The polarization characteristics of an artificial laser source in space were measured through space-to-ground atmospheric transmission paths. An existing Japanese laser communication satellite and optical ground station were used to measure Stokes parameters and the degree of polarization of the laser beam transmitted from the satellite. As a result, the polarization was preserved within an rms error of 1.6 degrees, and the degree of polarization was 99.4+/-4.4% through the space-to-ground atmosphere. These results contribute to the link estimation for quantum key distribution via space and provide the potential for enhancements in quantum cryptography worldwide in the future.
Wireless network virtualization is needed to build a virtual network over wireless and wired networks, which enables a rapid deployment of novel mobile services or novel mobile network architectures on a shared infrastructure. This paper proposes an airtime-based resource control technique for wireless network virtualization, in which wireless network resources are allocated among competing virtual networks while keeping their programmability. A WLAN system adopting the proposed technique is developed by enhancing an IEEE 802.11e EDCA (Enhanced Distributed Channel Access) MAC (Media Access Control) mechanism. The operation of the resource control technique is demonstrated by a simulation and the performance of airtime usage and throughput are investigated. It is shown that technique can successfully control the wireless network resource allocations with a target ratio even under conditions when the WLAN system suffers interferences.
Satellite quantum key distribution is a promising technique that overcomes the limited transmission distance in optical-fiber-based systems. The polarization tracking technique is one of the key techniques in the satellite quantum key distribution. With free-space quantum key distribution between an optical ground station and a satellite, the photon polarization state will be changed according to the satellite movement. To enable polarization based quantum key distribution between mobile terminals, we developed a polarization-basis tracking scheme allowing a common frame of reference to be shared. It is possible to orient two platforms along a common axis by detecting the reference optical signal only on the receiver side with no prior information about the transmitter's orientation. We developed a prototype system for free-space quantum key distribution with the polarization-basis tracking scheme. Polarization tracking performance was 0.092• by conducting quantum key distribution experiments over a 1 km free space between two buildings in a Tokyo suburb.
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