cdm-fdm tdm

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Time Division Multiplexing The concept of Time Division Multiplexing TDM Examples Frame SynchronizationTDM Hierarchy Packet TransmissionFrequency Division Multiplex Frequency Division Multiplex Separation of spectrum into smaller Separation of spectrum into smaller frequency bands frequency bands Channel gets band of the spectrum for the Channel gets band of the spectrum for the whole time whole time Advantages: Advantages: no dynamic coordination needed no dynamic coordination needed works also for analog signals works also for analog signals Disadvantages: Disadvantages: waste of bandwidth waste of bandwidth if traffic distributed unevenly if traffic distributed unevenly inflexible inflexible guard spaces guard spacesk3 k4 k5 k6ftcChannelskiftc k2 k3 k4 k5 k6k1Time Division Multiplex Time Division Multiplex Channel gets the whole spectrum Channel gets the whole spectrum for a certain amount of time for a certain amount of time Advantages: Advantages: only one carrier in the only one carrier in themedium at any time medium at any time throughput high even throughput high even for many users for many users Disadvantages: Disadvantages: precise precise synchronization synchronization necessary necessaryChannels kifTime and Frequency Division Multiplex Time and Frequency Division Multiplex A channel gets a certain frequency A channel gets a certain frequency band for a certain amount of time (e.g. band for a certain amount of time (e.g. GSM) GSM) Advantages: Advantages: better protection against tapping better protection against tapping protection against frequency protection against frequency selective interference selective interference higher data rates compared to higher data rates compared tocode multiplex code multiplex Precise coordination Precise coordinationrequired required tck2 k3 k4 k5 k6k1Channels kiCode Division Multiplex Code Division Multiplex Each channel has unique code Each channel has unique code All channels use same spectrum at same All channels use same spectrum at same time time Advantages: Advantages: bandwidth efficient bandwidth efficient no coordination and synchronization no coordination and synchronization good protection against interference good protection against interference Disadvantages: Disadvantages: lower user data rates lower user data rates more complex signal regeneration more complex signal regeneration Implemented using spread spectrum Implemented using spread spectrum technology technologyk2 k3 k4 k5 k6k1ftcChannels kiMultiplexing Two basic forms of multiplexing. Two basic forms of multiplexing. (a) (a) Frequency Frequency- -division multiplexing division multiplexing (F (FDM DM) ) (with guardbands). (with guardbands).(b) (b) Time Time- -division multiplexing division multiplexing ( (TDM TDM) ); no provision is made here for ; no provision is made here for synchronizing pulses. synchronizing pulses.FDMTDMTDM Composition of one frame of a multiplexed PAM signal incorporating four voice Composition of one frame of a multiplexed PAM signal incorporating four voice- -signals and a synchronizing pulse. signals and a synchronizing pulse. Frequency Division Multiplexing (FDM) Block diagram of FDM system, showing the important constituents of the transmitter and Block diagram of FDM system, showing the important constituents of the transmitter and receiver. receiver.Time Division MultiplexingDefinition: Time Division Multiplexing (TDM) is the time interleaving oI samples Iromseveral sources so that the inIormation Irom these sources can be transmitted seriallyover a single communication channel.At the TransmitterSimultaneous transmission oI several signals on a time-sharing basis.Each signal occupies its own distinct time slot, using all Irequencies, Ior the duration oI the transmission.Slots may be permanently assigned on demand.At the Receiver Decommutator (sampler) has to be synchronized with the incoming waveIorm Frame Svnchronizationow pass IilterISI poor channel Iiltering Feedthrough oI one channel's signal into another channel -- rosstalk55ications of TDM: Digital Telephony, Data communications, Satellite Access,Cellular radio.Time Division MultiplexingConceptual diagram oI multiplexing Conceptual diagram oI multiplexing- -demultiplexing. demultiplexing.!M TDM SystemIllustrating 4-Channel PAM TDM MultiplexingDigital Time Division MultiplexingDigit IntereavingWORD or Byte IntereavingIntereaving channe with different bit ratesIntereaving channe with different bit rates using two muti5exersTime Division Multiplexing (TDM) can be accomplished at bit or byte (word) level. Channhels having diIIerent data rates can also be TDM multiplexed but must beinterleaved accordingly.Block diagram of TDM system. Block diagram of TDM system.!M TDM System Ty5ica Framing Structure for TDMTime Division MultiplexingFrame structure of a certain TDM signaom5osite Signa FormatTime Division Multiplexing!ulse width oI TDM !AM:ssfT

nTs

!ulse width oI TDM !CM:s

satisIies Nyquist ratessf fT

Pulse Stuffing in TDMStuII bits, which are dummy bits are inserted in the TDM output data when the diIIerent inputs are not completeley synchronized or the diIIerent input rates are not related by a ratinal number.Pulse Stuffing in TDMStuII bits, which are dummy bits are inserted in the TDM output data when the diIIerent inputs are not completeley synchronized or the diIIerent input rates are not related by a ratinal number.Muti5exing of two data streams with bit stuffingTDM Example (Multiplexing Analog and Digital)Source : 2 kHz bandwidth.Source 2: 4 kHz bandwidth.Source : 2 kHz bandwidth.Source 4-: Digital 7200 bits/sec. kb/s1 ksam/s128 kb/sx7.257.6 kb/sUse stuII bits to complete 7.2 to kb/s.Now and 64 rates are complete multiplesFrame SynchronizationTo sort and direct the received multiplexed data to the appropriate output channel Two ways to provide Irame sync to the demultiplexer circuit- Over a separate channel- Deriving Irom the TDM signal itselIFrame sync (unique k-bits) InIormation words oI an N-channel TDM systemTDM PAM for Radio TelemetryCCITT Digital TDM HierarchyPacket Transmission SystemTDM is Synchronous TransIer Mode (STM) technology- Data source is assigned a speciIic time slot Iixed data rate- More eIIicient when sources have a Iixed data rate- IneIIicient to accommodate bursty data sourceSoution?!acket Transmission System- !artitions source data into data packets (destination address, header)- EIIiciently assigns network resources when the sources have bursty data - Examples : Internet TC!/I! technology and the Asynchronous TransIer Mode (ATM) technology.SummaryHow inIormation in analog waveIorms can be represented by digital signalingHow to compute the spectra Ior line codes How Iiltering oI the digital signal, due to the communication channel aIIects ourability to recover the digital inIormation at the receiver |ISI| How we can merge inIormation Irom several sources into one digital signal byusing time division multiplexing (TDM)