Comparison of modified dual queue and EDCA for VoIP over IEEE 802.11 WLAN

The popular IEEE 802.11 WLAN today does not provide any quality-of-service (QoS) because of its contention-based channel access nature of the medium access control (MAC). Therefore, we proposed a simple software upgrade-based solution, called a dual queue scheme, to provide QoS to real-time services such as Voice-over-IP (VoIP) in our previous work [7]. The dual queue scheme operates on top of the legacy MAC. In this paper, we present a modified dual queue (MDQ) scheme by considering a practical implementation limitation. On the other hand, the emerging 802.11e MAC includes a contention-based channel access mechanism, called enhanced distributed channel access (EDCA). Prioritized channel accesses are provided to different traffic classes under EDCA. In this paper, we comparatively evaluate the performances of MDQ and EDCA via simulations in terms of delay, jitter, and throughput for various scenarios. We also compare the two access schemes when multiple transmission rates are used via rate adaptation mechanism for reliable transmission over erroneous wireless channel. The simulation results show that EDCA apparently provides a better performance in most situations. However, MDQ provides an acceptable performance close to that of EDCA so that it can be used when the EDCA is not available and/or the hardware upgrade to 802.11e is not desirable for the cost reason.