Time-Division Multiplexing

Time-Division Multiplexing Definition
Time‑division multiplexing (TDM) is a method of sending multiple signals over the same channel. It splits the communication line into short time slots, and each signal uses its own slot to send data. This allows the signals to easily travel on the channel without interfering with each other.
TDM is used in telecommunications, broadcasting, and computer networks. It can transmit digital and analog signals (that are usually encoded and digitized), and works with wired and wireless networks.
How Time-Division Multiplexing Works
Typical steps in a TDM process include:
- Sampling the signals: Analog signals are first converted into digital data, allowing them to travel over digital networks. Digital signals can be used directly.
- Combining the signals: Each digital signal is assigned a short time slot. The system combines these into one stream, with signals taking turns in their slots.
- Keeping everything in sync: A transmission clock makes sure every signal uses its slot at the right time.
- Sending the data: The combined signal travels over the channel, which could be a cable, a fiber-optic line, or a wireless link.
- Splitting the signals back: The receiving system separates each signal from the stream based on its time slot.
- Rebuilding the original signals: The signals are converted back (if needed), cleaned up, and passed along for use.
Types of Time-Division Multiplexing
- Synchronous TDM: Sets a time slot for each signal, even if no data is being sent. Works well in systems with constant traffic, but can waste bandwidth when sources are idle. Typically used for wired connections because it relies on quick, stable timing, which wireless connections may not always have.
- Statistical/Asynchronous TDM: Assigns time slots based on demand, so only signals with data to send are allocated a slot. Increases efficiency by using bandwidth only when needed.
- Time‑Division Multiple Access (TDMA): Uses fixed time slots to let multiple devices take turns sending data over a shared wireless channel. It’s a multiple-access method (not a standalone TDM type) built on synchronous TDM, but it’s specifically for wireless channels and is often used in mobile networks.
TDM Examples
- Satellite communication: Satellites often use TDM for downlink transmissions, sending multiple streams of data (like video, voice, and control signals) over the same channel.
- Digital broadcasting: TV and radio stations use TDM to send content over a single frequency.
- Computer networks: Older or specialized computer systems can use TDM to let multiple devices share one communication line without interference.
- Fiber-optic internet systems: Fiber internet connections sometimes use TDM to send different streams through a single fiber line.
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FAQ
Time‑division multiplexing (TDM) is a transmission method that lets multiple signals share one channel. It splits the channel into short time slots, and each signal uses its assigned slot to transmit without interference.
TDM (time-division multiplexing) is used in systems that need to send multiple signals over one link without clashes. It appears in satellite communication, where different data types share a transmission path, and in digital broadcasting, where channels take turns on the same frequency. TDM is also used in certain computer networks and fiber-optic systems to manage data efficiently.
TDM (time-division multiplexing) comes in two main forms: synchronous and statistical. Synchronous TDM gives each signal a fixed time slot, even if there’s nothing to send. Statistical TDM improves efficiency by assigning slots only to active signals.
TDMA could be considered a third type of TDM, but it’s actually a method derived from it. It brings TDM principles to wireless networks, letting multiple users share the same frequency by taking turns in pre-assigned time slots.