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.
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