Quantum satellite communication is an essential part in building a global quantum communication network. In order to cope with the sudden interference brought by snowfall to the quantum satellite communication system, an adaptive adjustment strategy for quantum satellite communication performance based on the optimal average photon number is proposed based on the decoy state protocol and snowfall spectral distribution function for the depolarization channel characteristics. The relationship between snowfall intensity and communication elevation angle and the optimal average number of photons per pulse is established, and the bit error ratio(BER) and survival performance of the system before and after the adoption of this strategy is compared. The simulation results show that the BER of the system decreases from 0.07 and 0.085 to 0.046 and 0.064 for medium and heavy snowfall environments, respectively; if the minimum communication elevation angle is required to be 0.81, the survival capability of the system increases from 0.81 to 0.92 for heavy snowfall environment; if the channel survival capability is required to be 0.8, the minimum communication elevation angle of the satellite link can be adjusted from 26° to 18° for heavy snowfall environment. Therefore, the strategy proposed enables the system to cope with more intense snowfall, improves the transmission quality of small elevation angle communication, further reduces the BER of the quantum satellite communication system, and enhances the reliability of the system in the snowfall context.
Quantum satellite communication is an essential part in building a global quantum communication network. In order to cope with the sudden interference brought by snowfall to the quantum satellite communication system, an adaptive adjustment strategy for quantum satellite communication performance based on the optimal average photon number is proposed based on the decoy state protocol and snowfall spectral distribution function for the depolarization channel characteristics. The relationship between snowfall intensity and communication elevation angle and the optimal average number of photons per pulse is established, and the bit error ratio(BER) and survival performance of the system before and after the adoption of this strategy is compared. The simulation results show that the BER of the system decreases from 0.07 and 0.085 to 0.046 and 0.064 for medium and heavy snowfall environments, respectively; if the minimum communication elevation angle is required to be 0.81, the survival capability of the system increases from 0.81 to 0.92 for heavy snowfall environment; if the channel survival capability is required to be 0.8, the minimum communication elevation angle of the satellite link can be adjusted from 26° to 18° for heavy snowfall environment. Therefore, the strategy proposed enables the system to cope with more intense snowfall, improves the transmission quality of small elevation angle communication, further reduces the BER of the quantum satellite communication system, and enhances the reliability of the system in the snowfall context.
In order to study the communication performance and parameter analysis of the satellite-to-earth link of the quantum satellite under the condition of forming snowfall in the stratosphere, firstly, according to the distribution function and extinction characteristics of the concentric spherical ice water condensation nuclei in the stratosphere and the snowfall, according to the Mie theory, the system environment is obtained. The extinction efficiency factor establishes the relationship between the quantum signal transmission distance and link attenuation under different system environmental levels. Further studies have been done to establish the relationship between channel capacity, survival function, bit error rate, transmission distance, and system environment level under the condition of long-distance transmission of optical quantum signals at a moderate proportion of stratus cloud and snowfall. The simulation shows that as the transmission distance and environmental level increase, the link attenuation gradually increases, the channel capacity and survival function are greatly reduced, and the bit error rate increases. Therefore, when performing satellite-to-earth link communication, the relevant parameters of quantum communication should be adjusted adaptively to reduce the influence of snowfall caused by the formation of stratus clouds and improve the transmission performance of quantum communication.
In order to study the influence of snowfall on quantum positioning system, according to snowflake model and Mie scattering theory, the extinction coefficient of snowflake is defined, and the relationship between signal attenuation, snowfall intensity and transmission distance of quantum positioning system under different zenith angles is established. The mathematical models of positioning error, snowfall intensity and transmission distance are established through the opening angle of two quantum satellite baselines relative to users. The simulation results show that the signal of quantum positioning system attenuates with the increase of snowfall intensity and zenith angle, and the positioning error increases with the increase of snowfall intensity. Properly adjusting the opening angle can reduce the positioning error of users. Finally, the mathematical model between snowfall intensity, transmission distance and channel fidelity are established. The simulation results show that the minimum fidelity is not less than 0.9, which provides a theoretical basis for the impact of snow on quantum satellite positioning system. Therefore, in order to improve the reliability of quantum positioning system, the parameters of quantum satellite positioning system should be adjusted adaptively according to the relevant parameters of snowfall.
Quantum satellite communication has the natural advantages of strong survival reliability and wide coverage, and is currently a research hotspot in the field of communication at home and abroad. The successful launch of the "Mozi" scientific experimental satellite has laid the foundation for the construction of the quantum space-earth integrated communication network. In order to further improve the communication performance of the quantum satellite-ground link, a tuning strategy based on quantum coupled associative feedback control (QCAFC) is proposed in this paper. QCAFC estimates the state information of atoms by measuring the photons leaked in the optical cavity, and adjusts the controller to change the spin state of the atoms in the optical cavity. The evolution of the system is studied, the influence of the QCAFC system on the performance parameters of the satellite-ground quantum communication is analyzed, and the simulation is verified. The simulation results show that in the amplitude damped channel, the QCAFC system can significantly improve the channel capacity and coherence. When transmitting in the plasma environment, when the particle radius is 5, when the transmission distance between the satellite and the earth increases from 50km to 200km, the bit error rate of the system without QCAFC is increased from 7.34×10-3 to 21.93×10-3, and the bit error rate of the system with QCAFC is increased from 4.81×10-3 to 14.72×10-3. Simulation results show that the use of QCAFC system has a significant improvement in the performance of quantum satellite communication.
