Load-aware soft-handovers for multibeam satellites: A network coding perspective

Driven by the increasing demand of Internet anywhere and anytime, mobile broadband services are set to represent an important share of the satellite traffic due to the availability advantages of satellite networks. These services require a robust and flexible mobility support mechanism, which includes efficient soft-handovers between beams. The latter poses important practical challenges at a physical and network level in order to provide two simultaneous connections to a mobile terminal via two different beams. From a network perspective, typical soft-handover algorithms require the system to transmit repetitions of the packets over both connections. Our approach breaks with this concept by considering soft-handovers as a resource allocation problem driven by the uncertainty of terminal mobility and the time-varying nature of loads in a multibeam satellite system. We propose a set of techniques and algorithms that provide load-aware soft-handovers for multibeam satellites that exploit the ability of advanced terminals to receive and process several overlapping beams. To provide a flexible resource allocation mechanism that exploits multiple routes, we rely on packet-level coding techniques, such as network coding, in order to increase robustness and relax the allocation problem. An advantageous collateral effect of our algorithms is the provision of load balancing between beams in satellites with conventional payloads. We provide simulation results for the case of a multi-beam satellite covering Europe with 70 beams serving fixed and mobile terminals that illustrate that our techniques can increase overall throughput by (i) reducing the resources allocated to each terminal for roaming support when compared to state-of-the-art soft-handover mechanisms, and (ii) spreading the load to beams with light traffic requirements.