Transmitting information using a laser pointer. Atmospheric laser communication. Spit in the well

E. N. Chepusov, S. G. Sharonin

Today it is impossible to imagine our life without computers and networks based on them. Humanity stands on the threshold of a new world in which a single information space. In this world, communications will no longer be hampered by physical boundaries, time or distance.

Nowadays there are a huge number of networks all over the world that perform various functions and solving many different problems. Sooner or later, but there always comes a moment when throughput the network is exhausted and new communication lines need to be laid. This is relatively easy to do inside a building, but difficulties begin when connecting two adjacent buildings. Special permits, approvals, licenses to carry out work are required, as well as the fulfillment of a number of complex technical requirements and the satisfaction of considerable financial requests from organizations managing land or sewerage. As a rule, it immediately becomes clear that the shortest path between two buildings is not a straight line. And it is not at all necessary that the length of this path will be comparable to the distance between these buildings.

Of course, everyone knows a wireless solution based on various radio equipment (radio modems, small-channel radio relay lines, microwave digital transmitters). But the number of difficulties does not decrease. The airwaves are oversaturated and obtaining permission to use radio equipment is very difficult, and sometimes even impossible. And the throughput of this equipment significantly depends on its cost.

We offer you to take advantage of the new economical form wireless communication, which arose quite recently, is laser communication. This technology received the greatest development in the USA, where it was developed. Laser communications provides a cost-effective solution to the problem of reliable, high-speed short-range communications (1.2 km) that can arise when connecting telecommunications systems from different buildings. Its use will allow for the integration of local networks with global ones, the integration of local networks remote from each other, and also to meet the needs of digital telephony. Laser communication supports all interfaces necessary for these purposes - from RS-232 to ATM.

How is laser communication accomplished?

Laser communication, unlike GSM communication, allows for point-to-point connections with information transfer rates of up to 155 Mbit/s. In computer and telephone networks, laser communication ensures the exchange of information in full duplex mode. For applications that do not require high speed transmission (for example, for transmitting video and control signals in technological and security television systems), there is a special cost-effective solution with half-duplex exchange. When you need to combine not only computer, but also telephone networks, models of laser devices with a built-in multiplexer can be used for simultaneous transmission of LAN traffic and digital group telephony streams (E1/ICM30).

Laser devices can transmit any network stream that is delivered to them using optical fiber or copper cable in the forward and reverse directions. The transmitter converts electrical signals into modulated laser radiation in the infrared range with a wavelength of 820 nm and a power of up to 40 mW. Laser communication uses the atmosphere as a propagation medium. The laser beam then hits a receiver that has maximum sensitivity within the wavelength range of the radiation. The receiver converts laser radiation into signals from the electrical or optical interface used. This is how communication is carried out using laser systems.

Families, models and their features

In this section, we would like to introduce you to the three families of the most popular laser systems in the USA - LOO, OmniBeam 2000 and OmniBeam 4000 (Table 1). The LOO family is basic and allows data transfer and voice messages up to 1000 m. The OmniBeam 2000 family has similar capabilities, but operates over a longer range (up to 1200 m) and can transmit video images and a combination of data and voice. The OmniBeam 4000 family can provide high-speed data transfer: from 34 to 52 Mbit/s over distances up to 1200 m and from 100 to 155 Mbit/s up to 1000 m. There are other families of laser systems on the market, but they either cover shorter distances, or support fewer protocols.

Table 1.

Each family includes a set of models that support different communication protocols (Table 2). The LOO family includes economical models that provide transmission distances of up to 200 m (the letter "S" at the end of the name).

Table 2.

An undoubted advantage of laser communication devices is their compatibility with most telecommunications equipment for various purposes (hubs, routers, repeaters, bridges, multiplexers and PBXs).

Installation of laser systems

An important stage in creating a system is its installation. The actual switching on takes a negligible amount of time compared to the installation and configuration of laser equipment, which takes several hours if performed by well-trained and equipped specialists. At the same time, the quality of operation of the system itself will depend on the quality of these operations. Therefore, before presenting typical inclusion options, we would like to pay some attention to these issues.

When placed outdoors, transceivers can be installed on roof or wall surfaces. The laser is mounted on a special rigid support, usually metal, which is attached to the wall of the building. The support also provides the ability to adjust the angle of inclination and azimuth of the beam.

In this case, for ease of installation and maintenance of the system, its connection is made through distribution boxes (RK). The connecting cables are usually fiber optic for data transmission circuits and copper cable for power and control circuits. If the equipment does not have an optical data interface, then it is possible to use a model with an electrical interface or an external optical modem.

The power supply unit (PSU) of the transceiver is always installed indoors and can be mounted on a wall or in a rack that is used for LAN equipment or cross-structured cable systems. A condition monitor can also be installed nearby, which serves to remote control functioning of transceivers of the OV2000 and OV4000 families. Its use allows for diagnostics of the laser channel, indication of the signal magnitude, as well as looping the signal to check it.

When installing laser transceivers internally, it is necessary to remember that the power of laser radiation decreases when passing through glass (at least 4% on each glass). Another problem is water droplets running down the outside of the glass when it rains. They act as lenses and can cause beam scattering. To reduce this effect, it is recommended to install the equipment near the top of the glass.

To ensure high-quality communication, it is necessary to take into account some basic requirements.

The most important of them, without which communication will be impossible, is that buildings must be within line of sight, and there should be no opaque obstacles in the path of beam propagation. In addition, since the laser beam in the receiver area has a diameter of 2 m, it is necessary that the transceivers are located above pedestrians and traffic at a height of at least 5 m. This is due to ensuring safety regulations. Transport is also a source of gases and dust, which affect the reliability and quality of transmission. The beam must not be projected in close proximity to or cross power lines. It is necessary to take into account the possible growth of trees, the movement of their crowns during gusts of wind, as well as the influence of precipitation and possible disruptions due to flying birds.

The correct choice of transceiver guarantees stable operation of the channel in the entire range of climatic conditions in Russia. For example, a larger beam diameter reduces the likelihood of precipitation-related failures.

