HELCOM Baltic Marine Environment Protection Commission ... International Electrotechnical Commission .... In 1996, Federal Radio Navigation Plan defines.
P O L I S H N A V A L A C A D E M Y FACULTY OF NAVIGATION AND NAVAL ARMAMENT
Lieutenant, Ph.D Krzysztof JASKÓLSKI
AVAILABILITY AND INTEGRITY MODEL OF AUTOMATIC IDENTIFICATION SYSTEM (AIS) INFORMATION
Doctor’s thesis Submitted to the Faculty of Navigation and Naval Armament Board of Polish Naval Academy
Promoter: Professor, D.Sc. Ph.D Andrzej FELSKI
Gdynia 2014
I wish to sincerely thank Professor Andrzej Felski for the effort put into supervising and forming my scientific conduct and readiness to undertake research and troubleshoot problems from the widest spectrum of research issues.
2
TABLE OF CONTENTS
1.
2.
3.
4.
TABLE OF CONTENTS ABBREVIATIONS AND SYMBOLS INTRODUCTION DEFINITION OF RESEARCH PROBLEM 1.1. General remarks 1.2. Objectives and thesis dissertation SUMMARY OF THE AIS FUNCTIONING 2.1. Introduction 2.2. Idea of AIS introduction 2.3. Information transmitted by AIS used in the dissertation 2.4. AIS network structure of the Gulf of Gdansk 2.5. AIS malfunctions REVIEW OF AVAILABILITY AND INTEGRITY METHODS AND TOOLS FOR AIS INFORMATION RESEARCH 3.1. Methods and tools for research of AIS information integrity 3.1.1. Application of statistic methods to research AIS service information 3.1.2. Statistical analysis of AIS information in accordance with N.Bailey theory 3.1.3. End-user satisfaction model 3.2. Research methods and tools of AIS information availability 3.2.1. Research method of AIS information availability by A.Hori 3.2.2. Research method (LIC) of AIS availability and coverage area in accordance with Lapinski & Isenor 3.2.3. Research method (HPC) of AIS availability and coverage area in accordance with Hammond & Peters RESEARCH METHODOLOGY FOR ESTABLISHING THE PROBLEM THROUGH AVAILABLE TOOLS AND MODELS 4.1. Preliminary presentation of research models 4.1.1. General remarks 4.1.2. Option 1 – Method for research of AIS information integrity with the use of Fault Tree Analysis (FTA) 4.1.3. Option 2 – Method for research of AIS information availability and integrity with the use of Markov Processes 4.1.3.1. Definitions 4.1.3.2. Stationary distribution 4.2. Remedy research by available models and tools 4.2.1. General remarks 4.2.2. Developing data - "post-processing" 4.2.3. Decoding AIS information 4.2.4. Assumption for availability research of AIS information 4.2.5. Availability structure of AIS information – determination of the object study 4.2.6. Assumption for integrity research of AIS information 4.2.7. Evaluation completeness criteria of AIS information 4.2.8. Completeness structure of AIS information – determination of the object study 4.2.9. Evaluation integrity criteria of AIS information 4.2.9.1. Evaluation integrity criteria of AIS message No. 1 3
3 5 7 11 11 12 14 14 14 15 20 22 25 25 25 26 27 28 28 30 32 35 35 35 35 39 39 41 42 42 43 43 47 51 51 52 54 56 57
4.2.9.2. Evaluation integrity criteria of AIS message No. 5 4.2.10. Preliminary assumptions of integrity research for AIS information 5. RESEARCH SOLUTION 5.1. Characteristics of input data 5.2. Research outcomes of AIS binary data availability 5.3. Research method of AIS information availability 5.4. Research outcomes of information completeness concerning true heading 5.5. Research method of AIS information completeness concerning true heading 5.6. Research outcomes of information completeness concerning rate of turn 5.7. Research method of AIS information completeness concerning rate of turn SUMMARY, CONCLUSION, DIRECTION OF FURTHER RESEARCH BIBLIOGRAPHY
4
57 58 61 61 61 63 67 69 72 74 78 84
ABBREVIATIONS AND SYMBOLS A Aexp(t) AIS ARPA ASCII BER BRG CNIS CPA Ci CMexp COLREG DG DGNSS DSC E(X) E(Y) ENC ETA FRP FSK FTA GLONASS GMDSS HDG HELCOM HEX HS HSC h(i) IALA ICMexp IEC IMO ITDMA ITU LRIT MADSS MarSSIES MKD MMSI MOSG MRCC
Availability availability coefficient with the exponential distribution Automatic Identification System Automatic Radar Plotting Aid American Standard Code for Information Interchange Bit Error Ratio true bearing Channel Navigation Information Service Closest Point of Approach cell coverage estimate completeness coefficient with the exponential distribution International Regulations for Preventing Collisions at Sea Dangerous Goods Differential Global Navigation Satellite Service Digital Selective Calling expected value of lifetime expected value of failure time Electronic Navigation Chart Estimated Time of Arrival Federal Radionavigation Plan Frequency Shift Keying Fault Tree Analysis Globalnaya Navigatsionnaya Sputnikovaya Sistema Global Maritime Distress and Safety System heading Baltic Marine Environment Protection Commission Hexadecimal Hazardous Supplies High Speed Craft number of ‘hits’ in the i-th cell International Association of Marine Aids to Navigation and Lighthouse Authorities incompleteness coefficient with the exponential distribution International Electrotechnical Commission International Maritime Organisation Incremental Time Division Multiple Access International Telecommunication Union Long Range Identification and Tracking System Multi-agents Decision Support System Maritime Safety & Security Information Exchange System” (Polish acronym SWIBŻ) Minimum Keyboard Display Maritime Mobile Service Identity Maritime Regional Unit of the Border Guard Republic of Poland Maritime Rescue Coordination Centre 5
