"Physiology" and "anatomy" of digital communications of the GSM standard. Digital cellular systems

Digital communication and the prerequisites for its use.

The modern generation is no longer surprised by the words modem, leased line or “connection”. This is especially true for “fidoshniks” or people in one way or another connected with the Internet. But misunderstandings often arise between telecom operators and subscribers, precisely because of problems with modem communication over a dial-up or leased line. In addition, there are constantly discussions in conferences and “fidosh echoes” about “which numbers work best with which ones, which modems hold the connection better, and which ones are worse.” It is unfortunate, but such disputes and discussions rarely give rise to the truth. In such a situation, everyone really misses technical support local telecom operator.

Most often, all subscriber complaints about poor modem connection speeds are not accepted, and the answer is simple: the isolation is normal, there is no outsider. And the reasons bad connection may lie in such subtleties that voice communication never appear. For different types of Automated Telephone Exchanges (ATS), such reasons may be different.

Mechanical automatic telephone exchanges (Coordinate and Decadal-step).

These are already outdated types of automatic telephone exchanges, but, nevertheless, they are still used in Russia due to the high cost of new ones and the difficult economic situation in the country. And of course one cannot fail to mention that the cable industry Russian operators communications by 40% 60s. It is at these stations that no compression equipment is usually used, and the quality of communication depends only on the mechanical switching equipment. The general structure of interaction between the PBX and subscribers is shown in the figure:

In Tomsk, manual telephone exchanges have numbers starting with the numbers: 21, 22, 23, 25, 77, 78.

On the one hand, the advantage is that the connected subscribers are connected by a physical two-wire line. That is, the operating range of such a line is from 300 Hz to 20 kHz, which theoretically allows, when using broadband modems, to obtain exchange rates of up to 2 Mbit, and in rare cases, more. But such optimistic figures in real connections are impossible due to several factors:

The quality of switching contacts on the telephone exchange is very low.

Very high “station noise”.

Strong crosstalk in cable lines (50-100 pair cable with a small number of turns per meter).

Exposure of cable lines to many natural factors and electromagnetic interference(many people have experienced that the cable coming to your home or office either “freezes” when it rains, or outside conversations are listened to).

Several years ago in Tomsk, this problem was partially solved by the TsSP (Transmission Systems Workshop) by introducing a developed network of PCM paths (Pulse Code Modulation). Diagram No. 2 schematically shows the differences between multi-pair cable trunks and PCM paths:

As can be seen from the figure, a multi-pair copper cable due to the high cost of maintenance and low quality connections are now used more efficiently. But it was replaced by FOCL (Fiber Optic Communication Line), which transmits a digital stream at speeds of up to 300 Mbit/s or more (the transmission speed of a digital stream over a 4-pair copper wire is 2 Mbit/s). That is, now the subscriber connection, after switching on a mechanical PBX, the analog signal leaves the station and enters the DSP equipment. An analog-to-digital converter (ADC) converts this signal into a 64 kbit/s digital stream for transmission and a 64 kbit/s stream into an analog signal for reception. Then 30+2 digital streams (2 control) of 64 kbit/s are combined into one 2 Mbit stream E1 (PCM path). The fiber-optic line includes up to 64 E1 streams. On the other side of the highway the situation is repeated exactly the opposite. 64 E1 digital streams are taken from the fiber-optic line, then each is parsed into 64 kbit streams and fed to a digital-to-analog converter (DAC). The resulting analog signal arrives at the station, and after switching, it is sent to the subscriber.

Let's analyze what advantages and disadvantages the transition to digital multiplexing gives to the telecom operator, and which to the subscriber:

Advantages.

Telecom operator:

FOCLs are not susceptible to moisture penetration and electromagnetic interference, therefore, it is cheaper to lay shafts and maintain them.

The flexibility of this solution allows you to upgrade the volume of interstation connections without additional work.

Saving on cable cost 1m of 100-pair copper cable is currently more expensive than 1m of two-core optical fiber.

