With the development of ship technology, the ship system tends to be integrated and distributed. Although different ships have different functions, all definitions found in literature for a Ship Information System (SIS) have one key feature in common. This defining feature is that SIS is composed by several independent subnets (sensor networks, display networks, etc.) and a total ship communication network which can exchange information (reference input, plant output, control input, etc.) among subnets and systems. (Fig. 1)
Historically, electronic communication aboard ships used point-to-point wiring to exchange information. Due to the recent rapid increase in the number and type of shipboard electronic devices, wiring a ship had become a logistics nightmare. In this case, shipbuilders and vendors of marine electronics replaced old-style wiring with modern local area networks. Martin et al. summarized and analyzed some early naval data handling systems such as Shipboard Data Multiplex System (SDMS) and distributed switch system “SITACS”, these systems can be treated as transitions to the SISs (Martin and Richard, 1984). Later Robert et al. developed a real-time messaging system for token ring networks (SHIPNET) which is currently operation in a shipboard environment (Simoncic et al., 1988). This system conforms to the IEEE802.2 LLC and 802.5 token ring standards and emerging SAFENET (Andersen et al., 1990) specification. SAFENET stands for “Survivable Adaptable Fiber optic Embedded NETwork”. It is a real-time information transfer system jointly developed by industry and the U.S. Navy. SAFENET is a connectivity and flexibility system which allow for graceful evolution to fully distributed system architectures. Later, with the advent of networking technologies, supervisor controller systems are introduced into ship systems. C3I (Command, Control, Communication & Intelligence) systems is one of the most significant achievement in supervisor controller systems. And for this, Thomsett (1993) summarized some common C3I systems such as MHS and OSIS.
With the further development of SIS, it is mainly divided into three parts. Each part has different focus. The first focus is communication system, it provides ship system facilities required. RICE 10 is the Royal Navy’s first digital internal communications system (Lister and Rosie, 1995). Within RICE 10, mainly broadcast and ship’s alarms are totally integrated into the primary system. It uses nodes for routing which is also used in after systems, such as Ship System 2000 (Källberg and Stråhle, 2001). The second is display network, it works as a subnet for translation information to the displays. Gold and Suggs (1998) introduced a local area network which is used in Navy tactical display communication system. This system adopts central data buffer and fiber distributed data interface to exchange radar video signal. The last part is sensor network. Monitoring system (Staroswiecki et al., 2004) and navigation system (Murphy, 2004) are representative sensor networks in ship.
Later, with the development of ship intelligent, network scale gets a further extension. The ship control/monitoring systems (Integrated Bridge System, Standard Machinery Control System and Integrated Condition Assessment System, etc.) that are able to be linked together by the ship wide area networks and fiber-optic backbone as a smart ship which was introduced by Young and Gubbins (1997). Such technological advances make it possible to have a total real time control of ship (Geer, 1998). Recently, Raytheon Company’s Total Ship Computing Environment (TSCE) is one of late-model SIS which is designed to connect all Zumwalt (DDG 1000) systems by creating a shipboard enterprise network that integrates all on-board systems.
The basic capabilities of any SISs are information acquisition (users / decision system / sensors), command (controllers / users), display (monitor / HCI), network, and control (actuators). In broader terms, SIS research is categorized into the following two parts.
1) Information transmission. Studying and researching on networks and communications to make them suitable for exchange information, communication type, redundant, etc.
2) Information processing. These deal more with ship system design over the SIS to optimization data collecting and publishing information such as information fusion, information decision, message display and ship control (Martins and Lobo, 2011).
SIS RESEARCH TOPICS AND TRENDS
SIS communication type and method
An information network is the backbone of the SIS. Reliability, ease of use, security and availability are the main issues while choosing the communication type.
The world’s first operation packet switching network is ARPANET which is developed by the Advanced Research Projects Agency of the U.S. Department of Defense in 1969. And it can be also regarded as the predecessor of the Internet. Earlier SISs always used some similar networks such as SHIPNET. Later fieldbus technology is introduced in the SIS. It is a generic term which describes a modern industrial digital communication network intended to replace the existing 4-20mA (or 0-5V) analog signal standard. Controller Area Network-BUS (CAN Bus) is one of the commonest fieldbus, which is a serial asynchronous multi-master communication protocol designed for applications needing high level data integrity and data rates of up to 1
As Fiber-optic network is free from Electro-Magnetic Interference (EMI) and jamming, it is widely used to assure high data rate especially in the top communication network of SIS.