Laser equipment is not a source electromagnetic radiation(AMY). However, if placed near devices with EMR, the laser's electronics will pick up this radiation, which can cause a change in the signal in both the receiver and transmitter. This will affect the quality of communication, so it is not recommended to place laser equipment near EMR sources such as powerful radio stations, antennas, etc.

When installing a laser, it is advisable to avoid oriented laser transceivers in the east-west direction, since several days a year the sun's rays can block the laser radiation for several minutes, and transmission will become impossible, even with special optical filters in the receiver. Knowing how the sun moves across the sky in a specific area, you can easily solve this problem.

Vibration can cause the laser transceiver to shift. To avoid this, it is not recommended to install laser systems near motors, compressors, etc.

Figure 1. Placement and connection of laser transceivers.

Several typical inclusion methods

Laser communication will help solve the problem of short-range communication in point-to-point connections. As examples, let's look at several typical options or methods of inclusion. So, you have a central office (CO) and a branch (F), each of which has a computer network.

Figure 2 shows a variant of organizing a communication channel for the case in which it is necessary to combine the F and DSO, using Ethernet as the network protocol, and coaxial cable (thick or thin) as the physical medium. In the CO there is a LAN server, and in F there are computers that need to be connected to this server. With laser systems such as the LOO-28/LOO-28S or OB2000E models, you can easily solve this problem. The bridge is installed in the central center, and the repeater in F. If the bridge or repeater has an optical interface, then an optical minimodem is not required. Laser transceivers are connected via dual fiber optics. The LOO-28S model will allow you to communicate at a distance of up to 213 m, and the LOO-28 - up to 1000 m with a “confident” reception angle of 3 mrad. The OB2000E model covers a distance of up to 1200 m with a “confident” reception angle of 5 mrad. All these models operate in full duplex mode and provide a transfer speed of 10 Mbit/s.

Figure 2. Connecting a remote Ethernet LAN segment based on coaxial cable.

A similar option for combining two Ethernet networks, using as a physical medium twisted pair(10BaseT) is shown in Figure 3. Its difference is that instead of a bridge and a repeater, concentrators (hubs) are used that have the required number of 10BaseT connectors and one AUI or FOIRL interface for connecting laser transceivers. In this case, it is necessary to install a LOO-38 or LOO-38S laser transceiver, which provides the required transmission speed in full duplex mode. The LOO-38 model can support communication distances up to 1000 m, and the LOO-38S model can communicate up to 213 m.

Figure 3. Connecting a remote Ethernet LAN segment based on twisted pair.

Figure 4 shows a variant of combined data transmission between two LANs (Ethernet) and a group digital stream E1 (PCM30) between two PBXs (in the CO and F). To solve this problem, the OB2846 model is suitable, which provides data and voice transmission at a speed of 12 (10+2) Mbit/s over a distance of up to 1200 m. The LAN is connected to the transceiver using dual optical fiber through a standard SMA connector, and telephone traffic is transmitted via 75 Ohm coaxial cable via BNC connector. It should be noted that multiplexing of data and speech streams does not require additional equipment and is performed by transceivers without reducing the throughput of each of them separately.

Figure 4. Integration of computer and telephone networks.

An option for high-speed data transfer between two LANs (LAN "A" in the central center and LAN "B" in the F) using ATM switches and laser transceivers is presented in Figure 5. The OB4000 model will solve the problem of high-speed short-range communication in an optimal way. You will have the opportunity to transmit E3, OC1, SONET1 and ATM52 streams at the required speeds over a distance of up to 1200 m, and 100 Base-VG or VG ANYLAN (802.12), 100 Base-FX or Fast Ethernet (802.3), FDDI, TAXI 100/ 140, OC3, SONET3 and ATM155 with the required speeds - over a distance of up to 1000 m. The transmitted data is delivered to the laser transceiver using a standard dual optical fiber connected via an SMA connector.

Figure 5. Consolidation of high-speed telecommunications networks.

The examples given are not exhaustive possible options use of laser equipment.

Which is more profitable?

Let's try to determine the place of laser communication among other wired and wireless solutions, briefly assessing their advantages and disadvantages (Table 3).

Table 3.

Laser data transmission systems are designed to organize one-way and duplex communication between objects located within line of sight.
Free Space Optics - FSO technology, which includes atmospheric optical communication (AOLC) and wireless optical communication channel (BOX) is a way wireless transmission information in the short-wave part of the electromagnetic spectrum. It is based on the principle of transfer digital signal through the atmosphere (or outer space) by modulating radiation (infrared or visible) and its subsequent detection by an optical photodetector.
The current state of wireless optical communications makes it possible to create reliable communication channels at distances from 100 to 1500-2000 m in the atmosphere and up to 100,000 km in outer space, for example, for communication between satellites. Being alternative solution In relation to optical fiber, atmospheric optical data transmission lines (AODL) allow you to quickly create a wireless optical communication channel.

