What is the problem of WCDMA?

2 years ago, I did research on adaptive filter in channel equalizer. Nowadays, it seems to me that this field is saturated and seems like there is nothing to do with adaptive filtering in channel equalizer anymore. According to the research papers that I read recently, they tend to move on to 4G.
I am looking for the existing problem of WCDMA? I want to do research on this topic, but don’t know where to start.

Please advice me to some area that can be improved.
Please don’t say I’m not doing homework. I just need the starting point, and I think I can go from there.
Thank you.