Physical Layer Modulation Schemes in Inter-Satellite Laser Communication

Abstract

Due to the demand for high data capacities, space networks rely on satellite constellations. Inter-satellite laser communication can meet this need. Nevertheless, space channels still have spatial and dynamic impairments. In this paper, physical layer modulation schemes for these optical links are evaluated. Intensity Modulation/Direct Detection (IM/DD) systems are compared with coherent detection architectures. This paper uses theoretical channel models and aerospace application cases to show that different schemes are suitable for different environments. Pulse Position Modulation (PPM) gives the necessary power efficiency in the case of deep-space missions. Coherent systems, such as Phase-Shift Keying (PSK), give spectral efficiency for low Earth orbit (LEO) networks. The study points out the current hardware limitations. The system is constrained by the highspeed components and the high-power consumption of signal processing. In addition, pointing jitter and radiation degradation also limit the overall performance. This paper concludes that single-format architectures are inefficient for dynamic space channels. Therefore, future space networks need to have adaptive optical payloads, and these systems must have the ability to switch modulation formats dynamically in order to have reliable communication.