BK TP.HCM 2008 dce Chng 2 Truyn dn s liu Khi nim v thut ng Truyn dn d liu tng t v d liu s Suy hao ng truyn Dung lng knh truyn Mi trng truyn dn c nh hng Truyn dn khng dy Lan truyn khng dy Truyn ng thng (line-of-sight)2008 dce 2008, Dr. Dinh Duc Anh Vu 2 Data Communication and Computer Networks Thut ng Thnh phn trong m hnh truyn d liu (di gc vt l) Thit b Thit b pht (Transmitter) Thit b thu (Receiver) Mi trng truyn (Medium) Kt ni Kt ni trc tip (Direct link) Khng cn cc thit b trung gian Kt ni im-im (Point-to-point) Kt ni trc tip Ch c 2 thit b dng chung kt ni Kt ni nhiu im (Multi-point) > 2 thit b dng chung kt ni 2008 dce 2008, Dr. Dinh Duc Anh Vu 3 Data Communication and Computer Networks Ch truyn Simplex mode Khng dng rng ri v khng th gi ngc li li hoc tn hiu iu khin cho bn pht Television, teletext, radio Half-duplex mode B m Full-duplex mode in thoi 2008 dce 2008, Dr. Dinh Duc Anh Vu 4 Data Communication and Computer Networks Tn hiu Khi nim min thi gian T/h lin tc Thay i mn theo thi gian T/h ri rc Thay i tng mc theo thi gian T/h tun hon Mu lp li theo thi gian T/h khng tun hon Mu khng lp li theo thi gian 2008 dce 2008, Dr. Dinh Duc Anh Vu 5 Data Communication and Computer Networks Biu din tn hiu min tn s Tn hiu thc t c cu to bi nhiu thnh phn c tn s khc nhau Cc tn hiu thnh phn l cc sng hnh sin Tt c cc tn hiu (tng t ln s) u c th c phn tch thnh tng ca nhiu sng sin (khai trin Fourier) C th biu din tn hiu theo min tn s Trc honh: cc tn s c trong tn hiu Trc tung: bin nh ca tn hiu tng ng vi mi tn s 2008 dce 2008, Dr. Dinh Duc Anh Vu 6 Data Communication and Computer Networks V d 2008 dce 2008, Dr. Dinh Duc Anh Vu 7 Data Communication and Computer Networks Tn s, ph v bng thng Ph Tm tn s cha trong tn hiu Bng thng tuyt i rng ph (c o bng s chnh lch tn s cao nht v thp nht) Bng thng knh truyn cng ln, tc truyn cng cao Bng thng hiu dng Gi tt l bng thng Di tm tn s hp cha hu ht nng lng ca tn hiu Thnh phn mt chiu Thnh phn c tn s bng 0 2008 dce 2008, Dr. Dinh Duc Anh Vu 8 Data Communication and Computer Networks Ph m ca thoi v m nhc 2008 dce 2008, Dr. Dinh Duc Anh Vu 9 Data Communication and Computer Networks Tn hiu c thnh phn DC 2008 dce 2008, Dr. Dinh Duc Anh Vu 10 Data Communication and Computer Networks Tn hiu s Tn s f Chu k T = ? Thi gian truyn 1 bit Tbit = ? Tc truyn d liu? Bng thng? 2008 dce 2008, Dr. Dinh Duc Anh Vu 11 Data Communication and Computer Networks Tng hp tn hiu s 2008 dce 2008, Dr. Dinh Duc Anh Vu 12 Data Communication and Computer Networks Bng thng v tc truyn Trng hp 1: ng truyn c bng thng 4MHz Tn hiu c thnh phn f, 3f, 5f vi f = 1MHz Trng hp 2: ng truyn c bng thng 8MHz Tn hiu c thnh phn f, 3f, 5f, vi f = 2MHz Trng hp 3 ng truyn c bng thng 4MHz Tn hiu c thnh phn f, 3f vi f = 2MHz Kt lun? 2008 dce 2008, Dr. Dinh Duc Anh Vu 13 Data Communication and Computer Networks Truyn dn d liu tng t v s D liu Cc thc th cha