Full-duplex (FD) transmission in a point-to-point (P2P) link, wherein bidirectional traffic flows simultaneously share the same spectrum, has the capability of doubling the link rate by completely removing self-interferences. However, the rate performance of an FD heterogeneous network (HetNet)is not as clear as that of an FD P2P link due to the co-channel interferences induced by complex FD and half-duplex (HD) transmission behaviors in the HetNet. To thoroughly investigate the achievable link rate performances of users and base stations (BSs) in a HetNet with decoupled user association, a hybrid-duplex approach is proposed to model a HetNet in which all BSs and users can perform HD or FD transmission depending on their traffic patterns. We first characterize the decoupled rate-optimal user association scheme and use it to define and evaluate the downlink and uplink rates in the HetNet. The tight lower bounds on the link rates of the FD users and BSs are found in a neat form that characterizes general channel fading, imperfect self-interference cancellation and the intensities of users and BSs. These bounds outline the rate regions of the FD users that inspire us to propose the opportunistic FD scheduling algorithms that maximize the sum rate of each bidirectional traffic and stabilize each of the queues in the HetNet.

No abstract

We report a 17-km free-space quantum key distribution (QKD) experiment using an engineering model of the space-bound optical transmitter and a ground station for satellite-ground QKD. The final key rate of ~ 0.5 kbps is achieved in this experiment with the quantum bit error rate (QBER) of ~ 3.4%. An efficient error correction algorithm, Turbo Code, is employed. Compared with the current error correction algorithm of Cascade, a high-efficiency error correction is realized by Turbo Code with only one-time data exchange. For a low QBER, with only one-time data exchange, the final key rates based on Turbo code are similar with Cascade. As the QBER increases, Turbo Code gives higher final key rates than Cascade. Our results experimentally demonstrate the feasibility of satellite-ground QKD and show that the efficient error correction based on Turbo Code is potentially useful for the satellite-ground quantum communication.

No abstract

No abstract