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Wireless vehicular communications facilitate the exchange of particular information concerning safety and hazards among vehicles and other support systems through internet wireless connection. It is an emerging technology which provides safety and efficiency in transportation systems. Since Wireless Communication has been broad up to the next level the communication for vehicle also has been advanced to the higher level by introducing wireless communication protocol IEEE 802.11p.
There are two types of devices involved in vehicular communication that based o the wireless protocol 802.11p that are Roadside Units (RSUs) and On-Board Units (OBUs). These devices are important to transmitting data and receiving data that transmit from the host and also transmit by the vehicles.
An RSU is a device that operates at a fixed position whereas an OBU is a mobile device in vehicles that supports information exchange with RSUs and other OBUs.RSUs and OBUs communicate with each other.
2.2 Literature Review on Wireless Vehicular Communication
Vehicular Communication System is the newly implemented technology based on the wireless network protocol. This system has been well emerging in most of the developed nation such as in United States, London and many more European countries. This system is developed with highly integrated levels of networks that vehicles and roadside units are able to communicate by referring to the node. Wireless vehicular communications, covering Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I), and Vehicle -to-Person (V2P) communications, aim to increase road safety and transport efficiency, and provide ubiquitous wireless connectivity to the Main database .
The basic information that will be transmitting is the safety warnings such as road condition, speed limits, and traffic information. The emerging wireless vehicular communication network is closely relates with the Intelligent Transportation System (ITS) that base on collecting data packets that transmits between vehicle to vehicle and vehicle to the road side infrastructure such as traffic signals.
The ITS is the technology developed in order to manage some factors that is typically when on roadside. ITS seeks to achieve safety and productivity through intelligent transportation which integrates communication between mobile and fixed nodes. The mobile communication will be represents by the moving object in this case the vehicles and the fixed nodes represents by the Base Station with its speculation data transferring .
The wireless vehicular networks will always consider base on the nodes that is vehicle and Roadside Stations. These two nodes are integrated known as Dedicated Short Range Communications (DSRC) devices and Wireless Access in Vehicular Environments (WAVE). Both of this wireless topology will be based on IEEE 802.11(p) that use for communication among the vehicular to the vehicular and vehicular to infrastructure .
There are a lot of applications based on the wireless vehicular communication system. Vehicular communication networks will provide a wide range of applications with different characteristics. The main priority is to providing the safety information to the driver during on road. The information will be concern on dangerous and obstacle o roadside. Mainly the information about the road hazards will be transfer to the host or known as data base collector to save the data. This data will be transmitted to vehicle that approaching to the hazards area so the driver is aware about the hazards they going to face.
Figure 2.2(a): Animated version of the Wireless Vehicular Communication Network
The figure 2.2(a) shows the animated version of the wireless vehicular communication network that applied to the vehicles on roadside. As can see the signal of one approaching vehicle is able to detect and the data packet is transmitted to the other vehicle from other direction to notify. From the figure can reveal that this wireless vehicular is not concentrate on one particular vehicle or even one particular range. This network has wide range of applications and able to implement on any type of vehicle.
Moreover this wireless vehicular communication is engaged with the sensor in each cars that enable to detect the changing path or line switch by a vehicle and able to detect the speed of vehicle that approach towards other vehicle. In this issue the vehicle closely associate with the high speed vehicle able to notify the message send and can take better decision on driving attitude. In more advanced system there will be alert system to the driver on approaching vehicle and even give the solution for the message send.
In addition the vehicular communication systems also manage to utilize by the authorities to study about the traffic condition at certain area. This system able to detect the traffic flow and provide the information that happens currently. Such information will provide the authorities an alert sign on the traffic flow and able to manage the traffic by providing the second link or providing a route option to reduce the congestion.
Figure 2.2(b): Electronic Display Board Based on RSU
The Figure 2.2(b) shows the electronic display board that displays the message of 'CONGESTION AHEAD USE ALTERNTE ROUTE'. When drivers obtain this message definitely they will look into second link to avoid the highly congestion route. This will ensure the traffic flow on road side and give convenient drive to the drivers. In addition this type of display message also will cover the area of congestion and display the speed limit on particular area as a precaution to avoid collisions.
