TRNG I HC S PHM K THUT TP.HCM KHOA IN - IN T B MN IN T VIN THNG N TT NGHIP ti: QUY HOCH MNG 4G LTE GVHD: TS. L Quang Tun SVTH: Nguyn Th Thy Dng MSSV: 06117013 TP.H Ch Minh - Thng 1/ 2011 PHN A GII THIU n tt nghip Trang i LI CM N Sau khong thi gian hc tp ti trng, y l khong thi gian kh qun i vi chng em. Thy c ch bo tn tnh gip cho chng em trang b kin thc vng vng bc vo i. c nh ngy hm nay, em xin gi li cm n n cc thy c trong b mn in T Vin Thng cng nh cc thy c trong khoa in-in t hng dn, truyn t kin thc cho chng em. Em xin gi li cm n c bit n thy TS. L Quang Tun, cng ty Vin Thng Quc ni (VTN), ngi trc tip tn tnh hng dn em c th hon thnh ti ny. Xin gi li cm n n ba m ng vin gip c v vt cht v tinh thn cho con bao nhiu nm qua, ng cm n n bn b lun lun bn cnh mnh . Xin by t lng bit n su sc Ngi thc hin Nguyn Th Thy Dng n tt nghip Trang ii QUYT NH GIAO TI Sinh vin thc hin: Nguyn Th Thy Dng MSSV: 06117013 Ngnh: Cng ngh in t - Vin thng Tn ti: QUY HOCH MNG 4G LTE V P DNG CHO TP.HCM 1) C s ban u: ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... 2) Ni dung cc phn thuyt minh v tnh ton: ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... 3) Cc bn v: ....................................................................................................................... ....................................................................................................................... ....................................................................................................................... 4) Gio vin hng dn: TS. L Quang Tun 5) Ngy giao nhim v: 6) Ngy hon thnh nhim v: B GIO DC V O TO TRNG I HC S PHM K THUT TP. H CH MINH CNG HA X HICH NGHA VIT NAM c lp T do Hnh phc Gio vin hng dn TS. L Quang Tun Ngy .. thng .. nm 2011 Ch nhim b mn n tt nghip Trang iii NHN XT CA GIO VIN HNG DN .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. Ngy .. thng .. nm 2011 Gio vin hng dn TS. L Quang Tun n tt nghip Trang iv NHN XT CA GIO VIN PHN BIN .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. Ngy .. thng .. nm 2011 Gio vin phn bin 2 Ngy .. thng .. nm 2011 Gio vin phn bin 1 n tt nghip Trang v LI NI U Ngnh cng ngh vin thng chng kin nhng pht trin ngon mc trong nhng nm gn y. Khi m cng ngh mng thng tin di ng th h th ba 3G cha c thi gian khng nh v th ca mnh trn ton cu, ngi ta bt u ni v cng ngh 4G (Fourth Generation) t nhiu nm gn y. Th nhng, ni mt cch chnh xc th 4G l g? Liu c mt nh ngha thng nht cho th h mng thng tin di ng tng lai 4G? Ngc dng thi gian... Trong hn mt thp k qua, th gii chng kin s thnh cng to ln ca mng thng tin di ng th h th hai 2G. Mng 2G c th phn ra 2 loi: mng 2G da trn nn TDMA v mng 2G da trn nn CDMA. nh du im mc bt u ca mng 2G l s ra i ca mng D-AMPS (hay IS-136) dng TDMA ph bin M. Tip theo l mng CdmaOne (hay IS-95) dng CDMA ph bin chu M v mt phn ca chu , ri mng GSM dng TDMA, ra i u tin Chu u v hin c trin khai rng khp th gii. S thnh cng ca mng 2G l do dch v v tin ch m n mng li cho ngi dng, tiu biu l cht lng thoi v kh nng di ng. Hnh : S tm lc qu trnh pht trin ca mng thng tin di ng t bo Tip ni th h th 2, mng thng tin di ng th h th ba 3G v ang c trin khai nhiu ni trn th gii. Ci tin ni bt nht ca mng 3G so vi mng 2G l kh nng cung ng truyn thng gi tc cao nhm trin khai cc dch v truyn thng a phng tin. Mng 3G bao gm mng UMTS s dng k n tt nghip Trang vi thut WCDMA, mng CDMA2000 s dng k thut CDMA v mng TD-SCDMA c pht trin bi Trung Quc. Gn y cng ngh WiMAX cng c thu nhn vo h hng 3G bn cnh cc cng ngh ni trn. Tuy nhin, cu chuyn thnh cng ca mng 2G rt kh lp li vi mng 3G. Mt trong nhng l do chnh l dch v m 3G mang li khng c mt bc nhy r rt so vi mng 2G. Mi gn y ngi ta mi quan tm ti vic tch hp MBMS (Multimedia broadcast and multicast service) v IMS (IP multimedia subsystem) cung ng cc dch v a phng tin. Khi nim 4G bt ngun t u? C nhiu nh ngha khc nhau v 4G, c nh ngha theo hng cng ngh, c nh ngha theo hng dch v. n gin nht, 4G l th h tip theo ca mng thng tin di ng khng dy. 4G l mt gii php vt ln nhng gii hn v nhng im yu ca mng 3G. Thc t, vo gia nm 2002, 4G l mt khung nhn thc tho lun nhng yu cu ca mt mng bng rng tc siu cao trong tng lai m cho php hi t vi mng hu tuyn c nh. 4G cn l hin th ca tng, hy vng ca nhng nh nghin cu cc trng i hc, cc vin, cc cng ty nh Motorola, Qualcomm, Nokia, Ericsson, Sun, HP, NTT DoCoMo v nhiu cng ty vin thng khc vi mong mun p ng cc dch v a phng tin m mng 3G khng th p ng c. Theo dng pht trin Nht, nh cung cp mng NTT DoCoMo nh ngha 4G bng khi nim a phng tin di ng (mobile multimedia) vi kh nng kt ni mi lc, mi ni, kh nng di ng ton cu v dch v c th cho tng khch hng. NTT DoCoMo xem 4G nh l mt m rng ca mng thng tin di ng t bo 3G. Quan im ny c xem nh l mt quan im tuyn tnh trong mng 4G s c cu trc t bo c ci tin cung ng tc ln trn 100Mb/s. Vi cch nhn nhn ny th 4G s chnh l mng 3G LTE , UMB hay WiMAX 802.16m. Nhn chung y cng l khuynh hng ch o c chp nhn Trung Quc v Hn Quc. Bn cnh , mc d 4G l th h tip theo ca 3G, nhng tng lai khng hn ch gii hn nh l mt m rng ca mng t bo. V d chu u, 4G c xem nh l kh nng m bo cung cp dch v lin tc, khng b ngt qung vi n tt nghip Trang vii kh nng kt ni vi nhiu loi hnh mng truy nhp v tuyn khc nhau v kh nng chn la mng v tuyn thch hp nht truyn ti dch v n ngi dng mt cch ti u nht. Quan im ny c xem nh l quan im lin i. Do , khi nim ABC-Always Best Connected (lun c kt ni tt nht) lun c xem l mt c tnh hng u ca mng thng tin di ng 4G. nh ngha ny c nhiu cng ty vin thng ln v nhiu nh nghin cu, nh t vn vin thng chp nhn nht hin nay. D theo quan im no, tt c u k vng l mng thng tin di ng th h th t 4G s ni ln vo khong 2010-2015 nh l mt mng v tuyn bng rng tc siu cao. Vit Nam , hin nay 3G ang pht trin rm r v tin ln 4G khng cn xa na. Theo tin t Tp on Bu chnh vin thng Vit Nam (VNPT), n v ny va hon thnh vic lp t trm BTS s dng cho dch v v tuyn bng rng cng ngh LTE (Long Term Evolution), cng ngh tin 4G u tin ti Vit Nam v ng Nam . n nghin cu v Cng ngh 4G LTE l cng ngh cn mi m v ph hp vi thc trng hin nay ca Vit Nam. Ni dung ca n bao gm 3 phn : Phn A : Gii thiu Phn B : Ni dung Chng 1: Gii thiu v h thng thng tin di ng v tng quan v mng 4G Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Chng 3 : Quy hoch mng 4G LTE v p dng cho TP. HCM Chng 4 : M phng Phn C : Ph lc v ti liu tham kho Trong qu trnh thc hin ti, ngi thc hin c nhng hn ch v kh nng v cn nhiu sai st , rt mong s ng gp kin ca thy c v bn b . n tt nghip Trang viii MC LC PHN A : GII THIU LI CM N ......................................................................................................... i QUYT NH GIAO TI ................................................................................ ii NHN XT CA GIO VIN HNG DN .....................................................iii NHN XT CA GIO VIN PHN BIN ........................................................ iv MC LC ........................................................................................................... viii MC LC HNH .................................................................................................. xii MC LC BNG................................................................................................. xv PHN B : NI DUNG CHNG 1: GII THIU V H THNG THNG TIN DI NG V TNG QUAN V MNG 4G ............................................................................................ 1 1. 1 S pht trin ca h thng thng tin di ng .................................................. 1 1. 1. 1 H thng thng tin di ng th h 1 (1G) ............................................... 2 1. 1. 2 H thng thng tin di ng th h 2 (2G) ............................................... 3 1. 1. 3 H thng thng tin di ng th h 3 (3G) ............................................... 6 1. 1. 4 H thng thng tin di ng th h 4 (4G) ............................................... 7 1. 2 Tng quan v mng 4G [12] .......................................................................... 8 1. 3 S khc nhau gia 3G v 4G ....................................................................... 10 1. 3. 1 u im ni bt.................................................................................... 11 1.3.2 Cc ng dng to nn u im ca 4G LTE so vi 3G ...................... 11 CHNG 2 : CU TRC MNG 4G LTE V CC VN LIN QUAN .... 14 2.1 Gii thiu v cng ngh LTE........................................................................ 14 2.2 Cu trc ca LTE [1] .................................................................................... 24 n tt nghip Trang ix 2.3 Cc knh s dng trong E-UTRAN .............................................................. 29 2.4 Giao thc ca LTE (LTE Protocols) [2] ....................................................... 31 2.5 Mt s c tnh ca knh truyn .................................................................. 34 2.5.1 Tri tr a ng .................................................................................... 34 2.5.2 Cc loi fading ....................................................................................... 34 2.5.3 Dch tn Doppler .................................................................................... 35 2.5.4 Nhiu MAI i vi LTE ......................................................................... 35 2.6 Cc k thut s dng trong LTE .................................................................. 36 2.6.1 K thut truy cp phn chia theo tn s trc giao OFDM [1] .................. 36 2.6.2 K thut SC-FDMA [1] ......................................................................... 46 2.6.3 K thut MIMO [1] ................................................................................ 48 2.6.4 M ha Turbo [18] ................................................................................ 50 2.6.5 Thch ng ng truyn [18] ................................................................. 51 2.6.6 Lp biu ph thuc knh [18] ................................................................ 