Abstract Lubov Shapovalova Research and development of the model of data transmission in a radio access network based on technology of WiMAX taking into account qulity and safety

«Research and development of the model of data transmission in a radio access network based on technology of WiMAX taking into account qulity and safety»

A theme urgency

Postindustrial economy device, in which knowledge, information and transfer are the right products and the most advantageous business approved and in Ukraine. The capitalization of our leading mobile operators have already comparable to the cost of the largest domestic financial-industrial groups, which hold assets in metallurgy, chemistry and mechanical engineering. Compare the scales, one of which - the huge factories moving across the planet millions of tons of ore and iron, burning billions of cubic meters of gas and release neschislimogo amount of harmful substances into the atmosphere, on the other - the provision of telecommunications services to anyone.

But the biggest bonus, which the country has received from the development of information and communication economy in a significant increase competition, which encourages companies to adopt new technologies and marketing solutions. In addition, this competition leads to a marked reduction in the prices of their services and products.

Modern trends in telecommunications are associated with the emergence of new services and services that are more demanding to existing networks. Every day, these services become more relevant to users. Construction of a modern multi-service wireless network is a very convenient solution for existing providers, as a result - to attract even more subscribers, and thus increase profits. In recent years the development of network technologies has led to a significant expansion of the list, and possible ways of combining personal computers in the network, and the types of connections to the Internet.

Ukraine currently has external communication channels with sufficient capacity, in almost every village there are service providers access to the outside network, but the connection between them and the end user is still done mostly either switched or dedicated lines. As a result - a low rate of exchange of information, unreliable connection, limited connectivity options. Many important problem is the cable lines, sometimes it is impossible, inconvenient and economically impractical, especially in large cities. The importance and urgency of this topic is the question of the study and implementation of new technologies in modern telecommunication networks.The main requirement for the design of a modern telecommunications network, a selection of the most profitable and high-quality data transmission technology. Recently, in telecommunications, has been widely regarded generation wireless technology WiMAX, a standard IEEE 802.16. That is a very topical and important issue is the question about the study itself WiMAX technology and development models, which can be used to obtain a convenient mathematical device for calculating the surface depending on the parameters of the system.

Communication of work with academic programs, plans, concepts

As part of the development strategy of the city of Donetsk on favorable conditions in the field of electronic processing, transmission and dissemination of information, provision of services to all categories of consumers, creating a single multiservice network of the city, the creation and development of modern infrastructure in different areas, the executive committee of Donetsk municipal council decided to # 235 of 17.05.2009, concerning the harmonization of the concept of "digital city". This concept is aimed at socio-economic development of Donetsk, in particular on the development of communication infrastructure, increase investment attractiveness of sectors of information, a significant improvement of the city's telecommunication network based on the latest technologies, their integration into the global information resources, creation of access for the general population to modern telecommunications services and information resources. Under the "digital city" is very relevant and beneficial is the consideration of WiMAX.

Just my Master's work relates to development, projects produced by the Department.

The purpose and problems of the development (of the research)

The main purpose of this master's work is to study and develop models of data transmission in the radio access network to WiMAX technology with regard to quality and safety. And as the study of technology on the physical, data link and transport layers. Study of dependence of the parameters transmission medium and the technology in the calculation of design covering WiMAX. But the main building of a mathematical model of WiMAX and getting a convenient mathematical device for calculating the network depending on the parameters of quality and safety systems.

Methodology and methods of researches

In the course of writing a master's thesis will use basic research techniques and development:

• methodology for estimating the parameters of WiMax-based mathematical model,

• method of data transmission,

• method of calculating coverage WIMAX,

• multi-criteria analysis of existing mathematical models for wireless communication systems,

• methods for developing technical proposals,

• methods of economic analysis.

Prospective scientific novelty of the received results

1. Further development of methods for estimating the parameters of WiMax on the basis of the developed mathematical model;

2. Further development of methods of calculating coverage WIMAX.

Overview of developments and research on the topic:

Постиндустриальное устройство экономики, при котором знание, информация и их передача становятся нужнейшим товаром и наивыгоднейшим бизнесом, утверждается и в Украине. Капитализация наших ведущих мобильных операторов уже сопоставима со стоимостью наибольших отечественных финансово-промышленных групп, которые владеют активами в металлургии, химии и машиностроении. Сравнились чаши весов, на одной из которых - огромные заводы, перемещения по планете миллионов тонн руды и железа, сжигание миллиардов кубометров газа и выброс несчислимого количества вредных веществ в атмосферу, а на другой - предоставление телекоммуникационных услуг желающим.