The most important application of the wireless communication system is by becoming the assistance for the police and enforcement. This system will save all the data transmitted and received during a period of time. The data's are over speeding, speed limit warnings, base on road side surveillance. This enable the authorities to download the data received and take appropriate action on particular vehicle.
There are several types of Wireless Communication Technologies has been tried and implemented to develop the Intelligent Transportation System (ITS). These technologies are still in development and emerging with newly built up potential and capabilities to support this vehicular movement environment.
Wireless technologies are rapidly evolving, and this evolution provides opportunities to utilize these technologies in support of advanced vehicle safety applications. Whereas cellular technologies have contributed the ability to rapidly report accidents after they occur, new wireless data communications technologies have the potential to support crash avoidance countermeasures. In particular, the new Dedicated Short Range Communications (DSRC) at 5.9 GHz offers the potential to support low latency wireless data communications between vehicles, and between vehicles and infrastructure .
Literature Review on Wireless Communication Standards
Wireless communications is, by any measure, the fastest growing segment of the communications industry. Wireless networkÂ refers to any type ofÂ computer networkÂ that isÂ wireless. It is commonly associated with aÂ network whose interconnections betweenÂ nodesÂ are implemented without the use of wires. Wireless telecommunications networks are generally implemented with some type of remote information transmission system that usesÂ electromagnetic waves, such asÂ radio waves. For the carrierÂ and this implementation usually takes place at the physical level or "layer" of the network .
The vision of wireless communications supporting information exchange between people or devices is the communications frontier of the next few decades, and much of it already exists in some form . This enable people to connect any part of world or information by easily and it is accessible due to the computer interconnection. Moreover it widen the scope form direct face to face dealing to the direct access dealing that's happens just few seconds in time.
The types of the wireless connections that exist are as below:
The Wireless Personal Area Networks (WPAN) is focus more into interconnection of devices within a relatively small area that could reach a person. The examples of this type of wireless are Zigbee and the Bluetooth that supports the WPAN . Wireless Local Area Network (WLAN) is more into linking two or more devices using a wireless distribution method and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network. One of the examples is Wi-Fi that increasingly used as a synonym for 802.11 WLANs .
The Wireless Metropolitan Area Networks (WMAN) is type of wireless network that connects several Wirelesses LAN. The most common types of the WMAN connections are the WiMAX that comes with the IEEE 802.16d/e/j. The last categorized but strong has strong influence in terms of wireless connection are the Wireless Wide Area Network (WWAN) . This Wireless networks that typically cover large outdoor areas. These networks can be used to connect branch offices of business or as a public internet access system. They are usually deployed on the 2.4Â GHz band. A typical system contains base station gateways, access points and wireless bridging relays.
The IEEE is best known for developing standards for the computer and electronics industry. In particular, the IEEE 802 standards for local-area networks are widely followed. There are several types of the standards wireless bands recognized and still in development to reach the optimum level.
The IEEE 802.16(d) that represents the Worldwide Interoperability for Microwave AccessÂ (WIMAX) Network. This network only represents the fixed node for transmission line or data sending. This standard family defines the specification of the air interfaces for fixed broadband wireless access (FBWA) systems . This network has two operational modes that are the mesh and point-to-point (PMP) modes.
The IEEE 802.16(e) is the next generation broadband mobile wireless access networks which define from the earlier version IEEE 802.16 (d).This network develop to a certain level where it adopts Orthogonal Frequency Division Multiple Access (OFDMA) technology that mange to link bandwidth. The IEEE 802.16 (e) support for mobility also where it has Mobile Station (MS) .
The IEEE 802.11 (p) is the standards for improving the performance of CSMA/CA - based networks in vehicular environments. These environments also known as Wireless Access in the Vehicular Environment (WAVE) in standardize 802.11 network families for Intelligent Transportation System (ITS) .
2.4 Wireless Access in Vehicular Environment (WAVE)
The Wireless Access in Vehicular Environment (WAVE) is the mode of the operation used by IEEE 802.11(p) devices to operate in the Dedicated Short Range Communication (DSRC) Band. The primary architecture components are On Board Unit (OBU), Road Side Unit (RSU) and WAVE interface .
IEEE 802.11 is a set of standards defined for Wireless Local Area Network (WLAN) computer communication and WAVE technology will come under 802.11p. The main objective of WAVE is to provide connections with the applications in the vehicle and between the wireless devices in a quickly changing environment. The exchange of information must be completed in a very short time.
