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Difference Between FDM and FDMA

fdma_bookFDM vs. FDMA

Frequency Division Multiplexing, or FDM, is a multiplexing technique for the physical layer that allows multiple low bandwidth signals to share the same high bandwidth frequency range. It is achieved by allocating a smaller frequency range to each signal that is using the same channel. FDMA stands for Frequency Division Multiple Access, a technology commonly used in mobile communications. It’s an access method for the data link layer, that uses the concepts of FDM to basically achieve the same goal. It is popular knowledge that FDMA is the use of FDM to enable multiple users to share the same physical channel for concurrent communication.

For further details, FDM is a technique that is used in many other technologies. A multiplexer modulates all the signals that is going to use the channel into a single signal. FDMA foregoes the use of a multiplexer, since it acts on the data link layer. All the information is combined prior to generating a signal, making the use of a physical layer multiplexer unnecessary.

The need for multiplexing is very prominent in mobile phone networks, where you have a limited number of channels that have a huge amount bandwidth. Each mobile phone user only needs very minimal bandwidth, and they are stacked together into the same channel with the use of multiplexing technologies like FDMA. Aside from FDMA, which divides the frequency range into smaller channels, there are also other technologies at work in mobile phone networks. TDMA is one such technology, and it divides each channel into time slots that can be occupied by different users.

The use of FDM, or FDMA alone, is quite inefficient, as it still dedicates the entire channel allocated to the signal. Even when there is no information that is being sent across the medium, no one can utilize the channel that is being used. Mobile networks use both FDMA and TDMA to maximize the number of users that can use the network. The main channel is divided into smaller sub channels using FDMA. Each sub channel is then divided with the use of TDMA to let multiple users use the channel in an alternating manner. This happens so fast that end users do not know that this is happening.

Summary:

1. FDM is a physical layer multiplexing technique, while FDMA is a data link layer access method.

2. Using FDM to allow multiple users to utilize the same bandwidth is called FDMA.

3. FDM uses a physical multiplexer, while FDMA does not.


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