• Advantages of Fiber-optic network using in SIS: - Eliminates need for costly data communication switches, simplifies cable harness; - Single optical fiber replaces cable bundles; - EMI/RFI (Radio Frequency Interference) immune, no wavelength crosstalk in fiber; - Data signals transmitted in both directions, peer to multi-peer; - Signal distribution in the optical domain – no electrical-to-optical conversion delays; - Uses Wavelength Division Multiplex (WDM) to carry multiple protocols on different wavelengths; - Optically amplified, lossless optical network; Simplifies and alters platform Data Management Systems (DMS) from centralized to distributed control.
Goff and Million (2010) introduced a Blown Optical Fiber network technology (fiber-optic principles and connectors) which is using in amphibious assault ship local area network. The machinery control system of that amphibious assault ship utilized a fiber optic network that serves as the backbone connecting the Local Area Network (LAN) switches via blown optical fiber and the fiber-optic connectors was mentioned as well. And Jurdana et al. (2011) presented an optical communication network in ship’s engines controlling system with protection strategies which can obtain failures rates and mean time to repair.
And in infranet (underlying network such as monitoring system, engineering control system etc.) cable signal network and wireless network are used more. For example, a sensor network is made up with several sensors (such as electrochemical sensors, commercial temperature and humidity sensors etc.) and sensor nodes. Sensor nodes gather and exchange the information from sensors to the top network for monitoring and controlling the ship. The engineering requirements for a permanent sensor installation are markedly different than those for trials installations. Some of the issues addressed were: (1) network wiring must meet maritime standards. For trials work it can be permissible to run temporary visible wiring whereas permanent installation requires concealed unobtrusive wiring; (2) sensor nodes must be robust enough to withstand environmental abuse; (3) nodes must also withstand maintenance work and wiring through bulkheads needs to be watertight. Based on the above considerations, Vincent et al. (2008) introduced a wired sensor network on an RAN Armidale Class Patrol Boat. In this network sensors use RS232 and RS485 lines for communications to sensors nodes. They are normal ways for building the network, but the problems of signal attenuation and wiring difficulties are still existence. An alternative is to use the existing shipboard mains power wiring for communication. This is termed power line communications (PLC) and this technology is being pursued by a number of semiconductor manufacturers. It may be easy to set up and cheaper than other wired communication technologies. Different with other wired communication technologies, PLC could be tested directly, since the power line already exists in the ship which is introduced by Paik et al. (2010).
Nowadays, signals in PLC are normally assumed to travel on the ship’s power distribution network. The interferences of these services in PLC occur in frequencies from 2 to 30 MHz coinciding with frequencies assigned to the ship in the band of high frequency.
• Advantages of PLC using in SIS: - Decrease of the length and weight of the wires; - Simplification of data transmission nets on board; - Simplification of the maintenance and implementation of these nets; - Reduction of the costs installation of the internal communications and data transmission nets; Reduction of the cost production and the ship exploitation.
• Disadvantages of PLC using in SIS: - Electromagnetic noise; - Band contamination of short wave; - Interferences in pre-existent services: amateur radio and ships stations; - Interferences in public services are defined in the same band of frequency of the PLC, from 2 to 30 MHz like those of emergencies and security; - Smaller security in communications’ privacy for the inadequate use of wires for data transportation; Bigger contamination from the part of the radio electric spectrum in which is defined.
More effects of PLC can be found in Bakkali et al. (2007) as well.
The motivation behind wireless sensor network is due to fully mobile operations, flexible installations, and rapid developments in SIS. The present wireless communication methods include RFID (radio frequency identification), Zigbee, Bluetooth, Home RF (a wireless networking specification for home devices to share data), IEEE 801.11, and UWB (ultra-wide-band). Among these communication technologies, 2.4
Since the wireless sensor network can not transmit sensor data at the environment surrounded by thick steel walls, actual ship needs some suitable wired networks in the specific regions to avoid any hindrance caused by the inherent nature of ship. Paik et al. (2010) introduced a real-time monitoring system which combined PLC and Zigbee technologies in a full-scale ship. In this system, wireless sensor network was distributed in several areas and the collected data were transmitted to middleware by using PLC.
