GPRS modems. Mobile Internet on PDA and laptop Gps modem for computer

In the last couple of years, messages about the release of more and more new models of devices belonging to a special class of hardware - GPRS modems have already become regular. What is it?
Very briefly, GPRS modems can be described as another type of wireless data transmission devices. Their fundamental difference from other devices of this group is that they work using one of the variants of packet data transfer technology implemented in GSM cellular networks and called General Packet Radio Service, or abbreviated as GPRS. The development of this technology is the two largest Russian companies cellular communications - "VympelCom" and "Mobile TeleSystems" - started back in 2000, and now the total number of cellular networks in the world that have implemented GPRS is already in the hundreds. The issues of organizing international roaming for subscribers working in this mode are also being solved with might and main. All the main properties and features of the operation and parameters of this type of wireless modems, due to the use of such a technical solution, become clearer after getting acquainted with the essence of the GPRS technology itself. Our magazine already wrote about this topic about a year and a half ago, so now we will only briefly recall the main essence.

Why was GPRS created?
The current stage of development of our industrial society has led to the fact that for the successful operation of many modern "information industries" it is not required that a person be territorially "attached" to any particular machine, room, or even the entire production complex, but it is only necessary that he I just kept in touch all the time. Numerous modern means of telecommunications, and primarily mobile, partly allow us to solve this problem. But if a person, for example, by the nature of his work, must participate in the collective processing of large amounts of data, then the telephone does not really save the situation. After all, spending hours dictating or checking on the phone a lot of numbers in some summaries or reports is not a pleasant occupation. Yes, and it is difficult to call such work effective. Another thing is if this data, literally with one click on a key, can be quickly transferred to any necessary subscriber and just as easy to receive others. In this case, for successful collaboration, it doesn’t matter at all where you are: in the office, at home, in a train compartment, in another city or abroad...
In general, according to analysts, people's needs for mobile data transmission in the foreseeable future will increase annually by at least one and a half times.
Of course, we must not forget that the possibility of data transmission in cellular communications was implemented almost from the very beginning of the operation of such networks, but only in practice this possibility turned out to be almost theoretical for a long time - people did not really want to use it - literally a few percent of the total number of subscribers around the world! And there were two main reasons: slow and expensive. Indeed, for example, even modern cellular The second generation of the GSM standard provides data transmission at a speed of only 9.6 kbps. You can imagine how "modern" this speed is simply by remembering that modem users on ordinary telephone lines completely abandoned such speeds more than five years ago. Yes, and the very method of communication over a voice channel with a per-minute payment made being online, although possible, but very expensive.
To eliminate these shortcomings, GPRS technology was invented. Its goal was to significantly increase the speed of data transmission over cellular channels, as well as to provide a "constant connection" mode for subscribers, similar to how it is implemented in local area networks. But unlike local networks, the working area here is already the entire coverage area of ​​the used cellular network, and taking into account roaming, almost all areas of the Earth where GSM cellular networks operate. Such coverage today is not available, in fact, to any other wireless technology, with the exception of satellite. This is one of the fundamental advantages of GPRS technology.

Technical essence of GPRS
First of all, it should be noted that GPRS technology is intended for use only in digital cellular communication networks of the GSM standard, implemented on the basis of the Time Division Multiple Access (TDMA) method. It is the use of TDMA features that owes its appearance to GPRS.
Simplistically, the essence of the TDMA method is as follows. The entire time of operation of one radio communication channel is divided into time intervals of standard duration, distributed in turn among several subscribers. As a result of this, on one radio frequency it is possible to transmit several conversations at once, or to organize several independent data exchange channels. In the GSM standard, the maximum number of such channels is eight.
Such a temporary division of the communication channel between several users allows you to increase the number of simultaneously served subscribers, however, all channels are busy only at rare moments of peak loads in the cellular network. The rest of the time, some of these channels are free. It was on this feature that the idea of ​​GPRS technology was based: in cases where a subscriber needs high-speed information transfer, temporarily "give" him free time intervals in a given radio channel. Thus, the speed of information transfer can immediately increase several times.
But that is not all. The GSM channel itself can provide a slightly higher information transfer rate if other coding methods are used. Without a noticeable reduction in quality, the data rate can be increased to 14.4 kbps, and potentially even up to 22.8 kbps. This is where high data rates in GPRS arise: up to 115 kbps, and in the limit - more than 170 kbps. Moreover, it is precisely such high communication speeds that make it possible to fairly painlessly allocate increased resources to one of the users for some time, without the risk of significantly reducing the chances of other subscribers to get through to the network. Indeed, in the GPRS mode, for example, receiving even a fairly large e-mail the size of a whole typewritten page can be done in just tenths of a second. And if we take into account that the delay time of allocation of radio resources for the transmission of a data packet, which is inherent in the GPRS technology, should not exceed 1 second, then the exchange of small amounts of information between users will occur almost instantly. Such significant changes in the conditions of data exchange using mobile terminals open up numerous new opportunities.

