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There are several methods of tracking systems used by fleet management companies in my country. Almost all of the methods are some variants or combination of basic popular tracking technologies such as GPS tracking, GSM localization or Wi-Fi network localization. Locations tracked by these methods are sent to operative base centers by means of cellular, radio or satellite modem units that make use of existing networks and infrastructures and that are usually incorporated within tracking devices. These technologies used together provide connections between vehicles and main centers. Three of the most used tracking systems are GPS vehicle tracking with dead reckoning, GSM plus GPS vehicle tracking and Wi-Fi based vehicle tracking.
By using Global Position System, this tracking method finds a longitude and latitude position of a vehicle carrying a suitable GPS receiver device and sends the information to the center by using radio modem built in the device.
The device in the vehicle needs to receive signals from at least three satellites of the GPS satellites. This combination of signals gives a location of the vehicle within an accuracy of between 10 and 15 m. To improve this, the system needs terrestrial GPS receivers whose coordinates are known. These stationary receivers broadcast a range of errors that are calculated by checking their known coordinates with coordinates they receive from GPS satellites. The vehicle device can then pick up and use this error information to correct its previous location data from GPS. This system is known as Differential GPS, and gives an improved accuracy which is less than 5m.
Additionally to differential GPS, the tracking method improves its performance by using Dead Reckoning technology. When vehicles go into metropolitan areas where skyscrapers are prevalent, or into tunnels, or any other areas where signals from the satellites are blocked, an ordinary GPS receiver can no longer track its position. In such cases, the tracking method utilizes the dead reckoning technology. The technology calculates the current location of a car by computing directional and distance (or speed) information gathered from sensors such as gyroscopes and odometers. Moreover, although it alone cannot provide accurate location information when used for an extended period with any GPS signals, the technology also enhances the accuracy of the tracking method.
After gathering location information, the tracking device communicates with its base station. It has a built-in modem device. Using existing radio network the modem sends the coordinates of the vehicle gathered by the receiving counterpart of the device to the control station. The control station employs appropriate software to map the transmitted coordinates against pre-drawn maps.
Orbiting the globe at an altitude of about 20,200 nautical miles, the satellites transmit signals with two frequencies at about 1.58 GHz and 1.22 GHz. As with any electromagnetic waves, the signals are susceptible to dispersion due to earth atmosphere. In addition to dispersion effect, reflections of the signals from surrounding objects of the receiver device also cause interference.
Due to these reason, a normal GPS receiver has errors ranged between 10 and 15 m. This amount of errors is severe enough for a vehicle to find its location. As mentioned above, several technologies can reduce it to less than 5m. The tracking system makes use of differential GPS and dead reckoning methods to give an accuracy of less than 2m error range.
Basic information transmitted is the location of a vehicle: the longitude and latitude coordinates of a vehicle. In addition, it can give additional information about the car.
For navigation, the system can provides names of streets and best travel routes to a destination, helping driver when driving to unfamiliar places. Moreover, operators at the base station can monitor vehicle drivers such as vehicle mileages and stops, and give warning such as when the car is speeding up or whether speed limit areas and traps are ahead.
A GPS receiver can be categorized into three different categories concerning with how often data is transmitted.
Some GPS devices only stores data without any remote transmission. Data from this kind of devices, however, can be downloaded to a stationery device. For a fleet management system, daily data of a vehicle is recorded to computers for data analysis once the vehicle reaches its base station.
The second category of GSP devices transmits their data to base stations on specific intervals most commonly 1, 2 or 5 min intervals. This makes tracking a real-time process. In addition to static transmissions, the devices can also be programmed to send out at particular events such as stopping, ignition or going in and out of particular zones.
The final group of GSP devices only transmits when commanded to do so from a remote device as such computers. These devices need to be always on and connected a strong communication network such as internet, or cellular.
The current GSP tracking system only offers the first and second group of transmission in terms of frequency.
