N 2 : MNG 4G V K THUT LTEGVHD: Th.S NGUYN QUNH ANH

Th h 1G : y l h thng thng tin di ng tng t s dng phng thc a truy nhp phn chia theo tn s FDMA v iu ch tn s FM vi cc c im : Phng thc truy nhp: FDMA. Dch v n thun l thoi. Cht lng thp. Bo mt km.

Mt s h thng s dng : NMT (Nordic Mobile Telephone): s dng bng tn 450Mhz trin khai ti cc nc Bc u vo nm 1981. TACS (Total Access Communication System): trin khai Anh vo nm 1985.

AMPS (Advance Mobile Phone System): trin khai ti Bc M vo nm 1978 ti bng tn 800Mhz.

Th h 2G:

H thng mng 2G c c trng bi cng ngh chuyn mch k thut s (digital circuit-switched). K thut ny chim u th hn 1G vi cc c im sau: Dung lng tng. Cht lng thoi tt hn H tr cc dch v s liu Phng thc truy nhp : TDMA, CDMA bng hp.

Mt s h thng in Hnh : GSM (Global System for Mobile Phone) s dng phng thc truy cp TDMA c trin khai ti chu u. D-AMPS (IS-136-Digital Advance Mobile Phone System) s dng phng thc truy cp TDMA c trin khai ti M. IS-95 (CDMA One) s dng phng thc truy cp CDMA c trin khai ti M v Hn Quc. PDC (Personal Digital Cellular) s dng phng thc truy cp TDMA c trin khai ti Nht Bn. Th h 3G : H thng mng c s dng ph bin hin nay, c cc u im mnh m so vi 2 th h c. y l th h th ba ca chun cng ngh in thoi di ng, cho php truyn c d liu thoi v ngoi thoi (ti d liu, gi email, tin nhn nhanh, Hnh nh). 3G cung cp c hai h thng l chuyn mch gi v chuyn mch knh. H thng 3G yu cu mt mng truy cp radio hon ton khc so vi h thng 2G hin nay. im mnh ca cng ngh ny so vi 2G l cho php truyn, nhn cc d liu, m thanh, Hnh nh cht lng cao cho c thu bao c nh v thu bao ang di chuyn cc tc khc nhau. Mng 3G c trng bi tc d liu cao, capacity ca h thng ln, tng hiu qu s dng ph tn v nhiu ci tin khc. C mt lot cc chun cng ngh di ng 3G, tt c u da trn CDMA, bao gm: UMTS (dng c FDD ln TDD), CDMA2000 v TD-SCDMA :

UMTS (i khi cn c gi l 3GSM) s dng k thut a truy cpWCDMA. UMTS c chun ho bi 3GPP. UMTS l cng ngh 3G c la chn bi hu ht cc nh cung cp dch v GSM/GPRS i ln 3G. Tc d liu ti a l 1920Kbps (gn 2Mbps). Nhng trong thc t tc ny ch tm 384Kbps. ci tin tc d liu ca 3G, hai k thut HSDPA v HSUPA c ngh. Khi c 2 k thut ny c trin khai, ngi ta gi chung l HSPA. HSPA thng c bit n nh l cng ngh 3,5G. HSDPA: Tng tc downlink (ng xung, t NodeB v ngi dng di ng). Tc ti a l thuyt l 14,4Mbps, nhng trong thc t n ch t tm 1,8Mbps (hoc tt lm l 3,6Mbps). Theo mt bo co ca GSA thng 7 nm 2008, 207 mng HSDPA v ang bt u trin khai, trong thng mi ho 89 nc trn th gii. HSUPA: tng tc uplink (ng ln) v ci tin QoS. K thut ny cho php ngi dng upload thng tin vi tc ln n 5,8Mbps (l thuyt). Cng trong cng bo co trn ca GSA, 51 nh cung cp dch v thng tin di ng trin khai mng HSUPA 35 nc v 17 nh cung cp mng ln k hoch trin khai mng HSUPA. CDMA2000: bao gm CDMA2000 1xRTT (Radio Transmission Technology), CDMA2000 (Evolution -Data Optimized) v CDMA2000 EV-DV(Evolution -Data and Voice). CDMA2000 c chun ho bi 3GPP2. CDMA2000 l cng ngh 3G c la chn bi cc nh cung cp mng CdmaOne. CDMA2000 1xRTT: chnh thc c cng nhn nh l mt cng ngh 3G, tuy nhin nhiu ngi xem n nh l mt cng ngh 2,75G ng hn l 3G. Tc ca 1xRTT c th t n 307Kbps, song hu ht cc mng trin khai ch gii hn tc peak 144Kbps. CDMA2000 EV-DO: s dng mt knh d liu 1,25MHz chuyn bit v c th cho tc d liu n 2,4Mbps cho ng xung v 153Kbps cho ng ln. 1xEV-DO Rev A h tr truyn thng gi IP, tng tc ng xung n 3,1Mbps v c bit c th y tc ng ln n 1,2Mbps. Bn cnh , 1xEV-DO Rev B cho php nh cung cp mng gp n 15 knh 1,25MHz li truyn d liu vi tc 73,5Mbps.

CDMA2000 EV-DV: tch hp thoi v d liu trn cng mt knh 1,25MHz. CDMA2000 EV-DV cung cp tc peak n 4,8Mbps cho ng xung v n 307Kbps cho ng ln. Tuy nhin t nm 2005, Qualcomm dng v thi hn vic pht trin ca 1xEV-DV v a phn cc nh cung cp mng CDMA nh Verizon Wireless v Sprint chn EV-DO TD-SCDMA l chun di ng c ngh bi "China Communications Standards Association" v c ITU duyt vo nm 1999. y l chun 3G ca Trung Quc. TD-SCDMA dng song cng TDD. TD-SCDMA c th hot ng trn mt di tn hp 1,6MHz (cho tc 2Mbps) hay 5MHz (cho tc 6Mbps). Ngy xut hnh ca TD-SCDMA b y li nhiu ln. Nhiu th nghim v cng ngh ny din ra t u nm 2004 cng nh trong th vn hi Olympic gn y.

