In Simulink, the concept of accessing a future signal value (sometimes called "prediction" or "signal preview") is fundamentally different from delaying a signal. The Unit Delay block and similar blocks (like Delay, Transport Delay, etc.) can only access past or current values, not future ones, because Simulink executes models in a time-stepped, causal manner.
If you want to simulate a "future" value in Simulink, here are some approaches:
- For Known Signals (e.g., Step block): If the signal is deterministic (Step, Sine, Pulse, etc.), its future trajectory is fully defined. You can just tap that signal directly wherever you need it — there’s no need to "preview" it, since Simulink already knows its complete behavior.Example: If you want the value of a Step at "t+1", just place another Step block configured to switch one second earlier.
- Advancing a signal (negative delay): Simulink does not allow negative delays, since that’s non-causal. For offline simulation, you can pre-shift your signal in MATLAB before passing it to Simulink:
- Prediction / Model-based estimation: If the signal is not predetermined, then the only way to “see the future” is to predict it. This is exactly what Model Predictive Control (MPC) and forecasting algorithms do: they build an internal model and compute expected future values.
So basically, You cannot access a future value during simulation. If the signal is known in advance (Step, predefined waveform), you can just generate it ahead of time. If not, you must implement a predictor.
I hope this resolves your query.
