| Summary: | 碩士 === 國立中央大學 === 通訊工程研究所碩士在職專班 === 95 === 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.
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