H thng 4G LTE :

LTE l th h th t tng lai ca chun UMTS do 3GPP pht trin. UMTS th h th ba da trn WCDMA c trin khai trn ton th gii. m bo tnh cnh tranh cho h thng ny trong tng lai, thng 11/2004 3GPP bt u d n nhm xc nh bc pht trin v lu di cho cng ngh di ng UMTS vi tn gi Long Term Evolution (LTE). 3GPP t ra yu cu cao cho LTE, bao gm gim chi ph cho mi bit thng tin, cung cp dch v tt hn, s dng linh hot cc bng tn hin c v bng tn mi, n gin ha kin trc mng vi cc giao tip m v gim ng k nng lng tiu th thit b u cui. Cc mc tiu ca cng ngh ny l: Tc nh tc thi vi bng thng 20Mhz. Ti ln: 50 Mbps. Ti xung: 100 Mbps. Dung lng d liu truyn ti trung bnh ca mt ngi dng trn 1Mhz so vi mng HSDPA Rel.6. Ti ln: gp 2 n 3 ln. Ti xung: gp 3 n 4 ln. Hot ng ti u vi tc di chuyn ca thu bao l 0-15 km/h. Vn hot ng tt vi tc t 15-120 km/h. Vn duy trc c hot ng khi thu bao di chuyn vi tc t 120-350 km/h (thm ch 500 km/h ty bng tn). Cc ch tiu trn phi m bo trong bn knh vng ph sng 5km, gim cht t trong phm vi n 30km. T 30-100km th khng hn ch. di bng thng linh hot: c th hot ng vi cc bng tn 1.25Mhz, 1.6 Mhz, 10Mhz, 15Mhz v 20Mhz c chiu ln v chiu xung. H tr c hai trng hp di bng ln v bng xung bng nhau hoc khng.

t c mc tiu ny, s c rt nhiu k thut mi c p dng, trong ni bt l k thut v tuyn OFDMA (a truy cp phn chia theo tn s trc giao), k thut anten MIMO (Multiple Input Multiple Output). Ngoi ra h thng ny s chy hon ton trn nn IP (all-IP Network), v h tr c hai ch FDD v TDD.

Hnh 2.1 S tm lt s pht trin ca h thng TTDD2.3. im vt tri ca LTE so vi mng 3G :

S khc nhau : Hin nay cng ngh 3G cho php truy cp internet khng dy v cc cuc gi c Hnh nh. 4G LTE pht trin da trn cng ngh 3G. V mt l thuyt, mng khng dy s dng cng ngh LTE c tc nhanh hn mng 3G t 4 n 10 ln. Tc ti a ca 3G l tc 14Mbps cho down v 5.8Mbps cho up. Vi cng ngh LTE tc c th t 100Mbps i vi ngi dng di ng v 1Gbps i vi ngi dng c nh. 3G s dng cc di tn c nh quc t : UL : 1885-2025 MHz DL : 2110-2200 MHz Tc : 144kbps-2Mbps rng BW : 5MHz

4G s dng : Bng tn s dng : 700Mbps-2.6Gbps vi mc tiu tr thp, tc cao, cng ngh truy cp sng v tuyn gi d liu ti u. Tc d UL : 100Mbps BW 20 MHZ Tc DL : 50Mbps S dng 2 anten thu mt anten pht. tr nh hn 5ms v rng BW linh hot l u im ca LTE so vi WCDMA. BW t 1.25MHz, 2.5MHz, 5MHz, 10MHz, 15MHz, 20MHz. Hiu qu tri ph tng 4 n 10 ln s ngi dng/cell so vi WCDMA. u im ni bt : Tc truyn d liu rt cao so vi 3G. Tng tnh hiu qu so vi s dng ph v gim thi gian tr. Cu trc mng s n gin hn v khng cn s dng chuyn mch knh na. Hiu qu tri ph tng 4 n 10 ln user/cell so vi WCDMA. rng bng tn linh hot. Cc ng dng to nn u im so vi 3G : Hiu sut ph cao. o OFDM DL : - Chng nhiu a ng. - Hu ht d liu ngi dng t hn di ng. o SC-FDMA UL : - PAPR thp. - Ngi dng trc giao trong min tn s. o MIMO Tc d liu cao : o Thi gian ci t v thi gian delay chuyn tip ngn. o Tr HO v thi gian ngt ngn : TTI ngn, trng thi RRC n gin. Gi thnh r :

Kin trc mng n gi, gim cc thnh phn ca mng. Cht lng dch v cao : o S dng cc tn s cp php m bo cht lng dch v, LTE s dng cc di tn s khc nhau : 2100, 1900, 1700, 2600, 900, 800 MHz. o Lun lun th nghim (gim thi gian tr trong iu khin nh tuyn ). o Gim tr kh hi ( round trip delay ). Tn s ti s dng linh hot : o Gim nhiu lin cell v tn s ti s dng ln hn 1. o S dng 2 di tn s : - Di 1 : h s ti s dng ln hn 1cng sut pht cao hn. - Di 2 : ph cn li. o Cc user cnh cell : s dng di 1 SIR tt. o 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 nhin bn trong cell v can nhiu lin cell. Nhng i vi LTE th do tnh trc giao nn can nhiu trong cng 1 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.

CHNG 2: KIN TRC MNG LTE

Chng ny gii thiu v kin trc mng LTE , cc phn t v chc nng ca cc phn t trong mng.Kin trc v mng li v mng truy nhp ca LTE. Cc giao thc ca mt phng iu khin v mt phng ngi s dng. Qua hiu c hot ng ca mng LTE.2.1. KIN TRC MNG LTELTE c thit k h tr cho cc dch v chuyn mch gi, i lp vi chuyn mch knh truyn thng. N hng n cung cp cc kt ni IP gia cc UE (User Equipment) v PDN (Packet Data Network), m khng c bt k s ngt qung no i vi nhng ng dng ca ngi dng trong sut qu trnh di chuyn. Trong khi thut ng LTE cp quanh s tin trin vic truy cp v tuyn thng qua E-UTRAN (Evolved-UTRAN), n cn c kt hp cng vi cc phng din ci tin khng v tuyn di thut ng SAE (System Architecture Evolution)_bao gm mng li gi ci tin EPC (Evolved Packet Core). LTE cng vi SAE to thnh h thng gi ci tin EPS (Evolved Packet System).Hnh 2.1 cho thy cc thnh phn chnh ca mt mng li v mng truy nhp v tuyn LTE. So snh vi UMTS, mng v tuyn t phc tp hn. Mc ch chnh ca LTE l ti thiu ha s Node. V vy, ngi ta quyt nh rng cc RNC nn c g b, v chc nng ca chng c chuyn mt phn sang cc trm c s v mt phn sang nt Gateway ca mng li. phn bit vi cc trm c s UMTS, cc trm c s ca LTE c gi l Enhanced NodeB (eNodeB). Bi v khng cn phn t iu khin trung ng trong mng v tuyn na nn gi y cc trm c s thc hin chc nng qun l d liu truyn ti mt cch t lp, v bo m cht lng dch v. Tuy nhin cc RNC vn iu khin cc knh truyn ti dnh cho dch v thoi chuyn knh.

