Last week I read Learning OMNeT++ , the book is published by Packt Publishing which is about popular network simulation software. Book is 102 pages and it is easy to read and follow, it took a few days to go over and finish it. It is available in pdf, epub and Kindle formats which is good.
Book covers OMNET++ IDE, network structure, models, basic and compound modules, simulation environment, evaluation of simulation results and INET framework with example simulations.
It is a good resource to start learning OMNET++. It’d be nice if wireless related topics was included too. If you want to make quick start to OMNET++, I’d recommend reading the book: Learning OMNET++.