Subscriber:

Communication quality is improved by reducing crosstalk between inter-exchange connections.

The distance between subscribers ceases to affect the quality of communication (fiber-optic lines can transmit a signal over tens of kilometers without loss, in addition, due to the transmission of the signal in digital form correction algorithms can be used).

Flaws.

Telecom operator:

Complexity and high cost of digital transmission solutions.

The need to form and train installation and maintenance services for fiber-optic communication lines.

Subscriber:

Problems caused by passing through the ADC/DAC and compression equipment: operating frequency range 300-3300 Hz, “jitter” (phase jitter) and time delays (imperceptible in voice communications).

Crosstalk on distribution cabinet lines, moisture ingress into line shafts (last mile problem).

Since mechanical switching occurs with an analog signal, station noise enters the line, as before, without the use of PCM paths.

The advantages of the telecom operator are obvious, as are the benefits of the subscriber. But the disadvantages raise doubts whether the introduction of PCM paths improves the quality of service. Reducing the operating frequency range makes it impossible to use broadband modems, and “jitter” should negatively affect the connection speed. (ADC algorithm!!) At the same time, crosstalk will not disappear completely, since the line from the station to the distribution cabinet is carried out with a copper cable. And finally, the “station noise”, which has not decreased or increased, suggests that the transition to digital PCM paths in inter-exchange trunks at mechanical stations does not provide advantages for the subscriber’s modem communication.

Dedicated lines (straight lines).

Often for unification local networks two remote offices use a permanent modem connection. But for maximum efficiency of such a solution, a non-ordinary switched line is used, which has a number of the above disadvantages, but a straight (dedicated) line. By definition, a direct line is a non-switched physical line dedicated only to the needs of the subscriber (see figure).

As can be seen from the figure, providing subscribers with a direct line requires the allocation of a free pair in all trunk lines along the path of its installation. The pair does not enter the station, but connects with the pair from the next line at cross-country. And an important property of a straight line is that it does not enter into any PCM path or other multiplexing equipment, and, therefore, the operating frequency range is not limited to 3.3 kHz and there are no losses due to time delays and phase jitter. And the last important factor is the total length of the straight line (the longer the length, the worse parameters lines), and already having this parameter, you can start choosing a modem model. In such cases, either short-range modems (last mile modems) or broadband xDSL modems with a throughput of 2 Mbit/s or more are recommended.

Short-range modems or “last mile” modems are devices used for communication between computers, terminals, controllers and other data transmission equipment over relatively short distances. For example: inside buildings, on campus, or within city limits. These devices are designed to overcome limitations in the range of data link interfaces.

But in lately Due to the displacement of inter-exchange copper lines by PCM paths, the ability to lay a direct line to a subscriber in different areas of the city (different automatic telephone exchanges) is becoming a problem. Sometimes this is solved by running lines between distribution cabinets, and sometimes there are no options other than entering into the PCM path. This prompts telecom operators to implement modern technologies digital networks.

Electronic telephone exchanges.

In the subscriber's mind, electronic or digital PBXs are something ultra-modern and inaccessible. Although in Tomsk more than 100,000 subscribers are already served by electronic telephone exchanges. Key Difference electronic stations from mechanical in the method and environment of switching subscribers.

Mechanical telephone exchanges switch analog lines with contact pads controlled by an electromagnetic drive, while electronic ones switch with space-time manipulations of digital streams.

As can be seen from the figure, the analog signal from the subscriber arrives at the subscriber set, where it is combined with the input stream and, after echo cancellation, converted using an ADC into a digital stream of 64 kbit/s. The input stream is similarly transformed and supplied to the subscriber (see figure).

It is important to note that during switching there is no longer a mechanical connection and disconnection, but manipulation of the digital stream in the intra-channel space and distribution of this stream into dedicated transmission intervals. Due to this, electronic telephone exchanges have ideal “contact” quality and, thanks to the use of digital technologies, “station noise” does not pass through the line. However, there is also reverse side medals: “quantization noise.”