Hnh 2.1 S chuyn i cu trc UTRAN sang E-UTRANGiao 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 lmhai loi l S1-U l giao din gia eNodeB v SAE GW v S1-MME l giao dingia eNodeB v MME. X2 l giao din gia cc eNodeB vi nhau.

Hnh 2.2: Cu trc c bn ca LTE2.1.1 Cc phn t trong mng 4G : 2.1.1.1. Thit b ngi dng UE :

UE l thit b m ngi dng u cui s dng lin lc. Thng thng n l nhng thit b cm tay nh in thoi thng minh hoc mt th d liu nh mi ngi vn ang s dng hin ti trong mng 2G v 3G. Hoc n c th c nhng vo, v d mt my tnh xch tay. UE cng c cha cc moun nhn dng thu bao ton cu( USIM). N l mt moun ring bit vi phn cn li ca UE, thng c gi l thit b u cui (TE). USIM l mt ng dng c t vo mt th thng minh c th tho ri c gi l th mch tch hp ton cu (UICC). USIM c s dng nhn dng v xc thc ngi s dng ly kha bo mt nhm bo v vic truyn ti trn giao din v tuyn.

Cc chc nng ca UE l nn tng cho cc ng dng truyn thng m c tn hiu vi mng thit lp, duy tr v loi b cc lin kt thng tin ngi dng cn. iu ny bao gm cc chc nng qun l tnh di ng nh chuyn giao, bo co v tr ca thit b, v cc UE phi thc hin theo hng dn ca mng. C l quan trng nht l UE cung cp giao din ngi s dng cho ngi dng cui cc ng dng nh VoIP c th c s dng thit lp mt cuc gi thoi.

2.1.1.2. E-UTRAN NodeB (eNodeB)

Nt duy nht trn E-UTRAN l E-UTRAN NodeB ( eNodeB). n gin t eNB l mt trm gc v tuyn kim sot tt c cc chc nng v tuyn lin quan trong phn c nh ca h thng. Cc trm gc nh eNB thng phn b trn ton khu vc ph sng ca mng. Mi eNB thng c tr gn cc anten v tuyn hin ti ca chng.

Chc nng ca eNB hot ng nh mt cu ni gia 2 lp l UE v EPC, n l im cui ca tt c cc giao thc v tuyn v pha UE, v tip nhn d liu gia cc kt ni v tuyn v cc kt ni IP c bn tng ng v pha EPC. Trong vai tr ny cc EPC thc hin m ha / gii m cc d liu UP, v cng c nn / gii nn tiu IP, trnh vic gi i lp li ging nhau hoc d liu lin tip trong tiu IP.

eNB cng chu trch nhim v nhiu cc chc nng ca mt phng iu khin (CP). eNB chu trch nhim v qun l ti nguyn v tuyn (RRM), tc l kim sot vic s dng giao din v tuyn , bao gm : phn b ti nguyn da trn yu cu, u tin v lp lch trnh lu lng theo yu cu QoS, v lin tc gim st tnh hnh s dng ti nguyn.

Ngoi ra eNodeB cn c vai tr quan trng trong qun l tnh di ng (MM). iu khin eNB v o c phn tch mc ca tn hiu v tuyn c thc hin bi UE. iu ny bao gm trao i tn hiu chuyn giao gia eNB khc v MME. Khi mt UE mi kch hot theo yu cu ca eNB v kt ni vo mng, eNB cng chu trch nhim v vic nh tuyn, khi ny n s ngh cc MME m trc y phc v cho UE, hoc la chn mt MME mi nu mt tuyn ng n cc MME trc khng c sn hoc thng tin nh tuyn vng mt.

Hnh 2.3 cho thy cc kt ni vi eNB n xung quanh cc nt logic, v tm tt cc chc nng chnh trong giao din ny. Trong tt c cc kt ni eNB c th l trong mi quan h mt nhiu hoc nhiu nhiu. Cc eNB c th phc v ng thi nhiu UE trong vng ph sng ca n nhng mi UE ch c kt ni ti mt eNB trong cng mt thi im. Cc eNB s cn kt ni ti cc eNB ln cn vi n trong khi chuyn giao c th cn thc hin.

C hai MME v S-GW c th c gp li, c ngha l mt tp hp cc nt c phn cng phc v cho mt tp hp cc eNB. T mt vin cnh eNB n ny c ngha l n c th cn phi kt ni ti nhiu MME v S-GW. Tuy nhin mi UE s c phc v bi ch c mt MME v S-GW ti mt thi im v eNB phi duy tr theo di cc lin kt ny.

S kt hp ny s khng bao gi thay i t mt im eNodeB duy nht, bi v MME hoc S-GW ch c th thay i khi kt hp vi s chuyn giao lin eNodeB.

Hnh 2.3 eNodeB kt ni ti cc nt logic khc v cc chc nng chnh

2.1.1.3. Thc th qun l tnh di ng (MME)

Thc th qun l tnh di ng(MME) l thnh phn iu khin chnh trong EPC. Thng thng MME s l mt my ch mt v tr an ton ti cc c s ca nh iu hnh. N ch hot ng trong cc CP, v khng tham gia vo con ng ca UP d liu.

Ngoi giao din cui vo MME trong kin trc, MME cn c mt kt ni logic trc tip ti UE, v kt ni ny c s dng nh l knh iu khin chnh gia UE v mng. Sau y l danh sch cc chc nng chnh ca MME trong cu hnh kin trc c bn h thng :

Xc thc v bo mt : khi mt UE ng k vo mng ln u tin, MME s khi to s xc thc, bng cch thc hin nhng iu sau: n tm ra danh tnh thng tr ca UE, hoc t cc mng truy nhp trc hoc chnh bn thn UE, yu cu t b phc v thu bao thng tr (HSS) trong mng ch ca UE cc iu khin chng thc c cha cc mnh lnh chng thc tr li cc cp tham s, gi cc th thch vi UE v so snh cc tr li nhn c t UE vo mt trong nhng ci nhn t mng ch. Chc nng ny l cn thit m bo cc yu cu bo v vi UE. Cc MME c th lp li chc nng xc thc khi cn thit hoc theo chu k. Cc chc nng ny dng bo v cc thng tin lin lc khi vic nghe trm v t s thay i ca bn th ba tng ng tri php. bo v s ring t ca UE, MME cng phn b cho mi UE mt m tm thi gi l m nhn dng tm thi duy nht ton cu(GUTI), do cn phi gi m nhn dng thng tr UE m nhn dng thu bao di ng quc t ( IMIS) qua giao din v tuyn c gim thiu. Cc GUTI c th c cp tr li, v d nh k ngn chn theo di UE.