In the transition to the creation of broadband wireless access with integrated services, it became clear that the basic principles laid down in the wireless system at the previous stages, in great need of correction. At the signal level of priority had the optimal use of radio spectrum resources for any relationships between the "rate - jamming protection. At the protocol level it became necessary to provide a specified level Quality of Service (QoS) to any subscriber network. To this end, in 2004, was developed standard IEEE 802.16-2004, which represents a calculated on the introduction of urban wireless networks (WirelessMAN) technology without the leading broadband access, carrier-grade. Used commercially known as standard WiMax (Worldwide Interoperability for Microwave Access), which originates from an international organization WiMax Forum, which includes a number of advanced communications and semiconductor companies. The main purpose of these networks - is the provision of services to subscribers of high-speed and high quality bezveduschey transfer data, voice and video at a distance of several tens of kilometers. In October 2007, International Telecommunication Union (ITU-R) including technology WIMAX standard IEEE 802.16 family of standards in mobile 3G. In networks WIMAX Completed the latest achievements of science and technology in the field of radio communications, telecommunications and computer networks. IEEE 802.16 standard defines the application:

• the physical layer of broadband OFDM signal with multiple subcarriers;

• link-layer protocol used by modern multiple (Multiple) Access Time Divion Multiply Access (TDMA) and Scalable OFDM Access (SOFDMA);

• at the network (vehicle) level in WIMAX networks used IP-data transmission protocol, which is widely used in most modern data networks, in particular, on the Internet.

At the physical layer of IEEE 802.16 are three fundamentally different methods of data transfer - the method of modulation of single carrier (SC, in the range below 11 GHz - SCa), modulation technique using carrier OFDM (orthogonal frequency division multiplexing) and the method multipleksuvannya (multiple access) using orthogonal carrier OFDMA orthogonal frequency division access)[2].

Mode OFDM - a method of modulation of the data flow in a single frequency channel (width 1-2 MHz and greater) with a center frequency fc. The division into channels - frequency. When the modulation data under the influence of orthogonal carriers in the frequency channel is allocated N subcarriers, so that fk = fc + k * ^ f, where k - an integer in the range [-N / 2, N / 2]. The distance between the orthogonal carriers ^ f = 1/Tb, where Tb - the duration of data transmission. In addition to data in the OFDM-symbol is transmitted guard interval, which is a copy of the final fragment of a character. Its duration may be 1 / 4, 1 / 8, 1 / 16 and 1 / 32 of Tb.

OFDM modulation is based on two fundamental principles: a breakdown of one channel with replaceable parameters in parallel gausovskie channels with different ratios of signal to noise ratio and precise measurement of the channel. In accordance with the first principle of OFDM, each carrier is modulated independently under the influence of quadrature amplitude modulation.The total signal is calculated under the action of the inverse fast Fourier transform as

[1]

where Ck - integrated presentation of the character quadrature modulation. Complex presentation of convenient, because the signal is generated according to expression

Sk(t) = Ik*cos(2?fc)-Qksin(2?fc) (2),

where Ik and Qk - phase and quadrature component of the complex character.

For the algorithms SHPF, OSHPF convenient to the number of points consistent with 2m. Therefore the number of carriers is selected equal to the minimum number Nfff = 2m. While OFDM standard IEEE 802.16 N = 200, respectively Nfff = 256. Of these, 55 provide guard interval at the boundary of the frequency range of the channel. Other 200 - Information[8].

In accordance with the second principle of OFDM for accurate determination of channel parameters required so-called pilot carrier frequency, modulation technique and peredayuchy signal, which is exactly known to all stations in the network. In OFDM provides the use of 8 pilot frequency (with indices 88, 63, 38 and 13). Other 192 carriers are divided into 16 sub-channels to 12 in each bearing. Divide by subchannel is necessary because in the mode of WirelessMAN-OFDM envisaged the possibility to work not all 16, and 1, 2, 4 or 8 sub-channels - ie inherent assumptions OFDMA. To this end, each subchannel and each group has its own index (from 0 to 31).

