An Efficient Scheduling Mechanism for Simulating Concurrent Events in Wireless Communications Based on an Improved Priority Queue (PQ) TDM Layered Multi-Threading Approach

The physical activities of a real wireless network are represented by events which are the main components of a discrete event simulation (DES) system and are produced by its event generator during simulation time. Each network service (e.g. voice, data and video) constitutes an event for a particular mobile user. A critical component within the simulation system, called scheduler, runs by selecting the next earliest event, executing it till completion, and returning to execute the next event. Calendar queue is the state of the art implementation of the scheduler among the most popular networking simulation tools such as ns-2. However, Calendar queue time-stamping mechanism presents drawbacks in the case of complex dynamical systems, like wireless networks, where probability of events concurrency is large. In such a case sequential time-stamping of calendar queue scheduling does not reflect real network events occurrence and generation. It should be remarked that there are very few reports if any in the literature concerning research on events scheduling mechanisms in such real time systems. On the other hand, multi-threading technology offers advanced capabilities for modelling concurrent events. The main goal of this paper is to illustrate that multithreading architectures provide the means for designing efficient schedulers in the simulation of wireless networks resource allocation but, also, several critical issues such as deadlocks, synchronization and scheduling must be effectively faced. In this paper, a stable simulation model is presented based on a novel layered thread architecture and on an alternative network event scheduling mechanism, called the Priority Queue (PQ) – Time Division Multiplexing (TDM) Layered Multithreading mechanism, which supports concurrent events as compared to the state of the art approach which supports only sequential events. Moreover, specific drawbacks of the JVM multi-threading platform such as thread execution unpredictability are also faced and presented. Key-words: cellular network, simulation, event scheduling, concurrent events, multi-threading