The reference-frame-independent quantum key distribution (RFI-QKD) allows the authorized users to share secrete keys without active alignment of the reference frames, which is beneficial for the implementation over free-space channel. However, the performance of free-space RFI-QKD could notably degrade due to the influence of atmospheric conditions. In this paper, we investigate the transmission attenuation of free-space channel in uplink and downlink scenario, respectively. Furthermore, we also simulate the relationships between the diffraction-caused attenuation and the apertures of sending and receiving optics. Then, the key generation rate of RFI-QKD and BB84 protocol are compared in different links with reference frame deviations. Simulation results show that the transmission attenuation due to diffraction can be reduced by choosing appropriate optical apertures, and better performance of free-space RFI-QKD can be achieved in downlink configuration.

中文翻译：

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上行链路和下行链路自由空间信道中与参考帧无关的量子密钥分发

与参考帧无关的量子密钥分发（RFI-QKD）允许授权用户共享密钥而无需主动对齐参考帧，这有利于在自由空间信道上的实现。然而，由于大气条件的影响，自由空间 RFI-QKD 的性能可能会显着降低。在本文中，我们分别研究了上行链路和下行链路场景中自由空间信道的传输衰减。此外，我们还模拟了衍射引起的衰减与发送和接收光学器件的孔径之间的关系。然后，比较RFI-QKD和BB84协议在不同链路中参考帧偏差的密钥生成率。