You can focus on comparative analysis of two or more different technology. For example Performance analysis between VANET and MANET, Wireless Vs Wired Networks, 3G and 4G technology, etc. However, you can go beyond this if you wanted to have an intensive research.
If you do not intend to work on Linux, and are looking for an option to do your thesis based on research works in the field of networking (done on Windows), then I might suggest you to have a look on the Opportunistic Network Environment (ONE) Simulator based on Java programming language, which can be used in Windows. The ONE simulator is capable of simulating delay-tolerant routing protocols (also known as DTN routing protocols). If you are interested, you may like to visit the project page of the ONE simulator, which is as follows: https://www.netlab.tkk.fi/tutkimus/dtn/theone/. Otherwise, to avoid programming, you might opt for doing research on some theoretical topics, as suggested by others, such as, topics related to Software Engineering, System Analysis and Design, etc. Take care.