Multiservice network technology - MMDS. MMDS - another wireless access technology

If several years ago, the Internet was viewed as one of the means of communication or even as entertainment, now it is one of the most powerful communication mechanisms, work and information. Not surprisingly, the growth of the World Wide Web is simply catastrophically great. Therefore, the question of creating high-speed and reliable communication channels is becoming very relevant. The most natural and distributed until today is a wired connection: twisted para, fiber optic or telephone line. The use of radio resources was quite rarely phenomenon and was mainly used for satellite communications when transmitting a signal over the ocean. At the same time, creating effective network access channels based on a wired compound is quite difficult. The cable laying is expensive and time consuming, even if not to use fiber. All major companies and network operators can afford the gasket of such trunk lines. The use of general public telephone networks gives low bandwidth. In this situation, the use of a radio signal for transmitting information is very real. This is especially true on the "last mile" when you need to bring the signal to a specific subscriber. It is about this that will be discussed in this article.

Initially, briefly consider the physical side of the case. We are talking about the possibility of transferring and receiving a radio signal in a rather wide frequency range. Let us first remember that radio waves, visible light, radioactive radiation and those waves that we now speak - all this is electromagnetic radiation, only frequencies are lying in different ranges. The range that we speak, changes from Meghertz to several dozen Gigahertz. So what happens from the point of view of physics? The transmitter emits some special set of radio waves, and a receiver at some distance from the transmitter takes it. If even everything happened in vacuo and without obstacles, there would have a wave attenuation place, and inversely proportional to the square square. However, since radio waves propagate in the air, there is attenuation associated with air resistance. Moreover, as is well known on the example of visible light, which is refracted in a prism or in water drops, it is possible to refract radiation. Plus, the cities and towns are reflected from items, such as houses. The last two phenomena change the direction of radiation, but what is nice - none of the above effects changes frequencies. That is, to some extent, the frequency is the value that should be used to encode information in radar. However, there are two more phenomena that complicate this process. This is the diffraction and interference of radio waves. The first is just an overtance of the wave of obstacles. The second is the overlay of radio waves. The last most unpleasant. It is clear that there may be a situation where the waves when applying can even completely extinguish each other. It can be seen that the main technical problem of the transmission of the radio signal is the possibility of forming such a wave, which, even undergoing all the changes described, would reach the receiver, while maintaining initial information. And the problem is not only that information reached. The fact is that several waves fall on the receiver. They all carry the same information, but will go different ways.

In order to solve these technical problems, special ways of modulating a signal are being developed, that is, the encoding of information in it. If the voltage modulation is used when transmitting via the cable, i.e., change the amplitude of the signal, then when radio communications use frequency or phase modulation. Also often use mixed modulation. All this is done to ensure that when you get a reliable way to help distinguish the main signal from repeated, reflected, and the like. Also, with the original modulation of the signal, you get rid of the interference that can be if there is a transmitter with very close or multiple frequencies (differing from the integer for an integer time). The most advanced methods of modulation of the signal also use the effects of radiation polarization, that is, the ability to set the plane in which the oscillations of the electromagnetic field occur. In the ideal case, even with certain interference when the signal is propagated and, provided that the transmitter and the receiver are not in the zone of the direct visibility of each other, signaling is possible. One of these modulation technologies that allow you to install the receiver and the transmitter is not in direct mutual visibility, is the modulation of Vector Orthodal Frequency Division Multiplexing (VOFDM), used in Cisco radio devices. It allows you to transmit a signal in an indirect visibility at a distance of several kilometers. Let's just say a few words about distances. In terms of direct visibility and without interference, standard radio devices transmit a signal for several tens of kilometers. However, when we are talking about settlements, it is necessary to test directly on the place to determine possible problems. Also, other transmitters are in close proximity to the device can also influence the signal transmission. Atmospheric phenomena, such as precipitation, thunderstorms, simply increased humidity, also negatively affect the transmission of the signal. Therefore, to give any accurate data on the possibilities of radio devices simply incorrect. It is worth making one important remark. With an increase in the frequency of the signal, the effects of external factors increases, leading to problems with the transmission of such a signal. As one of the consequences, the distance on which it is possible to confident signal acceptance. On the other hand, with increasing frequency, there is a larger scope for coding, as the frequency band is increasing available for data transmission. This allows you to increase the bandwidth of the channel by simultaneously transmitting signals at several frequencies.

