The most challenging issue in WiMAX network planning is to measure and enhance the Quality of Service (QoS) of WiMAX networks. In this paper, a comprehensive WiMAX simulator is proposed to evaluate the performance of the system. The key parts of the simulator are described including end-to-end communication path, traffic generation, Medium Access Control (MAC) and Physical (PHY) layers, resource allocation, frame construction and configuration options such as Adaptive Modulation and Coding (AMC). Several experiments are conducted to assess different scenarios while varying one or more of the following: input traffic size, traffic load, presence of fragmentation and AMC. The results show the scalability of the system as it can support a large number of users while showing the real-life representation of the traffic models. The simulations also show the flexibility of implementing AMC schemes according to desired distributions. The high accuracy of the simulator is shown by comparing the simulator results to theoretical expected values.