Power Line Communication Technologies (PLC). Smart home with vending machines

Communication technologies and standards

LON is a local operating network. To implement smart home networks, network technologies that appeared in 1998 are used, such as LonWorks, HomeRF and Bluetooth.
Home radio network HomeRF is based on the open industrial Shared Wireless Acess Protocol (SWAP), developed by the Home Radio Frequency Working Group (HomeRF). The group, formed in March 1998, united more than 90 manufacturers (including Intel). The 2.4 GHz frequency band is used with frequency hopping capabilities. The network operates with a noise-like signal (NLS) and supports data transfer rates of 2 Mbps over a distance of up to 50 m. Products on the market include Intel's AnyPoint series networking products and Farallon's HomeLINE series networking products. AnyPoint includes an adapter to connect multiple PCs via USB to the nearest telephone jack.
Popular Bluetooth platform designed for the 2.45 GHz band. It involves the use of a frequency hopping transceiver (1600 hops/s) and operation in time multiplex mode. In the range from 10 cm to 10 m, the data transfer rate is 1 Mbit/s. The range is short, but can be increased to 100 m by increasing the power of the transmitted signal

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With the current level of development of computer technology and network technologies, strict requirements are imposed on networks. The computer network must provide the transmission speed required for specific conditions; it should also be mobile, with big amount access points, and cable laying should not be required; the network should have simple administration; it should provide high reliability with simple technical solutions; the network must support all possible types of network equipment and at the same time it must be cheap.

With the general global computerization of both the common population and enterprises, organizations and special services, there is a need to organize computer networks

One of the options for organizing networks is a data transmission system over power grids

The thesis will show a diagram of the organization of a data transmission network over power grids using the example of the village of Alkhan-Churt using PLC technology

The safety section is carried out with the aim of creating safe working conditions when working with power supply networks

In the economic part of the diploma, the cost of the designed network will be calculated and the economic feasibility of building a network based on PLC technology

PLC technology is, first of all, a solution to the “last mile” problem. Because this solution uses the in-house electrical network. The service itself is provided on a Plug&Play basis. That is, an adapter or subscriber modem purchased by a consumer in a store does not require any settings: when plugged into an outlet, it automatically communicates with the head unit, which is one in every home; The configuration is automatically configured and an IP address is assigned. Another advantage of the technology is that to connect to the Internet there is no need to wait for installers and let them into your home. Another additional advantage is roaming: the modem works in all homes where there is PLC coverage. It is not strictly assigned to a specific address and works within the district, within the city, and in another city too. Now networks are being built simultaneously in five cities, and at least another 5-6 cities in Russia are in the project preparation stage.

Despite all the advantages of this technology, the Internet access market is already saturated, and we literally feel how slowly the subscriber base is growing. If the client has already connected to the provider and made the wiring, then there is no point in attracting him with a low price, especially since by lowering the prices the operator puts himself in a difficult situation. The average broadband payment is already low. Therefore, for development it is necessary to introduce new services and services. For example, the so-called “constructor”. Various modules are “attached” to the basic PLC modem: Ethernet socket; Wi-Fi access point; a telephone module to which you can connect a regular analog landline telephone, an internal device, and a VoIP device. Using the latter, you can organize an internal telephone network within the city (for example, direct channels telephone communication with relatives).

Another plug-in module is a video camera, with which you can organize a video surveillance system at home without even connecting it to a computer. It transmits all traffic over the electrical network to the provider's server. And a user anywhere in the world can go online to his personal account on the client interface and check the situation at home. This solution is ideal for monitoring children, nannies and housekeepers. In addition, through the Web interface, you can configure various additional functions, such as, for example, a motion detection system, which will allow the camera to perform the functions of a volumetric motion sensor: when the picture has changed, a signal is sent to the server, and an SMS is sent to the user’s mobile phone - it connects to the Internet and checks if everything is ok.

PLC (Power Line Communications) technology, also called PLT (Power Line Telecoms), is a wired technology aimed at using the cable infrastructure of power networks to organize high-speed data and voice transmission. Depending on the transmission speed, it is divided into broadband (BPL) with a speed of more than 1 Mbit/s and narrowband (NPL).

A trial of a grid-based broadband internet service has been launched in Scotland. This initiative belongs to the electricity company Scottish Hydro Electrics. According to the British publication PC Advisor, about 150 users were involved in testing “Internet through a socket”. Each subscriber received Internet access at a speed of 2 Mbit/s. For the price it was more than double better than the offer another Internet provider. Several energy companies in the country have already shown interest in the new service. In addition, the leading electricity supplier in Germany, RWE, is dynamically implementing PLC. For example, in Germany, people don’t even fill out receipts for electricity: information from the meters comes directly to the electricity supplier via electrical wiring. Similar projects have been launched in Italy and Sweden.

In Russia, the first stage of network construction based on PLC technology was carried out by the Spark company and was completed in October 2005. At that time, the network included more than 750 access nodes located in residential buildings. All access nodes are connected by a Gigabit Ethernet backbone optical network. In 2006, a pilot project was launched to commission PLC technology in the Yuzhnoye Tushino region, and in 2007, active construction of the network and connection of subscribers began.