Signal modulation

Above, a verbal description of the signal propagation process and overcoming difficulties associated with interference and obstacles was given. Let's try to give a more technical description of the process. Real signal propagation can be illustrated by the following pattern.

From here it is clearly seen that several signals reaches the subscriber, and in this case - not a single direct thing that is quite real. It is also necessary to understand that when reflected from items, part of the energy is absorbed, which weakens the signal. In addition, the length of the signal path may be different, so in different ways the signals come at different times. As a result, the subscriber antenna may receive signals similar to those shown in the following figure.

In case of direct visibility, the solution to the problem of recognition of the correct signal is obvious, since the direct signal is always stronger than reflected, that is, its amplitude is greater. A truly problem occurs when there is no direct visibility.

Many modern radio transmission products work with QUADATURE AMPLITUDE MODULATION (QAM) technology. The easiest option is based on the Phase SHIFT KEYING system (PSK). There are two varieties of this system: binary and quadratic (BPSK and QPSK). In the first case, one bit per cycle is transmitted in the first case by using the phase shift, in the second case - two, using phase shift to 1/2F, F and 3 / 2F. If you combine the phase shift and modulation of amplitude, then the so-called technology16-QAM will be able to transmit 4 bits per cycle. This extension can be further further, but the effect of interference increases.

In order to make a radio signal transmission more reliable, the following technologies are used: QAM together with Decision Feedback Equalization (DFE), Direct Sequence Spread Spectrum (DSSS), Frequency Division Multiplexing (FDM) and Orthodal Frequency Division Multiplexing (OFDM)

DFE technology is designed to eliminate interference that is caused by the interference of adjacent characters. This is due to a possible large delay (up to 4 μs), when the signal of the previous symbol is superimposed on the received in this moment.

Technology is based on the QPSK method. But in addition to this, the transmitted signal is placed in a wider strip, and the latter width is determined based on the SNR value for this line (Sn is the ratio of the signal level to the noise level). More precisely, the width can be represented by formula 10 ^ (SNR / 10) * (initial width). It can be seen that this method is simply exponentially unstable to interference.

In the FDM technology, the transmission band is divided into several narrower bands, which allows you to use each of the carriers for data transmission. To protect the transmitted signal, a protective tone (Guard Tone) is given throughout the bandwidth, which reduces the bandwidth of the channel, but necessary to protect against interference.

In the OFDM technology, the signal is also divided into several carriers, which are considered independent. Therefore, there is no need to use a protective tone, which increases the bandwidth of the channel. To avoid the problems of interference caused by signal delays, the data is transmitted to portion (wave packets), and each such portion begins and ends the special signal.

VOFDM modification (Vector OFDM) uses the fact that, depending on the position of the antennas, various breaks of the transmission band on independent carriers are possible. That is, it is possible that one antenna confidently accepts one set of frequencies, and the other is different. This allows you to use several antennas in the neighborhood to transmit a signal at close frequencies.

So briefly looks in the modulation technologies that are currently used. Note that VOFDM technology is one of the most modern and efficient, especially in indirect visibility.