ng thng tin D liu tng t: gi tr lin tc trong 1 thi khong D liu s: gi tr ri rc theo thi gian Tn hiu D liu c biu din dng tn hiu in hoc in t Tn hiu tng t Thay i lin tc theo thi gian Truyn trn nhiu mi trng: hu tuyn, quang, khng gian Tn hiu s S dng 2 thnh phn DC Truyn dn Trao i d liu bng cch lan truyn v x l tn hiu 2008 dce 2008, Dr. Dinh Duc Anh Vu 14 Data Communication and Computer Networks Truyn dn d liu tng t v s Thng thng Tn hiu tng t truyn d liu tng t Tn hiu s truyn d liu s Trong mt s trng hp Tn hiu tng t mang d liu s Tn hiu s mang d liu tng t 2008 dce 2008, Dr. Dinh Duc Anh Vu 15 Data Communication and Computer Networks Truyn dn tn hiu tng t v s Truyn tn hiu tng t Khng quan tm ni dung d liu cha ng bn trong Suy gim tn hiu theo khong cch Dng amplifier khuch i tn hiu (k c nhiu) Truyn tn hiu s Cn ch ni dung d liu cha ng bn trong Khong cch truyn ngn Dng repeater tng khong cch truyn Nhiu khng b khuch i 2008 dce 2008, Dr. Dinh Duc Anh Vu 16 Data Communication and Computer Networks Truyn dn s u im Cng ngh s Cng ngh LSI/VLSI lm gim gi thnh Ton vn d liu Nhiu v suy gim tn hiu khng b tch ly bi cc repeater Truyn khong cch xa hn trn cc ng truyn km cht lng Hiu qu knh truyn TDM > FDM Bo mt Cc k thut m ha bo mt d liu d p dng Tch hp D liu s v analog c x l tng t nhau 2008 dce 2008, Dr. Dinh Duc Anh Vu 17 Data Communication and Computer Networks Suy gim tn hiu (impairments) T/h nhn c khc vi t/h truyn i Analog suy gim cht lng t/h Digital li trn bit Nguyn nhn Suy yu v mo do suy yu trn ng truyn Mo do tr truyn Nhiu 2008 dce 2008, Dr. Dinh Duc Anh Vu 18 Data Communication and Computer Networks suy yu tn hiu trn ng truyn nh ngha (signal attenuation) Khi mt tn hiu lan truyn qua mt mi trng truyn, cng (bin ) ca tn hiu b suy gim theo khong cch Ty thuc vo mi trng truyn dn i vi mi trng v tuyn, suy gim cng t/h l mt hm phc tp theo khong cch v thnh phn kh quyn Cng t/h nhn phi mnh thit b nhn nhn bit c cao so vi nhiu t/h khng b li Suy yu l mt hm tng theo tn s Dng b khuch i (khuch i tn s cao nhiu hn) o bng n v decibel (dB) Cng t/h suy gim theo hm m li/ hao ht ca cc tng ni tip c th c tnh bng php ton n gin (+/-) 2008 dce 2008, Dr. Dinh Duc Anh Vu 19 Data Communication and Computer Networks suy yu tn hiu trn ng truyn Cng thc Attenuation = 10log10(P2/P1) (dB) P1, P2: cng sut (watts) Decibel (dB) l gi tr sai bit tng i Cng sut suy gim hao ht l 3dB Cng sut tng gp i li l 3dB Attenuation = 20log10(V2/V1) Do cng sut tiu th trn in tr R l P = V2/R Gi tr sai bit tuyt i Decibel-watt (dBW) 1W l gi tr tham kho, tng ng vi 0dBW Cng sut (dBW) = 10log10 (cng sut theo W) Decilbel-milivolt (dBmV) 1mV l gi tr tham kho, tng ng vi 0dBmV in p (dBmV) = 20log10 (in p theo mV) y l in p gi s trn in tr 75O 2008 dce V d Tn hiu u vo c cng sut 4mW. Tn hiu ny c a vo mt b lc c suy gim 12 dB, sau c a qua b khuch i vi li 35 dB v cui cng i qua b lc khc c hao ht 10dB. Tnh cng sut