MSC m(i) N nR nT NUC P ( ) RAIM ROT R Rt R(u) SAR SOG SOLAS SOTDMA SNR SSL S TCPA TDMA Tt UAIS UTC VDM VHF VTS V(X) WAN WIG X(t) X Xmax Xmin (t) 𝛽(t)
λ
Maritime Safety Committee number of ‘misses’ in the i-th cell number of path reception numbers in one minute transmission numbers in one minute Not Under Command matrix of transition probabilities initial distribution transition probabilities Receiver Autonomous Integrity Monitoring rate of turn distance to object reception interval time reliability function Search and Rescue speed over ground Safety of Life at Sea Self-Organising Time Division Multiple Access Signal Noise Ratio Secure Socket Layer discrete set of states Time To Closest Point of Approach Time Division Multiple Access transmission interval time Universal Automatic Identification System Coordinated Universal Time VHF Data-link Message Very High Frequency Vessel Traffic Service Variance Wide Area Network Wing In Ground stochastic process arithmetic mean maximum value of variable in the measurement session minimum value of variable in the measurement session system state of AIS availability system state of AIS information completeness grid cell size time interval failure rate limit probability renewal rate standard deviation 6
INTRODUCTION Automatic Identification System (AIS) is a data exchange system which was introduced to improve shipping safety and the possibility of exchanging data, at a country and international level, about ships heading to or from ports, as well as exchanging data relating to passengers and dangerous or environment-polluting cargo carried by ships. The main purpose of introducing AIS was to offer a wider spectrum of available, continuous and reliable navigational data. It became common to use data transmitted through AIS in order to enhance shipping safety. Apart from being useful for traffic control in a marine area, AIS data can be a very important source of information used in collision avoidance process. However, some reservations are voiced with regard to the unconditional reliance on the data transferred through this channel. Thus, it is justifiable to question how and to what extent data coming from AIS is available, complete and reliable. The studies on the technical specification of the system [ITU-R.M.1371, 1998] allow to assume that errors classified as lack of reliability will depend on performance of sensors co-working with AIS and human errors made by operators, and those fitting the devices. The notion of integrity in marine navigation is referred to the radio navigation system. The integrity concept appeared in 2001. According to [FRS, 2001] integrity includes the ability of the system to provide timely warnings to users when the system should not be used for navigation. From 2005 according to [FRP, 2005] integrity is the measure of trust that can be placed in the correctness of the information provided by a navigation system. The referred to document also adds, that integrity assumes the ability of the radio navigation system to provide user with timely warnings when the system should not be used in navigation. It is questionable to call AIS a ‘navigation system’. Essentially, it is a radio information broadcast channel. For this reason, it does not provide information on data malfunctions. The author considers integrity as the measure of confidence in information received via AIS data. This measure will be expressed by statistical methods. The information integrity problem had been raised already at the stage of system implementation and some fragmentary outcomes were published in the past. However, it can be assumed that the results from the system introduction period may not represent reality. Thus, it seems reasonable to base the assessment on theoretical analysis, through the development of multi-criteria model describing the AIS information integrity. AIS information quality analysis published by [Drozd, W., et al., 2006] in A1 maritime area show that up to 30% of information transmitted by ships contain invalid data or is incomplete. Other sources report that only dynamic information coming from devices co-working with AIS can be considered reliable. Voyage related data, which should be input by the navigator is in 80% undefined or defined incorrectly [Bailey N., 2005]. Knowledge of