Functionality
One of the biggest advantages of the GPRS mode is that the subscriber device "does not occupy the line" in the pauses between receiving and transmitting data. The equipment of the cellular network operator simply "remembers" that the user is ready to transmit or receive data, and the radio channel resources are allocated to him only for the time of information exchange. In other words, any GPRS devices can be in constant communication (if, of course, they are turned on and located within the network coverage area) - in the "permanent virtual connection" state. In this case, the operator does not need to require the subscriber to pay for the entire time of his connection with the mobile network (actually 24 hours a day), but only for the intervals of active operation of his terminal or the volume of transmitted and received information.
GPRS technology also opens up great opportunities for the development of telemetry transmission systems, remote monitoring, security systems, industrial electronics, etc. GPRS technology is also convenient for cellular network operators, since it, being a modernization of existing GSM networks along the way of their development to communication systems third generation, does not require a radical replacement of equipment. True, subscribers, from this point of view, on the contrary, are the losers - to use GPRS services, special terminals that support this technology are required.

User Equipment
The accepted scenarios for the implementation of GPRS provide for a gradual increase in data rates. This was done, in particular, due to the restrictions imposed by the current user terminals. The fact is that the maximum rate of reception and transmission of information that a mobile terminal can provide depends on the number of channels (number of time slots) it supports for reception and transmission. So far, all manufactured GPRS subscriber terminals are capable of supporting from 2 to 4 channels for receiving information and 1 or 2 channels for transmitting. This allows you to get the maximum reception speed up to 57.6 kbps and transmission - up to 28.8 kbps and in practice be much lower). In the future, we should expect the appearance of GPRS terminals that support a larger (up to 7) number of channels for receiving and transmitting and capable of providing higher communication speeds. From the standpoint of the functioning algorithm, the standard provides for the existence of GPRS terminals of three different classes:
- class A models should provide the possibility of simultaneous operation in telephone mode and in GPRS mode;
- class B terminals also support both voice connections and packet data transmission, but these modes are not implemented simultaneously - in the process of data transmission via GPRS, the subscriber cannot make and receive voice calls, however, the terminal must promptly respond to incoming calls and allow without data loss pause the session to answer a phone call;
- class C is focused on working in turn in the modes - GPRS and telephone.
In fact, all mobile phones with GPRS support currently produced in the world (and this is already more than fifty models) belong to class B and have the means to connect them to a computer via a special cable or infrared port. And one of the preferred embodiments of class C devices (although classes A and B are not excluded) can be GPRS modems, performed either in the form of a PC card connected to a laptop computer, or in the form of small-sized GPRS modules oriented to use in the very various equipment - from portable computers to means of industrial electronics.

