CDMA Architecture HTVT2

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GII THIU H THNG THNG TIN DI NG NG DNG CNG NGH CDMA CDMA AND APPLICATIONSB Mn Vin Thng Khoa in-in T Trng i Hc Bch Khoa TP. H Ch Minh TP.HCM 2-2006

CC PHNG PHP A TRUY NHP MULTIPLE ACCESS SCHEMES

Khi qut cc phng php a truy nhp Trong h thng thng tin a truy nhp, s lng ln thng tin c chia s trn knh thng tin chung. Mc ch l phi hp tn hiu t cc my thu khc nhau trn cng mt knh thng tin chung, ti my thu cc tn hiu phn bit c lp ln nhau m khng gy nhiu do a truy nhp gy ra. Da trn c im ca vic phn chia cc tn hiu chia s cung knh thng tin, c cc phng php a truy nhp nh sau: a truy nhp phn chia theo tn s FDMA a truy nhp phn chia theo thi gian TDMA a truy nhp phn chia theo m CDMA

Cc phng thc a truy nhp

Cc phng thc a truy nhp-FDMA Cc ngi s dng c truy nhp vo knh thng tin chung trn c s phn chia theo tn s. FDMA c c im: Knh FDMA ch phc v duy nht mt thu bao ti mt thi im Nu mt knh FDMA khng c dng, th n khng c ti s dng bi mt user khc. Sau khi gn mt knh thoi, BS v MS tin hnh thu v pht mt cch lin tc ng thi. Bng thng knh FDMA nh (30KHz) Thi gian ca k hiu (symbol) thng ln hn thi gian tr tn hiu. FDMA l phng php truyn dn lin tc nn t cn cc bit phc v mc ch nh tuyn.

Cc phng thc a truy nhp-FDMAFDMA cn cu trc lc RF cht ch ti thiu ha giao thoa gia cc knh thng tin k cn. Tng s knh c th hot ng ng thi trong mt h thng FDMA l:

N=

Btot 2 Bguard Bc

Btot: Tng s ph c phn phi Bguard: Bng tn bo v xung quanh mi knh Bc: Bng tn s dng ca mi knh

Cc phng thc a truy nhp-TDMA Cc ngi s dng c truy nhp vo knh thng tin chung trn c s phn chia theo thi gian. TDMA c c im: Mi user chim mt khe thi gian TDMA chia mt sng mang n cho mt user. S khe thi gian trong mi khung ph thuc vo k thut iu ch, bng thng Truyn dn TDMA khng lin tc. Qu trnh x l chuyn giao cuc gi gia cc Cell l n gin, MS c th theo di cc trm gc khc nhau trong sut qu trnh ngh. TDMA s dng cc khe thi gian khc nhau cho pht v thu. Qu trnh ng b khung rt cn thit v i hi chnh xc pha thu tch sng ng.

Cc phng thc a truy nhp-TDMATrong TDMA, tng s knh trong h thng c xc nh:

N=

m( Btot 2 Bguard ) Bc

Btot: Tng s ph c phn phi Bguard: Bng tn bo v xung quanh mi knh Bc: Bng tn s dng ca mi knh m: S User cc i trong mt knh v tuyn

Cc phng thc a truy nhp-CDMA c im ca h thng a truy nhp phn chia theo m: Cc User cng chia s mt bng tn s CDMA c mt gii hn mm (soft limitation) i vi dung lng h thng (system capacity). Hn ch ng k nhiu Fading a ng bi v tn hiu c tri ra trn mt ph rt rng so vi ph ca tn hiu gc. Trong CDMA, tt c cc Cell u s dng li tn s ca cc cell k cn. Nhiu ng knh c hn ch nh vo s dng thu phn tp theo khng gian, h tr vic chuyn giao mm (Soft Handoff). Giao thoa gn-xa (Near-Far Problem) l mt hin tng ph bin trong CDMA.

So snh c trng ca FDMA/TDMA/CDMAFDMA Knh/Sng mang 1 TDMA N>1. Mt khung TDMA gm N khe thi gian uwojc ch nh dng cho mi khe thi gian khc nhau Khng lin tc, pht v thu ti cc khe thi gian khng cho nhau BW tng i CDMA N>1. Tt c cc thu bao pht ng thi trn cng mt bng thng. Lin tc ng thi trn ng Uplink v Downlink. BW rt rng.

