TCP Performance Issues in Satellite and WiFi Hybrid Networks for High-Speed Trains

GEO satellite communication systems are an efficient approach for broadband Internet provision on high speed trains, but some work is still needed to allow a seamless service. In the railway scenario, satellite communications suffer from strong variations in the received signal power and need suitable solutions to deal with long channel disruptions due to tunnels. The approach envisaged in this paper is based on a hybrid network (satellite and terrestrial WiFi coverage) and a Vertical Handover (VHO) procedure to switch seamlessly from one segment to another whenever link quality degrades and a new segment is available. This paper deals with the TCP performance in the presence of VHOs (based on the IEEE 802.21 Media Independent Handover, MIH, standard) from the satellite to a terrestrial wireless segment and vice versa to cover tunnels. Details are provided for the adoption of MIH and MIPv6 in such a context, referring to the BSM standard. Design criteria for the WiFi coverage extension outside the tunnel are also presented. Finally, we have shown that TCP goodput behavior and convergence time can be improved by means of suitable accelerated TCP versions or using cross-layer methods.