Novel Insights From a Cross-Layer Analysis of TCP and UDP Traffic Over Full-Duplex WLANs

Abstract

Full-duplex (FD) communication is a promising new technology that enables simultaneous transmission and reception in wireless local area networks (WLANs). The benefits of FD on the medium access control (MAC) layer throughput in IEEE 802.11 WLANs are well-documented. However, cross-layer interactions between the FD MAC protocol and transport layer protocols such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are less explored. We consider a WLAN with uplink and downlink TCP flows as well as UDP flows between stations (STAs) and a server via an FD access point (AP). We study an STA-initiated FD MAC protocol in which the AP can transmit on the downlink while receiving on the uplink. Using a novel FD-specific STA saturation approximation, Markov renewal theory, and fixed-point analysis, we derive novel expressions for the uplink and downlink TCP and UDP saturation throughputs. Our analysis shows that the AP is no longer a bottleneck and may be unsaturated unlike in conventional half-duplex (HD) WLANs. Despite greater contention and cross-link interference between STAs, FD achieves a higher TCP throughput than HD. FD causes a significant degradation in the UDP throughput. In the unsaturated regime, FD achieves a lower average downlink TCP packet delay than HD.