TRUYỀN HÌNH CÁP

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<p>Mc lc I GII THIU CHUNG V MNG TRUYN HNH CP. .3 I.1 Cc h thng truyn hnh cp trn th gii.........................3 I.2 - Cc thnh phn ca h thng truyn hnh cp....................4 I.3 - Truyn dn tn hiu trn mng truyn hnh cp.................7I.3.1 - Truyn dn tn hiu tng t.....................................................................9 I.3.2 - Truyn dn tn hiu s.............................................................................10</p> <p>I.4 - Mng phn phi tn hiu truyn hnh cp..........................11I.4.1 - Mng ton cp ng trc.........................................................................11 I.4.2 - Mng lai HFC (Hybrid Fiber/Coaxial)....................................................12 I.4.3 - Mng c cu trc kt hp cp quang v cp xon ng...........................15 I.4.4 - Mng ton cp quang..............................................................................16</p> <p>I.5 - Cc tc ng nh hng n h thng...............................16I.5.1 - Duy tr p ng tn s bin ................................................................18 I.5.2 - Tr nhm ca tn hiu khi i qua h thng cp........................................18 I.5.3 - Phn hi ca h thng.............................................................................18 I.5.4 - Nhiu pha................................................................................................19 I.5.5 - Mo khuch i v nh hng ca chng................................................19 I.5.6 - nh hng ca nhiu do cc tn s radio gy ra ....................................19</p> <p>I.6 - H thng qun l thu bao v tnh cc..............................20 I.7 - Kh nng dung lng cao ca h thng cp......................22I.7.1 - K thut nn video s...........................................................................22 I.7.2 - Video On Demand v Near Video On Demand.......................................23</p> <p>II - TRUYN S LIU TRN MNG TRUYN HNH CP ........................................................................................................24 II.1 - Gii thiu ............................................................................25 II.2 - Phn b tn s trong h thng cp....................................26 II.3 - Lu lng knh...................................................................26 III - THIT K H THNG CP HU TUYN...................27 III.1 S thit k h thng.....................................................27III.1.1 S tng qut ca mt mng cp a dch v.....................................27 III.1.2 S khi ti Headend /Hub...............................................................28 III.1.3 Cc thit b trung tm h thng truyn hnh cp hai chiu...................29 III.1.5 Kt ni h thng (Distribution Center).................................................30</p> <p>III.2 Cu hnh thit b...............................................................31III.2.1 CMTS router........................................................................................31 III.2.2 - CMTS...................................................................................................33 III.2.3 Cable modem.......................................................................................34 III.2.4 Setop box.............................................................................................35</p> <p>IV M hnh thit b ca hng Syspol Indonexia.....................351</p> <p>VI.1 Cc thit b c s dng:......................................................................35 VI.2 c im h thng..................................................................................36</p> <p>V H thng truyn hnh cp H Tnh......................................37c im:......................................................................................................37 