2cos.

2).(.2cos (2.13)

Cos(2fCt + )

Square lawdevice

BandpassFilter 2fC

FrequencyDivider f/2

Integrate andDump circuit

Bit Synchronizer

m(t)cos2(2fCt + )

m(t)cos(2fCt + )

Cos2(2fCt + ) Cos(4fCt + )m(t)cos(2fCt + )

Demodulated signalm(t)


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Tn hieu (2.13) c vao mach tch phan va xa, sau o se i vao mach quyetnh.

ien ap au ra cua mach tch phan:

b

b

b

kT

Tkc

b

b

b

kT

Tk

b

b

bb

T

EkTd

dttf

T

EkTddt

T

EkTdkTv

b

b

b

b

2

22cos

2

12

2

12)(

11

(2.14)

Nh vay chung ta a khoi phuc lai c chuoi d lieu d(t).4. Bieu dien hnh hoc cua t n hieu BPSK:

Chon mot tn hieu la c s la trc chuan:

tfT

tu cb

2cos.2

)(1 (2.15)

Ta co :

tutdEtS bBPSK 1.)( (2.16)Khoang cach gia hai tn hieu : bEd 2

Hnh 2.3 Khoang cach gia hai tn hieu BPSKXac suat loi trong BPSK:

0

2

2

1

N

E

erfcP

b

e (2.17)Vi Eb la nang lng cua bit .

N0 mat oxac suat nhieu trang.I I . KY THUAT IEU CHE QPSK:

1. Nguyen ly ieu che va pho cua QPSK :Tn hieu ieu che QPSK co dang:

2

12cos2

)( itfT

EtS c

S

SQPSK , 0 t TS , i = 1,2,3,4 (2.24)

Chuoi nh phan au vao m(t) codang NRZ vi Tb = 1/Rb.

b

bSR

TT 22 ; ES = 2Eb

Bien oi lng giac cua (2.24), ta co:

tfiT

Etfi

T

EtS c

S

S

c

S

S

QPSK 2sin

21sin.

22cos

21cos.

2 (2.25)

0b

EbE


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at tfT

tQ cS

2cos2

1 (2.26)

tfT

tQ cS

2sin2

2 (2.27)

)(21sin.)(21cos. 21 tQiEtQiEtS SSQPSK (2.28)

Pho cua QPSK tng t nh pho cua BPSK, nhng ay Eb va Tb c thaythe bang ES va TS:

22

22

2

2sin

2

2sin

sinsin

2

bc

bc

bc

bc

b

Sc

Sc

Sc

ScS

QPSK

Tff

Tff

Tff

TffE

Tff

Tff

Tff

TffEfP

(2.29)

Xac suat loi trong QPSK:

0

,

2

N

EQP bQPSKe (2.30)

Qua (2.30) va (2.17), ta thay xac suat loi cua BPSK va QPSK la nh nhau. Tuynhien, vi QPSK th hieu suat bang thong gap 2 lan BPSK. Bang thong cua QPSK xapx bang Rb.

o th xac suat loi bi t trong ieu che QPSK vi moi trng nhieu trang2. Ky thuat ieu che va giai ieu che QPSK :

Pe

)(0

dBN

Eb


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S o ieu che QPSK:

Hnh 2.6 S o may phat QPSKTn hieu m(t) sau khi i qua bo Serial to parallel converter se tao ra hai dongbit mI(t) ( cung pha vi m(t) ) va mQ(t) ( lech pha 90

0 ). Hai tn hieu nay c ieu cheoc lap qua boieu che can bang nh tn hieu BPSK. Sau o hai tn hieu nay c laytong e c tn hieu QPSK nh trong bieu thc (2.28).

Bo loc BPF at tai au ra cua cua bo ieu chee gii han pho cong suat cua tnhieu QPSK, tranh gay ra nhieu cho cac kenh lan can.

S o khoi cua bo giai ieu che QPSK.Hnh 2.7 S o khoi cua may thu QPSK.

Bo loc BPF at trc may thu co nhiem vu loai bo nhieu ngoai bang va giam giaothoa kenh ke.

Tn hieu tai au ra cua bo loc c chia lam hai phan, hai phan nay c avao hai bo giai ieu che ket hp. au ra cua hai bo giai ieu cheket hp ( mot cungpha va mot lech pha 900 ) c a vao mach quyet nh va sau o ta c hai chuoid lieu nh phan. Hai chuoi nay c don kenh e c d lieu mong muon.

LPF

LPF

BPF

900

LocaloscillatorSerial to

parallelconverter

Rb/2

Rb/2

QPSKsignal

Inputdata

Rb(m(t))

ReceivedSignal

BPF

LPFDecisionCircuit

CarrierRecoveryCircuit

900

SymbolTimingRecoveryCircuit

LPF

Decision

Circuit

RecoverySignalMultiplexer


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I I I .KY THUAT FSK:1.Nguyen ly ieu che FSK:

Trong FSK, tn hieu tn hieu song mang co bien okhong oi, tan so thay oitheo hai gia tr nh phan au vao la0 hoac 1 ( tng ng la tan so thap va cao ).

Tn hieu FSK co dang :

tftdfT

EtS c

b

bFSK 2)(2cos

2(2.31)

ay d(t) la chuoi d lieu nh phan au vao: d(t) = 1.2f : la o lech tan so so vi tan so song mang chuan 2fc.

Goi tan so cao la fH = fc + f va tan so thap fL = fc - f. Khi o tn hieu FSK cothe c bieu dien :

tffT

EtS

c

b

b

FSK 2cos.2

)( 0 t Tb , ( mc 1 ) (2.32)

tffT

EtS

c

b

b

FSK 2cos.2

)( 0 t Tb , ( mc 0 ) (2.33)

2. ieu che FSK :Goi PH(t) va PL(t) la hai gia tr ien ap co quan he vi d(t) nh bang sau:

d(t) PH(t) PL(t)+1V +1V 0V-1V 0V +1V

Khi o:

tffPTE

tffPT

E

tS cLb

b

cH

b

b

FSK 2cos.2

2cos.2

)( (2.34)

T(2.34), ta thay tn hieu SFSK(t) la tong cua hai tn hieu ieu che ASK vi tanso song mang la ( fc + f ) va ( f c - f ) va hai chuoi nh phan au vao laPH va PL.

S o ieu che FSK:

PL(t)

PH(t)

SFSK(t)

tffT

Ec

b

b 2cos2

tffT

Ec

b

b 2cos2


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Hnh 2.10 S o may thu FSK ket hp.Xac suat loi trong FSK:

0

,N

EercfP b

FSKe(2.37)

b. May thu FSK khong ket hp:S o khoi may thu FSK khong ket hp:

Hnh 2.11 S o khoi may thu FSK khong ket hp.

T

dt0

T

dt0

Cos2fct

sin2fct

Receivedsignal

DecisionCircuit

Output

MatchedFilter atfH

MatchedFilter atfL

EnvelopeDetector

EnvelopeDetector

DecisionCircuit

OutputReceivedSignal


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May thu bao gom hai bo loc cong hng va theo sau la hai bo tach song hnhbao. Hai bo loc cong hng tai hai tan so la fH = f c + f va fL = f c - f. Ngo ra cuamach tach song hnh bao c lay mau tai t =kTb, vi k la so nguyen, va giatr nayc so sanh va a en mach quyet nh e lay mc tn hieu ra tng ng.