Qun l tnh di ng: MME theo di v tr ca tt c cc UE trong khu vc ca mnh, khi mt UE ng k vo mng ln u tin, MME s to ra mt li vo cho UE v tn hiu vi v tr ti HSS trong mng ch ca UE. MME yu cu ti nguyn thch hp c thit lp trong eNodeB, cng nh trong cc S-GW m n la chn cho UE. Cc MME sau tip tc theo di v tr ca UE hoc l da trn mc ca eNB, nu UE vn kt ni, tc l truyn thng ang hot ng hoc mc khu vc theo di (TA). MME iu khin cc thit lp v gii phng ngun ti nguyn da trn nhng thay i ch hot ng ca UE. MME cng tham gia vo vic iu khin tn hiu chuyn giao ca UE trong ch hot ng gia cc eNB, S-GW hoc MME. MME tham gia vo mi thay i ca eNB v khng c phn t iu khin mng v tuyn ring bit nn n n hu ht cc s kin ny. Mt UE trng thi rnh ri n s bo co v tr ca n hoc l nh k, hoc l khi n chuyn ti mt khu vc theo di. Nu d liu nhn c t bn ngoi cho mt UE rnh ri, MME s c thng bo, n s yu cu cc eNB trong TA c lu gi cho UE ti v tr nh ca UE.

Qun l h s thu bao v dch v kt ni:

vo thi im mt UE ng k vo mng, cc MME s chu trch nhim ly h s ng k ca n t mng ch v. Cc MME s lu tr thng tin ny trong sut thi gian phc v UE. H s ny xc nh nhng g cc kt ni mng d liu gi c phn b ti cc mng tp tin nh km. Cc MME s t ng thit lp mc nh phn t mang, cho php cc UE kt ni IP c bn. iu ny bao gm tn hiu CP vi eNB v S-GW. Ti bt k thi im no sau ny, cc MME c th cn ti c tham gia vo vic thit lp phn t mang dnh ring cho cc dch v c hng li x l cao hn. Cc MME c th nhn c cc yu cu thit lp mt phn t mang dnh ring, hoc t cc S-GW nu yu cu bt ngun t khu vc dch v iu hnh, hoc trc tip t UE, nu UE yu cu kt ni cho mt dch v m khng c bit n bi khu vc dch v iu hnh, v do khng th c bt u t .

Hnh 2.4 cho thy cc kt ni MME n quanh cc nt logic, v tm tt cc chc nng chnh trong giao din ny. V nguyn tc MME c th c kt ni vi bt k MME khc trong h thng, nhng thng kt ni c gii hn trong mt nh iu hnh mng duy nht. Cc kt ni t xa gia cc MME c th c s dng khi mt UE i xa, trong khi i ng k vi mt MME mi sau tm kim nhn dng thng tr mi ca UE, sau ly nhn dng thng tr ca UE, m nhn dng thu bao di ng quc t (IMIS), t MME truy cp trc . Cc kt ni gia cc MME vi cc MME ln cn c s dng trong chuyn giao.

Kt ni ti mt s HSS cng cn c h tr, cc HSS nm trong mng ch ca ngi dng , v mt tuyn ng c th c tm thy da trn IMIS. Mi MME c cu hnh iu khin mt tp hp cc S-GW v eNodeB. C hai S-GW v eNodeB cng c th c kt ni ti cc MME khc. Cc MME c th phc v mt s UE cng mt lc, trong khi mi UE s ch kt ni ti mt MME ti mt thi im.

Hnh 2.4 MME kt ni ti cc nt logic khc v cc chc nng chnh

2.1.1.4. Cng phc v ( S-GW)

Trong cu hnh kin trc c bn h thng, chc nng cao cp ca S-GW l qun l ng hm UP v chuyn mch. S-GW l mt phn ca h tng mng n c duy tr cc phng iu hnh trung tm ca mng.Trong khi di chuyn gia cc eNodeB, S-GW hot ng nh nt cui di ng a phng. MME s lnh S-GW chuyn sang ng hm t mt eNodeB khc. MME cng c th yu cu S-GW cung cp ti nguyn ng hm cho d liu chuyn tip khi c nhu cu cn chuyn d liu t eNodeB ngun ti eNodeB ch trong thi im UE c chuyn giao v tuyn. Cc tnh hung di chuyn cng bao gm s thay i t mt S-GW ti mt ci khc, v MME s iu khin s thay i ny cho ph hp bng cch loi b cc ng hm trong S-GW c v thit lp chng trong S-GW mi.

i vi tt c cc lung d liu thuc v mt UE trong ch kt ni th S-GW s chuyn tip d liu gia eNodeB v P-GW. Tuy nhin khi mt UE ch nhn ri th cc ngun ti nguyn ny trong eNodeB s c gii phng, cc ng dn d liu c kt thc trong S-GW. Nu S-GW nhn c gi d liu t P-GW th n s lu cc gi vo b m v yu cu MME bt u nhn tin ti UE. Tin nhn s lm cho UE ti ch ti kt ni, v khi cc ng hm c ti kt ni th cc gi tin t b m s c gi v. S-GW s theo di d liu trong cc ng hm v n cng c th thu thp cc d liu cn thit cho vic hch ton v tnh chi ph ca ngi dng.

Trong Hnh 2.5 cho thy S-GW c kt ni ti cc nt logic khc v danh sch cc chc nng chnh trong cc giao din ny. Tt c cc giao din c cu hnh theo kiu mt nhiu t S-GW c thy. Mt S-GW c th ch phc v mt khu vc a l nht nh vi mt tp gii hn cc eNodeB, v tng t c th c mt tp gii hn ca cc MME iu khin khu vc . S-GW c th kt ni ti bt k P-GW no trong ton b mng li, bi v P-GW s khng thay i trong khi di chuyn, trong khi S-GW c th c nh v li trong khi UE di chuyn. Vi cc kt ni c lin quan ti mt UE, S-GW s lun bo hiu vi ch mt MME v cc im UP ti mt eNodeB ti mt thi im. Nu mt UE c php kt ni ti nhiu cc PDN thng qua cc P-GW khc nhau , th S-GW cn kt ni ti cc thnh phn ring bit. Nu giao din S5/S8 l da trn PMIP th S-GW s kt ni ti mt PCRF cho mi P-GW ring c UE s dng.

Hnh 2.5. Cc kt ni S-GW ti cc nt logic khc v cc chc nng chnh

Trn hnh cng cho thy trng hp chuyn d liu gin tip ni m d liu UP c chuyn tip gia cc eNodeB thng qua cc S-GW. Khng c tn giao din c th lin quan n giao din gia cc S-GW, v nh dng chnh xc ging nh trong giao din S1-U, v c th cho rng cc S-GW lin quan chng truyn thng trc tip vi cng mt eNodeB. y s l trng hp khi chuyn tip d liu gin tip din ra thng qua ch mt S-GW, tc l c hai eNodeB c th c kt ni ti cng mt S-GW.