1. Atmospheric optical communication link

The rapid development of the telecommunications market requires high-speed data transmission lines. However, laying optical fiber requires a significant investment, and in principle is not always possible.
A natural alternative in this case is microwave wireless communication lines, but the problem of quickly obtaining frequency permissions sharply limits the prospects for their use, especially in large cities.
Another method of wireless communication is optical communication lines (laser or optical communication), using a point-to-point topology or point-to-multipoint access mode. Optical communication is carried out by transmitting information using electromagnetic waves in the optical range. An example of optical communication is the transmission of messages used in the past using bonfires or semaphore alphabet. In the 60s of the 20th century, lasers were created and it became possible to build broadband optical communication systems. The first atmospheric communication line (ALC) in Moscow appeared in the late 60s: it was launched phone line between the Moscow State University building on the Lenin Hills and Zubovskaya Square with a length of more than 5 km. Quality transmitted signal fully complied with the standards. In those same years, experiments with ALS were carried out in Leningrad, Gorky, Tbilisi and Yerevan. In general, the tests were successful, but at that time experts considered that bad weather conditions made laser communication unreliable, and it was considered unpromising.
The use of signals with continuous (analog) modulation, which was used in those years, led to abnormal attenuation of the optical signal due to the influence of the atmosphere.
The modern widespread use of ALS in many countries around the world began in 1998, when inexpensive semiconductor lasers with a power of 100 mW or more were created, and the use of digital signal processing made it possible to avoid abnormal signal attenuation and retransmit a packet of information when an error is detected.
At the same time, the need for laser communications arose, as they began to develop rapidly information Technology. The number of subscribers requiring the provision of telecommunications services such as Internet, IP telephony, cable TV with a large number of channels, computer networks etc. As a result, the problem of the “last mile” (connecting a broadband communication channel to the end user) arose. Laying new cable networks requires large capital investments, and in some cases, especially in dense urban areas, is very difficult or even impossible.
The optimal solution to the problem of the last section is the use of wireless transmission lines.
The advantages of wireless communication lines are obvious: they are cost-effective (no need to dig trenches to lay cables and rent land); low operating costs; high throughput and quality of digital communications; rapid deployment and change of network configuration; easy overcoming of obstacles - railways, rivers, mountains, etc.
Wireless communications in the radio range are limited by congestion and shortage of frequency range, insufficient secrecy, susceptibility to interference, including intentional interference and from adjacent channels, and increased power consumption. In addition, radio communications require lengthy approval and registration with the assignment of frequencies by the State Communications Supervision Authority of the Russian Federation, rent for the channel, and mandatory certification of radio equipment by the State Commission for Radio Frequencies. The use of laser means eliminates this difficult issue. This is due to the fact that, firstly, the frequency of radiation from laser communication systems goes beyond the range in which coordination is necessary (in Russia), and secondly, the lack of practical possibilities for their detection and identification as means of information exchange.
Basic properties of laser systems:
almost absolute security of the channel from unauthorized access and, as a consequence, a high level of noise immunity and noise immunity due to the possibility of concentrating the entire signal energy in angles from fractions of arc minutes (in laser space communication systems) to tens of degrees (fully accessible indoor communication systems);
high information containers channels (up to tens of Gbit/s)
there are no delays in the transmission of information (ping<1ms) как у радиолиний
the absence of pronounced unmasking signs (mainly collateral electromagnetic radiation) and the possibility of additional camouflage, which makes it possible to hide not only the transmitted information, but also the very fact of information exchange.
In addition, many experts note the biological safety of these systems, since the average radiation power density in laser systems for various purposes is approximately 3–6 times less than the irradiation created by the Sun, as well as the simplicity of the principles of their construction and operation, and the relatively low cost compared to traditional means of transmitting information for a similar purpose.
Design:
The laser communication line consists of two identical stations installed opposite each other within line of sight (Fig. 1).

Rice. 1. ALS design

The structure of all ALS stations is almost the same: interface module, modulator, laser, transmitter optical system, receiver optical system, demodulator and receiver interface module. The transmitter is an emitter based on a pulsed semiconductor laser diode (sometimes a regular LED). The receiver in most cases is based on a high-speed pin photodiode or an avalanche photodiode.
The transmitted data stream from the user equipment goes to the interface module and then to the emitter modulator. The signal is then converted by a highly efficient injection laser into infrared optical radiation, collimated by optics into a narrow beam and transmitted through the atmosphere to the receiver. At the opposite point, the received optical radiation is focused by a receiving lens onto the site of a highly sensitive high-speed photodetector (avalanche or pin photodiodes), where it is detected. After further amplification and processing, the signal is sent to the receiver interface, and from there to the user equipment. Similarly, in duplex mode, counter data flow occurs simultaneously and independently.
Since the laser beam is transmitted between communication points in the atmosphere, its distribution is highly dependent on weather conditions, the presence of smoke, dust and other air pollutants. However, despite these problems, atmospheric laser communication has proven to be quite reliable over distances of several kilometers and is especially promising for solving the “last mile” problem.
Let's consider the influence of the atmosphere on the quality of wireless infrared communications. The propagation of laser radiation in the atmosphere is accompanied by a number of phenomena of linear and nonlinear interaction of light with the medium. Based on purely qualitative characteristics, these phenomena can be divided into three main groups:
1. absorption (direct interaction of a photon beam with atmospheric molecules);
2. scattering by aerosols (dust, rain, snow, fog);
3. fluctuations of radiation due to atmospheric turbulence.

Laser beam communication through the atmosphere has now become a reality. It ensures the transmission of a large amount of information with high reliability over distances of up to 5 km and solves many difficult problems. Therefore, interest in this type of communication has recently increased.

¹Fluctuations (from Latin fluctuatio - fluctuation), random deviations of physical quantities from their average values.
²Internet source: http://laseritc.ru/?id=93

2. Wireless optical communication channel

Wireless optical communication channel (BOX) is a device that transmits data through the atmosphere. It is designed to create a data transmission channel of the Ethernet standard. BOXING consists of two identical transceivers (optical pipes) installed on both sides of the communication channel. Each unit consists of a transceiver module, a visor, an interface cable (5 m long), a guidance system, a bracket, a power supply and an access unit.
The transceiver module includes a transmitter of highly directional optical radiation in the IR range (consisting of an infrared semiconductor LED) and a receiver - a highly sensitive LED. LEDs operate at a wavelength of 0.87 microns. Several examples of domestic manufacturers of BOX systems and their characteristics are described in Table 1.
Table 1. Devices for creating optical communication channels

Figure 2 clearly shows BOX-10M.

Rice. 2. BOX-10M

Principle of operation:
Let's consider the process of data transmission using an optical channel (Fig. 3). The electrical signal from the Ethernet port travels through the interface cable to the transmitter, where the LED converts it into IR radiation, which passes through the beam splitter and is focused by the lens into a narrow beam. Having passed through the atmosphere, part of the radiation hits the lens of another transceiver, is focused and sent to the receiver by a beam splitter. The receiver converts IR radiation into an electrical signal, which is sent via an interface cable to the Ethernet port. The power supply powers the transmitter, receiver, display unit and lens anti-fog/ice prevention system.

Rice. 3. General operating principle of the BOX family device.

