Application of satellite radio navigation methods to create systems and complexes of technical means for determining the location of moving objects..
Petrov Nikolay Nikolaevich, Candidate of Technical Sciences
APPLICATION OF SATELLITE RADIONAVIGATION METHODS
FOR CREATING SYSTEMS AND COMPLEXES OF TECHNICAL MEANS FOR LOCATION OF MOVING OBJECTS.
Source: magazine «Special Equipment»
Application of satellite radio navigation methods for creating systems and complexes of technical means for determining the location of moving objects
This is the second in a series of articles devoted to the use of vehicle location systems to solve problems of ensuring the safety of individuals, material assets, and property. This article attempts to find a place for the most widely used location methods — methods based on satellite radio navigation — in the general security system. The conclusions made in this article and the approaches to solving some problems are common to other location methods.
As noted in the first article on systems and complexes for determining the location of mobile objects, published in the third issue of the journal, location methods based on satellite radio navigation equipment make it possible to implement the widest range of systems and individual types of equipment for automated determination of the location of vehicles (AVL systems). Among these systems, aimed at solving the problems of comprehensive provision of security of the person, material assets and property, the following should be highlighted:
• Dispatching systems for monitoring and controlling the movement of cars from a limited park on the territory of the city.
• Systems for monitoring the movement of transport or cargo on an unlimited territory in real time.
• Systems for monitoring the movement of vehicles or cargo on an unlimited territory with subsequent data processing.
• Systems for searching for stolen cars.
A separate position is occupied by the so-called auto navigators, which have been rapidly developing recently — devices that help the driver navigate in unfamiliar areas. Indirectly, auto navigators can also be attributed to security systems, but in this article we will not consider such devices.
Before reviewing specific systems and individual types of equipment, we will try to highlight the main distinctive features of location systems from the end user's perspective and indicate their place in the overall security system. To do this, we will apply a method of resolving problematic situations that is currently popular in technical literature, when the user asks a question, and the developer tries to find the most complete and simple solution to the problem that arises. So…
1 User— the head of a company engaged in intercity cargo transportation. There is a fleet of heavy-duty mainline trucks from several units to many dozens. Some of the cargo is of significant value, the loss of or damage to cargo can cause irreparable damage to both the material well-being of the company and its image. It is known that the crime situation on our roads, and on many European roads, leaves much to be desired. Unfortunately, our own unscrupulous drivers also take advantage of this circumstance, and where is the guarantee that they will not let the goods go “to the left”, blaming them on some unknown “criminal elements”.
Question: Is it possible to suggest a means of monitoring the route of a vehicle in order to try to take timely measures to return the cargo or at least identify not entirely conscientious drivers?
Answer:Yes, such means are available. It is enough to equip the vehicle that transports especially valuable cargo with special equipment, and install a computer with an electronic map in the garage control room, which will display the current location of the vehicle.
The on-board equipment includes:
• a navigation receiver that receives signals from navigation satellites of the global satellite radio navigation system (American GPS NAVSTAR or Russian GLONASS) and calculates its coordinates;
• any means of global radio communication (currently, INMARSAT and EutelTracs satellite communication systems can be used; the IRIDIUM system will soon begin to function; with the development of cellular telephone systems, a larger coverage area, especially in Europe and along the most important Russian highways, can be obtained using GSM systems);
• an on-board computer that controls the operation of the navigation receiver and communication equipment.
The cost of such on-board equipment can range from 2 to 10 thousand dollars.
The on-board computer analyzes the current coordinates of the car and, according to the algorithm embedded in it, transmits data on the location of the controlled vehicle via the global communication system to the control room.
The algorithm of the on-board computer operation largely depends on the importance of the cargo being transported. If you don't mind spending any money for complete peace of mind, you can receive information every few minutes, paying a dollar or even several dollars for each message. It is much more reasonable to minimize the number of transmitted messages and turn on the communication equipment only in situations where there is a real threat to the vehicle. Such situations may include the driver turning on the alarm, a significant deviation of the vehicle from the route set in the on-board computer, a long unplanned parking of the vehicle, the activation of various sensors: a rollover sensor, a shock sensor, a container door lock sensor, etc.
