USE OF WIRELESS COMMUNICATION IN GEOGRAPHICALLY DISTRIBUTED SYSTEMS OF INFORMATION COLLECTION AND PROCESSING..
IVANOV Vitaly Viktorovich
USE OF WIRELESS COMMUNICATION IN TERRITORIALLY DISTRIBUTED SYSTEMS OF INFORMATION COLLECTION AND PROCESSING
The article considers the issue of using modern wireless communication technologies to build geographically distributed security systems. The ways of solving the emerging problems of information transfer are outlined and system tasks are formulated.
Protection of geographically distributed objects is a complex task, one of the key points of the solution of which is the creation of a distributed automated security system. Such a system is designed to solve the following tasks:
- collecting information on the state of technical security equipment (TSE);
- systematic analysis of the obtained collection results;
- visualization of the obtained results.
The key task in this list is the centralized collection of information that comes from the TSE to a certain dedicated control center for subsequent analysis and visualization. In the case of large geographically distributed objects, the existence of a hierarchy of control centers with varying degrees of responsibility is possible.
Using wire data transmission technologies allows building highly reliable, noise-resistant security systems. However, the need to organize temporary security lines and the complexity of laying cable lines in rock formations require the presence of wireless communication (radio channel) in the system. Leaving aside the entire range of problems associated with building a highly reliable and ideally undetectable radio channel, we will formulate the requirements for it and consider existing data transmission protocols in order to analyze their applicability in geographically distributed systems.
Like any system protocol, the radio channel must ensure the targeted exchange of information in the system. The exchange can be initiated by either automated workstations included in the system (e.g., a request for the current status of the TSO) or the TSO (e.g., a message about the detection of an intruder). In order to reduce the energy consumption of the TSO and reduce the probability of detection of both the boundary and the information processing center, the protocol must ensure the transmission of information in the absence of constant information exchange in the system. A digital television camera can be used as a TSO, transmitting an image upon command from the operator or upon detection of an intruder, which requires the transmission of large amounts of information in real time.
It is possible to use an approach where each TSO operates on a certain dedicated pair of radio channels (for reception and transmission). This approach, due to the lack of a limit on the number of channels used and the difficulties with distributing channels between TSOs, seems unpromising and is not considered further.
Existing information transmission technologies are divided into two large groups depending on the method of access to the information transmission channel:
- sequential access, when each device alternately gains access to the transmission channel;
- access with automatic collision resolution, due to which any device can start transmitting at any time.
The technology of sequential access to the transmission channel requires a special mechanism that ensures periodic information exchange to organize conflict-free data transmission. This leads to the fact that the time after which information will be received from any device will be directly proportional to the total number of connected devices. However, during the periodic information exchange, the state of the transmission channel and TCO is monitored. Finally, the mechanism that ensures conflict-free data transmission can adaptively change the period of TCO access to the transmission channel. Despite all its advantages, this technology requires periodic information exchange, which contradicts the previously formulated requirements.
The access technologies with automatic collision resolution are based on the assumption that all devices have the ability to determine the presence of transmission at any time. Devices that simultaneously start transmitting must be able to detect this fact and distribute the transmission channel between themselves using the conflict resolution mechanism. The radio channel is characterized by signal transmission in a heterogeneous environment due to various external conditions, which can lead to a situation when devices consider an already occupied channel to be free. In a situation when one transmitting station “does not hear the other”, they start transmitting, blocking each other. As a result, both stop transmitting and after a random time interval, often with the same result. This problem is called the hidden point problem and is typical for a geographically distributed network in which subscribers are connected using directional antennas. To eliminate such a situation, WiFi networks use the optional RTS/CTS (“request to transmit permission to transmit”) mechanism. In the case of geographically distributed objects, landscape features can lead to a situation when the mechanisms considered are fundamentally inoperative. For example, Fig. 1 shows a situation where, in mountainous terrain, two security lines provide protection for gorges. In this case, transmission collisions are inevitable, since the TSOs that make up the first line cannot hear the transmission from the TSO of the second line and vice versa.
Fig. 1. Using a radio channel in mountainous terrain
There is another problem, similar to the problem of hidden points and related to it, caused by the fact that the TCO in the mode of constant signal generation is capable of clogging the transmission channel due to the increase in the time for conflict resolution, repeated transmissions and other unproductive costs. Thus, existing approaches do not provide the required modes of operation of the radio channel.
To build a reliable wireless communication line, a two-phase approach is proposed that ensures reliable separation of access to the radio channel. In the first phase, which is the boundary configuration, the control center uses access technologies with automatic collision resolution to build a grid of TCO access to the communication channel. In the second phase, the operational phase, conflict-free access to the communication line is ensured by setting the access period to the communication channel for each TCO during the configuration process. Time synchronization is ensured by generating a sync pulse at random intervals. This approach ensures reliable operation of the radio channel, which is necessary for organizing a boundary of any complexity. It seems logical to use a special hardware address as the TCO address, which is strictly specified by the manufacturer and describes, among other things, the TCO type.
It should be noted that the mutual arrangement of the TSO at the boundary contains important system information. A spatially distributed installation of the TSO will allow determining the direction of intrusion, and the fact that the system “knows” the location of neighboring TSOs (whose detection areas overlap) will provide additional filtering of false alarms.
Constructing the spatial distribution of the TSO at the boundary, as well as positioning the boundary relative to the control center, is possible, for example, with global positioning technology using satellite systems. Such an approach will additionally allow for precise binding of the TSO and control center positions to a topographic map (geographical information system).
Thus, using a radio channel to construct territorially distributed systems requires a certain revision of existing information transmission protocols. The possibility of organizing temporary security boundaries will additionally require the use of global positioning technologies and the development of methods for system analysis of signals from the TSOs that make up a spatially distributed boundary.