Low fees for Internet access ensure good competitiveness, but the quality sometimes causes complaints from potential and current subscribers (judging by the numerous discussions on forums). For example, users complain about the problem of being able to connect to the Network only through a certain outlet in the apartment, which is not always convenient for the subscriber, as well as about a decrease in speed when turning on electrical appliances. This is due to the general condition of the apartment’s electrical wiring, but such problems are resolved by the provider’s specialists. In addition, to avoid any problems, it is recommended to plug the user device into a separate outlet. Nevertheless, telecommunications industry experts maintain a low assessment of the development potential of PLC networks. The reason for this is the technology itself. Ethernet technology was specially developed to transfer data from computer to computer; as a result, when using it, the cost of terminal equipment is the lowest, and the speed characteristics are the best. Any attempts to adapt a medium for data transmission that was not originally intended for this purpose lead to more high cost equipment and worse technical characteristics. This also applies to telephone copper wire(switched modems or ADSL), and to power networks (PLC technology).

The so-called “last mile problem”, which has been talked about so much lately, has given rise to many solutions. However, most of these solutions have one common drawback - they all require laying wires and cables. There is probably no point in talking about the complications and difficulties this sometimes causes - very often the cost of laying cables makes up a large part of the cost of setting up a network. Moreover, there are a number of cases in which laying new cables is impossible or extremely undesirable - a prime example of such an unpleasant situation is a recently completed renovation, immediately after which it suddenly turns out that it is necessary to lay additional wires for computer networks.

Therefore, of particular interest have always been those technologies that made it possible to do without laying new cables. There are currently two successful approaches to this problem: wireless network Wi-Fi and PLC technologies. While quite a lot has been written about wireless networks, much less information is available about PLC technologies.

PLC technologies make it possible to build computer local networks based on existing power lines. So, using PLC technologies, you can build a small home local network using the electrical wiring that is already installed.

In fact, methods of transmitting information using electrical wiring have existed for a long time. One of them is the well-known Soviet loudspeakers (which are also often incorrectly called radio points). The various technologies are based on a fairly simple idea of ​​signal separation - if somehow it were possible to transmit several signals simultaneously over one physical channel, then the overall data transfer rate could be increased. This can be achieved using modulation (in addition, a modulated signal is resistant to interference), and with different modulation methods, different data transfer rates can be achieved on the same physical data channels.

At first glance, the recipe for successful PLC technology may seem simple - just choose a modulation method that could provide the fastest data transfer, and a modern means of communication is ready. However, those modulation methods that provide the most dense signal packing require complex mathematical operations, and in order for them to be used in PLC technologies, the use of fast signal processors (DSP) is necessary.

A digital signal processor (DSP) is a specialized programmable microprocessor designed for real-time manipulation of a stream of digital data. DSP processors are widely used to process streams of graphic information, audio and video signals.

Transmitting information over power networks using Semtech IP (2015)

The range of products manufactured by Semtech Corporation includes many physical-level ICs that make it possible to organize the transmission of information both over wires and over a radio channel (optical transceivers, line drivers, radio transceivers, etc.). The acquisition in early 2015 of EnVerv, a leader in the development of PLC (Power Line Communications) modems, allowed Semtech to expand its line of communications products to include devices that provide data exchange over standard power lines. In this article, we will dwell on the principles of operation and construction of networks based on single-chip PLC microcircuits from Semtech, consider the features of individual representatives of the new family and give examples of the practical implementation of devices based on them.

INTRODUCTION
Transmitting information and organizing power over the same wires is used quite effectively in various applications. For example, we can recall standard telephone lines or Ethernet networks that connect remote nodes using technology in which power is supplied through individual wires of the communication cable. However, most of these solutions have an obvious drawback: they all generally require installation work, the costs of which often make up the majority of the cost of setting up a network. Moreover, there are a number of situations in which laying new cables is extremely undesirable or even impossible - an example of such situations is a recently completed renovation, after which it suddenly turns out that it is necessary to lay additional wires for computer networks, or a rented office with an unforeseen Internet connection. In these cases, you can almost always limit yourself to the existing infrastructure, namely, use the electrical wiring already available in almost every room to organize a relatively fast and reliable communication channel branched throughout the building.