This option allows you to constantly (or in alarming situations) have information about the location of the car and the condition of the cargo. Another question is, what can possession of this information give? Will you be able, having received an alarm signal, to promptly contact law enforcement agencies (traffic police) — well, if in Russia, but what if somewhere abroad? — and persuade them to take measures to save your cargo?
It is possible to control the integrity (or trustworthiness) of drivers at a much lower cost. In this case, communication equipment can be excluded from the on-board equipment (what is the point of promptly receiving information about a situation if there is no way to influence it?), which will reduce the upper limit of the cost of the equipment to the lower limit (i.e. to 2-3 thousand dollars). The on-board computer records and stores for a long time all information along the route of the vehicle (coordinates of route points, location and duration of stops, facts of engine on/off, opening of container doors, as well as, for example, fuel consumption, temperature of an isothermal or refrigerated container, etc.).
When the vehicle returns from a trip, the accumulated information is removed from the on-board computer and analyzed by a special program on the dispatcher's computer. Facts of deviation from the specified route, unauthorized impact on the cargo are determined. The information received may also be useful for subsequent route planning, for resolving disputes about possible damage to cargo with its owner (in the case, for example, of monitoring the temperature of the container). This method of control, especially if it can be used secretly from the driver, allows for significant discipline of the service personnel, getting rid of unscrupulous drivers.
What other qualities should the on-board equipment for monitoring vehicle routes have? First, it is necessary to solve the issue of protecting the equipment from external influences, including from the drivers themselves. At a minimum, the equipment should record the facts of its disconnection from the vehicle's on-board network, the facts of influence on the receiving antenna of the navigation receiver or the antenna of the communication system (an attempt to cover the antenna with radio-opaque material, to tear it off from the cable). Ideally, the equipment should be fully integrated with the electronic equipment of the vehicle in such a way that its failure would lead to the impossibility of further movement of the vehicle.
2 User— the head of a company that provides security for material assets or persons transported using specially equipped vehicles from a limited fleet. The vehicles are moved within a limited area (a large city with its suburbs). The area is characterized by the presence of a fairly well-developed infrastructure: operational radio communications, cellular communications. There are police squads operating within the city, and it is possible to use operational mobile law enforcement groups (including our own).
Question: How to ensure operational control over the movement and condition of controlled vehicles, and in the event of an emergency, determine options for optimal impact on it (find the closest operational mobile groups, give them target designation, possibly determine the route)?
Answer:The described situation is a classic version of a dispatch system for ensuring the safety of mobile objects. This is the most capacious area of application of location systems (the only task that can be considered more capacious is the task of managing the movement of public transport).
Let's consider the structure and functional features of such a system, implemented using satellite radio navigation methods.
The system has the general structure described in the previous article and consists of a subsystem for determining the location of moving objects, a data transmission subsystem, and a control and data processing subsystem (dispatch center).
The subsystem for determining the location of moving objects is built on the basis of navigation receivers of the GPS NAVSTAR or GLONASS satellite radio navigation systems. As a data transmission subsystem, it is advisable to use any system of mobile VHF radio communication based on linear, trunking or cellular communication systems combined with voice communication systems or specially designed for data transmission. The subsystem for control and data processing is built on the basis of a computer network. The network usually includes a communication server that ensures data exchange between the dispatch center and the moving objects assigned to it, equipped with the appropriate equipment; an information and control server that ensures the maintenance of databases of moving objects, analysis of operational situations, development of control algorithms, etc.; dispatcher workstations that ensure the organization of the work of the system dispatchers on monitoring the moving objects assigned to them using geoinformation technologies. In the simplest case, all these functions can be assigned to one computer, which is also the dispatcher's workstation.
