Difference between TDM and FDM

TDM (Time Division Multiplexing) and FDM (Frequency Division Multiplexing) both are multiplexing techniques where TDM is used in both analogue and digital signals. In contrast, FDM is only used in analogue signals. Here we will discuss both TDM and FDM in detail and we will also see the differences between these two.

What is Time Division Multiplexing (TDM)?

TDM (Time Division Multiplexing) is the multiplexing technique. TDM works with digital signals as well as analogue signals. TDM share the timescale for the various signals. Synchronization pulse is important in Time Division Multiplexing. TDM divides the available time on the channel into discrete time slots, and each space is allocated to a different signal or data stream.

In TDM, the data from each input source is interleaved from the transmitting device into the allocated time slots, which basically creates the composite signal for transmission and at the end of receiving, the signal is demultiplexed and is sent back to their respective time slot.

Types of TDM

There are two types of TDM (Time Division Multiplexing) that are discussed below.

• Synchronous Time-Division Multiplexing (STDM)
• Asynchronous Time-Division Multiplexing (ATDM)

1. Synchronous Time-Division Multiplexing (STDM): When all the input sources (signals or data streams) are synchronized and divided into a fixed time slot, then it is called Synchronous Time Division Multiplexing. Here, each time slot is assigned to some specific input source, regardless of whether that source has data to transmit during that time slot.

2. Asynchronous Time-Division Multiplexing (ATDM): When time slots are assigned to input sources dynamically as needed, then it is called Asynchronous Time Division Multiplexing (ATDM). It is more flexible as compared to Synchronous TDM. In the case of transferring data by input source, a time slot has been allocated. This dynamic allocation helps in better utilization of time slots, especially when some input sources have sporadic data transmission.

What is Frequency Division Multiplexing (FDM)?

FDM is the multiplexing technique which is used in analog system. In FDM, Guard band is required and the spectral efficiency of FDM is low. In FDM, Bandwidth(B) is committed to the different sources. Frequency Division Multiplexing (FDM) is mostly used in telecommunications and networking for transmitting multiple signals simultaneously over a single communication channel. FDM is generally used in such scenarios where multiple data streams has to be transmitted simultaneously without interfering with each other.

What is OFDM (Orthogonal Frequency Division Multiplexing)?

Orthogonal FDM is simply a type of digital communication technique that is developed for using in cable system mostly. In the case of wireless communication, OFDM is like as single carrier modulation as frequency division multiple access (FDMA), time-division multiple access (TDMA), and code-division multiple access (CDMA).

Differences Between TDM and FDM