Systems and complexes of technical means for determining the location of moving objects.

Specific implementations of AVL systems often include technical means that provide several methods for determining location.

Depending on the size of the geographic area in which the AVL system operates, it can be:

• local, i.e. designed for a short range, which is typical mainly for remote tracking systems;
• zonal, limited, as a rule, by the boundaries of a settlement, area, region;
• global, for which the zone of action is the territory of several states, the continent, the territory of the entire globe.

In terms of implementing the positioning functions, AVL systems are characterized by such technical parameters as positioning accuracy and data update frequency. Obviously, these parameters depend on the AVL system's coverage area. The smaller the coverage area, the higher the positioning accuracy should be. Thus, for zonal systems operating in a city, a positioning accuracy (also called the position uncertainty zone) of 100 to 200 m is considered sufficient. Some special systems require an accuracy of meters, while for global systems, an accuracy of kilometers is sufficient.

For zonal dispatch systems, receiving data on the location of a moving object up to once per minute can be considered ideal. Remote tracking systems require a higher frequency of information update.

The methods of determining the location used in AVL systems, according to the classification of the International Code of International Relations, can be divided into three main categories: approximation methods (which in Russian literature are also called zonal methods), navigation dead reckoning methods, and radio frequency location methods.

Below are considered the features of the equipment and systems of location that can actually be used in modern conditions.

1.1 Systems based on approximation methods

Using a sufficiently large number of road signs or checkpoints (CP), the exact location of which is known in the system, a network of control zones is created on the territory of the city. The location of the vehicle is determined as it passes the CP. The individual CP code is transmitted to the on-board equipment, which, through the data transmission subsystem, transmits this information, as well as its identification code, to the control and data processing subsystem. Thus, the direct approach method is implemented. However, in practice, the inverse approach method is more often used — detection and identification of vehicles is carried out using active, passive or semi-active low-power radio beacons installed on them, transmitting their individual code to the CP receiver, or using optical equipment for reading and recognizing characteristic features of an object, for example, license plates. Information from the CP is then transmitted to the control and data processing subsystem.

Obviously, for zonal systems, the accuracy of positioning and the frequency of data updates directly depend on the density of the checkpoints in the area of ​​the system's operation. Approach methods require a developed communications infrastructure to organize a subsystem for transmitting data from a large number of checkpoints to the command and control center, and in the case of using optical reading methods, they also require complex equipment at the checkpoint, and are therefore very expensive when building systems that cover large areas. At the same time, inverse approach methods allow minimizing the volume of on-board equipment — a radio beacon, or even doing without equipment installed on the car. The main application of these systems is the comprehensive provision of vehicle security, and the search for cars in case of theft. An example of such a system is the KORZ-GAI system, which records the approach of a stolen equipped car to a GAI picket post. In Moscow, it was planned to equip all posts at the exit from the city with such equipment. At present, it is unknown whether other similar systems exist in Russia, although in many foreign countries zonal systems have been in operation for a long time, both for the needs of public transport dispatching on fixed routes and for the needs of law enforcement agencies.

The most developed network of road signs, with the help of which both direct (7 cities according to data for 1980) and inverse approximation systems (16 cities) are implemented, is in Japan. Road signs in Japan form a nationwide network. In Europe in the 70-80s, systems of selective detection, identification and determination of the location of vehicles developed by Philips and Cotag International Ltd (Great Britain) were actively introduced. Road signs in the form of electromagnetic loops are placed directly in the road surface. A semi-active pulse radio responder is installed on the vehicle, which is switched on when exposed to the electromagnetic field of the loop. At present, the company ANANDA Holding AG is actively operating in European countries. Since 1992, INMED/VOLBACK systems have been deployed in France, and then in 12 European countries and in Mexico, designed to detect the location of stolen cars. Receiving antennas of checkpoints are built into the road surface, poles and other design elements of the roadways. The transmitter on the car has dimensions of about 5x4x2 cm. Checkpoints are connected into a single pan-European network. In France, 1,500 checkpoints form 400 zones. According to French experts, the efficiency of returning stolen cars equipped with INMED/VOLBACK system transmitters is more than 85% versus 60% for unequipped cars. The total number of equipped vehicles in Europe, according to ANANDA Holding AG, should be at least 500 thousand cars.