V.1 - La chn cng ngh:.................................................................................37 V.2 Thit b trin khai trong giai on 1 (Ti liu tham kho km theo)........38 V.3 Trin khai thit b cho h thng cp hai chiu..........................................38 V.3.1 Thit k h thng...............................................................................38 V.3.2 Yu cu dch v.................................................................................38 V.3.3 Thit b..............................................................................................39 V.3.4 Cc phn mm iu khin..................................................................41</p> <p>VI Mt s chun truyn d liu...............................................42VI.1 - Gii thiu chung v chun MPEG...........................................................42</p> <p>VII Ph lc.................................................................................42VII.1 - Telcordia IGCS (Ver2.3)........................................................................42 VII.2 Cisco AS5400........................................................................................44 VII.3 Cisco MGX 8000 Series .......................................................................45 VII.4 Samsung SCM 220U.............................................................................47 VII.5 Innomedia EMTA 3528.........................................................................48 VII.6 DV6000.................................................................................................50</p> <p>MNG TRUYN HNH CP HU TUYN</p> <p>2</p> <p>I GII THIU CHUNG V MNG TRUYN HNH CP I.1 Cc h thng truyn hnh cp trn th giiH thng truyn hnh cp xut hin vo nhng nm cui ca thp nin 40. Cc h thng ny c gi l truyn hnh ng ten chung hay CATV (community antenna telivision). Mc tiu ban u ca truyn hnh cp l phn pht cc chng trnh qung b ti nhng khu vc do cc iu kin kh khn v a hnh khng th thu c bng cc ng ten thng thng, gi l vng lm sng. Ni n truyn hnh cp c hai loi l truyn hnh cp v tuyn v truyn hnh cp hu tuyn. Truyn hnh cp v tuyn MMDS (Multiprogram Multipoint Distribution System) s dng mi trng truyn sng l sng viba ti di tn 900Mhz. Tuy trin khai mng MMDS rt n gin do ch dng angten m khng cn ko cp n tng nh nhng n c rt nhiu nhc im: Hn ch vng ph sng: do s dng di tn 900Mhz, MMDS i hi angten thu v pht phi nhn thy nhau. V vy vi nhng h gia nh sau cc vt cn ln nh cc ta nh th khng th thc hin c. Chu nh hng mnh bi nhiu cng nghip: do s dng phng thc iu ch tn hiu truyn hnh tng t khng c kh nng chng li, li truyn bng sng v tuyn, tn hiu MMDS b nh hng rt mnh bi cc ngun nhiu cng nghip. Chu nh hng bi thi tit: khi thi tit xu, v d nh ma to, sttn hiu MMDS v tuyn b suy hao rt ln trong khng gian, dn n gim mnh cht lng tn hiu hnh nh. Yu cu di tn s v tuyn qu ln: mi knh truyn hnh cn mt di tn l 8Mhz, nu mun cung cp 13 knh truyn hnh th cn mt di thng l 13 X 8= 104 MHz. y l mt di tn v tuyn ln trong khi ngun ti nguyn v tuyn l rt qu gi. Gy can nhiu cho cc i pht v tuyn khc: mc d c phn phi mt di tn ring, nhng my pht MMDS cng nh cc my pht v tuyn khc lun sinh ra cc tn s hi bc cao c th nh hng n cc trm pht sng v tuyn khc. Kh khn trong vic cung cp dch v truyn hnh s: Khng th cung cp cc dch v hai chiu:</p> <p>3</p> <p>Chnh v nhng kh khn trn, MMDS khng c pht trin mt cch rng ri. Truyn hnh cp hu tuyn l h thng m tn hiu truyn hnh c dn thng t trung tm chng trnh n h dn bng mt si cp (cp ng trc, cp quang hoc cp xon). Nh ngi dn c th c xem cc chng trnh truyn hnh cht lng cao m khng phi s dng cc ct angten. V gc k thut truyn hnh cp hu tuyn c nhng u im vt tri so vi cc h thng truyn hnh khc: t chu nh hng ca nhiu cng nghip: Tn hiu truyn hnh cp hu tuyn c dn n thu bao qua cc si cp quang hoc ng trc. Cc si cp ny c kh nng chng nhiu cng nghip cao