Let's consider the issues that need to be considered when choosing a specific system.
Onboard equipment The location determination subsystem and the data transmission subsystem are usually combined into one unit, which in English literature is called the Mobile Logic Unit (MLU). As a rule, the MLU is designed with a specific data transmission subsystem in mind. And here a lot of problems arise, since at present it is practically impossible to recommend the structure of the data transmission subsystem,that allows to satisfy the functional requirements of all users. The most difficult problems are: efficient use (or saving) of the radio frequency spectrum, which, as a rule, has to be shared with operational voice communication systems; minimization of the dimensions and power consumption of on-board equipment (which is especially important in the case of camouflaged placement of equipment on a car when it is necessary to use radio equipment operating with high transmission power); ensuring the required radio coverage of the territory with a given time of delivery of information from a mobile object to the control center (and back); protection of information in radio networks from possible unauthorized use.
The easiest way to solve the problems of building a data transmission subsystem is in a small settlement, for which it is possible to provide radio coverage of the entire territory using one radio center located directly in the control center premises. In this case, it is possible to allocate one or several communication channels for data transmission (radio equipment operates on fixed frequencies — «linear» channels). The functions of the MLU in this case consist of modulating/demodulating data and controlling the reception/transmission mode of a conventional VHF radio station. MLUs from different companies differ in the types of modulation, the methods of data encoding and error protection used. As a rule, when using conventional VHF radio stations designed for voice transmission, one can expect a data transmission rate of 1200-2400 bit/s. Such systems are characterized by minimal time of information delivery to the control center. In reality, this leads to the fact that using one simplex communication channel it is possible to build a control system consisting of 10-100 cars.
To provide radio coverage of the territory of large cities, it is necessary to use repeater systems. In its simplest form, this can be a system similar to the amateur packet data transmission public radio networks widely used in some Western countries. Such a network is built on the basis of the simplest data transmission repeaters (also called digipeaters — «data repeaters»), which include an amateur VHF range transceiver (for example, 144 or 430 MHz) and a TNC-2 standard radio modem that provides the formation and transmission of packets using the AX-25 protocol (a modification of the well-known X-25 protocol for work in radio networks). The simplicity of such a solution has to be paid for by a fairly long time for information to be delivered to the center along a chain of digipeaters, a very low utilization rate of the allocated radio spectrum and absolute vulnerability of the system to the introduction of «foreign» users (after all, it is based on solutions used specifically for public networks!).
More serious systems can be built on the basis of trunking radio networks. The issues of building such networks, their capabilities in terms of data transmission are considered in sufficient detail in various literature. True, the currently existing analog trunking communication systems are designed primarily to provide voice communications (and in Russia, in addition, they are considered as a cheaper substitute for cellular communications), so the transmission of large volumes of data in these networks may be ineffective. The latest digital trunking systems are more promising in this regard. Probably, only with the introduction of digital systems will it be possible to refute the opinion of some specialists that an attempt to combine voice and data in one radio network leads to a significant deterioration in the quality of voice communications, without achieving the required data transmission parameters.
The issue of creating special radio networks for data transmission is often resolved from an economic rather than a technical point of view. There are good technical solutions offered by some companies. For example, the DataTAC system from Motorola is very effective. However, significant capital investments are required to deploy such systems, and they can only pay off when the systems are heavily loaded. The DataTAC system on 10-12 dedicated communication channels could ensure the construction of data transmission subsystems for a large number of dispatch systems for ensuring the safety of mobile objects in Moscow.