Xac suat loi trong FSK khong ket hp:

0

,,2

exp2

1

N

EP bNCFSKe (2.38)


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CHNG I I I :MOI TRNG TRUYEN DAN SUY HAO

NG TRUYEN

I . TONG QUAN VE NG TRUYEN VO TUYEN:Hau het cac he thong vo tuyen te bao van hanh vung thanh th nen khong co

ng truyen trc tiep (line of sight) gia may phat va may thu, ma ay s hien diencua cac cau truc cao tang a sinh ra hien tng mat mac do nhieu xa. Bi do cac songphan xa t nhieu oi tng khac nhau, song i theo cac ng co o dai khac nhau nens tac ong cua cac song nay tai mot v tr nao o se gay ra hien tng Fading nhieung tai mot v tr nao o. e d oan cng o tn hieu thu tai mot khoang cach naoo so vi may phat, ngi ta dung cac mo hnh truyen dan.

Mo hnh dung e d oan cng o tn hieu trung bnh vi mot khoang cachmay phat may thu bat ky e c lng vung phu song vo tuyen cua mot may phat lamo hnh large scale. Ngc lai, e cho thay s thang gian cua tn hieu thu motkhoang cach ngan ( khoang vai bc song ) th ta dung mo hnh smal l scale.I I . MO HNH TRUYEN DAN TRONG KHONG GI AN T DO:

Mo hnh truyen dan trong khong gian t do dung e d oan cng o tn hieukhi ton tai duy nhat mot ng truyen l ine of sight gia may phat va may thu ( nhtrong he thong ve tinh, Viba). Cong suat tai mot iem bat ky tren ng truyen song la

ham cua khoang cach. Cong suat thu tai Anten may thu cach Anten phat mot khoangcach d th tuan theo phng trnh Friss:

Ld

GGPdP rttr 22

2

)4(

..)(

(3.1)

ay: Pt : cong suat may phat.Gt : o li Anten phatGr : o li Anten thu.L : he so mat mac he thong

o li cua Anten quan he vi goc m hieu dung Ae cua no :

2

4

eAG (3.2)

va bc song c tnh :

f

c (3.3)

c : van toc anh sangf : tan so song mang


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Suy hao truyen dan (PL) la s khac nhau ( c o dB) gia cong suat phatva thu:

22

2

)4(log10log10)(

d

GG

P

PdBPL rt

r

t

(3.4)

PL: la suy hao truyen dan ( path loss)Neu o li cua cac Anten c gia s la 1, th:

2)4(log10)(

2

dBPL (3.5)

Cong thc Friss ch hp le khi trng la vung xa. Khoang cach df t Anten mayphat thoa man trng vung xa la:

22Ddf (3.6a)

df >> D (3.6b)

df >> (3.6c)D: la ng knh ln nhat cua Anten phatNh vay, mo hnh truyen dan trong khong gian t do la moi trng ly tng

trong he thong thong tin. Nophu hp vi cac he thong ve tinh va Viba khi ton taing truyen trc tiep l ine of sight.I I I . SUY HAO NG TRUYEN:

thong tin vo tuyen iem en iem do anten at cao, nen suy hao ngtruyen ty le nghch vi bnh phng khoang cach R gia anten thu va phat (R2). thong tin di ong anten MS gan mat at (khoang 1.5 m) nen suy hao ty le vi luy than khoang cach R gia anten thu va phat (Rn), trong o n>2. e tnh cac suy hao ng

truyen ngi ta lap cac mo hnh truyen song khac nhau. Do at iem truyen songkhong on nh, nen cac mo hnh nay eu mang tnh thc nghiem.

Suy hao ng truyen trong moi trng vo tuyen di ong la do anh hng cuacau truc a l va s hien dien cua cac oi tng tan xa doc theo ng truyen song.Cac cau truc phc tap cua be mat a l va cac oi tng tan xa gay ra cac hien tngphan xa phan chieu ( Specular ref lection), phan xa lan truyen (di ffuse Reflection), vanhieu xa ( di ffraction).

1. Phan xa phan chieu:Phan xa phan chieu xay ra khi song vo tuyen gap mot be mat bang phang ma

khoang cach gia hai tram thu phat ln hn rat nhieu so vi bc song cua tn hieu votuyen. ay la loai phan xa tuan theo nh luat Snell, nh trong hnh 3.2

ay song ti t Anten se b phan xa tai Q. Tuy nhien, co thexem nh songphan xa nay c phat ra t Anten ao T , oi xng vi T qua be mat.


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Hnh 3.2 Ap dung nh luat Snel l2. Phan xa lan truyen:

Phan xa lan truyen xay ra khi song vo tuyen gap mot be mat gho ghe mas ghoghe cua be mat nay tng ng vi bc song cua tn hieu bc xa. Phan xa lantruyen khong tuan theo nh luat Snell. No b tan xa nang lng va gay ra cac hngsong phan xa khac nhau. Cng o cua song vo tuyen phan xa lan truyen th yeu hnphan xa phan chieu v nang lng cua no b tan xa qua be mat phan xa.

3. Nhieu xa:Nhieu xa xay ra khi tren ng truyen song gia may phat va may thu co s

hien dien cua cac oi tng tan xa ( nh oi nui, toa nha cao tang). S suy hao tn hieuphu thuoc vao cau truc nam tren hoac gan ng truyen line of sight.

Viec d oan suy hao ng truyen giup ch rat nhieu trong viec hieu biet

anh hng cua hien tng nhieu ng cua tn hieu vo tuyen. Tuy nhien, s anh hngnay rat phc tap cho viec tnh toan. au tien, chung ta phai tien hanh o ac cac trangthai tnh, va t cac so nay ta tien hanh phan tch lai cac trng hp khac nhau. Noc phan tch va anh gia tren c s l thuyet trng ien t.IV. D OAN SUY HAO NG TRUYEN:

1. D oan suy hao ng truyen qua a hnh bang phang:Khi tn hieu song vo tuyen c truyen qua a hnh co be mat bang phang

(khoang cach gia may phat va may thu la u ln so vi bc song tn hieu) th hientng phan xaphan chieu xay ra va ch co mot song phan xa en may thu, nh hnh

3.3.

T

T'

Q

Base station antenna


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Hnh 3.3 cau truc be mat anh hng en song phan xa.Nh a biet phan trc, phan xa phan chieu th tuan theo nh luat Snell,

ay tch cua heso khuc xa N1 vi cosine cua goc ti la mot hang so:N1 = cos = const (3.17)

He so phan xa:Ty so cua song en vi song phan xa ( lien ket vi no) goi la heso phan xa, k

hieu la a. e tnh he so phan xata dung cong thc Fressnel cho song phan cc doc va

phan cc ngang.Song phan cc ngang la song phan xa t cac toa nha cao tang.Song phan cc doc la song phan xa t mat at.Ta co he so phan xa cho trng hp phan cc ngang va doc theo cong thc

Fressnel:

2

1

2

1

21

1

2

1

)cos(sin

)cos(sin

c

cj

hhea (ngang) (3.18)

21

1

2

1

21

1

2

)cos(sin

)cos(sin

cc

ccj

vvea (doc) (3.19)

ay c = r j60r :hang so ty le cua he so ien moi c :odan ien cua moi trng.