52 2.6.7 HARQ vi kt hp mm [18] ................................................................ 52 2.7 Chuyn giao ................................................................................................ 53 2.7.1 Mc ch chuyn giao ............................................................................ 53 2.7.2 Trnh t chuyn giao ............................................................................. 54 2.7.3 Cc loi chuyn giao ............................................................................. 56 2.7.4 Chuyn giao i vi LTE [3] ................................................................ 59 2.8 iu khin cng sut [3] .............................................................................. 60 2.8.1 iu khin cng sut vng h [8] ........................................................... 61 2.8.2 iu khin cng sut vng kn [8] .......................................................... 62 CHNG 3 : QUY HOCH MNG 4G LTE V P DNG CHO TP.HCM ..... 65 3. 1 Khi qut v qu trnh quy hoch mng LTE ............................................. 65 n tt nghip Trang x 3. 2 D bo lu lng v phn tch vng ph ..................................................... 66 3. 2. 1 D bo lu lng ................................................................................. 66 3. 2. 2 Phn tch vng ph ............................................................................... 67 3. 3 Quy hoch chi tit ....................................................................................... 67 3. 3. 1 Quy hoch vng ph ............................................................................ 67 3. 3. 1. 1 Qu ng truyn [2] .................................................................... 68 3. 3. 1. 2 Cc m hnh truyn sng ............................................................... 77 3. 3. 1. 3 Tnh bn knh cell ........................................................................ 83 3. 3. 2 Quy hoch dung lng ......................................................................... 85 3. 4 Quy hoch cho TP H Ch Minh ................................................................. 90 3.5 Ti u mng ................................................................................................. 91 3.6 iu khin cng sut knh PUSCH ca LTE [7] ......................................... 92 CHNG 4: M PHNG ................................................................................... 95 4.1 Cc lu .................................................................................................... 95 4.2 Quy hoch mng LTE .................................................................................. 96 4.2.1 Quy hoch vng ph .............................................................................. 97 4.2.1.1 Qu ng truyn ............................................................................ 97 4.2.1.2 Cc m hnh truyn sng ................................................................. 98 4.2.1.3 Quy hoch vng ph ...................................................................... 100 4.2.2 Quy hoch dung lng ca LTE .......................................................... 100 4.2.3 Ti u s trm ..................................................................................... 102 4.2.4 So snh vng ph ca LTE v WCDMA .............................................. 103 4.3. Chuyn giao v iu khin cng sut ........................................................ 105 4.3.1 Giao din chnh .................................................................................... 105 4.3.2 iu khin cng sut ............................................................................ 106 n tt nghip Trang xi 4.3.3 Chuyn giao ........................................................................................ 109 4.3.3.1 Trng hp chuyn giao thnh cng .............................................. 110 4.3.3.2 Trng hp chuyn giao b rt ....................................................... 111 KT LUN V HNG PHT TRIN CA TI ..................................... 113 PHN C: PH LC V TI LIU THAM KHO PH LC 1 : CC T VIT TT .................................................................... 114 PH LC 2 : HNG DN S DNG ........................................................... 119 CHNG TRNH .............................................................................................. 119 TI LIU THAM KHO ................................................................................... 122 n tt nghip Trang xii MC LC HNH Hnh 2.1: So snh v cu trc gia UTMS v LTE ................................................ 24 Hnh 2.2: Cu trc c bn ca LTE ....................................................................... 25 Hnh 2.3: Cu trc h thng cho mng truy cp 3GPP ........................................... 27 Hnh 2.4 : Cu trc h thng cho mng truy cp3GPP v khng phi 3GPP .......... 28 Hnh 2.6: Giao thc ca UTRAN .......................................................................... 31 Hnh 2.7: Giao thc ca E-UTRAN ....................................................................... 32 Hnh 2.8: Phn phi chc nng ca cc lp MAC, RLC, PDCP ............................. 32 Hnh 2.9 : Truyn n sng mang.......................................................................... 36 Hnh 2.10 : Nguyn l ca FDMA ......................................................................... 36 Hnh 2.11 : Nguyn l a sng mang ..................................................................... 36 Hnh 2.12 : So snh ph tn ca OFDM vi FDMA .............................................. 37 Hnh 2.13 : Tn s-thi gian ca tn hiu OFDM ................................................... 37 Hnh 2.14 : Cc sng mang trc giao vi nhau ...................................................... 38 Hnh 2.15 : Bin i FFT ....................................................................................... 39 Hnh 2.16 : Thu pht OFDM ................................................................................. 39 Hnh 2.17: Chui bo v GI .................................................................................. 40 Hnh 2.18 Tc dng ca chui bo v ................................................................... 41 Hnh 2.19 Sng mang con OFDMA....................................................................... 42 Hnh 2.20 OFDM v OFDMA ............................................................................... 42 Hnh 2.21 : Ch nh ti nguyn ca OFDMA trong LTE ...................................... 43 Hnh 2.22 : Cu trc ca mt khi ti nguyn ........................................................ 44 Hnh 2.23 : Cu trc b tr tn hiu tham kho ....................................................... 45 Hnh 2.24: c tnh ng bao ca tn hiu OFDM ............................................... 45 n tt nghip Trang xiii Hnh 2.25: PAPR cho cc tn hiu khc nhau ......................................................... 46 Hnh 2.26: OFDMA v SC-FDMA ........................................................................ 47 Hnh 2.28 M hnh SU-MIMO v MU-MIMO ...................................................... 49 Hnh 2.29: Ghp knh khng gian ......................................................................... 50 Hnh 2.30 iu ch thch nghi .............................................................................. 51 Hnh 2.31: Nguyn tc chung ca cc thut ton chuyn giao ................................ 55 Hnh 2.32 : Chuyn giao mm ............................................................................... 57 Hnh 2.33 : Chuyn giao mm - mm hn ............................................................. 58 Hnh 2.34 : Chuyn giao cng ............................................................................... 58 Hnh 2.35: Cc loi chuyn giao ............................................................................ 59 Hnh 2.36: iu khin cng sut vng h .............................................................. 62 Hnh 2.37: iu khin cng sut vng kn ............................................................. 63 Hnh 3. 1: Khi qut v qu trnh quy hoch mng LTE ........................................ 65 Hnh 3. 2 : Cc tham s ca m hnh Walfisch-Ikegami ........................................ 79 Hnh 3. 3: Quan h gia bng thng knh truyn v bng thng cu hnh .............. 88 Hnh 4.1 : Lu phn m phng quy hoch LTE ................................................ 95 Hnh 4.2 : Lu phn chuyn giao v iu khin cng sut ................................ 96 Hnh 4.3: Giao din phn quy hoch mng LTE .................................................... 96 Hnh 4.4: Qu ng truyn ca LTE.................................................................... 97 Hnh 4.5 Mi trng truyn sng trong nh ........................................................... 98 Hnh 4.6 : Mi trng truyn sng ngoi tri ........................................................ 99 Hnh 4.7: Mi trng xe c ................................................................................... 99 Hnh 4.8: Quy hoch vng ph LTE .................................................................... 100 Hnh 4.9 : Quy hoc dung lng LTE .................................................................. 101 Hnh 4.10: Tnh ton tc nh ......................................................................... 102 n tt nghip Trang xiv Hnh 4.11: Ti u s trm .................................................................................... 102 Hnh 4.12 : So snh qu ng truyn ln ca LTE v WCDMA ........................ 103 Hnh 4.13: So snh qu ng truyn xung ca LTE v WCDMA .................... 103 Hnh 4.14: So snh vng ph ca LTE v WCDMA ............................................ 104 Hnh 4.15: Giao din phn chuyn giao v iu khin cng sut.......................... 105 Hnh 4.16: Nhp d liu cho iu khin cng sut ............................................... 106 Hnh 4.17: iu khin cng sut LTE ............................................................... 