Dynamic Control of Target BLER by nearRT-RIC for Enhanced TCP Throughput for 6G
Koki Horita, Akihiro Nakao · 2024
High-frequency bands such as millimeter wave (mmW) and Sub-THz are expected to be used in Beyond 5G and 6G. These bands can provide peak throughput but are vulnerable to disturbances owing to their high directivity. This makes achieving high throughput during line-of-sight (LoS) and nonline-of-sight (NLoS) challenging and affects the TCP congestion control algorithm. Previous studies have improved the TCP congestion control algorithm to realize throughput in mmW operations, but there are issues in practical implementation because the TCP must be replaced for each type of radio. To address this issue, this paper proposes a dynamic control method for the Target Block Error Rate (BLER), governing the characteristics of radio delay and error rates. This reduces the excessive bitrate reduction during NLoS and improves the TCP throughput reduction. The proposed method allows using high Modulation and Coding Scheme (MCS) during NLoS to suppress bit rate reduction. The Target BLER is calculated and set in the gNB, considering the UE’s Signal-to-Interference plus Noise Ratio (SINR) and the TCP congestion control algorithm in use. The proposed method does not require changes to the TCP congestion control algorithm because we modify the network characteristics to improve TCP throughput. The proposed method can be implemented using O-RAN’s near-real-time RAN Intelligent Controller (nearRT-RIC). Prototype evaluations show that it suppresses bitrate reduction during NLoS and accelerates throughput recovery under LoS/NLoS and changing environmental conditions. This results in a median improvement of 81% in TCP throughput.