BME 343 - WTF is Signal and System

Signal and Systems is one of the most difficult class I encountered because it’s hard to make physical analogies or visual representations. I’m hoping to be one in a krillion that can think of something to change that.

Very general example

I like to think that a signal is an event and a system modifies the signal in some way. This means that there is an input signal and output signal. We care about this because we want to know the information in the event even when we modify the original signal.

Here’s a more specific and relatable example: Riding a bike

Can you figure out an input signal, output signal, and system with this example? Take a moment to think…

• One input signal is how much force you are pedaling over time f(t)

• One response (output) is how fast you are moving over time v(t)

• The system is the bike itself, because it is modifying the force signal into a velocity signal

How would you show the velocity signal if you pedaled twice as hard because Ryan Reynolds was seen in the BME building?

1. See it as a Physics Problem

We can use a set of differential equations with formulas based on parameters like the gears, initial speed, friction, etc. Though this is based on reality, it is notoriously difficult to use when we want to look at the function as a whole.

2. See it as a System

As shown, we can generalized the system to everything that modifies the signal. Because operations, rules, and identities exist when it comes to signal and systems, we we can just mess with the signal instead of diving into the actual equations.

For example:

If you know this is a linear system, you would also know if you pedaled twice as hard, you will go twice as fast. We don’t need to dive into the nitty gritty physics differential formulas.