Describe the Multiplexing techniques for digital signal transmission | iiQ8
✅ Describe the Multiplexing Techniques for Digital Signal Transmission
Multiplexing is a technique used in digital signal transmission to combine multiple signals into one medium for efficient use of bandwidth. It helps in transmitting several data streams simultaneously over a single channel or link.
🔑 Main Multiplexing Techniques for Digital Signal Transmission:
- Time Division Multiplexing (TDM)
- Definition: TDM divides the channel into time slots, and each signal gets the whole bandwidth but only during its specific time slot.
- Types:
- Synchronous TDM: Each source gets a fixed time slot whether it has data to send or not.
- Asynchronous/Statistical TDM: Slots are assigned dynamically based on demand.
Example: Used in digital telephony systems.
- Frequency Division Multiplexing (FDM)
- Definition: The available bandwidth is divided into different frequency bands, and each signal is transmitted simultaneously on its own frequency.
- Common in analog signals, but digital signals can be modulated to use FDM.
Example: Cable TV broadcasting.
- Wavelength Division Multiplexing (WDM) (for optical fiber)
- Definition: Similar to FDM, but used for optical signals. Different wavelengths of light (colors) carry separate digital data streams over a single optical fiber.
- Common in high-speed fiber optic networks.
Example: Internet backbone fiber links.
- Code Division Multiplexing (CDM) / CDMA
- Definition: All signals are transmitted simultaneously across the same frequency spectrum, but each is encoded with a unique code.
- The receiver uses the same code to extract the intended signal.
Example: Used in mobile networks like 3G CDMA systems.
✅ Summary Table:
| Technique | Division Basis | Used In | Type of Signal |
| TDM | Time | Telephony, digital comms | Digital |
| FDM | Frequency | Radio, TV, analog systems | Analog/Digital |
| WDM | Wavelength | Fiber optics | Digital |
| CDM | Code | Cellular systems | Digital |
Multiplexing improves the efficiency and capacity of communication systems by allowing multiple signals to share a single medium. The choice of technique depends on the application, medium, and type of signal.
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Describe the Multiplexing techniques for digital signal transmission.
Here are the Top 5 Interview Questions and Answers related to digital signal transmission and multiplexing, commonly asked in IT, networking, or telecom job interviews:
✅ 1. What is Multiplexing and Why is it Important?
Answer:
Multiplexing is a technique that allows multiple signals to be transmitted over a single communication channel simultaneously. It improves bandwidth utilization, reduces infrastructure costs, and enables efficient communication between multiple devices.
✅ 2. What are the Different Types of Multiplexing Techniques Used in Digital Transmission?
Answer:
The main multiplexing techniques are:
- Time Division Multiplexing (TDM)
- Frequency Division Multiplexing (FDM)
- Wavelength Division Multiplexing (WDM) (for optical networks)
- Code Division Multiplexing (CDM)
Each technique separates signals by time, frequency, wavelength, or code to avoid interference.
✅ 3. How Does Time Division Multiplexing (TDM) Work?
Answer:
TDM divides time on a channel into separate slots and assigns each signal a specific time slot. All signals share the same frequency but transmit in turns. It can be:
- Synchronous TDM: Fixed time slots, regardless of data presence.
- Asynchronous (Statistical) TDM: Slots assigned dynamically based on need.
✅ 4. What is the Difference Between FDM and WDM?
Answer:
- FDM is used for electrical or analog signals and divides bandwidth into multiple frequencies.
- WDM is used for optical signals and uses different light wavelengths to carry data.
Both allow multiple signals to be sent simultaneously, but in different domains—electrical vs. optical.
✅ 5. Can You Explain Code Division Multiplexing (CDM) in Simple Terms?
Answer:
In CDM, all signals share the same frequency and time but are uniquely encoded with different spreading codes. The receiver uses the same code to separate and reconstruct the original signal. It’s like several people speaking different languages in the same room—each listener understands only the language they know.