Linear quadratic control of service rate allocation in a satellite network

The real-time control of multiple queues handling traffic of different nature is getting increasing relevance in both the uplink and downlink of wireless telecommunication networks, characterized by the presence of a central access point. Such is the case of satellite networks, with either on-board processing or double-hop configuration, besides a number of terrestrial local and metropolitan wireless networks. Given a certain amount of available bandwidth, the problem is that of deciding, within a certain time frame, the allocation of bandwidth partitions for each traffic queue, whose packets are awaiting transmission; eventually, this determines the transmission rates to be passed to the scheduler and to the physical layer Adaptive Coding and Modulation (ACM) devices. In a satellite network, where this task is accomplished by a master station, residing at the access point, it is possible to take such decisions by means of a centralized controller, based on real-time instantaneous (in the downstream direction) or delayed (in the upstream) information on the queues' state. The paper derives a control law to be used in this task, by adopting an approach based on optimal Linear Quadratic (LQ) regulation. Both cases of un-delayed and delayed information are considered. The control laws are tested in a geo-stationary satellite scenario of Digital Video Broadcasting - Return Channel via Satellite (DVB-RCS), and the queues are considered at the MAC (Medium Access Control) level. Simulation results under real-traffic traces are also presented, to highlight the effectiveness of the control and to compare alternative solutions.