And Talukdar et al. (2006) introduced a wireless sensors system which adopted ships hulls as wireless medium for data transfer among spatially distributed sensors. The test results were obtained for all of the modulation schemes for a distance of 50 feet. This kind of through-the-hull acoustic communication technology, provide a new direction for the research on the communication type and method in SIS.
Since survivability is the most indexes in the SIS design, redundant networked structure is necessary. There are many different redundant structures suit with SISs. American Bureau of Shipping (ABS) established Steel Vessel Rules (SVR) and Naval Vessel Rules (NVR) for different ships (Roa, 2007). For the SVR network redundancy should satisfy that no single point of failure, redundant data links required where same data link is used for two or more essential functions. And in the SVR network redundancy design, for N number of switches, N being less than five, each switch shall be connected to N-1 switches. For N greater than or equal to five, each switch shall be connected to three separate switches. Here several actual ship information networked redundant structures has been cited (Fig. 2):
Dual homing configuration
Dual Homing approach used a connector bus for the interconnection of the cards in each enclosure to form a FDDI ring network. It ruled require the B ports have priority over the A ports. Any failure of a B port on a card due to either fiber or port failure results in an automatic switchover and data transferred from the B port to the A port on that card. There are kinds of Dual-Homing switches using in ship network such as the Magnum ESD42 Switches designed by GarrettCom®, Inc. These unmanaged switches offer convenient plug-and-play dual connectivity in a physically small package, and they are hardened and rugged for use in the ship environment.
Star configuration made up the LAN’s backbone via strategically placed LAN switches. This configuration allowed for maximum redundancy to ensure reliable communication between the various systems. Conventional fiber cable (4-fiber conductors and 8-fiber conductors) was used to connect the LAN to other equipments, or end users. This kind of configuration had already been used in Amphibious Assault Ship, USS Makin Island (LHD 8).
Managed ring configuration
As introduced by Henry et al. (2009), several subnets such as the engineering control system in DDG1000 used “managed ring” Ethernet network interfaces for consisting of active and stand-by communication links (to ensure an active Ethernet ring is avoided). The managed ring approach kept one section of the ring designated as inactive and automatically activated it (deactivating the other side) less than 300ms upon any failure or fault on the active ring. Although the ring topology is not as robust as a mesh, this outperforms Spanning Tree algorithms that would have to be used with a mesh. Some other redundant structures were also introduced by Meier and Manfredi (2006).
SIS sensor information fusion
As a sensor network is formed by multi-sensors which are distributed throughout the total ship for a same goal. The ability of sensors information acquisition and utilization become an important aspect of sensor network design. The issue of these multi-sensors data fusion becomes a branch of the SIS. Since unmanned spaces aboard ships must be periodically monitored for damaging events such as flooding, pipe ruptures, fires and other severe cases to avoid partial to complete loss of vessels. The data fusion approach was used to integrate sensors data and transmit the results to the monitoring human-machine interface over some common industrial analog and digital communication protocols through a sensor network.
In recent years, the U.S. Naval Research Laboratory has developed a multisensory real-time detection system for situational awareness named “Volume Sensor” (Minor et al. 2007). The design framework developed for this system can serve as a template for a variety of real-time sensing and situational awareness applications. Christian et al. (2007) introduced a Volume Sensor system for fire detection which brings a message-based communications protocol in extensible markup language for the transfer of sensor data and command and control of a sensor network system with a modular and scalable system architecture.
With the development of ship network technology, more and more information can be acquired through different sensor networks. The information from different sensor networks may be fused again in a high accuracy. Li et al. (2012) put forward a new independent component analysis with reference algorithm (ICA-R) using the empirical mode decomposition based on reference extraction scheme was adopted to identify the characteristic source signals of the engine vibration collected from different sensor networks. The constructed three-level information fusion system integrated the wear debris and vibration analysis to make the fault diagnosis of marine diesel engines effective and comprehensive. Liu et al. (2012) introduced an information fusion method of infrared and radar sensor which is based on Support Vector Machine. By the ship communication network and sensor networks, the infrared sensor and radar could be cooperated to detect the target. Radar researched the far distance target and provided the azimuth of target for infrared sensor. On the other hand, the infrared sensor identified and tracked the target by the information of radar, which increased the precision.
A supervisor controller can be treated as the brain of a SIS. Different with distributed controllers in SIS, its main mission is making or bringing decisions of the total ship processing. The decision system can be seen as a deepening of information fusion system in the SIS. Decision Support System (DSS) and Decision Making System (DMS) are widely used in ship course planning, shipboard damage control and assessment system etc. The quality of decision support decisions depends on the level of information which can gain from SIS and its analysis policy (such as fuzzy policy, expert policy, etc.). Several decision systems are introduced as followed.