ti ng ra cui cng ca tn hiu. 2008, Dr. Dinh Duc Anh Vu 20 Data Communication and Computer Networks 2008 dce 2008, Dr. Dinh Duc Anh Vu 21 Data Communication and Computer Networks Tr lan truyn tn hiu Mo tr lan truyn Ch xy ra trong mi trng truyn dn hu tuyn Vn tc lan truyn thay i theo tn s Vn tc cao nht gn tn s trung tm Cc thnh phn tn s khc nhau s n ch cc thi im khc nhau Cng thc Transmission propagation delay Tp = S/V S: khong cch vt l (meter) V: vn tc lan truyn tn hiu trn mi trng truyn, vi sng in t: v = 2 x 106 (m/s) Round trip delayTx = N/R N: khi lng d liu truyn (bit) R: tc truyn bit trn ng truyn. 2008 dce 2008, Dr. Dinh Duc Anh Vu 22 Data Communication and Computer Networks Nhiu T/h khng mong mun thm vo gia thit b pht v thit b thu Nhiu nhit Do dao ng nhit ca cc electron trong cht dn Hm ca nhit Phn tn ng nht trn ph tn s Nhiu trng Khng th loi b gii hn hiu sut ca h thng Nhiu trong bng thng 1Hz ca bt k cht dn no N0 = kT N0: mt cng sut nhiu (watt/Hz) k: hng s Boltzmann (= 1.38 x 10-23 J/K) T: nhit (K) Nhiu trong bng thng B (Hz)N = kTB 2008 dce 2008, Dr. Dinh Duc Anh Vu 23 Data Communication and Computer Networks Nhiu Nhiu iu ch (intermodulation) T/h nhiu c tn s l tng hoc hiu tn s ca cc t/h dng chung mi trng truyn Do tnh phi tuyn ca thit b thu/pht Nhiu xuyn knh (crosstalk) T/h t ng truyn ny nh hng sang cc ng truyn khc Cng ln (hoc nh hn) nhiu nhit Nhiu xung Xung bt thng (spike) e.g. nh hng in t bn ngoi Thi khong ngn Cng cao nh hng nhiu n qu trnh trao i d liu s Xung 0.01s lm mt 50 bit d liu nu truyn tc 4800bps 2008 dce 2008, Dr. Dinh Duc Anh Vu 24 Data Communication and Computer Networks Tc d liu Baud rate (baud) Nghch o ca phn t d liu ngn nht (s ln thay i tn hiu ng truyn mi giy) Tn hiu nh phn tc 20Hz: 20 baud (20 thay i mi giy) Bit rate (bps hoc bit/s) c trng cho kh nng ca knh truyn Bng baud rate trong trng hp tn hiu nh phn Khi mi thay i ng truyn c biu din bng 2 hay nhiu bit, tc bit khc vi tc baud Quan h gia Baud rate v Bit rate R = Rs x log2M = Rs x m R: tc bit (bit/s) Rs: tc baud (baud/s) M: s mc thay i tn hiu trn ng truyn m: s bit m ha cho mt tn hiu 2008 dce 2008, Dr. Dinh Duc Anh Vu 25 Data Communication and Computer Networks Thut ng 2008 dce 2008, Dr. Dinh Duc Anh Vu 26 Data Communication and Computer Networks c im C th truyn nhiu hn mt bit ng vi mi thay i ca tn hiu trn ng truyn. Tc truyn thng tin cc i b gii hn bi bng thng ca knh truyn Cng thc Nyquist Nu tc truyn t/h l 2B th ch cn dng t/h vi cc tn s nh hn (hoc bng) B l ; ngc li nu bng thng l B th tc t/h cao nht l 2B C = 2B x log2M C: tc truyn t/h cc i (bps) khi knh truyn khng c nhiu W: bng thng ca knh truyn (Hz) M: s mc thay i tn hiu trn ng truyn hu hiu bng thng:C/B (bps Hz-1) Dung lng knh truyn (kh nng knh truyn) 2008 dce 2008, Dr. Dinh Duc Anh Vu 27 Data Communication and Computer Networks Signal to Noise ratio SNRdB = 10 x log10( ) (dB) S : cng sut tn hiu