Пояснительная записка Корнет Н.А (Проектирование сети LTE-A для микрорайона Строитель), страница 3

It is used to transmit user datafor mobility between LTE and 2G / 3G networks.S5 - interface between SAE and the PDN-Gateway. S5 serves for transmittinguser data between the SAE and PDN-Gateway/S6 - the interface between the MME and the HSS. It is used for transmission ofsubscriber profile data, and the authentication procedure in LTE network.Gx - the interface between the PDN-Gateway and the PCRF.

Gx for transmittingcharging rules from PCRF to the PDN-Gateway.SGi - the interface between the PDN-Gateway and external IP-networks1.5 The use of MIMO technology in LTE Advanced networks (Rel.10)MIMO technology in LTE Advanced networks (Rel.10) provides the basis oftransferring wireless data.MIMO (Multiple Input Multiple Output )- technology of multi antenna systemthat enables wireless access. This technology uses multiple transmission antennasand receiving antennas for simultaneous transmission of massive data.MIMO technology is based on the transmission of radio waves, called multipathpropagation .The main process is that the transmitted signals are reflected from theplurality of objects and obstructions such as buildings, cars, houses and people, theantenna receiver picks up signals from different angles, and above all at differenttimes.

By using MIMO technology, it becomes possible to increase the noise im17munity of communication channels to reduce the relative number of bits receivedwith an error.As regarded earlier technology essence is in the use of multiple antennas that arespread apart so that they do not interfere with transmission. This technology provideshigh levels of data transmission.Commonly used is the technique of frequency division multiplexing or FDM(Frequency Division Multiplexing).

Thanks to this technique, a huge number of devices are operating in the same area. Below principle of frequency division multiplexing is shown.Figure 1.4—FDM principle.This diagram shows how the frequency time and energy flows is allocated between columns designated with different colors. A significant drawback is the needto keep the frequency intervals between the different streams, to avoid interference.The frequency resource is not fully used .MIMO principleMIMO systems work can be arranged on two principles: space division principleand the principle of space-time coding.In the first case, the different transmitting antennas transmit different informationsymbols of the block or blocks of different information.

Data transfer is carried out in18parallel from two or four antennas. The reception and separation of signals from different antennas is obtained at the receiving side. In the second case, the same datastream are transmitted from all transmit antennas using the precoding schemes.Thus, the creation of a greater number of spaced channels is realized by the addition of multiple antennas at the transmitter or receiver, or both. The following figureshows a system MIMO 2 × 2 coefficient of time diversity is equal 2 × 2 = 4.Fig.

1.5— The scheme of signal transportation in MIMOIn this case, by the term of MIMO we will determine spatial multiplexing (Spatial Multiplexing) - the version of MIMO, achieve higher throughput by space-timeblock coding.Space-time block coding (STBC) based on the circuit shown Alamouti. Thisscheme provides transmission and reception at different times for MIMO. This figureshows the maximum ratio of the received combination (MRRC) .Three basic functions of the Alamouti scheme can be defined as follows[2]: Coding and decision-making information about transfer sequence are heldwith the use of criteria of The symbols in the transmitter are presented as the combining signals fromthe noise at the receiver.The maximum likelihood detection (Maximum likelihood detection).19The scheme of designing two channel transport system is shown on the Figure1.6.Suppose we have two antennas both on transmission and on reception, while thesymbol S1 is transmitted from antenna 1 and the symbol S2 is transmitted from antenna 2 at time T.Fig.1.6— Spatial Multiplexing scheme-S2 * is transmitted from antenna 1 and s1 * is transmitted from antenna 2 at timeT + 1, where (*) denotes the conjugate value.

In STBC coding system, symbols aredivided into 2 groups. {S1, s2} symbols of each group are transferred as shown inFigure 1.6The Transfer equation will be as followed one:The above matrix shows that the two rows / columns STBC matrix are orthogonalto each other. R11 and R12 denotes a receiver 1 and R21 and R22 denotes a receiver2. H is the channel matrix and W is a white Gaussian noise. The symbols S1 and S2and their associated values are placed on OFDM sub-carrier for transmission over thechannel.1.6 OFDM modulation in multi-antenna MIMOOFDM signals are generated in digital form, and the signal consists of a sum ofsub-carriers which are modulated using BPSK or QPSK, or QAM.

The relationshipbetween all sub-carriers should be monitored to maintain orthogonality. After modulation input data in digital form, the resulting spectrum is transformed back into its20time domain via the inverse Fourier transform (IFFT). IFFT converts a number ofcomplex data points with a power of 2, in a time domain signal of the same numberof points.

