FDM vs. TDM

FDM vs. TDM

TDM (Time Division Multiplexing) and FDM (Frequency Division Multiplexing) are two methods of multiplexing multiple signals into a single carrier. Multiplexing is the process of combining multiple signals into one, in such a manner that each individual signal can be retrieved at the destination. Since multiple signals are occupying the channel, they need to share the resource in some manner. The primary difference between FDM and TDM is how they divide the channel. FDM divides the channel into two or more frequency ranges that do not overlap, while TDM divides and allocates certain time periods to each channel in an alternating manner. Due to this fact, we can say that for TDM, each signal uses all of the bandwidth some of the time, while for FDM, each signal uses a small portion of the bandwidth all of the time.

TDM provides greater flexibility and efficiency, by dynamically allocating more time periods to the signals that need more of the bandwidth, while reducing the time periods to those signals that do not need it. FDM lacks this type of flexibility, as it cannot dynamically change the width of the allocated frequency.

The advantage of FDM over TDM is in latency. Latency is the time it takes for the data to reach its destination. As TDM allocates time periods, only one channel can transmit at a given time, and some data would often be delayed, though it’s often only in milliseconds. Since channels in FDM can transmit at any time, their latencies would be much lower compared to TDM. FDM is often used in applications where latency is of utmost priority, such as those that require real-time information.

FDM and TDM are often used in tandem, to create even more channels in a given frequency range. The common practice is to divide the channel with FDM, so that you have a dedicated channel with a smaller frequency range. Each of the FDM channels is then occupied by multiple channels that are multiplexed using TDM. This is what telecoms do to allow a huge number of users to use a certain frequency band.

Summary:

1. FDM divides the channel into multiple, but smaller frequency ranges to accommodate more users, while TDM divides a channel by allocating a time period for each channel.

2. TDM provides much better flexibility compared to FDM.

3. FDM proves much better latency compared to TDM.

4. TDM and FDM can be used in tandem.