Optimization Research On Link And Communication Performance For Intersatellite Laser Communications

As next-generation free space communication technology, satellite lasercommunication possesses outstanding advantages in high data rate and largecommunication capability, which is an effective way to fulfill the real-time high-data ratecommunication requirements. Intersatellite laser communication is the future informationsuperhighway and the key to establish space-ground real-time high-data rate opticalnetwork. Therefore it is beneficial to national economy and defence.To communicate between satellites, the distance ranging from several thousand toten thousand kilometers, pointing and tracking is necessary to establish and maintainintersatellite laser links, considering narrow laser beam, satellite relative motion,platform vibration, and so on. Only fast acquisition can guarantee largest informationtransmitted in limited link time, and high precise and stable tracking ensures reliablecommunication. Therefore, in order to take the advantages of laser communication andrealize the large capacity communication, it is critical to research the link andcommunication performance in detail.Intersatellite laser communication system is an advanced equipment which involvesoptics, mechanics, and electronics. Hence, the system is of complicated structure,multi-functional, and with interaction among many parameters. Therefore, the currentresearch on link and communication performance is still needed to be pushed forward.With the success of spatial experiments for intersatellite laser communication, it is urgedto promote this technology to practical applications. Thus, smart system structures aredesigned and key modules are developed. These bring new problems to be investigated.To address the problems stated above, this dissertation deals with the followingaspects: the acquisition performance was studied for beacon and beaconlessconfiguration; the optimum fine tracking sub-window (FTSW) was theoreticallyinvestigated and simulation was carried out for intersatellite laser communications whichadopts CMOS as single focal-plane detector array (FPAD); taking consideration ofCMOS detector error, the tracking performance especially the tracking stability wasanalyzed; and the influence of random pointing and tracking error angular jitter onchannel capacity and outage probability is investigated.Firstly, theoretical analysis and optimization are performed for acquisition ofintersatellite laser links. The single-scan mean acquisition for serial and parallelacquisition mode are derived, and analytical expressions were obtained. The acquisitionperformances of these two acquisition modes were compared taking different system andlink parameters. Beaconless acquisition configuration is suitable for LEO links, in whichmulti-scan is needed. Therefore, the multi-scan mean acquisition time was also derived,based on which the optimum uncertainty scan area is deduced.Secondly, the optimum FTSW of CMOS in single FPAD system was studied in the presence of satellite platform vibration. In the focal plane, the random jitter model ofreceived beam spot is established. And the equations about optimum FTSW size arepresented. Based on these equations, numerical simulation was performed for theoptimum FTSW, taking OLYMPUS platform vibration as an example.Thirdly, the influence of CMOS detector error on system tracking error and thestability of bi-directional closed tracking loop are investigated. The relation betweensystem tracking error and CMOS detector error was analyzed. The interaction relationbetween the two optical terminals’ tracking error is modeled. The stability ofbi-directional tracking was studied in case of identical tracking sub-systems. And theinfluence of CMOS parameters on tracking stability, the convergence range of varianceof tracking error and stable variance of tracking error were obtained.Fourthly, the channel capacity and outage probability is investigated in the presenceof pointing and tracking error angular random jitter with and without static bias errors,respectively. The transfer matrix is derived in the presence of random pointing andtracking error angular jitters. The optimum source input distribution and channel capacitywere obtained, on which the influences of system parameters are discussed. The outageprobability is modeled in the presence of random pointing and tracking error angularjitters, based on which the optimum beam divergence angle is obtained. And theinfluences of system parameters on outage probability are also discussed.What achieved in this dissertation contributes to the theory of acquisition trackingand communication for intersatellite laser communications, and can benefit theoptimization of intersatellite laser communication systems.