Transmission reliability is achieved primarily through correct guidance and energy reserves. With correct aiming, the energy reserve of the system should be fourfold for the BOX-10ML and BOX-10M models (in other words, by covering 4/5 of the objective lenses, we have a reliable 100% channel in good weather). The BOX-10MPD model has a 16-fold energy reserve. In this case, the availability of the channel throughout the year will be 99.7-99.9%. The higher the energy reserve of the system, the higher the reliability of the channel, which ideally reaches 99.99%.
In addition, reliable system operation is due to the CSMA/CD media access method used in Ethernet networks. Any collision - worsening weather conditions or the appearance of a short-term obstacle leads to retransmission of the packet at the physical level, but even if it happens that the collision will not be heard (this is possible, for example, in the BOX-10ML and BOX-10M models due to the fact that that the switching time from reception to transmission is, of course, equal to 4 μs) and the packet is lost, then higher-level protocols that work with a delivery guarantee will track this incident and the request will be repeated.
A connection through the atmosphere never gives a 100% guarantee of connection, so it is possible that, for example, in bad weather conditions (heavy snowfall, very dense fog, heavy rain, etc.) the channel will not work. But in this case, the cessation of communication will be temporary, and after conditions improve, the connection will be restored on its own. To reduce the likelihood of loss of communication due to weather conditions, it is necessary to install models with a larger operating distance, which increases the energy of the light flux and, as a result, the reliability of the system as a whole.
Another condition for reliable and stable operation of the system is the coincidence of the center of the geometric spot of illumination of the transmitter with the center of the receiver lens. Wind loads, as well as mechanical and seasonal vibrations of the support can remove the system from the light spot area, as a result of which the connection will disappear. The entire design of the systems and the size of the illumination spot from the transmitter are coordinated in such a way that the likelihood of loss of communication due to the above reasons is minimized. When pointing, the following geometric problem is solved: from the point obtained during rough pointing, it is required to move the system to the geometric center of the illumination spot from the light flux of the emitter, finally fixing the pointing system in this position. Using a standard guidance system, this problem is solved in 35 iterations.
Installation:
Transceivers can be installed on roof or wall surfaces. The BOX is mounted on a metal support, which allows you to adjust the angle of inclination horizontally and vertically (Fig. 4). The transceiver is connected through a special access unit; twisted pair category 5 (UTP) is usually used as connecting cables. On the optical channel side, the access unit is connected to the transceiver by an interface cable, which uses a regular twisted pair cable equipped with special connectors. On the other hand, the access unit connects to a computer or network device (router or switch).
The access unit and the transceiver power supply are always installed indoors next to each other. They can be mounted on the wall or placed in the same racks that are used for LAN equipment.
For reliable operation, the following recommendations must be taken into account:
buildings must be within line of sight (the beam must not encounter opaque obstacles along the entire path);
it is better if the device is located as high above the ground as possible and in a hard-to-reach place;
when installing the system, you should avoid orienting the transceivers in the east-west direction (this specific requirement is explained quite simply: the sun's rays at sunrise or sunset can block the radiation for several minutes, and the transmission will stop);
There should be no motors, compressors, etc. near the mounting point, since vibration can lead to the pipe shifting and breaking the connection.

Rice. 4. Guidance system diagram

Connection types:
Figure 5 shows the possible types of BOX connections.

Rice. 5. Types of BOX connections

In various sources there are a large number of names of equipment for wireless data transmission in the infrared wavelength range. Abroad, this class of systems is usually called FSO - Free Space Optics; in the post-Soviet space, there are a number of designations for wireless optical communication systems. As a basis, you should take the abbreviation BOX - wireless optical communication channel, as reflected in the certificate of the Communication system (CCS).

E. N. Chepusov, S. G. Sharonin

Today it is impossible to imagine our life without computers and networks based on them. Humanity is on the threshold of a new world in which a single information space will be created. In this world, communications will no longer be hampered by physical boundaries, time or distance.

Nowadays there are a huge number of networks all over the world that perform various functions and solve many different problems. Sooner or later, there always comes a time when the network capacity is exhausted and new communication lines need to be laid. This is relatively easy to do inside a building, but difficulties begin when connecting two adjacent buildings. Special permits, approvals, licenses to carry out work are required, as well as the fulfillment of a number of complex technical requirements and the satisfaction of considerable financial requests from organizations managing land or sewerage. As a rule, it immediately becomes clear that the shortest path between two buildings is not a straight line. And it is not at all necessary that the length of this path will be comparable to the distance between these buildings.

Of course, everyone knows a wireless solution based on various radio equipment (radio modems, small-channel radio relay lines, microwave digital transmitters). But the number of difficulties does not decrease. The airwaves are oversaturated and obtaining permission to use radio equipment is very difficult, and sometimes even impossible. And the throughput of this equipment significantly depends on its cost.

We propose to use a new, economical type of wireless communication that has emerged quite recently - laser communication. This technology received the greatest development in the USA, where it was developed. Laser communications provides a cost-effective solution to the problem of reliable, high-speed short-range communications (1.2 km) that can arise when connecting telecommunications systems from different buildings. Its use will allow for the integration of local networks with global ones, the integration of local networks remote from each other, and also to meet the needs of digital telephony. Laser communication supports all interfaces necessary for these purposes - from RS-232 to ATM.

How is laser communication accomplished?

Laser communication, unlike GSM communication, allows for point-to-point connections with information transfer rates of up to 155 Mbit/s. In computer and telephone networks, laser communication ensures the exchange of information in full duplex mode. For applications that do not require high transmission rates (for example, video and control signals in process and closed-circuit television systems), a special, cost-effective half-duplex solution is available. When it is necessary to combine not only computer but also telephone networks, models of laser devices with a built-in multiplexer can be used to simultaneously transmit LAN traffic and digital group telephony streams (E1/ICM30).

Laser devices can transmit any network stream that is delivered to them using optical fiber or copper cable in the forward and reverse directions. The transmitter converts electrical signals into modulated laser radiation in the infrared range with a wavelength of 820 nm and a power of up to 40 mW. Laser communication uses the atmosphere as a propagation medium. The laser beam then hits a receiver that has maximum sensitivity within the wavelength range of the radiation. The receiver converts laser radiation into signals from the electrical or optical interface used. This is how communication is carried out using laser systems.