nhn N: cng sut nhiu Cng thc Shannon C = W x log2(1 + ) (bps) C: tc truyn t/h cc i khi knh truyn c nhiu T s nng lng t/h ca 1 bit so vi nng lng nhiu ca 1 Hz Eb/N0 Tb: thi gian truyn 1 bit R: tc bit ca d liu nh phn Eb = STb = S/R Eb/N0 = S/(RN0) = S/(kTR) Tc sai bit l hm gim ca t s ny T l tn hiu trn nhiu NSNS2008 dce V d Ph ca mt ng truyn nm trong khong 3MHz n 4MHz v c t s SNRdB =24dB. Tnh tc ti a ca ng truyn. t c tc th phi dng bao nhiu mc tn hiu truyn theo cng thc Nyquist? 2008, Dr. Dinh Duc Anh Vu 28 Data Communication and Computer Networks BK TP.HCM 2008 dce Chng 2 Truyn dn s liu Khi nim v thut ng Truyn dn d liu tng t v d liu s Suy hao ng truyn Dung lng knh truyn Mi trng truyn dn c nh hng Truyn dn khng dy Lan truyn khng dy Truyn ng thng (line-of-sight)2008 dce 2008, Dr. Dinh Duc Anh Vu 30 Data Communication and Computer Networks Bc sng Khong cch sng truyn c trong mt chu k Khong cch gia 2 im pha tng ng trong 2 chu k lin tip K hiu Gi s vn tc t/h v = vT = v/f c = 3*108 ms-1 (tc nh sng) 2008 dce 2008, Dr. Dinh Duc Anh Vu 31 Data Communication and Computer Networks Mi trng truyn dn Hu tuyn (guided media wire) Cp ng Cp quang V tuyn (unguided media wireless) V tinh H thng sng radio: troposcatter, microwave, ... c tnh v cht lng truyn d liu c xc nh bi mi trng v tn hiu i vi hu tuyn, mi trng nh hng ln hn i vi v tuyn, bng thng to ra bi anten pht nh hng ln hn Yu t nh hng trong vic thit k: tc d liu v khong cch Bng thng Bng thng cao th tc d liu cao Suy yu truyn dn Nhiu (nhiu nhit, nhiu iu ch, nhiu xuyn knh, nhiu xung) S thit b nhn (receiver) Trong mi trng hu tuyn, cng nhiu thit b nhn, tn hiu truyn cng mau suy gim 2008 dce 2008, Dr. Dinh Duc Anh Vu 32 Data Communication and Computer Networks Cp ng: two-wire open line Single pairFlat ribonTerminating Connector2008 dce 2008, Dr. Dinh Duc Anh Vu 33 Data Communication and Computer Networks Cp ng: twisted-pair Insulating outer cover Multi core Insulating outer cover Protective screen (shield) Cch in trn mi dy Xon li vi nhau Thng c b li Chng nhiu crosstalk 2008 dce 2008, Dr. Dinh Duc Anh Vu 34 Data Communication and Computer Networks Cp ng: twisted-pair ng dng Mi trng truyn dn thng dng nht Mng in thoi Gia cc thu bao v hp cp (subscriber loop) Kt ni gia cc ta nh Tng i ni b (Private Branch eXchange PBX) Mng cc b (LAN) 10Mbps hoc 100Mbps u nhc im R D dng lp t, thao tc Tc d liu thp Tm ngn 2008 dce 2008, Dr. Dinh Duc Anh Vu 35 Data Communication and Computer Networks Cp ng: twisted-pair c tnh truyn dn Analog Cn b khuch i mi 5km ti 6km ( suy gim t/h: ~1dB/km, chun trong T: 6dB) Digital Dng tn hiu tng t hoc tn hiu s Cn b lp (repeater) mi 2km hoc 3km Khong cch gii hn Bng thng gii hn (1MHz) Tc d liu gii hn (100Mbps) D b nhiu v tc ng ca mi trng ngoi 2008 dce 2008, Dr. Dinh Duc Anh Vu 36 Data Communication and Computer Networks Cp ng: twisted-pair Khng v bc gip Unshielded Twisted Pair (UTP) Dy T bnh thng R nht D lp t D b nhiu trng in t bn ngoi V bc gip Shielded Twisted Pair (STP) V gip bn gip gim nhiu v tc ng bn ngoi t hn Kh lp t (cng, nng) 2008 dce 2008, Dr. Dinh Duc Anh Vu 37 Data Communication and Computer Networks Cp ng: twisted-pair UTP Cat 3 Ln n 16MHz c dng trong lin lc thoi hu ht cc vn phng Chiu di xon (twist length): 7.5cm ti 10cm UTP Cat 4 Ln n 20 MHz UTP Cat 5 Ln n 100MHz c dng ph bin hin nay trong cc vn phng Chiu di xon: 0.6cm n 0.85cm Thch hp cho tc truyn ln n 100 Mbps (LAN) STP Cat 3: thch hp cho tc truyn ln n 10 Mbps 2008 dce 2008, Dr. Dinh Duc Anh Vu 38 Data Communication and Computer Networks Cp ng: twisted-pair cable Cable standards TnLoiMbps Thng c dng Category 1UTP1Modem Category 2UTP4Token Ring-4 Category 3UTP1010Base-T Ethernet Category 4STP16Token Ring-16 Category 5UTP100100Base-T Ethernet Category 5STP100100Base-T Ethernet Category 5eUTP1001000Base-T Ethernet Category 6UTP2001000Base-T Ethernet Category 7STP6001000Base-T Ethernet 2008 dce 2008, Dr. Dinh Duc Anh Vu 39 Data Communication and Computer Networks Cp ng: coaxial 2008 dce Cp ng: coaxial 2008, Dr. Dinh Duc Anh Vu 40 Data Communication and Computer Networks 2008 dce 2008, Dr. Dinh Duc Anh Vu 41 Data Communication and Computer Networks Cp ng: coxial ng dng Mi trng truyn linh hot nht Cp truyn hnh Truyn dn T khong cch xa FDM C th mang ng thi 10.000 cuc gi S b thay th bi cp quang Kt ni cc thit b khong cch gn Mng cc b c tnh truyn dn Hiu ng b mt (skin effect) Analog Cn b khuch i mi vi km Khong cch cng ngn nu tn s cng cao Ln n 600MHz Digital Cn b lp (repeater) mi km Khong cch cng ngn nu tc d liu cng tng 2008 dce 2008, Dr. Dinh Duc Anh Vu 42 Data Communication and Computer Networks Cp ng: c im chung T l bit li trn ng truyn (Bit Error Rate BER) vo khong 10-6. D b nh hng ca nhiu (crosstalk, thermal,...) v mi trng xung quanh. Tc truyn thng tin thay i ty theo phm vi h thng c trin khai : LAN: tc 10Mbps ~ 100Mbps, khong cch khong vi trm mt (UTP: length < 100 m). WAN: tc truyn thp hn, t vi chc Kbps n viMbps. V d: T1 ~ 1,5Mbps, E1 ~ 2Mbps, telephone line: 64Kbps 2008 dce 2008, Dr. Dinh Duc Anh Vu 43 Data Communication and Computer Networks Cp quang: cu trc Single coreMulticorePlasticcoatingOptical core Optical claddingSingle coreMulticorePlasticcoatingOptical core Optical cladding2008 dce 2008, Dr. Dinh Duc Anh Vu 44 Data Communication and Computer Networks Cp quang: li ch v ng dng Li ch Dung lng cao Tc d liu hng trm Gbps (so vi 100Mbps trn 1km coaxial cable v thp hn ca twisted-pair cable) Kch thc v trng lng nh suy hao ca tn hiu trn ng truyn thp. Cch ly trng in t (khng b nh hng ca nhiu v mi trng xung quanh, kh cu trm) Khong cch gia cc b repeater xa T l bit li trn ng truyn vo khong 10-9 10-12 ng dng Phm vi trin khai rt a dng: LAN (vi km), WAN (hng chc km). Mi trng truyn thch hp trin khai cc ng dng mng s a dch v tch hp bng