Goc c minh hoa trong hnh 3.4

Hnh 3.4 Quan he gia song phan cc doc va phan cc ngang.(a) Phan cc ngang(b) Phan cc doc

E E

E

i r

t

ir

t

iE rE

tE

HH

H

HiHr

tH

aa a11a h v= =


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oi vi mat at trong moi trng vo tuyen di ong, th r rat ln va goc 1thng nho hn 1 Rad. Khi song ti la phan cc doc th :

av -1 (3.21)Khi song ti la phan cc ngang th :

ah -1 (3.22)Trong ca hai trng hp tren gia tr cua hang so ien moi la khong anh hng

en gia tr cua av va ah.Hnh 3.5 minh hoa mot tnh huong tieu bieu cho moi trng song vo tuyen l

tng. Be mat a l bang phang, ch co mot toa nha phan xa song phat. Tn hieu thutai MS c tnh nh sau:

)1( 21dj

h

dj

ir eaeEE (3.23)

ay d1 vad2 la o lech ng truyen dan:d1 = d1 d (3.24a)

d2 = d2 d (3.24b)

V goc ti rat nho nen phng trnh (3.23) c viet lai:)1( 21

jhj

ir eaeEE (3.25)

ayc

dii

Vi c la van toc anh sang.2. D oan suy hao ng t r uyen qua a hnh gho ghe:

Hnh 3.5 Phan xa trong moi trng vo tuyen di ong l tng.e co the d oan at tnh cua tn hieu qua a hnh gho ghe, ta phai nh

ngha tieu chuan e xac nh mc o gho ghe o.a. Xac nh t ieu chuan:

e xac nh mc o gho ghe cua be mat ta dung tieu chuan Rayleigh.Xet hnh 3.6.

r

h

h

1

2

E

E

E

E

E

E

H

H

H

HH

H

Directwaved

Groundreflectedwaved1

Scatterer reflectedwave d2

r > 1


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Hai tia ti cham vao be mat vi mc o loi lom khac nhau. Goc cua tiati va phan xa la, o lech ng truyen la :

d = 2Hsin (3.26)

Hnh 3.6 Mo hnh be mat gho ghe vi tieu chuan Rayleighva o lech pha cua hai tia:

sin

4.

2 Hdd (3.27)

Khi rat nho, co ngha la s khac nhau trong o cao cua be mat phan xala rat nho va be mat c xem nhu la bang phang. Trong trng hp ngc lai, co thexem va ket qua la hai tn hieu phan xa vi cung he so phan xa ai co the cbieu dien:

aiej + aie

j( + ) = aI aI = 0 (3.28)Tieu chuan Rayleigh cho viec xac nh mot be mat gho ghe la:

> /2 (3.29)Thay > /2 vao (3.27), ta c :

sin8

R

H (3.30)

va tieu chuan cho s gho ghe la: H > HR.b. Trng tan xa:Truyen dan qua mot be mat gn song c minh hoa trong hnh 3.7.Trng tan xa Es ti tai iem Ps theo hng Anten may thu co the c tnh

bang tch phan Helmhol tz. Gia s trng tan xa ch co thanh phan theo truc x va z,thanh phan theo truc y bang 0, d1 la khoang cach t Q en P. Theo tch phanHelmhol tz, trng tan xa thu tai iem P qua be mat gn song c bieu dien bi

z = S(x) la :

dxn

E

nE

yy

dSn

E

nEPE

L

L

SS

2

14

4

1

)(

21

(3.31)

Ray 1Ray 1 Ray 2

Ray 2

H

Wave front

d/2


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Hnh 3.7 Anh hng truyen dan qua be mat gn song.

Vi1d

e dj

Va n la vector phap tuyenV d1 >> , nen ta co moi quan he

cos.01 ddd (3.32)

d0 : la khoang cach ng trc tiep gia BTS va MS.d :la khoang cach t BTS en Q.

E :la song en van

E

la vi phan chuan cua S.

iem P c gia s la v tr cua MS.Khi phng phap tch phan Helmholtz cua phng trnh (3.31) c dung e

tnh trng tan xa tai iem thu qua be mat ghoghe, ieu can thiet ay la phaitnh toan be mat S(x). S(x) co the tnh bang phng phap xap x hoac phan bochuan.

Vi phng phap xap x. Ta gia s at tnh cua be mat S(x) la ngau nhien,ban knh cho loi c xem la ln hn rat nhieu so vi bc song ti. Khi o trngES c tnh :

EaeEdddj

S )1()( 01 (3.33)

a : la he so phang xa cua be mat bang phangKhi o trng HS la :

HaeHdddj

S )1()( 01 (3.34)

c. Be mat gho ghe la mot ham cua khoang cach:Cho chieu cao cua Anten tram goc la hI, khoang cach gia MS va BTS

la d, goc en la th :

S(x) Q(x,z)h1

>> 10

d0

d1d'

z

x

To point P

Base stationantenna

Wa

vefront

tothe

mob

ile


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d

hh 21 (3.35)

ma

sin8RH

Khi nho th

kdhh

dHR

)(88 21

(3.36)

Vi)(8 21 hh

k

(3.37)

Nh vay HR la mot ham cua khoang cach d.V. CAC HE SO CUA KENH VO TUYEN HIEU NG DOPPL ER:

1. Hieu ng Doppler :MS thu tn hieu khi ang chuyen ong, ngoai tn hieu song mang co tan so

tan so fc c thu, th lai co them mot tn hieu co tan so khac c thu, ma tan so nay

phu thuoc vao van toc cua MS, tan so o c goi tan so Doppler. No c sinh ra thieu ng Doppler.

Gia s MS ang di chuyen vi van toc v lahang so, doc theo oan ng cochieu dai la d gia hai iem X va Y. Trong thi gian nay, no ang thu mot tn hieu tnguon S, nh minh hoa trong hnh 3.8.

Hieu ng i cua song t S ti X va t S ti Y la :d = d.cos = v.t.cos (3.38)

Trong o: t la thi gian MS i t X en Y. c gia s la goc hp bi song ti tai X va Y vi mat ng

( gia s la nh nhau tai X va Y).

Hnh 3.8 Mo hnh truyen song qua be mat bang phang.o lech pha cua tn hieu thu:

cos.

22 tvl

(3.39)

Tan so Doppler:

Base stationantenna

DirectwaveReflectedwave

d

h1

h2


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cos.

2

1 v

tf

d

(3.40)

Phng trnh (3.40) cho thay moi quan he gia tan so Doppler vi van tocMS va goc en cua song ti so vi mat ng. No cung cho thay rang, neu MS dichuyen theo hng en cua song ti th fd > 0 ( < 90

0), con neu MS di chuyen theohng ngc lai th fd < 0 ( > 900).

2. He so phan tan Doppler :Phan tan thi gian cua kenh nhieu ng bang rong hau het c nh

lng bi tre qua trung bnh ( ) vaphan tan tre hieu dung () cua chung. Ta cova c nh ngha nh sau:

k

k

k

k

k

k

k

k

kk

P

P

a

a

)(

)(

2

2

(3.41)

22 (3.42)

va ay

k

k

k

k

k

k

k

k

kk

P

P

a

a

2

2

2

22

2

(3.43)

Gia trcua , 2 va phu thuoc vao cach chon ngng nhieu dung ex ly P(). Ngng nhieu dung e phan biet thanh phan nhieu ng va nhieu nhiet.

3. Bang thong ket hp:Bang thong ket hp Bc c nh ngha la so o thong ke cua day tan so cua

cac kenh c xem la bang phang. Hay noi cach khac, bang thong ket hp la day tanso ma trong o co hai thanh phan tan so co kha nang tng quan manh nhat ve bieno. Neu co hai tn hieu ieu hoa ma khoang cach tan so ln hn Bc th c xem nhla hai kenh hoan toan khac nhau. Neu bang thong ket hp c xem nh la bang thongma tng quan tan so tren 0.9 th ta co the xap x:

50

1cB (3.44)

Vi la phan tan tre c nh ngha phan tren.Con neu ham tng quan tan so la tren 0.5 th:

5

1cB (3.45)

4. Phan tan Doppler va thi gian ket hp:Phan tan Doppler va thi gian ket hp la he so mo ta at tnh bien thien

theo thi gian cua kenh truyen. Phan tan Doppler BD la so o cua s m rong pho gayra bi s thay oi thi gian cua kenh truyen. Va c nh ngha la day tan so ma quao pho Doppler thu la khong zero. Khi mot tn hieu thuan sine c phat vi tan so fc,


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vi

N

i

ii tfjtaatx1

00 )](2exp[).()( (3.59)

at

N

i

ii tftaR1

0 )](2cos[).( (3.60)

N

i

ii tftaS1

0 )](2sin[)( (3.61)

Luc o: x(t) = a0[R jS]

=A(t)exp(-j(t)) (3.62) ay bien o va pha cua x(t)la cac bien phuthuoc thi gian.

