Single channel full duplex RF comms, is that possible?

Hi, all the systems I am aware of, at least for voice coms, use two channels if full duplex is to be done.
Is there any system, or way, that uses a single channel for full duplex?
Obviously some kind of slicing must be employed.

https://en.wikipedia.org/wiki/TD-SCDMA

I was wondering if these DMR (digital two-way radios) use time division multiplexing as well or just two channels.
I think they use just two channels or one channel with double the bandwidth (i.e two channels).
What about GSM?

According to wiki, dmr uses tdma. Gsm uses two bands. Basically you can either split your channel in time, frequency, or code. None of them allow you to get two-way comms for the price of one...

"Time division multiple access (TDMA) is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots"

So DMR does use one channel for both users that are talking, as well as the GSM?

Yup, my mistake. I wrote code too which is also a multiple access technique...

As i recall GSM uses one band for uplink to the basestation and one band for downlink.