Evaluation of multi-user multiple-input multiple-output digital beamforming algorithms in B5G/6G low Earth orbit satellite systems

Satellite communication systems will be a key component of 5G and 6G networks to achieve the goal of providing unlimited and ubiquitous communications and deploying smart and sustainable networks. To meet the ever-increasing demand for higher throughput in 5G and beyond, aggressive frequency reuse schemes (i.e., full frequency reuse), combined with digital beamforming techniques to cope with the massive co-channel interference, are recognized as a key solution. Aimed at (i) eliminating the joint optimization problem among the beamforming vectors of all users, (ii) splitting it into distinct ones, and (iii) finding a closed-form solution, we propose a beamforming algorithm based on maximizing the users' signal-to-leakage-and-noise ratio served by a low Earth orbit satellite. We investigate and assess the performance of several beamforming algorithms, including both those based on channel state information at the transmitter, that is, minimum mean square error and zero forcing, and those only requiring the users' locations, that is, switchable multi-beam. Through a detailed numerical analysis, we provide a thorough comparison of the performance in terms of per-user achievable spectral efficiency of the aforementioned beamforming schemes, and we show that the proposed signal to-leakage-plus-noise ratio beamforming technique is able to outperform both minimum mean square error and multi-beam schemes in the presented satellite communication scenario

An interference estimation technique for Satellite cognitive radio systems

The increasing request of communication capacity for the introduction of modern multimedia services has collided with the problem of the spectrum shortage. One of the most known approach is represented by cognitive radios, which are supposed to exploit already deployed frequency bands in use by an incumbent system. Among other cognitive radio features, detection and estimation of the incumbent user are essential for implementing the cognitive radio system avoiding any interference. This is particularly important in SatCom cognitive scenarios due to transmission power impairments. In this paper, we focus on a joint interference and noise estimation algorithm aiming at detecting and estimating incumbent interference, for allowing the coexistence of the two systems. The behavior of the algorithm is analytically derived, and numerical results obtained through computer simulations confirm the effectiveness of the proposed approach