Martins and Lobo (2011) presented a decision support system for monitor load condition of a vessel. This system is Bridge Officer Support System (BOSS) which can help to decide what course of action should be followed in case of flooding, and presenting options to increase the vessel’s stability in such cases by using the information from draught reading sensors and tank level sensors. And in damage occurs, the system can switch into damage control mode and advise the crew the way to gain maximum stability. In other ship damage control DSS, the SIS allows several dispersed damage stations to retrieve coherent information and thereby effectuate a coordinated and effective action, resulting in reduced damage control response time, enhanced consistency of actions, and reduced manning (Calabrese et al., 2012). And Balmat et al. (2011) proposed a fuzzy approach based on a DMS, named MARISA, to define an individual ship risk factor. By adding ship’s speed and the ship’s position which accord to several fuzzy blocks, the new DMS can make a more comprehensive of risk assessment. A similar fuzzy analysis algorithm was introduced by Wibowo and Deng (2012) as well.
In a SIS, there are two kinds of messages needed to be displayed in monitors, one is sensors information (course, speed, etc.), and another is the decision messages from decision systems such as the displays Gonzalez et al. (2012) done. Among them, ship navigation and traffic control are often needed to display messages. Zhang et al. (2006) introduced sea digital map technology which could be used widely in such fields as ship navigation, maritime transaction, maritime safety traffic management, sea function planning management, etc This system used C/S network to store electronics data of map, distribute the resources, supervise and control the operation at terminal etc, accept customer's information of the GPS, Automatic Identification System (AIS), and show on the electronics map. Lin et al. (2009) designed an integrated target information system to display multi- messages such as radar message, AIS message, underwater information and navigational marks. Embedded technology is often used in display system. As it is a mature technology, this paper will not give a deep discuss of embedded system, and only give some applications nearby: Hu et al. (2007) designed an information display system of showing messages of AIS. On that basis, with fusion the data from GPS and GPRS, Zhao et al. (2009) designed a new display system.
Nowadays, one of the most mature display technologies using in the ship environment is for Integrated Bridge and Navigation System (IBS / INS). A latest version of an IBS / INS designed by Raytheon Anschütz has the characteristics of new widescreen, task-orientated Multifunctional Workstations. And the possible configurations are ranging from a stand-alone ECDIS workplace to a full integrated workstation that provides access to all nautical tasks such as route monitoring, collision avoidance, navigation control, status and data display or alarm monitoring. A central change of display color schemes as well as central dimming can be processed from any workstation within the bridge system. One the other hand, Sperry Marine and many other companies have developed several similar systems which had widely used in thousands numbers of ships.
There are two modes in ship control through SIS, if the task instruction is released by the controller itself (such as ship domain controller etc.) or the control centre, it's called automatic mode; if the task instruction is from HCI, the ship is in remote manual mode. And the SIS which afford a via for ship control system should face several challenging requirement for a diverse set of Quality of Service (QoS) properties, such as delays, jitter, losses, scalability, 24 × 7 availability, dependability, and security that must be satisfied simultaneously in real-time (Paulos et al., 2011). The mainly research subjects about control through SIS include network delay effect, fault-tolerant control, network security, coordinate control, etc. Since the research of ship control through SIS in this section has similar characters with the research of ship networked control systems, we will just make a brief analysis in this paper.
In time sensitive ship control systems, if the delay time of SIS exceeds the specified tolerable time limit, the plant or the device can either be damaged or have a degraded performance. In order to improve control performance, different mathematical- based approaches are taken for delay compensation in SIS. Qi and Yu (2011) designed a controller of Controllable Pitch Propeller which based on the combination of Support Vector Machine, Generalized Predictive Control and Queuing Strategy for compensate the influence of network delay.
On the other hand with the growing of shipping scale and capability, the difficulty of ship control increases further. This makes it harder to achieve one goal by a single control system. The control method of several independent objects towards a common goal becomes necessary. During several control systems are to be coordinated, information must be exchanged between them in order to complete the control task through SIS. The amount of control system papers in this field is vast. Such as the control system introduced by Zhou and Guo (2010) which coordinates ship steering system and main propulsion system in collision avoidance.