Improving Onboard Internet Services for High-Speed Vehicles by Multipath Transmission in Heterogeneous Wireless Networks

With the development of modern high-speed vehicles and mobile communication systems, there is a strong demand for operators to provide stable and high-quality onboard Internet services. However, the vehicle-to-ground links may suffer from several problems, such as insufficient bandwidth and long round-trip time (RTT). Although multiple wireless networks, such as Wi-Fi, third-generation (3G), and fourth-generation (4G), may be available along a track, onboard users do not have good experiences if they can only visit the Internet via one wireless network, which may be subject to coverage gaps and signal attenuation. In this paper, the link qualities of multiple existing 3G and 4G technologies are first measured in a typical high-speed environment. These 3G/4G networks are candidates for vehicle-to-ground communication. Then, a concurrent multipath transmission scheme, together with a network adaptive scheduling algorithm, is proposed. The scheme is independent of the protocol stack; therefore, it is easy to deploy. It also provides transparent Internet services for users, without requiring the participation of the user devices in any multipath signaling. Meanwhile, the scheduling algorithm works at the network layer, instead of the transport layer, to meet the diverse transmission requirements of the connection-oriented and connectionless user applications. The algorithm can effectively aggregate the bandwidth of multiple available wireless links, as well as avoid the reordering of packets based on both the practical tracing databases and the active path monitoring. Analysis and experiments show that the proposed algorithm can provide better onboard Internet services with lower cache requirements than the Earliest Delivery Path First (EDPF) and Weighted Round Robin (WRR) scheduling algorithms, in terms of bandwidth improvement and packet disorder reduction.