Introduction to Multiplexing

Overview of Multiplexing

• Multiplexing combines multiple data streams into a single medium for transmission.
• A multiplexer (MUX) is the hardware used to combine 'n' input lines into one output line, following a many-to-one approach.
• A demultiplexer (DEMUX) is used at the receiving end to separate the output back into 'n' component signals, following a one-to-many approach.

History of Multiplexing

• Multiplexing originated in telegraphy during the 1870s.
• Widely utilized in telecommunications to transmit several calls over a single wire.
• In 1910, George Owen Squier developed telephone carrier multiplexing.

Multiplexing Concept

• Input lines are transmitted through a multiplexer, creating a composite signal.
• The composite signal is then demultiplexed to deliver individual signals to their destinations.

Advantages of Multiplexing

• Enables multiple signals to share a single communication medium.
• Enhances the effective utilization of bandwidth.

Multiplexing Techniques

Frequency-Division Multiplexing (FDM)

• An analogue technique that divides the available bandwidth in a medium into several frequency channels.
• Input signals are modulated into frequency bands, combined by a multiplexer, and used for transmitting multiple signals simultaneously.
• Commonly employed in radio and television broadcasting.

Advantages of FDM

• Simple and effective for analogue signals, allowing multiple simultaneous transmissions.
• No synchronization is needed between sender and receiver.

Disadvantages of FDM

• Best suited for low-speed channels and can suffer from crosstalk.
• Requires many modulators and high-bandwidth channels for efficacy.

Wavelength Division Multiplexing (WDM)

• Similar to FDM but specifically for optical signals transmitted through fiber optic cables.
• Increases the capacity of fiber optics, utilizing its high data rate capabilities.
• A prism can serve both as a multiplexer and a demultiplexer for optical signals.

Time Division Multiplexing (TDM)

• A digital technique where signals share the same frequency but transmit at different times.
• Time slots within the channel are allocated for each user, with data transmitted sequentially rather than simultaneously.

Types of TDM

• Synchronous TDM:

  • Fixed time slots allocated to devices regardless of data presence.
  • Inefficient as empty slots remain transmitted, reducing overall channel capacity.

• Asynchronous TDM:

  • Dynamic allocation of time slots only to devices with data to transmit.
  • Optimizes channel capacity by avoiding the transmission of empty slots, leading to efficient data handling.

Conclusion

• Multiplexing is crucial in communication systems, enhancing the efficiency of data transmission across various mediums. Different techniques cater to specific signal types and operational requirements, influencing how data is formatted and transferred.