PLC telecommunication technology, based on the use of power electrical networks for data exchange by superimposing a useful signal on top of a standard alternating current with a frequency of 50 or 60 Hz, is characterized by ease of implementation and quick installation of devices based on it. The first data transmission systems over electrical networks appeared back in the 1930s, they were mainly used for signaling in power systems and on railways, characterized by very low bandwidth. At the end of the 1990s, a number of companies implemented the first large projects in this area, but during operation serious problems were identified, the main of which was poor noise immunity. The operation of energy-saving lamps, switching power supplies, chargers, thyristor dimmers and household electrical appliances, as well as electric motors and welding equipment, especially those included in the immediate vicinity of the PLC modem, caused impulse noise in wires unprotected from high-frequency radiation, which led to a sharp decrease in reliability data transmission. Also, the stability and speed of signal transmission were negatively affected by the heterogeneity of communication lines, in particular, the quality and deterioration of electrical networks, the presence of joints made of materials with different electrical conductivity (for example, copper and aluminum), the presence of twists, etc. As a result, the overall reduction in the nominal data rate ranged from 5 to 50%. In addition, in rooms where PLC devices operated, in some cases there was a disruption in radio reception at a distance of about 3-5 meters from the modem, especially on medium and short waves. This was due to the fact that the power grid wires began to act as antennas for radio repeaters, essentially radiating all traffic into the air.
The technology of data transmission over power grids received proper commercial application only at the beginning of the current century, and its introduction and widespread use is due to the emergence of the corresponding element base, incl. high-performance microcontrollers and fast DSP processors (digital signal processors), allowing the implementation of complex signal modulation methods and modern data encryption algorithms. This ensured not only a high level of reliability in the transmission of information, but also its protection from unauthorized access. Also important was the solution to the problem of standardization of various aspects of technology. Currently, the main organizations and communities regulating the requirements for PLC devices are IEEE, ETSI, CENELEC, OPERA, UPA and HomePlug Powerline Alliance. The last of them is an international alliance that unites about 80 well-known companies in the telecommunications market, including Siemens, Motorola, Samsung and Philips. The activities of the alliance, organized in 2000, are aimed at conducting scientific research and practical testing of the compatibility of devices from various manufacturers using this technology, as well as supporting and promoting a single standard called HomePlug.
All existing PLC systems are usually divided into broadband (BPL - Broadband over Power Lines) and narrowband (NPL - Narrowband over Power Lines). The range of problems solved with their help is very wide, and the choice of the required method is based on the characteristics and volume of transmitted information. Broadband devices (with speeds from 1 to 200 Mbit/s) are aimed at Internet access systems, for creating home computer networks, as well as for applications that require high-speed data exchange: video streaming, video conferencing systems, digital telephony, etc. Narrowband PLC modems are of greatest interest to hardware developers due to their relative low cost and improved characteristics that allow them to operate not only in regular networks, but also in networks with high levels of interference. Microcircuits and modules for narrowband modems (with channel capacity from 0.1 to 100 Kbps) are widely used as part of various products for household and industrial purposes, in the creation of distributed automated monitoring and control systems in workshops and life support systems of buildings (elevators, devices air conditioning and ventilation), means of metering the consumption of electricity, water, gas, heat, security and fire alarm devices.

FEATURES OF PLC TECHNOLOGY
The basis of PLC technology is the use of frequency division of the signal, in which a high-speed data stream is divided into several relatively low-speed ones, each of which is transmitted on a separate subcarrier frequency and then combined into the resulting signal (Fig. 1).

When using conventional frequency division multiplexing (FDM) modulation, the available spectrum is used inefficiently. This is due to the presence of guard intervals between individual subcarriers, which are necessary to prevent mutual influence of signals (Fig. 2a). Therefore, PLC devices use Orthogonal Frequency Division Multiplexing (OFDM), in which the centers of subcarrier frequencies are placed so that the peak of each subsequent signal coincides with the zero value of the previous one. As can be seen in Fig. 2b, the available frequency band in this case is spent more efficiently.

Before combining into one signal, all subcarrier frequencies are phase modulated - each with its own sequence of bits. After this, they pass through the formation block, where they are collected into a single information packet, also called an OFDM symbol. Figure 3 shows an example of differential quadrature phase shift keying (DQPSK) for each of the four subcarrier frequencies in the range 4.5-5.1 MHz. In reality, in PLC technology, transmission is carried out using 1536 subcarrier frequencies with the selection of 84 best ones in the range from 2 to 32 MHz, depending on the current state of the line and the presence of interference. This method gives PLC technology flexibility for use in various conditions. For example, as mentioned above, a working PLC device can “jam” radio reception at certain frequencies; this problem is well known to radio amateurs. Another example is when an application is already using part of the range. Technically, the elimination of unwanted mutual influence is realized by using settings, the so-called Signal Mode and Power Mask on devices that provide the corresponding capability. Signal Mode is a software method for determining the operating frequency range, and Power Mask is a software method for limiting the spectrum of frequencies used. Due to this, PLC devices can easily coexist in the same physical environment and do not cause noise in the frequency ranges used for radio communications.

When transmitting signals over a household electrical network, significant attenuation of the transmitted signal may occur at certain frequencies, which can lead to data loss and corruption. To solve the issue of adaptation to the physical transmission medium, a method is provided for dynamically switching on and off signal transmission, allowing detection and elimination of errors and conflicts. The essence this method consists of constant monitoring of the transmission channel in order to identify the part of the spectrum that exceeds a certain threshold attenuation value. If this fact is detected, the use of the problematic range is temporarily stopped until an acceptable attenuation value is restored, and the data is transmitted at other frequencies (Fig. 4).