GPRS modems and modules
The number of models of such devices really available now is already several dozen and in the very near future it will undoubtedly increase, because many well-known companies are involved in their creation today: Ericsson, Motorola, Nokia, Novatel, Olitec, Option International, Pretec Electronics, Real Time Devices, Siemens, Sony, Wavecom, Xircom, and others, who have keenly grasped the prospects of this direction.
What are the main advantages of using specialized devices compared to using conventional mobile phones with GPRS support?
They can be named several at once, and they are due, first of all, to the design features, as well as the functionality and parameters of such modules, which determine the areas of their predominant use. For ease of explanation, all these features can be divided into several groups:
- "Wide functionality". This is not just a slogan - many devices of this type are designed to operate in several (or even all!) Frequency bands used by modern GSM networks (EGSM-850 MHz, GSM-900 MHz, DCS-1800 MHz, PCS- 1900 MHz), which allows the use of such modems practically all over the world.The versatility of the use of such devices is also ensured by the fact that they often implement several data transmission technologies at once, which are possible in GSM networks: a traditional GSM modem (speed 9.6 kbps), packet transmission in GPRS mode and transmission in line switching mode using HSCSD (High Speed ​​Circuit Switched Data) technology, which is similar in methods and parameters to GPRS. In addition, modern GPRS modems, as a rule, support all functions, provided by the development phase of the GSM 2+ standard, including the SIM Application Toolkit, etc. As a result, the user also has access to the functions of the usual mobile phone: voice communication, receiving and sending faxes, SMS, etc.
-"Everything you need to get the job done and nothing more". This is how you can characterize the position from which the optimization of the very structure of these devices is carried out. Indeed, unlike phones, GPRS modems often have several user inputs/outputs at once, supporting completely standard interfaces RS-232, USB, etc., as well as connectors for connecting an external antenna and other devices. In addition, many modems have ample opportunities for remote parameter setting and operational program management their work. On the other hand, modems are made as light as possible by excluding from their composition such parts that are not used in this case, such as a microphone, speaker, display, keyboard, etc.
- "Performance in a variety of conditions"- provide the design of modems and the "unpretentiousness" of some of them to the supply voltage. Purely constructively, existing GPRS modems can be divided into three groups. The first of them, which can be conditionally called "office", includes devices made in the form of Type II PC cards (PCMCIA), focused on connection and use in conjunction with portable computers. The second group may include models intended for embedding in other devices, and therefore characterized by maximum "lightweight" design. The third group consists of models for industrial use, which, on the contrary, have a "protected" design that ensures their reliable operation in a wide range of temperatures, humidity, pressures, vibrations, electromagnetic fields and other types of influences. Such models often also have a wide-range (for example, from 5 to 32 V) internal voltage regulator, which makes it possible to directly connect them to a variety of sources (Li-ion batteries, car on-board network, various industrial devices, etc.). Some models of the last two groups are supplemented with other devices (GPS receiver, analog-to-digital converter, etc.), which further expands their functionality and scope.
The use of GPRS modems and modules is especially promising for the implementation of "machine-to-machine" communications, which cover a very wide range of various applications: car and home security, industrial and home automation, telemetry equipment and systems for monitoring the parameters and movements of various objects, mobile office and much, much more. In other words, GPRS modems can be useful in all those cases when laying a communication cable or deploying a specialized wireless system for one reason or another (organizational, technical, economic) is impossible or impractical. It is also important that you do not need to obtain any special permission to operate GPRS modems. To use them, you just need to buy SIM card and in the future pay for the standard services of a GSM operator.
In general, it should be noted that GPRS, despite the existence of other technologies for high-speed data transmission over cellular channels (for example, Cellular Digital Packet Data for networks of the D-AMPS standard, High Speed ​​Packet Data for systems with code division of signals according to the cdmaOne standard, etc. .), due to the current actual world domination of GSM, is simply "doomed" to become one of the key wireless data transmission technologies for the next decade (before the widespread use of 3G networks, Wi-Fi, etc.).
Igor Skolotnev

Transfer of information over networks GPRS allows you to easily create systems for remote dispatching and control of devices, as well as stationary and moving objects. By using GPRS modems for data transmission, it is possible to replace the widely used CSD connection (two-site modem connection) in GSM with a GPRS connection. This is economically much more profitable at the current tariffs of all telecom operators.

InSAT offers a wide range of GPRS modems. The most popular for industrial applications are GPRS modems manufactured by MOXA, ICP DAS, Segnetics, iRZ, ARIES, TELEOFFICE.

Russian manufacturers of GPRS modems

From domestic manufacturers, we offer products from such companies as ARIES, iRZ, Segnetics and TELEOFFICE.

OWEN produces a wide range of equipment for industrial automation, dispatching and accounting systems. GPRS modem PM01 manufactured by OWEN has proven itself in a large number of real projects.

The company TELEOPHIS specializes in the production of communication tools. It offers a wide range of products, including GPRS and GSM modems.

iRZ is an international manufacturer of wireless products and integrated solutions. The uniqueness of the iRZ policy lies in the flexibility of the architecture of products and solutions, the highly efficient use of the latest technologies and sensitivity to the dynamics of the market. The iRZ model range is distinguished by high quality components, support for the latest technologies and moderate cost. The company's products are not inferior in characteristics to the products of the world's leading manufacturers.

