Full duplex vs half duplex over RF

[Token]

Perhaps where we should go with this is to define half or partial duplex, duplex, and "full duplex". In some regard, the specific meaning is subjective. One of the dictionary definitions of duplex is having two parts. I lived in an apartment duplex once. A repeater fits that definition.

Does use of the term HAVE to imply two way simultaneous end-to-end communication? My opinion is no, it does not. It's contextual... In other words, a repeater is a transceiver. Most transceivers work in one direction at a time, but a repeater obviously transmits and receives simultaneously. It's duplex, even if the overall end-to-end communication is not. Take that same piece of hardware down and replace the repeater circuitry with a speaker and a microphone, and it can participate in full duplex communication, by YOUR definition.

The definitions I was weaned on are:

Simplex- tx and rx on a single frequency.
Half duplex - Tx and Rx on different frequencies.
Full duplex - Tx and Rx on different frequencies at the same time.

And a full duplex piece of hardware is separate from full duplex communications.

And there is a basic difference. While I pretty much got the same teaching of definitions for RF applications there is one difference. Full Duplex must be capable of bidirectional and simultaneous communications.

If you leave RF out of it, don’t use the term frequencies at all, then it becomes, for me, a bit easier to see.

Simplex – one path of data flow, any direction but only one direction at a time.

Half duplex – regardless of number of paths of data flow, only one node/station can transfer data at a time.

Full duplex – either multiple physical or multiple virtual paths of data flow, and both (all) nodes / stations can simultaneously transfer data.

And yes, a full duplex piece of hardware is separate from a full duplex system. In fact you can build a full duplex system without a single piece of full duplex hardware involved.

T!

 

[Token]

It gets back to my point that "duplex" is subjective, and there are vartying degrees. A transmitter- receiver pair configured to allow simultaneous non-interfering operation is, in my opinion, a duplex device, regardless of the usage within the rest of the network.

You asked for our thoughts on the subject. Those are mine. =)

Yep, and I am not trying to argue or convince anyone else of anything, only to get my head around why some people describe a traditional FM repeater as full duplex, when by my training it clearly, to me, is not. In fact I pretty vividly remember an instructor using that exact scenario to define what was missing for it to be a full duplex piece of hardware.

To me this is an interesting twist. Normally in the field of electronics there are very clearly defined standards and descriptions (although varying applications), interface control documents or definitions that clearly state something is or something is not. In this case that does not quite seem to be the case. And I can absolutely see why people claiming this type of repeater is full duplex do say so, it just does not fit what I was taught 40 years ago.

T!

 

[zz0468]

If you leave RF out of it, don’t use the term frequencies at all, then it becomes, for me, a bit easier to see.

Yes, but your first post on the subject specifically stated that you wished to discuss in terms of radio.

Clearly, the topic is a bit too complex to contain to one set of scenarios. You can have full duplex RF, but a one way audio path, such as with a repeater. So, in defining what "duplex" means, one needs to specify whether it's the RF, the audio path, or the entire system.

The term can be applied to any and all of the above and if one tries to constrain the definition that applies to, say audio, to the RF side of things, one is going to be wrong right out of the gate, neverminding the rest of the arguments.

duplex [doo-pleks, dyoo-pleks] adjective

1. having two parts; double; twofold.


2.(of a machine) having two identical working units, operating together or independently, in a single framework or assembly.


3.pertaining to or noting a telecommunications system, as most telephone systems, permitting the simultaneous transmission of two messages in opposite directions over one channel.

It seems you're trying to reduce the topic to the third definition only and, while I get your point, I think the other definitions have equal merit where they apply.

 

[Token]

Yes, but your first post on the subject specifically stated that you wished to discuss in terms of radio.

Clearly, the topic is a bit too complex to contain to one set of scenarios. You can have full duplex RF, but a one way audio path, such as with a repeater. So, in defining what "duplex" means, one needs to specify whether it's the RF, the audio path, or the entire system.

The term can be applied to any and all of the above and if one tries to constrain the definition that applies to, say audio, to the RF side of things, one is going to be wrong right out of the gate, neverminding the rest of the arguments.

When I said "leave RF out of it" I only meant leaving the words out of the description, not the concept. The RF is still the carrier, much like a conductor would be.

T!

 

[zz0468]

When I said "leave RF out of it" I only meant leaving the words out of the description, not the concept. The RF is still the carrier, much like a conductor would be.

I think I know what you mean, your concept of "duplex" being the audio path over an RF carrier.

My point is simply that the definition of "duplex" in terms of radio goes beyond what the two-way audio path is capable of doing, and it's all context dependent.

Anyway, it's been an interesting thread. Hopefully we all learned something from it.

 

[Token]

duplex [doo-pleks, dyoo-pleks] adjective

1. having two parts; double; twofold.