107 Hnh 4.18: Nhp liu ca WCDMA ..................................................................... 108 Hnh 4.19: So snh iu khin cng sut ca LTE v WCDMA .......................... 109 Hnh 4.20: Trng hp chuyn giao thnh cng .................................................. 110 Hnh 4.21: Trng hp chuyn giao b rt ........................................................... 111 n tt nghip Trang xv MC LC BNG Bng 2.1 : Cc thng s lp vt l LTE ................................................................. 17 Bng 2.2 : Tc nh ca LTE theo lp .............................................................. 18 Bng 2.3 : So snh cc dch v ca 3G so vi 4G LTE .......................................... 19 Bng 2.4 : So snh gia HSPA, WiMAX v LTE .................................................. 21 Bng 2.5 : S khi ti nguyn theo bng thng knh truyn ................................... 43 Bng 3. 1 :V d v qu ng ln ca LTE .......................................................... 71 Bng 3. 2 : V d ca qu ng xung LTE ......................................................... 73 Bng 3. 3 : So snh qu ng truyn ln ca cc h thng ................................... 74 Bng 3. 4 : So snh v qu ng truyn xung ca cc h thng ......................... 75 Bng 3. 5 : Cc gi tr K s dng cho tnh ton vng ph sng .............................. 85 Bng 3. 6 : Tc bit nh tng ng vi tng tc m ha v bng thng ........ 86 Bng 3. 7 Gi tr ca bng thng cu hnh tng ng vi bng thng knh truyn[4] .............................................................................................................................. 88 Bng 3.8 Din tch v dn s tng qun ca TP.HCM [11] ................................ 90 Bng 3.9 Cc lp cng sut ca UE [10] ............................................................... 93 PHN B NI DUNG n tt nghip Trang 1 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G CHNG 1: GII THIU V H THNG THNG TIN DI NG V TNG QUAN V MNG 4G Thng tin di ng l mt lnh vc rt quan trng trong i sng x hi. X hi cng pht trin, nhu cu v thng tin di ng ca con ngi cng tng ln v thng tin di ng cng khng nh c s cn thit v tnh tin dng ca n. Cho n nay, h thng thng tin di ng tri qua nhiu giai on pht trin, t th h di ng th h 1 n th h 3 v th h ang pht trin trn th gii - th h 4. Trong chng ny s trnh by khi qut v cc c tnh chung ca cc h thng thng tin di ng v tng quan v mng 4G. 1. 1 S pht trin ca h thng thng tin di ng Khi cc ngnh thng tin qung b bng v tuyn pht trin th tng v thit b in thoi v tuyn ra i v cng l tin thn ca mng thng tin di ng sau ny. Nm 1946, mng in thoi v tuyn u tin c th nghim ti ST Louis, bang Missouri ca M. Sau nhng nm 50, vic pht minh ra cht bn dn cng nh hng ln n lnh vc thng tin di ng. ng dng cc linh kin bn dn vo thng tin di ng ci thin mt s nhc im m trc y cha lm c. Thut ng thng tin di ng t bo ra i vo nhng nm 70, khi kt hp c cc vng ph sng ring l thnh cng, gii c bi ton kh v dung lng. n tt nghip Trang 2 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G Hnh 1: L trnh pht trin ca h thng thng tin di ng t bo 1. 1. 1 H thng thng tin di ng th h 1 (1G) Nhng h thng thng tin di ng u tin, nay c gi l th h th nht (1G), s dng cng ngh analog gi l a truy nhp phn chia theo tn s (FDMA) truyn knh thoi trn sng v tuyn n thu bao in thoi di ng. Vi FDMA, ngi dng c cp pht mt knh trong tp hp c trt t cc knh trong lnh vc tn s. Trong trng hp nu s thu bao nhiu vt tri so vi cc knh tn s c th, th mt s ngi b chn li khng c truy cp. 1. 1. 1. 1 c im Mi MS c cp pht i knh lin lc sut thi gian thng tuyn. Nhiu giao thoa do tn s cc knh ln cn nhau l ng k. Trm thu pht gc BTS phi c b thu pht ring lm vic vi mi MS trong cell. H thng FDMA in hnh l h thng in thoi di ng tin tin AMPS. 1. 1. 1. 2 Nhng hn ch ca h thng thng tin di ng th h 1 H thng di ng th h 1 s dng phng php a truy cp n gin. Tuy nhin h thng khng tha mn nhu cu ngy cng tng ca ngi dng v c dung lng v tc . N bao gm cc hn ch sau : Phn b tn s rt hn ch, dung lng nh. n tt nghip Trang 3 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G Ting n kh chu v nhiu xy ra khi my di ng chuyn dch trong mi trng fading a tia. Khng cho php gim ng k gi thnh ca thit b di ng v c s h tng. Khng m bo tnh b mt ca cc cuc gi. Khng tng thch gia cc h thng khc nhau, c bit chu u, lm cho thu bao khng th s dng c my di ng ca mnh cc nc khc. Cht lng thp v vng ph sng hp. Gii php duy nht loi b cc hn ch trn l phi chuyn sang s dng k thut thng tin s cho thng tin di ng cng vi k thut a truy cp mi u im hn v c dung lng v cc dch v c cung cp. V vy xut hin h thng thng tin di ng th h 2. 1. 1. 2 H thng thng tin di ng th h 2 (2G) H thng thng tin di ng s s dng k thut a truy cp phn chia theo thi gian (TDMA) u tin trn th gii c ra i chu u v c tn gi l GSM. Vi s pht trin nhanh chng ca thu bao, h thng thng tin di ng th h 2 lc p ng kp thi s lng ln cc thu bao di ng da trn cng ngh s. H thng 2G hp dn hn h thng 1G bi v ngoi dch v thoi truyn thng, h thng ny cn c kh nng cung cp mt s dch v truyn d liu v cc dch v b sung khc. Vit Nam, h thng thng tin di ng s GSM c a vo t nm 1993, hin nay ang c Cng ty VMS v GPC khai thc rt hiu qu vi hai mng thng tin di ng s VinaPhone v MobiFone theo tiu chun GSM. Tt c h thng thng tin di ng th h 2 u s dng k thut iu ch s. V chng s dng 2 phng php a truy cp: a truy cp phn chia theo thi gian (Time Division Multiple Access - TDMA): phc v cc cuc gi theo cc khe thi gian khc nhau. a truy cp phn chia theo m (Code Division Multiple Access - CDMA): phc v cc cuc gi theo cc chui m khc nhau. n tt nghip Trang 4 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G 1. 1. 2. 1 a truy cp phn chia theo thi gian TDMA: Trong h thng TDMA ph tn s quy nh cho lin lc di ng c chia thnh cc di tn lin lc, mi di tn lin lc ny c dng chung cho N knh lin lc, mi knh lin lc l mt khe thi gian (Time slot) trong chu k mt khung. Tin tc c t chc di dng gi, mi gi c bit ch th u gi, ch th cui gi, cc bit ng b v cc bit d liu. Khng nh h thng FDMA, h thng TDMA truyn dn d liu khng lin tc v ch s dng cho d liu s v iu ch s. Cc c im ca TDMA - TDMA c th phn pht thng tin theo hai phng php l phn nh trc v phn pht theo yu cu. Trong phng php phn nh trc, vic phn pht cc cm c nh trc hoc phn pht theo thi gian. Ngc li trong phng php phn nh theo yu cu cc mch c ti p ng khi c cuc gi yu cu, nh tng c hiu sut s dng mch. - Trong TDMA cc knh c phn chia theo thi gian nn nhiu giao thoa gia cc knh k cn gim ng k. - TDMA s dng mt knh v tuyn ghp nhiu lung thng tin thng qua vic phn chia theo thi gian nn cn phi c vic ng b ha vic truyn dn trnh trng lp tn hiu. Ngoi ra, v s lng knh ghp tng nn thi gian tr do truyn dn a ng khng th b qua c, do s ng b phi ti u. 1. 1. 2. 2 a truy cp phn chia theo m CDMA i vi h thng CDMA, tt c ngi dng s s dng cng lc mt bng tn. Tn hiu truyn i s chim ton b bng tn ca h thng. Tuy nhin, cc tn hiu ca mi ngi dng c phn bit vi nhau bi cc chui m. Thng tin di ng CDMA s dng k thut tri ph cho nn nhiu ngi s dng c th chim cng knh v tuyn ng thi tin hnh cc cuc gi, m khng s gy nhiu ln nhau. Knh v tuyn CDMA c dng li mi cell trong ton mng, v nhng knh ny cng c phn bit nhau nh m tri ph gi ngu nhin PN. Trong h thng CDMA, tn hiu bn tin bng hp c nhn vi tn hiu bng thng rt rng, gi l tn hiu phn tn. Tn hiu phn tn l mt chui m gi ngu n tt nghip Trang 5 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G nhin m tc chip ca n rt ln so vi tc d liu. Tt c cc users trong mt h thng CDMA dng chung tn s sng mang v c th c pht ng thi. Mi user c mt t m gi ngu nhin ring ca n v n c xem l trc giao vi cc t m khc. Ti my thu, s c mt t m c trng c to ra tch sng tn hiu c t m gi ngu nhin tng quan vi n. Tt c cc m khc c xem nh l nhiu. khi phc li tn hiu thng tin, my thu cn phi bit t m dng my pht. Mi thu bao vn hnh mt cch c lp m khng cn bit cc thng tin ca my khc. c im ca CDMA - Di tn tn hiu rng hng MHz. - S dng k thut tri ph phc tp. - K thut tri ph cho php tn hiu v tuyn s dng c cng trng rt nh v chng fading hiu qu hn FDMA, TDMA. - Vic cc thu bao MS trong cell dng chung tn s khin cho thit b truyn dn v tuyn n gin, vic thay i k hoch tn s khng cn vn , chuyn giao tr thnh mm, iu khin dung lng cell rt linh hot. - Cht lng thoi cao hn, dung lng h thng tng ng k (c th gp t 4 n 6 ln h thng GSM), an ton (tnh bo mt thng tin) cao hn do s dng dy m ngu nhin tri ph, khng nhiu tt hn, kh nng thu a ng tt hn, chuyn vng linh hot. Do h s ti s dng tn s l 1 nn khng cn phi quan tm n vn nhiu ng knh. - CDMA khng c gii hn r rng v s ngi s dng nh TDMA v FDMA. Cn TDMA v FDMA th s ngi s dng l c nh, khng th tng thm khi tt c cc knh b chim. - H thng CDMA ra i p ng nhu cu ngy cng ln dch v thng tin di ng t bo. y l h thng thng tin di ng bng hp vi tc bit thng tin ca ngi s dng l 8-13 kbps. n tt nghip Trang 6 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G 1. 1. 3 H thng thng tin di ng th h 3 (3G) H thng thng tin di ng chuyn t th h 2 sang th h 3 qua mt giai on trung gian l th h 2, 5 s dng cng ngh TDMA trong kt hp nhiu khe hoc nhiu tn s hoc s dng cng ngh CDMA trong c th chng ln ph tn ca th h hai nu khng s dng ph tn mi, bao gm cc mng c a vo s dng nh: GPRS, EDGE v CDMA2000-1x. th h th 3 ny cc h thng thng tin di ng c xu th ho nhp thnh mt tiu chun duy nht v c kh nng phc v tc bit ln n 2 Mbit/s. phn bit vi cc h thng thng tin di ng bng hp hin nay, cc h thng thng tin di ng th h 3 gi l cc h thng thng tin di ng bng rng. Nhiu tiu chun cho h thng thng tin di ng th h 3 IMT-2000 c xut, trong 2 h thng W-CDMA v CDMA2000 c ITU chp thun v a vo hot ng trong nhng nm u ca nhng thp k 2000. Cc h thng ny u s dng cng ngh CDMA, iu ny cho php thc hin tiu chun ton th gii cho giao din v tuyn ca h thng thng tin di ng th h 3. W-CDMA (Wideband Code Division Multiple Access) l s nng cp ca cc h thng thng tin di ng th h 2 s dng cng ngh TDMA nh: GSM, IS-136. CDMA2000 l s nng cp ca h thng thng tin di ng th h 2 s dng cng ngh CDMA: IS-95. Yu cu i vi h thng thng tin di ng th h 3 Thng tin di ng th h th 3 xy dng trn c s IMT-2000 c a vo phc v t nm 2001. Mc ch ca IMT-2000 l a ra nhiu kh nng mi nhng cng ng thi bo m s pht trin lin tc ca thng tin di ng th h 2. Tc ca th h th ba c xc nh nh sau: - 384 Kb/s i vi vng ph sng rng. - 2 Mb/s i vi vng ph sng a phng. Cc tiu ch chung xy dng h thng thng tin di ng th h ba (3G): n tt nghip Trang 7 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G - S dng di tn quy nh quc t 2GHz nh sau: ng ln : 1885-2025 MHz. ng xung : 2110-2200 MHz. - L h thng thng tin di ng ton cu cho cc loi hnh thng tin v tuyn: Tch hp cc mng thng tin hu tuyn v v tuyn. Tng tc vi mi loi dch v vin thng. - S dng cc mi trng khai thc khc nhau: trong cng s, ngoi ng, trn xe, v tinh. - C th h tr cc dch v nh: Mi trng thng tin nh o (VHE: Virtual Home Environment) trn c s mng thng minh, di ng c nhn v chuyn mng ton cu. m bo chuyn mng quc t. m bo cc dch v a phng tin ng thi cho thoi, s liu chuyn mch knh v s liu chuyn mch theo gi. - D dng h tr cc dch v mi xut hin. 1. 