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What is Multiplexing in Communications? A Plain English Explanation

What exactly is multiplexing? Let‘s break it down in simple terms.

Multiplexing refers to combining multiple signals or data streams together to transmit simultaneously over one shared communication channel. The key purpose is enabling efficient transmission of multiple conversations or streams of information together, without them interfering with each other.

Imagine you‘re at a dinner party engaging in a group conversation. Multiple people take turns talking, one after the other. Each person gets their chance to speak without interrupting others. Now imagine that conversation is a signal, and the dining room is a communication channel. Multiplexing works kind of like that layered conversation – multiple transmitters sharing one medium smoothly.

Multiplexing techniques are used extensively in telecommunications to optimize networks by maximizing the amount of data that can be sent over expensive infrastructure like fiber optic cables or radio waves. The world‘s insatiable hunger for streaming video, social media, online gaming, and other bandwidth-heavy applications makes multiplexing more crucial than ever.

A Brief History of Multiplexing

The origins of multiplexing date back to early electric telegraphy experiments in the 19th century.

In the 1870s, Thomas Edison developed the quadruplex telegraph system which allowed up to 4 messages to be sent simultaneously on one telegraph line. This was an early predecessor of frequency division multiplexing.

In the 1920s-1940s, frequency division became commonplace in radio and television broadcast systems as a way to efficiently transmit multiple channels.

Time division multiplexing later enabled multiple phone calls to share infrastructure in the 1960s, which helped the widespread adoption of digital telephony.

Code division multiplexing emerged in the 1980s-1990s to facilitate the explosion of cellular networks and mobile communications.

Today, global internet traffic exceeds 1 zettabyte per year, and mobile data traffic is growing at a compound annual rate of around 40%. Multiplexing is an indispensable technique allowing networks to keep up.

Chart showing exponential growth in global internet traffic over time

Global internet traffic has grown enormously thanks to multiplexing optimization of infrastructure.

How Multiplexing Works

Multiplexing combines multiple signals or data streams together to transmit across a single shared communication medium. This is accomplished using a multiplexer (mux) on the transmitting end and a demultiplexer (demux) on the receiving end.

The mux takes in multiple input signals from different sources. It processes them using a chosen multiplexing technique – like frequency, time, or code division multiplexing – to merge the signals together into one combined output stream. This consolidated signal can then be transmitted efficiently over the medium.

At the receiving end, the demux reverses the process. It extracts and reconstructs the individual input streams from the multiplexed signal. Each stream can then be routed to its intended destination.

Proper coordination between the muxing and demuxing ensures the signals stay isolated and separated. Like splitting apart strands of a braided rope back into individual strings.

Diagram showing multiplexing process from end-to-end

Multiplexers combine multiple signals, while demultiplexers split them apart again.

Next let‘s explore some of the most widely used multiplexing techniques.

Different Types of Multiplexing

There are three primary ways signals can be combined and transmitted using multiplexing:

Frequency Division Multiplexing

Frequency division multiplexing (FDM) assigns each signal a separate frequency band or channel within the available bandwidth.

For example, radio stations each transmit at their own unique designated frequency. Multiple signals can occupy the bandwidth simultaneously without interfering by allocating non-overlapping frequency ranges to each stream.

FDM is commonly used for applications like radio broadcasting, cable TV, WiFi networks, and 4G/5G cellular networks. It requires adequate overall bandwidth to accommodate the desired number of frequency channels.

Time Division Multiplexing

Time division multiplexing (TDM) divides access to the shared channel into timed intervals or frames. Each signal gets its own recurring time slot in which it can transmit data before the next signal‘s turn.

Think of taking orderly turns in a conversation – TDM creates transmission slots almost like that. This interleaves chunks of each signal together into one stream.

TDM enabled the widespread adoption of digital telephony and is still used in communication systems including PSTN, ISDN, and Ethernet networks. It is highly efficient and makes optimal use of capacity.

Code Division Multiplexing

Code division multiplexing (CDM) assigns a unique code to each user or signal. It allows all signals to transmit simultaneously in the same frequency band.

The coding isolates each signal at the receiving end, preventing interference between streams even as they overlap. This is similar to picking out a known voice in a noisy room by its unique sound.

CDM enabled the rapid growth of cellular networks by allowing many users to share the same radio spectrum frequencies smoothly. It provides excellent scalability and flexibility.

Understanding these core techniques provides insight into how our telecom systems are designed and optimized using multiplexing. Next we‘ll look at how multiplexed systems are built.

