What are the differences between FDMA, TDMA, and CDMA?

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Let us begin by understanding what Frequency-Division Multiplexing FDMA is.


Frequency-Division Multiplexing is an analog technique used when the channel’s bandwidth is larger than the consolidated bandwidths of the signals to be advertised.

In FDM, there are several frequencies that are combined into an individual composite signal and shared on the channel. At the receiver end, the reverse procedure is used to get the single frequencies back for working. The whole bandwidth of the channel is breaked into logical channels, and each sending device is given with the control of a logical channel.

When the signal appears at the receiver in the composite framework, it has to be disconnected into individual signals. This is done by a device referred to as a demultiplexer.


TDM is a digital procedure. In TDM, each sender is given the entire possession of the whole bandwidth of the channel for a constant period of time. After this, the control is transformed to the next sender, and the procedure advances on a round-robin basis.

An example of TDM is the television broadcast. In a television serial, generally, a 10 minutes serial is followed by a 5 minutes advertisement. The time in which the serial is being transmitted. The complete frequency is dedicated to serial.

Variants of TDM

The following variants on TDM are as follows −

  • ATDM (Asynchronous Time Division Multiplexing) − Multiplexing in which the data is shared asynchronously.

  • STDM (Statistical Time Division Multiplexing) − A multiplexing approach that polls nodes and directly skips some nodes with nothing to share.

  • STM (Synchronous Transfer Node) − It is designed for use in BISDN (broadband ISDN) and also provided in the SONET (Asynchronous Optical Network) architecture.


A final form of multiplexing used in parts of the mobile telephone system and for some satellite communication is known as Code Division Multiplexing (CDM). The definite form of CDM used in cell phones is referred to as the Code Division Multi-Access (CDMA).

CDM does not base on physical properties, including frequency or time. It is based on an interesting mathematical idea including values from orthogonal vector spaces that can be joined and separated without interference. The definite form used in the telephone network is simpler to understand. Each sender is created a unique binary code Ci that is called a chip sequence.

The advantage of CDM improves from its ability to scale and because it provides lower delay in a highly used network. Because a sender sends, a TDM multiplexor enables N–1 other senders to send before supporting the first sender with another turn. Thus, if all senders are active, the probable delay among successive connections from a given sender can be high.

Updated on 19-Nov-2021 05:58:13