Another significant difficulty when transmitting data over a household electrical network, now for the PLC devices themselves, is impulse noise, the sources of which can be various chargers, halogen lamps, turning on or off various electrical appliances (Fig. 5). The complexity of the situation lies in the fact that, using the method described above, the PLC modem does not have time to adapt to rapidly changing conditions, because their duration may not exceed one microsecond, as a result, some bits may be lost. To solve this problem, two-stage (cascade) noise-resistant coding of bit streams is used before they are modulated and entered the data channel. Its essence is to add redundant (“protection”) bits to the original information flow according to certain algorithms, which are used by the decoder on the receiving side to detect and correct errors. Cascading a block Reed-Solomon code and a simple convolutional code decoded using the Viterbi algorithm makes it possible to correct not only single errors, but also bursts of errors, which significantly increases the integrity of the transmitted data. In addition, noise-resistant coding increases the security of transmitted information from the point of view of protection from unauthorized access.

Since an extensive household power supply network is chosen as the data transmission medium, several connected devices can start transmitting at one time. In such a situation, a regulatory mechanism is used to resolve traffic collision conflicts - the CSMA/CA medium access protocol. Collision resolution occurs on the basis of one or another priority specified in special fields for prioritizing data packets.

SEMTECH IS FOR IMPLEMENTATION OF PLC TECHNOLOGY
Semtech PLC products are designed for use in typical power supply lines with low or medium operating voltage. Any modem that works with an analog physical line must have the functional units necessary to process analog data, convert it to digital form and, of course, to process digital data. On the transmission side, the modem must also encode digital data in accordance with a given algorithm, convert it to analog and send it to the line.
All these actions are performed by EV8xxx series microcircuits. Narrowband SoCs are highly integrated and contain all the necessary building blocks to implement the physical, MAC and other protocol layers (6LoWPAN and IEC). They support several types of modulation; in practice, OFDM is most often used to organize a stable and noise-resistant communication channel. Single-chip ICs that have passed interoperability testing in the HomePlug Alliance Netricity are distinguished by their versatility in application; both end nodes and network coordinators are designed on their basis. The Netricity specification is designed for network communications over long-distance power lines and is intended for out-of-home infrastructure, smart power distribution networks and industrial process control. The technology can be used in both dense urban and rural power grids using frequencies below 500 kHz. It also includes an IEEE 802.15.4-based access layer (MAC), which is key to the development of hybrid wired/wireless networks. The main technical characteristics of Semtech PLC chips are presented in Table 1.

The EV8xxx series ICs have programmable frequency ranges from 10 to 490 kHz, covering CENELEC A (10 - 95 kHz), CENELEC B (95 - 120 kHz), CENELEC C (120 - 140 kHz), FCC (10 - 490 kHz) and ARIB (10 – 490 kHz) bands without changes in device design. By remotely downloading the appropriate firmware over the power line, they can be configured to operate in ITU-T G.9903 (G3-PLC), ITU G.9902, ITU-T G.9904 (PRIME), IEEE P1901.2 and IEC-61334 (S-FSK). In addition, they support the proprietary high-performance 4GPLC mode. Structurally, the family’s microcircuits are manufactured in low-profile surface-mount packages designed for operation in the operating temperature range from -40 to +85°C. A simplified structure depicting the main functional units is shown in Fig. 6; the following blocks can be distinguished here:
The AFE (Analog Front-End) block is a set of analog components that provide isolation using a transformer with a coupling capacitor, filtering and amplification of the input signal, and the formation of specified levels of the output transmitted signal using a line driver on the op-amp;
PHY is a block designed to interface the digital part of the microcircuit with an analog line;
A 32-bit RISC microcontroller provides in-circuit implementation of the MAC level, performs data processing, packet generation, data encoding using the symmetric AES block encryption algorithm, etc., and also solves applied problems;
Peripheral blocks that interface the built-in microprocessor with external microcircuits - EEPROM memory, high-resolution ADC and host controller. For communication, hardware implementation of the widely used SPI, I2C and UART interfaces is used;
Integrated RAM and flash memory. The size of the built-in program memory varies from 1 to 2 MB, RAM - from 256 kB for the EV8100 to 384 kB for the others, other options are possible upon request from the manufacturer;
Timing control unit;
A power subsystem that provides all the voltages necessary for individual nodes. As a rule, a source is used that operates from the same AC network that is used for data transmission.
Separately, it is worth noting the EV8100 IC, which, in addition to standard components, contains a built-in 6x33 segment LCD display controller and a touch keyboard driver.

APPLICATIONS OF EV8XXX FAMILY ICs
PLC chips from Semtech are primarily aimed at use in automation systems, remote control and control of remote objects, the most popular areas of their application:
Building automation networks (AMI);
Airport landing light control systems;
;
Home local networks;
Intelligent equipment (“smart things”), incl. consumer electronics;
Monitoring and control systems for solar power plants;
Street lighting networks;
Communication equipment with substations;
Traffic flow management systems.
Among all of the above, the main focus is AMI (Intelligent Metering Infrastructure) networks that integrate smart meters, data concentrators, energy management tools, displays and other components of building automation systems (Fig. 7).