Families, models and their features

In this section, we would like to introduce you to the three families of the most popular laser systems in the USA - LOO, OmniBeam 2000 and OmniBeam 4000 (Table 1). The LOO family is basic and allows data and voice communications up to 1000 m. The OmniBeam 2000 family has similar capabilities, but operates over a longer distance (up to 1200 m) and can transmit video images and a combination of data and voice. The OmniBeam 4000 family can provide high-speed data transfer: from 34 to 52 Mbit/s over distances up to 1200 m and from 100 to 155 Mbit/s up to 1000 m. There are other families of laser systems on the market, but they either cover shorter distances, or support fewer protocols.

Table 1.

Each family includes a set of models that support different communication protocols (Table 2). The LOO family includes economical models that provide transmission distances of up to 200 m (the letter "S" at the end of the name).

Table 2.

An undoubted advantage of laser communication devices is their compatibility with most telecommunications equipment for various purposes (hubs, routers, repeaters, bridges, multiplexers and PBXs).

Installation of laser systems

An important stage in creating a system is its installation. The actual switching on takes a negligible amount of time compared to the installation and configuration of laser equipment, which takes several hours if performed by well-trained and equipped specialists. At the same time, the quality of operation of the system itself will depend on the quality of these operations. Therefore, before presenting typical inclusion options, we would like to pay some attention to these issues.

When placed outdoors, transceivers can be installed on roof or wall surfaces. The laser is mounted on a special rigid support, usually metal, which is attached to the wall of the building. The support also provides the ability to adjust the angle of inclination and azimuth of the beam.

In this case, for ease of installation and maintenance of the system, its connection is made through distribution boxes (RK). The connecting cables are usually fiber optic for data transmission circuits and copper cable for power and control circuits. If the equipment does not have an optical data interface, then it is possible to use a model with an electrical interface or an external optical modem.

The power supply unit (PSU) of the transceiver is always installed indoors and can be mounted on a wall or in a rack that is used for LAN equipment or structured cabling systems. A condition monitor can also be installed nearby, which serves to remotely monitor the functioning of transceivers of the OB2000 and OB4000 families. Its use allows for diagnostics of the laser channel, indication of the signal magnitude, as well as looping the signal to check it.

When installing laser transceivers internally, it is necessary to remember that the power of laser radiation decreases when passing through glass (at least 4% on each glass). Another problem is water droplets running down the outside of the glass when it rains. They act as lenses and can cause beam scattering. To reduce this effect, it is recommended to install the equipment near the top of the glass.

To ensure high-quality communication, it is necessary to take into account some basic requirements.

The most important of them, without which communication will be impossible, is that buildings must be within line of sight, and there should be no opaque obstacles in the path of beam propagation. In addition, since the laser beam in the receiver area has a diameter of 2 m, it is necessary that the transceivers are located above pedestrians and traffic at a height of at least 5 m. This is due to ensuring safety regulations. Transport is also a source of gases and dust, which affect the reliability and quality of transmission. The beam must not be projected in close proximity to or cross power lines. It is necessary to take into account the possible growth of trees, the movement of their crowns during gusts of wind, as well as the influence of precipitation and possible disruptions due to flying birds.

The correct choice of transceiver guarantees stable operation of the channel in the entire range of climatic conditions in Russia. For example, a larger beam diameter reduces the likelihood of precipitation-related failures.

Laser equipment is not a source of electromagnetic radiation (EMR). However, if placed near devices with EMR, the laser's electronics will pick up this radiation, which can cause a change in the signal in both the receiver and transmitter. This will affect the quality of communication, so it is not recommended to place laser equipment near EMR sources such as powerful radio stations, antennas, etc.

When installing a laser, it is advisable to avoid oriented laser transceivers in the east-west direction, since several days a year the sun's rays can block the laser radiation for several minutes, and transmission will become impossible, even with special optical filters in the receiver. Knowing how the sun moves across the sky in a specific area, you can easily solve this problem.

Vibration can cause the laser transceiver to shift. To avoid this, it is not recommended to install laser systems near motors, compressors, etc.

Figure 1. Placement and connection of laser transceivers.

Several typical inclusion methods

Laser communication will help solve the problem of short-range communication in point-to-point connections. As examples, let's look at several typical options or methods of inclusion. So, you have a central office (CO) and a branch (F), each of which has a computer network.

Figure 2 shows a variant of organizing a communication channel for the case in which it is necessary to combine the F and DSO, using Ethernet as the network protocol, and coaxial cable (thick or thin) as the physical medium. In the CO there is a LAN server, and in F there are computers that need to be connected to this server. With laser systems such as the LOO-28/LOO-28S or OB2000E models, you can easily solve this problem. The bridge is installed in the central center, and the repeater in F. If the bridge or repeater has an optical interface, then an optical minimodem is not required. Laser transceivers are connected via dual fiber optics. The LOO-28S model will allow you to communicate at a distance of up to 213 m, and the LOO-28 - up to 1000 m with a “confident” reception angle of 3 mrad. The OB2000E model covers a distance of up to 1200 m with a “confident” reception angle of 5 mrad. All these models operate in full duplex mode and provide a transfer speed of 10 Mbit/s.

Figure 2. Connecting a remote Ethernet LAN segment using coaxial cable.

A similar option for combining two Ethernet networks using twisted pair cable (10BaseT) as a physical medium is shown in Figure 3. Its difference is that instead of a bridge and a repeater, concentrators (hubs) are used that have the required number of 10BaseT connectors and one AUI interface or FOIRL for connecting laser transceivers. In this case, it is necessary to install a LOO-38 or LOO-38S laser transceiver, which provides the required transmission speed in full duplex mode. The LOO-38 model can support communication distances up to 1000 m, and the LOO-38S model can communicate up to 213 m.

Figure 3. Connecting a remote Ethernet LAN segment based on twisted pair.

Figure 4 shows a variant of combined data transmission between two LANs (Ethernet) and a group digital stream E1 (PCM30) between two PBXs (in the CO and F). To solve this problem, the OB2846 model is suitable, which provides data and voice transmission at a speed of 12 (10+2) Mbit/s over a distance of up to 1200 m. The LAN is connected to the transceiver using dual optical fiber through a standard SMA connector, and telephone traffic is transmitted via 75 Ohm coaxial cable via BNC connector. It should be noted that multiplexing of data and speech streams does not require additional equipment and is performed by transceivers without reducing the throughput of each of them separately.