2

0

2

00)( SRatA (3.63)

vaR

Sarctgt )( (3.64)

Hnh 3.10 Tn hieu thu khi Ms chuyen ong.

(a) Hieu ng Doppler.(b) Fading do song ng.Trong trng hp nay, ta co the gia s rang MS ang di ong th co ba tnh

huong xay ra :(1) Khong co cac vat tan xa;(2) Ch co mot vat tan xa;(3) Co nhieu vat tan xa;


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xung quanh MS. Ta co thegia s rang MS ang di chuyen theo hngdng cua truc x vi mot van toc v la hang so va thu mot tn hieu co mot goc en tngng vi truc x nh minh hoa trong hnh 3.10.

Tn hieu thu trong khi MS di chuyen:)]cos.(exp[)( 000 vttjats (3.65)

Trong o

2 , la bc song.

cos.v

fd la tan so phat sinh do hieu ng Doppler (se c

khao sat sau)e hieu ro anh hng cua hien tng nhieu ng, ieu can thiet phai

hieu khai niem song ng ap dung tn hieu vo tuyen. Neu tn hieu en t mot hng vac phan xa hoan toan theo hng ngc lai nh hnh 3.10b, th tn hieu thu tai MSang di chuyen vi van toc v c tnh (gia s = 0):

2exp.

2sin2

)](exp[)](exp[)(

0

00

0

0

0000000

tjvtaj

vttjavttjats(3.66)

la thi gian ma song i ti vat tan xa va tr ve tai ng t = 0. Hnh bao cuaphng trnh (3.66) la song ng, no co the c xem nh la hien tng Fading ngian.

Trong trng hp tach song bang luat bnh phng th hnh bao cua (3.66) la

0

2

0

022

0

2

2cos12

2

sin4)(

vta

vtatx

(3.67)

Tan so Dopplr ay la

vfd

2 .

c. Ca MS va cac vat tan xa xung quanh eu chuyen ong:ay la mot trng hp kha phc tap, tn hieu thu tai MS thng khong

c tot, bi v tn hieu thu la tong cua cac tn hieu phan xa vi cac goc i khac nhau.Tn hieu thu trong trng hp nay la:

001

000

exp.exp

cosexp)(

jjA

vttjaats

tt

N

i

iii

(3.68)

Vi2

12

1

0

2

1

0 sincos

N

i

ii

N

i

iit aaaaA (3.69)


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Hnh 3.11 ac tnh kenh Fading bang phang.BS > (3.76)Trong o

S

ST

B1

la bang thong cua tn hieu.

BC va la bang thong ket hp va phan tan tre cua kenh.3. Fading chon loc tan so:

Neu mot kenh vo tuyen co bang thong co o li hang so va ap ng phatuyen tnh, ma no nho hn bang thong cua tn hieu phat th kenh tao nen Fading chonloc tan so tren tn hieu thu. Vi ieu kien nay, ap ng xung cua kenh co mot phan tantre nhieu ng ln hn nghch ao bang thong cua tn hieu phat. Khi ieu nay xay ra,tn thu bao gom nhng phien ban cua dang song phat ma no b suy hao va tre theo thi

gian va v vay tn hieu b meo. Fading chon loc tan so la do s phan tan thi gian cuak t phat theo kenh truyen. V vay kenh xay ra giao thoa k t (ISI). Theo quan iemtrong mien tan so, mot vai thanh phan tan so pho tn hieu thu co o li ln hn cac

h(t,)s(t)r(t)

s(t) h(t,) r(t)

00 0

tt tTs Ts +


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Hnh 3.13 Ma tran cac loai Fading la ham cua:(a) Chu k k t;(b) Bang thong tn hieu dai nen.

Fading cham dien ra khi s thay oi ap ng xung cua kenh cham hn toc ocua tn hieu dai nen phat. Trong trng hp nay, kenh c xem nh la tnh qua motvai chu ky cua bang thong nghch ao. Theo quan iem trong mien tan so, phan tanDoppler cua kenh nho hn bang thong cua tn hieu dai nen. V vay, mot tn hieu bFading cham khi:

TS > BD ( 3.82)Ta thay ro rang rang van toc cua MS ( hay van toc cua cac oi tng trong

kenh truyen ) va toc o cua tn hieu dai nen quyet nh tn hieu b Fading nhanh haycham. Fading nhanh va Fading cham la loai Fading xay ra do s phan tan Doppler.

6. Cac bien phap chong fadinh:

e chong fadinh ngi ta s dung cac bien phap sau ay: Mahoa kenh chong loi ket hp vi an xem tn hieu S dung nhieu song mang (MC:mul ti Carrier) Phan tap Can bang thch ng Trai pho May thu RAKE ( thong tin di ong CDMA)

Flat SlowFading

Flat SlowFading

Flat FastFading

Flat FastFading

Frequency SelectiveFast Fading

Frequency SelectiveFast Fading

Frequency SelectiveSlow Fading

Frequency SelectiveSlow Fading

Ts

Ts

TcTransmitted Symbol Period

(a)Bs

BsBd

Bc

Transmitted Baseband Signal Bandwidth

Sym b

olPeriodof

Trans

mittin

gSymbol

TransmittedBa

seband

Sign

al

Bandwidth

(b)


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CHNG IV:KHAO SAT CAC LOAI GIAO THOA

TRONG HE THONG GSM

I . ANH HNG CUA GIAO THOA:Trong he thong ien thoai di ong te bao, van e giao thoa luon c quan tam

trong luc thiet ke. Conhieu loai giao thoa: giao thoa ong kenh, giao thoa kenh ke,giao thoa au gan au xa, giao thoa k tTrong o giao thoa ong kenh va giaothoa kenh ke la quan trong nhat.

Mot oi tng c e cap au tien trong he thong vo tuyen di ong thngmai hoac quan oi la van e sdung tan so, ieu nay dan en s hien dien cua cackenh cung tan so trong mot he thong vano lam xay ra hien tng giao thoa ong kenh.

Mat khac trong he thong GSM s dung phng phap truy cap FDMA va TDMA, nenkhoang cach gia cac kenh tan so ke nhau phai c toi thieu e toi u pho. Tuynhien, ieu nay lam cho cac kenh ke nhau co anh hng qua lai gay ra giao thoa kenhke. Trong phan nay, chung ta se khao sat at tnh cua cac loai giao thoa anh hng lenhe thong GSM.I I . GI AO THOA ONG KENH:

1. Heso giam giao thoa ong kenh:Nh a gii thieu trong chng I, khoang cach s dung lai tan so cua cac cell tronghe thong GSM la D:

RkD 3 (4.1)

Trong o k la mau s dung lai tan so, tuan theo phng trnh:k = i2 + ij + j2 i,j N.

R la ban knh cell ( xem nh cac cel l co ban knh bang nhau)Viec s dung lai cac kenh tan so giong nhau cac cell khac nhau b gii han

bi giao thoa ong kenh gia cac cel l vavan e giao thoa ong kenh tr thanh van echnh. Bay gi, chung ta phai tm khoang cach s dung lai tan so ma co the toi thieuc giao thoa ong kenh.

Heso giam giao thoa ong kenh q c nh ngha :

kR

Dq 3 (4.2)

Khi q tang giao thoa ong kenh se giam.Trong khi o, khoang cach D la ham cua K I va C/I.

D = f(K I, C/I) (4.3)K I la so cell giao thoa ong kenh.C/I la ty so song mang tren giao thoa may thu.