Now let's talk a little about the frequencies on which data is being transferred. It is intuitive that theoretically frequency can change from zero to infinity. The limit for radio waves is a few hundred Gigahertz. However, as we know well, the frequencies of several hundred megahertz are already used by conventional radio stations, the frequency 900 and 1800 MHz are occupied by cellular communications. In addition to this, there are television frequencies, a special communication frequency (for example, government), frequencies on which signals from satellites are transmitted, frequencies occupied by the military, etc. It is clear that the use of the specified inverse frequency cannot be used, and moreover, in our the country using the transmitter of any power and at any frequency it is necessary to license (the exception is the ranges for amateur radio stations In the region of 27 MHz and the range of 1890-1900 MHz for radio telephones operating according to the DECT standard). As for the frequencies themselves, there is some table under the management of the GCRC (State Committee on Radio Frequids), which contains information about the frequencies used: "The frequency band distribution table between radio services Russian Federation In the frequency range from 3 kHz to 440 GHz. " It still has empty stripes and sections reserved for future use. True, it does not contain specifically dedicated areas for the Internet radio channels, but this is probably only about the fact that it is impossible to take into account at once. To use some frequency you need to get the permission of the GCRC. Then it is necessary to obtain the permission of the Glavgoszvyaznadzor to install the equipment, which is associated with obtaining permission from civil and military broadcasting services. After that, the installation of equipment is possible. True, recently there is a decision of the GCRH on the use of transmitters in the range of 2400-2483.5 MHz on a secondary basis without the permission of the GCRC for each user. The secondary framework implies the possibility of interference related to the operation of other transmitters in this range. That is, it is clear that you get permission to use a radio device - the matter is not easy. True, there is an advantage that must be taken into account. Having permission to use the channel, you are guaranteed from interference when working.

In this article, we did not plan to discuss in detail the problem of frequency allocation in our country, so we will restrict ourselves to the above remark and note that it is not only difficult, but also for a long time and expensive. The most important question that comes to the buyer of radio equipment is the possibility of obtaining the right to use the frequency on which this device can work. And this is a problem not only sellers, but also buyers. There may be a situation where permission for sale will be obtained, but permission to install, for example, in this particular locality, is not. Let's see which specific ranges can be interested in. I mean not what can resolve, but what is used in other countries, since it is possible that you want to get the equipment of a foreign company. Here are three Gigaretse bands recommended in the USA:

MMDS \u003d 2,500-2,690 GHz (Multichannel Multipoint Distribution Systems);

Unii \u003d 5,725-5,825 GHz (Unlicensed National Information Infrastructure);

LMDS \u003d 27,500-28,350 GHz, 29,100-29,250 GHz, 31,000-31,300 GHz (Local MultiPoint Distribution Services).

In essence, in terms of physics in all bands, everything is the same in principle. The difference lies in bandwidth and resistance to external influences. As mentioned above, the first increases with increasing frequency, and the second decreases. Let us explain more specifically what we have.

• MMDS. Due to the use of low frequency, there is no need for direct visibility. Distances on which a confident receipt of the signal is possible is estimated at 30 km. The bandwidth reaches 10 Mbps.
• LMDS. Works on much higher frequencies. It makes it makes it possible to use radio devices mainly in direct visibility of each other. And distances confident reception become an order of magnitude lower, but increases bandwidthwhich can reach up to 45 Mbps.
• The average range of UNII We will not discuss, let's just say that, as follows from the name, it is not licensed, but this applies only to the United States.

An example of a device operating in the MMDS range is the development of Cisco WT2772-PAA Broadband Fixed Wireless Transverter. This is a "point-point" type solution (Point-to-Point). The maximum bandwidth can reach 44 Mbps, and the distance is 30 km. In fact, this system It is the creation of a dedicated radio signal-based channel. Much more interesting for telecom operators will develop a "point-lot point" (Point-to-MultiPoint), but as regards Cisco, at the moment such devices have not yet been released and their appearance is expected in the near future.

In general, if we talk about "point-lots" systems, then the LMDS range is preferable, since it is possible to create a large number of channels and an increase in bandwidth. Now there are already developments that operate in this range. Then we will talk about one of them: Evolium Lmds company Alcatel.

The technical characteristics of this system are as follows:

• working distance in direct visibility - up to 5 km;
• one concentrator is able to maintain bilateral communication with 4 thousand subscribers;
• throughput reaches 8 Mbps;
• it is possible to transfer not only data, but also the voices;
• operating range: from 3.5 to 38.0 GHz, although only 24.5-29.0 GHz is now used;
• the system allows you to create wireless subscriber access; Switching voice, data and mixed traffic (voice / data); Virtual dedicated lines (T1 / E1 or N × 64 Kbps); IP / Ethernet / ATM / FRAME RELAY; bandwidth on demand;
• there is a small reconfiguration and an increase in the network;
• high quality and communication speed comparable to fiber optic systems.