The second generation of systems based on optical reading and recognition of car numbers is already being introduced in Japan and Great Britain.

The location of a vehicle is determined by measuring the difference in distances of the vehicle from three or more relative positions.

This group of methods can be divided into two subgroups: methods that calculate coordinates based on the results of receiving special radio signals on board a mobile object (methods of direct or inverse radio navigation), and methods that are generally referred to in this article as radio direction finding methods, when the absolute or relative location of a mobile object is determined by receiving the radio signal emitted by it by a network of stationary or mobile receiving points.

With the help of a network of direction finders distributed throughout the city or with the help of mobile direction finding equipment, it is possible to track the location of objects equipped with radio transmitters-beacons.

An example of an AVL system based on radio direction finding methods is the GIPS system (new name — «SKIF»), offered by Pyramid LLC. The operating principle of the system is the reception of a signal emitted by a small-sized radio beacon on a moving object, a network of stationary radio receiving centers, and the calculation of the uncertainty area of ​​the vehicle's position using the triangulation method. The use of broadband signals with a base of 103 — 108 ensures an update frequency of up to 5000 objects per second with high noise immunity. The accuracy of location depends on the density of the stationary radio receiving network on the territory of the city and can be units of meters in the mode of continuous tracking and correction of data on the electronic map.

A similar system using two-way pagers and a network of transceiver stations is offered by MegaPage. A broadband transmitter installed in a car is switched on by a signal from a standard paging receiver or by a signal from an anti-theft alarm system. The location of the transmitter is determined using a network of base stations of the paging system.

An example of a system based on mobile direction finders is the Lo Jack system, well known from TV shows. The direction finders of this system are installed in cars of the special battalion of the traffic police road patrol service and in traffic police picket posts at the exit from the city.

They are implemented on the basis of pulse-phase ground navigation systems (such as Loran-S — Chaika) and satellite medium-orbit navigation systems (SRNS) GPS NAVSTAR — GLONASS. The best accuracy and operational characteristics are currently found in satellite navigation systems, which achieve a positioning accuracy in standard mode of no worse than 50-100 m, and with the use of special methods for processing information signals in phase determination mode or differential navigation — up to units of meters.

The advantages of these methods are the globality of location, which allows it to be used in almost any territory and on any route of any length, good accuracy, the ability to determine the location of an object directly on a map of the area, the ability to determine not only the coordinates, but also the height, speed and direction of the object's movement, a high degree of compatibility with automated information processing systems. It is no coincidence that such systems have the widest range of application. These are dispatching systems for urban and special transport, ensuring the safety of transport and material assets, operating in real time on the territory of a city with tens and hundreds of moving objects. These are systems for monitoring the routes of transport carrying out long-distance intercity and international transportation (with the transmission of information about the route using global communication systems such as Inmarsat or with passive accumulation of information about the route with subsequent processing).

The high technology of the navigation equipment produced has determined a large number of offers of ready-made systems from many domestic companies. The undisputed leader is the oldest company in this market area, PRIN, which offers the widest range of navigation equipment and positioning systems based on them. But this does not mean that the solutions offered by this company are not subject to criticism and are the de facto standard. It should be noted right away that the technical solutions offered by various companies are quite close in their indicators and differ in details, which, however, may be significant for a specific user of the system. As a rule, the system equipment includes an on-board navigation computer, a VHF radio station or a cell phone.

A computer with an electronic map and dispatching system software is installed in the dispatch center. A detailed analysis of the proposed projects is beyond the scope of this article and will be presented in the following issues. Here we will only list the most complete systems from the end user's point of view, designed for dispatching and monitoring of motor transport in the city. These are the Magellan system by Transnetservice, the Unicom-AVL system by Unicom, the Granit system by NTC Set, the KORD system by KORD, the GrantGuard system by the GRANT-Vympel group of companies, the systems by Termotech, and others. The widespread introduction of these systems is constrained by the insufficient development of the mobile communications infrastructure in Russia for organizing a reliable channel for transmitting information between on-board and central equipment in large cities. A certain breakthrough in this area can be expected with the expansion of the coverage area and capacity of data switching centers of the implemented digital cellular communication systems of GSM standards, the implementation of digital mobile communication systems of other standards, and their integration with European networks.

