Full-duplex | Half-duplex | Simplex
Communication systems are point-to-point systems, where two devices or groups / parties are connected.
Some devices can communicate in both directions, simultaneously. These two paths or channels can transmit audio or data
Full-duplex systems can also be employed in communication / control networks to allow two-way communication or to use the reverse path for monitoring or remote control of field equipment.
If the devices don’t establish their communication paths simultaneously but in a competing way, then we speak of half-duplex connections or links.
Some systems do not need full- or half-duplex capabilities and use simplex communication instead. The source sends and the target just receives the data / audio (speak / listen).
Examples for simplex communication are: broadcast radio or wireless microphones.
But simplex communication philosophy won’t be our story today…
Full-duplex (FDX)
A full-duplex system allows communication in two directions, different to others, it happens simultaneously. Normal telephones are full-duplex devices, since they allow both subscribers to listen and speak at the same time.
In industrial communication systems often handsets are used for full-duplex voice transmission, due to the high ambient noise and the risk of acoustic feedback.
Also station-to-station connections in full-duplex mode are possible and used in industrial environments. Feedback suppressors, DSPs and echo cancellers are techniques to get adequate results of full-duplex performance.
But remember: Harsh environment conditions and high ambient noise can destroy your plan to use full-duplex due to the ‘Unwanted Effects’.
Full-duplex and the ‘Unwanted Effects’
Acoustic feedback
Acoustic feedback is an unwanted effect that causes the system to override with a constant tone. Everybody has already heard this effect on pop or rock concerts.
The reason is that the output from speaker is fed into the microphone, then amplified and finally fed again into microphone with an increased volume level and so on. This effect has to be suppressed, because the intelligibility goes to zero.
Acoustic feedback suppression can be done mechanically and / or electrically.
Echo
An Echo is an effect that let you hear yourself with a certain delay. It is very disturbing while you speak and get you rather confused. The reason of that effect is that the return (listen) line is fed from the far end and comes back with a delay.
This effect should also be removed? – Of course it should!
These aspects above make it worth to have an eye on…
Half-duplex (HDX)
A half-duplex system also enables communication in both directions, but not simultaneously. This means only one direction is used at a time. Examples are a walkie-talkie or push-to-talk communication stations.
Push-to-talk is a good synonym for half-duplex voice communication: Push button to talk, release to listen. This is a common procedure in industrial communication systems due to the demands of process communication mainly in the steel industry or on water treatment plants.
Who is the winner?
For industrial applications with their very special and acoustically difficult surroundings with high ambient noise you will not find the ‘One and Only Solution’.
Depending on the working environment and demands, a half-duplex connection can be the medium of choice, due to a disciplined communication style (push-to-talk, release-to-listen).
For other applications, a full-duplex connection is the only way to go – e.g. if a worker has no hands free for a push-to-talk operation or in terms of telephone conversations when you want to communicate ‘In Private’.
