# DNN Beamforming for LEO Satellite Communication at Sub-THz Bands
## 1 Introduction  
The next generation of communication systems (B5G and 6G) will extensively rely on artificial intelligence (AI) for the efficient and robust design of transceiver systems. These transceiver systems will be designed at sub-THz bands to achieve higher spectral efficiency, data rate and energy efficiency [1]. The lower frequency bands are also congested so the communication systems, new emerging applications and devices are to be designed at higher frequency bands [2]. The system design at sub-THz bands will enable many new services beyond 5G with enhanced security and frequency reuse. The existing 5G NR has already been planned to complement the non-terrestrial networks (NTN) to provide access to the remote locations. In its release 15 [3], 3 GPP studied the scenario of the New Radio (NR) to support the Non-Terrestrial Network (NTN). The NTN refer to the satellite, high altitude platforms, air-to-ground networks. The study identified the role of NTN to support the Transportation, Safety, eHealth, Agriculture, Finance, Automotive, Entertainment Media and Energy. The services enabled by the NTN integrated with the Terrestrial network include the eMBB (enhanced Mobile Broadband) and and mMTC (massive Machine Type Communications). The Release 16 Study of 3 GPP focused on adapting the NR systems to support NTN by minimizing the need for new interfaces and protocols [4]. The Release 17 study focuses on providing support of Narrow-Band Internet of Things (NB-IoT) and enhanced Machine Type Communication (eMTC) based satellite access [5]. These satellite networks have been assumed to have the beam steering capabilities towards the users on the ground using beamforming techniques [6]. As the communication system will evolve into the future generation e.g., B5G and 6G, the NTN will be integrated into the densely connected communication network coherently to provide cost effective services, better network capacity and coverage with higher energy efficiency [7, 8]. The larger available bandwidth at sub-THz bands will lead to a wideband communication system with very high data rates. However, the design of communicationsystem at such higher frequencies poses unique set of challenges [9]. Such challenges include the beamforming and antenna array design [10; 11; 12], channel modelling and estimation, massive MIMO communication [13] along with novel modulation techniques and signal processing algorithm [14; 15]. Several LEO satellite constellations have been launched, e.g., Starlink, Oneweb, Globastar, Orbcomm to provide access and connectivity to remote and unconnected areas. There are planned launches in 2023 by the Project Kuiper of Amazon [16]. The Lynk Global satellite that is expected to provide satellite-to-mobile-phone connectivity will deploy its 5G payload sooner rather than later [17]. Emergency SOS via satellite, a feature provided in iPhone-14 will connect to satellite in case of non-availability of cellular and Wi-Fi networks [18]. Such developments show the growing importance of the LEO communication in providing global services and connectivity. These LEO constellations will provide the communication services with lower latency due to faster propagation in free-space with thousands of satellites in the orbit [19]. For the design of satellite links at the higher frequencies in sub-THz bands (100-300 GHz), one such challenge to system design consideration comes due to higher absorption loss of the propagating signal in the atmospheric channel. In addition, the rapid movement of LEO satellites require phased array antenna at the ground station for electronic beam steering that can be pointed to a desired direction in real time [20; 21]. The higher losses due to the atmospheric absorption can be compensated by using very large number of antenna elements that employ beamforming to form very narrow pencil beams in order to achieve very high gain in the desired direction [22; 23].