Multiplexing In FE Electrical

Are you gearing up for the FE Electrical exam? Here’s a heads-up: Multiplexing might not be the flashiest term you’ll come across, but it’s an absolute must-know for acing the FE Electrical exam. 

It’s a vital exam topic according to the NCEES® syllabus and guidelines, and we’re about to break down this crucial topic to help prepare it in your FE preparation journey. 

Ready to explore multiplexing in FE Electrical exam? Let’s start with the fundamentals.

The Need for Multiplexing

Implementing multiplexing in network communications is driven by two pivotal objectives:

  • Optimizing resource utilization
  • Facilitating communication between network devices.

These objectives address critical limitations in transmitting multiple signals separately while concurrently elucidating the role of multiplexing in enhancing the efficiency of communication channels.

Transmitting Multiple Signals Separately

Dedicated Connections – In the absence of multiplexing, a dedicated connection is necessitated between each pair of communicating devices. Such an arrangement imposes substantial infrastructure overhead regarding physical cabling and routing, thus rendering it impractical for large-scale, complex network architectures.

Scarcity of Resources – Network resources are often scarce and expensive, with bandwidth being a prime example. Transmitting signals separately is inefficient regarding resource utilization as it fails to leverage the full potential of the available infrastructure.

Inefficient Bandwidth Utilization – Transmitting multiple signals individually results in underutilization of available bandwidth, as each signal operates independently, and network resources may remain idle when not in use by specific devices.

How does Multiplexing help Resolve Limitations?

  • Shared Media and Statistical Multiplexing – Multiplexing addresses the limitations by enabling multiple signals to coexist on shared communication channels. Statistical multiplexing, a form of multiplexing, allows for efficient sharing of resources by allocating bandwidth dynamically per the connected devices’ requirements. This approach ensures optimal resource utilization without requiring dedicated connections.
  • Resource Conservation – Multiplexing, through its various techniques, such as time-division multiplexing (TDM) or frequency-division multiplexing (FDM), maximizes resource utilization by allocating time slots or frequency bands to different signals. This ensures network resources are conserved and shared effectively among numerous devices, thus economizing physical infrastructure and financial investments.
  • High Throughput and Scalability – Multiplexing fosters high throughput by concurrently transmitting multiple signals over the same channel, enhancing network scalability. With multiplexing, network architectures can accommodate increasing devices and applications without compromising performance.
  • Signal Isolation and Demultiplexing – The demultiplexing process at the receiving end effectively separates multiplexed signals, ensuring that each device receives the intended data stream. This enables individual devices to function as if connected through dedicated links despite the shared medium.
  • Adaptability to Diverse Network Topologies – Multiplexing techniques can be tailored to suit various network topologies: terrestrial or satellite communications, terrestrial fiber optics, or wireless networks. This adaptability ensures that multiplexing remains a fundamental mechanism for efficient resource utilization across diverse network infrastructures.

Basics of Multiplexing

basics of multiplexing

Multiplexing, often abbreviated as muxing, is a telecommunication method to transmit multiple signals or data streams concurrently over a communication link as a single composite signal.

Upon reaching its destination, the composite signal undergoes a process known as demultiplexing, or demuxing, to segregate and route the individual signals to distinct output lines.

Before exploring how multiplexing works, look at critical terminologies and devices often used.

  1. Multiplexer (Mux): A multiplexer, denoted as a “mux,” is an electronic device or system aggregating multiple discrete signals into a unified composite signal. It functions by selecting and directing individual signals, which may originate from different sources, into a shared data stream for efficient transmission.
  2. Demultiplexer (Demux): The demultiplexer, commonly referred to as a “demux,” complements the multiplexer’s role by disassembling the composite signal upon its arrival at the destination. It accurately isolates each original signal and directs it to the appropriate output line for subsequent processing.
  3. Multiplexed Signal: A multiplexed signal, often termed a “muxed signal,” represents the outcome of the multiplexing process. It is a consolidated signal comprising multiple distinct digital or analog signals originating from various sources or data streams.

How Multiplexing Works?

The multiplexing technique is utilized in network communications to optimize the efficient utilization of communication channels. At its core, multiplexing involves the combination of multiple signals into a single, shared data stream for concurrent transmission. 

This amalgamation can be achieved through various multiplexing techniques, such as Time-Division Multiplexing (TDM) or Frequency-Division Multiplexing (FDM).

In practical terms, multiplexing is akin to merging multiple lanes of traffic onto a single highway, facilitating more efficient use of the shared road. This process significantly enhances the capacity and data throughput of the communication channel, enabling the simultaneous transmission of multiple data streams.