2.1.1.5. Cng mng d liu gi( P-GW)

Cng mng d liu gi (P-GW, cng thng c vit tt l PDN-GW) l tuyn bin gia EPS v cc mng d liu gi bn ngoi. N l nt cui di ng mc cao nht trong h thng, v n thng hot ng nh l im IP ca cc thit b cho UE. N thc hin cc chc nng chn lu lng v lc theo yu cu bi cc dch v c cp. Tng t nh S-GW, cc P-GW c duy tr ti cc phng iu hnh ti mt v tr trung tm.

in hnh l P-GW cp pht cc a ch IP cho UE, v UE s dng n giao tip vi cc my ch IP khc trong cc mng bn ngoi. ( v d nh Internet ). N cng c th l PDN bn ngoi m UE c kt ni cp pht cc a ch l s dng bi cc UE, cc ng hm P-GW cho tt c lu lng vo mng . a ch IP lun c cp pht khi UE yu cu mt kt ni PDN, n s din ra t nht l khi UE c gn vo mng, v n c th xy ra sau khi c mt kt ni PDN mi. Cc P-GW thc hin chc nng giao thc cu hnh my ch ng (DHCP) khi cn, hoc truy vn mt my ch DHCP bn ngoi, v cung cp a ch cho UE. Ngoi ra t cu hnh ng c h tr bi cc tiu chun. Ch IPv4, ch IPv6 hoc c hai, cc a ch c th c phn b ty theo nhu cu. UE c th bo hiu rng n mun nhn a ch ngay trong tn hiu kt ni hoc nu n mun thc hin cu hnh a ch sau khi lp lin kt c kt ni.

P-GW bao gm c PCEF, c ngha l n thc hin cc chc nng chn lu lng v lc theo yu cu bi cc chnh sch c thit lp cho UE v cc dch v ni n, n cng thu thp cc bo co thng tin chi ph lin quan.

Lu lng UP gia P-GW v cc mng bn ngoi di dng cc gi tin IP thuc v cc dng dch v IP khc nhau. Nu giao din S5/S8 hng ti S-GW l da trn GTP th P-GW thc hin nh x cc dng d liu IP ti cc ng hm GTP, cc P-GW thit lp cc phn t mang c bn da trn yu cu qua PCRF hoc t S-GW, m chuyn tip cc thng tin t MME. Nu giao din S5/S8 l da trn PMIP, P-GW s nh x tt c cc lung dch v IP t cc mng bn ngoi thuc v mt UE ti mt ng hm GRE duy nht, v tt c cc thng tin iu khin ch c trao i vi PCRF. P-GW cng c chc nng gim st cc lung d liu cho mc ch hoch ton cng nh cho ngn xen theo lut.

P-GW l im cui di ng mc cao nht trong h thng. Khi mt UE di chuyn t mt S-GW ti mt ci khc, cc phn t mang phi c chuyn vo P-GW. P-GW s nhn c ch dn chuyn cc lung t cc S-GW mi.

Hnh 2.6 cho thy cc kt ni P-GW n xung quanh cc nt logic, v danh sch cc chc nng chnh trong giao din ny.

Hnh 2.6 P-GW kt ni ti cc node logic khc v cc chc nng chnh

Mi P-GW c th c kt ni ti mt hoc nhiu PCRF, S-GW v mng bn ngoi. i vi mt UE lin kt vi P-GW th ch c duy nht mt S-GW, nhng c cc kt ni ti nhiu cc mng bn ngoi v tng ng c nhiu cc PCRF c th cn phi c h tr, nu c kt ni ti nhiu cc PDN c h tr thng qua mt P-GW.

2.1.1.6. Chc nng chnh sch v tnh cc ti nguyn ( PCRF)

Chc nng chnh sch v tnh cc ti nguyn(PCRF) l phn t mng chu trch nhim v chnh sch v iu khin tnh cc ( PCC). N to ra cc quyt nh v cch x l cc dch v v QoS, v cung cp thng tin cho PCEF c t trong P-GW, v nu c p dng cho c BBERF c t trong S-GW, cho vic thit lp cc phn t mang thch hp v vic lp chnh sch. PCRF l mt my ch v thng c t vi cc phn t CN khc ti cc trung tm iu hnh chuyn mch.Cc thng tin PCRF cung cp cho PCEF c gi l cc quy tc PCC. PCRF s gi cc quy tc PCC bt c khi no mt phn t mang mi c thit lp. Thit lp phn t mang l cn thit, v d khi UE bc u c gn vo mng v phn t mang mc nh s c thit lp, v sau khi c mt hoc nhiu cc phn t mang dnh ring c thit lp. PCRF c kh nng cung cp cc quy tc PCC da trn yu cu, hoc t P-GW v cng nh S-GW trong tng hp PMIP, ging nh trong trng hp kt ni, v cng da trn yu cu t chc nng ng dng(AF) nm trong cc dch v tn min. V d, vi IMS v AF s thc y dch v QoS thng tin ti PCRF, t to ra mt quyt nh PCC v n s y cc quy tc PCC n P-GW, v mang thng tin nh x ti S-GW trong trng hp S5/S8 l PMIP. Cc phn t mang EPC sau s c thit lp da trn nhng iu .

Hnh 2.7 PCRF kt ni ti cc nt logic khc & cc chc nng chnh

Cc kt ni gia PCRF v cc nt khc c th hin nh trong Hnh 2.7, mi PCRF c th c kt ni vi mt hoc nhiu AF, P-GW v S-GW. Ch c mt PCRF lin kt vi mi kt ni PDN l mt UE duy nht c.

2.1.1.7. My ch thu bao thng tr (HSS)

My ch thu bao thng tr (HSS) l kho d liu thu bao cho tt c d liu ngi dng thng xuyn. N cng ghi li v tr ca ngi s dng mc ca nt iu khin mng tm tr, chng hn nh MME. N l mt my ch c s d liu v c duy tr ti cc phng trung tm ca nh iu hnh.

HSS lu tr bn gc ca h s thu bao, trong cha cc thng tin v cc dch v c p dng i vi ngi s dng, bao gm thng tin v cc kt ni PDN c cho php, v liu c chuyn ti mt mng tm tr ring c hay khng. HSS cng lu nhng nhn dng ca cc P-GW c s dng. Kha thng trc c s dng tnh ton xc thc v c gi ti mng tm tr xc thc ngi dng v cc kha pht sinh tip sau m ha v bo v tnh ton vn l c lu tr ti cc trung tm xc thc(AUC), thng l mt phn ca HSS. Trong tt c cc tn hiu lin quan ti cc chc nng ny th HSS phi tng tc vi MME. Cc HSS s cn phi c kh nng kt ni vi mi MME trong ton b h mng li, ni m cc UE ca n c php di chuyn. i vi mi UE, cc h s HSS s ch ti mt MME phc v ti mt thi im, v ngay sau l bo co v mt MME mi m n phc v cho UE, HSS s hy b v tr ca MME trc.

