Real-time frequency transfer system over ground-to-satellite link based on carrier-phase compensation at 10-16 level

We demonstrate a novel and stable frequency transfer scheme over ground-to-satellite link based on real-time carrier-phase detection and compensation.We performed a zero-baseline measurement with the designed system,an uninterrupted frequency standard signal is recovered in the reception station without additional post-correction of delay error caused in the route,which is because the phase error of the entire route is tracked and compensated continuously in real-time.To achieve this goal,we employed two carriers in the system and the differential signal is transferred in order to eliminate the instability results from the local oscillator at the satellite transponder as well as the common-mode noise induced in the transfer route and microwave components.The stability of 3×10^(-16) with an integration time of 1 day was achieved and the time fluctuation during one day was measured to be about±20 ps.Error sources and possible solutions are discussed.Our zero-baseline method shows a promising result for real-time satellite-based time and frequency transfer and deserves further research to find whether it works between long-baseline stations.

Performance Comparison of PIN and APD based FSO Satellite Systems for various Pulse Modulation Schemes in Atmospheric Turbulence

In this paper, the performance of various Pulse Position Modulation (PPM) schemes has been analysed for PIN and APD receivers in the presence of atmospheric turbulence. It is observed that the performance of the APD receiver is always better than that of the PIN receiver as expected. Among the various modulation schemes, the performance of Differential Amplitude PPM (DAPPM) scheme with more number of amplitude levels is better than that of the other schemes for the same single level peak amplitude. Further, the optimum gain of APD receiver does not change substantially for different modulation schemes and turbulent conditions.