The technical evolution of wireless communication technology and the need for accurately modeling these increasingly complex systems causes a steady growth in the complexity of simulation models. At the same time, multi-core systems have become the de facto standard hardware platform. Unfortunately, wireless systems pose a particular challenge for parallel execution due to a tight coupling of network entities in space and time. Moreover, model developers are often domain experts with no in-depth understanding of parallel and distributed simulation. In combination, both aspects severely limit the performance and the efficiency of existing parallelization techniques. We address these challenges by presenting parallel expanded event simulation, a novel modeling paradigm that extends discrete events with durations that span a period in simulated time. The resulting expanded events form the basis for a conservative synchronization scheme that considers overlapping expanded events eligible for parallel processing. We then put these concepts into practice by implementing Horizon, a parallel expanded event simulation framework specifically tailored to the characteristics of multi-core systems. Our evaluation shows that Horizon achieves considerable speedups in synthetic as well as real-world simulation models and considerably outperforms the current state-of-theart in distributed simulation.