hn gp nhiu ln so vi tn hiu v tuyn, v th s hn ch ti a nhiu cng nghip, m bo cht lng cho tn hiu. Khng b nh hng ca thi tit: Cc chng trnh truyn hnh trn cp s khng chu nh hng ca thi tit do kh nng cch ly v chng nhiu tt ca cp. Khng chim dng ph tn s v tuyn: l mt mng thng tin hu tuyn ring bit, mng truyn hnh cp c xy dng s cho php cung cp hng chc chng trnh truyn hnh m khng chim dng cng nh nh hng n ph tn s v tuyn cht chi, iu ny cng tr nn qu gi khi cng ngy cc i pht thanh truyn hnh mt t cng tng s lng chng trnh pht sng. Khng gy can nhiu cho cc trm pht sng nghip v khc: Cc tn hiu truyn trn cc si cp c cch ly v chng nhiu tt s khng gy ra nhiu v tuyn cho cc trm pht v tuyn khc. C kh nng cung cp tt dch v truyn hnh s v cc dch v hai chiu khc: Di thng ln ca mng truyn hnh cp hu tuyn s cho php khng ch cung cp cc dch v truyn hnh tng t m cn cho php cung cp nhiu cc chng trnh truyn hnh s, truyn hnh tng tc v c bit l kh nng cung cp cc dch v vin thng hai chiu, truy cp Internet, truyn s liu tc cao m mt mng vin thng cng kh m t c.</p> <p>I.2 - Cc thnh phn ca h thng truyn hnh cpMng phn phi Mng truyn b H thng thit hnh cp hu tuyn bao gm 3 thnh phn chnh: H thng thit tn hiu trung tm b ti trung tm, h thng mng phn phi tn hiu v thit b thu Thit b thu bao bao. (Headend System) (Customer System)(Distribution Network)</p> <p>4Hnh 2.1: S khi h thng truyn hnh cp hu tuyn</p> <p>H thng thit b trung tm (Headend System): l ni cung cp, qun l chng trnh cho h thng mng truyn hnh cp. y cng chnh l ni thu thp cc thng tin gim st trng thi, kim tra hot ng mng v cung cp cc tn hiu iu khin mng. Ngoi kh nng cung cp cc dch v tng tc, truyn s liu, h thng thit b trung tm cn c thm cc nhim v nh: m ha tn hiu qun l truy nhp, tnh cc truy nhp, giao tip vi cc h thng mng vin thng nh mng Internet Mng phn phi tn hiu truyn hnh cp l mi trng truyn dn tn hiu t trung tm mng n cc thu bao. Mng phn phi tn hiu truyn hnh cp hu tuyn c nhim v nhn tn hiu ra t cc thit b trung tm, iu ch, khuch i v truyn vo mng cp, cc thit b khc trong mng c nhim v khuch i, cp ngun v phn phi tn hiu truyn hnh n tn thit b ca thu bao. H thng mng phn phi tn hiu truyn hnh cp l b phn quyt nh n cht lng dch v, khong cch phc v, s lng thu bao v kh nng m rng v nng cp mng. Cp ng trc c s dng rng ri trong vic phn phi cc chng trnh truyn hnh. ng knh chun ca cp l 0.5; 0.75; 0.875 v 1 Inch. Tr khng c tnh ca cp l 75. Tn hiu s b suy gim khi truyn theo chiu di ca cp. Lng suy gim ph thuc vo ng knh cp, tn s tn hiu, h s sng ng v nhit . c th phn phi c tn hiu i xa, trn ng truyn ngi ta s dng cc b khuch i b li s suy hao, cc b khuch i ny ng vai tr quan trng khi thit k h thng. Mi b khuch i cn cha mt b n nh b li s suy gim cc tn s khc nhau. Trong truyn hnh cp thng s dng b khuch i cu. Vi tr khng vo ln, tn hiu t ng trung chuyn c th c ly ra m khng nh hng n</p> <p>5</p> <p>cht lng ca ton b knh truyn. Yu cu i vi mt b khuch i n nh l rt nghim ngt, do c s tch ly suy hao ca rt nhiu thnh phn mc ni tip: Chng phi lm vic c trn mt phm vi di tn s rng, h s khuch i phi t c gi tr thch hp ti cc min tn s cao. B n nh c kh nng b li suy gim theo tn s mt cch tha ng. B khuch i c c tuyn tuyn tnh cao, trnh xuyn m v to ra cc tn s gia cc knh. T ng iu chnh h s khuch i va c tuyn tn s b li s thay i do nhit . T s gia tn hiu trn nhiu ca mt b khuch i ring phi cao chng c mc nhiu tng ca cc b khuch i.