Abstract: To overcome the limitations of traditional terrestrial communication coverage and establish seamless, all-time, all-domain connectivity capabilities through direct-to-phone connection of integrated space-ground services, this study conducts a systematic review of communication technologies for direct-to-phone connection to LEO satellite networks. Firstly, the application background, concepts and connotations of direct-to-phone LEO satellite network are elaborated. Subsequently, the network architecture for direct-to-phone LEO satellite network is provided, along with the service characteristics and performance indicator requirements for individual and enterprise users. The development trends, comparative strengths, limitations, and technological evolution of the three main technical routes for direct-to-phone LEO satellite network are specifically analyzed. The key issues and technical challenges faced by LEO satellite network are identified, including severe spectrum resource constraint, link limitation and power imbalance, multi-user concurrent access collision, high dynamic spatio-temporal mismatch, and difficulties in ensuring continuity communication. Based on the foregoing analyses, the critical technologies for direct-to-phone LEO satellite network communication are distilled, such as spectrum resource optimization, the evolution of 5G/6G standardized protocols, ultra-large-scale satellite-borne antenna technology, efficient management and control of satellite network resources. Finally, to address the demands of 6G service applications, novel enabling roles of 6G technologies in direct-to-phone LEO satellite networks are proposed, including integrated space-ground architecture, AI-driven optimization, space-based computing networks, and wireless communication-sensing-computing convergence. This review offers a practical and feasible technical direction for the development of direct-to-phone LEO satellite network communication technology.

Key words: direct-to-phone LEO satellite, standardized protocol evolution, on-board satellite antennas, spectrum optimization, resource management and control