Future satellite communications systems face a challenge to provide higher bitrates, together with improved QoS (quality of service) guarantees, to more GT (ground terminals). Moreover, this should be achieved with higher spectral and power efficiencies, with less energy.
This project considers future very high bitrate LEO (Low Earth Orbit) satellite systems with satellite MPR (multipacket reception), compatible with low-cost portable GTs. A cross-layered approach is proposed: a physical layer team will handle the signal design, the synchronization and estimation issues, and the receiver design, including MPR development; a data link layer team will handle the Multiple Access control protocol design and the scheduling algorithm to support different QoS (Quality of Service) classes, and the interaction with the network layers. Both teams will be involved in the design and test of the cross-layering features involving both layers, required to provide guaranteed QoS, even during satellite handover.
In this project we will develop OQPSK-type schemes with reduced envelope fluctuations and high power and spectral efficiencies and compatible with an efficient and low cost power amplification. To further improve the overall system power efficiency we also consider schemes with spectral overlapping between different frequency channels. With respect to the receiver design, the main goal is an efficient multipacket detection technique able to cope with collisions, already shown by the research team to allow significant improvements in personal area networks. We will consider turbo frequency-domain equalizers suitable to cope with time-dispersion effects and able to handle spectral overlapping between frequency channels. Hybrid ARQ/FEC (Automatic Repeat reQuest/Forward Error Correction), namely with packet combining, will be proposed to handle fading for the most demanding QoS classes and control packets. To cope with Doppler effects, suitable synchronization and channel estimation methods will be developed for MPR on a LEO scenario. Joint detection and estimation schemes will be considered. Since MPR needs to know which users are involved in a collision, suitable methods to detect them will be developed. The statistical characterization of block error rates with MPR will be evaluated using simulations for homogenous and heterogeneous SNR GTs. We will develop a new MAC protocols for MPR that combine random access with demand assigned access on the uplink controlled by a downlink control channel, offering improved QoS support compared to other LEO MAC protocols.

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