Duration useful part of the Tb OFDM-symbol depends on the channel bandwidth BW and the system clock frequency (sampling frequency) Fs. Fs = Nfff / Tb. Value Fs / BW = n is normalized, and depending on the channel bandwidth is set to 86/75 (BW fold 1.5Mgts), 144/125 (BW fold 1.25Mgts), 316/275 (BW fold 2,75 MHz), 57/50 (BW multiple of 2 MHz) and 7 / 8 (BW multiple of 1.75 MHz, and in all other cases).

Also at fizichsekom level to decide the modulation. The important thing is that the technology WIMAX is the highest in the class of BWA (Broadband Wireless Access) energy parameters of the communication channel that provides the desired high speed data transfer (bandwidth) at the maximum range and vice versa - at a given range WIMAX network has the highest throughput .Thus, the system WIMAX provide the highest density of data flow, measured throughput in Mbps in recalculation on one square kilometer area that is covered. High throughput systems WIMAX is achieved through the possibility of support for long range high-speed character due to the high energy of the system. Symbol Rate, or such other rate modulation (or code rate), characterizes the rate of information transmission (data) on the physical (radio) network level.And as is the transmission rate of a sequence of characters, which is implemented by the modulation signal. Symbolic transfer rate is completely determined by the type of modulation used, ie each type of modulation provides a symbol rate. Thus the high density of data flow in networks of WIMAX is achieved by the possibility of support for large compared to other systems with ranges of high-speed types of modulations.

In systems WIMAX used quadrature amplitude and phase modulation QAM, as well as phase shift keying QPSK and BPSK. To date, QAM is one of the most effective methods of modulation, which allows to achieve the highest possible data rate[7].

QPSK (Quadrature Phase Shift Keying - quadrature phase shift keying) is a method which generates a complex sequence of binary digits corresponding to symbols of higher order. The first stage is converted characters of a higher order modulation, and generates an output signal QPSK-modulation, corresponding to the first points of the constellation. In the second phase modulation is converted characters of a higher order in the second constellation point, and generates an output signal corresponding to the second point of the constellation. The points of the constellation of higher order modulation are obtained by adding the output signals of the first and second phases of modulation. In the QPSK-modulation quality assessment connection is performed using threshold values.Estimated unit gives the thresholds components QPSK-modulation. In this method, carried out the serial reception of signals, and calculated psevdobitovy error rate when sending hexadecimal QAM-signals.

OFDMA (Orthogonal Frequency Division Multiple Access) is a multiplayer version of schema digital OFDM-modulation. Subsets of subcarriers assigned to individual subscribers, to provide a simultaneous low-speed transfer of data from multiple users. BS receives a packet with a higher level, translates them to multiple mobile stations (MS), and performs channel coding separately for each package, which will be transferred to different MS. REF independently interleaves and modulates the encoded broadcast service packages. At the end of modulation each of the segments the BS broadcasting service packages for a number of blocks of data transmitted and the number of these blocks is redistributed within the package to change the content. After segmentation BS performs multiplexing, whereby the segmented signal is transmitted sequentially, or through pre-established time intervals. When you send a signal time division MC selectively receives only a single frame transmission. After that unites the entire MS signal for the formation of the desired package. In order to recognize packets MS uses the method of designating unique identifiers connection (CID) broadcast services. BS writes information to the appropriate identifier CID in the information part of the physical layer (DL-MAP), present in every frame transmission. MS (adopting special frame) receives information about the transfer at the physical level of the frame and determines the CID, matching services. MS can get the desired character of broadcast stations.

With the implementation of QAM, each carrier OFDM signal is modeled by a useful signal at the same time the amplitude and phase, forming a signal whose position in the coordinate space phase and amplitude is a diagram of the constellation (constellation diagramm) and carries information about the coded symbols to. Figure 1 A chart of the constellation modulation 16QAM.

Рисунок 1 - Диаграмма созвездия модуляции 16 QAM

Figure 2 - The constellation diagram of modulation of 16 QAM

Vector 16 QAM signal has 16 possible positions in the coordinate space of the amplitude and phase, which encodes the 16 values character from 0000 to 1111. Vector 64 QAM signal has 64 positions, which encodes a 64 character value. Modulation BPSK and QPSK 2 and 4 encode the character value by, respectively, two and four possible values of the phase. The amplitude of the signal in BPSK and QPSK modulation is not changed. Thus, these two types of modulation can be regarded as a special case of amplitude-phase modulation, QAM. Thus, modulation 64qam is the fastest, because permits to pass 64 possible values in one data symbol, which provides a higher symbol rate and, consequently, a higher data rate compared with lower modulations.

