FDMA Vs TDMA: Key Differences Explained

multiple access
wireless communication
fdma
tdma
mobile communication

FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access) are both multiple access techniques used for wireless communications in mobile computing devices such as smartphones, tablets, laptops etc. These techniques allow multiple users to share a common communication medium, such as a wireless channel or a wired link.

FDMA divides the available frequency spectrum into multiple non-overlapping channels in which each user is allocated a specific frequency channel for the entire duration of their communication. TDMA divides time into multiple time slots in which each user is allocated specific time slot for their communication.

What is FDMA?

In FDMA scheme, entire frequency spectrum is divided into multiple RF channels or carrier frequencies. Each RF carrier is allocated to different users for entire duration of their communication. Each user’s signal occupies its designated frequency channel without overlapping with other users’ channels. FDMA is commonly used in analog communication systems and early digital systems.

Example:

  • In GSM system, entire frequency band of 25 MHz is divided into 124 RF carriers of 200 KHz bandwidth each.
  • In Satellite communication system, entire transponder band of 500 MHz is divided into 24 channels having 40MHz bandwidth each (36 MHz useful BW, 4MHz guard band).

![FDMA - Frequency Division Multiple Access](../../assets/FDMA-Frequency Division Multiple Access.jpg)

There are two main types of FDMA scheme used in satellite network: SCPC (Single channel per carrier) and MCPC (multiple channel per carrier). MCPC uses FDM or TDM as multiplexing scheme.

Following are the FDMA types:

  • FAMA: The full form is Fixed Assignment Multiple Access. In FAMA, frequencies are pre-allocated to users or subscribers or VSATs.
  • DAMA: The full form is Demand Assignment Multiple Access. In DAMA, frequencies are dynamically allocated based on requests.

What is TDMA?

In TDMA scheme, entire bandwidth is shared among different subscribers at fixed pre-determined or dynamically assigned time intervals (i.e. time slots). TDMA divides time into multiple time slots, and each uses is allocated a specific time slot for their communication. The user take turns to transmit or receive data within their assigned time slots and channel is shared among multiple users by dynamically allocating time resources.

![TDMA - Time Division Multiple Access](../../assets/TDMA-Time Division Multiple Access.jpg)

TDMA uses TDM multiplexing technique. TDMA is widely used in digital communication systems, especially in cellular networks like GSM (2G) and some satellite communication systems. It is suitable for applications where users can share the same frequency band efficiently by utilizing different time slots, allowing more users to be served simultaneously.

Example:

In GSM each RF carrier is used by 8 users at different time slots. Total duration of 4.615 ms frame is divided among 8 time slots having 577 µs each on all the 124 channels. Figure depicts channel number 124.

Let us compare FDMA vs TDMA and mentions the difference between FDMA and TDMA techniques.

ParametersFDMATDMA
Full formFrequency Division Multiple AccessTime Division Multiple Access
PrincipleDivides frequency spectrum into multiple channels, each user is allocated dedicated channel for communication.Divides time span into multiple time slots, each user is allocated dedicated slot for communication.
Resource allocationFrequency based , users are assigned specific frequencies for entire durationTime based, users are assigned specific time slots for duration of communication
Simultaneous communicationPossible using different frequency channelsNot possible, users take turns to communicate on their assigned time slots
InterferenceMore susceptible to interference especially in crowded channel environmentsBetter interference management since users only transmit in their unique dedicated slots reducing likelihood of collision.
SynchronizationUsers need to synchronize to specific assigned frequencyUsers need to synchronize to timing of their assigned slots
System flexibilityMore rigid since each user is tied to specific frequency channelMore flexible as time slots can be allocated dynamically based on demand
Efficiency in handling usersIt becomes less efficient when number of users increases.It is efficient in handling large number of users due to dynamic allocation
Duplex communicationFDMA can operate in either half duplex or full duplexTDMA can operate in full duplex mode
Guard spacingRequires guard bands to separate channelsRequires guard intervals to avoid overlap
Handover complexityMore complex due to different frequency channel assignementsMore straightforward if same time slots are used in neighboring cells
Implementation complexityMore complexLess complex
Resource wastageIt is observed in FDMA systems if some channels remain under-utilized while others are heavily loaded.It is not observed in TDMA as time slots can be allocated dynamically as per demand.
ExamplesAnalog AMPS (Advanced Mobile Phone System), Analog TV broadcastingIS-136 (Digital AMPS), GSM (2G) etc.

Conclusion

FDMA and TDMA techniques enable efficient utilization of the communication medium while allowing multiple users to communicate concurrently. FDMA provides continuous and dedicated access to channels where as TDMA allows users to share the same band by utilizing different time slots. The specific usage of these techniques depend on the requirements and constraints of the wireless communication system being deployed.

Both FDMA and TDMA schemes are used together in satellite communication and cellular mobile communication to offer several advantages, including increased system capacity, reduced interference between users and their ability to support large number of users across a wide coverage area. OFDMA (Orthogonal Frequency Division Multiple Access) utilizes both FDMA and TDMA principles simultaneously. OFDMA is a multi-user communication technique commonly used in modern wireless communication systems, particularly in 4G LTE and 5G cellular networks.

TDMA and FDMA: Advantages and Disadvantages

TDMA and FDMA: Advantages and Disadvantages

Explore the benefits and drawbacks of Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) technologies in wireless communication.

tdma
fdma
wireless communication
FDMA vs FHMA: Understanding the Key Differences

FDMA vs FHMA: Understanding the Key Differences

Explore the distinctions between FDMA and FHMA, two multiple access techniques used in wireless communication. Learn about frequency division and hopping approaches.

frequency division
multiple access
fhma
TDD vs. TDMA: Understanding the Difference

TDD vs. TDMA: Understanding the Difference

Explore the differences between Time Division Duplex (TDD) and Time Division Multiple Access (TDMA) in wireless communication. Learn how they manage frequency and time.

wireless communication
tdd
tdma
Spectral Efficiency: FDMA, TDMA, and CDMA

Spectral Efficiency: FDMA, TDMA, and CDMA

Explore spectral efficiency in wireless communication, comparing FDMA, TDMA, and CDMA techniques for optimizing radio frequency resource utilization.

spectral efficiency
multiple access
fdma
Top 10 Radio Frequency (RF) Applications

Top 10 Radio Frequency (RF) Applications

Explore the diverse applications of radio frequency (RF) technology, from broadcasting and mobile communication to medical imaging and smart home devices.

rf
wireless communication
radio frequency