Difference Between FDMA, TDMA and CDMA

In communication systems, FDMA, TDMA, and CDMA are three different methods used to share a single communication channel among multiple users. Understanding these methods helps us see how multiple users can efficiently share communication channels without interference.

FDMA (Frequency Division Multiple Access) divides the channel into separate frequency bands for each user. TDMA (Time Division Multiple Access) assigns different time slots to each user on the same frequency. CDMA (Code Division Multiple Access) uses unique codes to differentiate users sharing the same frequency band at the same time. In this article, we are going to discuss the differences between these communication channels in detail.

What is FDMA?

Frequency Division Multiple Access (FDMA): FDMA is a type of channelization protocol. This bandwidth is divided into various frequency bands. Each station is allocated a band to send data and that band is reserved for the particular station for all the time which is as follows.

The frequency bands of different stations are separated by small bands of unused frequency and unused frequency bands are called as guard bands that prevent the interference of stations. It is like the access method in the data link layer in which the data link layer at each station tells its physical layer to make a bandpass signal from the data passed to it. The signal is created in the allocated band and there is no physical multiplexer at the physical layer. 

Advantages of FDMA

• FDMA uses simple hardware resources and is easy to set up.
• It efficiently handles smaller groups of users.
• The system isn't overly complicated.
• All stations can transmit continuously without waiting their turn.
• It lowers the amount of data transmitted, which can increase capacity.
• It reduces interference between symbols, improving communication quality.

Disadvantages of FDMA

• FDMA works only with analog signals.
• It lacks flexibility, so existing traffic patterns must change gradually.
• Transponders need extensive bandwidth.
• It doesn't support high traffic capacity.
• RF filters must meet strict adjacent channel rejection standards, which can increase costs.
• The maximum bit rate per channel is small and remains fixed.

What is TDMA?

Time Division Multiple Access (TDMA) : TDMA is the channelization protocol in which bandwidth of channel is divided into various stations on the time basis. There is a time slot given to each station, the station can transmit data during that time slot only which is as follows.

Each station must aware of its beginning of time slot and the location of the time slot. TDMA requires synchronization between different stations. It is type of access method in the data link layer. At each station data link layer tells the station to use the allocated time slot. 

Advantages of TDMA

• As cell sizes decrease, TDMA requires substantial investment in space, support, and base-station hardware.
• It can transmit data at speeds ranging from 64 kbps to 120 Mbps.
• TDMA separates users based on time, ensuring no interference from simultaneous transmissions.
• It supports services like fax, voiceband data, SMS, multimedia applications, and video conferencing.
• TDMA extends battery life by allowing devices to transmit only part of the time during conversations.
• It effectively handles both data transmission and voice communication needs.

Disadvantages of TDMA

• If all time slots in the current cell and the next cell are occupied, users allocated specific slots may not connect to a call.
• Frequency/slot allocation in TDMA can be complex.
• High data rates in TDMA require equalization.
• Network and spectrum planning in TDMA is complex and time-consuming, needing expertise and resources.
• TDMA focuses on organization and range planning.

What is CDMA?

Code Division Multiple Access (CDMA) : In CDMA, all the stations can transmit data simultaneously. It allows each station to transmit data over the entire frequency all the time. Multiple simultaneous transmissions are separated by unique code sequence. Each user is assigned with a unique code sequence.

In the above figure, there are 4 stations marked as 1, 2, 3 and 4. Data assigned with respective stations as d₁, d₂, d₃ and d₄ and the code assigned with respective stations as c₁, c₂, c₃ and c₄. 

Advantages of CDMA

• CDMA has a very high spectral capacity, supporting many users within a wide bandwidth.
• It doesn't require synchronization between users.
• CDMA channels are hard to decode, improving cellular communication security.
• It provides better secure transmission capabilities.
• Dropouts only occur when the user is twice the distance from the base station.

Disadvantages of CDMA

• CDMA faces channel pollution when a user's phone connects to multiple cell sites, but only one has strong signal.
• CDMA isn't as mature as GSM, since it's newer.
• CDMA requires time synchronization.
• Performance of the CDMA system decreases as the number of users increases.
• CDMA equipment tends to be more expensive due to its complexity.

Difference Between FDMA, CDMA and TDMA

Conclusion

In conclusion, FDMA, TDMA, and CDMA are different methods to allow multiple users to share the same communication channel without interference: FDMA divides the channel into different frequency bands for each user. TDMA assigns different time slots to each user on the same frequency. CDMA uses unique codes to differentiate users sharing the same frequency band at the same time. Each method has its strengths and weaknesses, and the choice of method depends on the specific needs and constraints of the communication system. Understanding these methods helps us appreciate how multiple users can communicate efficiently and effectively.