A signal with one mode or with three or more modes
The term "Discrete" uses to describe a signal with two modes, but is there a term to describe a signal with just one mode or with three or more modes?
Question update: Also, isn't a wave with just one mode named a carrier wave?
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A "discrete" signal can only have a one of a fixed number of values, rather than a continuous value like real numbers. If that fixed number is two then we say that we have a binary system, or a binary signal. It is convenient to describe these states as 0 and 1, but we could also call them "on" and "off" or "true" and "false".
It is possible to have three distinct logic values. Such a system or signal is referred to as being ternary. Computing systems using ternary logic have been built but binary systems are clearly dominant today.
In communications systems it is possible to define many more "states", or discrete values, that can be transmitted. These are usually called "symbols" and systems with 16 or more discrete states are common.
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with just one mode
Others have already explained that "discrete" means a finite set of values, not just two.
This is to point out that having just one "mode" (it seems you mean symbol) doesn't make any sense. A signal that can only ever be in one value is no signal at all since it can't carry any information. At a minimum, any "signal" needs to have at least two distinguishable states.
If there is no choice in what a signal can tell you, then any receiver can just substitute the signal value with a constant locally.
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The term "Discrete" uses to describe a signal with two modes.
Wrong. Discrete means it can only take some values , not all values.
I suspect by 'modes' you mean # of possible outputs. If we have a system which outputs only have 1 possible output then what would be the point of that system?
Sure we can make a system which has 3 possible outputs , I think this kind of system already exists in spintronics where not only do we measure the charge state but also the spin state. So we can have 3 different states[no charge state,charge state/spin up,charge state/spin down]
Hope this helps.
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