Revisiting TCP Pacing for Throughput Performance Enhancement over TDD Band in Private Mobile Networks

Private mobile networks, such as local 5G, have attracted the attention of industry players who expect flexible radio resource allocation by methods such as time-division duplex (TDD) scheduling based on the uplink and downlink traffic demand of their solutions. However, there are two challenges when communicating using TCP congestion control algorithms (CCAs) over the TDD link: TDD-induced ACK-waiting time and misestimating congestion states due to deterministic delay variation caused by TDD scheduling. In this paper, we propose a TDD-aware TCP pacing method for improving TCP throughput by pacing the sending time between two consecutive segments within the ACK-waiting time. We determine the pacing rate on the basis of the TDD-induced delay variation for sending TCP segments within allocated TDD slots while reducing round-trip time (RTT). We evaluate the performance of our method by using a network simulator (ns-3). TCP pacing improves throughput by about 10-70% compared with when there is no pacing, especially for TCP Illinois. We also verify that our TDD-aware pacing improves throughput by about 10% compared to the default pacing rate on the Linux kernel.