1. 4 H thng thng tin di ng th h 4 (4G) H thng thng tin di ng th h 3 sang th h 4 qua giai on trung gian l th h 3,5 c tn l mng truy nhp gi ng xung tc cao HSDPA. Th h 4 l cng ngh truyn thng khng dy th t, cho php truyn ti d liu vi tc ti a trong iu kin l tng ln ti 1 cho n 1.5 Gbps. Cng ngh 4G c hiu l chun tng lai ca cc thit b khng dy. Cc nghin cu u tin ca NTT DoCoMo cho bit, in thoi 4G c th nhn d liu vi tc 100 Mbps khi di chuyn v ti 1 Gbps khi ng yn, cho php ngi s dng c th ti v truyn ln hnh nh ng cht lng cao. Chun 4G cho php truyn cc ng dng phng tin truyn thng ph bin nht, gp phn to nn cc nhng ng dng mnh m cho cc mng khng dy ni b (WLAN) v cc ng dng khc. n tt nghip Trang 8 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G Th h 4 dng k thut truyn ti truy cp phn chia theo tn s trc giao OFDM, l k thut nhiu tn hiu c gi i cng mt lc nhng trn nhng tn s khc nhau. Trong k thut OFDM, ch c mt thit b truyn tn hiu trn nhiu tn s c lp (t vi chc cho n vi ngn tn s). Thit b 4G s dng my thu v tuyn xc nhn bi phn mm SDR (Software - Defined Radio) cho php s dng bng thng hiu qu hn bng cch dng a knh ng thi. Tng i chuyn mch mng 4G ch dng chuyn mch gi, do , gim tr thi gian truyn v nhn d liu. 1. 2 Tng quan v mng 4G [12] 4G l h thng thng tin bng rng c xem nh IMT tin tin (IMT Advanced) c nh ngha bi ITU-R. Tc d liu ra l 100Mbps cho thu bao di chuyn cao v 1Mbps cho thu bao t di chuyn, bng thng linh ng ln n 40MHz. S dng hon ton trn nn IP, cung cp cc dch v nh in thoi IP, truy cp internet bng rng, cc dch v game v dng HDTV a phng tin 3GPP LTE c xem nh l tin 4G, nhng phin bn u tin ca LTE cha cc tnh nng theo yu cu ca IMT Advanced. LTE c tc l thuyt ln n 100Mbps ng xung v 50Mbps ng ln i vi bng thng 20MHz. V s hn na nu MIMO, cc anten mng c s dng. LTE c pht trin u tin hai th Stockholm v Olso vo ngy 14/12/2009. Giao din v tuyn vt l u tin c t tn l HSOPA (High Speed OFDM Packet Access), by gi c tn l E-UTRA (Evolved UMTS Terrestrial Radio Access). Thc t cho thy, hu ht cc hng sn xut thit b vin thng hng u th gii: Alcatel-Lucent, Ericsson, Motorola, Nokia, Nokia Siemens Networks, Huawei, LG Electronics, Samsung, NEC, Fujitsu. . . bt tay vi cc nh mng ln trn th gii (Verizon Wireless, AT&T, France Telecom-Orange, NTT DoCoMo, T-Mobile, China Mobile, ZTE. . . ) thc hin cc cuc th nghim quan trng trn cng ngh LTE v t nhng thnh cng ng k. LTE Advanced l ng vin cho chun IMT-Advanced, mc tiu ca n l hng n p ng c yu cu ca ITU. LTE Advanced c kh nng tng thch vi thit b v chia s bng tn vi LTE phin bn u tin. n tt nghip Trang 9 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G Di ng WiMAX (IEEE 802. 16e-2005) l chun truy cp di ng khng dy bng rng (MWBA) cng c xem l 4G, tc bt nh ng xung l 128 Mbps v 56 Mbps cho ng xung vi rng bng thng hn 20 MHz. UMB (Ultra Mobile Broadband) : UMB c cc t chc vin thng ca Nht Bn, Trung Quc, Bc M v Hn Quc cng vi cc hng nh Alcatel-Lucent, Apple, Motorola, NEC v Verizon Wireless pht trin t nn tng CDMA. UMB c th hot ng bng tn c rng t 1,25 MHz n 20 MHz v lm vic nhiu di tn s, vi tc truyn d liu ln ti 288 Mbps cho lung xung v 75 Mbps cho lung ln vi rng bng tn s dng l 20 MHz. Qualcomm l hng i u trong n lc pht trin UMB, mc d hng ny cng ng thi pht trin c cng ngh LTE. Mc tiu v cch tip cn 4G cung cp QoS v tc pht trin hn nhiu so vi 3G ang tn ti, khng ch l truy cp bng rng, dch v tin nhn a phng tin (MMS), chat video, TV di ng m cn cc dch v HDTV, cc dch v ti thiu nh thoi, d liu v cc dch v khc. N cho php chuyn giao gia cc mng v tuyn trong khu vc cc b v c th kt ni vi h thng qung b video s. Cc mc tiu m 4G hng n : Bng thng linh hot gia 5 MHz n 20 MHz, c th ln n 40 MHz. Tc c quy nh bi ITU l 100 Mbps khi di chuyn tc cao v 1 Gbps i vi thu bao ng yn so vi trm. Tc d liu t nht l 100 Mbps gia bt k hai im no trn th gii. Hiu sut ph ng truyn l 15bit/s/Hz ng xung v 6.75 bit/s/Hz ng ln (c ngha l 1000 Mbps ng xung v c th nh hn bng thng 67 MHz)/ Hiu sut s dng ph h thng ln n 3 bit/s/Hz/cell ng xung v 2.25 bit/s/Hz/cell cho vic s dng trong nh. Chuyn giao lin (Smooth handoff) qua cc mng hn hp. n tt nghip Trang 10 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G Kt ni lin v chuyn giao ton cu qua a mng. Cht lng cao cho cc dch v a phng tin nh m thanh thi gian thc, tc d liu cao, video HDTV, TV di ng Tng thch vi cc chun khng dy ang tn ti Tt c l IP, mng chuyn mch gi khng cn chuyn mch knh na. Cc im cn xt n Vng bao ph, mi trng v tuyn, ph, dch v, m hnh thng mi v s ngi s dng. Cc k thut c s dng K thut s dng lp vt l - Khng s dng CDMA - MIMO : t c hiu sut ph tn cao bng cch s dng phn tp theo khng gian, a anten a ngi dng. - S dng lng t ha trong min tn s, chng hn nh OFDM hoc SC-FDE (single carrier frequency domain equalization) ng xung : tn dng thuc tnh chn lc tn s ca knh m khng phi lng t phc tp. - Ghp knh trong min tn s chng hn nh OFDMA hoc SC-FDMA ng xung : tc bit thay i bng vic gn cho ngi dng cc knh con khc nhau da trn iu kin knh. - M ha sa li Turbo : ti thiu yu cu v t s SNR bn thu. Lp biu knh c lp : s dng cc knh thay i theo thi gian. Thch nghi ng truyn : iu ch thch nghi v cc m sa li. 1. 3 S khc nhau gia 3G v 4G Hin nay, cng ngh 3G cho php truy cp Internet khng dy v cc cuc gi c hnh nh. 4G c pht trin trn cc thuc tnh k tha t cng ngh 3G. V mt l thuyt, mng khng dy s dng cng ngh 4G s c tc nhanh hn mng n tt nghip Trang 11 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G 3G t 4 n 10 ln. Tc ti a ca 3G l tc ti xung 14Mbps v 5.8Mbps ti ln. Vi cng ngh 4G, tc c th t ti 100Mbps i vi ngi dng di ng v 1Gbps i vi ngi dng c nh. 3G s dng cc di tn quy nh quc t cho UL : 1885-2025 MHz; DL : 2110-2200 MHz; vi tc t 144kbps-2Mbps, rng BW: 5 MHz. i vi 4G LTE th Hot ng bng tn : 700 MHz-2,6 GHz vi mc tiu tc d liu cao, tr thp, cng ngh truy cp sng v tuyn gi d liu ti u. Tc DL :100Mbps( BW 20MHz), UL : 50 Mbps vi 2 aten thu mt anten pht. tr nh hn 5ms vi rng BW linh hot l u im ca LTE so vi WCDMA, BW t 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz. Hiu qu tri ph tng 4 ln v tng 10 ln s ngi dng/cell so vi WCDMA. 1. 3. 1 u im ni bt Tc d liu cao hn rt nhiu ln so vi 3G Tng hiu qu s dng ph v gim thi gian tr Cu trc mng s n gin hn, v s khng cn chuyn mch knh na Hiu qu tri ph tng 4 ln v tng 10 ln user/cell so vi WCDMA. rng bng tn linh hot cng l mt u im quan trng ca LTE i vi WCDMA 1.3.2 Cc ng dng to nn u im ca 4G LTE so vi 3G Hiu sut ph cao - OFDM DL Chng nhiu a ng Hu ht d liu ngi dng th t hn di ng - SC-FDMA UL PAPR thp Ngi dng trc giao trong min tn s - MIMO n tt nghip Trang 12 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G Tc d liu cao -Pht nhiu dng d liu c lp song song qua cc anten ring l => tng tc d liu. (s dng MIMO) tr thp -Thi gian ci t v thi gian tr hon chuyn tip ngn -Tr HO v thi gian ngt ngn : TTI ngn, trng thi RRC n gin Gi thnh r -Cu trc mng n gin, gim cc thnh phn ca mng Cht lng dch v cao -S dng cc tn s cp php m bo cht lng dch v : LTE s dng cc di tn s khc nhau : 2100 MHz, 1900 MHz, 1700 MHz, 2600 MHz, 900 MHz, 800 MHz. -Lun lun th nghim ( gim thi gian tr trong iu khin nh tuyn) -Gim tr kh hi ( round trip delay) Tn s ti s dng linh hot Gim nhiu lin cell vi tn s ti s dng ln hn 1. -S dng hai di tn s: Di 1 : h s ti s dng ln hn 1 => cng sut pht cao hn Di 2 : ph cn li -Cc user cnh cell : s dng di 1 => SIR tt -Cc user trung tm cell : s dng ton b bng => tc d liu cao Dung lng v vng bao ph ca WCDMA UL b gii hn bi can nhiu: can nhiu bn trong cell v can nhiu lin cell. Nhng i vi LTE th : do tnh trc giao nn can nhiu trong cng mt cell c th khng xt n v gim can nhiu inter-cell bng ti s dng cc b, thm cc anten c th trit can nhiu. n tt nghip Trang 13 Chng 1 : Gii thiu v h thng thng tin di ng v tng quan v mng 4G Chng 1 khi qut c nhng nt c trng, u nhc im v s pht trin ca cc h thng thng tin di ng th h 1, 2 v 3, 4 ng thi s lt tng quan ca h thng thng tin di ng th h 4. Hai thng s quan trng c trng cho cc h thng thng tin di ng s l tc bit thng tin ca ngi s dng v tnh di ng, cc th h tip theo cc thng s ny cng c ci thin. Nu c u im ca 4G so vi 3G v cc c s hnh thnh u im . tm hiu thm v 4G ta qua chng tip theo. n tt nghip Trang 14 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan CHNG 2 : CU TRC MNG 4G LTE V CC VN LIN QUAN H thng 4G c xy dng nhm chun b mt c s h tng di ng chung c kh nng phc v cc dch v hin ti v tng lai. C s h tng 4G c thit k vi iu kin nhng thay i, pht trin v k thut c kh nng ph hp vi mng hin ti m khng lm nh hng n cc dch v ang s dng. thc hin iu , cn tch bit gia k thut truy cp, k thut truyn dn, k thut dch v (iu khin kt ni) v cc ng dng ca ngi s dng. Chng ny s trnh by h thng di ng 4G LTE :cc c im k thut, so snh LTE vi WiMAX, cu trc mng 4G LTE s nh th no, n lin kt vi cc mng khc ra sao, cc knh s dng trong E-UTRAN, cc k thut s dngcho ng ln, ng xung trong LTE, ng thi khi qut v cc th tc lin quan n giao din v tuyn bao gm chuyn giao v iu khin cng sut. 2.1 Gii thiu v cng ngh LTE H thng 3GPP LTE, l bc tip theo cn hng ti ca h thng mng khng dy 3G da trn cng ngh di ng GSM/UMTS, v l mt trong nhng cng ngh tim nng nht cho truyn thng 4G. Lin minh Vin thng Quc t (ITU) nh ngha truyn thng di ng th h th 4 l IMT Advanced v chia thnh hai h thng dng cho di ng tc cao v di ng tc thp. 3GPP LTE l h thng dng cho di ng tc cao. Ngoi ra, y cn l cng ngh h thng tch hp u tin trn th gii ng dng c chun 3GPP LTE v cc chun dch v ng dng khc, do ngi s dng c th d dng thc hin cuc gi hoc truyn d liu gia cc mng LTE v cc mng GSM/GPRS hoc UMTS da trn WCDMA. Kin trc mng mi c thit k vi mc tiu cung cp lu lng chuyn mch gi vi dch v cht lng, tr ti thiu. H thng s dng bng thng linh hot nh vo m hnh a truy cp OFDMA v SC-FDMA. Thm vo , FDD (Frequency Division Duplexing) v TDD (Time Division Duplexing), bn song cng FDD cho php cc UE c gi thnh thp. Khng ging nh FDD, bn song cng FDD khng yu cu pht v thu ti cng thi im. iu ny lm gim n tt nghip Trang 15 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan gi thnh cho b song cng trong UE. Truy cp tuyn ln da vo a truy cp phn chia theo tn s n sng mang (Single Carrier Frequency Division multiple Access SC-FDMA) cho php tng vng ph tuyn ln lm t s cng sut nh trn cng sut trung bnh thp (Peak-to-Average Power Ratio PAPR) so vi OFDMA. Thm vo , ci thin tc d liu nh, h thng LTE s dng hai n bn ln h s ph cell so vi h thng HSPA Release 6. ng c thc y - Cn th h tip theo ci thin cc nhc im ca 3G v p ng nhu cu ca ngi s dng - Ngi dng i hi tc d liu v cht lng dch v cao hn - Ti u h thng chuyn mch gi - Tip tc nhu cu i hi ca ngi dng v gim gi thnh (CAPEX v OPEX) - Gim phc tp - Trnh s phn on khng cn thit cho hot ng ca mt cp hoc khng phi mt cp di thng Cc giai on pht trin ca LTE - Bt u nm 2004, d n LTE tp trung vo pht trin thm UTRAN v ti u cu trc truy cp v tuyn ca 3GPP. - Mc tiu hng n l dung lng d liu truyn ti trung bnh ca mt ngi dng trn 1 MHz so vi mng HSDPA Rel. 6: Ti xung: gp 3 n 4 ln (100Mbps). Ti ln: gp 2 n 3 ln (50Mbps). - Nm 2007, LTE ca k thut truy cp v tuyn th h th 3 EUTRA- pht trin t nhng bc kh thi a ra cc c tnh k thut c chp nhn. Cui nm 2008 cc k thut ny c s dng trong thng mi. - Cc k thut OFDMA c s dng cho ng xung v SC-FDMA c s dng cho ng ln. n tt nghip Trang 16 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Mc tiu ca LTE - Tc d liu cao - tr thp - Cng ngh truy cp sng v tuyn gi d liu ti u Cc c tnh c bn ca LTE - Hot ng bng tn : 700 MHz-2,6 GHz. - Tc : - DL : 100Mbps( BW 20MHz) - UL : 50 Mbps vi 2 aten thu mt anten pht. - tr : nh hn 5ms - rng BW linh hot :1,4 MHz; 3 MHz; 5 MHz; 10 MHz; 15 MHz; 20 MHz. H tr c 2 trng hp di bng ln v bng xung bng nhau hoc khng. - Tnh di ng : Tc di chuyn ti u l 0-15 km/h nhng vn hot ng tt vi tc di chuyn t 15-120 km/h, c th ln n 500 km/h ty bng tn. - Ph tn s: - Hot ng ch FDD hoc TDD - ph sng t 5-100 km - Dung lng 200 user/cell bng tn 5Mhz. - Cht lng dch v : - H tr tnh nng m bo cht lng dch v QoS. - VoIP m bo cht lng m thanh tt, tr ti thiu thng qua mng UMTS. - Lin kt mng: n tt nghip Trang 17 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan - Kh nng lin kt vi cc h thng UTRAN/GERAN hin c v cc h thng khng thuc 3GPP cng s c m bo. - Thi gian tr trong vic truyn ti gia E-UTRAN v UTRAN/GERAN s nh hn 300ms cho cc dch v thi gian thc v 500ms cho cc dch v cn li. - Chi ph: chi ph trin khai v vn hnh gim Bng thng linh hot trong vng t 1.4 MHz n 20 MHz, iu ny c ngha l n c th hot ng trong cc di bng tn ca 3GPP. Trong thc t, hiu sut thc s ca LTE ty thuc vo bng thng ch nh cho cc dch v v khng c s la chn cho ph tn ca chnh n. iu ny gip ng k cho cc nh khai thc trong chin lc v kinh t v k thut. Trin khai ti cc tn s cao, LTE l chin lc hp dn tp trung vo dung lng mng, trong khi ti cc tn s thp n c th cung cp vng bao ph khp ni. Mng LTE c th hot ng trong bt c di tn c s dng no ca 3GPP. N bao gm bng tn li ca IMT-2000 (1.9-2 GHz) v di m rng (2.5 GHz), cng nh ti 850-900 MHz, 1800 MHz, ph AWS (1.7-2.1 GHz)Bng tn ch nh di 5MHz c nh ngha bi IUT th ph hp vi dch v IMT trong khi cc bng tn ln hn 5MHz th s dng cho cc dch v c tc cc cao. Tnh linh hot v bng tn ca LTE c th cho php cc nh sn xut pht trin LTE trong nhng bng tn tn ti ca h. Cc thng s lp vt l ca LTE [14] Bng 2.1 : Cc thng s lp vt l LTE K thut truy cp UL DTFS-OFDM (SC-FDMA) DL OFDMA Bng thng 1.4MHz, 3 MHz , 5 MHz, 10 MHz, 15 MHz, 20 MHz TTI ti thiu 1ms n tt nghip Trang 18 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Khong cch sng mang con 15KHz Chiu di CP Ngn 4.7s Di 16.7 s iu ch QPSK, 16QAM, 64QAM Ghp knh khng gian 1 lp cho UL/UE Ln n 4 lp cho DL/UE S dng MU-MIMO cho UL v DL Bng 2.2 : Tc nh ca LTE theo lp Lp 1 2 3 4 5 Tc nh Mbps DL 10 50 100 150 300 UL 5 25 50 50 75 Dung lng cho cc chc nng lp vt l Bng thng RF 20MHz iu ch DL QPSK, 16QAM, 64QAM UL QPSK, 16QAM QPSK, 16QAM, 64QAM Dch v ca LTE Qua vic kt ni ca ng truyn tc rt cao, bng thng linh hot, hiu sut s dng ph cao v gim thi gian tr gi, LTE ha hn s cung cp nhiu dch v a dng hn. i vi khch hng, s c thm nhiu ng dng v dng d liu ln, ti v v chia s video, nhc v ni dung a phng tin. Tt c cc dch v s n tt nghip Trang 19 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan cn lu lng ln hn p ng cht lng dch v, c bit l vi mong i ca ngi dng v ng truyn TV r nt cao. i vi khch hng l doanh nghip, truyn cc tp tin ln vi tc cao, cht lng video hi ngh ttLTE s mang c tnh ca Web 2.0 ngy nay vo khng gian di ng ln u tin. Dc theo s bo m v thng mi, n s bng qua nhng ng dng thi gian thc nh game a ngi chi v chia s tp tin. Bng 2.3 : So snh cc dch v ca 3G so vi 4G LTE Dch v Mi trng (3G) Mi trng 4G Thoai (rich voice) m thanh thi gian thc VoIP, video hi ngh cht lng cao Tin nhn P2F(P2F messaging) SMS, MMS, cc email u tin thp Cc tin nhn photo, IM, email di ng, tin nhn video Lt web(browsing) Truy cp n cc dch v online trc tuyn, Trnh duyt WAP thng qua GPRS v mng 3G. Duyt siu nhanh, ti cc ni dung ln cc mng x hi. Thng tin cc ph(paid information) Ngi dng tr qua hoc trn mng tnh cc chun. Chnh yu l da trn thng tin vn bn. Tp ch trc tuyn, dng m thanh cht lng cao. Ring t(personalization) Ch yu l m thanh chung(ringtone), cng bao gm mn hnh ch (screensavers)v nhc ch(ring tone) . m thanh thc(thu m gc t ngi ngh s), cc trang web c nhn. Games Ti v v chi game trc Kinh nghim game trc n tt nghip Trang 20 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan tuyn. tuyn vng chc qua c mng c nh v di ng. Video/TV theo yu cu (video/TV on demand) Chy v c th ti video. Cc dch v qung b tivi, Tivi theo ng yu cudng video cht lng cao. Nhc Ti y cc track v cc dch v m thanh. Lu tr v ti nhc cht lng cao Ni dung tin nhn Tin nhn ng cp s dng ba thnh phn cng nh tng tc vi cc media khc. Phn phi t l rng ca cc video clip, dch v karaoke, video c bn qung co di ng. M-comerce( thng mi qua in thoi) Thc hin cc giao dch v thanh ton qua mng di ng. in thoi cm tay nh thit b thanh ton, vi cc chi tit thanh ton qua mng tc cao cho php cc giao dch thc hin nhanh chng. Mng d liu di ng(mobile data netwoking) Truy cp n cc mng ni b v c s d liu cng nh cch s dng ca cc ng dng nh CRM. Chuyn i file P2P, cc ng dng kinh doanh, ng dng chia s, thng tin M2M, di ng intranet/extranet. n tt nghip Trang 21 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan So snh LTE vi HSPA v WiMAX [17] Bng 2.4 : So snh gia HSPA, WiMAX v LTE Cc tiu ch HSUPA WiMAX LTE Phin bn 3GPP release 6 802.16e (2005) 3GPP release 8 (3/2009) C s h tng v cc thit b c gi tr Bt u nm 2007 Bt u nm 2007 Bt u nm 2010 Di tn hot ng 700MHz, 850 MHz,1.5 GHz, 1.8 GHz, 1.7/2.1 GHz 2.5GHz, 2.6GHz, 3.5GHz, 3.65 GHz, 5.8 GHz, 700MHz, 850 MHz,1.5 GHz, 1.8 GHz, 1.7/2.1 GHz, 2.1GHz, 2.3GHz, 2.6GHz Cc thng s hng n Tc d liu ln 5.6 Mbps i vi knh 5MHz, bn knh cell l 680m Tc d liu ln 75Mbps/25 Mbps i vi knh 10MHz vi 2x2 MIMO, bn knh cell ln n 2-7Km, 100-200 ngi dng Tc d liu ln 100Mbps/50 Mbps i vi knh 10MHz vi 2x2 MIMO, bn knh cell ln n 5Km, ln hn 400 ngi dng Kh nng tng thch li Tng thch li vi Release 99 Khng tng thch li vi 3GPP hoc 3GPP2 K tha chun 3GPP, nhng khc k thut nn i hi thit b mi RAN nu di tn khc nhau c s dng V cng ngh, LTE v WiMax c mt s khc bit nhng cng c nhiu im tng ng. C hai cng ngh u da trn nn tng IP. C hai u dng k n tt nghip Trang 22 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan thut MIMO ci thin cht lng truyn/nhn tn hiu, ng xung t trm thu pht n thit b u cui u c tng tc bng k thut OFDM h tr truyn ti d liu a phng tin v video. ng ln t thit b u cui n trm thu pht c s khc nhau gia 2 cng ngh. WiMax dng OFDMA (Orthogonal Frequency Division Multiple Access mt bin th ca OFDM), cn LTE dng k thut SC-FDMA (Single Carrier - Frequency Division Multiple Access). V l thuyt, SC-FDMA c thit k lm vic hiu qu hn v cc thit b u cui tiu th nng lng thp hn OFDMA. LTE cn c u th hn WiMax v c thit k tng thch vi c phng thc TDD (Time Division Duplex) v FDD (Frequency Division Duplex). Ngc li, WiMax hin ch tng thch vi TDDs. TDD truyn d liu ln v xung thng qua 1 knh tn s (dng phng thc phn chia thi gian), cn FDD cho php truyn d liu ln v xung thng qua 2 knh tn s ring bit. iu ny c ngha LTE c nhiu ph tn s dng hn WiMax. Tuy nhin, s khc bit cng ngh khng c ngha quyt nh trong cuc chin gia WiMax v LTE. Trn th gii, 4G d cha phi ph bin song cng c quc gia v cc hng vin thng trin khai. Chng hn nh Ericsson. Thng 1/2009, Ericsson v nh mng ti Thy in trin khai thng mi TeliaSonera mng LTE/4G u tin ti Thy in. Ti thng 1/2010 trin khai din rng mng TeliaSonera trn ton quc Na Uy v Thy in. Ngoi ra, Ericsson k hp ng trin khai LTE trong thi gian ti vi cc nh mng AT&T (M), MetroPCS, Verizon Wireless (M), NTT Docomo (Nht). Ericsson cng tin hnh cc th nghim LTE/4G vi cc mng Telstra, SingTel, T-Mobile Hungary, Zain Saudia Arabia. Vi Vit Nam, thi im ny, c quan qun l nh nc cha a ra quyt nh s i ln 4G bng Wimax hay LTE m quan im s t chc mt hi tho gia B vi cc doanh nghip tm ra s la chn hp l nht. Theo phn tch ca cc chuyn gia, hin ti Wimax c li th i trc LTE. Khng ch trn th gii m ngay c Vit Nam, mng Wimax c trin khai cung cp th nghim t nm 2004 ti gi. Cn LTE, li c cho rng phi ti khong nm 2012-2013 mi tr n tt nghip Trang 23 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan nn ph