Modeling Compound TCP Over WiFi for IoT

Compound TCP will play a central role in future home WiFi networks supporting Internet of Things (IoT) applications. Compound TCP was designed to be fair but can manifest throughput unfairness in infrastructure-based IEEE 802.11 networks when devices at different locations experience different wireless channel quality. In this paper, we develop a comprehensive analytical model for compound TCP over WiFi. Our model captures the flow and congestion control dynamics of multiple competing long-lived compound TCP connections as well as the medium access control layer dynamics (i.e., contention, collisions, and retransmissions) that arise from different signal-to-noise ratios (SNRs) perceived by the devices. Our model provides accurate estimates for TCP packet loss probabilities and steady-state throughputs for IoT devices with different SNRs. More importantly, we propose a simple adaptive control algorithm to achieve better fairness without compromising the aggregate throughput of the system. The proposed real-time algorithm monitors the access point queue, drives the system dynamics to the desired operating point which mitigates the adverse impacts of SNR differences, and accommodates the sporadically transmitting IoT sensors in the system.