Figure 4. Integration of computer and telephone networks.

An option for high-speed data transfer between two LANs (LAN "A" in the central center and LAN "B" in the F) using ATM switches and laser transceivers is presented in Figure 5. The OB4000 model will solve the problem of high-speed short-range communication in an optimal way. You will have the opportunity to transmit E3, OC1, SONET1 and ATM52 streams at the required speeds over a distance of up to 1200 m, and 100 Base-VG or VG ANYLAN (802.12), 100 Base-FX or Fast Ethernet (802.3), FDDI, TAXI 100/ 140, OC3, SONET3 and ATM155 with the required speeds - over a distance of up to 1000 m. The transmitted data is delivered to the laser transceiver using a standard dual optical fiber connected via an SMA connector.

Figure 5. Consolidation of high-speed telecommunications networks.

The examples given do not exhaust all possible applications of laser equipment.

Which is more profitable?

Let's try to determine the place of laser communication among other wired and wireless solutions, briefly assessing their advantages and disadvantages (Table 3).

Table 3.

Today it is impossible to imagine our life without computers and networks based on them. Humanity is on the threshold of a new world in which a single information space will be created. In this world, communications will no longer be hampered by physical boundaries, time or distance.

Nowadays there are a huge number of networks all over the world that perform various functions and solve many different problems. Sooner or later, there always comes a time when the network capacity is exhausted and new communication lines need to be laid. This is relatively easy to do inside a building, but difficulties begin when connecting two adjacent buildings. Special permits, approvals, licenses to carry out work are required, as well as the fulfillment of a number of complex technical requirements and the satisfaction of considerable financial requests from organizations managing land or sewerage. As a rule, it immediately becomes clear that the shortest path between two buildings is not a straight line. And it is not at all necessary that the length of this path will be comparable to the distance between these buildings.

Of course, everyone knows a wireless solution based on various radio equipment (radio modems, small-channel radio relay lines, microwave digital transmitters). But the number of difficulties does not decrease. The airwaves are oversaturated and obtaining permission to use radio equipment is very difficult, and sometimes even impossible. And the throughput of this equipment significantly depends on its cost.

We propose to use a new, economical type of wireless communication that has emerged quite recently - laser communication. This technology received the greatest development in the USA, where it was developed. Laser communications provides a cost-effective solution to the problem of reliable, high-speed short-range communications (1.2 km) that can arise when connecting telecommunications systems from different buildings. Its use will allow for the integration of local networks with global ones, the integration of local networks remote from each other, and also to meet the needs of digital telephony. Laser communication supports all interfaces necessary for these purposes - from RS-232 to ATM.

How does communication work?

Laser communication allows for point-to-point connections with information transfer rates of up to 155 Mbit/s. In computer and telephone networks, laser communication ensures the exchange of information in full duplex mode. For applications that do not require high transmission rates (for example, video and control signals in process and closed-circuit television systems), a special, cost-effective half-duplex solution is available. When it is necessary to combine not only computer but also telephone networks, models of laser devices with a built-in multiplexer can be used to simultaneously transmit LAN traffic and digital group telephony streams (E1/ICM30).

Laser devices can transmit any network stream that is delivered to them using optical fiber or copper cable in the forward and reverse directions. The transmitter converts electrical signals into modulated laser radiation in the infrared range with a wavelength of 820 nm and a power of up to 40 mW. Laser communication uses the atmosphere as a propagation medium. The laser beam then hits a receiver that has maximum sensitivity within the wavelength range of the radiation. The receiver converts laser radiation into signals from the electrical or optical interface used. This is how communication is carried out using laser systems.

Families, models and their features

In this section, we would like to introduce you to the three families of the most popular laser systems in the USA - LOO, OmniBeam 2000 and OmniBeam 4000 (Table 1). The LOO family is basic and allows data and voice communications up to 1000 m. The OmniBeam 2000 family has similar capabilities, but operates over a longer distance (up to 1200 m) and can transmit video images and a combination of data and voice. The OmniBeam 4000 family can provide high-speed data transfer: from 34 to 52 Mbit/s over distances up to 1200 m and from 100 to 155 Mbit/s up to 1000 m. There are other families of laser systems on the market, but they either cover shorter distances, or support fewer protocols.

Table 1.

Each family includes a set of models that support different communication protocols (Table 2). The LOO family includes economical models that provide transmission distances of up to 200 m (the letter "S" at the end of the name).

Table 2.

An undoubted advantage of laser communication devices is their compatibility with most telecommunications equipment for various purposes (hubs, routers, repeaters, bridges, multiplexers and PBXs).

Installation of laser systems

An important stage in creating a system is its installation. The actual switching on takes a negligible amount of time compared to the installation and configuration of laser equipment, which takes several hours if performed by well-trained and equipped specialists. At the same time, the quality of operation of the system itself will depend on the quality of these operations. Therefore, before presenting typical inclusion options, we would like to pay some attention to these issues.

When placed outdoors, transceivers can be installed on roof or wall surfaces. The laser is mounted on a special rigid support, usually metal, which is attached to the wall of the building. The support also provides the ability to adjust the angle of inclination and azimuth of the beam.

In this case, for ease of installation and maintenance of the system, its connection is made through distribution boxes (RK). The connecting cables are usually fiber optic for data transmission circuits and copper cable for power and control circuits. If the equipment does not have an optical data interface, then it is possible to use a model with an electrical interface or an external optical modem.

The power supply unit (PSU) of the transceiver is always installed indoors and can be mounted on a wall or in a rack that is used for LAN equipment or structured cabling systems. A condition monitor can also be installed nearby, which serves to remotely monitor the functioning of transceivers of the OB2000 and OB4000 families. Its use allows for diagnostics of the laser channel, indication of the signal magnitude, as well as looping the signal to check it.

When installing laser transceivers internally, it is necessary to remember that the power of laser radiation decreases when passing through glass (at least 4% on each glass). Another problem is water droplets running down the outside of the glass when it rains. They act as lenses and can cause beam scattering. To reduce this effect, it is recommended to install the equipment near the top of the glass.