Figure 2 Presentation of the service area different modulations of fixed network subscribers in the WIMAX frequency range of 5 GHz. Since service subscribers equipped with an external directional antenna on the modulation 64QAM3 / 4, which supports a maximum symbol rate and the corresponding data rate is provided at a distance of 25 km., 16QAM1 / 2 - at a distance of 40-45 km. Thus, the range of services to the velocity modulation 64 QAM and 16 QAM in the WIMAX network in four or more times greater than the corresponding distances in similar modulations of service systems preWiMax.

The ability to support one or another of the modulation depends on many parameters of connection, and above all, from the energy parameters of the system.

Figure 2 - Service areas network WIMAX

As seen from the diagram of the constellation modulation QAM, the higher the modulation type, the smaller the amplitude and phase are different vectors of neighboring values of the symbol, which is transmitted. Thus, for error-free reception of a symbol (reception with some acceptable level of error) needs a strong signal, but rather, a higher ratio of signal power to noise.

Each type of modulation to transmit the symbol with the level of error, which does not exceed a certain maximum value, requires a certain minimum value, the level of signal to noise Signal / noise Ratio (SNR or S / n). In addition to SNR relationship is often used almost identical to the concept Snr Carrier / noise Ratio, or C / n.

Each type of modulation is characterized by the necessary level of signal-to-noise ratio SNR, needed to transfer bits of information from the mistakes of Bit Error Rate (BER) not exceeding a certain permissible level. Figure 3 shows the relationship SNR of bit errors for each type of modulation.

Figure 3 - The dependence of the signal / noise ratio of bit errors

IEEE 802.16-2004 standard specifies support for 64 QAM modulation at the level of error not exceeding Ber = 10e-6 with regard to error correction Fec = 3 / 4 ratio of signal to noise ratio for each carrier OFDM signal SNR equal to 24.4 db. A more recent standard IEEE 802.16e-2005 defines for fixed and mobile networks, WIMAX more stringent Snr = 21 db for 64QAM3 / 4, Ber = 10e-6. Calculation of cell radius for different types of modulation is somewhat idealistic. To achieve these results in the practical construction is necessary to evaluate additional energy characteristics of the system, such as receiver sensitivity and the ratio of system gain. Thus, to obtain the necessary level of SNR (and hence the corresponding BER) signal at the receiver input system should be higher than the threshold equal sensitivity.

Modulation 64QAM.

The threshold level of sensitivity Rx receiver for OFDM systems for modulation 64QAM3 / 4 is defined as:

Rx 64QAM3 / 4 = No + Snr64qam3 / 4 + 10 Log (Bwef) + Nf + Implementation Loss, dbw; (3)

where Snr64qam 3 / 4 - the necessary level of relations SNR for modulation 64QAM3 / 4 = 21 db;

No = 10 log (kto) = -144 db (W / mhz) - Receiver Noise Floor power spectral density of thermal noise receiver, kto - the law of equitable distribution;

Nf - meaning self-noise receiver (noise figure) equal to - 8 db (IEEE 802.16e-2005).

Implementation loss equal to 5 db. This figure shows the so-called loss of implementation, which take into account nonideal receiver, phase noise, etc.

Bwef - effective width of the spectrum of the group signal OFDM. This value is proportional to the number піднесучих in the spectrum of group signal. Due to the presence of the guard interval between carriers under the effective width of the spectrum of OFDM signal is somewhat less band pass receiver (channel width). For a channel width of 10 MHz without subchannelisation (used by all sub-carriers) Bwef = 9.15 MHz, 10 Log (Bwef) = 9.6 MHz.

After

Rx 64QAM3 / 4 = -101 + Snr64qam3 / 4 +10 Log (Bwef), dbm; (4)

Thus, the required threshold level of sensitivity of standard WIMAX IEEE 802.16e-2005 with the implementation loss of 5 db bandwidth 10 MHz is 70.4 dbm. As standard, IEEE 802.16-2004, this value was 68 before dbm. Note that the standard IEEE 802.16e-2005 describes the requirements not only to mobile OFDMA networks, WIMAX, and also contains new, more stringent requirements (the so-called Rev Cor1) to fixed OFDM networks WIMAX.