The system consists of several components. Basic station consisting of base radio station (RBS) and Digital Base Station (DBS). It is the concentrator that supports up to 4,000 communication channels. Subscriber terminal consisting of a solid antenna with a diameter of 26 cm, installed outside the room, and an interface unit. Control Center providing administration functions, observation and system maintenance.

It should be mentioned about the problems arising from the use of radio devices for the Internet. The first has already been said - this is licensing the use of such funds. The second problem is interference. Even if you have received permission to use some frequency, it does not mean that you can easily use acquired radio devices. What was told above about the warranty from the interference means only that there are no more transmitters in this area that use the band allocated to you. However, especially when using devices running in the LMDS range, you need to take care of at least about direct visibility. Second factor can be precipitation and fog. This situation is possible when the signal will not reach the receiver at all as a result of multiple refraction in the water microcapors. Of course, this problem is not ubiquitous, since at least there is no permanent fog in Moscow, but still the question remains. Another problem is protection. Of course, as in the wired network, there are algorithms for encrypting information that protect data from reading or changed, but still a purely intuitive radio signal looks more open. It is open in the literal sense of the word, and the interception of it with another receiver cannot be excluded. To change the signal, of course, is difficult, since this requires a transmitter at the same frequency, which will be quickly detected by the same services of the State Unitary Enterprise, which provide permits for the use of equipment. But despite the existence of these problems, radio communications for the Internet develops and attracts more and more attention.

In conclusion, I want to say that the latest technologySuch as LMDS are very attractive for telecom operators, providing a technical ability to quickly connect subscribers to the network and easy to change the structure of networks. I would like to hope that in the future one of the problems - the problem of licensing such means - will find a solution, for example, a similar permission to use a range of 2400.0-2483.5 MHz.

ComputerPress 12 "2000

Strengthening your alleged antenna You can quickly consider using mine, can be somewhat outdated by design, program for radio accounts .
Successes to you, and a long-range telepremium! E.Shustikov (UO5OHX EX RO5OWG)

Answers to visitors' questions about antenna applicability for Wi-Fi range

Critical loop sizes? (It is difficult to make a small regular square loop 7 * 7mm from the cable (from oscillating) with an outer diameter of 3.5 mm and on braid 2.5mm.) Easier 7 * 27 in the size of the quarter-wave line

Yes, the dimensions are critical. In the length of the cable proposed by you, taking into account the coefficient of its shortening, more than 1 wavelength are laid, i.e. In the loop there will be sections with the inverse movement of the current and according to the supply of the signal. According to my reasons, the loop should not exceed the half-length wave in the cable or be shorter. I used a semi-rigid cable 50 ohms, climbing a silver cable braid with fluoroplastic insulation, a diameter of 3 mm, which coincides with the diameter with a capileum tube from which the irradiator was made.
And further. Usually, cables with a wave resistance of 150 ohms are used in oscillographic ends, as having the smallest rapid container. The use of such a cable to connect with the converter will lead to the appearance of standing waves in it due to the mismatch of the resistance. The input resistance of the converters is usually 50 ohms.
It is necessary to strive for strict rectangles of the loop, it can be sufficiently rounded (but the short, as I wrote above) can be tightly attracted to the quarter-wave line in its lower part, where the current density is maximal and the electrical component is small. In this case, the symmetrization of the emitter is automatically obtained.

-The design of the irradiator. I think to bend from a wire 1.5-2 mm - should be fine

The irradiator can certainly be done from the wire, but if you plan to use an antenna for the Wi-Fi range, then the length of all design elements is desirable to recalculate. The antenna was calculated and modeled for the MMDS range of 2.5-2,5GHz with an average frequency of 2,6gc and its broadcase due to a large relative diameter of the elements of the irradiator. The use of a smaller diameter wire, of course, will reduce broadband, which, however, for a narrow Wi-Fi range is insignificant. But the best results will still be obtained if the length of all structural elements increase in 2600/2441.75 \u003d 1.0648 times, transferring its resonant frequency in the middle of the Wi-Fi range. Such recalculation of the sizes is desirable to do even if you use the same 3 mm capable as me, because For communication, each decibel signal is important.