In the absence of a real possibility of creating a special data transmission system using VHF radio channels, the prospect of using cellular telephone systems looks very tempting. The main advantage of cellular communication systems is the availability of a developed infrastructure that provides very good radio coverage in the city and along the main routes when using low-power subscriber radio transmitting equipment. The possibilities of interregional and interstate roaming allow building systems with global coverage. As in the case of VHF trunking radio systems, the greatest advantage can be provided by digital cellular systems. The use of analog systems leads to a significant increase in data transmission time (primarily due to the long time it takes to establish a connection between subscriber devices) or an unjustified increase in the cost of data transmission. At the same time, the capabilities of GSM cellular networks provide for such a service as short message transmission. Short messages (140-160 bytes of information) are transmitted at lower rates via service network channels, without significantly affecting the quality of voice communication. The performance of the short message service center can reach several hundred messages per second with the delivery time of information from one subscriber to another from several seconds to half a minute. These are quite acceptable indicators for most dispatch systems for ensuring the safety of mobile objects.
The basis of the hardware data control and processing subsystem is usually a local network of personal computers and servers. The structure of the communication server is closely related to the structure of the data transmission subsystem. For the information and control server and the dispatchers' workstations, some characteristic features inherent in any dispatching system can be identified. The dispatcher's workstation is an electronic map of the territory, which displays the location of the vehicles assigned to the dispatcher and auxiliary information. The software should make the dispatcher's work as easy as possible, relieving him of routine operations of direct monitoring of vehicles. Dispatching and information display algorithms should provide a multi-window interface for monitoring several objects, as well as the ability to activate the monitoring mode for a specific object when an exceptional situation occurs, determined by the information and control server (alarm on board, sensor response, deviation from the route, etc.). In the event of an alarm situation, response options should be proposed based on an analysis of the location of the nearest response forces (location of police posts, operational mobile groups on the move or at bases, etc.), as well as options for delivering control information to the response forces. The most important function of the information and control server can be considered the function of ensuring economy (or efficient use) of the allocated radio frequency spectrum in the case of using linear communication systems or a schedule in the case of using public systems. Economy can be achieved through the use of adaptive algorithms for exchanging information with on-board equipment (changing the frequency of receiving location information depending on the importance of the tracking object, its speed, group synchronized requests, requests indicating the boundaries of the object's area of presence, etc.).
3 User — the head of the public order protection unit or rescue service, whose operational mobile forces carry out their work on the territory of a large city.
Question:How can we ensure constant monitoring of the location of operational units so that, in the event of a critical situation, we can determine the units closest to this location and give them target designation?
Answer:In general, your problems can be solved by the same means as for the previous user. Some functions of the dispatch system for ensuring the safety of mobile objects are aimed specifically at determining the location of mobile response forces and communicating control actions to them. Probably, the greatest attention should be paid to ensuring the protection of information circulating in the data transmission subsystem from unauthorized use, as well as increasing the reliability of this subsystem by duplicating communication channels or even using several parallel subsystems. In this case, the requirements for the “intellectual” capabilities of the on-board equipment of the system increase: the on-board computer must determine situations of disruption of the data transmission subsystems and have the ability to actively influence this subsystem.
4 User — the head of an insurance company that insures owners of expensive cars against theft.
Question: Is it possible to offer a means of determining the location of a stolen car if some time has passed since the theft?
Answer:If your city has a functioning dispatch system for ensuring the safety of mobile objects (see User Question 2), you can recommend that your clients equip their cars with on-board equipment for such a system. The mode for transmitting data on the location of a car can be activated both when the car's security alarm sensors are triggered and remotely when the owner reports a car theft. The same units that ensure the safety of other cars in their system can return the car.
In this case, the on-board equipment must comply with certain requirements common to all anti-theft vehicle protection systems. It is necessary to ensure minimum dimensions of the equipment, camouflage its placement on the vehicle, and provide autonomous power supply in case of a power outage. The greatest opportunities in this case can be provided by systems operating on the basis of cellular networks, since this can minimize the energy consumption of the on-board equipment in data transmission mode.
Conclusion
This article does not cover all the options for using satellite positioning systems to ensure security. However, the proposed approach and the described examples can become a basis for specialists in analyzing a specific situation and choosing methods for organizing the system. The next article will consider specific methods for implementing systems, analyze their positive and negative sides from the point of view of possible use for security purposes.