AIS information integrity is fragmentary and it is difficult to recognize it as objective. It should be also taken into account that it comes from the system implementation period. The accelerated implementation of AIS post September 11th 2001 resulted in lack of proper crew training. . This might have been one of the causes of improper system operation in the first years of the twenty-first century. Information integrity can refer to the information accuracy and could be assessed as position, course or speed error. This error can result from gauge or data transmission quality. The human factor is also important. It affects the occurrence of errors in the transmitted information. AIS information completeness is equally important. AIS information integrity is questioned when the received message contains blank spaces. Thus, the question arises, what tools can provide a full assessment of the information integrity and what is its real integrity. The measure of system confidence can be information unfitness [Felski A., Jakubowski B., 2004]. AIS information integrity can be described as data sensitive-fault or information unfitness. This is the 7
result of datasets processing [Oleraczuk E., Frydrych A, 1994]. Having established that the matter regards the analysis of the collision avoidance process followed by the watch officer on bridge, valid AIS information components – dynamic, static and voyage related, must be selected. With such approach, analysing all elements of AIS information is not necessary. Quality of navigational information may be evaluated by the scale of error of processed information expressed in mistake of designate position, course, speed or factors such as human error. The question arises: to what extent information from the AIS is or may be reliable in the future and consequently, what tools can be used to perform such research? Integrity assessment can be based on the assumption that the transmission of navigational information between users can be considered analogously to assess the equipment reliability. If a process of data transfer, resulting in providing a user with complete data at any moment, is a reliable process it can be viewed as a functioning of an information channel and can be investigated with methods included in the theory of reliability as in [Specht C., 2003], [Jakubowski B., 2005], [Felski A., Jakubowski B., 2004], [Specht C., Nowak A., 2005], [Trautenberg H. L., 2005]. Above analysis of the literature allows formulating the following hypothesis. Hypothesis: There are test methods that can be used to predict the state of the availability and integrity of navigational information provided by AIS. On the basis of verified hypotheses, determination of data unfitness as a function of time and data processing allows to classify the system to integrity state. Here follows the conclusion that, AIS information is divided into three categories and it is required to investigate them in various methods. Another problem of system operation is the availability of AIS data transmission channel. Definition of system availability is used for a long time. In 1996, Federal Radio Navigation Plan defines availability as the ability of the system to provide applicable service within the specified coverage area [FRP, 1996]. This definition is repeated in all subsequent editions of this document, most recently in 2008. AIS service availability is questionable, thus treating AIS as a radio navigation system is debatable. In fact, this is data transmission channel [Felski A., Jaskólski K., 2010]. Data sources come from outside of the system. Potential distortion of information imparted by the system can be considered. However, observations made during the execution of this study allows identification of the availability of AIS with the availability of the data transmission channel. Then, it is justified to carry out availability research on the basis of received and recorded messages from devices transmitting AIS signals. Given the extraordinarily volatile conditions, even on a limited area (variable number of vessels, their differentiated nature, mutual location, etc.) it is proposed to limit the immutable elements. Number of base stations in the area does not change, their antennas are located at fixed altitudes and are arranged in the same places. Another advantage of these stations in terms of site AIS availability is constant time interval of transmitted messages from these stations. The investigations related to determining the degree of AIS information integrity should be divided into three main stages. Stage I: a. Analysis of the current state of knowledge on the AIS information availability and integrity; b. Analysis of AIS imperfections indicating availability and integrity limitations of the information system; c. Selection of components for AIS information integrity research;
8
d.