-Appeaded with antenna cable of centimeters 50. I read that at such frequencies the length of the cable should be multiple the wavelength - and how is the actual length of the cable to pick up?

Not necessary! With a consistent connection, when the cable's wave resistance coincides with the input resistors of the irradiator and the converter (or receiving Wi-Fi transmitter), the running wave mode is set in the cable at which the cable length does not affect the passage of the signal, adding only a small attenuation (in your case About 0.5DB) due to losses in conductors and the cable insulation dielectric at these frequencies.

- Clear. And if you make a cable-loop in 2 wavelengths and put it with eight, as in the figure you can get a larger signal and observe the "phase" current

I drew you the instantaneous distribution of currents (red arrows and pliers) and stresses (blue arrows and plumes) in the symmetrically matching line and two vibrators. From the figure it is clear that the maximum current in the quarter-wave line is at the very bottom of its inflection. There is also the maximum of its magnetic field. In the same place there is a loop of communication (in the figure I shifted it conditionally down). It can be seen that the junction of the loop and lines coincide. In the case of eights, such a coincidence will not succeed. Moreover, in the case of a double wavelength in the loop, there will be 4 (!) Sections with the opposite direction of currents. In the loop pattern, the current is shown current by the internal conductor of the cable, it is it that creates its magnetic field. The cable shell in the loop serves only an electrostatic screen that prevents the capacitive current of the line into the central cable conductor. So as not to be turned out for a short circuit for the magnetic component. This screen should not be closed on yourself in the location of the sucking of the cable (short-circuit round). In addition, at the top of the line at the points of connection it with vibrators there are high voltage lines and vibrators. Patto the room there hinges, as well as
using a large loop, will cause large capacitive currents on the cable braid causing signal loss and antenna alignment. In general, in an antenna farming near the ends of the antennas with a voltage maximum, there should be no metallic items to eliminate the distortion of the field in the near zone and the loss of the signal. It does not apply to the quarter-wave line. It has an infinitely large resistance at the ends and well agreed with the ends of the vibrators.

Earlier we mentioned such systems of cellular television, as MMDS. (MULTICHANNEL Microwave Distribution System), Lmds.() or MVDS. (). Now we will analyze each system in detail and determine the pros and cons of each of them.

Multichannel multipoint switchgear - in english abbreviation MMDS. (MULTICHANNEL MULTIPOINT DISTRIBUTION SYSTEM) - this is a terrestrial television system, analog cable televisionBut without a cable, in some way similar to the satellite television broadcasting system - only satellite repeater in this case, as it were on Earth. In many cases, this method of propagation of television and radio programs has undeniable advantages over long-known and widely used - cable networks and through satellites - repeaters. So, in particular, the receiving antennas can be significantly less satellite, because capacity MMDS.- The signal is much larger than the signal from the satellite. The width of the frequency range is 2686-2500 \u003d 186 MHz. In this band, you can accommodate up to 24 analog television channels adopted in Russia standard D (SECAM, 8 MHz) or up to 31 channels of the European standard B (PAL, 6.5 MHz). For Western countries it is a bit, so the systems MMDS. It is usually built, where the creation of the cable network is impossible or inexpedient.

Advantages of MMDS:

· Cheap subscriber service

· Minimum (compared to cable television networks) Number of technical specialists

· Easy to connect the end user due to the absence of binding to cable infrastructure

· Low cost of channel ownership channels and maintenance of channel-forming equipment compared with the cost of owning and supporting the efficiency of similar cable infrastructure

Disadvantages of MMDS:

· The total number of broadcast television channels can not exceed 24

· Fast deployment Systems in a specific locality due to the simplicity of installation of both basic transmitting equipment and retransmission networks

· The ability to use the network MMDS. As a repeater of both state and local cable TV channels

Fig. 3 - MMDS structural scheme

Lmds.(Local MultiPoint Distribution System) It is a broadband system of wireless telecommunications type "point-multiple", which operates in the frequency range above 20 GHz (a specific range depends on the country and local licensing ranges). The LMDS system is designed for single or two-way voice, data, Internet traffic and video. LMDS can be translated as a local multipoint distribution system.

