What Is The Key Difference Between TDMA, FDMA, and CDMA?

The key difference between TDMA, FDMA, and CDMA lies in the way they allocate and utilize the available bandwidth. TDMA divides the channel into time slots, allowing multiple users to transmit signals sequentially. Meanwhile, FDMA assigns unique frequency channels/bands to each user, enabling simultaneous transmission by different users on separate frequencies. Conversely, CDMA utilizes unique code sequences to differentiate between users, allowing multiple users to transmit over the same frequency band simultaneously.

In this article, we will explore the difference between TDMA, FDMA, and CDMA in depth. But before we move further, let's explore the topics we will cover in this article. 

Table of Contents (TOC)

• Difference Between TDMA, FDMA, and CDMA
• What is TDMA?
• What is FDMA?
• What is CDMA?
• Key Differences Between TDMA, FDMA, and CDMA

Difference Between TDMA, FDMA, and CDMA

For better clarity, let's explore the difference between FDMA, TDMA, and CDMA in a tabular format.

Characteristic	TDMA	FDMA	CDMA
Resource Sharing	Time slots on the same frequency channel	Different frequency channels	Unique code sequences on the same frequency channel
User Access	Users take turns transmitting in their assigned time slots	Users transmit simultaneously on different frequency bands	Users transmit simultaneously on the same frequency channel
Channel Usage	One user at a time on the entire frequency channel	Each user uses a portion of the total bandwidth	All users share the entire frequency channel
Bandwidth Efficiency	Moderate efficiency, as only one user can transmit at a time	Low efficiency due to the fixed allocation of frequency channels	High efficiency, as multiple users can transmit simultaneously
Synchronization	Requires precise time synchronization between transmitters and receivers	No synchronization required	Requires code synchronization between transmitters and receivers
Signal Separation	Time slots separate users' signals	Different frequencies separate users' signals	Unique codes separate users' signals
Interference	Inter-symbol interference due to multipath propagation	Adjacent channel interference due to imperfect filtering	Near-far problem due to different signal strengths
Applications	GSM (2G), DECT cordless phones, satellite communications	Analog TV broadcasting, early mobile communications	CDMA2000 (3G), WCDMA (3G), LTE (4G)
Complexity	Moderate complexity	Simple implementation	Complex implementation due to code management and synchronization
Power Control	Required for efficient operation	Not required	Strict power control required to mitigate near-far problem
Handoff	Hard handoff between time slots or frequencies	Hard handoff between frequencies	Soft handoff between cells due to code sharing
Voice/Data Support	Suitable for voice and low-rate data	Suitable for voice and low-rate data	Suitable for voice and high-rate data
Scalability	Limited by the number of time slots	Limited by the available frequency spectrum	More scalable due to code reuse in different cells
Security	Moderate security due to time slot allocation	Low security as frequencies are publicly known	Higher security due to unique code sequences
Quality of Service (QoS)	Variable QoS depending on channel conditions	Fixed QoS based on allocated bandwidth	Adaptive QoS based on code management and power control

What is TDMA?

In TDMA (Time Division Multiple Access), the same radio frequency channel is shared among multiple users by dividing the signal into different time slots. Each user is assigned a periodic time slot during which they can transmit data. Users take turns transmitting one after the other, each using the entire frequency channel for a short burst of time.

What is FDMA?

In FDMA (Frequency Division Multiple Access), the available bandwidth is divided into separate frequency channels, and each user is assigned a unique frequency channel or a portion of the total bandwidth. Users transmit simultaneously but on different frequency bands, allowing parallel data transmission.

What is CDMA?

In CDMA (Code Division Multiple Access), all users simultaneously share the same frequency channel. Each user is assigned a unique code sequence that encodes their data before transmission. The encoded data signals from different users are superimposed on the same channel, and they can be separated at the receiver end by correlating the received signal with the unique code sequence assigned to each user.

Key Differences Between TDMA, FDMA, and CDMA

Here are the key differences:

• In TDMA, users share the same frequency channel by taking turns transmitting in their assigned time slots. Meanwhile, in FDMA, users transmit simultaneously on different frequency bands, each occupying a portion of the available bandwidth. On the other hand, in CDMA, all users share the same frequency channel simultaneously by using unique code sequences to separate their signals.
• TDMA exhibits moderate bandwidth efficiency, as only one user can transmit simultaneously on the entire frequency channel. On the other hand, FDMA has relatively low bandwidth efficiency due to the fixed allocation of frequency channels. CDMA, however, offers high bandwidth efficiency by allowing multiple users to transmit simultaneously on the same frequency channel.
• In TDMA, inter-symbol interference can occur due to multipath propagation. Meanwhile, FDMA suffers from adjacent channel interference caused by imperfect filtering. Whereas in CDMA, the near-far problem, arising from different signal strengths, needs to be addressed through strict power control.
• TDMA is commonly used in systems like GSM (2G), DECT cordless phones, and satellite communications, and it is suitable for voice and low-rate data. FDMA was employed in early mobile communications and analog TV broadcasting, and it is also suitable for voice and low-rate data. CDMA is widely used in 3G and 4G networks (CDMA2000, WCDMA, LTE), and it is capable of supporting voice and high-rate data services.

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Conclusion

Here are the key points to take note of:

• TDMA separates users by time slots on the same frequency.
• FDMA separates users by different frequency channels.
• CDMA separates users by unique code sequences on the same frequency.

CDMA is considered more efficient in utilizing the available bandwidth than TDMA and FDMA, as it allows multiple users to transmit simultaneously on the same frequency channel.

If you are interested in learning about such topics and techniques, you can take the Foundations of Advanced Wireless Communication, Fundamentals Of Wireless Communication, CCNA Wireless, or Fundamentals of Wireless Communication for Telecom Engineers using MATLAB, courses.