CHNG 3: TRUY CP V TUYN TRONG LTE

i vi vic truyn d liu qua giao tip v tuyn, ngi ta quyt nh dng mt phng thc truyn mi trong LTE, phng thc ny hon ton khc bit vi gii php CDMA ca UMTS. Thay v dng mt knh truyn ti qua mt di tn rng, ngi ta quyt nh dng mt phng thc truyn gi l Orthogonal Frequency Division Multiple Access (a Truy cp Phn Tn Trc giao), vit tt l OFDMA. Bi v nhiu bit c vn chuyn song song vi nhau, nn tc truyn trn mi knh truyn ti con c th thp hn nhiu so vi tc truyn d liu tng cng, nhm gim thiu nh hng ca vic suy gim a ng dn (multipath fading) do thi im n ni khc bit i cht ca tn hiu t cc hng khc nhau. L do th hai gii php ny c chn l, tc dng ca suy hao a ng dn v s phn tn tr s tr nn c lp vi lng di tn c dng cho knh.

i vi vic truyn d liu hng ln, 3GPP chn mt phng thc iu ch hi khc mt cht. Vic truyn OFDMA phi chu mt PAPR (Peak to Average Power Ratio _ t l cng sut nh so vi trung bnh) cao, iu ny c th dn n nhng h qu tiu cc i vi vic thit k mt b pht sng nhng trong UE. Do , 3GPP chn phng thc SC-FDMA cho hng ln vi PAPR thp

3.1. TRUYN D LIU HNG XUNG:

H thng truyn dn ng xung ca LTE da trn cng ngh OFDM. Nh bit th OFDM l mt h thng truyn dn ng xung hp dn vi nhiu l do khc nhau. V thi gian k t OFDM tng i di trong vic kt hp vi mt tin t chu trnh, nn OFDM cung cp mnh chng li s la chn tn s knh (channel frequency selectivity). Mc d trn l thuyt th vic sai lch tn hiu do knh truyn chn lc tn s c th c kim sot bng k thut cn bng ti pha thu, s phc tp ca k thut cn bng bt u tr nn km hp dn trong vic trin khai i vi nhng thit b u cui di ng ti bng thng trn 5 MHz.V vy m OFDM vi kh nng vn c trong vic chng li fading la chn tn s (Bng cch chia knh thng tin ra thnh nhiu knh con fading phng bng hp, cc h thng OFDM chu ng fading la chn tn s tt hn nhng h thng sng mang n) s tr thnh s la chn hp dn cho ng xung, c bit khi c kt hp vi ghp knh khng gian (spatial multiplexing).

3.1.1. Nguyn tc a truy nhp ng xung OFDMA:

K hoch truyn dn ng xung cho E-UTRAN ch FDD v TDD l c da trn OFDM truyn thng .OFDM cng c s dng trong WLAN, WIMAX v cc cng ngh truyn qung b nh DVB. OFDM c mt s li ch nh bn ca n vi phaing a ng v kin trc thu nhn hiu qu ca n. Ngoi ra OFDM cn c mt s li ch khc nh:

OFDM d dng h tr cho vic phn b bng thng mt cch linhhot, bng cch bin i bng tn c s thnh cc sng mang con truyn i, mi sng mang con c iu chW c lp bi mt dng d liu tc thp.

H tr truyn dn broadcast/multicast, khi m nhng thng tin ging nhau c truyn i t nhiu trm gc

Mt s c im c bn ca OFDM:

S dng mt lng tng i ln cc sng mang con bng hp. Truyn OFDM s dng vi trm sng mang con c truyn trn mt lin kt v tuyn n cng mt my thu.

Dng xung n gin nh trong hnh 3.1a . iu ny p ng ph dng sa mi sng mang , nh minh ha trong hnh 3.1 b.

Nhng sng mang con c sp xp cht ch trn min tn s vi khong cch gia cc sng mang con f=1/Tu (hnh 3.2), vi TU l thi gian iu ch symbol trn mi sng mang con. Khong cch sng mang bng tc iu ch trn mi sng mang con.

Hnh 3.1: Dng xung v ph ca mi sng mang cho truyn OFDM c bn

Hnh 3.2: Khong cch gia cc sng mang con OFDM3.1.2. K thut truy cp phn chia theo tn s trc giao OFDM [1]

Hnh 3.3. Truyn n sng mang

Hnh 3.4. Nguyn l ca FDMA

Hnh 3.5. Nguyn l a sng mangK thut iu ch OFDM, v c bn, l mt trng hp c bit ca phngphp 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 chng ln ph tn hiu ny lm cho h thng OFDM c hiu sut s dng ph lnhn nhiu so vi cc k thut iu ch thng thng.Trong min thi gian, mt khong bo v c th c thm vo mi k hiu chng li nhiu lin k hiu OFDM do knh lan truyn tr. Trong E-UTRAN, cc khong bo v l mt tin t vng m c chn vo trc mi k hiu OFDM. Trong thc t, tn hiu OFDM c th c to ra bng cch s dng IFFT ( bin i Fourier nhanh nghch o ). IFFT chuyn i s lng N cc k hiu d liu phc c s dng nh cc phu bin i tn hiu min tn s sang tn hiu min thi gian. N im IFFT c minh ha nh trong hnh 3.6, ni m c a(mN+n) tham chiu ti k hiu d liu iu ch sng mang con th n, trong khong thi gian mTu < t M sau c thc hin nh trong OFDM, tip l thm tin t vng v chuyn i song song thnh ni tip.

S x l DFT l s khc bit c bn gia vic to tn hiu SC-FDMA v OFDMA. iu ny c th hin bng thut ng DFT-tri-OFDM. Trong mt tn hiu SC-FDMA, mi sng mang con c s dng cho vic truyn dn thng tin bao gm tt c cc k hiu iu ch c truyn, k t khi dng d liu u vo c lan truyn bi s bin i DFT qua cc sng mang con sn c. Tri ngc vi iu ny, mi sng mang con trong mt tn hiu OFDMA ch mang thng tin lin quan ti cc k hiu iu ch c th.