As mentioned earlier, the recorded location data of a vehicle can be stored within the tracking device. Or it can be sent to the operational base using a radio, cellular or satellite modem included in the device. This tracking system uses radio network infrastructure to transmit vehicles' data to the central system.
The blockage of signal transmission by obstacles such as mountains, high buildings, tunnels, urban canyons, or thick-branched trees is one drawback of the system. In addition, multipath signals generated by reflections from nearby surfaces or fences can also interfere with the GPS data. Operational Cost of the system is reasonable about US$ 1 to 2 per day per vehicle.
Ordinarily used by telecommunication companies to approximate a mobile phone user to search for nearest antenna towers, GSM tracking locates phone bearers by the multilateration and/or triangulation principles.
A mobile phone emits roaming signals without any active call while moving. The signals are received by nearby antennas. Distance to each antenna tower is then calculated from the signals and then, the location of the user is computed by interpolating patterns of signal data of adjacent towers.
Depending on towers density, GSM tracking can provide coordinates of bearers with precision between 50 m and a few km, i.e., in urban areas with the largest number of antennas localization is within an accuracy with 50m deviation, whereas in rural areas, an accuracy with roughly 2km deviation.
As technologies for mobile handsets evolve rapidly, several kinds of mobiles has built-in GPS. The GSM tracking method (plus GPS) makes use of availability of such receivers and satellites provided by GPS. This enhances its accuracy well enough for the tracking system to work for fleet management.
Gathered location data is transmitted to base stations by GSM network GPRS service. The GSM network's servers serve as gateways on internet. The control station can connect the internet and locates its vehicles online.
Initially intended just to approximate an area where a phone bearer is, mobile phone tracking does not give coordinates of the phone with high accuracy. Phone service providers take priority over providing best coverage when considering construction of cell towers. Therefore, even in urban areas where concentration of cell towers is more likely the highest, the positions of cell towers can only support cell tracking with 50 m accuracy. This accuracy number is too large for a typical fleet management company to operate well.
Therefore, the current vehicle tracking system incorporates GPS tracking capability with its service. As mentioned in GPS Tracking Method above, GPS with differential GPS system can provide a precision with less than 5 m error.
Information transmitted of this tracking system is more or less the same with that of GPS Tracking method system. This is due to advancement in technologies, softwares and digital maps.
Therefore in addition to coordinates of a car with a phone device, the system's devices have several useful features such as route suggestion, voice recommendation while driving, etc. Operators at the system's base station can also monitor closely their cars in the fields and give appropriate suggestions and commands over the two way voice communication of GSM network.
Since the system already utilizes GSM network infrastructure, transmission of cars' data are easily and frequently transmitted to the base station over GPRS service. This ease gives the operators at base stations to observe the vehicles on real-time basis and in addition, can request on demand. The devices of the system normally transmit every 30 sec interval.
The system uses GSM services and GPRS services to transmit data while voice or sms services are operating GPRS services are temporarily turned off.
Since this method uses GPRS services to transmit vehicles' data, it relies heavily on 2.5G or 3G that are not widely present among GSM providers. Even in a single provider's network, outskirts of the network are likely not to be upgraded into 2.5G or 3G and hence, if a vehicle has to go around the border of the network coverage, it cannot transmit data. Operational cost for this system is between US$ 5 to 8 per day per vehicle.
Wi-Fi based Vehicle Tracking method is similar to GSM tracking method. The former tracking method has three basic tracking technologies: closest access point (AP), triangulation and radio fingerprinting (RF), in an order of increased in accuracy
Closest access point, as in the case of GSM networking searching for the closest cell tower for a phone bearer, looks for the closest AP for an IEEE 802.11 compatible device. This gives an area about between 5,000 and 10,000 square feet where the device is located at.
Triangulation narrows it down to under 1,000 square feet. The way it works is that several access points pick up the device signals, each AP giving area estimation. By intersecting area varied by signal strength, the location area of the device is approximated. Similar to GSM tracking, this wi-fi triangulation mapping's accuracy also depends on density of AP in a particular region.