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IK

k

kI

C

I

C

1

(4.4)

Gia s rang bo qua cac loai nhieu khac, he thong ch b anh hng bi giao thoath:

IK

k

kD

R

I

C

1

(4.5)

la o doc ng suy hao, trong moi trng vo tuyen gia s = 4, vaK I = 6 (cau truc hnh luc giac).

Khi o ta co:

II

K

k

k

K

k

k qR

DI

C

11

11

(4.6)

ViR

Dq k la he so giam giao thoa ong kenh cua cell th k.

2. Tn hieu thu khi co giao thoa ong kenh:Gia s tn hieu can thu la s(t) va tn hieu giao thoa la i(t) th ta co quan he sau :

))((exp)( ttjts c (4.7)

))((exp)( 0 ttjrti c (4.8)

Vi (t) vai(t) la thanh phan ieu che pha cua tn hieu can thu va tn hieugiao. r la ty so bien o cua tn hieu giao thoa va tn hieu can thu. Tn hieu trc bo giaiieu che la tong cua hai tn hieu nay:

)(exp).(.)(exp

)()(exp1.)(exp

)()()(

0

tjtRttj

ttjttj

titstv

c

ic

c

(4.9)

at 0)()(exp1 ttjre ix (4.10)

Va )(tjxx r (4.11)

Nh vay ta co: 0)()(exp1ln ttjrx i (4.12)

T (4.11) va (4.12), ta suy ra :

0)()(exp1lnIm)( ttjrt i (4.13)Ta co bieu thc gan ung:

1

1.

11)1ln(

k

kk yk

y (4.14)

Khi o (4.13) tr thanh :


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1

0

1

1

0

1

)()(sin..1

1

)()(exp`..1

1Im)(

k

i

kk

k

i

kk

ttkrk

ttjkrk

t

(4.15)

Nh vay tn hieu thu tai may thu sau khi i qua bo gii han )()(exp. tttjAv cd (4.16)

Vi A la bien o hang so.3. Giao thoa ong kenh tr ong moi tr ng khong Fading:

e tnh pho cua (t) trong moi trng khong Fading, can thiet phai bietc tng quan trung bnh cua goc pha ngau nhien 0 t phng trnh (4.15). Gia s0co phan phoi chuan, oc lap va cogia tr t 0 en 2, th ham tng quan cua (t) la :

12

2

12

2

)()0(exp2

1

)()(cos121

.().(2

1lim)(

lim

0

k

kk

k

k

T

Tii

T

k

T

TT

RRk

r

dtttttkTk

r

dttET

tR

(4.17)

Vi Rk(t) la ham phng sai cua )()( ttk i

)()( ttk ik (4.18)

Mat o pho cong suat Sk(t) co the c mo ta:

0

)0(

)(

k

k

R

tS (4.19)

Va ham phng sai Rk() cua k c cho bi :

W

WRdfefSR

k

jW

kk2

2sin).0()()(

(4.20)

Ham cua phng trnh (4.19) va (4.20) c ve trong hnh 4.1Pho tan so S(f) cua (t) c viet:

)(2

1

2exp)()(

12

2

fSk

r

dfjRfS

vk

k

k

(4.21)

Trong o:

dfjRRfSkkvk

2exp)()0(exp)(

(4.22)

Wf

ni khac


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0

2)(

2

wfS

(4.24)

Hnh 4.1 Mat o pho cong suat va ham phng sai cua k.Thay (4.20) vao (4.22), taco:

dppjp

pR

wfS kvk

exp

sin1)0(exp

2

1)( (4.23)

Viw

f va wp 2

Phng trnh (4.23) rat kho giai bang phng phap giai tch. V vay, can co motcach khac etm gan ung.

Gia s rang (t) vaI(t) la oc lap va co pho la hnh ch nhat vi hai bien la w va+w Hz, th pho cua S(f) c bieu dien:

He so ieu chebnh phng trung bnh 2 c nh ngha: dffStE

22 (4.25)

Ham t tng quan cua (t) la :

w

wR

2

2sin2 (4.26)

Tng t ta co pho cua SI(f) la:

0 1 2 3 4 5 6 7 8 9 10

1.0

0.8

0.6

0.4

0.2

0

-0.2

-0.4

Frequency,Hz-W W

W

DRk

2

)(

Spectral density

Rad2/Hz

2

)0(

)(

k

k

R

R

2W

wf

Rad2/

Hz


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(4.27)

va ta cung co :

dffStEi

i 2 (4.28)

w

wR

ii 2

2sin. (4.29)

Khi ota tnh c :

i

T

T

iT

k

k

RRk

dttkT

R

i

22

2

22

)0(

)(2

1)0( lim

(4.30)

Hnh 4.2 Mat o pho cua giao thoa dai nen trong moi trng khong fading.Thay (4.30) vao (4.23) va sau othay vao (4.21), ta se co S(f) la mot ham cua

r2, 2 va 2i , vi = I = 2.55 va cac mc r2 khac nhau c ve trong hnh 4.2. Nhvay, gia tr cua S(f) giam khi hoac f giam hoac r giam.

4. Giao thoa ong kenh t r ong moi tr ng Fading Rayleigh:Ty so giao thoa tren song mang tai IF la:

)(

)(2

22

ts

tir (4.31)

Rad2/Hz wf

Ni khac

0

2)( wfS

i

i

r2

= 0.9

r2

= 0.5

r2

= 0.1

r2

= 0.01

0 1 2 3 4 5 6 7 8 9 10 11 12 13

10-6

10-5

10-4

10-3

10-2

10-1

1

f/W

= I = 2.55

)(2

fsr

W


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Vi hai tn hieu s(t) va r(t) eu b Rayleigh Fading. Ham mat o xac suatpr(x) c bieu dien nh sau:

212

xp

r

(4.32)

va c nh ngha:

0

22 )(1

2 dxxprrE r (4.33)

la CIR trung bnh .Cong suat giao thoa ong kenh E[ I] tai mc nhieu nen.

SNEwSEIE )0(2 (4.34)

vi :

121

11ln

1.

2

3

2)1((2

3

)1(

2)()0(2

2

2

1

2

2

1

0 22

2

i

dxx

dxx

x

wSxpwSE

i

i

i

i

r

(4.35)

NS phng trnh (4.34) la cong suat cua tn hieu nhieu do Fading ns(t) cbieu dien :

))(()()( tEttns (4.36)

Vi (t) la tn hieu au ra dai nen:E((t)) la tn hieu au ra co Fading.

1

)()()(

1

)()()(

)()())((

1

1

0

2

2

2

tdxxpt

tdxxpt

dxxpttE

r

r

r

(4.37)

Thay (4.37) vao (4.36), ta co:

t

t

tEttns

1

1

1

)()( (4.38)

Gia tr trung bnh cua )(2 tns la :

2

2

22

2

2

2

2

2

2

2

.11

1

1

1

1

)(

t

t

tnNsS

(4.39)

r2

1

r2

< 1

r2

> 1

r2

< 1

r2

> 1


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Cong suat trung bnh E[NS]:

0

1

0 1

2

222

22

22

2

11111)(2

dx

xdx

xdxNxpNE

SrS

(4.40)Nh vay ta co cong suat trung bnh cua giao thoa la:

2

2

22

221121

1)1ln(

1

2

3

i

i

tIE (4.41)

Cong suat tn hieu au ra trung bnh:

2

2

22

2

21

0

2

11)(2

dxxptE r (4.42)

Nh vay:

QIE

EE

i

1

11ln

1

2

3

1

22

2

2

2

22

(4.43)

Trong o

2

2

22

112

iQ (4.44)

Chung ta co the giam giao thoa ong kenh cach tang so mau s dung tan so k.Tuy nhien, khi o hieu suat s dung pho khong cao. Mot bien phap thng thc hien lathiet ke cac Anten ang hng. ieu nay lam giam ro ret hien tng giao thoa ongkenh.