WAVE technology is getting very popular in the discipline of vehicular communications and it is expected to be implemented in near future. There are several topics that are being studied, including physical layers related to mobile channels, network configuration, security, Media Access Protocols (MAC), and congestion control system to name a few .
This standard is approved. 802.11p aims to provide specifications needed for MAC and Physical Layer (PHY) layers for specific needs of vehicular networks 1609 is a family of standards which deals with issues such as management and security of the network:
1609.1 -Resource Manager: This standard provides a resource manager for WAVE, allowing communication between remote applications and vehicles.
1609.2 -Security Services for Applications and Management Messages
1609.3 -Networking Services: This standard addresses network layer issues in WAVE.
1609.4 -Multi-channel Operation: This standard deals with communications through multiple channels.
The major application of WAVE is vehicle safety. Some of the examples of safety applications will be curve warning, emergency brake light, collision warning, and emergency braking. For these applications the vehicles need to communicate with each other and they need to analyze the data from RSU as well . The major challenges to WAVE arise due to the fact that the communication environment varies rapidly and duration of communications between the communicating nodes can be short. Also, the data (especially multimedia data) that needs to be transmitted might be large and could not be delivered to all users with limited transmission time and bandwidth .
Next issue is regarding security, the system should make sure that the data is genuine to avoid incorrect information. There are diverse kinds of data that can be transmitted by RSUs and OBUs. Prioritizing which data would be transmitted first needs to be addressed. Also, we need to figure out a method to find the address of the other nodes and information distribution . An RSU is a device that operates at a fixed position whereas an OBU is a mobile Device in vehicles that supports information exchange with RSUs and other OBUs. RSUs and OBUs communicate with each other through the DSRC band .
The components of the WAVE architecture will describe the key components of WAVE system architecture and defines the data flows. It also defines the command message formats and data storage formats. Moreover it comes with secure message formats and processing that could be exchange securely.
There are different mechanisms of communication between vehicles like Car-to-Infrastructure (C2I) communication and Car-to-Car (C2C) communication. Car-to-Car communication (C2C) is also known as Vehicle-to-Vehicle communication.
Figure 2.4(a): Architecture of the WAVE
The figure 2.4(a) shows the architecture of the WAVE that includes the structure and the location of wave communication. The physical (PHY) and Medium Access Control (MAC) layers employ IEEE 802.11p standard. MAC addresses are assigned a random value initially and when an OBU receives a message from another OBU or RSU, a new MAC address is assigned MAC layer also implements IEEE P1609.4, which is a Multi-Channel operation standard and it determines the behavior of MAC layer on the available control channel (CCH) and service channel (SCH) .
Control Channel is used for safety communication. Network Layer uses IEEE P1609.3 Networking Service Standard. The message may be transferred using Internet Protocol Version 6 (IPv6) or Wave Short Message Protocol (WSMP). WSMP employs non IP based application and uses high priority messages . The block which sends WSMP is known as a provider. The channels at the edges are reserved for future use to avoid accidents. Channel 178 is the control channel and the remaining ones are service channels .
2.5 Dedicated Short Range Communications (DSRC)
Dedicated Short Range Communications (DSRC) can support the wireless communication between vehicles, and vehicle and Infrastructure at low latency. DSRC is a short to medium range wireless communication employed in vehicular Communication in transportation systems.
There many possible applications of the DSRC on wireless vehicular system. The most important one are the emergency warnings system for the vehicles and the cooperative forward collision warning. The emergency warning system is to give warning based on the road situation and the driving behaviors. This enable the driver to notified the alert message and be caution about the warnings . The cooperative forward collision stands for the high speeding that alert message will display about the chances of forward collisions if remains at this speed.
The other application are the blue waves or known as the approaching emergency vehicle warnings. Most of the time the driver forgot to notices the high speed cars approaching from behind and this attitude of driving would cause a lot of accidents. This DSRC system will alert the drivers about the movement of the other vehicles regarding their speeds, their position and also alert the slow drive vehicle to step a side from the fast approaching vehicles .
