What Is Frequency-Division Multiplexing (FDM)?

If you've ever been to a party where everyone is talking to each other, and you can't understand what in the world is going on. Simply the party had too many people talking at once. Then you know what frequency-division multiplexing is like. The basic idea behind frequency-division multiplexing (FDM) is that many signals are combined onto a shared medium. Each movement is then transmitted at a different frequency so they don't interfere with each other. The most helpful way to visualize this is to think about how many people can talk in the same room without anyone else hearing them. You can have one person talking in the corner of the room, two talking near each other on opposite sides of the room, three talking near each other in separate corners of the room, four talking together in one spot and so on. Each group of speakers has its frequency range within which it can operate without interfering. This same principle applies to FDM: multiple data streams are transmitted over a shared medium using different carrier frequencies so they don't interfere. When FDM allows numerous users to share a single physical communications medium (i.e., not broadcast through the air), the technology is called frequency-division multiple access (FDMA). This can be confusing because the "F" part of FDM stands for "frequency." this is only because it's convenient to do so: technically speaking, FDMA uses time slots instead of frequencies. Since you have multiple people sharing a single medium, each person gets their time slot, similar to how you might share a parking spot by taking turns with your neighbors while at work. Everyone must know when their time slot starts and ends to avoid overlapping with other people's time slots.