3.2.2. Cc tham s ca SC-FDMA:

Cu trc khung: cng tng t nh ng xung gm c 2 loi khung , khung loi 1 dnh cho FDD, khung loi 2 dnh cho TDD. Mi khe mang 7 k hiu SC-FDMA trong trng hp cu hnh tin t vng thng thng, v 6 k hiu SC-FDMA trong trng hp cu hnh tin t vng m rng. K hiu SC-FDMA s 3 ( k hiu th 4 trong mt khe ) mang tn hiu chun cho vic gii iu ch knh.

Ti nguyn vt l ng ln:

Cc thng s c bn ca truyn dn ng ln LTE c la chn cn chnh, cng nhiu cng tt, vi cc thng s tng ng ca ng xung LTE da trn OFDM. Do , khong cch sng mang con DFT-s-OFDM ng ln tng ng vi f=15 KHz v cc khi ti nguyn bao gm 12 sng mang con cng c xc nh cho ng ln.

Cng v mt kin trc min thi gian c lm chi tit hn, ng ln LTE rt ging vi ng xung, nh c th c nhn thy trong hnh 3.23. Mi khung con ng ln 1ms bao gm hai khe c di bng nhau Tslot =0.5 ms. Mi khe sau bao gm mt s lng cc khi DFT km theo c tin t tun hon (Cyclic Prefix - CP). Cng tng t ng xung, hai di tin t tun hon c nh ngha cho ng ln, tin t tun hon thng thng v tin t tun hon m rng.

Hnh 3.23.a. Khung con ng ln LTE v cu trc khe ( cp bnh thng )

Hnh 3.23.b. Khung con ng ln LTE v cu trc khe ( cp m rng )

Mt khung con bao gm hai khe kch thc bng nhau. Mi khe bao gm 6 hoc 7 khi DFTS-OFDM trong trng hp tng ng vi tin t chu trnh bnh thng v m rng

Hnh 3.24. Cp pht ti nguyn ng ln LTENgc vi ng xung, cc khi ti nguyn ng ln c n nh n mt u cui di ng phi lun lun c lin tip nhau trong min tn s, nh c minh ho trong hnh 3.24. Ch rng, tng t nh ng xung, khi ti nguyn ng ln c nh ngha nh 12 sng mang con DFT-s-OFDM trong sut mt khe 0.5 ms. Ti cng mt thi im, lp k hoch ng ln c thc hin trn c s mt khung con 1 ms. Do , tng t nh ng xung, n nh ti nguyn ng ln c thc hin di dng cc cp khi ti nguyn lin tc trong min thi gian.

3.2.3. Truyn dn d liu hng ln:

Lp k hoch ngun ti nguyn hng ln c thc hin bi eNodeB. eNodeB s cp cc ti nguyn thi gian/tn s nht nh cho cc UE v cc UE thng bo v cc dng truyn ti m n s dng. Cc quyt nh lp lch biu c th da trn cc thng s QoS, tnh trng b nh m ca UE, cc thng s cht lng knh ng ln, kh nng ca UE, cc o c khong cch ca UE, v.v.

Vic pht tn hiu trong min tn s c th hin nh trong hnh 3.25. B sung thm cho OFDMA thuc tnh ca dng sng ph tt hn tri ngc vi vic pht tn hiu trong min thi gian vi mt b iu ch QAM thng thng. Do nhu cu v bng tn bo v gia cc ngi dng khc nhau l c th trnh c, tng t nh nguyn l ng xung ca OFDMA. Nh trong h thng OFDMA, mt tin t vng cng c thm vo theo nh k, nhng khng phi sau mi k hiu nh l tc k hiu l nhanh hn trong min thi gian so vi trong OFDMA, cho vic truyn d liu c th ngn nga c nhiu lin k t v n gin ha vic thit k my thu. My thu vn cn phi i ph vi nhiu lin k t nh l tin t vng by gi s ngn cn nhiu lin k t gia mt khi cc k hiu, do s vn cn nhiu lin k t gia cc tin t vng. Do my thu s chy b cn bng cho mt khi cc k hiu cho n khi t c tin t vng m ngn chn s lan truyn nhiu lin k t sau .

Hnh 3.25. Thu pht SC-FDMA trong min tn s

So snh OFDMA& SC-FDMA

Hnh 3.26. OFDMA v SC-FDMABn tri hnh 3.26, M cc sng mang con 15kHz lin k c t vo a im mong mun trong bng thng knh v mi sng mang con c iu ch vi chu k k hiu OFDMA l 66,7s bi mt k hiu d liu QPSK.

Trong v d ny, bn sng mang con, bn k hiu c a ra song song. y l cc k hiu d liu QPSK do ch c pha ca mi sng mang con l c iu ch v cng sut ca sng mang con vn gi khng i gia cc k hiu. Sau mt chu k k hiu OFDMA tri qua, cc CP c chn vo v bn k hiu tip theo c truyn i song song. cho hnh nh nhn c r rng nn cc CP c hin th nh mt khong trng, tuy nhin, n thc s c lp y vi mt bn sao ca s kt thc ca k hiu tip theo, c ngha l cng sut truyn dn l lin tc nhng c mt s gin on pha bin ca k hiu. to ra tn hiu truyn i, mt IFFT c thc hin trn mi sng mang con to ra M tn hiu min thi gian. Chng ln lut l vect tng hp to ra dng sng min thi gian cui cng c s dng truyn dn.

S to thnh tn hiu SC-FDMA c bt u vi mt qui trnh ng trc c bit ri sau n cng tip tc mt cch tng t nh OFDMA. Tuy nhin trc ht ta s xem hnh bn phi ca hnh 3.26. S khc bit r rng nht l OFDMA truyn bn k hiu d liu QPSK song song trn mi sng mang con, trong khi SC-FDMA truyn bn k hiu d liu QPSK trong lot bn ln , vi mi k hiu d liu chim M 15kHz bng thng.

Nhn mt cch trc quan, tn hiu OFDMA r rng l a sng mang vi mt k hiu d liu trn mi sng mang con, nhng tn hiu SC-FDMA xut hin nhiu hn mt sng mang n ( v th m c SC trong tn SC-FDMA ) vi mi k hiu d liu c biu din bng mt lot tn hiu. Lu rng chiu di k hiu OFDMA & SC-FDMA l nh nhau vi 66,7s, tuy nhin, k hiu SC-FDMA c cha M cc k hiu con m biu din cho d liu iu ch. l vic truyn ti song song ca nhiu cc k hiu to ra PAPR cao khng mong mun vi OFDMA. Bng cch truyn M cc k hiu d liu trong dy vo M thi im, SC-FDMA chim bng thng cng nh a sng mang OFDMA nhng ch yu l PAPR tng t nh c s dng cho cc k hiu d liu gc. Thm vo cng nhau nhiu dng sng QPSK bng hp trong OFDMA s lun to ra cc nh cao hn c th thy trong bng thng rng hn, dng sng QPSK n sng mang SC-FDMA.