To support some level of OFDM modulation signal at the receiver input Receive Strength Signal Level (RSSL) in the band pass channel BW should the value of SNR signal to noise ratio higher than the level of thermal noise in the light of the internal receiver noise and loss realization.

Thus, to support the modulation 64QAM3 / 4 level OFDM signal at the receiver input Receive Strength Signal Level (RSSL) should be for WIMAX systems in accordance with standard IEEE 802.16e-2005 is not below a level of sensitivity of 70.4 db (Snr = 21 db) in the band widthChannel Bw = 10 MHz. Real WIMAX system, as usual, are the highest in comparison with the requirements of the standard level of sensitivity, because the value of loss realization implementation loss of 5 db standard thing overestimated. For example, the sensitivity of the Airspan MICROMAX SOC 5 Ghz (standard IEEE 802.16e-2005) in the channel width of 10 MHz for 64QAM3 / 4 is -77 dbm (at Snr = 21 dbm), which corresponds to almost ideal receiver (Implementation loss close to zero) low intrinsic noise of the noise figure is less than 6 db. The sensitivity of the system Axxcelera AB-MAX 5 Ghz (standard IEEE 802.16-2004) in the channel width of 10 MHz for 64QAM3 / 4 is 72.7 dbm (at Snr = 21 dbm). The sensitivity of the system UNIDATA Maxbridge CPE 5 Ghz (standard IEEE 802.16e-2005) is 70.5 dbm (at Snr = 20 dbm, and for a much lower level of errors Ber = 10-11, which corresponds to the sensitivity of Ber = 10-6 about -74 dbm)5].

In principle, the system can support the modulation 64QAM3 / 4 and at a significantly (a few db) lower values of the signal, but at the same level of bit error will be the worst value Ber = 10e-6.Accordingly, in calculating the sensitivity of the receiver, we can estimate a specific factor degradation or improvement in the communication channel, which means - to change the size of the cell.

In real systems, apart from thermal noise and internal receiver noise is present interference.Therefore, SNR is estimated as C / N + I, where C - the signal power, N - the power of thermal noise, I - signal interference. Influence of interference leads to the degradation of the sensitivity of the receiver. The higher the level of interference, in order to значнішу value of the signal at the receiver input RSSL exceed the sensitivity level to support the appropriate modulation.

The value index Snr = a / n + i (as usual denoted briefly as a C / i) is continuously measured during the operation as a base station and each subscriber terminal, WIMAX, in order to dynamically assign the most appropriate modulation for each data packet to issue information.This indicated the measured SINR (Signal to interference plus noise ratio) or CINR (Carrier to interference plus noise ratio).

Experimentally that if the level of interference is lower for the level of thermal noise Receiver Noise Floor on the value of 6 db, then this interference does not influence the receiver system.Specifically, when I = No - 6 dbm level of reduction (degradation) peer receiver sensitivity does not exceed 1 db.

The level of thermal noise in the light of the internal receiver noise is N = 10log (kto) + Nf = -136 db (W / mhz). Volume I рівень interference in the channel width of 10 MHz, receiver sensitivity, which does not lead to significant degradation, equal

I = -136 + 30 + 10 Log(10) - 6 = -102 dbm

In a channel width of 5 MHz level of interference, which does not lead to significant degradation of the sensitivity of the receiver, equal to -105 dbm.

By exceeding the power level of interference is a threshold level of degradation of the sensitivity is increased by more than 1 db and interference can affect the operation of the system. The degree of negative impact depends on the type of signal interference (obstruction). When assessing the sensitivity of the receiver noise is considered as noise Gause or "white noise".The real signal obstacles in its structure, of course, may differ from the "білого noise and its effect on system performance can be both stronger and слабкіший for the influence of white noise. For example, vuzkosmugova obstacle may not affect the signal shirokosmugovy OFDM.Accurate theoretical evaluation of the influence of different types of obstacles in the work of the receiver system is quite a challenge. Less accurately assess the mutual influence of interference is possible for the consistency of equipment in the analysis of electromagnetic compatibility. In practice, to assess the feasibility of systems in terms of interference of various types, as usual, operate marginal value of CINR[5].

