Sharing transmission opportunity in ad-hoc WLANs supporting VoIP

Abstract

Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enables modern Wireless Local Area Networks (WLANs) to efficiently exploit network resources. It is essentially a resource allocation technique that enables a contention winning station with multiple backlogged frames belonging to a specific traffic class to transmit a burst of packets for a pre-defined time interval without having to re-content for medium access. However, while multimedia traffic flows are allowed to benefit from TXOP, best effort applications are precluded from utilizing it. In the recent IEEE 802.11ac amendment an enhanced TXOP version allows multiple applications belonging to different traffic classes (including best effort and background traffic) to share the contention-free period and transmit simultaneously. That feature is available only when the Down-Link Multi-User Multiple-Input Multiple-Output (DL-MU-MIMO) is enabled in a Quality of Service (QoS) Access Point (QAP) of a WLAN that operates in infrastructure mode. In this paper, an alternative mechanism is presented that allows the sharing of the TXOP in a sequential manner and can be applied to stations in ad-hoc WLANs with co-existing Voice over IP (VoIP) and non-multimedia flows. The proposed mechanism is analyzed and the results obtained are encouraging.