Frequential techniques of noise reduction

Archived from groups: rec.audio.tech (More info?)

A common problem in mobile communications is conversating in noisy
places (cars, bars, etc).
To get audible this kind of conversation exist many *frequential
techniques of noise reduction*.
For my university I have to find out the most common techniques and
code in Matlab at least 2. I don't have any
idea on the subject and on the possible solutions. What can I do? Do
you can suggest to me some sort of
internet articles or books?

Thank you in advance