In essence, LMDS technology is a cellular information transfer system for fixed subscribers based on the radiocanal of a millimeter wave range. The basis of its organization is copied by the principle of networking in mobile cellular communication. To cover a certain territory (usually cities), the network of overlapping cells is unfolded, in the center of each of which is established base station. One such station in the LMDS system allows you to cover the area with a radius of several kilometers and connect several thousand subscriber stations. At the same time, the stations in the LMDS system are combined with each other high-speed ground-based communication channels by either by radio channels.

Advantages of LMDS:

Wireless systemthat does not require the laying of expensive cable lines of communication.

The possibility of network deployment over a short time

If necessary, the system can be dismantled in a short time and installed elsewhere.

Compared with similar transmission rate with wire communication channels, deploying the LMDS subscriber terminal and the subscription fee for the channel below.

In Russia, the LMDS system has not yet been distributed.

MVDS. (MultiPoint Video Distribution System) It is a broadband system of wireless telecommunications type "Point - Multiple", the main purpose of which is the transfer of video (including TV programs). Today, in the MVDS system to a video signal using an IP encapsulator, you can add Internet, IP voice and other types of services. Therefore, the differences between LMDS and MVDS systems are gradually erasing, although the first one of them was intended for broadband data in the main data, and the second - only video. MVDS can be translated as a "multipoint video distribution system". In essence, MVDS is a cellular information transfer system for fixed subscribers based on a radiocanal of a millimeter wave range. According to the principle of its organization, MVDS copies the principle of the organization of the network in a mobile cellular communication. To cover a certain territory (usually cities), the network of overlapping cells is deployed, in the center of each of which the base station is established (BS). One BS allows you to cover the area in the form of a circle (in reality is a polygon) with a radius of several kilometers and connect several thousand subscriber stations (AC). The BS themselves unite with each other high-speed ground-based communication channels or radio channels.

The most attractive quality of MVDS systems is the width of the range provided - 2 GHz. Another feature of the waves of this range is the rectinence of their distribution. They are not able to overeat even small obstacles, and on the contrary - they are reflected from them almost without distortion. Practice has shown that at a frequency of 40 GHz, signals have been satisfactory, which have passed a 4-fold reflection. This property can be used when designing high-frequency signal distribution systems. In MVDS systems, both analog and digital information transmission methods, as well as various modulation systems, can be used. However, for the purposes of building multimedia networks, the development of purely digital systems is relevant. You can select 2 types of systems: cable and satellite.

In the "cable" type of systems, QAM modulation and channel width of 8 MHz are used, and in the "satellite" - QPSK modulation and channel width of 36-40 MHz.

The MVDS satellite version allowed to transmit up to 30 TV channels of standard quality and provided a signal to a 25-centimeter enemy antenna within 10 km radius, and cable - up to 100 channels, but up to 4.5 km, subject to an admission to a 60-centimeter antenna. The MVDS multimedia network is based on the head station. When forming information flows A wide variety of sources can be used - Internet, essential, cable and satellite tV channelsVarious local sources of information.

Fig. 5 - Structural diagram of the MVDS system.

Caused by high development dynamics information technologies To ensure the level of information services, as well as an increasingly increasing number of available content for a broadcaster. According to its principle, MMDS is similar to traditional air television in analog or digital forms, the exception that it is initially intended only for limited Circle consumers (used coded pay channels for collecting subscription fees).

IN present in Russia for broadcasting in straight Canal A range of 2.5 - 2.7 GHz (24 channels with a strip of 8 MHz) is selected. For a reverse channel (in the case of interactive MMDS), the frequency portion in the range of 2.1 - 2.3 GHz is released.

TO The advantage of MMDS should include the simplicity of delivery of TV signals to the subscriber when reaching a significant area. MMDS has a relatively low cost of transmitting equipment, mainly dependent on the number of translated channels, the power of transmitting devices and the type of MMDS.

P The low channel transmitter channel (usually not more than 100 W) can be covered by a significant broadcast zone (up to 50-70 km) due to the high gain of the receiving antenna (18 ... 25 dB). At the same time, it is important to choose the right place to install an antenna system, taking into account the required sanitary zone (usually not more than a few tens of meters) and terrain.

