{"created":"2021-03-01T06:24:05.552344+00:00","id":7323,"links":{},"metadata":{"_buckets":{"deposit":"e1f8f3bd-edf2-4fb9-bb70-896e7be38603"},"_deposit":{"id":"7323","owners":[],"pid":{"revision_id":0,"type":"depid","value":"7323"},"status":"published"},"_oai":{"id":"oai:repository.dl.itc.u-tokyo.ac.jp:00007323","sets":["6:291:292","9:233:280"]},"item_7_alternative_title_1":{"attribute_name":"その他のタイトル","attribute_value_mlt":[{"subitem_alternative_title":"ランダムな擾乱媒質と指向誤差を伴う光宇宙通信における光波伝搬"}]},"item_7_biblio_info_7":{"attribute_name":"書誌情報","attribute_value_mlt":[{"bibliographicIssueDates":{"bibliographicIssueDate":"2003-06-12","bibliographicIssueDateType":"Issued"},"bibliographic_titles":[{}]}]},"item_7_date_granted_25":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2003-06-12"}]},"item_7_degree_grantor_23":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_name":"University of Tokyo (東京大学)"}]}]},"item_7_degree_name_20":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士(工学)"}]},"item_7_description_5":{"attribute_name":"抄録","attribute_value_mlt":[{"subitem_description":"This study is devoted to lightwave propagation in the presence of random pointing jitter and atmospheric turbulence. The intrinsic narrow beam/high gain nature of free-space laser communications produces several extremely valuable advantages when compared to microwaves, but also requires a very high tracking and pointing accuracy. Furthermore, space-to-ground optical communications are strongly affected by scintillation effects due to the turbulent atmosphere. The purpose of this study is to establish the optimum design methods for optical communication links in the presence of random pointing jitter and atmospheric turbulence. The study is based on theoretical statistical analysis and the results obtained from laser transmission experiments between a ground station and a satellite. The following summary presents the major results and the advantages for the study objectives. (1) In-orbit verification of the recent established theory about uplink/downlink lightwave propagations// In recent years the theory of Gaussian beam wave propagation has been well developed but the characteristics in bi-directional ground-to-satellite slant paths were not verified by real experiments. In this thesis, for the first time to the author's best knowledge, the propagation characteristics of actually performed satellite-to-ground and ground-to-satellite laser communication experiments are discussed. The downlink scintillation is almost constant with respect to the off-axis direction of the beam in spite of a Gaussian roll-off in the mean intensity. On the other hand, the atmospheric turbulence influences the uplink laser beam more severely than the downlink one. The uplink scintillation shows a square behavior with respect to the off-axis direction of the beam. The propagation data can be applied to the lognormal distribution under the assumption of weak atmospheric turbulence, and the joint probability density function (PDF) of both random pointing jitter and atmospheric turbulence reveals a good agreement with the results. Owing to the in-orbit laser propagation experiments, it was possible to explain well and verify the recent established theory in this dissertation. (2) Evaluation of the narrow beam pattern in the presence of random pointing jitter// A new technique to evaluate the very narrow optical beam pattern of an onboard laser transmitter is proposed. The method is based on the statistical analysis for fluctuated downlink irradiance data in an atmospheric satellite-to-ground optical path. The pointing jitter error dominates in the downlink optical beam. In the new technique the pointing jitter effects are included in the link equations. The proposed technique gives the exact beam profile if the pointing jitter and atmospheric turbulence effects broaden the measured far-field pattern. The atmospheric turbulence does not significantly broaden the downlink optical beam because the turbulent medium is close to the receiver for the downlink path. The result is very useful for the evaluation of a very narrow beam transmitted with random pointing jitter. (3) Time averaging effect of the optical scintillation// A new temporal behavior for the variance of turbulence-induced log-intensity fluctuations is analyzed with respect to the uplink laser beam that the atmospheric turbulence seriously influences. The PDF of the received optical signal coincides with the joint PDF of both random pointing jitter and atmospheric turbulence. The time-averaged signal on the optical sensor has smaller fluctuation than that on the high frequency bandwidth detector. Here, this index of reduction is for the first time interpreted as the time-averaging factor that is given by the integration of the autocovariance function. The approximated engineering model of the autocovariance function of the optical signal is newly developed based on the measured results that have the 1/e2 correlation lengths of a few ms. The fade level at an allowable fade probability is improved by the time-averaging effect. The consideration of the fade improvement contributes to the link budget design for the optical tracking channel in presence of atmospheric turbulence. (4) Microvibrational disturbance// In the past some in-orbit measurements were done by using the accelerometers, however, there is still not enough data to establish the proper database for microvibration of space-borne optical systems. In this dissertation, the database of in-orbit angular microvibrations on the satellite platform has been updated by the power spectral densities (PSDs) measured in the laser tracking experiments. The tracking capability of the laser communication terminal is useful for the accurate microvibration measurement. To the author's best knowledge it was the first time that the high-sampled information data was sent via the optical carrier through the established laser communication link. A proposed PSD model varies with the power of -4 in frequency, which corresponds to the slope of a constant acceleration level. The obtained results are useful for the future design of a tracking control loop for optical communication systems. (5) In-orbit co-alignment error owing to the optical deformation// Optical devices in free-space laser communication systems are affected by their environment, particularly with regard to temperature effects while being in orbit. So far it has not been known that the mutual alignment errors between the transmitted and received optical axes arise owing to the