I I I . GI AO THOA K ENH KE:Mo hnh dung e tnh giao thoa ong kenh c n rong e ap dung cho giao

thoa kenh ke. Giao thoa kenh ke c chia ra lagiao kenh ke trong bang va giao thoakenh ke ngoai bang. Dang giao thoa trong bang khi trung tam cua bang thong tn hieugiao thoa ri vao trong bang thong tn hieu can thu. Ngc lai vi dang giao thoa bangngoai. Do anh hng ln cua dang giao thoa bang trong, nen chung ta ch tap trung vaodang nay, v vay ch xet trng hp r < 1. Khi o tn hieu can thu

s(t) = expj[ ct + (t)] (4.45)va tn hieu giao thoa kenh ke:

0)(exp)( ttjrti iac (4.46)ay f = fc + fa la tan so giao thoa kenh ke.Cung nh phan trc ta co pha giao thoa (t) la :

0

1

1sin

11

tttkr

kt

ic

k

k

k (4.47)

oi vi giao thoa kenh ke, ta cung chia ra hai loai moi trng khac nhau lakhong co Fading vaco Fading.


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1. Giao thoa kenh ke tr ong moi tr ng khong co Fading:Trong moi trng khong Fading, gia s r2 la hang so va0 la hieu pha gia s(t)

va i(t) co phan bo chuan va oc lap. Ham tng quan R() cua (t) la

12

2

cos)0(exp2

1

)(2

1)( lim

k

ckk

k

T

TT

RRk

r

ttET

R

(4.48)

va mat o pho cong suat S(f) cua (t) la :

12

2

4

1

2exp

k

avkavk

k

kffSkffSk

r

dxfjRS

(4.49)

vi dppjp

pR

w

fS kvk

exp

sin10exp

2

1(4.49)

trong o:w

f va p = 2w

Ty so tn hieu tren giao thoa (SIR) dai nen la :

02

2

wSSIR (r2 < 1) (4.50)

2. Giao thoa kenh ke trong moi t r ng Fading:Trong moi trng vo tuyen di ong, tn hieu can thu va tn hieu giao thoa kenh

ke co the tng quan tng phan do s suy giam cua chung. Xac suat ton tai r2 r1,

vi r1, r2 la hnh bao cua tn hieu can thu va giao thoa. Xac suat nay c tnhvi ( 22221 2 rErE )

2222

0 22

2102

2

2

2

12.11

0 221112

41

1

2

1

2

1

112exp

,

1

1

r

rr

r

r

r

drrr

Irr

rrdr

drrrpdrrrp

(4.51)

Trong or la he so tng quan gia r1 va r2.Ham mat o xac suat pr(y) cua r = r2/r1 co the c tnh :

y

rr

rp

d

dyp

1

2 (4.52)

at rGR . , ma G la o li cong suat tai au ra cua mach loc trung tan, luco:


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23

2

41

11

2

1).()(2

G

x

G

xG

G

x

yGypxp

r

r

G

xy

rR

(4.53)

Vi r c tnh :

221

1

r(4.54)

Vi

2

f la hieu pha cua tan sogia tn hieu thu vatn hieu giao thoa.

la phan tan tre

Cong suat giao thoa : S

NEwSEIE 02

(4.55)

Trong o:

dx

G

x

G

xG

G

x

dx

G

x

G

xG

G

x

wSE

i

r

r

i

r

r

1

22

23

2

1

0 223

2

2.

41

11

.2

3.

41

11

02

(4.56)

ay ch tnh cho trng hp 35.222 i .

Cong suat tn hieu au ra co Fading la:

1

02

3

1

0

41

11

)()().( 22

dx

G

x

G

xG

G

x

t

dxptdxxpttE

r

r

RR

(4.57)

V ch ap dung cho giao thoa bang trong nen r < 1.Tn hieu nhieu au ra:

tEttns

(4.58)


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Vi E((t)) a c tnh tren.

1

02

3

41

11

1.)( dx

G

x

G

x

G

G

x

ttN

r

r

S

(4.59)

ma

21

0 23

2 .

41

11

1)(

G

x

G

xG

G

x

tnN

r

r

sS (4.60)

T(4.60) ta tnh c

0

.2 dxNxpNE SRS (4.61)

Thay (4.61) va (4.56) vao (4.55) ta co E[I].

To ta tnh c SIR : IE

ESIR

(4.62)

Van e giao thoa kenh ke co the giam khi chung ta co mot phng phap annh tan so e bao am cho khoang cach gia cac kenh ke nhau la ro rang. Ngoai ra,con co the ap dung bo loc bang thong coo li cao tai may thu.IV. GI AO THOA AU GAN - AU XA:

Giao thoa au gan au xa xay ra khi khoang cach gia may thu MS va BTS cuano th xa hn khoang cach gia no va mot BTS khac. Hoac trong trng hp giao thoaau gan au xa xay ra tai BTS th co hai MS, nhng chung thuoc hai BTS khac nhauva BTS gan nhat cung thu tn hieu khi chung phat ong thi. ay, ta xet trng hpth nhat. Goi d1 la khoang cach t MS en BTS cua no, d2 la khoang cach t MS enBTS khac cocung kenh tan so ma noang s dung. Nh vay, hien tng giao thoa augan au xa xay ra khi d1 > d2.

Hieu cong suat gay ra do ng suy hao gia v tr cua may thu va hai hngcua v tr may phat c goi la ty so giao thoa au gan au x, va c nh ngha:

Near end to far end Ratio =2

1

__

__

dlosspath

dlosspath(4.63)

e co the tnh xap x c ty so giao thoa au gan au xa mot cach nhanh nhat

( dB ) ta dung o doc suy hao la 40dB/decade vi mot moi trng vo tuyen tieu bieu,th ta co:

Near end to far end ratio = 40log(distance Ratio) (4.64)V. GI AO THOA KY T:

Neu mot he thong truyen dan so la tuyen tnh va khong meo qua cac tan so, thhe thong phai co mot bang thong vo han. Tuy nhien, trong thc te, mot he thong soluon co mot bang thong gii han va mot lng meo tan so. Trong mot he thong khong


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meo, mot chuoi xung c ban s(t) la khong b bien dang theo ap ng tan so. Nh vay,x(t) bieu dien mot chuoi xung:

N

k

kR

ktsatx

1

)( (4.65)

R la toc o bit.ak = 1.Khi s(t) la khong meo, viec tang toc o bit cua tn hieu co the at c bang

cach giam o rong xung va tang so xung phat trong mot khoang thi gian. Tuy vay, vihe thong thc te co mot bang thong gii han va lng meo tan so se gay ra s phan tancua cac xung rieng biet va chong trap, o goi la giao thoa ky t ( ISI).

Mot nguyen nhan khac gay ra ISI la do toc o bit cua tn hieu va tan so phat banh hng cua phan tan thi gian tredo moi trng vo tuyen (). Phan tan treb giihan bi gii han bang thong, vas phan xa tn hieu nhieu ng en tai Anten may thutai cac thi iem khac nhau. Khi toc o bit cua tn hieu 1/R >> th phan tan treco the

bo qua va ay la xem nh khong co ISI.e giam hien tng ISI, ta co the dung ky thuat lay dang xung, bo Equal izer

hoac mach ma hoa so ac biet.


