New multibeam processing schemes for high throughput satellites

Resumo

Satellite systems can play a relevant role in future communication networks to provide broadband services to broad or remote areas. Also, it can also complement terrestrial services like the possible integration of satellite systems to the core network of 5G or beyond 5G. Under this premise, both satellite technologies and processing techniques in High Throughput Satellite (HTS) systems have evolved to be competitive. Following this evolution, this thesis focuses on developing multibeam processing techniques to increase the spectral efficiency, and hence the throughput under the scope of current satellite technologies and standards. Bandwidth is the most precious and disputed resource for every wireless telecommunication system. As a result, it is common that the available frequencies are reused within the coverage area of a communications system to achieve high spectral efficiencies. In the satellite case, the available frequencies are traditionally deployed to maintain an acceptable level of co-channel interference. High co-channel interference levels are found in the satellite system if the available spectrum is more aggressively reused. Consequently, the spectral efficiency improvement is tied to the application of interference mitigation techniques to cope with the increased co-channel interference. Linear precoding is the preferred solution due to its theoretical system capacity gains, but the satellite environment imposes some practical constraints that compromise its implementation. In particular, the necessity of accurate full channel state information at the transmitter (CSIT) and the requirement of the joint computation of the precoded signal can be challenging tasks in satellite systems. The former can be difficult to satisfy in practice due to the phase estimate. Alternative solutions that only rely on the partial knowledge of the CSIT, for example the channel magnitude, have gained interest. In contrast to precoding, these alternative solutions are based on advanced receivers with Multi-User Detection (MUD) capabilities that place the interference mitigation at the receiver side. On the other hand, future satellite systems advocate for satellite architectures with flexible power and bandwidth allocation. In such scenarios, the techniques for radio resource management are fundamental to efficiently allocate the satellite resources and deliver the throughput where is needed. In this thesis, several strategies for satellite communication are proposed to increase the system spectral efficiency in high throughput satellites and numerically tested under realistic diagram pattern models and technological constraints. For a full frequency reuse scheme, a precoding solution is explored for the inter-cluster and intra-cluster interference mitigation when multiple ground stations manage different clusters of beams. Furthermore, the interference mitigation is also addressed for a 2-Colour reuse pattern with a rate-splitting technique that relies on partial CSIT and MUD receivers. The application of MUD receivers is also explored with Power-Domain Non-Orthogonal Access (PD-NOMA) for the coexistence of two different user services under the same frequencies where there is a high power imbalance between receivers classes. Its possible implementation is proposed together with an unorthodox approach where the traditional beam boundaries are broken when serving the users. Finally, this boundaryless approach for the user assignment is also addressed for resource management in flexible satellite payloads. The free user assignment can take advantage of the particular user locations to increase the frequency reuse in the system, especially in skewed traffic demand distributions, without the requirement of any interference mitigation technique.