Besides that this DSRC system also can send information about the intersection collisions avoidance. Road networks are designs with a lot of junctions and intersections. On these types of heavily intersections road the speed of on coming cars at the junction is unable to detect. The developed DSRC system will display the approaching cars speeds and the locations for the other vehicle in the junction before make decision to make move out of the junction.
European standardization organizationÂ (CEN), sometimes in co-operation with theÂ International Organization for StandardizationÂ (ISO) the following DSRC standards have been developed:
EN 12253:2004 Dedicated Short-Range Communication - Physical layer using microwave at 5.8 GHz (review)
EN 12795:2002 Dedicated Short-Range Communication (DSRC) - DSRC Data link layer: Medium Access and Logical Link Control (review)
EN 12834:2002 Dedicated Short-Range Communication - Application layer (review)
EN 13372:2004 Dedicated Short-Range Communication (DSRC) - DSRC profiles for RTTT applications (review)
EN ISO 14906:2004 Electronic Fee Collection - Application interface
The range of spectrum assigned to DSRC is between 5.850 to 5.925 GHz bands with bandwidth of 75 MHz based on line of sight of 1km with maximum speed of 140km/hr. DSRC provides high rate for data transfer and is useful in situations where low delay is important. Wireless Access for the Vehicular Environment (WAVE) is the wireless communication component of DSRC and together, they provide architecture for vehicular networks .
DSRC has many other applications. It can be implemented for safety purposes to reduce traffic accidents, to improve the traffic flow, and to provide internet access and file downloads. Wireless Access for the Vehicular Environment (WAVE) is the wireless communication component of DSRC and together, they provide architecture for vehicular networks. Figure 2.5(a) shows the DSRC Channel Allocation. The range of the channels are divided into 7 channels that each represents by 10 MHz .
Channels 172, 174, 176, 180, 182, 184 are service channels and channel 178 is the control channel. The control channel creates a connection between RSU and OBU. The control channel will also help connect OBUs with one another . RSU and OBU cannot transmit messages simultaneously so due to this the DSRC is half-duplex. The communication or data transmission can happens in both direction but one at a time
Figure 2.5(a): DSRC Channel Allocation
The RSU and OBU can send messages only when the channel is confirmed to be idle. If the channel is busy, RSU and OBU need to wait and if the channel is idle, then RSU or OBU will send the signal to control channel. The control channel will allocate the channel on the basis of high priority first followed by low priority. The high priority messages are those messages related to public safety.
On-Board Units (OBUs) are located on the vehicles and act as a transmitter and a receiver. OBU is a part of On-Board Equipment (OBE). OBE consists of a processor, interface with vehicle services, human machine interface, GPS. OBU helps the vehicle to communicate with other vehicles or with RSU . The information is exchanged using communication links and DSRC is used as short distance communication technology.
The OBU will collect data and store it in memory. It will then be sent to RSU. The rate at which the data is collected depends on the storage size of OBU and the size of communication link. In V2V communication, OBU will transmit data related to the status of the vehicle to other OBUs within its range at certain time intervals. Similarly, other OBUs will also send data to this OBU. The content of the data that the OBU sends has not been determine due to the IP address assign for security purpose .
Roadside Units (RSUs) are usually stationary. They are distributed at different locations to collect data. They are usually located at intersection points with high risks of accidents, and other strategic locations. RSUs could be linked to the traffic system for sending warning messages to road side displays. An RSU sends and receives messages from the OBUs that are within its range.
The information on the application that RSU interacted with is contained in PST. These applications can be safety applications in highways or intersections. The safety application would warn the drivers about the condition of the road ahead such as if there is construction going on, if the road is slippery, or if there is an accident or emergency vehicle warning ahead. Figure 2.5(b) represents the communication between RSUs and OBUs.
Figure 2.5(b): Communication Between RSUs and OBUs.
The communication between the OBU and RSU in reality will be like shown in the figure 2.5(c) . When an OBU on the vehicle detects any RSU within its range, it will exchange data with that RSU. In this way, RSU collects data from OBUs and RSU will forward the data to a switch. The switch works like a router, which will distribute the information throughout the network. This data can be stored and later accessed by other vehicles .