3. Methods of navigational dead reckoning

These methods of determining the location of vehicles are based on measuring the parameters of the car's movement using acceleration sensors, angular velocity sensors in combination with distance sensors and direction sensors, and calculating the current location of the moving object relative to a known starting point based on this data. In general, these methods can be used in the same systems as methods based on radio navigation. The main advantage of these methods compared to radio navigation methods is independence from the conditions of receiving navigation signals by on-board equipment. It is no secret that in a modern city with densely built-up areas with tall buildings, there may be areas where it is difficult to receive signals from ground-based and even satellite navigation systems. On such areas, on-board navigation equipment is unable to calculate the coordinates of a moving object. Receiving antennas of radio navigation systems must be placed on vehicles taking into account the best conditions for receiving navigation signals. This makes them vulnerable to intruders if used to protect vehicles or the cargo they carry. Existing methods of camouflaging receiving antennas are quite complex and expensive.

The dead reckoning and inertial navigation methods are free from these shortcomings, since the equipment is completely autonomous and can be integrated into the structural elements of the car in order to complicate their detection and protect them from deliberate failure. The disadvantages of the dead reckoning methods include the need to correct accumulated errors in measuring the motion parameters, the generally large dimensions of the on-board equipment, the lack of an accessible small-sized element base for creating on-board equipment (accelerometers, autonomous distance counters, direction sensors), the complexity of processing the motion parameters in order to calculate the coordinates in the on-board computer. The most promising area of ​​application of such methods can be considered their joint use with radio navigation methods, which will compensate for the shortcomings inherent in both methods. A positioning system using this method is offered by ZAO Avtonavigator. The on-board equipment of the system uses: a path sensor connected to the speedometer of the car, a direction sensor based on fluxgates measuring the deviation of the car axis from the Earth's magnetic meridian, and an acceleration sensor (accelerometer) ensuring the elimination of fluxgate sensor errors arising due to the non-horizontal location of the object relative to the Earth's surface. The correction of dead reckoning errors is performed using a digital vector map of the city's transport network polylines, which allows achieving location accuracy of up to a few meters. It is possible to use the on-board equipment elements together with the SRNS receiver.

Conclusion

Even a brief overview of the methods and equipment for positioning allows us to conclude that there is no universal system capable of satisfying all the requirements of the end user. The task of creating effectively working positioning systems turns out to be much broader than the choice of a specific method. The following system-wide problems can be identified that need to be taken into account by customers and developers of such systems.

Of great importance is the availability of the appropriate infrastructure for creating a data transmission subsystem in the proposed deployment area. Thus, the availability of a system for calculating and broadcasting corrective information for the operation of navigation equipment in differential mode (similar, for example, to the radio beacon system of the US Coast Guard) will significantly improve the accuracy of positioning using the SRNS without significantly complicating the onboard equipment. The availability of mobile communication systems with a cellular and microcellular structure will reduce the power of the onboard transmitter, which reduces the size of the equipment, simplifies energy supply issues (especially in covert installation modes), and makes it difficult for intruders to detect the onboard equipment. In turn, the microcellular structure of communication systems can become the basis for building zonal positioning systems or will allow solving positioning issues using “radio direction finding methods.

The issues of creating electronic maps intended for use with AVL systems and updating them are separate. Often, geoinformation systems used to solve location problems, in addition to the usual display functions, must perform the functions of data correction, recalculation of data obtained in various coordinate systems, logical binding of trajectories of mobile objects to elements of the transport network, taking into account the model of movement of the mobile object. From this point of view, the advantages will be those systems in which operational correction of the traffic situation is organized, up to taking into account information about traffic jams on individual sections of highways.

Companies that take responsibility for the safety of a person or property, using location systems, must resolve the issue of information and legal interaction with law enforcement agencies that ensure physical security or the return of material assets (a good example is the special battalion of the State Automobile Inspectorate, working with the LOJEK system). Equipping mobile teams with means of access to information bases, automated location and target designation can significantly increase the efficiency of their work.

Solving all these problems will allow us to create an AVL system that best meets the customer's needs and is capable of returning the funds spent on the development and implementation of the system in the shortest possible time.