Multiple Access Techniques

Multiple access refers to the methods that allow multiple devices to access a shared communication channel or medium. These techniques enable multiple users to share a communication channel by allocating resources such as frequency, time, or code.

“Multiple access refers to the method that allocates devices to access a shared communication channel or medium.“

Types of Multiple Access Techniques:

Time Division Multiple Access (TDMA)
Frequency Division Multiple Access (FDMA)
Code Division Multiple Access (CDMA)
Carrier Sense Multiple Access (CSMA)
Space Division Multiple Access (SDMA)

1. Time Division Multiple Access (TDMA)

TDMA divides time among all devices that are connected to the server advantage in speed and maintenance. The disadvantage if one of them is disconnected, their time will be wasted

Working Principle:

Time is divided into slots, and each device is allocated a specific time slot to transmit data.
Devices take turns sending data in their assigned slots.

Example:

In a conference call, each participant is given a fixed time to speak while others listen.

Advantages:

Efficient use of bandwidth.
Suitable for digital communication.

Disadvantages:

Time synchronization is required.
Wasted slots if a device has no data to transmit.

2. Frequency Division Multiple Access (FDMA)

Working Principle:

The available bandwidth is divided into distinct frequency channels.
Each device is assigned a unique frequency channel for communication.

Example:

Radio stations broadcast on different frequencies (e.g., 98.5 MHz, 101.1 MHz) to avoid interference.

Advantages:

Simple to implement.
No need for synchronization.

Disadvantages:

Requires a large frequency spectrum.
Limited scalability due to fixed channel allocation.

3. Code Division Multiple Access (CDMA)

Working Principle:

All devices share the same frequency and time but use unique codes to distinguish their signals.
Each station encodes its data with a specific code, and the receiver decodes it using the same code.

Example:

In a crowded room, multiple conversations happen simultaneously, but you focus only on the person speaking your “code” (language).

Advantages:

Efficient frequency reuse.
Supports many users simultaneously.

Disadvantages:

Complex coding and decoding processes.
Requires precise power control.
Advantages
→ Station sends code to the user and checks the code as a receiver that is connected to the station, then the frequency will match (IP)(address).
→ Encode each user code with a unique code.
→ Intended to decode the user code (needs a high frequency).
→ High user capacity.
→ Many users share one frequency.
→ Station broadcasting will never be mixed up (950, 100) with the help of the code (Mismatch) system.
Disadvantage (CDMA) → Complexity in coding and decoding
→ Check whether the connected station is free or not, which is called carrier sense multiple access coding.

4. Carrier Sense Multiple Access (CSMA)

Working Principle:

Devices first check if the channel is free before transmitting data.
If the channel is busy, the device waits for a random time before retrying.

Example:

Like waiting for a pause in a conversation before speaking to avoid interrupting others.

Advantages:

Reduces collisions in shared channels.
Simple and widely used in Ethernet networks.

Disadvantages:

Collisions can still occur if two devices transmit simultaneously.
Inefficient in high-traffic scenarios.

5. Space Division Multiple Access (SDMA)

Working Principle:

Uses spatial separation to allow multiple devices to communicate simultaneously.
Achieved through directional antennas or beamforming.

Example:

A router serving multiple devices in different rooms by directing signals spatially.

Advantages:

Increases capacity by reusing space.
Reduces interference.

Disadvantages:

Requires advanced antenna technology.
Limited by physical space constraints.

Summary Table

Technique	Allocation Method	Example	Advantages	Disadvantages
TDMA	Time slots	Conference call turns	Efficient bandwidth use	Wasted slots, sync needed
FDMA	Frequency channels	Radio stations	Simple, no sync	Large spectrum required
CDMA	Unique codes	Crowded room conversations	High capacity, frequency reuse	Complex coding
CSMA	Listen before transmit	Waiting to speak in a group	Reduces collisions	Collisions possible
SDMA	Spatial separation	Router serving multiple devices	Space reuse, less interference	Needs advanced antennas

Multiple Access Techniques