Controlling TCP ACK Transmission: Suitable Value of Discard Ratio in LTE-Advanced Pro

The first release of standards for 5^th generation (5G) mobile communication has been approved in the 3^rd Generation Partnership Project (3GPP). During the 5G standardization, performance of Transmission Control Protocol (TCP) in the 5G mobile networks was studied. It has been observed that the TCP performance is improved when protocols in the Radio Access Network (RAN) take the TCP behavior into consideration. The authors have been studying TCP ACK filtering that can work well with the link layer protocols in RAN, where the TCP ACKs can be intentionally discarded. It has been shown that proposed methods accomplish good TCP throughput while the number of TCP ACKs is largely reduced. In this paper, the authors tackle a remaining issue: finding the suitable value of “discard ratio”. It is proposed that the suitable value is obtained based on the average number of TCP ACKs transmitted in one transmission time interval. Simulation results demonstrate that the suitable value for the TCP ACK filtering can further improve the TCP performance when the number of mobile stations is small. In addition, it improves both throughput and fairness of the TCP when the number of mobile stations becomes large.