rng (Broadband Integrated Services Digital Networks) ng trung k khong cch xa Trung k th Trung k tng i nng thn Thu bao LAN 2008 dce 2008, Dr. Dinh Duc Anh Vu 45 Data Communication and Computer Networks Cp quang: c tnh truyn dn Sng lan truyn c hng 1014 n 1015 Hz Mt phn ph hng ngoi v ph nhn thy c Light Emitting Diode (LED) R Tm nhit hot ng rng Tui th cao Injection Laser Diode (ILD) Hiu qu hn Tc d liu cao hn Wavelength Division Multiplexing 2008 dce 2008, Dr. Dinh Duc Anh Vu 46 Data Communication and Computer Networks Cp quang : ch truyn multimode: several paths/time delays narrow: 1 wavelength no time delays 2008 dce 2008, Dr. Dinh Duc Anh Vu 47 Data Communication and Computer Networks Cp quang : ch truyn Step-index multimode Graded-index multimodeSingle-mode Ngun sngLED/ILDLED/ILDILD Bng thngRng (ln n 200MHz/km) Rt rng (200MHz-3GHz/km) Cc rng (3GHz-50GHz/km) Ghp niKhKhKh ng dngTruyn d liu my tnh ng in thoi (khong cch trung bnh) Vin thng ng di Gi thnhR nhtTrung bnht nht ng knh li (m) 50-12550-1252-8 ng knh v (m) 125-440125-44015-60 suy gim (db/km) 10-507-150.2-2 2008 dce 2008, Dr. Dinh Duc Anh Vu 48 Data Communication and Computer Networks Cp quang2008 dce 2008, Dr. Dinh Duc Anh Vu 49 Data Communication and Computer Networks Mi trng truyn dn hu tuyn c tnh truyn dn im-im 2008 dce 2008, Dr. Dinh Duc Anh Vu 50 Data Communication and Computer Networks V tuyn Truyn v nhn thng qua anten C hng Chm nh hng (focused beam) i hi s canh chnh hng cn thn V hng Tn hiu lan truyn theo mi hng C th c nhn bi nhiu anten Tm tn s 2GHz n 40GHz Vi sng (microwave) nh hng cao im-im V tinh 30MHz n 1GHz V hng radio 3 x 1011 n 2 x 1014(Hz) Hng ngoi Cc b Khc phc nhng kh khn v a l khi trin khai h thng T l bit li trn ng truyn (BER) thay i ty theo h thng c trin khai. V d: BER of satellite ~ 10-10 Tc truyn thng tin t c thay i, t vi Mbps n hng trm Mbps Phm vi trin khai a dng: LAN (vi km), WAN (hng chc km) Chi ph trin khai h thng ban u rt cao 2008 dce 2008, Dr. Dinh Duc Anh Vu 51 Data Communication and Computer Networks V tuyn: cc bng tn truyn thng 2008 dce 2008, Dr. Dinh Duc Anh Vu 52 Data Communication and Computer Networks V tuyn: sng viba mt t Cho parabol (thng bn knh 3m) Chm sng nh hng theo ng ngm (line of sight) suy gim t/h d: khong cch : bc sng suy gim t l thun bnh phng khong cch cn amplifier/repeater mi 10-100km suy gim thay i theo mi trng (cng tng khi c ma) ng dng: Thay th cho cp ng trc trong vin thng khong cch xa (cn t b amp/repeater, nhng phi nm trn ng thng) Truyn im - im khong cch ngn in thoi di ng Tn s cng cao th tc d liu cng cao ( ) dB Ld24log 10t=2008 dce 2008, Dr. Dinh Duc Anh Vu 53 Data Communication and Computer Networks V tuyn: sng viba mt t Band (GHz)Bandwidth (MHz)Data rate (Mbps) 2712 63090 114090 18220274 Hiu sut sng viba s 2008 dce 2008, Dr. Dinh Duc Anh Vu 54 Data Communication and Computer Networks V tuyn: sng v tinh V