Regeneratively mode-locked optoelectronic oscillator.

A regeneratively mode-locked optoelectronic oscillator is proposed to realize multi-mode phase locking in optoelectronic oscillators by coupling a modulating signal generation loop. To verify the feasibility of the scheme, a numerical simulation model is established. In addition, a proof-of-concept experiment is demonstrated in a single-loop optoelectronic oscillator with a 2.2 km polarization-maintaining single-mode fiber, using an electric amplitude modulator/Mach-Zehnder modulator as an active mode-locking device. The generated microwave pulse signal has a center frequency of 10 GHz and a repetition rate of 95 kHz. We believe this scheme can provide a new approach to overcome the problem of detuning between the modulating frequency and the mode spacing during long-term operation.

A Novel Satellite PRN Code Assignment Method Based on Improved RLF Algorithm.

Low Earth Orbit (LEO) satellites have stronger received signals and more rapid geometry changes than Global Navigation Satellite System (GNSS) satellites, making them attractive for positioning, navigation, and timing (PNT) applications. Due to the low altitude, the LEO constellation requires more satellites to cover the entire globe and more Pseudo Random Noise (PRN) codes to realize Code Division Multiple Access (CDMA), which means greater receiver storage resources and receiver acquisition time. In this paper, different from the traditional methods that assign a unique PRN code to each satellite, we propose a novel method in which several satellites share the same PRN code, and simply demonstrate the feasibility and benefits of this method. To determine the minimum number of PRN codes needed for a constellation, we build a mathematical model. After the algorithm comparison, we improve the recursive largest first (RLF) algorithm so that it has a higher running speed and a smaller approximate optimal solution within a certain time period. By studying polar-orbiting and walker constellations, we find that if other satellite parameters remain the same, the higher the orbital altitude is, the more PRN codes are needed, and no matter what the orbital inclination is, the minimum number of PRN codes remains the same. Overall, it is feasible and meaningful for several satellites sharing the same PRN code to save storage resources and reduce the satellite acquisition time of the receiver. If this new technology is applied, the storage resources and the average satellite acquisition time of the receiver will be, at most, one-third of previous ones.