Figure 2.5(c): Communication between the OBU and RSU in Reality
RSU will send messages using PST to all the OBUs in its range via DSRC channel 178. OBUs will send a reply back for some information on a particular application that it has. For example, if the "Sharp road turn detection" application is existing in an OBU, and RSU supports that application, RSU will connect to a security system which will find the necessary information. RSU will then transmit the data to an OBU on the vehicle and the driver receives the information about the curve beforehand.
Literature Review on NCTU Network Simulator (NCTUns)
NCTU Network Simulator (NCTUns) is a simulator and emulator that have many unique features. It is an open - source software that's running under Linux. The reason to use this software in this project is because of its high - fidelity in simulation results. This software directly use the real - life Linux IP protocol stack to simulate .
Moreover NCTUns supports various important networks for designing and simulation. For example NCTUns simulates Ethernet-based IP networks with fixed nodes and point-to-point links. It simulates IEEE 802.11(a)(b) wireless LAN networks, including both the ad-hoc and infrastructure modes. It simulates GPRS cellular networks It simulates IEEE 802.11(b) wireless mesh networks, IEEE 802.11(e) QoS networks, tactical and active mobile ad hoc networks, and wireless networks with directional and steer able antennas. It simulates 802.16(d) WiMAX networks, including the PMP and mesh modes. It simulates 802.16(e) mobile WiMAX PMP networks. It simulates 802.16(j) transparent mode and non-transparent mode relay WiMAX networks. It simulates the DVB-RCS satellite networks for a GEO satellite located 36,000 Km above the earth. It simulates 802.11(p)/1609 vehicular network .
Over this platform, one can easily develop and evaluate advanced V2V (vehicle-to-vehicle) and V2I (vehicle-to-infrastructure) applications in the ITS (Intelligent Transportation Systems) research field. It simulates multi-interface mobile nodes equipped with multiple heterogeneous wireless interfaces . This type of mobile nodes will become common and play an important role in the real life, because they can choose the most cost-effective network to connect to the Internet at any time and at any location.
Other than that this software has High Simulation Speeds and Repeatable Simulation Results. NCTUns combine the kernel re-entering simulation methodology with the discrete event simulation methodology. As a result, it executes simulations quickly. NCTUns modifies the process scheduler of the Linux kernel to accurately control the execution order of the simulation engine process and all involved real-life application processes. If the same random number seed is used for a simulation case, the simulation results are repeatable across different runs.
Moreover this NCTUns are able to reuse all real-life application. This provides several unique advantages such as these real-life application programs generate realistic network traffic to drive simulations, which leads to more convincing results than using the artificial traffic generated. In additions the performances of these real-life applications under various network conditions can be evaluated and then improved before they are released to the public. The applications developed at the simulation study stage can be readily used and deployed on real-life UNIX machines when the simulation study is finished. This will save time and effort significantly.
In addition NCTUns provides a highly-integrated and professional GUI environment in which a user can easily conduct network simulations. The NCTUns GUI program is capable of :
Drawing network topologies
Configuring the protocol modules used inside a node
Configuring the parameter values used inside a protocol module
Specifying the initial locations and moving paths of mobile nodes
Plotting network performance graphs
Playing back the animation of a logged packet transfer trace
Pasting a map graph on the background of the network topology
Constructing a road network for wireless vehicular network simulations
Since this wireless network has own protocol stack, this protocol stack have to set according to the requirement of the Mobile Node. The protocol stack is shown in the figure 2.6(a) below.
Figure 2.6(a): Interface protocol stack for Mobile Node and Wireless Network
The wireless protocol stands with nine stack that interface each function in order to make sure the mobile node function completely. The protocol stack starts with the mobile node OBU and proceeds to the Interface. The function of the Interface is to apply communication in between the wireless signal and the mobile node. In conjunction to that there will be parameter settings such as IP address for each mobile node and include with the net mask or sub netting for dividing the networks into sub network. This is essential so that the data can be stored and transfer at various point of time to the mobile node.
The second stack for the wireless protocol is the GOD is where the place to save the routing and the subnet details. This stack function is essential because it able to keep the data code such as IP address and net mask for each vehicle. This function enables to refer the mobile node attitude on the wireless signal. Moreover in case of the data lost on the OBU this stack help to recover the data.
The next stack represents the Address Resolution Protocol (ARP). This stack is for routing the internetworking traffic across gateways that known as the routers based on the IP address . TheÂ Address Resolution Protocol (ARP)Â uses a simple message format that contains one address resolution request or response. The size of the ARP message depends on the upper layer and lower layer address sizes, which are given by the type of networking protocol .