Organizing Internet access on a PDA or laptop today is not a problem. In principle, a laptop is an ordinary computer, which, as a rule, has all standard interfaces (Ethernet, USB) or a conventional analog modem for dial-up access via a public telephone line (dial-up). It will be more difficult with a pocket computer (unless, of course, it is a communicator) - to connect to a modem via USB, it must have a USB-Hub or some kind of wireless interface (respectively, the device that organizes Internet access must have the same wireless interface ).

It is clear that both a PDA and a laptop are mobile devices, so it would be foolish to entangle them with wires to access the Internet. Therefore, let's talk about wireless methods of accessing the Internet from these mobile devices.

There are several ways to organize mobile wireless Internet access. Of these, the most popular and universal at present in Russia is cellular communication using a conventional GSM phone, which allows you to organize high-speed Internet access using GPRS technology (in this case, a cell phone is the gateway to the Network). However, in this case, sometimes there are problems with sharing a laptop and a phone, since this requires a wired connection (USB or RS-232), which is not very convenient when traveling, or wireless communication(Bluetooth, InfraRed, Wi-Fi), which is also not always suitable (after all, you still need to talk on the phone).

GSM/GPRS modem with USB interface

The cheapest and most versatile solution for equipping a PDA or laptop with mobile Internet are GSM/GPRS modems with a USB interface. And there are quite a lot of such devices on sale today.

Some of them are just GPRS / GPS modems - without the possibility of using the talk mode, while others allow you to connect a hands-free headset, with which you can talk on the phone from your computer.

However, despite their compactness, such models are not very convenient to use, as they are “hung” on a PDA or laptop using an additional cord, require separate storage, get lost, and generally limit mobility (for example, to use a USB device with a PDA, you often need additional interface - cradle).

GSM/GPRS PCMCIA cards

If you do not want to use a connection from your phone and laptop to access the Internet, then you can purchase a special PCMCIA card that allows you to organize high-speed access to the global network and turn your laptop into a full-featured mobile phone with the ability to negotiate and send faxes and SMS/MMS messages. By the way, keep in mind that in order to connect to the Internet, the GSM operator and the corresponding tariff plan must support GPRS.

There are not so many cards with PCMCIA interface (PC-card Type II) on sale today. Some of them, like the ones described above, are simply GPRS/GPS modems without the possibility of using the talk mode, but such an acquisition does not seem successful to us. Indeed, at the speed of a GPRS connection, the use of tools such as Skype, or others that allow you to speak, can cause delays in voice transmission, and a lot of voice traffic will have to be paid at GPRS rates, which will certainly be more expensive than a regular call to a mobile phone located in another city or even country.

So, in our opinion, more attractive are modems that have a headset connector that allows you to talk on the phone from a computer, and simple software for emulating all the functions of a telephone set - such as, for example, OvisLink WGP-1500, Billionton PCMCIA GPRS / GSM Wareless modem or Neodrive GPRS-100S (included is a passive headset on a special clip - an earpiece and a sensitive microphone).

Other features of such modems include the presence of two or three GSM bands (GSM 900, 1800, 1900), the convenient location of the SIM card compartment and the original design of the antenna (it can be removable). For example, in the Billionton modem, the antenna design allows you to either hide it inside the device, making it as compact as possible, or extend it, positioning it for better reception quality. And the Neodrive GPRS-100S modem has an external rotating antenna, but although its design looks more reliable than the Billionton modem, this device is less compact.

To access the Internet, it is enough to install the drivers for the corresponding PCMCIA card and configure network connection, however, if you want to use all the functions of your phone, you need to install special software. Virtual keyboard and the functions of this software are usually implemented in a familiar "telephone" design and provide a simple dialing and answering call function. Of course, navigating through the menu of such a phone on a large laptop screen is much easier than looking at icons on a small screen. cell phone. In addition, such software may provide panels with additional functions. From the program, you can establish a GPRS connection, send SMS, e-mail and fax, as well as manage your notebook, synchronize data with the organizer and perform all the operations that are on the phone.

To use such a card as a regular mobile phone, you must, of course, connect the headset included in the kit (these devices do not work from the microphone and speakers of the laptop). After that, you can answer incoming calls or call someone, just like with a regular phone headset. The only difference between a PCMCIA card and a phone with a headset is that the system can only be used while working with a laptop, that is, if the laptop is turned off, then you will not be able to use such a phone.