Development of research methods to define coefficient of information availability and integrity on the basis of the assumptions made.
Stage II: a. Gathering research material for performing research of system information availability and integrity; b. Decoding of AIS navigational information based on designed decoding tool; c. System examination in terms of information unfitness using specialized software (pilot study). Stage III: a. Estimating AIS information unfitness on the basis of the criteria adopted for research; b. Selecting the optimal solution to the problem of the research based on stochastic homogeneous Markov Chains, homogeneous semi-Markov Chains; c. Determination of quantitative distribution of transitions between different states of the process of AIS information availability and integrity; d. Prediction of system state of the process of AIS information availability and integrity. To estimate the availability and integrity of AIS information following test methods were contemplated: a.
b.
c.
d.
Fault Tree Analysis (FTA) – method of analysis designed to determine which type of unfitness, damage of the object, an external event or a combination thereof can generate an object failure. This method is presented in the form of failure tree [Jakubowski B., 2003]; Multivariate statistical analysis – method that examines the confidence degree of received information. Method is based on analysis of recorded data detailing the study of information affecting the safety of navigation. It is possible to determine integrity and availability of binary channel transmission. Multivariate statistical estimation is used in this method; Operating states graph – method of presentation for the reliability structure of the object. This method is used for reliability evaluation. On the basis of stochastic processes, this method is an effective way for reliability estimation of renewable objects [Jakubowski B., 2003]; Stochastic methods with the use of Markov Chains – provide a convenient mathematical apparatus enabling the description and investigation of actual random processes. They are an important class of stochastic processes, which allows a mathematical description of the change of random quantities in time.
The advantages and disadvantages of particular solutions are discussed in Chapter 4. In connection with the above a model based on the Theory of the Markov Processes related to Operating Technical Objects was proposed. The characteristics of Markov Chain is that the process state at the moment n + 1 depends exclusively on the moment state n and does not depend on states at previous moments. Furthermore, there is a possibility of short-term prediction of the system after n steps. AIS, a specific kind of navigation system, which uses radio waves to transmit data with regard to the ship motion parameters, can deliver more accurate information than radar. It can be assumed that it is a data transmission channel from ship sensors. This approach will facilitate research to develop methods for investigating the system information availability and integrity. The navigation characteristics of the system will be determined with use of post-processing method. Not only from the operational point of view, enhanced navigation systems require reliability assessment. Processed navigation information 9
should also be evaluated. A situation may occur, when properly operating system sends out incorrect information that does not fall within the expected limits. Crucial element will be the search for solution in the form of method to examine the AIS information availability and integrity based on the system information and to determine the cause of navigation characteristics limitations. The AIS availability and integrity assessment is intended to: a. b. c. d.
Develop a method used to investigate the availability of AIS data transmission channel and the associated information integrity; Analyse the information integrity on the basis of proposed method; Process the information derived from devices and to determine the extent to which information is available and reliable; Verify the developed method to estimate availability and integrity coefficients of system. To solve this task, dissertation is presented in five chapters, as characterized below.
Chapter 1: The research problem was formulated; arguments to prove and dissertation objectives were presented. Chapter 2: The problem of the functioning of AIS, performance characteristics, principles and purpose of the AIS introduction, the information provided by AIS, the system structure in the Gulf of Gdansk was presented. This chapter ends with the system imperfections presentation. Chapter 3: Current state of knowledge on research methods for assessing the AIS availability and integrity was presented. Chapter 4: Description of selected methods of investigating the information availability and integrity has been effected. Choice of methods and tools to solve the problem of research integrity was discussed. The research tool selected by author was characterized. Chapter 5: Research methodology was presented. Contribution to the development of scientific discipline in terms of system availability and integrity has been presented. Research approach to estimate the characteristics of the navigation system based on selected methodology was presented.
10