bin. Xong, so vi Wimax, LTE li c mt th mnh c cho l rt quan trng. LTE nu c trin khai cho php tn dng dng h tng GSM c sn d vn phi u t thm thit b. Cn Wimax, nu mun trin khai th phi xy dng t u mt mng mi. Vi Vit Nam, trong bi cnh hin nay, theo nhiu chuyn gia, vn cha n thi im chn mui pht trin 4G cho d l Wimax hay LTE. thi im ny, Vit Nam vn cha c k hoch trin khai 4G. Nu c, phi t nht l nm 2012. V vi mc thi gian ny, bit u, LTE li thng th hn Wimax? Nhng d c la chn cng ngh g i chng na, iu quan trng nht m ngi dng Vit t k vng cc nh khai thc mng, cung cp dch v l lm sao p ng c ba tiu chun. Mt chuyn gia ca Ericsson chia s.Th nht, l tnh thn thin v n gin ca dch v cng ngh cung cp. a s ngi dng trc y cha bit nhiu v Internet do tnh thn thin gip h s dng ln u tin m khng b nhm ln l iu rt quan trng. Th hai chnh l nhng ni dung ting Vit m h c th hng th t dch v.V th ba, l gi c hp l. c bit l dch v tr trc. C th ni, a s ngi s dng khng hiu v s lin quan gia Megabyte v gi c nn chnh sch gi phi d hiu. n tt nghip Trang 24 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan 2.2 Cu trc ca LTE [1] Cu trc c bn SAE ca LTE Hnh 2.1: So snh v cu trc gia UTMS v LTE Hnh trn cho ta thy s khc nhau v cu trc ca UTMS v LTE. Song song vi truy nhp v tuyn LTE, mng gi li cng ang ci tin ln cu trc tng SAE. Cu trc mi ny c thit k ti u hiu sut mng, ci thin hiu qu chi ph v thun tin thu ht phn ln dch v trn nn IP. Mng truy nhp v tuyn RAN (Radio Access Network): mng truy nhp v tuyn ca LTE c gi l E-UTRAN v mt trong nhng c im chnh ca n l tt c cc dch v, bao gm dch v thi gian thc, s c h tr qua nhng knh gi c chia s. Phng php ny s tng hiu sut ph, lm cho dung lng h thng tr nn cao hn. Mt kt qu quan trng ca vic s dng truy nhp gi cho tt c cc dch v l s tch hp cao hn gia nhng dch v a phng tin v gia nhng dch v c nh v khng dy. n tt nghip Trang 25 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan C nhiu loi chc nng khc nhau trong mng t bo. Da vo chng, mng c th c chia thnh hai phn: mng truy nhp v tuyn v mng li. Nhng chc nng nh iu ch, nn, chuyn giao thuc v mng truy nhp. Cn nhng chc nng khc nh tnh cc hoc qun l di ng l thnh phn ca mng li. Vi LTE, mng truy nhp l E-UTRAN v mng li l EPC. Mc ch chnh ca LTE l ti thiu ha s node. V vy, ngi pht trin chn mt cu trc n node. Trm gc mi phc tp hn NodeB trong mng truy nhp v tuyn WCDMA/HSPA, v v vy c gi l eNodeB (Enhance Node B). Nhng eNodeB c tt c nhng chc nng cn thit cho mng truy nhp v tuyn LTE, k c nhng chc nng lin quan n qun l ti nguyn v tuyn. Giao din v tuyn s dng trong E-UTRAN by gi ch cn l S1 v X2. Trong S1 l giao din v tuyn kt ni gia eNodeB v mng li. S1 chia lm hai loi l S1-U l giao din gia eNodeB v SAE GW v S1-MME l giao din gia eNodeB v MME. X2 l giao din gia cc eNodeB vi nhau. Hnh 2.2: Cu trc c bn ca LTE n tt nghip Trang 26 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Mng li: mng li mi l s m rng hon ton ca mng li trong h thng 3G, v n ch bao ph min chuyn mch gi. V vy, n c mt ci tn mi: Evolved Packet Core (EPC). Cng mt mc ch nh E-UTRAN, s node trong EPC c gim. EPC chia lung d liu ngi dng thnh mt phng ngi dng v mt phng iu khin. Mt node c th c nh ngha cho mi mt phng, cng vi Gateway chung kt ni mng LTE vi internet v nhng h thng khc. EPC gm c mt vi thc th chc nng. - MME (Mobility Management Entity): chu trch nhim x l nhng chc nng mt bng iu khin, lin quan n qun l thu bao v qun l phin. - Gateway dch v (Serving Gateway): l v tr kt ni ca giao tip d liu gi vi E-UTRAN. N cn hot ng nh mt node nh tuyn n nhng k thut 3GPP khc. - P-Gateway (Packet Data Network): l im u cui cho nhng phin hng v mng d liu gi bn ngoi. N cng l Router n mng Internet. - PCRF (Policyand Charging Rules Function): iu khin vic to ra bng gi v cu hnh h thng con a phng tin IP IMS (the IP Multimedia Subsystem) cho mi ngi dng. - HSS (Home Subscriber Server): l ni lu tr d liu ca thu bao cho tt c d liu ca ngi dng. N l c s d liu ch trung tm trong trung tm ca nh khai thc. Cc min dch v bao gm IMS (IP Multimedia Sub-system) da trn cc nh khai thc, IMS khng da trn cc nh khai thc v cc dch v khc. IMS l mt kin trc mng nhm to s thun tin cho vic pht trin v phn phi cc dch v a phng tin n ngi dng, bt k l h ang kt ni thng qua mng truy nhp no. IMS h tr nhiu phng thc truy nhp nh GSM, UMTS, CDMA2000, truy nhp hu tuyn bng rng nh cp xDSL, cp quang, cp truyn hnh, cng n tt nghip Trang 27 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan nh truy nhp v tuyn bng rng WLAN, WiMAX. IMS to iu kin cho cc h thng mng khc nhau c th tng thch vi nhau. IMS ha hn mang li nhiu li ch cho c ngi dng ln nh cung cp dch v. N v ang c tp trung nghin cu cng nh thu ht c s quan tm ln ca gii cng nghip. Tuy nhin IMS cng gp phi nhng kh khn nht nh v cng cha tht s chn thuyt phc cc nh cung cp mng u t trin khai n. Kin trc IMS c cho l kh phc tp vi nhiu thc th v v s cc chc nng khc nhau. IMS da trn cc nh khai thc: l IMS c tch hp sn trong cu trc ca h thng 3GPP - IMS khng da trn cc nh khai thc: l IMS khng c nh ngha trong cc chun. Cc nh khai thc c th tch hp dch v ny trong mng ca h. Cc UE kt ni n n qua vi giao thc c chp thun v dch v video streaming l 1 v d. - Cc dch khc khng c cung cp bi 3GPP v cu trc ph thuc vo yu cu ca dch v. Cu hnh in hnh s c UE kt ni n my ch qua mng chng hn nh kt ni n trang ch cho dch v lt web. Cu trc ca LTE lin kt vi cc mng khc Hnh 2.3: Cu trc h thng cho mng truy cp 3GPP n tt nghip Trang 28 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Hnh 2.4 : Cu trc h thng cho mng truy cp3GPP v khng phi 3GPP Hnh 2.5: Cu trc h thng cho mng truy cp3GPP v lin mng vi CDMA 2000 H thng 3GPP hin ti (GSM v WCDMA/HSPA) v 3GPP2 (CDMA2000 1xRTT, EV-DO) c kt hp vo h thng mi thng qua nhng giao din chun ha, min l ti u tnh di ng vi LTE. Vi h thng 3GPP, iu ny c ngha l n tt nghip Trang 29 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan mt giao din bo hiu gia SGSN (Serving GPRS Support Node) v mng li mi, vi h thng 3GPP2 cng c mt giao din bo hiu gia CDMA RAN v mng li mi. V d tn hiu iu khin cho di ng c x l bi node Mobility Management Entity (MME), tch ri vi Gateway. iu ny thun tin cho vic ti u trong trin khai mng v hon ton cho php chia t l dung lng mt cch linh ng. Home Subscriber Server (HSS) ni n Packet Core qua mt giao din IP, v khng phi SS7 nh s dng trong mng GSM v WCDMA. Mng bo hiu cho iu khin chnh sch v tnh cc c da trn giao din IP. H thng GSM v WCDMA/HSPA hin ti c tch hp vo h thng mi qua nhng giao din c chun ha gia SGSN v mng li mi. Ngi ta c gng kt hp truy nhp CDMA cng s a n tnh di ng lin tc gia LTE v CDMA, cho php s mm do trong vic chuyn ln LTE. LTE-SAE tip nhn khi nim QoS theo tng lp. iu ny cung cp mt gii php n gin v n by gi vn hiu qu cho nhng nh khai thc c c s phn bit gia nhng dch v gi. 2.3 Cc knh s dng trong E-UTRAN Knh vt l : cc knh vt l s dng cho d liu ngi dng bao gm : - PDSCH (Physical Downlink Shared Channel) : ph ti c ch (payload) - PUSCH (Physical Uplink Shared Channel) : PUSCH c dng mang d liu ngi dng. Cc ti nguyn cho PUSCH c ch nh trn mt subframe c bn bi vic lp biu ng ln. Cc sng mang c ch nh l 12 khi ti nguyn (RB) v c th nhy t subframe ny n subframe khc. PUSCH c th dng cc kiu iu ch QPSK, 16QAM, 64QAM. - PUCCH(Physical Uplink Control Channel): c chc nng lp biu, ACK/NAK. - PDCCH(Physical Downlink Control Channel): lp biu, ACK/NAK. - PBCH(Physical Broadcast Channel): mang cc thng tin c trng ca cell. n tt nghip Trang 30 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Knh logic : c nh ngha bi thng tin n mang bao gm: [18] - Knh iu khin qung b (BCCH) : c s dng truyn thng tin iu khin h thng t mng n tt c my di ng trong cell. Trc khi truy nhp h thng, u cui di ng phi c thng tin pht trn BCCH bit c h thng c lp cu hnh nh th no, chng hn bng thng h thng. - Knh iu khin tm gi (PCCH) : c s dng tm gi cc u cui di ng v mng khng th bit c v tr ca chng cp v v th cn pht cc bn tin tm gi trong nhiu (vng nh v). - Knh iu khin ring (DCCH) : c s dng truyn thng tin iu khin ti/t mt u cui di ng. Knh ny c s dng cho cu hnh ring ca cc u cui di ng chng hn cc bn tin chuyn giao khc nhau. - Knh iu khin a phng (MCCH) : c s dng truyn thng tin cn thit thu knh MTCH. - Knh lu lng ring (DTCH) : c s dng truyn s liu ca ngi s dng n/t mt u cui di ng. y l kiu logic c s dng truyn tt c s liu ng ln ca ngi dng v s liu ng xung ca ngi dng khng phi MBMS. - Knh lu lng a phng (MTCH) : c s dng pht cc dch v MBMS. Knh truyn ti : bao gm cc knh sau [18] - Knh qung b (BCH) : c khun dng truyn ti c nh do chun cung cp. - N c s dng pht thng tin trn knh logic. - Knh tm gi (PCH) : c s dng pht thng tin tm gi trn knh PCCH, PCH h tr thu khng lin tc (DRX) cho php u cui tit kim cng sut c quy bng cch ng v ch thc thu PCH ti cc thi im quy nh trc. n tt nghip Trang 31 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan - Knh chia s ng xung (DL-SCH) : l knh truyn ti pht s liu ng xung trong LTE. N h tr cc chc nng ca LTE nh thch ng tc ng v lp biu ph thuc knh trong min thi gian v min tn s. N cng h tr DRX gim tiu th cng sut ca u cui di ng m vn m bo cm gic lun kt ni ging nh c ch CPC trong HSPA. DL-DCH TTI l 1ms. - Knh a phng (MCH) : c s dng h tr MBMS. N c c trng bi khun dng truyn ti bn tnh v lp biu bn tnh. Trong trng hp pht a s dng MBSFN, lp biu v lp cu hnh khun dng truyn ti c iu phi gia cc tham gia pht MBSFN. 