Noise is caused by the quantization of analog signals, which is necessary to convert the analog signal to digital before sending it over the telephone network. The incoming analog signal changes 8000 times per second, and each time its amplitude is recorded as Pulse Code Modulation (PCM). The sampling system uses 256 discrete 8-bit PCM codes. Since the analog signal is continuous and the digital code is discrete, the digital stream transmitted over the telephone network is recreated at the other end in approximately their corresponding analog source signal. There is a difference between the original signal and the recreated one quantization noise, which limits the speed of modems. Quantization noise limits the speed to approximately 35 kbit/s (according to Shanon's theorem). But noise only appears during analog-to-digital conversion, not during digital-to-analog conversion.

Material from Wikipedia - the free encyclopedia

Digital communication- field of technology related to transmission digital data to a distance.

Currently, digital communications are also widely used to transmit analog(continuous in level and time, for example speech, image) signals, which for this purpose are being digitized(discretized). Such a transformation is always associated with losses, i.e. the analog signal is represented digitally with some inaccuracy.

Modern digital communication systems use cable (including fiber optic), satellite, radio relay and other communication lines and channels, including analogue.

Point-to-point communication line

Equipment that generates data from user information, as well as presenting data in a form understandable to the user, is called terminal equipment (DTE, data terminal equipment). Equipment that converts data into a form suitable for transmission over a communication line and carries out the reverse conversion is called communication line terminal equipment (DTC, data channel equipment). The terminal equipment can be a computer; the terminal equipment is usually a modem.

Signal transmission is carried out symbols. Each symbol represents a specific signal state on the line; the set of such states is finite. Thus, a symbol conveys some amount of information, usually one or more bits.

The number of transmitted symbols per unit time is called the keying rate or symbol rate (baud rate). It is measured in baud (1 baud = 1 character per second). The amount of information transmitted per unit of time is called the information transfer rate and is measured in bits per second. There is a common misconception that bits per second and baud are the same thing, but this is only true if each character only carries one bit, which is not very often the case.

Converting data into a form suitable for transmission over a communication line/channel is called modulation.

Digital communication technologies

The following technologies find application in digital communications:

Encoding the source of information

Source coding is concerned with the task of creating an effective description of the source information. An efficient description allows for a reduction in the memory or bandwidth requirements associated with storing or transmitting discrete implementations of the original data. For discrete sources, the ability to create data descriptions at a reduced bit rate depends on the information content and statistical correlation of the source symbols. For analog sources, the ability to create data descriptions at a reduced bit rate (according to the accepted accuracy criterion) depends on the amplitude distribution and temporal correlation of the source signal. The purpose of source encoding is to obtain a description of the source information with good accuracy at a given nominal bit rate, or to tolerate a low bit rate to obtain a description of the source with a given accuracy.

Data compression

Data encryption

Noise-resistant coding

Any communication system is subject to noise and features of lines and communication channels (and, as a result, distortion), which can lead to incorrect signal reception. To combat the errors that arise, a specially designed redundancy is introduced into the signal, which allows the receiving side to detect and, in some cases, correct a certain number of errors. There are a large number of noise-resistant (IE) codes that differ in redundancy, detection and correction capabilities.

Main classes of noise-resistant codes:

• Block codes, transforming fixed blocks of information of length k symbols (these symbols may differ from those used during modulation) into blocks of length n characters. In this case, each block is decoded separately and independently of the others. Examples of block codes: Hamming codes, BCH codes, Reed-Solomon codes.

• Convolutional codes work with a continuous stream of data, encoding it using shift registers with linear feedback. Decoding of convolutional codes is carried out, as a rule, using the Viterbi algorithm.

Modulation

Modulation(lat. modulatio - regularity, rhythm) - the process of changing one or more parameters of a high-frequency carrier oscillation according to the law of a low-frequency information signal (message).

