Difference Between FDM and TDM (With Table)

FDM is a Frequency Division Multiplexing that shares the frequency available for the signals. It works with analog signals and has complex circuitry. It is made of complex chips or wiring. This technique requires a guard band and has a very high level of interference. FDM has low spectral efficiency and higher conflict.

TDM is a Time Division Multiplexing that shares the timescale available for the signals. It works with both analog signals and digital signals. It has very simple circuitry. It is made up of simple chips or wiring. It requires a synchronization phase and has a low level of interference. TDM has two types of timescale signals and they are synchronous TDM and asynchronous TDM.

Comparison Table Between FDM And TDM

What is FDM?

FDM is the acronym of Frequency Division Multiplexing. It is an analog technique that is used for analog signals only. It is used when the bandwidth of the link is higher than that of the bandwidth of the signals that are to be transmitted. Carrier frequencies are used to modulate the signals from the donor devices. They are isolated with adequate bandwidth to modulate the signals.

FDM uses the signals and transfers them into one single compound of the signal by the link. The signals transferred travel through the channel. FDM also controls signals overlapping. The signal overlapping is controlled by the unutilized bandwidth strips that are used for segregating the channels. They are known as Guard Bands which are very essential and are prerequisites for the FDM technique.

FDM deals only with analog signals and has a complex circuitry system. They are made up of complex chips and wiring. It also has a very high level of interference. There should not be any overlapping of carrier frequencies with the original frequencies that leads to a failure condition where the original signals cannot be recovered from the system.

FDM involves the distribution of frequencies with the respective bandwidths. Guard Bands are used to separate the signals and prevent the overlapping of various signals. They also require different bandpass filters to help in doing the mechanism. It divides the link into multiple channels which is not in the case of other multiplexing techniques that make it less efficient than others.

What is TDM?

TDM is an acronym of Time Division Multiplexing that is used in sharing the timescale to both analog and digital signals as well. This technique is used when the transmission rate quantity is higher when compared to the rate of transmitting and receiving signals devices. the signals are transmitted from different sources that require a synchronization pulse.

TDM has different frames that consist of different sets of time slots to which the time slot is assigned to different frames. There are two different types of TDM. The first one would be the Synchronous Time Division Multiplexing that assigns the time slot individually to the device that either sends or not sends the signals. If there is no signal sent the time slot would be empty.

TDM uses Framing Bits to synchronize at the beginning of each time frame. Bit stuffing is a mechanism used to equalize the speed between the devices that appends into the source system. The Synchronous Time Division Multiplexing uses interleaving between the frames where one can take the data units at a particular time from each device.

TDM has a second type called Asynchronous Time Division Multiplexing that makes use of the unused space that is wasted in Synchronous Time Division Multiplexing. Asynchronous means were flexible and not fixed where several low-rate input lines are multiplexed into a single line of the frame. The number of slots is less than the number of data lines in ATDM.

Main Differences Between FDM And TDM

1. FDM is called Frequency Division Multiplexing that shares the frequencies through channels divided into various bandwidths, whereas TDM is called Time Division Multiplexing that shares the timescale through various time slots for the signals.
2. FDM uses only analog signals and has complex chips and wiring whereas TDM uses both analog signals and digital signals and has simple chip and wiring in it.
3. FDM uses guard bands to separate the signals and prevent overlapping whereas TDM uses Framing Bits or synchronous pulse to trigger the synchronization mechanisms.
4. FDM is less efficient as it manually divides the link into multiple channels that have empty spaces as well which makes it less efficient, whereas TDM is more efficient as it properly utilizes the physical link.
5. FDM has a non-linear character in its distortion as it has various amplifiers and has a high level of interference whereas TDM has a low level of interference as it has separate time slots for individual signals.

Conclusion

FDM and TDM are two kinds of multiplexing techniques that are used in transmitting various signals over a single data linked to it. FDM shares its frequencies and used only analog signals, whereas TDM shares the timescale and uses both the analog signals as well as the digital signals. FDM is less efficient in terms of its mechanism when compared to the TDM techniques.

FDM and TDM have prerequisites for their mechanism. FDM requires guard bands to separate it from other signals received and also prevents the overlapping of the signals. TDM requires a Synchronous pulse to enhance the mechanism. FDM has complex wiring and chips of which it is made of whereas TDM has simple wiring and chips made of.

References

1. https://ieeexplore.ieee.org/abstract/document/1092391/
2. https://ieeexplore.ieee.org/abstract/document/923482/