WIMAX is a system with automatic control of power Atpc. At the base stations is given the highest possible level of input signal RSSL. For the 5 GHz systems with a channel width of 5 or 10 MHz, this level is, as usual, is set to 65-70 dbm. At minimum required signal level at the receiver input RSSL in 65-70 dbm (close to the level of sensitivity to light fade margin) and the signal / noise + interference with / n + i> = 21 + 6 = 27 db on the modulation 64QAM3 / 4reached the level of degradation of receiver sensitivity is not higher than 1 db for BER = 10E-6.Thus, as measured in the value of the WIMAX CINR> = 27 db at least fairly equal RSSL guarantee that interference is the lowest level of thermal noise receiver by an amount not less than 6 db, and regardless of the type of signal interference practically does impact on system performance.

If you work in conditions of strong interference or other reasons, the maximum input level at the base station can be upgraded to 65-60 dbm. In this case, raising the level of the signal at the receiver input, CINR level requirements to support the modulation 64QAM3 / 4 slightly decreases until the minimum required level of 21 db.

Thus, in the presence of interference for support, for example, modulation 64QAM3 / 4 is not enough to have a signal level RSSL, which exceeds the level of sensitivity of the receiver for 64QAM3 / 4 on the value of fade margin. That is, only on the value of the signal RSSL in the presence of interference is impossible to determine what type of modulation can be supported by the system. For example, the input level RSSL may be equal to - 65 dbm, that in the absence of interference more than enough to support the modulation 64QAM3 / 4 at any bandwidth. Nevertheless, the presence of interference actually received CINR may be less than 20 db, which does not allow to maintain modulation 64QAM3 / 4 with the error rate Ber = 10e-6. If the measured value system CINR exceeds 21 db, then it means that the signal RSSL higher than the threshold sensitivity for 64QAM3 / 4. If the measured value system CINR exceeds 27db, then by the former signal exceeds the level of RSSL порогової sensitivity 64QAM3 / 4, but the level of interference does not exceed the permissible level and does not affect the receiver system.

Thus, for system support WIMAX highest symbol rate on the modulation 64QAM3 / 4 it is necessary and sufficient that the signal / noise + interference CINR value exceeded the value of 21-27 db fade margin. Thus, an objective indicator of ability to support one or another of modulation is measured system WIMAX ratio CINR. That the values of CINR WIMAX system establishes a working modulation signal, which ensures stable operation channel of communication with the level of bit error is not above Ber = 10e-6.

Assessing the impact of the Fresnel zones on the quality of the signal within the WiMax route

Figure 4 - Construction of a Fresnel zone.

Radio waves in the propagation process in a large volume is in the form of an ellipsoid of treatment with a maximum radius in the middle of the span, which is called the Fresnel zone.Natural (land, humps, trees) and artificial (buildings, poles) obstacles that fall into this space weaken the signal.

It is extremely important especially for the 802.16 standards and 802.16a that operate only when there is line of sight between peredayuchoyu and the receiving antenna[9].

Radius of first Fresnel zone to be calculated using the following formula:

Here n = 1 - number of Fresnel zone, R1 and R2 - the distance from передаючої and the receiving antenna to the point calculations of the radius r and r - the radius of the Fresnel zone in meters.

Normal blocking 20% of the Fresnel zone contributes little attenuation in the channel. Over 40% - attenuation is already significant, so we want to avoid hitting obstacles on the path propagation.

For standards, WiMax, which work in the absence of direct line of sight maximum range of the base station at a frequency of 2.5 GHz in a closed Fresnel zone is less than 3km.

Despite the urgency and relevance of this technology in the design of networks, some issues and concerns are very important and unresolved. In most cases, designing WiMax networks is quite complex and ambiguous process. Coverage calculations are based on measurements of the noise level on the ground. This process depends on many parameters of the transmission medium, and parameters, properties and characteristics of the technology WiMax. Among the major factors that affect the transmission range of information should be provided such as the influence of type of modulation, the receiver sensitivity, the coefficient of the system gain, the effect of interference, as well as a number of other factors and parameters. There are two strategies for constructing infrastructure мережевої WIMAX[12].

The first strategy focuses on getting maximum flux density of data on a given territory. This strategy is used in large cities with high population density with advanced provodovoyu merezhevoyu infrastructure. The main purpose is to ensure provodovim shirokosmugovim DSL access and the provision of мультимедійних services.

The second strategy is applicable in the absence or low level of competition from wire systems, is turned up base stations, which provides maximum coverage with provision of a given flux density data. This strategy is applicable in rural areas, as well as in cities and regional centers with low development of wire infrastructure, which is typical for most regions of Ukraine. This strategy allows to obtain the flux density data 1-6 Mbps / sq. The purpose of implementing this strategy is to provide the necessary services for the speed, which are provided by the operator, the transfer to the maximum areas.

