In **Bitcoin proof-of-work**, the **difficulty** of Proof-of-Work is estimated and calculated based on total **hashing power** of the participants. If total hashing power of the participants is higher, then PoW is more difficult.

- If we use a **Memory-Hard-Proof-of-Work** scheme, the difficulty of Proof-of-Work is still estimated based on the **hashing power** ? OR based on the **size of memory** ?

- In other word, **is it feasible** to design a **Memory-Hard-Proof-of-Work** scheme in which we could estimate the Pow difficulty **based on the size of memory**, **instead of hashing power** of participants ?

- Has such a Memory-Hard-Proof-of-Work scheme **designed yet** by which we could estimate the difficulty based on **memory size**?

Just as an example: a Memory-Hardened Proof-of-Work Scheme: https://eprint.iacr.org/2017/1168.pdf

**P.S. 1:** Related question: https://crypto.stackexchange.com/q/29890/68724

**P.S. 2:** If you need any further complementary explanation about the question, please let me know.