RF fingerprinting uses more advance technologies and algorithms than triangulation. RF creates grids and maps all physical things surrounding access points in a given area while accounting for factors such as interaction of RF with the physical objects, reflection, attenuation and multi-paths. Comparing this data with existing correct data about the area, RF pinpoints the location of the device to within a few meters. This gives necessary accuracy for vehicle fleet management.
RF fingerprinting creates high-precision topology with each grid point as small as a foot. It also compares the acquired topology with real-life information to give a virtual environment of a target area.
However, RF fingerprinting still is subject to limitation of how many AP are present in a given area. Therefore, the accuracy will decrease as a device moves to outer regions of a circular area formed by access points.
Similar to GPS and GSM tracking, Wi-Fi based tracking can give necessary information for a fleet management system such as coordinates, stoppage time, ignition time, arrival and departure time, and best routes to destination and so on.
Additionally, since it has to map and give topology of a target area, the Wi-Fi tracking system can provide traffic congestion or construction blockage information along a particular route. This therefore let fleets respond in advance in choosing alternative routes.
Due to high quality data connection speed of wireless network, transmission of vehicles' data is much more convenient and frequent than the other two tracking methods described above.
Wi-Fi services are not prevalently used in our country. Although this tracking system is superior to other two systems, it is not promising in the current time. Operational cost for this system is also high between US$ 8 to 10 per day per vehicle.
All methods can provide varying additional services which are almost identical. Functions such as theft alarms, zoning in and out alarms, speed limit alarms and speed-limit check zones alarms are configured as desired. In addition, daily reports such as igniting times, stoppage times, idle times and number of services can also be programmed into the tracking devices.
Since GSM/GPRS networks are the most prevalent in our country, it is best to use the second tracking method. Due to GSM mobile users are increasing every year, the network or cell sites are expanding rapidly to meet the demand. Increases in cell sites can give more and more accurate location data. In addition, this tracking method also makes use of existing GPS functionality to enhance accuracy.
GPRS, the data transmission method it uses, can also provide reliable and secure network for data transmission compared with traditional radio transmission used by the first tracking system.
Moreover, using GSM/GPRS network for tracking is also compatible with two-way voice communication system using PoC (Push-to-talk over Cellular) if decided to use.
There are several methods of two-way communication for a particular fleet management company. These include using cell phones, pagers, mobile data terminals, two-way radios and so on. The most widely-used methods of communication used by taxi companies are using mobile/cellular phones over GSM network and two-way radios (walkie talkie).
GSM (Global System for Mobile Communication) is a digital mobile communication system and is the most commonly used compared with its counterparts, such as CDMA and TDMA. It operating frequencies are at 900, 1800, 1900 MHz bands with channel bandwidth of 30 kHz. It is a full duplex communication over a single channel, allocating time slots for users. Each communication between mobile phones uses up a channel, with two frequencies, one for the forward link for transmitting from cell sites and the other for reverse link for receiving users call by cell sites.
Push to talk over cellular (Poc), however, doesn't use two frequencies. It functions similar to walkie-talkie, using only a single frequency and providing one to one or one to many voice communication services with cellular network. Contrast to regular cellular communication method, it is a half duplex mode and, it also only allows one user to transmit while the other can only listen until the former use finishes talking. In addition, the user does not require to dial and wait for other party to answer.
Since it uses GPRS service of GSM cellular network, PoC also offers fixed PC to participate in the group talk via internet. In fact, PoC uses SIP (session initiation protocol) and RTP (real-time transport protocol), which are required for multimedia communications over internet.
Since the GSM networks in my country are owned by the government, there have not been any legal requirements established to setup private GSM networks. In fact, to use the network a person or company needs to apply for phone number(s) and subscribe a line.
PoC over GSM network requires 2.5G or 3G networks especially the packet-switching GPRS network. Therefore, it can only operate well on urban areas as only in those areas of our country one can get 3G network.