tinh l trm trung chuyn V tinh nhn trn mt tn s, khuch i (lp li tn hiu) v pht trn mt tn s khc Cn qu o a tnh Cao 35.863 km ng dng Truyn hnh in thoi ng di Mng ring (VSAT) c tnh Thng trong khong tn s 1-10 GHz < 1 GHz: qu nhiu nhiu t mi trng t nhin >10 GHz: hp th bi tng kh quyn Cp tn s thu/pht (3.7-4.2 downlink, 5.925-6.425 uplink) 4/6 GHz band (11.7-12.2 downlink, 14-14.5 uplink) 12/14 GHz band Tn s cao hn i hi tn hiu phi mnh khng b suy gim Tr 240-300ms, ng ch trong vin thng 2008 dce 2008, Dr. Dinh Duc Anh Vu 55 Data Communication and Computer Networks V tuyn: v tinh SatelliteFootprintEarthEarth groundstationUplinkdownlinkpoint-to-pointSatelliteHub stationpoint-to-multipointUplinkdownlinkdownlinkVSATVSATVSAT : very smal aperture terminalEquatorial Orbit22,300 miles2008 dce 2008, Dr. Dinh Duc Anh Vu 56 Data Communication and Computer Networks V tuyn: sng radio V hng, 30MHz 1GHz Antena khng cn c hnh a v khng cn chnh hng Sng FM, truyn hnh UHF v VHF t b suy gim do ma, xuyn qua kh quyn Truyn theo ng ngm (line of sight) B nh hng bi nhiu a knh (multipath) Phn x Radio towerRadio towerIonosphereTroposphereRefractedwaveReflectedwaveDirect wave2008 dce 2008, Dr. Dinh Duc Anh Vu 57 Data Communication and Computer Networks V tuyn: sng hng ngoi Truyn theo ng thng (hoc phn x) Cn bi cc bc tng B iu khin TV t xa, cng iu khin bng hng ngoi (IRD port) 2008 dce 2008, Dr. Dinh Duc Anh Vu 58 Data Communication and Computer Networks Mi trng truyn dn 2008 dce 2008, Dr. Dinh Duc Anh Vu 59 Data Communication and Computer Networks Lan truyn khng dy Lan truyn sng mt t (ground wave) Tn hiu i theo b mt cong ca tri t Tn s ln n 2MHz AM radio 2008 dce 2008, Dr. Dinh Duc Anh Vu 60 Data Communication and Computer Networks Lan truyn khng dy Sng khng gian (sky wave) Radio nghip d, BBC world, VoA Tn hiu b tng in ly phn x li mt t (thc t l b khc x) 2008 dce 2008, Dr. Dinh Duc Anh Vu 61 Data Communication and Computer Networks Lan truyn khng dy Truyn theo ng ngm Tn s trn 30Mhz C th truyn xa hn ng ngm nh sng v b hiu ng khc x 2008 dce 2008, Dr. Dinh Duc Anh Vu 62 Data Communication and Computer Networks Truyn theo ng ngm Khong cch max ca ng ngm h: chiu cao ca anten k: hng s hiu chnh khc x ca sng (k=4/3) V d: thp anten cao 100m c th truyn n mt im trn mt t cch xa 41km Khong cch max gia 2 anten h1, h2:chiu cao cc anten kh d 57 . 3 =) 2 1 ( 57 . 3 kh kh d + =2008 dce 2008, Dr. Dinh Duc Anh Vu 63 Data Communication and Computer Networks Truyn theo ng ngm Suy gim tn hiu trong khng gian (free space loss) Tn hiu b phn tn theo khong cch i vi cng 1 anten, suy gim cng nhiu i vi tn s thp (bc sng di) ( ) dB d f Lcfd56 . 147 ) log( 20 ) log( 20 log 1024 + = =t( ) ( )2424cfddrtPPtt= =2008 dce 2008, Dr. Dinh Duc Anh Vu 64 Data Communication and Computer Networks Truyn theo ng ngm Hp th ca kh quyn Hi nc v oxy hp th sng v tuyn Hi nc nh hng ln nht ti 22GHz, t hn i vi tn s