</p> <p>Cc mch khuch i ng dy chia ng trc ra thnh nhiu on c chiu di khc nhau v suy gim ti tn s cao nht bng h s khuch i ca b khuch i. B n nh c cng thm vo nhm lm gim khuch i tn s thp hn v tn s cng cao suy gim cng ln. Nh vy khuch i ca mi on trung chuyn gm c b khuch i n nh l 0 dB. Mt h thng cp c nhiu tng khuch i c mc ni tip. S thay i h s khuch i hay c tuyn tn s ca mt thnh phn s gy ra s thay i ln ca ton h thng. duy tr s n nh ca h s khuch i v c tuyn tn s, mt tn hiu pilot c cng vo u v cui mi di bng tn. Cc tn hiu ny s l cc tn hiu chun theo cc tham s ca c tuyn tn s v h s khuch i c duy tr n nh. Thit b ti thu bao: Vi mt mng truyn hnh cp s dng cng ngh tng t, thit b ti thu bao c th ch l mt my thu hnh, thu tn hiu t mng phn phi tn hiu. Vi mng truyn hnh cp s dng cng ngh hin i hn, thit b thu bao gm cc b chia tn hiu, cc u thu tn hiu truyn hnh (Set-top-box) v cc modem cp Cc thit b ny c nhim v thu tn hiu v a n tivi v cc my tnh thu bao s dng cc dch v ca mng: chng trnh tivi, truy nhp Internet, truyn d liu</p> <p>6</p> <p>I.3 - Truyn dn tn hiu trn mng truyn hnh cpTn hiu cung cp cho h thng truyn hnh cp c ly t nhiu ngun khc nhau: t h thng truyn hnh qung b mt t, t v tinh, t vi ba hoc c cung cp trc tip t b phn sn xut chng trnh. Tt c cc tn hiu trc khi truyn vo mng cp phn phi c x l theo s khi di y:</p> <p>Data</p> <p>Baseban Baseban d d Physical Physical Interfac Clock Interfac eeand and Syn Syn</p> <p>Energy Energy Dispersal Dispersal</p> <p>Outer Outer Coding Coding</p> <p>Interleaver Interleaver I=12 I=12</p> <p>Cable Network</p> <p>QAM Modulator QAM Modulator IE Physical IE Physical Interface Interface</p> <p>Waveform Waveform Shaping Shaping</p> <p>Qu trnh x l tn hiuu tin, cc tn hiu truyn hnh nhiu dng iu ch khc nhau c gii iu ch, gii m a v m c s. Cc tn hiu ny cng cc byte ng b c chuyn thnh nh dng khung chun chun MPEG-2. Theo chun MPEG-2 th dng d liu video c chia thnh cc gi tin c kch thc 188 bytes, trong c 1 byte ng b v 187 bytes thng tin. Khi Out Coding c nhim v to thm cc thng tin sa li cho cc gi tin, thng s dng m Read-Solomon. Khi s dng m sa sai Reed-Solomon vi T=8 th mi gi tin c thm vo 16 bytes sa li v n c kh nng sa c 8 bytes li trong mi gi tin. Nh vy kch thc ca mi gi bao gm c phn sa li l 28-1= 255 bytes, trong phn mang tin l 255-16=239 bytes, nhng kch thc ca mt gi tin video ch c 188 bytes cho nn trc khi vo b m ha mi</p> <p>7</p> <p>gi tin c thm vo 51 bytes c t gi tr ton bng 0. Sau khi m ha xong 51 bytes ny li b loi b, nh vy sau m ha kch thc mi gi tin video l 204 bytes. Do m sa sai Reed-Solomon cng ch sa c cc li ri rc ln tip theo dng bt c ghp xen hn ch kh nng sai, li mt dy bt lin tip gy kh khn cho vic sa li u thu. S nguyn l chung ca vic ghp xen ngoi vi su l=12 c minh ha trong hnh v di y: B ghp gm 12 nhnh, c kt ni theo kiu vng vi cc byte s liu bng chuyn mch u vo. Mi nhnh j s l mt thanh ghi dch First in-First out, vi j x M nh. Trong : M = 17 = N/I, N = 204 byte, mi ca thanh ghi dch cha mt byte. Trong trng hp ny l ghp xen cc bytes vi nhau, chu k ghp xen ng bng 204.</p> <p>Hnh 2.3: S nguyn l ca b ghp v tch ngoi Khi Baseband Shaping c nhim v chia dng tn hiu thnh hai tn hiu I v Q (In-phase, Quadrature phase) tin hnh iu ch QAM (Quadrature Amplitude Modulation). Sau cng, tn hiu c iu ch ny c a vo mng cp truyn dn chuyn n thu bao. Truyn hnh cp s dng cc knh truyn nm trong phm vi di thng cn di ca bng UHF. Cc knh truyn hnh cp c chia thnh cc bng VHF thp, VHF gia, VHF cao v siu bng (superband). Cn c vo di thng hay s lng knh m h thng c th phc v ngi ta chia lm cc h thng nh va hay ln. Bng di y ch ra mt cch phn chia cc h thng:</p> <p>Di thng Small 170 MHz</p> <p>Phm vi tn s hot ng 50 MHz- 220MHz</p> <p>8</p> <p>220 MHz Medium 280 MHz 350 MHz 400 MHz 500 MHz Large 700 MHz 950 MHz</p> <p>50 MHz- 270MHz 50 MHz- 330MHz 50 MHz- 400MHz 50 MHz- 450MHz 50 MHz- 550MHz 50 MHz- 750MHz 50 MHz- 1000MHz</p> <p>Phn loi cc h thng truyn hnh cp Ton b di thng ca h thng c chia thnh cc knh v tuyn c kch thc 8 Mhz theo tiu chun ca Chu u hoc 6 Mhz theo tiu chun Bc M. S d c hai cch chia l cho mi knh c th mang c mt knh truyn hnh tng t, m Chu u th truyn hnh tng t theo tiu chun PAL c di thng 8 MHz cn Bc M v Nht Bn truyn hnh tng t theo tiu chun NTSC c di thng l 6 Mhz. Tt nhin trong mi knh ny c th truyn mt knh truyn hnh tng t hoc nhiu knh truyn hnh s.</p> <p>I.3.1 - Truyn dn tn hiu tng tDi...</p>