As one of the most common weathers in daily life, the rain can change the atmospheric compositions and humidity in a short time, which may cause non-ignorable attenuation in free-space quantum communication system. Besides, the absorption and scattering effects caused by raindrops can also bring huge attenuation to photon's propagation. In order to solve this burst interference caused by rain weather, optimal mean photon number per pulse and chameleon self-adaptive algorithm (CSA) are proposed based on the rainfall distribution model and decoy-state quantum key distribution. Due to the lack of producing mature ideal single photon source technology, the decoy-state protocol with highly attenuated laser becomes the most practical and most widely used quantum secure communication protocol currently. Among all the different kinds of decoy-state protocols, the vacuum+weak decoy state quantum communication secure protocol is chosen to be the basis of our research. Besides, in order to study the influence of mean photon number per signal pulse, we set the pulse ratio between signal state, decoy state and vacuum state to be fixed at 2:2:1. Since the performance of the vacuum+weak decoy state quantum communication system is closely related to the mean photon number per pulse, it is very necessary to confirm the optimal value. Combining the Weibull rainfall distribution model and Mie scattering theory, we first analyze the attenuation caused by rainfall in a free-space quantum communication system. Then the functional relationship among opt, rainfall intensity (J) and link distance (L) is built by studying the propagation of highly attenuated laser in depolarizing channel. Finally, two parameters, secure key rate and channel survival function, are chosen to evaluate the system's performance of reliability and validity. These two parameters are respectively compared between the system with and without CSA. Simulation results show that, as J=30 mm/24 h, L=30 km, the secure key generation rate rises from 210-4 up to 3.510-4 when using the CSA in the quantum communication system; as J=60 mm/24 h, L=20 km, the quantum channel survival function value increases from 0.52 to 0.63; as the quantum channel survival function value is required no lower than 0.5, the rainfall intensity in which quantum communication system can survive rises from 62 mm/24 h up to 74 mm/24 h. These results prove that there is a close relationship between opt and the channel parameters of the quantum communication system under the background of rainfall. Therefore, it is necessary for us to self-adapt the opt value by combining rainfall intensity with the CSA strategy if the reliability and survivability of free space quantum communication system are required to be improved.
Quantum communication in free space will be disturbed by natural environment such as fog and dust. However, to build a global quantum satellite wide area communication network, we must solve the problem of 24-h all-weather communication between satellite and earth. With the evolution of time, the degree of interference becomes deeper. In order to improve the performance of quantum communication under such an interference, in this paper we analyze the change of single quantum state channel over time under the background interference, and propose an quantum state-hopping communication strategy based on the kangaroo entanglement hopping model (KEHM), and simulate the performance and parameters of the strategy. Kangaroos are social animals. When they are frightened, they will jump synchronously in the same way with the same step length, height and frequency. According to this model, we make the two communicating parties realize synchronous quantum state jump according to the prearranged pattern. The simulations show that when the ratio between the average power of background quantum noise and the average power of quantum signal is 5, the quantum bit error rate decreases from 0.4524 to 0.1116 with the quantum state hopping frequency increasing from 1 to 15. When the single quantum state transmission success rate is 0.95 and the quantum bit rate is greater than 200 qubit/s, the probabilities of successful transmission of quantum bits at different state hopping frequencies are greater than 0.97. When the quantum reception efficiency of the receiver is 0.8, the quantum state pass rate increases from 0.3667 to 0.9986 with the average quantum number of the source increasing from 1 to 10. When the average quantum number of the source is 6, the passing rate of quantum state increases from 0.6262 to 0.9855 with the quantum receiving efficiency of the receiver increasing from 0.2 to 0.99. However, if the average quantum number of the transmitter is large enough and the receiving efficiency of the receiver is close to 1, the passing rate of the quantum state is also close to 1. The adaptive control strategy of quantum state hopping is based on real-time quantum channel state detection. Its core idea is to remove the quantum states which are seriously disturbed from the quantum state hopping set, and to realize the synchronous hopping of communication parties on the quantum states with low interference. Adopting the strategy of quantum state hopping adaptive control can further reduce the quantum bit error rate of the system. The error rate gain of adaptive control system increases with the increase of the success probability of processing the disturbed quantum state. When the probability of processing the disturbed quantum state is 0.95, the system error rate gain can reach 1.301. The performance of quantum state hopping system is improved obviously. To sum up, the adaptive quantum state-hopping communication strategy based on the kangaroo entanglement hopping model proposed in this paper greatly enhances the comprehensive immunity of the system and ensures the security of quantum information network, and provides an important reference for the healthy development of wide-area quantum satellite communication network in the future.
In order to study the effect of the coexistence of rain and fog on the communication performance of satellite terrestrial quantum link, the relationship between link attenuation and transmission distance and visibility was analyzed based on the attenuation model of optical quantum under the coexistence of rain and fog, and the influence of the coexistence of rain and fog on channel capacity, channel fidelity, channel survival function and channel bit error rate was studied. The findings reveal that at a visibility of 0.5 km and a transmission distance of 0.3 km, the link experiences an attenuation of1 0. 2 2 d B⋅k m−1. Furthermore, at the same visibility of 0.5 km and transmission distance of 0.25 km, the channel capacities for the amplitude damped and depolarized channels are recorded as 0.41 bit/sand 0.29 bit/s respectively. When visibility is 0.5 km and transmission distance is 0.3 km, the survival function values of amplitude damped channel and depolarized channel are 0.901 and 0.979 respectively. At a visibility of 0.5 km and with a transmission distance of 1 km, the channel's bit error rate reaches 0.24. Consequently, the coexistence of rain and fog significantly affects the efficiency of satellite terrestrial quantum communication systems. System parameters should be adjusted adaptively according to different environmental parameters to ensure the stability and reliability of the system.