Upon arrival at the destination, the multiplexed signal is subject to demultiplexing. The demultiplexer precisely separates the composite signal, extracting and directing each constituent signal to its designated output line. 

This ensures that the original data streams are made available for further processing, analysis, or routing as if they had been transmitted through dedicated communication paths.

Multiplexing Types

Below are several common multiplexing types and an explanation of how each works.

Frequency-Division Multiplexing (FDM)

multiplexing types

FDM divides the available bandwidth on a communication link into subchannels, each with different frequency widths. Each subchannel carries a signal in parallel with others.

For example, analog radio transmissions and cable TV use FDM to multiplex signals across radio waves or coaxial cables. 

Orthogonal Frequency-Division Multiplexing (OFDM), an offshoot of FDM, transmits subchannel frequencies closer together, allowing them to overlap while remaining separate.

As this method, Frequency Division Multiplexing (FDM), involves dividing a communication channel’s bandwidth into separate frequency channels, it can lead to unwanted interference between adjacent channels, called inter-channel cross-talk. 

To mitigate this interference, we introduce empty sections of bandwidth between each channel, referred to as guard bands. Guard bands act as a buffer to ensure that the signals in adjacent channels do not interfere with each other, maintaining the quality and integrity of the transmitted information.

frequency division multiplexing

Wavelength-Division Multiplexing (WDM)

wavelength-division multiplexing

WDM consolidates multiple communication channels and transmits them on lightwaves with distinct wavelengths. While similar to FDM, WDM pertains specifically to wavelengths. It is common in telecommunication systems and computer networks to use laser systems to transmit light signals over fiber optic cables. 

Variations include Coarse WDM and Dense WDM (DWDM), differing in the number of channels they support simultaneously.

1. Dense Wavelength Division Multiplexing (DWDM)

Operation: DWDM is used to multiplex a large number of optical signals onto a single fiber, typically up to 80 channels, with a spacing of 0.8 nm or less between the channels.

Use-case: DWDM is favored for high-capacity applications, enabling efficient utilization of optical fiber resources.

2. Coarse Wavelength Division Multiplexing (CWDM)

Operation: CWDM is used for lower-capacity applications, typically up to 18 channels with a wider spacing of 20 nm between the channels.

Use-case: CWDM is suitable for scenarios with acceptable lower data rates or more extended channel spacing.

Time-Division Multiplexing (TDM)

time-division multiplexing

TDM involves transmitting multiple digital signals over the same channel in alternating time slots. Unlike FDM and WDM, TDM operates at the temporal level.

It is widely used in digital telephony for multiple conversations over a shared medium and on Synchronous Optical Network (SONET) links for enterprise WAN and internet connectivity. TDM can be synchronous or asynchronous.

1. Synchronous Time Division Multiplexing (Synchronous TDM)

synchronous time division multiplexing

Basic Concept: In Synchronous TDM, the input data frame already has an assigned time slot in the output frame. Time slots are organized into frames, with one frame encompassing a complete cycle of time slots.

Inefficiency: Synchronous TDM has a drawback in that it is not particularly efficient. If the input frame contains no data to transmit, an empty slot remains in the output frame, resulting in underutilized bandwidth.

Synchronous Bit: To ensure synchronization, each frame in Synchronous TDM starts with a synchronous bit that marks the beginning of the frame.

2. Statistical (Asynchronous) Time Division Multiplexing (Statistical TDM)

statistical tdm

Basic Concept: In Statistical TDM, the output frame accumulates data from the input frame until it’s complete, unlike Synchronous TDM, which leaves empty slots.

Data Addressing: In Statistical TDM, it’s essential to include the address or identification of each specific data unit within the slot sent to the output frame.

Efficiency: Statistical TDM is a more efficient form of time-division multiplexing. It ensures the channel capacity is fully utilized, enhancing overall bandwidth efficiency.

Code-Division Multiplexing (CDM)

code-division multiplexing

In CDM, each signal is assigned a spreading code, a sequence of bits that distinguishes one signal from another. The spreading code combines the original signal to create an encoded data stream transmitted on a shared medium. 

Demultiplexing, achieved by subtracting the spreading code, retrieves the original signals. CDM is used in digital television, radio broadcasting, and 3G mobile cellular networks, while 4G and 5G primarily use OFDM.

CDM can support multiple signals from multiple sources, known as Code-Division Multiple Access (CDMA).

Space-Division Multiplexing (SDM)

space-division multiplexing

SDM spatially separates signal paths using multiple conductors, such as optical fibers or electrical wires. These conductors are bundled into a single transport medium but are physically separated, with each conductor handling a transmitted channel. 

Further multiplexing can be applied to individual conductors using FDM, TDM, or other multiplexing techniques. SDM is commonly used in submarine cable systems to increase capacity and can also be employed in wireless communications.

