# Smart Beamforming for Direct LEO Satellite Access of Future IoT
## 1 Introduction
Bearing in mind the good performance achieved by RBSA in terrestrial networks in terms of probability of collision and achievable rate, the work presented in this paper investigates its application to massive LEO satellite communication systems operating at Ka-band for massive access. Ka-band has already become the priority spectrum band for some LEO satellite operators [21], which incorporate leading-edge technologies and features, such as sophisticated phased array antennas on each satellite to create multiple dynamic beams. It is noteworthy to mention that analogously to [16], the work presented in this paper leverages on the massive MIMO technology to achieve shapeable and steerable beams, which is crucial to materializing massive access. In this paper we depart from the IoT requirements of low-rate services and low-power, and low-cost terminals. We envisage a more futuristic IoT ecosystem, where networks will extend its range to more sophisticated IoT terminals and new segments of IoT services with higher data rate demands. In the same vein, the authors in [22] investigate the application of massive MIMO to high-rate IoT systems. As an example, surveillance and security systems that need to send multiple photos or high-volume sensor data, could benefit from the proposed technology in poor connectivity areas. RBSA could also play a role in maritime IoT to handle large data rates [23]. As for the devices, the application scope should be circumscribed to advanced platforms with tracking antennas, providing the necessary gains at Ka-band. Although RBSA goes beyond the current deployments, it has remarkable features that are suitable for IoT. For instance, RBSA lies within the category of random access schemes that are able to perform blind user detection at the receiver. A recent study on direct NGEO satellite access over millimeter waves (mmWaves) has conducted a feasibility analysis from a regulatory, UE characteristics, space segment, link budget, and system point of view [24]. Despite the advancements in this new landscape, further investigations need to be carried out to deepen into the role of NGEO satellites in the RAN. For example, to allow spectral coexistence between satellite and terrestrial systems and to improve beam management mechanisms. The intention of this work is to contribute to the development of a new access scheme suitable for mMTC in LEO satellite communications systems. Building upon the work presented in [16], we investigated the application of the RBSA scheme to LEO satellite communications with massive MIMO.The link budget feasibility at Ka-band is studied and the necessity of compensating the delay and the Doppler effects to ease the detection is highlighted. The major contributions of this paper are described in the following:A thorough analysis has been conducted to show that the proposed method is able to obtain a beamformer in the direction of the target user, without neither acquiring channel state information nor carrying out an exhaustive search through multiple angles;
* The theoretical throughput has been derived. The expressions reveal that the proposed RSBA can benefit from beamforming techniques to lower the collision probability when a large population of terminals is transmitting simultaneously;
* Practical implementation aspects have been tackled, such as the estimation of the covariance matrices and the determination of the number of users;
* We have shown by simulations that the proposed beamforming technique is able to distinguish and separate users that are located in different spots. Numerical results also reveal that performance gains can be achieved with respect to fixed beamforming networks. The rest of the paper is organized as follows. The application of massive MIMO to LEO satellite communications is discussed in Section 2. In Section 3, we formulate the system model. Section 4 describes the beamforming design and conducts the throughput analysis. The numerical results are presented in Section 5 and finally, the conclusions are drawn in Section 6.