Perhaps you should try some spelling variations:
optimization algorithms » optimisation algorithm, estimation algorithms, estimation algorithm
risk approximation » _ approximation, one approximation, rough approximations
time approximation » one approximation, _ approximation
qoe optimization » game optimization, _ optimization, stage optimization

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (( qoe optimization algorithms ) or ( ((risk approximation) OR (time approximation)) algorithms ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( qoe optimization algorithms ) OR ( ((risk approximation) OR (time approximation)) algorithms )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( qoe optimization algorithms ) or ( ((risk approximation) OR (time approximation)) algorithms ))".
• Adding a wildcard symbol may retrieve word variants: (( qoe optimization algorithms ) or ( ((risk approximation) OR (time approximation)) algorithms ))*.