3.3.MIMO

MIMO l mt k thut i mi quan trng ca LTE, c s dng ci thin hiu sut ca h thng. K thut cho php LTE ci thin hn v dung lng v hiu qu s dng ph. Mc d, s dng MIMO lm cho h thng phc tp hn v qu trnh x l tn hiu v yu cu s lng anten, nhng n c th tng tc d liu ln mc cao, cho php hiu qu s dng ph tn. MIMO l mt k thut khng th thiu ca LTE.

Chun LTE ch nh hai v bn cuc truyn ring bit trn cng mt bng tn, tc i hi phi c hai hoc bn ng-ten tng ng c my pht ln my thu. H qu l, nhng cuc truyn nh vy c gi l 2x2 MIMO v 4x4 MIMO. Trong thc t, 2x2 MIMO nhiu kh nng s c dng trc, do bi nhng rng buc v kch c ca cc UE v do s kin l cc ng-ten phi c t cch nhau t nht mt na bc sng.

Bi v cc knh MIMO phn bit vi nhau, nn 2x2 MIMO c th lm tng tc truyn tng th ln hai ln, cn 4x4 MIMO th tng ln bn ln. Tuy nhin iu ny ch c th t c trong nhng iu kin tn hiu l tng. V vy, MIMO ch c dng cho cc cuc truyn hng xung trong LTE, bi v b pht sng ca trm c s t b rng buc v cng sut hn b pht sng hng ln. Trong nhng iu kin truyn t thun li hn, h thng t ng quay tr li kiu truyn mt dng d liu duy nht v cng gim lun cp iu ch t 64-QAM xung 16- QAM hay thm ch QPSK.

Gii hn chnh ca knh truyn thng tin l can nhiu a ng gii hn vdung lng theo quy lut Shannon. MIMO li dng tn hiu a ng gia mypht v my thu ci thin dung lng c sn cho bi knh truyn. Bng cch sdng nhiu anten bn pht v thu vi vic x l tn hiu s, k thut MIMO c th to ra cc dng d liu trn cng mt knh truyn, t lm tng dung lng knh truyn.

3.3.1. Cc ch truy cp ca MIMO:

Hnh 3.27. Cc ch truy cp ca MIMO

3.3.1.1. n u vo n u ra (SISO)

Ch truy nhp knh v tuyn n gin nht l n u vo n u ra (SISO), trong ch c mt ng ten pht v mt ng ten thu c s dng. y l hnh thc truyn thng mc nh k t khi truyn v tuyn bt u v n l c s da vo tt c cc k thut a ng ten c so snh.

3.3.1.2. n u vo a u ra (SIMO)Mt ch th hai th hin trong hnh 3.27 l n u vo a u ra (SIMO), trong s dng mt my pht v hai hoc nhiu hn my thu. SIMO thng c gi l phn tp thu. Ch truy nhp knh v tuyn ny c bit thch hp cho cc iu kin tn hiu-nhiu(SNR) thp. Trong c mt li l thuyt c th t c l 3dB khi hai my thu c s dng, khng c thay i v tc d liu khi ch c mt dng d liu c truyn, nhng vng ph sng bin c ci thin do s gim ca SNR s dng c.

3.3.1.3. a u vo n u ra (MISO)

Ch a u vo n u ra (MISO) s dng s my pht l hai hoc nhiu hn v mt my thu( hnh 3.27 cho thy ch c 2 my pht v mt my thu cho n gin ). MISO thng c gi l phn tp pht. Cng mt d liu c gi trn c hai ng ten pht nhng vi ch m ha nh vy m my thu ch c th nhn bit tng my pht. MISO khng lm tng tc d liu, nhng n h tr cc tc d liu tng t nhau bng cch s dng t nng lng hn. Phn tp pht c th c tng cng vi phn hi vng ng t my thu ch ra s truyn cn bng ti u ca pha v cng sut c s dng cho mi ng ten pht.

3.3.1.4. a u vo a u ra (MIMO)Phng thc truyn cui cng c th hin trong hnh 3.27 l truyn y MIMO, n yu cu hai hoc nhiu my pht v hai hoc nhiu my thu.MIMO lm tng cng sut ph bng cch pht nhiu lung d liu cng mt lc trong cng mt tn s v thi gian, tn dng y cc li th ca cc ng dn khc nhau trong knh v tuyn. i vi mt h thng c m t nh MIMO, n phi c t nht l nhiu my thu vi nhiu lung pht. S lng cc lung pht khng c nhm ln vi s lng cc ng ten pht. N lun c th c s my pht nhiu hn s lung d liu.

Hnh 3.28. MIMO 2x2Mt yu t quan trng cho hot ng MIMO l vic truyn t mi ng ten phi c nhn dng duy nht mi my thu c th xc nh c ci g kt hp trong vic truyn m n nhn c. Vic nhn dng ny thng c thc hin vi cc tn hiu ch o, trong s dng cc mu trc giao cho mi ng ten. S phn tp khng gian ca knh v tuyn ngha l MIMO c kh nng lm tng tc d liu. Hnh thc c bn nht ca MIMO l gn mt dng d liu cho mi ng ten v c th hin nh trong hnh 3.28. Trong dng ny, mt lung d liu duy nht c gn cho mt ng ten v c bit n nh nh x trc tip. Knh ny sau c trn ln nh l s truyn c hai vi bn nhn, mi ng ten s nhn thy mt s kt hp ca mi lung. Gii m cc tn hiu nhn c l mt qu trnh kho lo bn nhn, bi vic phn tch cc mu nhn dng duy nht mi my pht xc nh xem kt hp ci g ca mi lung truyn hin ti. Vic p dng mt b lc nghch o v tng hp cc lung nhn c ti to li d liu gc.

Hnh 3.29. 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 SUMIMO 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 dung 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(SU-MIMO) hoc nhng ngi dng khc nhau (MU-MIMO). Trong khi SUMIMO tng tc d liu cho mt ngi dng, MU-MIMO cho php tng dung lng. Da vo hnh 3.30, 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.

Thng thng, tn hiu trc khi pht c m ha tng hiu ngphn tp. MIMO c s dng khai thc vic phn tp v mc tiu l lm tngtc . Vic chuyn i gia MIMO truyn phn tp v ghp knh khng gian cth 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 mhnh MU-MIMO (Multi-User MIMO). S dng m hnh ny BS yu cu s dngnhiu anten, cn thit b di ng ch dng mt anten gim chi ph cho thit bdi 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.

Hnh 3.30. Ghp knh khng gian

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