A Comprehensive Overview of TCP Congestion Control in 5G Networks: Research Challenges and Future Perspectives

SDN-Based Congestion Control and Bandwidth Allocation Scheme in 5G Networks

5G cellular networks are already more than six times faster than 4G networks, and their packet loss rate, especially in the Internet of Vehicles (IoV), can reach 0.5% in many cases, such as when there is high-speed movement or obstacles nearby. In such high bandwidth and high packet loss network environments, traditional congestion control algorithms, such as CUBIC and bottleneck bandwidth and round-trip propagation time (BBR), have been unable to balance flow fairness and high performance, and their flow rate often takes a long time to converge. We propose a congestion control algorithm based on bottleneck routing feedback using an in-network control mode called bottleneck routing feedback (BRF). We use SDN technology (OpenFlow protocol) to collect network bandwidth information, and BRF controls the data transmission rate of the sender. By adding the bandwidth information of the bottleneck in the option field in the ACK packet, considering the flow fairness and the flow convergence rate, a bandwidth allocation scheme compatible with multiple congestion control algorithms is proposed to ensure the fairness of all flows and make them converge faster. The performance of BRF is evaluated via Mininet. The experimental results show that BRF provides higher bandwidth utilization, faster convergence rate, and fairer bandwidth allocation than existing congestion control algorithms in 5G cellular networks.

Improvement of AlGaN/GaN High-Electron-Mobility Transistor Radio Frequency Performance Using Ohmic Etching Patterns for Ka-Band Applications

In this paper, AlGaN/GaN high-electron-mobility transistors (HEMTs) with ohmic etching patterns (OEPs) "fabricated to improve device radio frequency (RF) performance for Ka-band applications" are reported. The fabricated AlGaN/GaN HEMTs with OEP structures were used to reduce the source and drain resistances (Rs and Rd) for RF performance improvements. Within the proposed study using 1 μm hole, 3 μm hole, 1 μm line, and 3 μm line OEP HEMTs with 2 × 25 μm gate widths, the small signal performance, large signal performance, and minimum noise figure (NFmin) with optimized values were measured for 1 μm line OEP HEMTs. The cut-off frequency (fT) and maximum oscillation frequency (fmax) value of the 1 μm line OEP device exhibited optimized values of 36.4 GHz and 158.29 GHz, respectively. The load-pull results show that the 1 μm line OEP HEMTs exhibited an optimized maximum output power density (Pout, max) of 1.94 W/mm at 28 GHz. The 1 μm line OEP HEMTs also exhibited an optimized NFmin of 1.75 dB at 28 GHz. The increase in the contact area between the ohmic metal and the AlGaN barrier layer was used to reduce the contact resistance of the OEP HEMTs, and the results show that the 1 μm line OEP HEMT could be fabricated, producing the best improvement in RF performance for Ka-band applications.

Smart cities at risk: Systemic risk drivers in the blind spot of long-term governance

In this article, we analyze "digital massification" in smart cities, that is, an ever-growing number of market participants, consumers, and Internet of Things devices with simultaneous accommodation of users to increasing disturbances and inconveniences due to data congestion-as a driver for systemic risk. We argue that digital massification phenomena largely escape societal awareness due to their protracted evolution and are therefore still in the blind spot of long-term governance. Our analysis makes methodological use of historical and relational analogy, and we introduce and elaborate concepts and terms that allow us to discuss the evolutionary nature of massification, that is, the foreseeable increasing probability of the occurrence of trigger events. Using the analogy to the history of road traffic congestion, we deduce that digital massification will most likely lead to a future "risk transition" where tolerated disturbances and inconveniences of the present will turn into systemic impacts. This insight calls for heightened sensitivity in governance to massification phenomena to ensure the long-term resilience of smart cities.

Congestion Analysis of Transport Layer in a Multicell 5G DL Communication System

The fifth generation (5G) marks an important advance in mobile network capabilities. When it comes to high data rates, capacity, spectrum efficiency, and availability, 5G mobile broadband goes above and beyond what was previously possible with standard mobile broadband. The construction of 5G networks is still in the planning stages. These 5G networks will create intelligent networked communication environments by connecting people, things, data, applications, and transport networks. Mobile networks have made it possible for customers' mobile devices (such as smartphones, tablets, laptops, and so on) to connect to the internet. A variety of distinct protocols will be required to take into consideration the various aspects that 5G possess. One of these is the transport protocol, which is intended to deliver extremely high data transfer rates up to 400 Gbps. The transmission control protocol (TCP) is one of the numerous protocols that are necessary for supporting 5G's many capabilities. Our work focuses on the detection and analysis, on the downlink (DL) side, of the congestion of the transport layer in single- and multicell environments. For the purpose of the analysis, the following metrics were analyzed: physical resource blocks (PRBs), user throughput, cell throughput, cell edge user throughput, and delay. The work emphasizes the activation of the TCP slow-start algorithm using file transfer protocol (FTP) model two according to 3GPP standards.

mmS-TCP: Scalable TCP for Improving Throughput and Fairness in 5G mmWave Networks

The millimeter-wave (mmWave) band, which can provide data rates of multi-gigabits per second, could play a major role in achieving the throughput goals of 5G networks. However, the high-bandwidth mmWave signal is susceptible to blockage by various obstacles, which results in very large and frequent degradation in the quality of the received signals. TCP, the most representative transport layer protocol, suffers from significant performance degradation due to the very dynamic channel conditions of the mmWave signal. Therefore, in this paper, we propose a congestion control algorithm that guarantees sufficient throughput in 5G mmWave networks and that does not significantly worsen TCP fairness. The proposed algorithm, which is a modification of Scalable TCP (S-TCP) that is designed for high-speed networks, provides a more stable performance than the existing TCP congestion control algorithm in mmWave networks through simple modifications. In various simulation experiments that considered the actual mobile user environment, the proposed mmWave Scalable TCP (mmS-TCP) algorithm demonstrated throughput up to 2.4 times higher than CUBIC TCP in single flow evaluation, and the inter-protocol fairness index when competing with CUBIC flow significantly improved from 0.819 of S-TCP to 0.9733. Moreover, the mmS-TCP algorithm reduced the number of duplicated ACKs by 1/4 compared with S-TCP, and it improved the average total throughput and intra-protocol fairness simultaneously.