The remarkable power of radio signals for sending information over long distances at low power levels has been emphasised by the achievements of the Voyager mission to Jupiter and Saturn. Naturally one asks, what are the fundamental limitations?
Superconducting quantum interference devices (SQUIDs) are promising for detection of extremely weak power regimes for the Internet of Things and long-distance satellite networks. In low-frequency magnetic signal measurements, it has demonstrated superior performance over the traditional systems. We review the resistively and capacitively shunted junction model of dc SQUIDs and investigate its transfer function to magnetic flux signals while taking thermal fluctuation into account. We numerically evaluate the influence of bias current and bias flux signal to determine the operating parameters of the device. The performances related to SQUID ring inductance operating at 4.2 K and 77 K are demonstrated. Combined with common radio frequency front-end modules, including low-noise amplifier and low-pass filter, we evaluate the bit-error-rate performance of the system under different inductance values and inferred that the sensitivity of the system can reach −99 dBm at 100 MHz bandwidth.
The satellite time service technology is limited by the measurement accuracy of the classical radio signal, and the time service accuracy can only reach the ns level.In this paper, a satellite time service scheme based on microwave - optical wave -entangled signals is proposed.The advantages of long -distance transmission of microwave signals and single - photon detection of optical wave signals are effectively combined using a cavity electro -opto -mechanical converter.The phase difference is calculated using a phase -conjugating processor to obtain accurate time -difference information.Through theoretical analysis and simulations, it is demonstrated that even if the quantum signal is in low entanglement, the proposed scheme can improve the satellite time service accuracy to the ps level.
Due to the limitation of the measurement accuracy of classical radio signals, the time comparison accuracy can only reach ns level. In this paper, a time comparison scheme of BeiDou system based on microwave-optical entangled signal is proposed, which effectively combines the long-distance transmission advantage of microwave signal with the single photon detection advantage of optical signal by electro-opto-mechanical converter, and the phase difference is solved by a phase conjugate processor ,so as to calculate the accurate time difference information. Through theoretical analysis and simulation, it is proved that even if the quantum signal is under the condition of low entanglement degree, the proposed scheme can improve the time comparison accuracy to the ps level.