GSM/GPRS CompactFlash cards

However, only laptops have a PCMCIA interface, so it will not be possible to connect a PDA to the Internet using the above devices. But there are more versatile solutions based on CompactFlash (CF) or Secure Digital (SD) interfaces that can be used with both laptops and PDAs.

For example, Neodrive has a GPRS-110S model, which is identical in its characteristics to the GPRS-100S model for PCMCIA, but has a CF interface, which allows you to connect it to a pocket computer with such an interface and turn it into a communicator.

GSM/GPRS CF-, SD-cards are usually more complex and therefore more expensive than PCMCIA-based GPRS modems. This is due to the need to use an additional battery, which is placed on the device. And this battery, respectively, requires an additional indication of its status, the possibility of supplying external power and a plug for charging. To charge the battery in the Neodrive GPRS-110S, a special USB adapter is used, which is connected to the power connector located on the front side of the device, next to the antenna.

Neodrive GPRS-110S comes with a headset on a special clip - an earpiece and a sensitive microphone.

Devices based on CompactFlash and Security Digital are universal - in order to use them in a laptop, you only need a special adapter for PCMCIA (for Neodrive GPRS-110S, a CF / PCMCIA adapter is included in the delivery package). To use the GPRS-110S model together with a PDA, the delivery package also includes the Pocket PhoneTools program, which is similar to the PhoneTools version for a laptop in its functionality and interface, that is, it turns the PDA into a regular cell phone (more precisely, into a communicator).

Unfortunately, when using such GPRS modems as a telephone, it is impossible to connect a Bluetooth wireless headset, even if the PDA has such an interface. The fact is that GSM-telephony of such modems works only with their own headsets and does not use the capabilities of a computer.

In conclusion, we note that the price of such devices offered on the Russian market varies from $100 to $300.

Modern energy metering systems are increasingly using GSM networks for data transmission, which is supported by GSM operators, who have largely exhausted the possibility of increasing the subscriber base of voice services. GSM networks are characterized by infrastructure developed in all regions, high reliability, rapid deployment and low cost characteristics.

LLC "Analytic-TS", Moscow

All modern GPRS modems are built on the basis of GSM modules from several foreign manufacturers. The simplicity of organizing access from a computer to the Internet on their basis creates a deceptive impression that there are no difficulties when using them in industrial systems (the presence on a computer Windows drivers and periodic freezes that require operator intervention are not evident). The following can be used to control the GSM module:

Functional controller of a meter, heat meter or concentrator;

Specialized (telecommunication) controller;

Software built into the GSM module and taking on all the tasks of managing communication stability.

With all types of control implementation, it is necessary to go through a thorny path to turn the GSM module into a full-fledged GPRS modem that ensures stable operation in a continuous and unattended mode:

Systems running on the table suddenly start to fail and "hang" when switching to real objects, when changing the operator, - installing in a different region or increasing network load;

It turns out that significant efforts are needed to handle emergency situations, ensure stability and security, test solutions, take into account the regional characteristics of operators, support work with dynamic IP addresses, provide access to the state of the modem and network during data transfer, etc.

Of course, there will be organizations that can solve the problems that arise, but is it economically justified for the majority? The implementation difficulties discussed above lead to the appearance on the market of complete solutions with high functionality. Their cost, of course, is a little higher, but this is the price for a kind of PnP (turned on and working).

Let's try to formulate the basic requirements for GPRS modems and, as far as possible, justify them.

Basic requirements for GPRS modems

General requirements

Support for basic GSM network services: GPRS/EDGE, CSD and SMS.

Interfaces for connection to metering devices: RS-232C (including "three-wire" - RxD, TxD and GND), RS-485, Industrial Ethernet.

Design: DIN-rail mounting, built-in primary power supply with extended ranges ~140...286 V / 45...55 Hz or =18...36 V, operating temperature range -40...+70°С.

GSM-antenna: it is necessary to provide the possibility of connecting an external antenna, which can be moved from the equipment installation area (for example, from the basement) to the zone of reliable radio reception.

Automatic connection establishment

After turning on the power, the modems should automatically activate the establishment of a GPRS / EDGE or CSD channel and, in some cases, provide automatic generation of SMS messages when “events” occur on additional logical inputs (for example, when fire alarm sensors are triggered).

Ensuring Reliability

It is necessary to use the following methods of redundant transmission channels:

At the routing level - between GSM operators (two SIM cards);

At the level of GSM services - transition from GPRS/EDGE to CSD or SMS messages.

