scholarly journals Qubit-Based Clock Synchronization for QKD Systems Using a Bayesian Approach

Entropy ◽  
2021 ◽  
Vol 23 (8) ◽  
pp. 988
Author(s):  
Roderick D. Cochran ◽  
Daniel J. Gauthier
Keyword(s):  
Quantum Key Distribution ◽  
Clock Synchronization ◽  
Photon Number ◽  
Model System ◽  
Dark Count ◽  
Probabilistic Algorithm ◽  
Essential Step ◽  
Available Information ◽  
Clock Offset ◽  
Provably Secure

Quantum key distribution (QKD) systems provide a method for two users to exchange a provably secure key. Synchronizing the users’ clocks is an essential step before a secure key can be distilled. Qubit-based synchronization protocols directly use the transmitted quantum states to achieve synchronization and thus avoid the need for additional classical synchronization hardware. Previous qubit-based synchronization protocols sacrifice secure key either directly or indirectly, and all known qubit-based synchronization protocols do not efficiently use all publicly available information published by the users. Here, we introduce a Bayesian probabilistic algorithm that incorporates all published information to efficiently find the clock offset without sacrificing any secure key. Additionally, the output of the algorithm is a probability, which allows us to quantify our confidence in the synchronization. For demonstration purposes, we present a model system with accompanying simulations of an efficient three-state BB84 prepare-and-measure protocol with decoy states. We use our algorithm to exploit the correlations between Alice’s published basis and mean photon number choices and Bob’s measurement outcomes to probabilistically determine the most likely clock offset. We find that we can achieve a 95 percent synchronization confidence in only 4140 communication bin widths, meaning we can tolerate clock drift approaching 1 part in 4140 in this example when simulating this system with a dark count probability per communication bin width of 8×10−4 and a received mean photon number of 0.01.

scholarly journals Determination of Varying Group Sizes for Pooling Procedure

2019 ◽  
Vol 2019 ◽  
pp. 1-8 ◽  
Author(s):  
Wenjun Xiong ◽  
Hongyu Lu ◽  
Juan Ding
Keyword(s):  
Group Size ◽  
Rare Diseases ◽  
Population Heterogeneity ◽  
Sequential Procedure ◽  
Data Driven ◽  
Equal Group ◽  
Essential Step ◽  
Available Information ◽  
Individual Information

Pooling is an attractive strategy in screening infected specimens, especially for rare diseases. An essential step of performing the pooled test is to determine the group size. Sometimes, equal group size is not appropriate due to population heterogeneity. In this case, varying group sizes are preferred and could be determined while individual information is available. In this study, we propose a sequential procedure to determine varying group sizes through fully utilizing available information. This procedure is data driven. Simulations show that it has good performance in estimating parameters.

scholarly journals Adaptive Fractional-Order Operator Clock Synchronization Algorithm Based on Grey Prediction

2020 ◽  
Vol 2020 ◽  
pp. 1-15
Author(s):  
Hongwei Yang ◽  
Long Wang ◽  
Jing Zhang ◽  
Li Li
Keyword(s):  
Fractional Order ◽  
Clock Synchronization ◽  
Sensor Nodes ◽  
Prediction Algorithm ◽  
Grey Prediction ◽  
Order Operator ◽  
Message Transmission ◽  
Synchronization Algorithm ◽  
Improved Stability ◽  
Clock Offset

As a result of the influence of clock drift and uncertainty delay in synchronous message transmission, the clock synchronization model based on statistical distribution cannot accurately describe clock deviation. This model also requires a large number of timestamp samples that cause a storage occupation issue for wireless sensor nodes with limited resources. The modeling method based on grey prediction has advantages of low sample demand and simple modeling process. However, the accuracy of the existing clock synchronization models needs to be improved. Based on the grey prediction theory, this paper proposes an adaptive fractional-order operator clock synchronization algorithm considering uncertainty delay. First, based on the clock model and clock offset model, the frequency offset between nodes is optimized by taking the mean on the clock frequencies. Second, a grey prediction algorithm based on a fractional-order operator is proposed by estimating the uncertainty delay in message transmission to obtain the clock offset. Finally, the order of the fractional-order accumulation is adjusted adaptively in the grey prediction model according to the collected timestamp sample values so that the estimation of the uncertainty delay is more accurate, thereby improving the accuracy of the clock offset. Compared with the first-order accumulative grey prediction clock synchronization algorithms and timing-sync protocol for sensor networks, the proposed scheme improved the synchronization accuracy by 29.18% and 44.01%, respectively, and reduced the variance of the clock offset by 48.66% and 64.89%. Thus, the proposed algorithm is characterized by improved stability.

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