2 multiplexing
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Multiplexing enables two or more transmission sources to share a common circuit. The two most common forms are frequency division multiplexing (FDM) and time division multiplexing (TDM). FDM involves the simultaneous transmission of analog signals modulated to different carrier frequencies, while TDM involves interleaving digital signals in pre-assigned time slots.
2 multiplexing
- 1. Multiplexing • Enable two or more transmission sources to share a common circuit • Most common forms – FDM and TDM • FDM – associated with analog signal, simultaneous transmission • TDM – associated with digital signal (could also be analog, but single frequency) with time slices 1
- 2. Multiplexing 2
- 3. Frequency Division Multiplexing • FDM • Each signal is modulated to a different carrier frequency • Carrier frequencies separated so signals do not overlap (guard bands) • e.g. broadcast radio • Channel allocated even if no data • Broadband 3
- 5. Wavelength Division Multiplexing • Multiple beams of light at different frequency • Carried by optical fiber • A form of FDM • Each colour of light (wavelength) carries separate data channel 5
- 6. WDM Operation • Same general architecture as other FDM • Number of sources generating laser beams at different frequencies • Multiplexer consolidates sources for transmission over single fiber • Optical amplifiers amplify all wavelengths —Typically tens of km apart • Demux separates channels at the destination 6
- 7. Synchronous Time Division Multiplexing • Multiple digital signals interleaved in time • May interleave bits, so not necessarily synchronous transmission • Time slots pre-assigned to sources and fixed • Time slots allocated even if no data • Time slots do not have to be evenly distributed amongst sources 7