To ensure high-quality communication, it is necessary to take into account some basic requirements.

The most important of them, without which communication will be impossible, is that buildings must be within line of sight, and there should be no opaque obstacles in the path of beam propagation. In addition, since the laser beam in the receiver area has a diameter of 2 m, it is necessary that the transceivers are located above pedestrians and traffic at a height of at least 5 m. This is due to ensuring safety regulations. Transport is also a source of gases and dust, which affect the reliability and quality of transmission. The beam must not be projected in close proximity to or cross power lines. It is necessary to take into account the possible growth of trees, the movement of their crowns during gusts of wind, as well as the influence of precipitation and possible disruptions due to flying birds.

The correct choice of transceiver guarantees stable operation of the channel in the entire range of climatic conditions in Russia. For example, a larger beam diameter reduces the likelihood of precipitation-related failures.

Laser equipment is not a source of electromagnetic radiation (EMR). However, if placed near devices with EMR, the laser's electronics will pick up this radiation, which can cause a change in the signal in both the receiver and transmitter. This will affect the quality of communication, so it is not recommended to place laser equipment near EMR sources such as powerful radio stations, antennas, etc.

When installing a laser, it is advisable to avoid oriented laser transceivers in the east-west direction, since several days a year the sun's rays can block the laser radiation for several minutes, and transmission will become impossible, even with special optical filters in the receiver. Knowing how the sun moves across the sky in a specific area, you can easily solve this problem.

Vibration can cause the laser transceiver to shift. To avoid this, it is not recommended to install laser systems near motors, compressors, etc.

Picture 1.
Placement and connection of laser transceivers.

Several typical inclusion methods

Laser communication will help solve the problem of short-range communication in point-to-point connections. As examples, let's look at several typical options or methods of inclusion. So, you have a central office (CO) and a branch (F), each of which has a computer network.

Figure 2 shows a variant of organizing a communication channel for the case in which it is necessary to combine the F and DSO, using Ethernet as the network protocol, and coaxial cable (thick or thin) as the physical medium. In the CO there is a LAN server, and in F there are computers that need to be connected to this server. With laser systems such as the LOO-28/LOO-28S or OB2000E models, you can easily solve this problem. The bridge is installed in the central center, and the repeater in F. If the bridge or repeater has an optical interface, then an optical minimodem is not required. Laser transceivers are connected via dual fiber optics. The LOO-28S model will allow you to communicate at a distance of up to 213 m, and the LOO-28 - up to 1000 m with a “confident” reception angle of 3 mrad. The OB2000E model covers a distance of up to 1200 m with a “confident” reception angle of 5 mrad. All these models operate in full duplex mode and provide a transfer speed of 10 Mbit/s.

Figure 2.
Connecting a remote Ethernet LAN segment using a coaxial cable.

A similar option for combining two Ethernet networks using twisted pair cable (10BaseT) as a physical medium is shown in Figure 3. Its difference is that instead of a bridge and a repeater, concentrators (hubs) are used that have the required number of 10BaseT connectors and one AUI interface or FOIRL for connecting laser transceivers. In this case, it is necessary to install a LOO-38 or LOO-38S laser transceiver, which provides the required transmission speed in full duplex mode. The LOO-38 model can support communication distances up to 1000 m, and the LOO-38S model can communicate up to 213 m.

Figure 3.
Connecting a remote Ethernet LAN segment based on twisted pair.

Figure 4 shows a variant of combined data transmission between two LANs (Ethernet) and a group digital stream E1 (PCM30) between two PBXs (in the CO and F). To solve this problem, the OB2846 model is suitable, which provides data and voice transmission at a speed of 12 (10+2) Mbit/s over a distance of up to 1200 m. The LAN is connected to the transceiver using dual optical fiber through a standard SMA connector, and telephone traffic is transmitted via 75 Ohm coaxial cable via BNC connector. It should be noted that multiplexing of data and speech streams does not require additional equipment and is performed by transceivers without reducing the throughput of each of them separately.

Figure 4.
Integration of computer and telephone networks.

An option for high-speed data transfer between two LANs (LAN "A" in the central center and LAN "B" in the F) using ATM switches and laser transceivers is presented in Figure 5. The OB4000 model will solve the problem of high-speed short-range communication in an optimal way. You will have the opportunity to transmit E3, OC1, SONET1 and ATM52 streams at the required speeds over a distance of up to 1200 m, and 100 Base-VG or VG ANYLAN (802.12), 100 Base-FX or Fast Ethernet (802.3), FDDI, TAXI 100/ 140, OC3, SONET3 and ATM155 with the required speeds - over a distance of up to 1000 m. The transmitted data is delivered to the laser transceiver using a standard dual optical fiber connected via an SMA connector.

Figure 5.
Consolidation of high-speed telecommunication networks.

The examples given do not exhaust all possible applications of laser equipment.

Which is more profitable?

Let's try to determine the place of laser communication among other wired and wireless solutions, briefly assessing their advantages and disadvantages (Table 3).

Table 3.

Let's start with the well-known ordinary copper cable. Some of its characteristics make it possible to almost accurately calculate the parameters of the created communication channel. For such a channel, it does not matter what the direction of transmission is and whether objects are in line of sight; there is no need to think about the influence of precipitation and many other factors. However, the quality and transmission speed provided by this cable leave much to be desired. The bit error rate (BER) is on the order of 1E-7 or higher, which is significantly higher than that of fiber optics or wireless communications. Copper cables are a low-speed communication link, so before installing new cables, consider whether they are worth using. If you already have a cable, then you should think about how to increase its capacity using HDSL technology. However, it should be taken into account that it may not provide the required quality of communication due to the unsatisfactory condition of the cable lines.