IN The quality sources of the signal use traditional head stations that are used and when constructing the CCT.

ABOUT check an important point When designing MMDS systems is the right energy calculation of the coverage area, taking into account the height of the antenna installation. This calculation is very laborious and complicated. You can only perform using machine calculation methods. If you need to increase the coverage area or with the presence of shadow zones, repeaters are installed on autonomous mode.

IN Currently, MMDS should be considered as a multiservice wireless (Wireless) system of television, i.e. For the complete analogy with the skt. This bidirectional system must necessarily be able to connect a wireless head system of the modem (WMTS - Wireless Modem Termination System) operating according to DocSis 2.0 WMTS. The interactive MMDS structural scheme must include a transmitter, receiver, head station (the same as in HFC) and WMTS in combination with the necessary servers. In one of the detailed embodiments of interactive MMDS, the schemes for connecting the main function modules with an option for connecting channel transmitters and a controlled switching matrix (48 inputs) allowing in manual or automatic mode Translate the required channels to ether set time From a variety of or formed by their own television studios.

P Users can be connected both individually and collectively. From the point of view of the formation of a reverse direction, the collective connection is more preferable. In this case, a transceiver from the receiving-transmitting antenna (transverter) or an additional collective transmitting antenna is installed in the head of the cable segment. At the same time, users connected to the Internet can take advantage of such a service as an iPRV (one-time review fee), as well as any other services of traditional interactive networks. For segmentation of active subscribers, several technical techniques are usually used.

T. Actually, you can draw the following recommendations and conclusions:

• MMDS systems in their structural construction are very close to traditional cable networks (CCT). Fundamental difference It is to replace cable sections to ether.
• In MMDS, all types of signals used and when constructing CTC: AM TV, DVB-C, DVB-T, DVB-H, and others can be translated into MMDS.
• MMDS has a lower cost and significantly less time consumption in comparison with CT. However, MMDS provides for the use of individual (or collective for a small number of subscribers) antennas. And this entails an inevitable decrease in the number of connected subscribers (including the mandatory presence of shadow zones).
• Interactive MMDS, providing for the mandatory presence of a reverse channel (on the telephone line or by ether), have significantly greater attractive possibilities.
• Very important point when choosing a type of MMDS is not only her technical specifications (eg, output power and frequency stability), but also functionality. First of all, they include:
  Ø The possibility of connecting WMTS operating according to DocSis 2.0;
  Ø The presence of a remote management / monitoring system;
  Ø the possibility of its conjugation with RF digital pathogens (first of all DVB-C / T / H);
  Ø Availability of automatic backup system for all modules used.
• The larger coverage area has channel MMDS in comparison with the bands. However, the latter have a lower cost.
• To increase the coverage area (as well as increasing the possibilities and quality of the provision of multiservice services) more economical is the inclusion of several low-power MMDs according to the scheme of the cellular structure. At the same time, the cost of the system as a whole is not only reduced, but also facilitate the conditions for obtaining a license for broadcasting.
• MMDS has very significant advantages, in which the final power amplifier is made in the dust-precipitated case and is installed in a special container in the immediate vicinity of the transmitting antenna. When installing the same transmitter, as part of the HS, some contradictions are observed, which consist in the following: to expand the coverage area, it is necessary to raise the transmitting antenna as possible (thereby providing a zone of direct radiance). But the antenna rise means a decrease in the radiated power due to the inevitable losses in the supply cable. A decrease in the radiated power leads to a decrease in the coverage area at a fixed transmitter power.
• By purchasing MMDS, you should immediately pay attention to the possibility of its work according to the DOCSIS 2.0 WMTS standard (or version 3.0). According to this standard, the requirements for the stability of the output frequency, the unevenness of the GVZ and a number of other parameters are substantially tightened. No modernization of MMDS will allow in the future to introduce a wide range of sought -led services.
• Correctly calculate the interactive MMDS coverage area can only highly qualified specialists who have sufficient experience in this direction and having at their disposal the necessary machine calculation methods.

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