Communication via power lines is the main element of automated control and energy accounting systems used public utilities. The main advantages of this technology: the ability to automatically obtain information from residential and industrial premises located in remote areas with low population density and low quality infrastructure, long service life, scalability and low costs. The principle of operation of the system is quite simple. Electricity from the power plant is transmitted through a high-voltage cable to the substation. Here the voltage is reduced and distributed across a large number of low-voltage transformer substations that reduce voltage to household voltage. Typically between 500 and 1000 end consumers are connected to one transformer. Thus, we can propose the following option for constructing PLC systems for these purposes: a hub, acting as a central node, is based on low-voltage substations and regularly (for example, once an hour) collects measurement results from meters (this can be not only electricity meters, but also water, heat, gas). Next, the information is sent to the server for further processing, for example via a GSM channel. This type of system is not limited to receiving information from meters and can perform other functions.
For the practical implementation of this system, Semtech offers a developer starter kit, which includes both ready-made solutions based on EV8000, EV8100 and EV8200 chips for the fastest possible organization of data transfer via a PLC network, and debugging tools for assessing the capabilities of the system (Table 2).

The latter are modules for end nodes (meters) and hubs, the delivery package of which includes everything necessary, including recommendations for use, as well as software for setting the parameters of individual nodes and monitoring the quality of communication in the designed network. The included graphical user interface allows you to program the operating frequency range, modulation type, transmission speed, output power level, etc., as well as visually monitor the PER and BER error rates in received data packets.
Development kits EVM8K-01, EVM8K-02 and EVM8K-03 can act both as remote measuring nodes and as hubs that provide data collection. The modules are designed for operation in single- and three-phase networks, powered from a built-in AC source with a voltage of 80-280 V (EVM8K-01 and EVM8K-02) or from a DC source with a standard voltage of 12 V (EVM8K-01 and EVM8K-03). Communication with the host controller is carried out via RS-232 or USB interfaces. The EVM8K-13 kit is a network hub that combines on a single PLC board an EV8000 IC-based modem with a 32-bit RISC microcontroller required to run a custom application. The kit is capable of servicing up to 500 end nodes (up to 2000 optionally); its distinctive features include the presence on board of a 3G/EDGE/GPRS modem, a GPS module and an 8 GB SD card. Besides wireless transmission You can also use RS-232, USB or Ethernet interfaces to transfer data to the server. Appearance debug kits are shown in Fig. 8.

CONCLUSION
The widespread use of low-voltage electrical networks of 0.22-0.38 kV and the absence of the need for costly installation work for laying cables are stimulating increased interest in electrical networks as a data transmission medium. The current development of PLC technology is largely due to the emergence of generally accepted regulatory standards and the improvement of the corresponding element base. PLC modems from Semtech, characterized by a high degree of integration, provide a stable and noise-free communication channel with a sufficiently high throughput.

BIBLIOGRAPHY
1. Okhrimenko V. PLC technologies. // Electronic components. 2009. No. 10. With. 58-62.
2. Official website of Semtech. www.semtech.com
3. Product brochure. EV8000: Single-chip multimode PLC modem.
4. Product brochure. EV8010: Single-chip standards-based PLC modem.
5. Product brochure. EV8020: Single-chip standards-based PLC modem.
6. Product brochure. EV8100: Split-meter display SoC with integrated PLC.
7. Product brief. Power line communication products.

17.10.1999 Yuri PODGURSKY, Vladimir Zaborovsky

Recently, there has been a surge of interest in means of transmitting data over power lines. This is due, first of all, to the ever-increasing need for telecommunications on both a global and local scale.

Control and monitoring systems in industry and transport, medicine, energy, environmental safety systems and other areas of human activity are becoming increasingly intelligent and distributed. At the same time, new types of information exchange are becoming widespread - home automation equipment, networks of small and home offices (SOHO), distributed security and other alarm systems, which also require a developed communications infrastructure. In this case, the economic factor plays a decisive role: the means of information exchange, being a “tool” of communications, must be cheap and universally available.

Against the backdrop of weak Russian infrastructure wired communication It is the widespread prevalence of electrical networks, the absence of the need for expensive work associated with the creation of trenches and wells, breaking through walls and laying cables, as well as the possibility of forming symmetrical communication channels (Fig. 1) that stimulate increased interest in electrical networks as a data transmission medium.

Features of power lines

The difficulty of organizing communication over power lines lies in the fact that existing power networks were not originally intended for data transmission. They are characterized by a high noise level and rapid attenuation of the high-frequency signal, as well as by the fact that the communication parameters of the line, constant for traditional physical media, vary significantly over time depending on the current load. A specific feature of power lines is their branched tree topology. In addition, when organizing communications, electromagnetic compatibility and shielding of data transmission processes from actual power consumption must be ensured.

