I can recommend the keynote from this year's S3 student workshop by Kyle Jamieson, "Should I Work on Wireless Networks." There are some recent challenges for mobile wireless networks inside and good advice.
Networking-Finding the Feasible minimal path between Transmitting and Receiving Nodes in Minimum time,Vertical Handover,a combination of the two to decide where to handover to the other provider are a few of the challenging tasks.