Pht

Lin tc, ng thi trn ng Uplink v Downlink

Bng Bng tn hp tn/knh tn s

So snh c trng ca FDMA/TDMA/CDMAFDMA Nhiu giao thoa gia cc k hiu Tng s Bit/Khung Khng ng k TDMA CDMA

C gi tr, dn n C gi tr, my s phn chia thu RAKE c khong cch pht s dng. N phn Cao, cha cc Bit ng bm bit bo v v Bit gim st Tng i thp, nhng yu cu c thm knh Pilot yu cu cho vic tch sng lin tc

Thp

Phn cng

n gin

BW tng i phc Rt phc tp do tp do b cn bng yu cu x l tc ng b phc tp cao trn bng rng

So snh c trng ca FDMA/TDMA/CDMAFDMA Ghp Duplex Yu cu TDMA CDMA

Khng cn thit v Yu cu pht v thu ti nhng khe thi gian khc nhau Thc hin c v MS lun hat ng gim st cc BS trong N-1 khe thi gian khc. Do c th thc hin c Handoff nhanh. Thp Thc hin c v MS s dng my thu RAKE kim tra BS khc. Ngoi ra cn c chuyn giao mm. Chi ph ng truyn RF thp nhng b x l BS chi ph cao.

Chuyn giao My pht v thu Handoff ca BS lin tc nn khng hiu c Handoff

Chi ph BS

Cao, mt my pht v my thu cho mi knh

So snh c trng ca FDMA/TDMA/CDMAFDMA Nhiu bng hp TDMA CDMA Khng nh hng v nhiu bng hp b suy gim ng k ti b nn ph my thu Khng cn thit iu khin nhanh, c tnh hu hiu Phc v cc dch v vi tc bit pht khc nhau

B nh hng, nh hng v lm lm gim c tnh gim c tnh h h thng thng

Ti s dng tn s iu khin cng sut

Cn thit iu khin chm

Cn thit iu khin, dung lng khng tng Dung lng pht bng s lng cc khe thi gian ti cc knh tn s

Cc dch v Dung lng pht mi bng s lng khe thi gian ti cc knh tn s

So snh c trng ca FDMA/TDMA/CDMAFDMA Nhiu bng hp 1 TDMA N>1. Mt khung TDMA gm N khe thi gian uwojc ch nh dng cho mi khe thi gian khc nhau Khng lin tc, pht v thu ti cc khe thi gian khng cho nhau BW tng i CDMA N>1. Tt c cc thu bao pht ng thi trn cng mt bng thng. Lin tc ng thi trn ng Uplink v Downlink. BW rt rng.

Pht

Lin tc, ng thi trn ng Uplink v Downlink

Bng Bng tn hp tn/knh tn s

Bng thng s k thut ca FDMA/TDMA/CDMAThng s Di tn v tuyn Ti s dng tn s Di thng knh v tuyn S knh v tuyn/di S knh v tuyn/1cell S knh lu thng trong 1 knh v tuyn S knh lu thng trong mt cell S di qut trong 1 cell S knh lu thng/di Dung lng FDMA 12.5MHz K=7 0.03MHz 416 58 1 57 3 19 100% TDMA 12.5MHz K=7 0.03MHz 416 58 3 168 3 56 300% CDMA 12.5MHz K=1 1.25MHz 10 10 20 200 3 200 1000%

GII THIU CDMA INTRODUCTION TO CODE DIVISION MULTIPLE ACCESS

CDMA l g ?

M hnh ti s dng tn s FDMA: h s ti s dng tn s K=7; CDMA: h s K=1.

Chui nh phn gi ngu nhin PRBSChui tn hiu nh phn gi ngu nhin PRBS (Pseudo Random Binary Sequence): 1. Gii thiu PRBS: L mt chui nh phn 0,1. Trong 0,1 xut hin c v nh ngu nhin, khng tun theo mt qui lut n gin. PRBS l chui nh phn tun hon c chu k rt ln ng dng PRBS: S dng trong qun i S dng trong k thut CDMA Phn loi k thut tri ph: Cc h thng tri ph c phn loi trn c s phng php iu ch v cu trc ca h thng, thng gm: Tri ph chui trc tip DS-SS (Direct Sequence-Spread Spectrum). Tri ph nhy tn FH-SS (Frequency Hopping-Spread Spectrum) Trong , phng php tri ph chui trc tip a truy nhp theo m DS-CDMA c s dng v bit n rt rng ri.

