Coded Taking and Giving (COTAG): Enhancing Transport Layer Performance over Millimeter Wave Access Networks

Millimeter wave (mmWave) access networks have the potential to meet the high-throughput and low-latency needs of immersive applications. However, due to the highly directional nature of the mmWave beams and due to their susceptibility to human-induced blockage, the associated wireless communication links are vulnerable to large fluctuations in channel quality. These large fluctuations result in disproportionately adverse effects on performance of transport layer protocols such as Transmission Control Protocol (TCP). Furthermore, we show in this paper, that TCP continues to significantly under perform even when dual-connectivity is used to combat the effects of channel quality fluctuations. To overcome this challenge, we propose a network layer solution, Coded Taking and Giving (COTAG) scheme to sustain low-latency and high-throughput end-to-end TCP performance. In particular, COTAG creates network encoded packets at the network gateway and each mmWave access point (AP) aiming to adaptively take the spare bandwidth on each link in the network for packet transmission. Further, if one link does not have enough bandwidth, COTAG actively gives up the transmission opportunity via conditionally dropping packets. Consequently, the proposed COTAG actively adapts to changes in mmWave link quality and enhances the TCP performance without jeopardizing the latency of immersive connect delivery. To evaluate the effectiveness of the proposed COTAG, we conduct experiments and simulations using off-the-shelf APs and NS-2. The evaluation results show the proposed COTAG significantly improves end-to-end TCP performance.