The adoption of aggressive frequency reuse schemes along with interference management techniques has become the leading paradigm in satellite communications to increase the spectral efficiency. In general terms, one cannot rely on precoding techniques in the absence of channel phase information. Nevertheless, the availability of channel magnitude information, makes it possible to explore power-based separation of superimposed signals. In this paper, rate splitting (RS) ideas are exploited, whereby the separation of messages into private and public parts serves to improve the performance of successive cancellation decoding (SCD). Numerical results reveal that in some pertinent system scenarios, the proposed schemes achieve a larger rate region than that of orthogonal schemes that do not exploit the interference and other strategies that either do not allow beam cooperation or do not apply RS.
This paper deals with the problem of beamforming design in a multibeam satellite, which is shared by different groups of terminals -clusters-, each served by an Earth station or gateway. Each gateway precodes the symbols addressed to its respective users; the design follows an MMSE criterion, and a regularization factor judiciously chosen allows to account for the presence of mutually interfering clusters, extending more classical results applicable to one centralized station. More importantly, channel statistics can be used instead of instantaneous channel state information, avoiding the exchange of information among gateways through backhaul links. The on-board satellite beamforming weights are designed to exploit the degrees of freedom of the satellite antennas to minimize the noise impact and the interference to some specific users. On-ground beamforming results are provided as a reference to compare the joint performance of MMSE precoders and on-board beamforming network. A non-adaptive design complements the results and makes them more amenable to practical use by designing a coarse beamforming network.
This paper investigates a novel technique to deal with the interference in the forward link of multibeam satellite systems when aggressive frequency reuse schemes are employed. Taking into account only magnitude information about the forward channel, the gateway judiciously splits the messages to be transmitted into private and public parts. At the receive terminals, partial cancellation of the public messages is applied prior to private message detection. The practical significance of the absence of channel phase information is stressed and complemented by some additional insights on the implementation. Our numerical results show that, in terms of average total throughput, this technique combined with a 2-colour frequency reuse scheme can outperform a classic orthogonal system with a conservative 4-colour frequency reuse scheme, despite the additional co-channel interference.
This work addresses the uneven traffic demand scenario in multi-beam satellite systems, in which a hot-spot beam is surrounded by cold beams. After partitioning the hotspot beam in different sectors, resource pulling from cold neighbouring beams is allowed following an aggressive frequency-reuse scheme. As a consequence, the level of the co-channel interference within the hot-spot beam increases. A scheme known as Non-Coherent Rate-Splitting (NCRS) is employed to cope with this interference, based on the exclusive use of magnitude channel state information at the transmitter (CSIT). The receiver complexity is increased with respect to full CSIT precoding schemes, which are considered for benchmarking purposes. Different NCRS strategies are analyzed and compared with several partial and full CSIT schemes. The proposed solution not only shows an improvement with respect to partial CSIT benchmarks, but also displays a competitive performance against full CSIT precoders.* The relative gain G t h is used for theoretical purposes. In an actual satellite system, it would be more practical to use instead
We consider the forward link of a multibeam satellite system with high spectral reuse and the novel low-complexity transmission and detection strategies from [1]. More specifically, we study the impact of a time offset between the antenna beams that cooperate to simultaneously serve a given user. Assuming Gaussian signaling, we provide closed-form expressions for the achievable rate region. It is demonstrated that, in the absence of timing information at the gateway, this region is not affected by a time offset. Our numerical results further show that, in case timing is known at the gateway, an offset of half a symbol period at both user terminals is optimal in terms of spectral efficiency.
This paper addresses the application of nonorthogonal multiple-access techniques (NOMA) to those satellite relayed communications for which a significant imbalance in the link quality of user terminals can be expected. The Signal-to-Interference and Noise Ratio (SINR) imbalance could be caused by the coexistence of different types of terminals, possibly with different antenna sizes, and offering different classes of service. This link SINR asymmetry can be exploited to outperform orthogonal access schemes under different rate metrics, paying special attention to fairness in the service provision. Both forward and asynchronous return link are addressed, with minimum signaling information and emphasis on some relevant implementation issues such as framing and synchronization.
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