The transmitted information is contained in the control (modulating) signal, and the role of the information carrier is performed by a high-frequency oscillation, called the carrier (modulated). Modulation, therefore, is the process of “landing” an information oscillation on a known carrier in order to obtain a new, modulated signal.

As a result of modulation, the spectrum of the low-frequency control signal is transferred to the high-frequency region. This allows, when organizing broadcasting, to configure the functioning of all receiving and transmitting devices at different frequencies so that they do not “interfere” with each other.

Oscillations of various shapes (rectangular, triangular, etc.) can be used as a carrier, but harmonic oscillations are most often used. Depending on which of the parameters of the carrier oscillation changes, the type of modulation is distinguished (amplitude, frequency, phase, etc.). Modulation with a discrete signal is called digital modulation or keying.

See also

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Literature

• Sklar, Bernard. Digital communication. Theoretical foundations and practical application= Digital Communications: Fundamentals and Applications. - 2nd ed. - M.: "Williams", 2007. - P. 1104. - ISBN 0-13-084788-7.
• Prokis, J. Digital communications = Digital Communications / Klovsky D. D. - M.: Radio and Communications, 2000. - 800 p. - ISBN 5-256-01434-X.
• Feer K. Wireless digital communication. Modulation and Spread Spectrum Methods = Wireless Digital Communications: Modulation and Spread Spectrum Applications. - M.: Radio and communication, 2000. - 552 p. - ISBN 5-256-01444-7.
• Vasilenko G.O., Milyutin E.R. Calculation of quality and readiness indicators digital lines communications. - St. Petersburg: Publishing House "Link", 2007. - 192 p.

Excerpt characterizing Digital Communication

We are lucky, we live in a time of great discoveries and rapidly developing innovations. Increasingly, when purchasing equipment, we give preference to models that use digital technologies: photo and video cameras, mobile phones, laptops, tablets, MP3 players and much more.

However, choosing a device is always difficult. When we go into a store, it can be very difficult to decide, which is why it is so convenient to make purchases through an online store, where each item is supplied detailed description, the main characteristics are listed, photographs and reviews are posted.
Sitting at home in the comfort of your favorite chair, you study information, compare and choose the product that best meets your requirements. Digital technology is very complex, so if you have any questions, you can always turn to the help of our experienced managers who will advise on any issues that arise and tell you about the advantages of this or that option.

Mobile (cellular) phones

For example, a large number various models from leading manufacturers are presented in the category mobile (cellular) phones. Having appeared on the market relatively recently, they have firmly entered our lives. Now it’s hard to imagine that we once lived without them.
In our catalog you will find new products and phones that have gained popularity among consumers in past years. This and expensive phones and cheaper, bright, stylish ones. But there is one thing that unites them: they have excellent user reviews. The models we offer from global manufacturers (Samsung, Nokia, Elgie, Sony) have all the necessary certificates guaranteeing quality, reliability and safety.

New cell phones

Rice. 1.2. Block diagram digital communication system.

Fig.1.3. - The process of converting a discrete message into a signal and converting the signal back into a message

Let us give a description of each block of the block diagram of a digital system for transmitting continuous messages.

1. Source of information(messages) generates a signal intended for further transmission in the communication channel. This signal must contain a random component, otherwise it will not carry any information.

The source of information can provide data for transmission over a communication channel both in digital form (modern digital media, various sensors With digital interface etc.) and in analog form (analog sensors, sound and image transmission, etc.). Regardless of the type of information source, data should be presented in the most compressed digital form possible. The process of efficiently converting data into a sequence of binary characters is called source encoding or data compression. As a rule, data on digital media is already compressed (for example, MP3 lossy digital audio coding format, MPEG video compression algorithms, JPEG images), while data from analog information sources is often too redundant and requires compression.