deformation of the optics even if common optics was used for transmission and reception of the optical beams. The alignment errors come from the difference between the transmitted Gaussian beam and the received plane wave. 3rd-order Coma aberrations are most influential on the mutual alignment error, and causes an inevitable open pointing error under only the Tip/Tilt tracking control. Also, truncation and obscuration effects of the optical telescope act as a weighting function of each aberration. The proposed method for an antenna design mitigates the wave-front error in an expensive optical system and contributes to its system design. (6) Optimum beam divergence angle in the presence of random pointing jitter// The greatest concern in designing an optical communication system is to determine the divergence angle of the transmitted laser beam given the random pointing jitter because of the intrinsic narrow beam. There is an optimum value between the beam divergence angle w0 and the rms random pointing jitter σ. For smaller beam divergence angles stronger fluctuation in the optical signal due to the random pointing jitter degrades the average bit error rate (BER) performance, which gradually occurs at w0/σ<12. At larger beam divergence angles the mean intensity is reduced in proportion to w0-2. Both phenomena increase the power penalty with respect to the average BER. An approximated engineering model for the optimum ratio is proposed and believed very useful for the optical system engineers. The results also contribute to design the link budget of optimum communication and tracking channels in the presence of random pointing jitter. (7) Designing methods to establish the optimum communication link// So far it has not been reported how to design the optimum communication link in the presence of both atmospheric turbulence and random pointing jitter. There exists also an optimum value for the beam divergence angle and the pointing jitter in the presence of atmospheric turbulence. The optimum value slightly changes with the strength of atmospheric turbulence in which the zenith angle of the propagation path, the wind speed, and the structure parameter vary with time. As a result of this study the beam divergence angle should be 7 times larger than the beam pointing jitter when aiming for the average BER of 10-9, which minimizes the transmitting power penalty for the optical ground station. The multibeam laser transmission system is effective in the reduction of optical fluctuations. A simple treatment of the multibeam and the aperture averaging gains is useful in facilitating parametric estimation and optimization of the overall system design in free-space laser communication systems. The proposed approach can also be applied to the link design in the case of strong turbulence by employing the PDF of the gamma-gamma distribution instead of the lognormal PDF. Different from various past studies, the current study has paid special attention to the pointing jitter in the theoretical analysis, and the practical verifications of the uplink/downlink lightwave propagations have been performed. The methodology for designing the optimum free-space laser communication link has been established by using the several defined parameters based on a statistical approach. Optical space communications are considered to be used in various fields such as military, governmental, and commercial applications in the future. Now, the development of optical space communications enters the onset of the next generation development phase. A serious drawback is the probability of link outage due to clouds or bad weather, however, multiple ground-site diversity can compensate for this drawback. The contents of the thesis should give a guideline to get the best performance out of the optical space communication system in terrestrial and space free-space communication infrastructures in the future.","subitem_description_type":"Abstract"}]},"item_7_dissertation_number_26":{"attribute_name":"学位授与番号","attribute_value_mlt":[{"subitem_dissertationnumber":"乙第15706号"}]},"item_7_full_name_3":{"attribute_name":"著者別名","attribute_value_mlt":[{"nameIdentifiers":[{"nameIdentifier":"14851","nameIdentifierScheme":"WEKO"}],"names":[{"name":"豊嶋, 守生"}]}]},"item_7_identifier_registration":{"attribute_name":"ID登録","attribute_value_mlt":[{"subitem_identifier_reg_text":"10.15083/00007314","subitem_identifier_reg_type":"JaLC"}]},"item_7_select_21":{"attribute_name":"学位","attribute_value_mlt":[{"subitem_select_item":"doctoral"}]},"item_7_subject_13":{"attribute_name":"日本十進分類法","attribute_value_mlt":[{"subitem_subject":"547","subitem_subject_scheme":"NDC"}]},"item_7_text_22":{"attribute_name":"学位分野","attribute_value_mlt":[{"subitem_text_value":"Engineering(工学)"}]},"item_7_text_24":{"attribute_name":"研究科・専攻","attribute_value_mlt":[{"subitem_text_value":"Department of Electronic Engineering, Graduate School of Engineering (工学系研究科電子工学専攻)"}]},"item_7_text_27":{"attribute_name":"学位記番号","attribute_value_mlt":[{"subitem_text_value":"第15706号"}]},"item_7_text_4":{"attribute_name":"著者所属","attribute_value_mlt":[{"subitem_text_value":"National Space Development Agency of Japan"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"Toyoshima, Morio"}],"nameIdentifiers":[{"nameIdentifier":"14850","nameIdentifierScheme":"WEKO"}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2017-06-02"}],"displaytype":"detail","filename":"K-215706.pdf","filesize":[{"value":"261.3 MB"}],"format":"application/pdf","licensetype":"license_note","mimetype":"application/pdf","url":{"label":"K-215706.pdf","url":"https://repository.dl.itc.u-tokyo.ac.jp/record/7323/files/K-215706.pdf"},"version_id":"c2f2f1fe-c616-41d7-8b62-8e53a992d9bd"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"thesis","resourceuri":"http://purl.org/coar/resource_type/c_46ec"}]},"item_title":"Lightwave Propagation in the Presence of Random Turbulent Media and Pointing Jitter in Optical Space Communications","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Lightwave Propagation in the Presence of Random Turbulent Media and Pointing Jitter in Optical Space Communications"}]},"item_type_id":"7","owner":"1","path":["280","292"],"pubdate":{"attribute_name":"公開日","attribute_value":"2015-12-03"},"publish_date":"2015-12-03","publish_status":"0","recid":"7323","relation_version_is_last":true,"title":["Lightwave Propagation in the Presence of Random Turbulent Media and Pointing Jitter in Optical Space Communications"],"weko_creator_id":"1","weko_shared_id":null},"updated":"2022-12-19T03:47:30.550465+00:00"}