Walkie Talkie is a two way radio voice communication method with half duplex connection mode. Connection between an individual and a group of individuals is made once a button is pushed by the individual. That is no connection has to be confirmed between the two parties in prior to communication. A simple button push and, then commands like "over" and "out" are only needed for the communication from users' side.
The radio network this method uses is PTMR (Public Trunked Moblie Radio) network. To overcome frequency congestion existed on one end of a conventional radio system's problem and to efficiently use idle frequencies existed on the other end, PTMR utilizes trunking system by dynamically allocating and sharing a small number of frequencies for different user groups. Despite this sharing of frequencies, there is no interfering with each other's conversation.
The frequencies for walkie talkie highly vary among countries and among purpose of usage, more so than GSM frequencies do. For commercial purposes in urban areas where straight line of sight is rarely a given, a few UHF frequencies are pre-specified and programmed into devices of a company. In fleet management businesses, mobile walkies talkies devices are installed in vehicles, broadcasting with 25 to 50 watts and fixed walkies talkies devices are stationed in base centers broadcasting with 100 watts. Additional repeaters are places, as required for effective coverage, up high.
Although it makes use of frequencies efficiently, trunking system is still susceptible to channel congestion. The system assigns multiple users over a single channel and therefore during irregular peak times, some users will not be able to access.
Another disadvantage of usage of single frequency for several groups is lack of privacy. With suitable walkie talkie, users can tune and listen to conversation in the channel.
In addition, coverage limitation and interference with other sensitive electronic devices are also of concern for walkie talkie. That is data transfer covers only a several kilometers about 25 km. And higher power of pulse nature transmission sometimes interferes especially with other RF transmission devices.
The easy-to-use walkie-talkie function is necessary for a particular communication to be heard by all taxi drivers and operators. Traditional walkie-talkie radio services are more susceptible to security threats. In contrast, PoC GSM/GPRS network can provide reliable and secure services by taking necessary measures available to the network.
In addition, traditional walkie-talkie radio services are limited in coverage range. Having multiple cell sites and using hand-over function, GSM/GPRS network can greatly overcome this limitation.
The system will have a main server, or servers, and branches clients. Therefore, possible network topologies for the system needs to have a connection that would have a server/client connection features. The servers would store all information about clients, instructors and processes involved in for driving lessons such as booking, making payments, etc.
Since the company will start out with small number of fleet, it seems possible to use bus, ring, mesh or grid network and star topologies intended for small companies.
In this topology, all servers and clients are interconnected by a main, common link. Having equal access to the network, none of the nodes have the power to control the connection.
Data from a node is sent along the main connection line in both directions until the data reaches to its intended destination, or terminals, which are the ends of the main link to absorb wandering data.
Since data from nodes flows through only one main line, it is possible for data collision. One solution is to use CSMA/C. The topology has a medium tolerance of fault. That is all nodes are connected first to the main link. Therefore even if one node fails in the network, the rest of the nodes can still be accessed. However, if the backbone fails, none of the nodes will have connection.
In this topology, the nodes are connected to each other forming a loop. When one node sends out a data, the data goes in and out of every node, finding its destination. If a data doesn't find its destination and reaches back to its source node, the source node either finds an error and resends the data, or waits for sending later.
The topology has a common token to judge whether the network is busy. A token becomes busy when sending out data from a node. The token contains information about source and destination addresses in its header portion in addition to the data. The token is free again when it reaches either to its source or destination.
Since there is only one token per network, it is not possible for the nodes to use the network in parallel. In addition, all nodes need to be functioning for the network to operate. That is if one client or server has fault in connectivity, the entire network will stop working.
All nodes are interconnected to each other through all available routes, forming a grid-structured network.
Data from a node is sent out to all connected routes to its destination. The topology hence has high tolerance of faulty nodes, as one node has multiple routes to connect to the rest. However due to its complex connection, it will be hard to troubleshoot the faulty routes.