The forth stack is the First In, First Out (FIFO) stack of the wireless protocol that organized and help to manipulate the data's relative time according to the prioritization . This expression describes the principle of aÂ queueÂ processing technique or servicing conflicting demands by ordering process. Despite of this, the first data that received by the OBU will be listed according to the priority on the Mobile Node movement. Then the next protocol stack is the MNode that represent the mobile node parameter setting .
The sixth protocol stack is the MAC 8021 that stands for the Media Access Control Address. This is unique identifier that assign for the network communication on physical network segment. In this segment the performance of the mobile node can be evaluate through their IP address .
The Wireless Transmission Control Protocol (WTCP) stack is the seventh stack that makes sure the wireless performance is improves relative to time . The next protocol stack is the Wireless Physical (WPhy) that representing the in detail parameter evaluation for antenna. These parameters cover the beam width of the antenna, the signal pattern, the variance evaluation and pointing direction . In addition on this stack there are link Bandwidth parameter that consists of the Bit Error Rate (BER), frequency Channel and antenna gain . The last protocol stack is the Channel Mode (CM) that comes with the propagation channel mode.
Propagation Channel Model
In NCTUns there are two types of propagation channel model that included in the system for wireless communication that is theoretical propagation model and empirical propagation model. Theoretical propagation model is based on the basic antenna types and the basic fading type for transmitter antenna and receiver antenna.
The Theoretical Channel Model consists of the Path Loss Model that set to be Two Ray Ground and the fading model. The two-ray ground reflection model considers both the direct path and a ground reflection path . The two-ray model does not give a good result for a short distance due to the oscillation caused by the constructive and destructive combination of the two rays. If the rays are shadowed by obstacles, they are not considered . The model can be used for all applications with a frequency range between 300 MHz and 300 GHz .
Empirical propagation model antenna is the specified propagation model that consists of certain limit of frequency according to the area such as urban and suburban area. Since the frequency setting for this project required to be higher so that the COST 231 HATA model is used. This is a model that is widely used for predicting path loss in mobile wireless system . It was devised as an extension to the Hata-Okumura model . The COST-231 Hata model is designed to be used in the frequency band from 500 MHz to 2000 MHz . It also contains corrections for urban, suburban and rural (flat) environments. Although its frequency range is outside that of the measurements, its simplicity and the availability of correction factors has seen it widely used for path loss prediction at this frequency band. Empirical propagation models have found favor in both research and industrial communities owing to their speed of execution and their limited reliance on detailed knowledge of the terrain. The COST-231 Hata model show the most promise .
Propagation models are used extensively in network planning, particularly for conducting feasibility studies and during initial deployment. They are also very useful for performing interference studies as the deployment proceeds. Empirical models are those based on observations and measurements alone. These models are mainly used to predict the path loss, but models that predict rain-fade and multipath have also been proposed .
Most mobile communication systems are used in and around center of population. The transmitting antenna or Base Station (BS) are located on top of a tall building or tower and they radiate at the maximum allowed power. In the other hand, the mobile antenna or Mobile Station (MS) is well below the surrounding buildings.
Consequently, the radio channel is in sequenced by the surrounding structures such as cars, buildings .
The wireless channel can be described as a function of time and space and the received signal is the combination of many replicas of the original signal impinging at receiver (RX) from many different paths . If either the transmitter or the receiver is moving, then this propagation phenomena will be time varying, and fading occurs. In addition to propagation impairments, the other phenomena that limit wireless communications are noise and interference. It is interesting to notice that wireless communication phenomena are mainly due to scattering of electromagnetic waves from surface .
Small scale fading known as Rayleigh and Ricean . Multipath fading cause high bits error rate (BER), in such an unstable transmission environment. And high BER cause high dropping probability of packets.
A wireless sensor network is a collection of tiny and low power devices that are becoming more common forms of networks over time. These sensor nodes are devices that sense changes in attributes within the scope of the network.
Each node consists of a sensing module, a communications module, memory, and a small battery. This information is then sent through wireless transmissions to surrounding nodes to a root node. The root node will convert the information received into human readable information. They hold applications in fields relating to and within computer science .