The implementation of data transmission systems over electrical lines in Russia is associated with additional difficulties, namely that the technical characteristics of domestic electrical networks differ from the characteristics of Western networks and, perhaps (more importantly), there are no standards defining the main parameters of data transmission systems over power lines.

Main Applications

Currently, there are several standard system approaches to transmitting information along power lines. The differences between them consist primarily in the focus on a specific class of applications, as well as in the methods and means of ensuring reliable information interaction.

The most important areas of application of communications based on electrical networks are shown in Fig. 2. Each class of applications is characterized by specific requirements for transmission speed and range, access method and other indicators that determine transmission quality.

Low-speed distributed control and accounting systems include automatic control systems in workshops and production areas, life support systems for buildings (elevators, air conditioners, ventilation), warehouse systems, energy metering devices, security and fire alarm systems in holiday villages, garage cooperatives, etc. d.

Another class of applications consists of home automation tools, which allow for comprehensive control of household appliances up to the automatic coordinated switching on of coffee makers and toasters, as well as displaying images from the entrance video camera on the TV screen when unexpected guests appear. This also includes local networks for home and small offices deployed within a small building or individual apartment.

Of undoubted interest are examples of the successful use of electrical networks to organize telephone communications in villages and limited areas, and in addition, to provide high-speed Internet access. Progress in this area can not only change the balance of power in the Internet provider market, but also bring to life new principles for the design of power electrical networks and their optimal structuring, taking into account both energy and communication requirements.

Interaction Architecture

The architecture of information interaction based on electrical networks has a hierarchical structure; it is summarized in Fig. 3. Even within the same application area, specific implementations differ in methods of reliable data delivery at different levels of the hierarchy.

Increasing the reliability of transmission at the physical level is associated with the choice of modulation method and frequency range, using digital signal processing and adaptive control methods. Here, first of all, it should be noted that the broadband (Spread Spectrum) modulation algorithms are promising, which significantly increases the noise immunity of transmission.

When using SS modulation, the signal power is distributed over a wide frequency band, and the signal becomes invisible against the background of interference. At the receiving side, meaningful information is extracted from a noise-like signal using a pseudo-random code sequence unique to a given signal. Using different codes, you can transmit several messages at once in one wide frequency band. The described principle underlies the Code Division Multiple Access (CDMA) method. SS modulation and CDMA technologies are discussed in detail in the literature (mainly using examples of use in cellular telephone networks). Here we just note that in addition to noise immunity, SS modulation provides a high level of information protection.

The main ways to increase transmission reliability at the link level are as follows:

• splitting data packets into short frames;
• use of correction codes to identify and correct errors;
• application of low-level reliable transmission protocols based on confirmations of receipt of short frames;
• use of effective methods for controlling access to the data transmission medium.

Short packets make it possible to increase not only the probability of reliable transmission of a piece of data, but also the efficiency of adaptation of the transmitting side to rapidly changing network characteristics. When using wideband modulation, this is expressed in the optimal redistribution of signal power in the frequency band, taking into account the actual interference spectrum.

Some companies have developed optimized media access protocols that take into account the characteristics of “power grid” applications and the noisy nature of power lines. Since a significant part of such applications (automatic accounting, security alarms, home automation) assumes the presence of one active node in the network, it is advisable to use polling or token passing methods to provide access. This eliminates the problem of carrier recognition in noisy networks and the need to detect collisions. In order to increase the reliability of the access control itself, the principle of a “three-time handshake” is used when transmitting a token.

Basic components

A typical functional diagram and main components of the communication node of the “electrical communication network” are presented in Fig. 4.

The core of the communication node is controllers of the network, data link and physical layers; the latter are often also called transceivers or transceivers. As a rule, these components are implemented on the basis of universal or specialized microprocessors and are produced by a number of companies in the form of chipsets.

An isolating (connecting) module generally performs two functions: it isolates the communication node equipment from the supply voltage and separates the information signal from the power voltage. Typically this module is made of separate radio-electronic components.

Some companies manufacture special power amplifier chips that allow signal transmission over long distances. Based on these components, an electric modem with a standard or custom user interface can be built.

To ensure compatibility between products from different manufacturers (within the same class of applications), efforts are being made to standardize technologies for transmitting information over power lines.

Technologies and products

The most common technologies for transmitting data over 120/220 V electrical networks are:

• X-10 of the same company ( http://www.x10.com);
• Intellon CEBus ( http://www.intellon.com);
• Echelon Corporation's LonWorks ( http://www.echelon.com);
• Adaptive Networks, proposed by a company with the same name ( http://www.adaptivenetworks.com);
• DPL 1000 manufactured by NOR.WEB ( http://www.nor.webdpl.com).

X-10 technology developed in 1978 by the X-10 Corporation with a focus on the tasks of remote control of lamps and simple household appliances. To transmit binary information, the generation of short radio pulses with a frequency of 120 kHz is used here at the moment the alternating voltage passes through zero. The choice of such a coding scheme is due to the fact that null value voltage is characterized by lower noise levels and the influence of other devices connected to the network.