2.(of a machine) having two identical working units, operating together or independently, in a single framework or assembly.


3.pertaining to or noting a telecommunications system, as most telephone systems, permitting the simultaneous transmission of two messages in opposite directions over one channel.

It seems you're trying to reduce the topic to the third definition only and, while I get your point, I think the other definitions have equal merit where they apply.

I was trying to stay with the definitions as found in most electronic references that I have seen, since those are typically the most common places you find "half" and "full" duplex broken out from just "duplex".

Such as:

"Reference Data for Radio Engineers", 6th edition, defines full duplex as “Full Duplex: A type of operation that permits simultaneous communication in both directions between the called and the calling parties.”


"IEEE Standard Dictionary of Electrical and Electronics Terms", Third Edition. Defines full duplex as "Full Duplex (telecommunications). Method of operation where each end can simultaneously transmit and receive. Note: Refers to a communications system or equipment capable of transmission simultaneously in two directions."

If you don't stay to these types / sources of definitions then the range of what is "duplex" opens up considerably, as you have said. The non-telecommunications definition of duplex does indeed have merit, but when trying to define a communications device as either half or full duplex I am not really sure it is the way to go.

However, by the last 2 of the 3 definitions you posted I still would not call a repeater a full duplex device. And the first one is rather sweeping.

The stand alone FM repeater typically does not have "two identical working units, operating together or independently, in a single framework or assembly". It has two dissimilar working units, the RX and the TX, working together.

The stand alone FM repeater typically does not have the ability of "permitting the simultaneous transmission of two messages in opposite directions over one channel". It can support one message at a time, whichever one captures the receiver and is transferred to the transmitter. That one message does go in opposite (two) directions.

Of course, if you add console, land line, or additional RF channel inputs you may be able to support multiple messages and directions at one time, but that is not the kind of repeater I was talking about. That was introduced to the thread by others. Early on in the thread I defined what I meant by a traditional FM repeater, an FM receiver demodulates the audio to baseband, then the baseband audio is applied to an FM transmitter and some kind of control signal keys the transmitter while an appropriate or desired signal is in the receiver.

But it appears a number of people define full duplex as the simple ability to receive (take a signal in) while simultaneously transmitting (putting that signal out). And the IEEE definition (and others I have seen) I posted arguably says that in its first part when that part is taken alone. By such a definition the traditional FM repeater would be full duplex. But when does that definition stop applying? Would a mixer be a full duplex device, since it takes a signal in on F1 and simultaneously puts it out on F2?

And yeah, I think it has been an interesting thread, and glad it has not devolved into confrontation. I know on my part, even if I do not necessarily agree with someone's definition I am still interested in hearing it, and why they think it.

T!

 

[biomedbob]

I hate to jump in where I can't quote definitiions, but I know how half and full duplex worked in the past.

I owned a network of ship to shore Public Correspondence stations. Cruise vessels would communicate on full duplex with landline stations.

Smaller vessels, the casual boaters, had a VHF radio which had a ppt operation. That is what I called half duplex.

The same was true for my RCC licenses. Cheap customers, ppt, the rich had full duplex. (This was in Palm Beach,Florida.

All of this led to the cell phones which are full duplex.

kf4br

 

[majoco]

All of this led to the cell phones which are full duplex.

I though we'd already decided that cell phones aren't full duplex as the receiver is muted when you are talking, perhaps VOX? Old style telephones with wires are full duplex thanks to hybrid line transformers.

 

[mikepdx]

Let's argue the definition of 'simplex' next.
That ought to be good for another forty-some replies....:roll:

 

[jackj]

Now that you guys have defined "Duplex" you need to work on defining "Full" and "Half". Then you can work on "Simplex".

 

[Raccon]

Simultaneous transmitting and receiving is only part of the requirement for full duplex, the other part is to be capable of multiple parties simultaneously (can't communicate with a party of one).

Full-duplex refers to communication where a user is able to listen and talk simultaenously, regardless of how many parties are involved. To achieve this it requires transmitting and receiving at the same time, on the RF path as well as the lines between base station, switching infrastructure and dispatch station etc.

In TETRA for example it's possible that the radio uses full-duplex while the dispatcher does not - the dispatcher would need to PTT when he wants to talk and cannot listen at the same time while the radio user can listen and talk at the same time, just like using a cell phone (although the dispatcher would not hear him when he talks).
The system would (only) allocate "full-duplex resources" for the radio and semi-duplex for the dispatcher.

Full duplex is like cell phones or even the old IMTS VHF/UHF mobile phone system. Both base station and mobiles require duplexers to have a true duplex system.

A base station may have different antennas for transmitting and receiving and thus can do without a duplexer. Same would be technically possible for the mobile station but not necessarily practical.