Abstract
This article investigates uplink transmission from a single-antenna mobile phone to a cluster of satellites, emphasizing the role of intersatellite links (ISLs) in cooperative signal detection. We study nonideal ISLs, focusing on terahertz (THz) and free-space optical (FSO) links with respect to ergodic capacity. A scenario based on the recent 3GPP standard specifies the frequency band, bandwidth, antenna gains, power levels, and channel characteristics for nonterrestrial networks. We also propose a satellite selection method to identify the optimal master node for signal processing, considering both the user-satellite link and ISL channels. For THz ISLs, we derive a closed-form capacity approximation under instantaneous or statistical channel state information, while for FSO ISLs, we present a closed-form approximate upper bound incorporating pointing error loss. We further assess the impact of ISL frequency and pointing errors on spectral efficiency. Simulations show that multisatellite multiple-input multiple-output communications significantly outperforms single-satellite systems, and that the proposed upper bound closely matches Monte Carlo results.