Investigation on the linewidth tolerance of the space coherent laser communication system under atmospheric turbulence

Abstract

Quadrature Phase Shift Keying (QPSK) is an important digital signal modulation method, which has the advantages of high spectrum efficiency and strong anti-interference. Coherent laser communication has the advantages of high speed, large capacity, light and small equipment as well as high sensitivity. In order to better introduce the QPSK modulation method into the space downlink coherent laser communication system, we give a bit error rate (BER) of QPSK modulation model with laser linewidth suitable for space downlink coherent laser communication system with QPSK modulation under atmospheric turbulence. Based on the model, we simulate and analyze the effects of atmospheric wind speed, zenith angle, gain of Erbium doped optical fiber amplifier (EDFA) and communication rate on the linewidth tolerance of space downlink coherent laser communication system with QPSK modulation. The results show that the linewidth tolerance of the system increases when the zenith angle decreases or the gain of EDFA increases or the wind speed decreases. And the effects of zenith angle, gain of EDFA and communication rate on the linewidth tolerance of the space downlink coherent laser communication system with QPSK modulation are large. The effect of wind speed on the linewidth tolerance of space downlink coherent laser communication system with QPSK modulation is smaller. And the larger the wind speed is, the smaller the effect of increasing wind speed on the linewidth tolerance. For the communication rate, the linewidth tolerance increases and then decreases with the increase of the communication rate. This work can be a reference for the design of space downlink coherent laser communication system with QPSK modulation.