Building a Multiplexed Communication System

Constructing an end-to-end multiplexed communication system requires careful planning and coordination. Here is a general step-by-step overview:

Step 1) Select the optimal multiplexing technique

Determine the appropriate method – FDM, TDM, CDM – based on factors like types of signals, number of channels, available bandwidth, and required isolation.

Step 2) Design and implement mux/demux hardware

Build specialized multiplexer hardware for the transmitting side and demultiplexer hardware for the receiving side. This handles tasks like frequency filtering, timing, synchronization, and encoding/decoding.

Step 3) Integrate system into the network

Connect the multiplexing hardware into the communication network, linking muxes and demuxes at either end. Coordinate timing parameters between ends.

Step 4) Optimize performance

Conduct testing to monitor signal quality, interference, capacity usage and other metrics. Fine-tune the system for optimal reliability and efficiency.

With careful engineering, the result is an efficient multiplexed system transmitting multiple simultaneous signals over one shared medium.

Crucial Role of Multiplexing in Modern Networks

Multiplexing now plays an absolutely vital role in nearly all modern telecommunication networks and systems transmitting high volumes of data, from phone calls to streaming video and more. Let‘s look at some examples:

  • Telephone networks – Multiplexing enabled the widespread digitization of phone systems by efficiently transmitting many calls over the same lines. It continues allowing large-scale voice traffic daily.

  • Cable TV – Multiplexing makes it possible to economically deliver hundreds of cable channels through the same cable line using different frequency bands.

  • Cellular – Multiplexing allows cellular base stations to serve large numbers of users simultaneously by assigning each device a coded signal to transmit/receive on the same frequencies.

  • Fiber optic – Multiplexing techniques maximize fiber capacity, with a single strand carrying terabits per second by transmitting up to 80+ separate signals on different wavelengths.

  • WiFi – Routers use multiplexing to enable smooth access for multiple devices by assigning each short time slots on the shared wireless channel.

Without multiplexing, the volumes of data transmission we rely on simply would not be possible. Our modern telecom infrastructure has been transformed and optimized using multiplexing techniques.

Multiplexing in Action: Real-World Examples

To better understand multiplexing in practice, let’s look at some specific real-life applications:

Cable TV

Cable TV relies heavily on frequency division multiplexing (FDM) to deliver numerous channels efficiently. Hundreds of channels, each containing video and audio data, are allocated to non-overlapping frequency bands across the available spectrum – typically 50 MHz to 1 GHz on the cable line.

At the customer‘s home, the cable box or modem acts as the demultiplexer by tuning to the correct frequency to extract the desired channel signal for viewing a particular channel. This FDM system allows economical delivery of many channels simultaneously through the same cable line.

Digital Telephony

Modern digital telephone systems use time division multiplexing (TDM) to transmit large volumes of voice data between switching centers. Voice data from each call is assigned a recurring time slot, and these slots from 24-30 calls are interleaved together into a combined signal.

The time slots are tracked and extracted at the receiving end to reconstruct individual calls. This TDM approach allows efficient sharing of infrastructure without interference, reducing costs compared to dedicated circuits per call.

Cellular Networks

Cellular networks rely heavily on code division multiplexing (CDM) to maximize efficiency of limited radio spectrum. Each user‘s device transmits encoded with a unique code assigned by the network.

The cellular base station receives a combined encoded signal from many users sharing the same frequencies. It uses the coding to extract each user‘s transmission from the pool of overlapping codes.

This key CDM technique is what enables large-scale spectrum reuse in cellular networks, allowing big populations of users to be served in the same geographic area simultaneously.

Fiber Optic Backbone

Fiber optic backbone networks utilize dense wavelength division multiplexing (DWDM) to achieve enormous capacity. DWDM combines up to 80 or more signals by transmitting each on a different wavelength through the same fiber optic cable.

Each wavelength functions as a channel, carrying up to 40 Gbps capacity. By combining dozens of wavelengths, overall capacity reaches astonishing levels – terabits per second over a single strand. This is how high-traffic fiber links can reliably carry staggering data volumes.


In summary, multiplexing is the vital process of combining multiple signals or data streams to transmit simultaneously over one shared medium. Multiplexing methods like FDM, TDM, and CDM maximize telecom network capacity and efficiency without interference.

Multiplexing has evolved from early telegraphy experiments to an essential pillar of modern networks, from streaming media to mobile broadband. Our bandwidth-hungry digital world relies on multiplexing operating behind the scenes to power our near-insatiable appetite for communication and data transmission.