Polarization-Division Multiplexing (PDM)

polarization-division multiplexing

PDM polarizes incoming electromagnetic signals into orthogonal channels, then transmitted through a shared medium. It is frequently utilized in fiber optics communications and radio and microwave transmissions. Satellite TV providers often use PDM to deliver TV signals to satellite dishes.

Multiplexing Techniques and Devices

This section explores the various multiplexing devices used in different methods and multiplexing types.

Multiplexing Techniques

1. Frequency Division Multiplexing (FDM)

Technique: FDM divides the available bandwidth into non-overlapping frequency channels, each carrying an independent signal.

Multiplexing Devices: Multiplexers, such as passive RF combiners and filters.

Role: Multiplexes different signals into separate frequency bands for parallel transmission.

Applications: Analog radio broadcasting and cable TV. Limitations include susceptibility to cross-talk and the need for guard bands.

2. Time Division Multiplexing (TDM)

Technique: TDM allocates time slots within a fixed frame for multiple signals to share the same channel.

Multiplexing Devices: TDM switches and digital cross-connect systems.

Role: Enables time-sharing of the channel by allocating time slots to various signals.

Applications: Digital telephony and data communication. Limitations include inefficient utilization of bandwidth in synchronous TDM.

3. Wavelength Division Multiplexing (WDM)

Technique: WDM multiplexes optical signals with different wavelengths onto a single fiber.

Multiplexing Devices: WDM multiplexers, demultiplexers, and optical amplifiers.

Role: Combines multiple optical signals onto a single fiber for transmission.

Applications: Optical networks for telecommunications and data centers. Advantages include high data capacity, reduced equipment complexity, and flexibility for network upgrades.

4. Space Division Multiplexing (SDM)

Technique: SDM uses multiple antennas to create independent communication channels.

Multiplexing Devices: Multiple Input Multiple Output (MIMO) systems and smart antennas.

Role: Exploits spatial separation to enable multiple users to transmit simultaneously without interference.

Applications: Cellular networks and Wi-Fi. Enhances capacity and quality of wireless communication.

5. Code-Division Multiplexing (CDM)

Technique: CDM assigns unique spreading codes to each signal for simultaneous transmission.

Multiplexing Devices: CDMA transmitters, receivers, and spreading codes.

Role: Encodes and decodes signals using unique spreading codes to separate users on the same channel.

Applications: Cellular networks and satellite communication. Provides secure, interference-resistant communication. 

Multiplexing Types – Comparison Chart

Multiplexing TechniqueKey DifferentiatorUse-Case Scenario
Frequency-Division MultiplexingSignals divided by frequencyAnalog radio and cable TV
Wavelength-Division MultiplexingSignals divided by wavelengthFiber optic networks
Time-Division MultiplexingSignals transmitted in timeDigital telephony and SONET
Code-Division MultiplexingSignals encoded with codesDigital broadcasting and CDMA
Space-Division MultiplexingSignals separated spatiallySubmarine cable systems
Polarization-Division MultiplexingSignals polarized and transmittedFiber optics and satellite TV

Multiplexing Applications – Practical Use-Cases in Real-Life Scenarios

1. Telecommunications

Multiplexing: Wavelength Division Multiplexing (WDM) allows multiple data streams to be transmitted over a single optical fiber, increasing data capacity while minimizing network complexity.

Demultiplexing: At the receiving end, demultiplexers split the combined optical signals back into individual data streams for processing.

Advantages: High data capacity, efficient bandwidth utilization, and scalability.

Limitations: Costly infrastructure and maintenance.

2. Wireless Communication

Multiplexing: Space Division Multiplexing (SDM) employs multiple antennas to create parallel, interference-free channels for simultaneous wireless transmissions.

Demultiplexing: Multiple Input Multiple Output (MIMO) technology decodes the signals at the receiving end, enhancing signal quality.

Advantages: Increased capacity and improved signal quality.

Limitations: Requires complex antenna arrays and signal processing.

3. Satellite Communication

Multiplexing: Code-Division Multiplexing (CDM) allows multiple users to securely transmit data over the same frequency band.

Demultiplexing: Demultiplexers use unique spreading codes to extract individual user data.

Advantages: Secure communication resistance to interference.

Limitations: Complexity in spreading code management.


As you step into the FE preparation journey, remember that mastering topics like multiplexing in FE Electrical exam is crucial to success. To supercharge your preparation strategy, explore the comprehensive resources at Study for FE

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Licensed Professional Engineer in Texas (PE), Florida (PE) and Ontario (P. Eng) with consulting experience in design, commissioning and plant engineering for clients in Energy, Mining and Infrastructure.