Considering the air-water interface and ocean water’s optical attenuation,the performance of quantum key distribution(QKD)based on air-water channel is studied.The effects of photons’various incident angles to air-water interface on quantum bit error rate(QBER)and the maximum secure transmission distance are analyzed.Taking the optical attenuation of ocean water into account,the performance bounds of QKD in different types of ocean water are discussed.The simulation results show that the maximum secure transmission distance of QKD gradually reduces as the incident angle from air to ocean water increases.In the clearest ocean water with the lowest attenuation,the maximum secure transmission distance of photons far exceeds the the working depth of underwater vehicles.In intermediate and murky ocean waters with higher attenuation,the secure transmission distance shortens,but the underwater vehicle can deploy other accessorial methods for QKD with perfect security.So the implementation of OKD between the satellite and the underwater vehicle is feasible.
Combining heralded pair coherent state(HPCS) with passive decoy-state idea,a new method is presented for quantum key distribution(QKD).The weak coherent source(WCS) and heralded single photon source(HSPS) are the most common photon sources for state-of-the-art QKD.However,there is a prominent crossover between the maximum secure distance and the secure key generation rate if these two sources are applied in a practical decoy-state QKD.The method in this paper does not prepare decoy states actively.Therefore,it uses the same experimental setup as the conventional protocol,and there is no need for a hardware change,so its implementation is very easy.Furthermore,the method can obtain a longer secure transmission distance,and its key generation rate is higher than that of the passive decoy-state method with WCS or HSPS in the whole secure transmission distance.Thus,the limitation of the mentioned photo sources for QKD is broken through.So the method is universal in performance and implementation.
In this paper,by utilizing the angle of arrivals(AOAs) and imprecise positions of the sensors,a novel modified Levenberg-Marquardt algorithm to solve the source localization problem is proposed.Conventional source localization algorithms,like Gauss-Newton algorithm and Conjugate gradient algorithm are subjected to the problems of local minima and good initial guess.This paper presents a new optimization technique to find the descent directions to avoid divergence,and a trust region method is introduced to accelerate the convergence rate.Compared with conventional methods,the new algorithm offers increased stability and is more robust,allowing for stronger non-linearity and wider convergence field to be identified.Simulation results demonstrate that the proposed algorithm improves the typical methods in both speed and robustness,and is able to avoid local minima.