Under conditions of periodic channel destruction without server and client signaling (for example, when APN servers are rebooted by a GSM operator), system hang control using an independent watchdog timer, built-in transparent Ping connection control and data outage time control play an important role. At the same time, it is necessary to ensure that the user can optimize the ratio “channel control depth / traffic (cost)”.

Rice. Scheme of organization of the GPRS-channel of ASKUE

Security

Authentication at the stages of initialization, connection establishment and data transfer, including:

To prevent the possibility of using SIM cards for other purposes (when setting up the modem, the values ​​​​of their PIN codes must be entered, which are subsequently stored in the modem's memory, checked at startup and unavailable for reading);

Authentication of access to the APN server;

Control exchange of identifiers when establishing a TCP connection (between two modems or a modem and a server);

Caller number control when establishing a CSD channel.

Using a VPN tunnel between the GSM operator and the dispatch center server.

In some cases, additional data encryption is required, the use of which is restricted by law.

Comprehensive solution for the communication channel

Using modems on distributed network metering devices must be supported software(telecommunications server), which is installed on the server in the control room and provides:

Easy connection of functional software, e.g. via TCP/IP;

Security and stability of the transmission channel (ping, identifiers, etc.);

Built-in routing, such as for additional ports or process software.

Data flow optimization

The data buffering built into the modem (8…32 kB) allows to increase the transmission speed by optimizing the interaction between the RS-232C/RS-485 interface and the TCP/IP socket, as well as to use modems in systems with a “three-wire” interface.

Rice. Scheme of organization of the GPRS-channel of the MOSCAD system

Providing support for various modes of operation

Depending on the specifics of the problem being solved, modems must support modes of operation combined into two classes.

Monitoring and management of remote objects from the central site with the possibility of optimization according to various criteria, such as maximum functionality, minimum traffic, the inability to use the Internet on the server side, or the need to use SMS service along with GPRS / EDGE channels.

The second class of tasks to be solved is the organization of communication between two points - the radio interface extension (RS-232C or RS-485). In this case, the modems should automatically provide a transparent data transfer channel between the interfaces when the power is turned on.

Ensuring Compatibility

To organize a reliable GPRS / EDGE connection with metering devices that are critical to breaking the packets they receive, for example, using Modbus or Profibus field buses, it is necessary to eliminate time gaps in data packets on the receiving side. Hoping to be able to parry "broken" packets through re-polling or working with short packets leads to systems that work only on the developer's desk.

Operational Requirements

Automated remote configuration of modems via CSD or GPRS/EDGE channels without visiting the facilities, for example: during installation, the factory configuration is used, during testing it is changed to the system integrator's configuration, during operation - to the customer's configuration;

Modernization of the software built into the modem directly at the facility, ideally via the GSM network;

Local and remote analysis of GSM network parameters, allowing you to adjust the position of the antenna, analyze the surrounding GSM cells, select a telecom operator that provides the best working conditions at the point of installation of the modem, analyze the reasons for the deterioration of communication during operation;

Automatic control of the balance of the SIM-card account and notification in case of its decrease to a predetermined level;

Creation and provision of remote access to log-files of processes of interaction with the GSM network.

Additional features

Of particular interest is the combination of the functions of the modem and the meter (or part of it) in one device to reduce the overall cost. A prerequisite for this is the presence of powerful computing resources in modems. Examples of such devices:

Modems with built-in functional software that provides interaction with metering devices (for example, autonomous reading and accumulation of measurement results);

Multi-interface modems that multiplex data from multiple interfaces on a common radio channel for independent operation of multiple systems.

Service software

Working with GPRS modems should be supported by a set of technological software that provides configuration, testing, remote configuration, monitoring and control of additional interfaces, remote analysis of GSM network parameters, firmware upgrades for the modem, TCP/IP and OPC server functions.

findings

GPRS modems used in energy metering systems have significant differences from modems used to access the Internet. The requirements for them are constantly increasing. To date, the author is not aware of the implementation of all the above requirements in one modem, which, probably, is not required, given the cost criterion. The article would not be complete without the following examples of using AnCom RM/D GPRS modems in energy accounting systems.

Implementation examples

ASKUE (Automated system for commercial accounting of energy consumption). Project implemented by OAO MOEK (Moscow United Energy Company), 2009

The goal of the project is to provide technical and commercial metering of thermal energy at Moscow facilities serviced by MIPC, which is 70% of all residential buildings and industrial facilities in the capital.