2. Analog-to-digital converter. Included digital channel devices are provided for converting a continuous message into digital form – analog-to-digital converter on the transmitting side and a device for converting a digital signal into a continuous one - a DAC on the receiving side. The ADC, using pulse-code modulation, converts the signal from analogue form to digital form, presented as a sequence of m-ary code combinations. On the receiving side, the DAC restores the original message using the received code combinations.

Fig.1.4. ADC block diagram

The essence of converting analog quantities is to represent a certain continuous function (for example, voltage) of time into a sequence of numbers related to certain fixed moments in time. Let, for example, there be some signal (continuous) and to convert it into a digital signal it is necessary to represent this signal as a sequence of certain numbers, each of which refers to a certain point in time. To convert an analog (continuous) signal into a digital one, 3 operations must be performed: sampling, quantization and encoding.

The concept of analog-to-digital conversion is closely related to the concept of measurement. Under measurement The process of comparing a measured value with a certain standard is understood; during analog-to-digital conversion, the input value is compared with a certain reference value (usually a reference voltage). Thus, analog-to-digital conversion can be considered as a measurement of the value of the input signal, and all the concepts of metrology, such as measurement errors, apply to it.

3. Modulator(lat. modulator- rhythm-keeping) - a device that changes the parameters of the carrier signal in accordance with changes in the transmitted (information) signal. This process is called modulation, and the transmitted signal modulating.

Based on the type of controlled parameters, modulators are divided into: amplitude, frequency, phase, quadrature, single-lane etc. If the carriers are pulse signals, then they are modulated using pulse-amplitude, pulse-frequency, pulse-time and pulse-width modulators. The quality of operation of modulators is determined by the linearity of its modulation characteristics.

The modulator is one of the components of transmitting devices for radio communications, radio and television broadcasting. Here, the carriers are high-frequency harmonic oscillations, and the modulating oscillations are audio frequency and video signals. Modulators are also used in radar, pulse-code communication systems, telecontrol and telemetry. Modulators converting constant voltages into variables, used in amplifiers DC, operating on the principle of modulation-demodulation, to eliminate zero drift and increase the sensitivity of analog computing devices. A device operating on the modulator-demodulator principle is called modem.

Fig.1.5. Analog signal modulation

4. Communication channel(English) channel, data line) - system technical means or signal propagation medium for transmitting data from source to destination. In the case of using a wired communication line, the signal propagation medium can be optical fiber or twisted pair.

The communication channel is integral part data channel. Communication line is the medium used to transmit signals from a transmitter to a receiver. In electrical communication systems, this is a cable or waveguide; in radio communication systems, it is a region of space in which electromagnetic waves propagate from the transmitter to the receiver.

Communication channel is a set of means that ensure the transmission of a signal from a certain point A of the system to point B. Points A and B can be chosen arbitrarily, as long as the signal passes between them. If the signals arriving at the input of a channel and removed from its output are discrete (according to states), then the channel is called discrete. If the input and output signals of a channel are continuous, then the channel is called continuous. There are also discrete-continuous And continuous-discrete channels whose input receives discrete signals, and continuous ones are removed from the output, or vice versa. It can be seen that the channel can be discrete or continuous, regardless of the nature of the messages being transmitted. Moreover, in the same communication system, both discrete and continuous channels can be distinguished. It all depends on how the channel entry and exit points A and B are selected.

A continuous communication channel can be characterized in the same way as a signal, by three parameters: time T k during which transmission is carried out over the channel, dynamic range D k and channel bandwidth F k . Also in the communication channel the signal is subject to interference caused by different characteristics distribution environment.

The most important indicators communication system operation are:

Transfer speed;

Bandwidth;

Noise immunity.

In addition, in all communication systems the following condition must be met: bandwidth > transmission speed.

Noise immunity refers to the ability of a system to withstand harmful influence interference with message transmission. The maximum amount of information that can be conveyed by a binary symbol is called bit. There are many other parameters that characterize the quality of a communication system from various points of view. These include communication secrecy, system reliability, overall dimensions And weight of equipment, equipment cost, operating costs etc.