Binary “1” corresponds to the transmission of a frequency of 120 kHz for 1 ms, and binary “0” corresponds to the absence of a radio pulse. To reduce errors, two zero crossings are used to transmit one bit. Therefore, the transmission speed is limited to 60 bps (for a 120 V, 60 Hz network).

The application level corresponds to the language for controlling the simplest devices. A complete X-10 command consists of two packets separated by three periods and requires 47 cycles or approximately 0.8 seconds to transmit.

X-10 controllers and adapters are produced by many US companies. X-10 products adapted to European power grids are available in a number of European countries. The cost of X-10 modules ranges from $8 for a passive receiver to $50-100 for a multifunctional active device.

The main disadvantages of the X-10 based system are low speed transmission and functional limitations.

Intellon CEBus (Intellon SSC) technology was created by Intellon to transmit data over power lines (120 V, 60 Hz) in accordance with the standard home network CEBus (more detailed information This standard can be found on the Internet at http://www.CEBus.com). The CEBus standard (EIA-600) defines the requirements that will make interoperability possible. household appliances and home automation devices based on various physical transmission media: power lines, radio and infrared channels, coaxial cable, etc. The CEBus model includes application, network, link and physical layer protocols of the OSI reference model.

Application layer functions are performed by the CAL (Common Application Language) application language, described in the EIA-721 document. It defines a unified syntax for describing the operation of various devices and a set of standard commands. CAL is an object-oriented language that allows you to specify application interaction contexts, in particular the sound control of a TV, stereo system, VCR and CD player. Each context is further broken down into objects that represent control parameters such as volume, brightness, etc.

The network layer protocol generates data packets containing all the necessary information about the source and destination addresses.

The CEBus standard provides a peer-to-peer interaction model, in which any node has free access to the network. To prevent collisions at the link layer, the CSMA/CDCR mechanism is used.

At the physical level, Intellon CEBus Powerline Carrier Protocol uses SS modulation technology, which provides for the transmission of each bit of data in the frequency band 100-400 kHz.

Intellon offers a family of Power Line Evaluation Kit products that implement Intellon CEBus technology, from chipset to system solution and network design tools. Its cost is $245. According to available information, Microsoft has acquired a license to use Intellon CEBus technology for transmitting data over electrical networks.

LonWorks technology (Local Operation NetWorks) developed by the American corporation Echelon with the aim of creating distributed control systems (networks) for industrial and domestic use. LonWorks provides the tools and building blocks needed to design, install, and maintain intelligent, interconnected components and subsystems that include Various types sensors, control devices, indications, etc.

The main components of LonWorks technology are:

• LonTalk protocol;
• Neuron Chip microprocessor (3 x 8 bit CPU, 10 KB RAM, 10 KB ROM);
• specialized modules - transceivers for various transmission media, control modules, network adapters and routers;
• design tools - LonBuilder (configuring and debugging LonWorks networks), NodeBuilder (configuring an individual node), LonMaker (protocol analysis);
• software gateways - Ethernet, T1, X.25, Bitbus, Profibus, CAN, Modnet, SINEC, Grayhill, Opto22 (digital), OptoMux, Modbus, ISAbus, STD32 bus, PC/104, VMEbus and EXMbus.

The basis of LonWorks technology is the LonTalk protocol, used by network nodes to exchange information. Each network node must contain a microprocessor that implements the functions of this protocol.

The LonTalk protocol is open and can be built into any suitable microprocessor. An example of such embedding is the Neuron Chip microprocessor mentioned above, which was developed using LonWorks technology and manufactured by Motorola and Toshiba. This chip provides a reference implementation of LonTalk and can be used both in data exchange control tasks and for testing other implementations of the specified protocol.

LonTalk is a seven-layer communication protocol that allows reliable data transmission over various physical media - twisted pair, radio (RF), infrared, power lines, coaxial or optical cable. Transceivers have been developed for each type of environment to support network operation across a variety of channel lengths, transmission rates, and network topologies. The access method used is CSMA.

For power lines 24/120/220/380/480 V AC (50/60/400 Hz) and direct current Several transceivers (PLTs) have been developed, made in the form of microcircuits and microassemblies.

The price of LonWorks components is quite high: $42 for a transceiver, from $2000 for a programming system.

LonWorks technology is used primarily in life support systems for buildings, industrial and home automation. It is one of the leaders in the field of distributed control networks. This is also confirmed by the fact that recently Microsoft has been actively involved in the development of home networks based on LonWorks, and Cisco Systems has demonstrated the ability to access LonWorks network nodes via the Internet using regular browsers.

Corporation Adaptive Networks (ANI) produces a number of products that support highly reliable data transmission over any type of electrical wiring, including those that comply with the European CENELEC standard. ANI's patented technology provides effective transmission speeds of up to 115 kbps (physical speed 268 kbps) and reliability comparable to that of dedicated dedicated cable infrastructure.