2.4 Giao thc ca LTE (LTE Protocols) [2] LTE chc nng ca RLC c chuyn vo eNodeB, cng nh chc nng ca PDCP vi m ha v chn tiu . V vy, cc giao thc lin quan ca lp v tuyn c chia trc y UTRAN l gia NodeB v RNC by gi chuyn thnh gia UE v eNodeB. Hnh 2.6: Giao thc ca UTRAN n tt nghip Trang 32 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Hnh 2.7: Giao thc ca E-UTRAN Giao thc ca E-UTRAN pht trin thm ca UTRAN bng cch thm L1 v MAC mi. Hnh 2.8: Phn phi chc nng ca cc lp MAC, RLC, PDCP n tt nghip Trang 33 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Chc nng ca MAC(Medium Access Control) bao gm : - Lp biu - iu khin u tin (Priority handling) - Ghp nhiu knh logic khc nhau trn mt knh truyn n RLC, cng nh trong WCDMA c chc nng sau: o Truyn li trong trng hp giao nhn cc lp thp (MAC v L1) b hng, tng t trong trng hp ch ACK ca RLC UTRAN o Phn on ph hp cho cc giao thc n v d liu o Cung cp cc knh vt l cho cc lp cao hn Chc nng ca PDCP bao gm: - M ha (ciphering) - Chn tiu Trong sut nm 2006, PDCP vn c gi s trong mng li, nhng quyt nh hin ti l a PDCP vo eNodeB bao gm m ha. iu ny lm cho chc nng v tuyn ca LTE tng t nh ca HPSA ci tin. Trong giao din iu khin, chc nng ca giao thc RRC th cng ging nh bn UTRAN. Giao thc RRC cu hnh cc thng s kt ni, iu khin bo co o lng thit b u cui, cc lnh chuyn giaoM ASN1 c s dng cho RRC ca LTE, n dn cch s khc bit gia cc phin bn ng tng thch li. Giao thc RRC s bao gm t trng thi hn EUTRAN. Ch c trng thi tch cc hay ri c d on bi v c tnh linh ng ca s phn b ngun ti nguyn. Cc trng thi ca RRC trong LTE l: - RRC-ri: thit b s quan st bn tin paging v s dng cell cho di ng. Khng c RRC no lu tr trong bt k eNodeB c nhn no. UE ch c duy nht mt ID nhn dng n trong vng di chuyn. - RRC-kt ni: bit v tr ca UE cell no v d liu c pht v nhn. n tt nghip Trang 34 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Kt ni RRC tn ti n mt eNodeB. iu khin chuyn giao bi mng c s dng cho di ng. 2.5 Mt s c tnh ca knh truyn Ta tm hiu mt s c tnh ca knh truyn nh hng n vic truyn tn hiu, cc c tnh ny bao gm tri tr, fading, dch tn Doppler, nh hng ca dch tn Doppler i vi tn hiu OFDM, nhiu MAI, v cch khc phc nhiu MAI. 2.5.1 Tri tr a ng Tn hiu nhn c ni thu gm tn hiu thu trc tip v cc thnh phn phn x. Tn hiu phn x n sau tn hiu thu trc tip v n phi truyn qua mt khong di hn, v nh vy n s lm nng lng thu c tri rng theo thi gian. Khong tri tr (delay spread) c nh ngha l khong chnh lch thi gian gia tn hiu thu trc tip v tn hiu phn x thu c cui cng. Trong thng tin v tuyn, tri tr c th gy nn nhiu xuyn k t nu nh h thng khng c cch khc phc. i vi LTE, s dng k thut OFDM trnh c nhiu xuyn k t ISI. 2.5.2 Cc loi fading Fading l s bin i cng tn hiu sng mang cao tn ti anten thu do c s thay i khng ng u v ch s khc x ca kh quyn, cc phn x ca t v nc trn ng truyn sng v tuyn i qua. 2.5.2.1 Rayleigh fading Fadinh Rayleigh l loi Fading sinh ra do hin tng a ng (Multipath Signal) v xc sut mc tn hiu thu b suy gim so vi mc tn hiu pht i tun theo phn b Rayleigh. 2.5.2.2 Fading chn lc tn s v fading phng Bng thng kt hp: l mt php o thng k ca di tn s m knh xem nh l phng. Nu tri tr thi gian a ng l D(s) th bng thng kt hp Wc(Hz) xp x bng: D Wc 2 / 1 ~ n tt nghip Trang 35 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Trong fading phng, bng thng kt hp ca knh ln hn bng thng ca tn hiu. V vy, s lm thay i u tn hiu sng mang trong mt di tn s. Trong fading chn lc tn s, bng thng kt hp ca knh nh hn bng thng ca tn hiu. V vy, s lm thay i tn hiu sng mang vi mc thay i ph thuc tn s. 2.5.3 Dch tn Doppler H thng truyn v tuyn chu s tc ng ca dch tn Doppler. Dch tn Doppler l hin tng m tn s thu c khng bng tn s ca ngun pht do s chuyn ng tng i gia ngun pht v ngun thu. C th l: khi ngun pht v ngun thu chuyn ng hng vo nhau th tn s thu c s ln hn tn s pht i, khi ngun pht v ngun thu chuyn ng ra xa nhau th tn s thu c s gim i. Khong tn s dch chuyn trong hin tng Doppler tnh theo cng thc sau : cvf f0 = A (2.1) Trong f A l khong tn s dch chuyn, f0 l tn s ca ngun pht, v l vn tc tng i gia ngun pht v ngun thu, c l vn tc nh sng. i vi LTE, khc phc hin tng dch tn Doppler, ngi ta chn khong cch gia cc sng mang ln (f = 15 Khz). 2.5.4 Nhiu MAI i vi LTE i vi LTE, ng ln s dng k thut SC-FDMA, n cng nhy cm vi dch tn. Cc user khc nhau lun c dch tn s sng mang CFO (Carrier Frequency Offset). Khi tn ti nhiu CFO, tnh trc giao gia cc sng mang b mt. Nhiu lin sng mang (ICI : Inter Carrier Interference) v MAI (Multi Access Interference) to ra lm gim cht lng ca tn hiu thu c. Mt phng php trit ICI cng nh MAI, l da trn cc k hiu hoa tiu khi (block type pilots). Cc user khc nhau giao tip vi trm gc ti cc khe thi gian khc nhau. Phng php ny ly trc tip thnh phn nhiu bng cch li dng cc k hiu hoa tiu khi, v vy n khng cn s dng c lng CFO nhiu ln. Sau , ma trn can nhiu c th c khi phc li v nh hng ca cc CFO c th c trit d n tt nghip Trang 36 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan dng bng cch s dng phng php o ma trn. Phng php trit nhiu MAI c th c cp [19]. 2.6 Cc k thut s dng trong LTE LTE s dng k thut OFDMA cho truy cp ng xung v SC-FDMA cho truy cp ng ln. Kt hp ng thi vi MIMO, cc k thut v lp biu, thch ng ng truyn v yu cu t ng pht li lai ghp. 2.6.1 K thut truy cp phn chia theo tn s trc giao OFDM [1] Hnh 2.9 : Truyn n sng mang Hnh 2.10 : Nguyn l ca FDMA Hnh 2.11 : Nguyn l a sng mang K thut iu ch OFDM, v c bn, l mt trng hp c bit ca phng php iu ch FDM, chia lung d liu thnh nhiu ng truyn bng hp trong vng tn s s dng, trong cc sng mang con (hay sng mang ph, sub-carrier) trc giao vi nhau. Do vy, ph tn hiu ca cc sng mang ph ny c php chng ln ln nhau m pha u thu vn khi phc li c tn hiu ban u. S n tt nghip Trang 37 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan chng ln ph tn hiu ny lm cho h thng OFDM c hiu sut s dng ph ln hn nhiu so vi cc k thut iu ch thng thng. Hnh 2.12 : So snh ph tn ca OFDM vi FDMA Hnh 2.13 : Tn s-thi gian ca tn hiu OFDM LTE s dng OFDM trong k thut truy cp ng xung v n c cc u im sau: - OFDM c th loi b hin tng nhiu xuyn k hiu ISI (Inter-Symbol Interference) nu di chui bo v (guard interval) ln hn tr truyn dn ln nht ca knh truyn. n tt nghip Trang 38 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan - Thc hin vic chuyn i chui d liu t ni tip sang song song nn thi gian symbol tng ln do s phn tn theo thi gian gy bi tri tr do truyn dn a ng gim xung. - Ti u hiu qu ph tn do cho php chng ph gia cc sng mang con. Hn ch c nh hng ca fading bng cch chia knh fading chn lc tn s thnh cc knh con phng tng ng vi cc tn s sng mang OFDM khc nhau. - OFDM ph hp cho vic thit k h thng truyn dn bng rng (h thng c tc truyn dn cao), nh hng ca s phn tp v tn s (frequency selectivity) i vi cht lng h thng c gim thiu nhiu so vi h thng truyn dn n sng mang. - Cu trc my thu n gin. - Thch ng ng truyn v lp biu trong min tn s. - Tng thch vi cc b thu v cc anten tin tin. Hnh 2.14 : Cc sng mang trc giao vi nhau Mt vn gp phi OFDM trong cc h thng thng tin di ng l cn dch cc tn s tham kho i vi cc u cui pht ng thi. Dch tn ph hng tnh trc giao ca cc cuc truyn dn n nhiu a truy nhp. V vy n rt nhy cm vi dch tn. LTE chn khong cch gia cc sng mang l 15KHz, i vi khong cch ny l khong cch ln i vi dch tn Doppler. n tt nghip Trang 39 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan iu ch tn hiu OFDM s dng bin i FFT v IFFT cho bin i gia min thi gian v min tn s. Hnh 2.15 : Bin i FFT Chiu di bin i FFT l 2n vi n l s nguyn. Vi LTE chiu di c th l 512 hoc 1024...Ta s dng bin i IFFT khi pht i, ngun d liu sau khi iu ch c chuyn i t ni tip sang song song. Sau c a n b bin i IFFT. Mi ng vo ca IFFT tng ng vi tng sng mang con ring bit (thnh phn tn s ring bit ca tn hiu min thi gian) v mi sng mang c iu ch c lp vi cc sng mang khc. Sau khi c bin i IFFT xong, tn hiu c chn thm tin t vng (CP) v pht i. b thu ta lm ngc li. Hnh 2.16 : Thu pht OFDM Mc ch ca vic chn thm tin t vng l c kh nng lm gim hay loi tr nhiu xuyn k hiu ISI (Inter Symbol Interference). Mt mu tn hiu c di n tt nghip Trang 40 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan l TS, chui bo v tng ng l mt chui tn hiu c di TG pha sau c sao chp ln phn pha trc ca mu tn hiu nh hnh v sau: Do , GI cn c gi l Cyclic Prefix (CP). S sao chp ny c tc dng chng li nhiu xuyn k hiu ISI do hiu ng phn tp a ng. Nguyn tc ny gii thch nh sau: Gi s my pht i mt khong tn hiu c chiu di l Ts, sau khi chn thm chui bo v c chiu di TG th tn hiu ny c chiu di l T = TS+TG. Do hiu ng a ng multipath, tn hiu ny s ti my thu theo nhiu ng khc nhau. Trong hnh v, hnh a, tn hiu theo ng th nht khng c tr, cc ng th hai v th ba u b tr mt khong thi gian so vi ng th nht. Tn hiu thu c my thu s l tng hp ca tt c cc tuyn, cho thy k hiu ng trc s chng ln vo k hiu ngay sau , y chnh l hin tng ISI.Do trong OFDM c s dng chui bo v c di TG s d dng loi b hin tng ny. Trong trng hp TG MAX nh hnh v m t th phn b chng ln ISI nm trong khong ca chui bo v, cn thnh phn tn hiu c ch vn an ton. pha my thu s loi b chui bo v trc khi gi tn hiu n b gii iu ch OFDM. Do , iu kin cn thit cho h thng OFDM khng b nh hng bi ISI l: TG MAX vi MAX l tr truyn dn ti a ca knh. Hnh 2.17: Chui bo v GI n tt nghip Trang 41 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan a ) Khng c GI b) C GI Hnh 2.18 Tc dng ca chui bo v OFDM lng t ha trong min tn s da trn c lng p ng tn s ca knh. Do n hot ng n gin hn WCDMA v n khng ph thuc vo chiu di ca knh (chiu di ca a ng trong cc chip) nh khi lng t WCDMA. Trong WCDMA cc cell khc nhau c phn bit bi cc m tri ph khc nhau nhng trong OFDM tri ph khng c gi tr, n s dng cc k hiu tham kho ring bit gia cc cell hoc gia cc anten khc nhau. LTE s dng OFDMA (Orthogonal Frequency Division Multiple Access) cho tuyn ln. OFDMA gi l a truy nhp phn chia theo tn s trc giao l cng ngh a truy cp phn chia theo sng mang, l mt dng nng cao, l phin bn a ngi dng ca m hnh iu ch s OFDM K thut a truy nhp ca OFDMA cho php nhiu ngi dng cng truy cp vo mt knh truyn bng cch phn chia mt nhm cc sng mang con (subcarrier) cho mt ngi dng ti mt thi im. cc thi im khc nhau, n tt nghip Trang 42 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan nhm sng mang con cho 1 ngi dng cng khc nhau. iu ny cho php truyn d liu tc thp t nhiu ngi s dng. Hnh 2.19 Sng mang con OFDMA Hnh 2.20 OFDM v OFDMA Ti nguyn thi gian - tn s c chia nh theo cu trc sau : 1 radio frame c chiu di l 10ms, trong chia thnh nhiu subframe nh c chiu di l 1ms, v mi subframe nh li c chia thnh 2 slot vi chiu di ca mi slot l 0.5ms. Mi slot s bao gm 7 k t OFDM trong trng hp chiu di CP thng thng v 6 k t OFDM trong trng hp CP m rng. Trong OFDMA, vic ch nh s sng mang con cho ngi dng khng da vo tng sng mang con ring l m da vo cc khi ti nguyn (Resource Block). Mi khi ti