while we've been away

[joham]

So that's what you've been up to while we've been away?

This sentence comes from LONGMAN CONTEMPORARY ENGLISH DICTIONARY second edition, (so). I'd like to know why the present perfect tense is used in the two clauses (Grammar books doesn't include this use in a while-clause). Could we simplify the tense without changing the original meaning? Like:
So that's what you've been up to while we were away?

Thank you very much.

(Thank dawoodusmani for pointing out my mistake. It was careless of me to miss out the 'been'.)

 

[Dawood Usmani]

So that's what you've been up to while we've been away?

This sentence comes from LONGMAN CONTEMPORARY ENGLISH DICTIONARY second edition, (so). I'd like to know why the present perfect tense is used in the two clauses (Grammar books doesn't include this use in a while-clause). Could we simplify the tense without changing the original meaning? Like:
So that's what you've up to while we were away?

Thank you very much.

They are both fine. They refer to a period of time up to the present; up to the time of speaking.
Remember:
be up to not have up to
Regards!
Dawood

 

[albertino]

Two actions go in parallel.
have been up to (pp) /while/ have been away(pp).
No problem at all.
(Not a teacher)