Fiber optic cables have significant advantages over copper cables. High throughput and transmission quality (BER)

Nowadays radio communications are widely used, especially radio relay lines and radio modems. They also have their own set of advantages and disadvantages. Existing radio communication technologies when creating a channel for data transmission will provide you with more high quality(BER

Laser communication - quickly and efficiently, reliably and effectively solves the problem of short-range communication between two buildings located at a distance of up to 1200 m and in direct visibility. Without these conditions being met, laser communication is impossible. Its undoubted advantages are:

• "transparency" for most network protocols (Ethernet, Token Ring, Sonet/OC, ATM, FDDI, etc.);
• high data transfer speed (up to 155 Mbit/s today, up to 1 Gbit/s for equipment announced by manufacturers);
• high quality of communication with BER=1E-10...1E-9;
• summing up network traffic to the laser transceiver using cable and/or fiber optic interface devices;
• no need to obtain permission to use;
• relatively low cost of laser equipment compared to radio systems.

Laser transceivers, due to the low power of their radiation, do not pose a health hazard. It should be noted that although the beam is safe, the birds see it and try to avoid it, which significantly reduces the likelihood of failures. If the transmitted information is delivered to and from the laser transceiver via a standard multimode fiber optic cable, then data transmission is guaranteed without radio waves and electromagnetic radiation. This not only ensures that there is no impact on equipment operating nearby, but also makes unauthorized access to information impossible (it can only be obtained by approaching the transceiver directly).

Wired data transmission systems now have a competitor - laser.

A laser beam can transmit up to 10 Gbits of information per second: such a speed is impossible in radio communication networks. Laser communication is completely harmless to humans and has many other advantages.

True, a laser beam cannot penetrate fog.

Laser communication has its own niche - it is used over short distances in places where there are difficulties with laying cables. Laser communications operators do not need to obtain permission to import equipment or use frequencies.

Light in the window In Moscow and St. Petersburg, all office centers are divided between various telecom operators. If, for example, a building is served by Sovintel, then it is extremely difficult for Comstar to install a line to this office complex (only in very rare cases is one building served by two telecom operators). every now and then they open up the asphalt to repair city communications, often cutting the laid cables in the process. Suspended cables often fall victim to cranes and storm winds.

An excavator is not afraid of a laser beam. In addition, the light beam cannot be stolen and sold as non-ferrous scrap metal, so laser communications are not dangerous for thieves who make a living by digging cables out of the ground.

20 years without scientific correspondence

Attempts to build wireless communications using a laser beam were made in Moscow back in the late 1960s. The transmitters were installed in the Moscow State University building on the Lenin Hills and in one of the houses on Zubovskaya Square, not far from the Park Kultury metro station.

The room-sized installation transmitted the signal successfully, but only in clear weather. Experts decided that the dependence on the state of the atmosphere is too high.

Communication using an infrared beam was recognized as an unpromising direction, and research was curtailed for 20 years. This pause cost Russian science dearly. At the end of the 1980s, Soviet researchers returned to the topic, but did not have time to bring their tests to commercial samples. Western competitors did it for them. Data transmission systems using infrared beams appeared on the world market in the early 1990s. One of the pioneers was the Canadian A.T. Schindler. Following this, Jolt and SilCom launched their developments. In the late 1990s, PAV Data Systems became the leader among manufacturers of laser communications equipment in the West, while the pioneers SilCom and A.T. Schindler had to make room a little. In addition, in the field of laser communications, the American-German Lightpointe Communications (formerly Eagle Optoelectronics), the American Astroterra, LSA Photonics, and Lucent Technologies have their own developments. Rain and fog

At a distance of up to 1600 m, the systems work perfectly. However, when transmitting data over a longer distance, the quality of communication decreases. In addition, laser systems are not free from weather dependence. The worst obstacle to laser communication is fog.

In turn, radio relay systems “fall” during rain. In this regard, developers propose to build highly reliable communication channels based on two lines, one of which transmits information via radio, and the other via a laser beam. Accordingly, one “falls” in the rain, and the other in the fog. “If you need to get a highly reliable channel at a distance of up to 3 km, then this is an ideal option,” says Alexander Klokov, technical director of the representative office of the American MicroMax, a distributor and integrator of wireless.

optical systems

There are other natural barriers as well. For example, they say that one of the cellular companies is still considering what to do with a tree that has grown in the path of a laser beam - either cut it down, or rearrange the device...

Western and Russian manufacturers do not compete with each other Source

: MicroMax Computer Intelligence, Inc.

Spit in the well Transtelecom appreciated the advantages of the laser beam. This company is having difficulties with Rostelecom and local Elektrosvyazy: ​​competitors who own the communications infrastructure do not allow Transtelecom to access the cable wells. As a result, Transtelecom gave up on the wells and is going to connect corporate clients

to their highways via a laser beam.

In addition, cellular operators use the laser beam as a signal transmission channel.

They use the laser in areas where there is a lot of interference in the radio air - for example, at airports.

Deputy Technical Director of the Sonic Duo company (MegaFon network) Igor Parfenov told Ko that more than 10 optical systems operate in the Moscow MegaFon network. The company intends to monitor their operation during 2003 and, based on the results of observations, make a decision on the advisability of mass use of this equipment. These systems are best used at a distance of up to 500 m. In addition to fog, sunlight is an obstacle for them, so it is necessary to install special filters,” says Pavlenko.

At MTS, the Ko correspondent was told that laser devices now provide communications in areas whose total length does not exceed 1% of the total length of the network. Most likely, laser communication will not exceed this threshold. “Optical networks are good for building micronetworks; the use of a laser does not require permission from the State Communications Supervision Authority. But, unfortunately, the practice of our company has shown that the laser still provides reliable communication at a distance of no more than 500 meters.”

In Russia, equipment for wireless communication based on an infrared beam is produced by the Research Institute of Precision Instrumentation, the Catharsis company from St. Petersburg, the Ryazan State Instrument Plant, the NTC companies from Novosibirsk and Sceptor (the latter created on the basis of the Moscow Energy Institute), and also Voronezh Institute of Communications.

None of the manufacturers, except for Catharsis, have advanced beyond pilot production. In Russia there are good engineers who create the right equipment, but do not know how to sell it at all. “For example, the simplest connector should be standard. And domestic devices have multi-pin connectors.

This is, of course, a good connector, but it is more suitable for rockets,” says Alexander Klokov. “Installation of Russian systems requires unsoldering the cable on site, but what sane operator would send their workers to solder something on the roof?”