In 1991, Adaptive Networks technology was approved as a data communications standard for airborne refrigerated container monitoring systems (ISO 10368). Its distinctive features are:

• ensuring reliable data transmission under high levels of interference by quickly adapting the broadband signal to the actual characteristics of the power grid;
• the ability to work with existing network software focused on twisted pair or other type of cable;
• use of a transparent, reliable link layer protocol with error correction (the probability of an erroneous bit transmission is 10 -9);
• integrated implementation that does not require additional interface logic;
• a hybrid scheme of token access to the medium, used when the network is quite congested.

Currently, chipsets and modules are available that provide effective throughputs of 4.8 (AN48), 19.2 (AN192) and 100 kbps (AN1000). An Evaluation Kit is provided for each chipset. The cost of components and tools is quite high.

TechnologyDPL 1000 allowing data transmission over power grids at speeds of up to 1 Mbit/s, developed by the English company NOR.WEB (a joint venture of Nortel Networks and United Utilities).

DPL 1000 can rightfully be considered a revolutionary step in the development of data transmission over power lines, since it opens up the possibility of almost universal direct access to the Internet at extremely low prices. If tests currently being carried out in several European countries confirm the performance of DPL1000-based systems, then in the future we can expect significant changes in the provider services market and lower prices for Internet access.

The new technology is based on patented means of shielding data from electrical noise. There are practically no technical details of its implementation in available sources. DPL 1000 is a complete solution for data transmission from a step-down transformer substation to end user in your home or office.

In accordance with the DPL 1000 technology, certain adjustments are made to the operating parameters of a fragment of the electrical distribution network connected to the low-voltage winding of the step-down transformer, after which it can be used as local network. This eliminates the problem of the “last mile” for Internet providers and provides constant direct access to the Internet for users without loading telephone subscriber lines.

DPL 1000-based LANs include the following hardware components:

• central station, which provides connection of the local network to the main communication channels and network administration;
• a base station located at a transformer substation and implementing the connection of an information local network to low-voltage power supply lines;
• a connecting device that is installed at the entrance of the power cable to the house (next to the electric meter) and provides connection to the internal information network;
• a communication module connected to a computer on which communication software is installed.

Currently, demonstration zones have been deployed in several European countries to “test” the DPL 1000 technology. For example, in the UK, it is used to connect to the Internet comprehensive school, and in Germany, based on DPL 1000, the first users received constant access to the World Wide Web at speeds of up to 1 Mbit/s in both directions.

Other companies also create separate components for data transmission over power grids, among which Intelogis and ITRAN should be noted.

List of abbreviations used

AMR (Automated Meter Reading)- automatic reading of meter readings. ASK (Amplitude-Shift Keying)- amplitude manipulation. ASST (Adaptive Spread Spectrum Transmission)- adaptive broadband transmission; patented technology from Adaptive Networks. BPSK (Binary Phase-Shift Keying)- two-position phase shift keying. CAL (Common Application Language)- unified application language of the CEBus standard. CEBus (Consumer Electronics Bus)- consumer electronics bus; A home networking standard developed by the EIA. CENELEC (European Committee for Electrotechnical Standardization)- European Electrical Standards Committee. CDMA (Code Division Multiple Access)- code division multiple access. Access method using wideband (SS) modulation. It is carried out by multiplying a sequence of useful bits of information by an individual pseudo-random sequence of shorter pulses. DCSK (Differential Code Shift Keying)- differential code keying; Wideband modulation technology developed by ITRAN Communications. DPL (Digital Power Line)- “digital” power supply line. EIA (Electronics Industry Association)- Electronic Industry Association. FCC (Federal Communications Commission)- Federal Communications Commission (USA). FSK (Frequency-Shift Keying)- frequency shift keying. ICSS (Integrated Circuit/Spread Spectrum)- integrated circuits for wideband modulation; a trademark of National Semiconductor. PLT (Power Line Tranceiver)- transceiver for data transmission via power line. PSK (Phase-Shift Keying)- phase keying, in which the carrier phase takes only fixed values ​​from a range of permissible values ​​(for example, 0, 90, 180 and 270 degrees), and information is included in changes in the carrier phase. SOHO (Small Office/Home Office)- small/home office. SSC (Spread Spectrum Carrier)- “broadband” carrier. SST (Spread Spectrum Transmission)- broadband transmission.

Electromodems EM-20 and EM-30

Manufacturer: Central Research Institute RTK Device type: a means of transmitting information over a 220/380 V power supply network Communication lines: power supply networks 24/120/220/380 V AC (50/60/400 Hz) or DC, as well as de-energized lines Transmission range, km: 0.5-1.0 (territory of one substation) Transfer rate, kbit/s: 4.8; 9.6 or 50.0 Interfaces: RS-232, RS-485, custom Possibility of direct call Bidirectional transmission capability Multichannel speech transmission Areas of use: comprehensive security systems (security, fire, emergency alarms in garages, garden cooperatives, museums, nature reserves, hotels); systems for remote recording of parameters and distributed control ( local systems energy saving, pumping and storage systems); quickly deployable information transmission systems (exhibitions, outdoor events); automation of buildings and special regime facilities; local data and speech networks based on existing 220/380 V power lines.