5. Demodulator, detector(fr. demodulateur) - an electronic unit of devices that separates the useful (modulating) signal from the carrier component.

The transmitted message is usually restored at the receiver in this sequence. First, the received signal is demodulated. In systems for transmitting continuous messages, as a result of demodulation, the primary signal representing the transmitted message is restored. This signal is then sent to the playback or recording device.

In discrete message transmission systems, as a result of demodulation, a sequence of signal elements is converted into a sequence of code symbols, after which this sequence is converted into a sequence of message elements issued to the recipient. This transformation is called decoding.

The operations of demodulation and decoding are not just the inverse operations of modulation and encoding. As a result various distortions and interference, the received signal may differ significantly from the transmitted one. Therefore, you can always make several assumptions about what kind of message was being transmitted. The task of the receiving device is to decide which of the possible messages was actually transmitted by the source. That part of the receiving device that analyzes the incoming signal and makes a decision about the transmitted message is called decisive scheme.

6. Digital-to-analog converter (DAC) - a device for converting a digital (usually binary) code into an analog signal (current, voltage or charge). Digital-to-analog converters are the interface between discrete digital world And analog signals

Common types of electronic DACs:

- pulse width modulator- the simplest type of DAC. A stable source of current or voltage is periodically turned on for a time proportional to the digital code being converted, then the resulting pulse sequence is filtered by an analog low-pass filter. This method is often used to control the speed of electric motors, and is also becoming popular in Hi-Fi audio;

- Oversampling DAC, such as DACs based on variable pulse density. Oversampling allows you to use a DAC with a lower bit depth to achieve a higher bit depth of the final conversion. Often, a delta-sigma DAC is built on the basis of a simple one-bit DAC, which is practically linear. A low-bit DAC receives a pulse signal with pulse density modulated(with a constant pulse duration, but with a variable duty cycle), created using negative feedback. Negative feedback acts as a high-pass filter for quantization noise.

- Weighing type DAC, in which each bit of the converted binary code corresponds to a resistor or current source connected to a common summation point. The source current (conductivity of the resistor) is proportional to the weight of the bit to which it corresponds. Thus, all non-zero bits of the code are added to the weight. The weighing method is one of the fastest, but it is characterized by low accuracy due to the need for a set of many different precision sources or resistors and variable impedance. For this reason, weighing DACs have a maximum width of eight bits;

- Ladder DAC(chain R-2R circuit). In the R-2R-DAC, values ​​are created in a special circuit consisting of resistors with resistances R And 2R, called a constant impedance matrix. This matrix has two types of inclusion: direct - current matrix and inverse - voltage matrix. The use of identical resistors can significantly improve accuracy compared to a conventional weighing DAC, since it is relatively simple to produce a set of precision elements with the same parameters. DACs of the R-2R type allow you to push back the limitations on bit depth. With laser trimming of resistors on one substrate, an accuracy of 20-22 bits is achieved. Most of the conversion time is spent in operational amplifier, so it should have maximum performance. DAC speed of units of microseconds and below (that is, nanoseconds)

DACs are located at the beginning of the analog path of any system, so the parameters of the DAC largely determine the parameters of the entire system as a whole.

7. Recipient of information(signal output) – it can be a speaker, a TV screen, or any device that reproduces the received signal.

Since a person, as a recipient of information, is a key element of any telecommunication system, the signal quality is assessed by his subjective perception of speech. The main indicators of the quality of received speech include: legibility (understandability), volume And naturalness.

Speech intelligibility- the defining characteristic of the speech transmission path, since if the path does not provide complete speech intelligibility, then none of its other advantages matter - it is not suitable for use. To directly determine this qualitative characteristics there is only one method - subjective statistical tests (SST), which requires large quantity speech material processed by codecs and transmission path, and the involvement of a group of experts (trained listeners and speakers). Developed indirect, objective quantitative method determining the understandability of speech through its legibility.