nguyn bao gm 12 sng mang con cho khong thi gian 1 slot v khong cch gia cc sng mang con l 15KHz dn n kt qu bng thng ti thiu ca n l 180 KHz. n v nh nht ca ti nguyn l thnh phn ti nguyn (RE), n bao gm mt sng mang con i vi khong thi gian ca mt k t OFDM. Mt RB bao gm 84 RE (tc 7 x12) trong trng hp chiu di CP thng thng v 72 RE (6x12) trong trng hp chiu di CP m rng. n tt nghip Trang 43 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Hnh 2.21 : Ch nh ti nguyn ca OFDMA trong LTE Bng 2.5 : S khi ti nguyn theo bng thng knh truyn Bng thng knh truyn (MHz) 1.4 3 5 10 15 20 S khi ti nguyn 6 15 25 50 75 100 n tt nghip Trang 44 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Hnh 2.22 : Cu trc ca mt khi ti nguyn Tn hiu tham kho (RS) : LTE s dng cc tn hiu tham kho c bit d dng c lng dch sng mang, c lng knh truyn, ng b thi gianCc tn hiu tham kho c b tr nh hnh sau: n tt nghip Trang 45 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Hnh 2.23 : Cu trc b tr tn hiu tham kho Cc tn hiu tham kho ny c pht k t OFDM th nht v th nm ca mi slot v sng mang th su ca mi subframe. Tn hiu tham kho cng c s dng c lng tn hao ng truyn s dng cng sut thu tn hiu tham kho (RSRP). Nhc im ca OFDM l g? Ta xt cc hnh sau Hnh 2.24: c tnh ng bao ca tn hiu OFDM n tt nghip Trang 46 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Hnh 2.25: PAPR cho cc tn hiu khc nhau T cc hnh trn ta thy, dng sng OFDM th hin s thng ging ng bao rt ln dn n PAPR cao. Tn hiu vi PAPR cao i hi cc b khuch i cng sut c tnh tuyn tnh cao trnh lm mo dng tn hiu. t c mc tuyn tnh ny, b khuch i phi lm vic ch cng tc vi li (so vi im bo ha cao). iu ny dn n hiu sut s dng cng sut (t s cng sut pht vi cng sut tiu th mt chiu) thp v th c bit nh hng i vi cc thit b cm tay. khc phc nhc im ny, 3GPP nghin cu s dng phng php a truy nhp ng ln s dng DTFS-OFDM vi tn gi l SC-FDMA v p dng cho LTE. 2.6.2 K thut SC-FDMA [1] Cc tn hiu SC-FDMA c tn hiu PAPR tt hn OFDMA. y l mt trong nhng l do chnh chn SC-FDMA cho LTE. PAPR gip mang li hiu qu cao trong vic thit k cc b khuch i cng sut UE, v vic x l tn hiu ca SC-FDMA vn c mt s im tng ng vi OFDMA, do , tham s hng DL v UL c th cn i vi nhau. Ging nh trong OFDMA, cc my pht trong h thng SC-FDMA cng s dng cc tn s trc giao khc nhau pht i cc k hiu n tt nghip Trang 47 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan thng tin. Tuy nhin cc k hiu ny pht i ln lt ch khng phi song song nh trong OFDMA. V th, cch sp xp ny lm gim ng k s thng ging ca ng bao tn hiu ca dng sng pht. V th cc tn hiu SC-FDMA c PAPR thp hn cc tn hiu OFDMA. Tuy nhin trong cc h thng thng tin di ng b nh hng ca truyn dn a ng, SC-FDMA c thu ti cc BTS b nhiu gia cc k t kh ln. BTS s dng b cn bng thch ng min tn s loi b nhiu ny. Hnh 2.26: OFDMA v SC-FDMA Hnh trn cho thy s khc nhau trong qu trnh truyn cc k hiu s liu theo thi gian. Trn hnh ny ta coi mi ngi s dng c phn thnh 4 sng mang con (P = 4) vi bng thng con bng 15KHz, trong mi k hiu OFDMA hoc SC-FDMA truyn 4 k hiu s liu c iu ch QPSK cho mi ngi s dng. i vi OFDMA 4 k hiu s liu ny c truyn dng thi vi bng tn con cho mi k hiu l 15KHz trong mi khong thi gian hiu dng TFFT ca mt k hiu OFDMA, trong khi i vi SC-FDMA, 4 k hiu s liu ny c truyn ln lt trong khong thi gian bng 1/P (P = 4) thi gian hiu dng k hiu SC-FDMA vi bng tn con bng P x 15KHz (4 x 15 KHz) cho mi k hiu. n tt nghip Trang 48 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Trong OFDM, bin i Fourier nhanh FFT dng bn thu cho mi khi k t, v o FFT bn pht. Cn SC-FDMA s dng c hai thut ton ny c bn pht v bn thu. Hnh 2.27 : Thu pht SC-FDMA trong min tn s 2.6.3 K thut MIMO [1] MIMO l mt phn tt yu ca LTE t c cc yu cu y tham vng v thng lng v hiu qu s dng ph. MIMO cho php s dng nhiu anten my pht v my thu. Vi hng DL, MIMO 2x2 (2 anten thit b pht, 2 anten thit b thu) c xem l cu hnh c bn, v MIMO 4x4 cng c cp v a vo bng c t k thut chi tit. Hiu nng t c ty thuc vo vic s dng MIMO. Trong , k thut ghp knh khng gian (spatial multiplexing) v pht phn tp (transmit diversity) l cc c tnh ni bt ca MIMO trong cng ngh LTE. Gii hn chnh ca knh truyn thng tin l can nhiu a ng gii hn v dung lng theo quy lut Shannon. MIMO li dng tn hiu a ng gia my pht v my thu ci thin dung lng c sn cho bi knh truyn. Bng cch s dng nhiu anten bn pht v thu vi vic x l tn hiu s, k thut MIMO c th n tt nghip Trang 49 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan to ra cc dng d liu trn cng mt knh truyn, t lm tng dung lng knh truyn. Hnh 2.28 M hnh SU-MIMO v MU-MIMO Hnh trn l v d v SU-MIMO 2x2 v MU-MIMO 2x2. SU-MIMO y hai dng d liu trn vi nhau (m ha) ph hp vi knh truyn nht. 2x2 SU-MIMO thng dng trong tuyn xung. Trong trng hp ny dung lng cell tng v tc d liu tng. MU-MIMO 2x2 y dng d liu MIMO a ngi dng n t cc UE khc nhau. Dung lng cell tng nhng tc d liu khng tng. u im chnh ca MU-MIMO so vi SU-MIMO l dung lng cell tng m khng tng gi thnh v pin ca hai my pht UE. MU-MIMO phc tp hn SU-MIMO. Trong h thng MIMO, b pht gi cc dng d liu qua cc anten pht. Cc dng d liu pht thng qua ma trn knh truyn bao gm nhiu ng truyn gia cc anten pht v cc anten thu. Sau b thu nhn cc vector tn hiu t cc anten thu, gii m thnh thng tin gc. i vi tuyn xung, cu hnh hai anten trm pht v hai anten thu thit b u cui di ng l cu hnh c bn, cu hnh s dng bn anten ang c xem xt. y chnh l cu hnh SU-MIMO, v s dng k thut ghp knh khng gian vi li th hn cc k thut khc l trong cng iu kin v bng thng s dng v k thut iu ch tn hiu, SU cho php tng tc d liu (data rate) bng s ln ca s lng anten pht. Ghp knh khng gian cho php pht chui bit d liu khc nhau trn cng mt khi ti nguyn tuyn xung. Nhng dng d liu ny c th l mt ngi dng n tt nghip Trang 50 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan (SU-MIMO) hoc nhng ngi dng khc nhau (MU-MIMO). Trong khi SU-MIMO tng tc d liu cho mt ngi dng, MU-MIMO cho php tng dung lng. Da vo hnh 2.29, ghp knh khng gian li dng cc hng khng gian ca knh truyn v tuyn cho php pht cc d liu khc nhau trn hai anten. Hnh 2.29: Ghp knh khng gian K thut phn tp c bit n t WCDMA release 99 v cng s l mt phn ca LTE. Thng thng, tn hiu trc khi pht c m ha tng hiu ng phn tp. MIMO c s dng khai thc vic phn tp v mc tiu l lm tng tc . Vic chuyn i gia MIMO truyn phn tp v ghp knh khng gian c th ty thuc vo vic s dng knh tn s. i vi ng ln, t thit b u cui di ng n BS, ngi ta s dng m hnh MU-MIMO (Multi-User MIMO). S dng m hnh ny BS yu cu s dng nhiu anten, cn thit b di ng ch dng mt anten gim chi ph cho thit b di ng. V hot ng, nhiu thit b u cui di ng c th pht lin tc trn cng mt knh truyn, nhiu knh truyn, nhng khng gy ra can nhiu vi nhau bi v cc tn hiu hoa tiu (pilot) trc giao ln nhau. K thut c cp n, l k thut a truy nhp min khng gian (SDMA) hay cn gi l MIMO o. 2.6.4 M ha Turbo [18] sa nhng bit b li do s thay i knh v nhiu, m ha knh c s dng. Vi knh chia s hng xung ca LTE (DL-SCH), s dng mt b m ha Turbo vi tc 1/3, theo sau l mt b so khp tc thch ng vi tc m. Trong mi khung con chiu di 1ms, mt hoc hai t m c th c m ha v truyn i. n tt nghip Trang 51 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan 2.6.5 Thch ng ng truyn [18] Thch ng ng truyn gii quyt vn lin quan n cch thit lp cc thng s truyn dn ca ng truyn v tuyn x l cc thay i cht lng ng truyn v tuyn. N s dng iu ch thch nghi (Adaptive Modulation). Phng php ny cho php h thng iu chnh nguyn l iu ch tn hiu theo t l tn hiu trn nhiu (SNR) ca ng truyn v tuyn. Khi ng truyn v tuyn c cht lng cao, nguyn l iu ch cao nht c s dng lm tng thm dung lng h thng. Trong qu trnh suy gim tn hiu, h thng LTE c th chuyn sang mt nguyn l iu ch thp hn duy tr cht lng v s n nh ca ng truyn. c im ny cho php h thng khc phc hiu ng fading la chn thi gian. c im quan trng ca iu ch thch nghi l kh nng tng di s dng ca nguyn l iu ch mc cao hn, do h thng c tnh mm do i vi tnh trng fading thc t. Hnh 2.30 iu ch thch nghi n tt nghip Trang 52 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan K thut iu ch v m ho thch nghi l mt trong nhng u vit ca OFDM v n cho php ti u ho mc iu ch trn mi knh con da trn cht lng tn hiu (t l SNR) v cht lng knh truyn dn. 2.6.6 Lp biu ph thuc knh [18] Lp biu ph thuc knh gii quyt vn cch thc chia s cc ti nguyn v tuyn gia nhng ngi s dng (cc u cui di ng) khc nhau trong h thng t c hiu sut s dng ti nguyn tt nht. Lp biu ph thuc knh cho php gim thiu lng ti nguyn cn thit cho mt ngi s dng, v th cho php nhiu ngi s dng hn trong khi vn p ng c cc yu cu cht lng dch v. Nguyn l lp biu cng nh vic chia s cc ti nguyn gia nhng ngi s dng, t nht v mt l thuyt, ph thuc vo cc c tnh ca giao din v tuyn, vo vic ng truyn l ng truyn ln hay truyn xung v vo vic truyn dn ca nhng ngi s dng vi nhau c trc giao hay khng. Thch ng ng truyn v lp biu ph thuc knh lin quan mt thit vi nhau v thng th chng c coi nh l mt chc nng lin kt. 2.6.7 HARQ vi kt hp mm [18] Do tnh cht ngu nhin ca cc thay i cht lng ng truyn v tuyn, khng bao gi c th t c thch ng cht lng knh v tuyn tc thi mt cch hon ho. HARQ v th rt hu ch. HARQ vi kt ni mm c s dng trong LTE, cho php u cui di ng yu cu truyn li nhanh chng nhng khi vn chuyn b li, v cung cp mt cng c cho thch ng tc ngm nh. Giao thc bn di l nhiu x l hybrid ARQ dng v ch (stop-and-wait) song song nhau. Trong ARQ, u thu s dng mt m pht hin li kim tra gi d liu c b li hay khng. u pht c thng bo bng NAK hoc ACK. Nu gi d liu b li v c thng bo NAK, gi s c truyn li. Mt s kt hp ca FEC (Forward Error Correction) v ARQ c bit nh l HARQ. HARQ trong thc t phn ln c xy dng xung quanh m CRC pht hin li v m Turbo sa li, nh trong trng hp ca LTE. n tt nghip Trang 53 Chng 2 : Cu trc mng 4G LTE v cc vn lin quan Trong HARQ vi kt ni mm, nhng gi nhn c b sai, c lu trong mt b m v sau c kt hp vi truyn li t c mt gi ng tin cy. Trong LTE, Incremental Redundancy (IR) c p dng, ngha l nhng gi c truyn li khng ging nhng gi truyn u tin, m n mang thng tin b sung. 2.7 Chuyn giao Chuyn giao l phng tin cn thit thu bao c th di chuyn trong mng. Khi thu bao chuyn ng t vng ph sng ca mt cell ny sang mt cell khc th kt ni vi cell mi phi c thit lp v k