| Quantum cryptography is a method of communication based on quantum physics theorem,because of its natural characters, quantum cryptography is safer than any other method of communication. From the emerging of quantum cryptography in the 1980s, to quantum cryptography manages to transfer one hundred, the technique of quantum optical fiber and short length free-space correspondence has progressed. However, because of strict demand for building optical fiber channel, and transmission range, long distance quantum cryptography can't be accomplished. For building global quantum communications in the future, we must increase the distances of quantum cryptography, and lessen the influence of geographical features. Satellite communication has succeed today, it builds channel between satellite and ground, and it enlarge the areas of communication and enhance the speed of communication. Using the single-photo optical communication technique to distribute the secret keys required for confidential communications, it will conquer the limitation of distance, and accomplish the building of global quantum communications.Based on analysis of atmosphere, whether or not the space quantum communication system can be built will be proved and the library space quantum communication system will be devised. Through analysis and emulation,the article study the quantum communication channel, and proves the feasibility of building global quantum communications, and it is worthy for research in the future. |