Let's consider a system of remote access to heat metering devices implemented in ASKUE. KOMCOR (trademark AKADO-Telecom) is building a corporate multi-service network for MIPC OJSC, which provides access to heat metering devices via AKADO digital channels, where available, and via GPRS channels of the GSM operator MTS. The task of ensuring information security of data transmission is solved using a special MTS service for corporate clients (dedicated APN, local static IP address). System integrators (NPO "Teplovizor" and OOO "Evrokom") use AnCom RM/D modems in the automated control system (more than 800 metering points).

When installing modems, the main problems were related to the choice of the location for installing the GSM antenna in the basement. The following methodology has been developed:

All operations considered below are carried out with the SIM card of the GSM operator selected in the system;

Search for signal zones (at least the minimum level) - using a cell phone, often near windows, air vents or specific places against walls;

Zone monitoring with AnCom RM/D modem and NetMonitor GSM_RM software. The signal strength, number and type of visible GSM cells are measured. It is necessary to provide:

Level over minus 95 (RxLev: -65…-95);

The MNC of visible cells must match the MNC of the SIM card operator (if the cells of the SIM card operator are not available to access emergency services information about available cells of other operators is given);

Visibility is more than 3 cells, one of which is desirable GSM-1800 - it has more free slots (BCCHfreq: GSM-900 from 1 to 124 and GSM-1800 from 512 to 885);

The presence of a high signal level, but 1 ... 2 GSM-900 cells may in some cases not provide a stable GPRS connection due to their high workload (IP address is not provided);

Control of GPRS operation (providing an IP address from the network side) using a modem (the mode of issuing technological information is enabled) and GTem software (the presence of a GSM connection does not always guarantee the operation of GPRS);

Control of work in the system (standard settings).

The general approach to the organization of GPRS communication is defined:

It is wrong to try to use antennas with very long wire (attenuation per 5 m of RG58 wire at 1800 is 4.5 dB);

In most cases, it is more correct to move the modem to the zone of reliable reception, using the RS-485 interface for communication between the modem and the heat meter;

As a result, the use of modems built into the heat meter is often difficult;

Timeouts to ensure communication stability must be selected taking into account the polling period for heat metering devices (including in test mode) and the period of disconnection of unused sockets from the GSM operator;

It is advisable to use an antenna with low cable attenuation and high gain (for example, Ant K996A 900/1800 MHz: gain, dBi - 5/4; cable attenuation 5 m, dB - 1.8 / 2.5).

The telemetry system for gas metering units MOSCAD was implemented by Indasoft LLC, 2007–2009.

Commercial metering system that provides control over gas consumption modes, monitoring of the state of equipment of the metering unit and security alarm. Installation and commissioning of the first and second stages were carried out: 1464 objects in 15 regions of the Russian Federation. Significant experience in the use of GPRS communications in various regions has been obtained.

The implementation features are based on the ideology of an “active control point”: the remote controller independently monitors changes in technological parameters and makes a decision to send data to the upper level in accordance with predefined settings, and does not wait for its turn in a cyclic poll of metering stations.

The use of Motorola's proprietary MDLC protocol ensures data delivery to the control room of a regional gas company, remote configuration and programming of all controllers in the system. Through the Internet gateway of the regional gas company and the communication server, the data enters the top-level controller ACE 3600. The controller “parses” the MDLC packet, extracts the data from the gas metering station, processes them, places them in the internal database and initiates transmission to the data server, which provides providing data to the dispatching systems of a regional gas company.

Protection of information from unauthorized access is provided at the MDLC protocol level due to the isolation of telemetry system modems from other GPRS subscribers mobile operator by separating them into a separate group with their own access point (APN server) and creating a VPN tunnel. Reliability parameters are provided by redundancy of the GSM operator (two SIM cards).

Conclusion

The AnCom RM/D wireless GPRS modem is an important element of any modern distributed energy metering system. Providing reliable communication in the system, GPRS modems allow you to combine hundreds and thousands of remote metering devices into a single information network. The use of AnCom RM/D GPRS modems in automated metering systems allows you to receive accurate, reliable information on energy consumption in real time, eliminate the influence of the human factor, prevent emergencies, monitor the technical condition of devices and premises and, as a result, generally increase economic effect from the use of metering devices.

I.V. Dianov, technical director,

OOO "Analytic-TS", Moscow,