Implementation of an IEEE 802.11 Wireless LAN Model using OPNET



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INTRODUCTION

Building a simulation model from a specification is a frustrating process. The specification is invariably large, seemingly unorganized, and details about important subsystem interactions can be scattered throughout the document. The document may also contain apparent (or actual) contradictions and ambiguities. Furthermore, in group projects, different interpretations of the specification will occur and significant time will be wasted reworking the model.


THE MODEL

The IEEE 802.11 model is to be used to conduct research into the real-time capabilities of IEEE 802.11. The model implements the distributed coordination function (DCF) of IEEE 802.11. Stations within model form an ad-hoc network (i.e., an independent basic service set (IBSS) in IEEE 802.11 terms).


MODEL VALIDATION

The model was validated by comparing the performance metrics of our model against those obtained in [BiF96]. Because [BiF96] was based on an earlier draft, several of that paper’s parameters did not match those in the latest IEEE 802.11 standard. For the validation, we changed the values of these parameters in our model to match [BiF96].
Figure 7 shows throughput for 5, 10 and 20 station networks. Figure 8 shows the average transmission attempts per packet for various values of the contention window, CWmin, and CWmax. Figure 9 shows saturation throughput versus number of stations for various values of the contention window, CWmin, and CWmax.



CONCLUSION

In this paper, we demonstrated the advantages of implementing a simulation model using a formal specification of the system mapped to OPNET objects.

The validation data showed excellent agreement between our model and other published results. In addition, using this approach we were able to construct this model in a short time with no prior experience using OPNET. Our model is highly parameterized and can model a wide range of input traffic. We expect that by modifying the default backoff algorithm in IEEE 802.11 we can significantly enhance its real-time performance.