Fairness-Oriented Hybrid Precoding for Massive MIMO Maritime Downlink Systems with Large-Scale CSIT

Different from conventional cellular networks, a maritime communication base station(BS) has to cover a much wider area due to the limitation of available BS sites. Accordingly the performance of users far away from the BS is poor in general. This renders the fairness among users a challenging issue for maritime communications. In this paper, we consider a practical massive MIMO maritime BS with hybrid digital and analog precoding. Only the large-scale channel state information at the transmitter(CSIT) is considered so as to reduce the implementation complexity and overhead of the system. On this basis, we address the problem of fairness-oriented precoding design. A max-min optimization problem is formulated and solved in an iterative way. Simulation results demonstrate that the proposed scheme performs much better than conventional hybrid precoding algorithms in terms of minimum achievable rate of all the users, for the typical three-ray maritime channel model.

Simultaneous two-way classical communication and measurement-deviceindependent quantum key distribution on oceanic quantum channels

Simultaneous two-way classical and quantum(STCQ)communication combines both continuous classical coherent optical communication and continuous-variable quantum key distribution(CVQKD),which eliminates all detection-related imperfections by being measurement-device-independent(MDI).In this paper,we propose a protocol relying on STCQ communication on the oceanic quantum channel,in which the superposition-modulation-based coherent states depend on the information bits of both the secret key and the classical communication ciphertext.We analyse the encoding combination in classical communication and consider the probability distribution transmittance under seawater turbulence with various interference factors.Our numerical simulations of various practical scenarios demonstrate that the proposed protocol can simultaneously enable two-way classical communication and CV-MDI QKD with just a slight performance degradation transmission distance compared to the original CV-MDI QKD scheme.Moreover,the asymmetric situation outperforms the symmetric case in terms of transmission distance and optical modulation variance.We further take into consideration the impact of finite-size effects to illustrate the applicability of the proposed scheme in practical scenarios.The results show the feasibility of the underwater STCQ scheme,which contributes toward developing a global quantum communication network in free space.