Another disadvantage of the topology is that its cost is high.
This topology has client/server features. That is the network has a main node, the main server, connected to the rest of the nodes, clients. Between a client and the server, there is a dedicated link, but between each client, there is the server serving as a medium for the connection.
This topology also has high tolerance for defective nodes. As long as the server is working, all functioning nodes can have the network access.
Since the company's system will be featuring the client/server data accessing model, it is best to use star topology.
First the topology matches the data accessing model of the system. The system has the server to store all data, to do all the processes and to sync data management. Main works among the system will be connection between a client and the server. There is much less connection between one client and another.
The system will sometimes need operators to access the server at the same time. In bus topology, data collision will make it not optimal for the system to use the topology. Ring topology does not provide parallel connection in the network. Only the mesh or grid network, or the star network provides such parallel access function. However in the grid-like network, data accessing will not be efficient and cost for operating such topology will not be high. In contrast, the star topology will provide the system needs effectively and efficiently.
Methods for both vehicle data communication and voice communication recommended use GPRS function of GSM network. GSM service provides SIM lock method which prevents unauthorized use of devices. However, a vehicle's location data and other additional data are sent to the base station through internet via GPRS network. In addition, voice communications between operators and drivers also mostly use 'Push-to-talk over Cellular' method that sends packet-switched voice data through internet via GPRS network. Therefore the whole fleet management system is mainly susceptible to security threats related to GPRS network, and the interfaces between GPRS and internet and between internet and the central station.
Since it is only using existing GSM and GPRS networks, the vehicle system needs to take into account of security threats possible on the network it will subscribe, and to carefully choose a secure and reliable service provider. A GSM/GPRS service provider is vulnerable to threats that can reduce 'availability' of service and damage 'Integrity and Confidentiality' of data among other kinds of threats to the provider.
The fleet management system especially has to see what kind of security solution measures the service provider has taken for integrity and confidentiality of data. Capturing a subscriber's data session and alteration of data by intermediate parties are of high risk for the vehicle control system.
Security threats on the interfaces between GPRS and central station over internet
In addition to threats in the GSM/GPRS network, several threats arise when data are sent from the provider to central station via internet. This interface is called Gi interface and threats related to this particular interface are commonly occurred on today internet businesses such as worms, viruses, Trojans, DoS (denial of service) attacks and network traffic attacks. These too will harm availability, integrity and confidentiality, and authentication and authorization of the system, resulting in inaccessibility by subscribers due to DoS attacks, alteration and lost of privacy of data and unwanted external access to company networks.
Since threats related solely to service providers are not possible for the fleet management system to take measures, the management system can prevent the threats by selecting a reliable and secure service provider that makes use of several technologies such as firewalls, data encryption, user identification and packet filtering.
To prevent threats on Gi interface, the fleet management system can setup methods commonly used in internet businesses.
The system can request VPN (virtual private network) connection between the GPRS network supplier and the base station. VPN has security firewalls that can be configured to necessary security protections.
The system and the provider can use encryption methods for data integrity and confidentiality. Established encryptions like SSL (Secure Socket Layer) Protocol can encode voice and data communications instead of transmitting plain information.
Among available fleet management systems, A2B Cars Company should use GSM plus GPS vehicle tracking system with two-way voice communications over GSM/GPRS network. The GSM/GPRS network is expanding fast. Due to this expansion, the tracking system can give more and more accurate data and, provide rapid transmission of vehicles' data. Hence, if the company wants to expand in the future, it can readily do so. PoC (Push-to-talk over Cellular) service of GSM/GPRS can support the necessary and most effective method of voice communications. The GSM/GPRS network can also provide necessary security measures for data and voice communications transmission.
The network topology that the company should use in its base station is star topology. Star topology has high fault-tolerance should there be a break in one of the network nodes. The topology supports server and client function. This function can give necessary security measures from external hindrances in addition to the ease of data management and data access within the system.