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CHNG V:CAC PHNG PHAP CAI THIEN NG

TRUYEN VO TUYEN

I . KY THUAT CAN BANG:Giao thoa ky t (ISI) sinh ra do hieu ng nhieu ng trong mot kenh phan tap

thi gian bang thong hu han, va lam meo tn hieu, sinh ra loi bi t tai may thu. ISI cxem la mot tr ngai chnh cho cac kenh votuyen khi truyen toc o cao. Can bang lamot ky thuat chong lai ISI.

dang tong quat, can bang co the c mo ta nh mot ky thuat x ly tn hieue giam ISI. cac kenh vo tuyen, nhieu bo can bang thch ng (Adaptive Equal izer)co thec dung e loai bo nhieu. Trong kenh Fading, s thay oi thi gian la ngaunhien, nhiem vu cua bo can bang la ieu chnh ac tnh thay oi thi gian cua kenh votuyen, v vay c goi la bo can bang thch ng.

Mo hnh tong quat cua bo can bang thch ng bao gom hng dan va ieuchnh.

au tien, mot chuoi hng dan c phat t may phat en bo can bang cuamay thu theo mot khoang thi gian at trc. Chuoi hng dan la mot tn hieu nhphan gia ngau nhien hoac mot mau bits hng dan. Sau chuoi hng dan nay, d lieu(no co the hoac khong co the cha bit ma hoa) c gi, va bo can bang thch ng tai

may thu dung mot giai thuat e anh gia va c lng cac he so loc e bu cho kenh.Chuoi hng dan c tnh toan lam sao cho phep mot bo can bang tai may thu phaia ra nhng he so loc trong trng hp xau nhat cua kenh, sao cho khi chuoi hngdan ket thuc th cac he so loc gan bang vi gia tr toi u cua d lieu can thu. Khi dlieu c thu, giai thuat thch ng cua bo can bang se ieu chnh s thay oi cua kenh.Va nh the, bo can bang luon thay oi mot cach lien tuc ac tnh thi gian bo loc cuano.

Pham vi thi gian trong mot bo can bang la mot ham cua giai thuat can bang,cau truc bo can bang va toc o thay oi thi gian cua kenh vo tuyen nhieu ng. Bocan bang yeu cau cac chuoi hng dan phai c lap lai e at c muc ch loai bo

ISI, va thng trong cac he thong thong tin so, d lieu phai c chia ra tng khoingan e phat. He thong vo tuyen TDMA rat thch hp vi ky thuat can bang.

Hnh 5.1 trnh bay s o khoi cua mot he thong thong tin vi bocan bang thchng tai may thu.


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Hnh 5.1 S o khoi cua mot he thong n gian cos dung bo can bang tai may thu.

Neu x(t) la tn hieu tin tc nguyen thuy, va f(t) la ap ng xung dai nen phctong cong cua may phat, kenh va phan RF/IF cua may thu, th tn hieu thu c bi bocan bang la:

)()()()( tntftxty b (5.1)

f*(t) la lien hiep phc cua f (t).

nb(t) la nhieu dai nen tai au vao cua bo can bang.Neu ap ng xung cua bo can bang la heq(t), th au ra cua no la:

)()()()(

)()()()(*)()(

thtntgtx

thtnthtftxtd

eqb

eqbeq

(5.2)

Trong o, g(t) la ap ng xung cua may phat, kenh, phan RF/IF cua may thu vabo can bang. ap ng xung dai nen phc cua bo can bang loc ngang la

n

neqnTtcth )()( (5.3)

Trong o cn lacac he so loc phc cua bo can bang.

Tn hieu tai au ra cua bo can bang c mong i la x(t). Gia s nb(t) = 0, th)()( txtd , trong (5.2) th g(t) phai la:

)()()()( tthtftg eq (5.4)

Trong mien tan so(5.4) tr thanh:1)()( fFfHeq (5.5)

ay Heq(f) va F(f) la bien oi Fourier cua heq(t) va f(t).

Modulator Transmitter Radiochannel

DetectorMatched Fil ter IF Stage

RF ReceiverFront End

Equalizerheq(t)

DecisionMaker

+

f(t) = ap ng xung tong cong cua may phat,kenh vo tuyen nhieu ng va phan RF/IF may thu.Original

basebandMessagex(t)

EquivalentNoise nb (t)

y(t)

f(t)

ReconstructedMessage Datad(t)

e(t)

+_d(t)v


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Neu kenh la chon loc tan so, bo can bang se nang cao cac thanh phan tan so cobien o nho va suy hao manh tai pho tan so thu e a ra mot ap ng tan so thungang nhau va bang phang va co pha tuyen tnh.5I I . GII THIEU VE KY THUAT CAN BANG:

Hnh 5.2 Qua trnh chia lp cua bo can bang.Ky thuat can bang c chia lam hai loai: tuyen tnh va khong tuyen tnh. S

phan loai nay c quyet nh t viec au ra cua bo can bang co c hoi tiep ve auvao hay khong. Tn hieu tng t )( td c x ly bang mach quyet nh may thu.

Mach quyet nh lay gia tr cua bit d lieu ang thu va a en mach gi hoac layngng e quyet nh gia tr cua d(t).

Neu d(t) khong c dung e hoi tiep, th qua trnh can bang c goi la tuyentnh.

Neu d(t) c hoi tiep th qua trnh can bang goi la khong tuyen tnh.

Co nhieu cau truc bo loc c dung e thc hien bo can bang tuyen tnh vakhong tuyen tnh. Them vao o, moi cau truc co nhieu giai thuat e ieu chnh bo canbang.

Hnh 5.2, trnh bay mot qua trnh phan loai tong quat cua cac ky thuat can bangtheo cac loai, cac cau truc va cac giai thuat c dung.

Equalizer

Linear NonlinearTypes

DFEML SymbolDetector MLSE

Transversal Lattice Transversal LatticeTransversalChennal Est.

Zero ForcingLMSRLSFast RLSSq.Root RLS

Gradient RLSLMSRLSFast RLSSq. Root RLS

Gradient RLSLMSRLSFast RLSSq. Root RLS

Algorithms


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Cau truc bo can bang pho bien nhat la bo can bang ngang tuyen tnh (LinearTransversal Equalizer LTE). Mot bo loc ngang tuyen tnh c tao nen bi cac tangcua ng tre, vi moi tang lam tremot chu ky ky t (TS), nh trong hnh 5.3.

Hnh 5.3 Cau truc bo can bang ngang tuyen tnh c ban.Gia s, moi thanh phan Delay cooli la 1, va thi gian trela TS, th ham

truyen cua bo can bang ngang tuyen tnh la exp(-jTS) hay z-1

. Mot LTE n giandung ch cac tang tao tre (khong co hoi tiep), th ham truyen cua no co dang la a thccua z-1. Bo loc nay co nhieu zero nhng ch co mot cc tai z = 0, no c goi la bo locap ng xung hu han (FIR) hoac mot cach n gian la bo loc ngang.

Neu mot bot bo can bang va co tang ti va tang hoi tiep th ham truyen cua nola mot ham phan so cua z-1, no c goi la bo loc ap ng xung vo han (IIR) vi nhieucc va zero.

TS ST ST TS

Taps

clockwithperiod

Delay elements

y(t) + nb(t)


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Hnh 5.4, trnh bay mot boloc cac tang cua ng tre vi ca ng ti va nghoi tiep.

I I I . KY THUAT PHAN TAP:Phan tap la mot ky thuat rat manh c s dung trong cac may thu thong tin, no

gop phan cai thien chat lng ng truyen vi mot chi ph thap. Khong nh ky thuatcan bang phai can mot mao au hng dan (chuoi hng dan). Qua trnh phan tapc s dung mot cach rong rai va rat thc te ma chi ph phat sinh thap.

Phan tap li dung ac tnh ngau nhien cua ng truyen vo tuyen bang cachtm ra cac ng tn hieu oc lap vi he thong. Phan tap ch s dung may thu.

Khai niem phan tap c giai thch nh sau: Neu mot ng truyen vo tuyen bsuy hao manh, con cac ng khac co mot tn hieu manh. Nh vay phan tap la chonmot trong cac tn hieu nay hoac chon ong thi va SNR trung bnh tai may thu c caithien, thong thng t 20 30dB.