WHY DIGITAL?

Digital two-way radio technology is designed to solve the problem of radio frequency spectrum congestion and ensure efficient use of it. There are millions of analogue radios in use around the world, andThe huge number of users in the radio frequency ranges significantly degrades the quality and reliability of communication. Some countries have already passed legislation obliging manufacturers to produce and sell only digital radio communication equipment. As a result, most radio equipment manufacturers are investing in the development of new digital radio technologies to meet the ever-increasing demand for more efficient two-way radio equipment. Digital is changing the way users view communication and use of radio stations.

Disadvantages of analogue radio communications

Analogue radio communication systems are still widely usedapplication, and their users are well aware of their disadvantages:

^^ Sound quality

Background noise and atmospheric disturbances.

^^ Unstable operation

Random failures when transmitting or receiving calls.

^^ Radio range

Efficiency decreases with increasing distance.

^^ Insufficient security of radio communications

Lack of control over listening to conversations.

^^ Channel congestion

Risk of losing an important call due to the work of strangers

radio stations and interference.

^^ Call management

Inability to establish a direct call to a specific

DIGITAL TECHNOLOGY IS CHANGING IMAGINATION LINE ABOUT RADIO COMMUNICATION

With the development of new digital technologies, which include the traditional functionality of analog devices with a number of additional functions, users get a wide range of radio communication options. Sustainably high quality calls Audio - digital technologies provide more effective noise and interference suppression, maintaining sound quality at greater distance, and users hear what is said to them clearly and distinctly. Using the AMBE+2™ vocoder can significantly improve the quality of transmitted audio in noise-rich environments to achieve RF spectrum efficiency. Coverage - Digital technology helps users make more calls to more places. The digital signal remains strong and clear throughout the entire radio transmission range. The increased stability of the digital radio signal provides a greater communication range that was previously unavailable.

IMPROVED CALL MANAGEMENT

Control- the usual desire of users of analog radio stations is to control those who receive

messages, and avoid broadcasting messages to a wide range of listeners. Digital technology makes this possible through a unique identifier that is assigned to each digital radio station. The user can selectively call an individual radio station or group, sending calls only to those subscribers who need to convey specific information.

Call Control Features

^^ Individual call- a user can directly call another specific user, and no one else in the channel will hear them.

^^ Group call- the user can call a specific user group. In this case, all group members can hear each other, but other users who are not members of this group cannot hear them, despite the fact that they will use the same channel.

^^ General call- the user makes a call to all radio stations in the channel.

^ ^ Late entry- during the active phase of an individual or group call, other users can join the conversation at a later stage.

Text messages— digital technologies make it possible to send and receive text messages, both programmed and arbitrary. So

This way, the user can stay connected when voice communication is not possible, and also when you need to save messages for later use.

Information protection— in digital mode, no additional equipment is required to protect communication channels. When the encryption function is turned on, messages are heard only by those subscribers to whom they are addressed, and there is no significant reduction in sound quality inherent in scrambling in analog mode.

GO TO DIGITAL RIGHT NOT ALL DIGITAL TECHNOLOGIES ARE THE SAME

Unlike analog radio communication systems, which, regardless of brand, can interact perfectly with each other, digital systems use one of two protocols: TDMA or FDMA. It is important to note that these two protocols are incompatible, i.e. In a digital system, an FDMA radio will not communicate with a TDMA radio. Worldwide, more than 74% of digital radios use the TDMA protocol to increase efficiency and power.

A NEW STAGE OF THE GREAT JOURNEY

What suited you before does not mean that it will suit you in the future - you canafford better communication. Overcoming the shortcomings of analog devicesprevious generations and the desire for better quality sound, reliable protection and longer communication range - these are inexpensive two-way radio Vertex eVerge. Compatible with other analog devices, these high-tech solutionsprovide more opportunities to better solve radio communication problems.

^^ output power 45W VHF/

^^ 16 channels