Modeling and analysis of TXOP differentiation in infrastructure-based WLANs

The Access Point (AP) is the bottleneck of infrastructure-based Wireless Local Area Networks (WLANs) due to its responsibility for forwarding all the incoming and outgoing frames. As a result, the network performance is significantly deteriorated by the unbalanced traffic loads at AP and other mobile stations. A potential solution to the bottleneck problem is to assign different Transmission Opportunity (TXOP) limits to the AP and mobile stations, respectively. This study develops a new analytical model to investigate the Quality-of-Service (QoS) performance metrics including throughput, total frame delay, and frame loss probability in infrastructure-based WLANs with TXOP differentiation under the unbalanced traffic loads. To this end, the transmission queue is modeled as a bulk service queueing system in order to address the challenge of queueing analysis arising from the TXOP burst transmission mechanism. The accuracy of this model is validated through extensive NS2 simulation experiments. The analytical results demonstrate that the implementation of TXOP differentiation can substantially alleviate the bottleneck effects of unbalanced traffic loads, increase the aggregate throughput and decrease the frame delay and loss probability. Moreover, the developed model can be adopted as a cost-efficient tool to evaluate the impact of TXOP limits on the network performance and to investigate the optimal setting of TXOP limits under different working conditions.