Research on Bandwidth of Optical Filter in GEO-LEO Laser Communication

Abstract

In this paper, we present an optimal bandwidth of optical filter in GEO-LEO laser communication considering Doppler Effect between the different orbit satellites by using matched filter method. To satisfy the requirements of communication system, the relation of the normalized SNR of signals and optical filter bandwidth is analyzed and the optimum bandwidth is derived. Based on the optimum bandwidth, the optical filter can improve the performance of the laser satellites communication systems effectively. Satellites laser communication links are playing more and more important role in modern communications. Laser communication systems operate in a frequency range above the regulated spectrum. Laser provides many advantages for using in point-to-point ISLs (Inter-Satellites Links) such as for links between satellites and spacecraft in deep space. Such advantages include: high speed; high bandwidth; small antenna size; narrow field of view; and narrow antenna beam. These advantages combined with the advantages in fiber optic components have made laser links attractive for satellites communication. Because satellites are in free-space, there are strong background noises, such as galactic noise, sunlight, star light and other light. The optical noise will affect system performance and makes SNR descend. Strong background optical noise can interrupt communication. A majority of background noise can be filtered with narrow line-width fiber grating in satellites laser communication. To satisfy the requirements of Satellite Optical Communications, the effects of optical filter bandwidth on communication performance are researched in the design of high performance optical filter. Considering Doppler Shift, the relation of the normalized SNR and filter bandwidth is analyzed and the optimum bandwidth is derived. Based on the optimum bandwidth, the optical filter can be designed. In this paper, we propose a matched filter model to overcome the background noises of the satellites laser communication system. In section II, we will study the Doppler shift in GEO-LEO laser communication in details. In section III, the optimal bandwidth of matched filter is presented. We give the bandwidth of the optical filter and the SNR performance analysis of the communication system in section IV, simulation results are also given in this section. Finally, we conclude with summary in section V. II. BANDWIDTH OF MATCHED FILTER Optical receiver system of GEO-LEO laser communication system receives not only the light source signal, but also strong background optical noise in communication. The background optical noise can reduce the system BER (Bit Error Rate); strong background optical noise can cover up optical signal and make the communication interrupt.