In the context of mobile communication, one of the hottest topics is video coding for mobile phones using H.264/AVC. Many papers and books on H.264 are available on the DSP forum at Edaboard.
uwb signalling
COGNITIVE RADIO
TDD CDMA are some good areas of research speacially the first on if u r interested in antena theory. It finds good applns even in the industry
MIMO&OFDM and STC are new research area. you can find good topics in this area by studing some paper about it.
decreasing peek to average in OFDM
soft STC
channel equalization in MIMO antenna
You can work on Interleave Division Multiple Access. It is a technology a step ahead of CDMA. You can ask for papers on edaboard or search it on EDABOARD itself.