Trong moi trng Fading ty le nho (Small Scale Fading) th s thang gianbien o xay ra sau va nhanh khi di ong di chuyen qua mot khoang cach ch vai bcsong. Loai nay b gay ra bi nhieu tia phan xa t cac vat xung quanh di ong. e giams suy giam sau ta dung ky thuat phan tap vi mo, ma co the li dung s thay oi motcach nhanh chong cua tn hieu.

Fading ty le ln (Large Scale Fading) b gay ra bi s chong trap do s adang cua be mat a ly va ac tnh cac vat xung quanh. Trong ieu kien chong trapmanh, cng o tn hieu thu tai di ong b suy giam manh. e tranh tnh trang nay ta

chon cac tram goc sao cho no t chong trap vi cac tram goc khac. Nh vay co the caithien c SNR trung bnh tai may thu. ay goi la phan tap v mo.Phan tap v mo c dung rat nhieu may thu tram goc. Bang cach dung cac

Anten tram goc co s phan tap ro rang trong khong gian va tram goc cung co the caithien chat lng ng truyen ngc lai bang cach chon Anten vi cng o manhnhat t di ong.IV. CAC KY THUAT PHAN TAP:

TS

X

ST SST T

X X X X

X X X

Feedback taps

Feedforward taps

y(t)

b1 b2 b3 b4

d1 d2 d3 d4

d(t)v


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1. Phan tap khong gian:Phan tap khong gian con goi la phan tap Anten, lamot dang phan tap pho bien

trong he thong thong tin di ong. Trong he thong nay, ng truyen trc tiep gia mayphat va may thu kho ton tai va ston tai cua cac vat tan xaxung quanh di ong cxem nh la mot tn hieu Fading Rayleigh. Mo hnh a ra e thu cac tn hieu nay tcac Anten oc lap tren di ong se co hnh bao khong tng quan vi s cach ly cua cacAnten bc song hoac dai hn.

Khai niem phan tap khong gian Anten cung c dung trong luc thiet ke tramgoc. Tai tram goc, nhieu Anten thu c dung cho viec thu phan tap.

2. Phan tap phan cc:Tai tram goc, phan tap khong gian t c e cap trong thc te hn tai di ong,

bi v khong gian Anten ln hn goc en cua trng. Them vao o, s phan tap phancc chi ph thap hn so vi phan tap khong gian. Ch can co hai nhanh phan tap, no acho phep cac thanh phan Anten c hoat ong tot.

3. Phan t ap t an so:Phan tap tan so la phat nhieu kenh thong tin tren mot song mang. Loai naythng c ap dung trong ng L ine Of Sight cua Viba (Microwave).

4. Phan tap thi gian:Phan tap thi gian la phat thong tin mot cach lap lai tai cac khoang thi gian

ln hn thi gian ket hp cua kenh, sao cho cac qua trnh lap lai nay cua tn hieu sec thu vi cac ieu kien Fading oc lap.

V. C BAN VE MA HOA KENH:Ma hoa kenh e bao ve dlieu so t loi bang cach a them cac bits tha trong

d lieu phat. Ma kenh c dung e kiem tra loi goi la ma kiem tra loi, con ma dung

e kiem tra va sa loi goi la ma sa loi.Cong thc dung lng kenh cua Shannon c ap dung trong kenh nhieu trang l a:

N

SB

BN

PBC 1log1log 2

0

2 (5.6)

Trong o: C la dung lng kenh.B la bang thong truyen dan (Hz).P la cong suat tn hieu thu (W).N0 mat o cong suat nhieu n bien (W/Hz).

Cong suat thu c tai may thu:

P = EbRb (5.7)Eb: nang lng bi t trung bnh.Rb : toc o bit truyen dan.Phng trnh (5.6) co the c chuan hoa:

BN

RE

B

C bbog

0

1log (5.8)


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B

Cla hieu suat bang thong.

Muc ch c ban cua ky thuat kiem tra va sa loi la them cac bits tha vao dlieu e cai thien chat lng ng truyen. Cac bits nay lam tang so bit cua d lieucha ieu che va v vay lam tang bang thong yeu cau cho mot toc o d lieu nguon.ieu nay lam giam hieu suat bang thong cua ng truyen ieu kien SNR cao,nhng cho BER tot vi gia tr SNR thap.

Bo ma hoa kenh ma hoa d lieu thong tin nguon ra mot chuoi ma khac e phatlen kenh truyen. Co hai loai ma phat hien sai va sa sai c ban la: ma khoi (Blockcode) va ma chap (Convolutional code).VI . CAC MA HOA K ENH THNG DUNG:

1. Ma khoi:Ma khoi la ma sa sai truyen thang (Forward Error Correction FEC), no cho

phep mot so bits loi c sa sai ma khong can truyen lai. Ma khoi co the c dung

e cai thien chat lng ng truyen khi cac phng phap khac khong hieu qua.Trong ma khoi, cac parity bi ts c them vao khoi bi t thong tin e tao nen cact ma khac hoac khoi ma. bo ma hoa khoi, k bits thong tin c ma hoa ra thanh nbi ts. Tong cac bits (n k) c cong vao cac bits thong tin vi muc ch phat hien saiva sa sai. Ma khoi c xem lamot ma (n,k), va ty le ma c nh ngha Rc = k/n vabang toc o thong tin chia cho toc o kenh cha ieu che.

2. Ma chap:Ma chap la khac c ban so vi ma khoi. Thay cho cac chuoi thong tin ma

khoi c chia ra cac khoi rieng le va ma hoa la mot chuoi bits thong tin c sap xepthanh mot chuoi lien tuc tai au ra cua bo ma hoa. Vi cung mot o phc tap th o li

ma hoa cua ma chap ln hn ma khoi.Mot ma khoi c sinh ra bang cach cho chuoi thong tin i qua cacthanh ghi dch trang thai hu han. Thanh ghi dch nay cha N(k bi ts) tang va phat ra mham ai so tuyen tnh da tren viec phat ra cac a thc, ieu nay c minh hoa tronghnh 5.5. D lieu ngo vao c dch vao va theo thanh ghi dch k bi ts tai moi thiiem. So bits au ra vi moi chuoi d lieu ngo vao k bits la n bits. Ty le ma Rc =k/n.He so N c goi la chieu dai bat buoc va cho thay so bits d lieu ngo vao phu thuocvao ngo ra hien hanh. No quyet nh the manh va o phc tap cua ma.


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Hnh 5.5 S o khoi tong quat cua boma hoa chap.

Encoded Sequence

1

+

1k Databits

k 1

2

+

n

+

N Stages

k 1 k


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PHAN 2:KHAO SAT VE WAVELETS

CHNG I:GII THIEU VE WAVELETS

I . OI NET VE S PHAT TRIEN CUA WAVELET:1.Tr c nam 1930:Trc nam 1930, ly thuyet phan tch tn hieu c bat au vi ly thuyet phan

tch tan so cua Fourier (1807) ma chung ta thng goi la phan tch Fourier. Ong phatbieu rang moi ham f(x) tuan hoan chu ky 2 eu co the c bieu dien bang tong

1

0

k

kkkxsinbkxcosaa

Cac he so a0, ak, va bk c tnh theo cac tch phan

2

0

2

0

2

0

0

11

2

1dx)kxsin()x(fb,dx)kxcos()x(fa,dx)x(fa kk

Tong tren c goi la chuoi Fourier.Sau nam 1807, qua qua trnh nghien cu ban chat cua cac ham, s hoi tu cua

chuoi Fourier, va cac he trc giao, cac nha toan hoc dan dan chuyen y tng phan tchtan so sang phan tch ty le. Co ngha la, phan tch f(x) bang cach tao cac cau truc toan

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