Chui gi ngu nhin PN2. Chui gi ngu nhin PN:

-

-

Tn hiu PRBS c to ra bng cch dng N cc D-Flip-Flop ghp li to thnh mt thanh ghi dch. u vo ca thanh ghi l tn hiu hi tip c to ra t ghp cng XOR cc tn hiu ly t cc u ra ca Flip-Flop. Nhng khng phi mi u ra u uwojc cng li hi tip. Mi kiu t hp trn s to ra mt tn hiu hi tip ring v do to ra mt qui lut bin i ring u ra ca thanh ghi dch, Mt h nh th c gi l h tun t, v do tn hiu u ra s tun hon c chu k. Ty theo cch chn t hp hi tip m chu k lp ca tn hiu c th di ngn khc nhau, to tn hiu gi ngu nhin, chu k lp li cng ln cng tt. Tuy nhin nu gi N l s Flip-Flop trong thanh ghi dch, chu k ny khng th ln hn 2 N .

Cc chui m tri ph Hin nay, mt s m tri ph c s dng ph bin trong h thng thng tin v tuyn: Chui M

S to chui M

Chui Gold

Cc chui m tri ph

S to chui Gold

Chui Kasami

Paradigm Shift of CDMA

Dung lng h thng CDMA

ngha gi tr Eb/N0 trong h thng CDMA L t s nng lng ca mi bit trn mt ph cng sut tp m, l gi tr chun so snh hiu sut ca phng php iu ch v m ha s. nng cao hiu sut, h thng CDMA s dng cc knh bng rng v s dng cc m chun ha li vi d phng cao. Dung lng ca h thng CDMA t l nghch vi t s Eb/N0, cho nn nu gim c Eb/N0 xung, dung lng h thng s tng ln, v cng sut pht cng c gim.

B thu RAKE

ng B

iu khin cng sut

iu khin cng sut

iu khin cng sut trn ng ln

iu khin cng sut vng m

iu khin cng sut vng ng

iu khin cng sut vng ng

Cn bng gia Dung lng, Cht lng, Vng ph sng l 3 yu t c bn trong bt k mng v tuyn no. Trong CDMA, 3 yu t ny c mi quan h qua li cht ch, mt yu t ny c th c ci thin bng cch h thp yu t khc mt cch hp l v c li cho h thng. V d, mt h thng CDMA vn d c dung lng h thng kh cao. Bng cch gim vng ph sng hoc cht lng xung n mc nht nh, dung lng ca h thng s c ci thin. S dung ha linh ng gia 3 yu t ny to nn mt c tnh quan trong cho cc nh khai thc, thit k v vn hnh h thng CDMA.

S KHI H THNG CDMA ARCHITECTURE OF CDMA SYSTEM

H thng CDMA

MS: Mobile StationMS

BS: Base Station MX: Mobile ExchangeBSC MSC ASS PSTN

HLR: Home Location Registration BSC:Base Station Controller

BTS

CCS BSM

BSS

MX

BSM: Base Station Manager ASS: Access Switching Subsystem CCS: Central Control Subsystem

HLR

Trm di ng Mobile Station MS MS c 3 chc nng: Thit b u cui: Thc hin cc dch v ca ngi s dng Kt cui di ng: thc hin truyn dn giao din v tuyn vi mng truy nhp Kt ni trung gian: thc hin giao tip 2 chc nng trn

Cu hnh BSS RF: Radio Frequency Block CD: CDMA Digital BlockCKD RF CD

BCP: BTS Control Processor CIN: CDMA Interconnection NetworkMX

BIN GPS BCP

CIN

TSB

CKD: Clock Distributor TSB: Transcoder Selector Bank CCP: Call Control Processor.

CCP

BTS

BSC

BSMP

ALM

BSM

BIN: BTS Interconnection Network BSMP: Base Station Manager Processor. ALM: Alarm

Cu hnh Mobile Exchange MX

Chc nng ca MXCc chc nng trong khi MX: ASS: Access Switching Subsystem ASS-7: Truy cp mng bo hiu s 7 ASS-T: Truy cp mng trung k PSTM ASS-M: Truy cp mng thu bao di ng INS: Interconnection Network Subsystem CCS: Central Control Subsystem AMS: Administration and Maintenance Subsystem LRS: Location Register Subsystem

Chc nng ca MXMX c cc chc nng nh sau: Phn h chuyn mch truy cp ASS Phn h lin kt mng INS, cung cp u ni cho ASS v CCS, x l tp trung cuc gi v ng b ha mng chuyn mch. Phn h iu khin trung tm CCS: Bao gm cc khi AMS, LRS. Mi cuc gi cn c gn vo mt b chn v b Vocoder tng ng.

Cu trc b HLR

AES: Application Entity Subsystem DBS: Database Subsystem OMS: Operation Maintenance Subsystem

Chc nng HL