Simplex, half-duplex and full-duplex systems

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Communication systems can be classified into simplex, half-duplex and full-duplex systems.

Information can be sent in a one-way or a two-way direction in communication systems. When information can only be transmitted in a one-way direction, e.g. in television and radio broadcasting, the system is a simplex system.

Conversely, both you and your friend can talk simultaneously on the telephone. When your friend speaks into the phone, a signal is transmitted from their side to your side. Similarly, when you speak into the phone, a signal is transmitted from your side to their side. Therefore, information is two-way in a telephone system. When it’s possible to send information in both directions, such systems areduplex systems. It is also possible to classify duplex systems into full-duplex and half-duplex systems.

In a full-duplex system, signals can travel in both directions at the same time. A half-duplex system is midway between simplex and full-duplex systems. Information can go in either direction, but only in one direction at a time. A walkie-talkie is an example of this category. When one of the users speaks, the other user must stop speaking until the first user ends their turn and the channel is handed-over to the other user.

Figure 1.2 The timing diagram of the three systems

 

Now, can you identify examples of simplex, full-duplex and half-duplex systems in the real world?