The strategy of maximizing the density of the data stream allows for a limited frequency resource to get competitive with DSL flux density data (20-40 Mbps / sq km) with a high density of base stations (BS) Base Spacing, which is equal to 1-2 km. In this case TDD BS have the ability to reuse frequencies on a single BS and the possibility of collocation BS - synchronization of BS in order to exclude mutual constraints. Given the limited frequency resource that allows TDD BS reach high values of flux density data in comparison with продуктивнішим equipment FDD, which requires for its work, a significant frequency resource.

The strategy to maximize the surface area, which will cover the services, is complicated by relatively high power loss signal in the propagation of radio waves in the range of about 5 GHz.The loss at 5 GHz slightly higher for the same loss at the lower frequencies, 2.5 GHz and 3.5 GHz. Nevertheless, the use of strategies to maximize the territory they cover, at a frequency of 5 GHz for fixed bezveduschego access effectively. The thing to because the fixed access equipment turns up subscriber terminals external antennas. In WIMAX networks this may be an antenna for indoor use, which rigged (self-installable) subscriber terminals which are installed the subscribers themselves, and external antennas that are installed outdoors requires professional installation service provider. According to experts, the majority of subscriber terminals, which operate in fixed access networks, WIMAX in the range of 5 GHz, will be equipped with external antennas. The external antenna 5 GHz have an average of 5-7 dbi high gain antennas in comparison with the similar size range of 2.5 and 3.5 GHz. Higher gain external subscriber antenna at the very time and compensates for the increased losses in the propagation of radio signals.

Thus, the use of equipment standard IEEE 802.16-2004 permits cover service shirokosmugovogo access обширні territory with minimum cost, ie effectively implement a strategy to maximize the area that is covered. This important feature WIMAX networks have a relatively small radius of service self-installable subscriber terminals. Power losses in the propagation of radio signals in urban areas outside the direct line of sight in the 5 GHz band is much more significant than, for example, in the frequency range 2.5 GHz. These increased losses can not compensate for the use of self-installable subscriber terminals powerful antennas. Therefore, the maximum range of services to such customers outside of the visible base station is much smaller than the lower frequencies, and less than 1 km. Thus, in networks WIMAX frequency range of 5 GHz self-installable subscriber terminals is practically not apply.Installing outdoor subscriber terminals with external directional antennas (in particular with integrated terminal building antennas) require professional skills and, as usual, carried out by the telecom operator. Installing the subscriber terminal does not require line of sight to the base station, subject to two conditions:

1) the presence of the right to use the modulation ratio SNR signal to noise ratio, 2) the required excess (fade margin 6-12 db) level of the signal modulation used the threshold of sensitivity. As usual, these conditions are satisfied for the subscriber terminals equipped with an external antenna or integrated antenna with high gain, at a distance of no more than 3-5 km. from the base station. At the higher ranges when you install subscriber terminals to provide line of sight (without restrictions on the degree of closure Fresnel zone).

Our main purpose the operator of a WiMAX network in providing quality services is the task of effective management of radio networks. The office aims to ensure that network capacity has been assessed in the appropriate proportions between subscribers and services at the right time in the right place at the expense of the use of efficient algorithms of traffic planning to ensure a balance between the required QoS for each service user and in accordance with available resources and needs subscribers.

Block diagram of the network WIMAX

Figure 1 - Block diagram of the network WIMAX

(Animation: volume – 91 KB; size – 1000x633; number of shots – 11; delay between shots – 300 ms; delay between the last and first shots – 300 ms; number of repetition cycles – infinity)

Result Master's thesis

In this master's work will be developed a mathematical model of the WIMAX. A key element of the Dana model is the ability to build WIMAX networks using the obtained convenient mathematical tool, taking into account the parameters of the system.

Findings

Thus, at this time substantiated the need for research and development of the model data in a radio access network technology for WiMAX. The dependences of the parameters of the transmission medium and the technology in the calculation of design cover WiMAX. And discussed methods predachi data and calculation of network WIMAX. A block diagram of the network, the main tasks that are executed its components.

Literature

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Note

When writing this Autosummary master work was not yet completed. The final completion - December 10 2010 Full text of the work and materials on the topic can be obtained from the author or his manager after that date.