| 摘要: | AIS船舶自動識別系統，是一種新型助航系統及設備，AIS的正確使用，有助於加強海上生命的安全，提高航行的安全性和效率。 從1990年由SAAB首度向國際海事組織(IMO)提出書面提案，歷經多年研討修訂，於1998年AIS性能標準被正式採納，2002年國際海事組織要求船舶開始使用AIS，並且規定從2008年7月1日起，所有300噸以上航行於國內外船隻，都必須安裝AIS船舶自動識別系統，因此在市面上已經有很多相關商品，如SAAB R4，SAMSUNG SIS-5，SR-162等。這些商品實現的架構都必須遵守國際海事組織(IMO)，所規定AIS性能標準與技術特性，而這些廠家在商品實現的過程，相信也使用了不少通訊工程技術。本篇論文焦點放在AIS Software Defined Radio (SDR)實現，SDR提供給射頻設計者更具有靈活性的一種實現技術-針對工作模式、無線電頻帶寬、實體層功能架構實現和波形產生更具有適應性，再利用性(re-configurability)、和多功能性。SDR具體的實現，就是使用軟體應用程式在一個普通硬體平台上，實現各式各樣的射頻功能，如頻帶選擇濾波器、載波同步、通道進接、符碼同步、訊框同步、調變與解調、媒介存取控制(MAC)等功能與機制。 在本篇論文中，我們首先針對AIS用途，起因背景做簡介，相關國際標準與技術文件參考蒐集整理，接著，介紹AIS的架構，進入論文研究主題，軟體無線電去實現實體層GMSK/FM與資料鏈結層中三大部份。我們先根據IEC61993-2測試規範與ITU-R.M.1371-1系統規範，尋找出論文研究所需要規範整理，然後就這些規範相關理論技術，從課本與相關技術參考論文或書籍研讀整理。可大致區分成NRZI編碼、GMSK濾波、FM調變，構成AIS訊號的產生。接下來就是使用MATLAB工具來模擬整個AIS收發機過程。從高斯濾波器成形，使用AIS一個slot時間含有256個位元的測試訊息，通過高斯濾波器產生pulse shaping波形，加上FM調變後，產生AIS的調變波完成發射。 接下來經過傳輸通道部分，區分加與不加高斯分佈通道雜訊，接著進行接收訊息，FM解調，經過高斯濾波器整形，取樣後經過判決還原原來測試訊息，完成AIS的接收過程。在整個AIS的收發過程中，將發射前與發射後的測試訊息，通過不同高斯濾波器頻寬積，與不同雜訊大小繪出眼形圖與星座圖進行觀察與比較，考慮同步的問題，進行訊框同步(Frame Synchronization)，使用相關性法則來辦別AIS資料起始點等，最後也模擬理論值與測試資料經過不同高斯濾波器頻寬積，位元接收錯誤率曲線大小的比較。這些做法主要原因是將模擬過程與結果，能夠貼近真實AIS通訊系統的運作。 至於AIS收發期間，NRZI編解碼過程中位元冗碼(Bit Stuffing)處理，判別資訊收發正確與否之週期性多餘資訊檢驗(Cyclic redundancy check)，接收訊息編碼與解碼，資料鏈路時槽的建立進行listen、activate、release的工作，這些都由AIS資料鏈結層中服務層DLS(data link service)來負責。相關的演算法與規則在第四章有詳細闡述。至於資料鏈路通道進接管理機制，採用SOTDMA、ITDMA、RATDMA、FATDMA等四個機制來控制資料傳輸媒體(MAC)的使用權，是由AIS資料鏈結層中管理層LME(Link Management Entity)負責。 相關的演算法使用時機、相關參數都有整理與比較。最後就是談到AIS的操作模式，有自主且連續(autonomous and continuous)，指定(assigned)、詢問(polled)等三種，這是在一定範圍內裝有AIS的所有船隻如何建立共享的資訊網路的方法。使AIS真正發揮識別船隻、協助追蹤目標、簡化資訊交流、提供其他輔助資訊以避免碰撞發生功能。 AIS (Automatic Identification System) is a kind of new auxiliary system for ship/boat navigation. Using AIS correctly will be greatly to enhance the safety and efficiency of navigation and especially for life safety improvement. In 1990, SAAB first propose the AIS standard to IMO(International Maritime Organization), through many year’ amendment in this standard, the AIS performance standard officially was adopted and IMO request all the abroad/non-abroad ships above 300 tons must install AIS starting from July first 2008. Until now, there are many kind of AIS in the market for example, SAAB R4，SAMSUNG SIS-5，SR-162 and so on. All these merchandise’s structure must follow the AIS specification defined by IMO and there are many kind of communication technology be used in these devices as well. This thesis will focus on the implementation of AIS Software Defined Radio (SDR). For RF designer, SDR can provide the flexibility for implementation and also provide more adaptability, re-configurability, and multifunction for operation mode, radio bandwidth, implementation-of-real-layer-structure, and wave generation. The concrete implementation of SDR is to use application software in ordinary platform to carry out various radio functions for example, bandwidth-selective-filter, carrier- synchronization, channel-entering, symbol-code-synchronization, message-frame-synchronization, modulation-demodulation, and media access control (MAC) etc. In this article, the background of AIS will be introduced first and all the related standard and technical documents were summarized and referred as well. Then the introduction of AIS structure, the main subject of this article, software-radio carrying out the real layer GMSK/FM and data-link layer was also addressed. Based on specifications, IEC61993-2 and ITU-R.M.1371-1, I summarized the needed parts as the NRZI coding、GMSK filtering、FM modulation, and forming signal generation of AIS. Further, the MATLAB will be used to simulate the complete process of transmitting-receiving of AIS. From the forming of Gauss filter, using one slot of AIS test message which includes 256 bits, pass through the Gauss filter to generate pulse shaping waveform, then after FM modulation to generate the AIS radiation wave for radiation. In the part of transmission channel, Gauss distribution or non- Gauss distribution noise will be discriminated, then receiving message, FM demodulation, pass through Gauss filter shaping, by sampling it to return to the original test message in order to complete the receiving process. During the AIS transmitting-receiving process, the test signal before transmitting and the test signal after transmitting will pass through different Gauss filter bandwidth-product and with different noise to draw the figure-of-vision and the figure-of-constellation for further observation and comparison, the comparison in resolving the magnitude of receiving-error-rate curve. The processes, Synchronization-consideration, Frame-Synchronization, using related algorithm to distinguish AIS starting-point-of-data are used for letting the simulation process really close to real AIS communication process. Regarding in the duration of AIS transmitting-receiving, the Bit Stuffing in NRZI encoding process, Cyclic-redundancy-check used in determination of correct transmitting-receiving message, encoding and decoding of receiving message, the establishment-of-data-link-slot for listen, active, and release task processing, and all of these are processed in DLS (data link service) which is in data-link layer and will be dilated in detail in chapter 4. As for the processing mechanism of data-link-channel, the four mechanism, SOTDMA、ITDMA、RATDMA、FATDMA will be used to control the using of MAC and all of these will be charged by LME(Link Management Entity) which also is in data-link-layer. All the detailed using-occasion-of-algorithm, related parameters will be addressed and compared. The last, the operation mode of AIS will be discussed, including autonomous-and-continuous, assigned, and polled, and by these methods share-information internet was established for the ships equipped with AIS within certain range. Let AIS completely achieve the auto-ship-identification function to support target tracking, to simplify information-sharing and to provide more auxiliary information about ships within certain region for fear of collision. |
