计算机通信网

3.1• – – – – 3.23.2.1PCPC• • FDM– FDM(FrequencyDivisionMultiplexing)• (modem)– (MOdulator)300~3400Hz– (DEModulator)• • – – • 600bps• 600bps9600bps• 9600bps3.2.2• ——• ——()• ——(baseband)(broadband)• 10• 3.2.3• • • • • 3.2.4• (Shannon)• C• C=Wlog2(1+S/N)b/s– WHz– S– N• • • WS/NC• • – – – – – • 3.3.1• – STP(ShieldedTwistedPair)– UTP(UnshieldedTwistedPair)UTPSTP• (CoaxialCable)• 50Ω• 10M1km• 75Ω• CATVRG-8RG-1150ΩRG-5850ΩRG-5975ΩRG-6293ΩARCnetIBM3270• – – =1=0– LED(• RadioMicrowaveInfraredVisiblelightUVXrayγrayCoaxSatelliteTerrestrialMicrowavesAMFMFiberopticsTV(Hz)f(Hz)fLFMFHFVHFUHFSHFEHFTHF104105106107108109101010111012101310141015101610010210410610810101012101410161018102010221024ElectromagneticSpectrum• • • – – • – – fHzδmf/250=δ• – • – – α)()()(tntstr+=α• • c(t))(d)()()()()()(tntsctntctstr+−=+∗=∫∞∞−τττ• )(d)();()();()()(tntstctntctstr+−=+∗=∫∞∞−ττττ• {ak}L{τk}∑=−=Lkkktatc1)()();(ττδτ• PCMPulseCodeModulator• a• 2• 300Hz—3.4kHz• 4kHz8kHz125µs• b• nØ 1(AM)• 0101Ø 2(FM)• 010f11f2Ø 3(PM)• 0100011800• 010011100f1f21.2.A(V)f0(Hz)ω0=2πf0(rad/s)θ(rad)0()cos()stAtωθ=+0()cos(2)stAftπθ=+ASKAmplitude-shiftkeying---FSKFrequency-shiftkeying---PSKPhase-shiftkeying---1f1f2f2f(2ASK)• ω02πf0• :– – TtttAts≤+=0)cos()()(0θω⎩⎨⎧=00,1)(AtAcosω0ts(t)A(t)cosω0ts(t)A(t)(2FSK)• • – – 1100cos()1()cos()0AtstAtωϕωϕ+⎧=⎨+⎩“”“”A(t)10s(t)f1f0A(t)s(t)(2PSK)• )cos()(0θω+=tAts⎩⎨⎧=100πθ⎩⎨⎧+=1)cos(0)cos()(00πωωtAtAts⎩⎨⎧−=1cos0cos)(00tAtAtsωω• – FDMFrequencyDivisionMultiplex– TDMTimeDivisionMultiplex– CDMCodeDivisionMultiplexing)– WDMWavelengthDivisionMultiplexing)3.5• 3.5.1– – 12345BCDBCDBCDBCDAAAATDMTDMTDMTDMTDM…TDMCDCDCDAAAABBBBCDTDMTDMTDMTDMTDM…TDMBDBDBDAAAABCCCCDTDMTDMTDMTDMTDM…TDMBCBCBCAAAABCDDDDTDMTDMTDMTDMTDM…TDMABCDaabbcdbcattttt4#1acbcd#2#3#4STDMABCDabcdttttt3STDM#1acbabbcacd#2#31550nm01551nm11552nm21553nm31554nm41555nm51556nm61557nm701550nm11551nm21552nm31553nm41554nm51555nm61556nm71557nm3.5.2WDM• 8×2.5Gb/s1310nm20Gb/sEDFA120km3.5.3CDM• CDMA(CodeDivisionMultipleAccess)• • • m(chip)(chipsequence)• mbit– 1mbit– 0• S8bit00011011– 100011011– 011100100• S(–1–1–1+1+1–1+1+1)CDMA• (orthogonal)• • Sbb/smSmbb/sSm• SST• ST(innerproduct)0011=≡•∑=miiiTSmTS• 1• –1∑∑∑====±===•mimiimiiimSmSSm112211)1(111SSCDMASS110ttttttmtSSxTTxSx+TxSŸSxSŸTx60• 61• • 62• FDMA• TDMA• CDMA• SDMA6364FDMA65FDM/FM/FDMA66TDMATDMATDMA“”67TDMA68TDMADABC69TDMATDMAABCABC70TDMATDMA123n……71TDMA• • (TDM)72CDMA• CDMA• CDMAØ Ø Ø 73CDMA3-8DS/CDMA74CDMA• • • • • • EIA-232-EEIA• 1962RS-232• EIA-232-EDTEDCE3.73.7.1EIA-232-E• DTE(DataTerminalEquipment)• DCE(DataCircuit-terminatingEquipment)DTEDTEDCEDTEDCEDCEDTEEIA-232• 25DB-2513121131425.• EIA-2320”—+3v1”—-3v15m20kb/sEIA-232/V.24(1)(2)(3)(4)(5)(6)DCE(7)(8)(20)DTE(22)DTEDCEEIA-232/V.24DTE-ADTE-BDCE-ADCE-BEIA-232/V.24123456DCE7820DTE22123456DCE7820DTE22