Figure 1.8. illustrates a block diagram of an OFDM transceiver, and eachblock is discussed further.Fig.1.7— OFDM transceiverSerial-to-parallel conversion method: In OFDM, each symbol typically transmits40-4000 bits, so that the serial-parallel conversion is necessary. The data allocated toeach symbol depends on the modulation scheme and number of subcarriers. For example, for QPSK modulation of the subcarrier, each subcarrier carries 2 bits, and thusfor transmission using 100 sub-carriers, the number of bits per symbol is 400.Modulation scheme: The modulation scheme is a display of data to the real (inphase) and imaginary (quadrature) constellation, also known as the IQ constellation.When you select a different modulation to determine the number of bits per symbolbecomes very easy. For instance when using 16 QAM (log2 (M) gives 4 bits persymbol)IFFT is used to transfer the signal to the time domain.

IFFT reduces the amountof computation by using the regularity of transactions in the IDFT. Using the algorithm of Radix-2.N-point IFFT requires only (N / 2) log2N complex multiplications.Guard: One of the most important advantages is OFDM it resistant to multipathdelay spread, and that input is achieved by dividing the stream into Ns subcarriersymbol duration times Ns is taken smaller, which reduces the relative delay spreadmultipath with respect to symbol time, by the same coefficient . Protection time isgiven for each character to eliminate interference between the carriers.

The compo21nent of one symbol, can not interfere with the next character. There is another problem, which is called Inter Carrier Interference (ICI). The presence of ICI means thatcarriers are no longer orthogonal. To eliminate ICI, OFDM symbol must be cyclicallyextended in the guard intervalTransmission channel .We consider the scattering of Rayleigh fading model.

Rayleigh statistical channel model for the representation of the effect of environment impact on multipath propagation , transmission symbols or radio . Rayleigh fading ismainly used only when there is no direct line of sight between transmitter and receiver. Thus, if s (T) is transmitted, the received symbol is given by:R(T) = s(t) * A(t) + η(t)(1.2)Where R (T) is distributed by means of a Rayleigh distribution function.Where n (r) is the additive white Gaussian noise (AWGN).ReceiverOFDM signal demodulation is performed in the same way. At the receiver, thefast Fourier transform is used for evaluating the amplitude and phase of each subcarrier .The first task performed in the receiver (in the simulation) is a cyclic prefix removal.

This procedure avoids interference among symbols (ISI). Then, data is transferred via serial-parallel converter and then passed to the FFT for converting the frequency domain. The signal is distorted, however, to restore the original signal in theOFDM system uses a channel estimation (ML-maximum likelihood) and interpolation, and the reverse process (including decoding) is performed to obtain the originaldata bits.MaximumLikehood- method makes it possible to take a decision on the minimumsignal for the difference between the received signal and dedicateddirect searching of all sub-channels and the possible signals.In LTE-Advanced technology MIMO 8x8 downlink (base station to mobile stations) and MIMO 4x4 uplink (mobile station to base station) have been added.22For this purpose, new transmission modes (TM, Transmission Mode) and a newcategory of mobile stations are introduced. New transmission modes differ from previously identified (Release 8 & 9) in the following aspects:The number of data streams (Layers), i.e.

how many different data streams maybe transmitted simultaneously; The use of different ports (antenna ports); maintainingof different signals pilots (CRS, DM-RS); various pre-coding .LTE-A technology provides support up to 8 transmit antennas at downlink datatransfer and use of improved structure of a reference signal. When uplink transmission provides support for up to 4 antennas.Fig.1.8— Simplified MIMO schemeTwo transport units (Transport Block, TB) can be transmitted in the downlink toa UE in one time.Each transport block may be encoded by its modulation codingscheme (MCS).

UE may transmit up to Two transport blocks simultaneously In theuplink.As with the downlink transmission, the transport blocks may be encoded by different MCS.LTE -A is considered a fourth-generation standard for mobile networks . Thischapter discussed the main characteristics of LTE -A standard methods of signalmodulation in the forward and reverse channels. Also, the principle of MIMO technology were discussed , allowing to transfer large amounts of data.232.

ПОСТРОЕНИЕ СЕТИ БАЗОВЫХ СТАНЦИЙ2.1 Характеристика района строительства системыСогласно заданию, проектируемая сеть должна обеспечивать услугой ШПДнаселение и субъектов экономики часть города Хабаровска, относящаяся к Индустриальному району. Данный район находится частично на стадии строительства. Застройка включает в себя здания высотой от 2 до 25 этажей. Расстояние между границами района в наиболее протяженном сечении составляет 2.8км. Общая площадь выбранного микрорайона составляет 2,65 кв.км. Рельефместности равнинный.

Карта выбранного района представлена на рис.2.1.Рис.2.1— Карта микрорайона «Строитель»Численность населения микрорайона «Строитель» составляет около 20 тысяч человек. Количество предприятий и организаций превышаетединиц.Основными крупными операторами мобильной связи в г. Хабаровске являются «Билайн» «Мегафон», «МТС» и. В качестве предприятия связи, наиболее24заинтересованного в строительстве сети LTE, рассматривается оператор «Мегафон». Этот оператор много лет предоставляет услуги сотовой связи и хорошозарекомендовал себя в предоставлении услуги беспроводного ШПД. По результатам аукциона компания «Мегафон» 11 февраля 2016 года выкупила в Хабаровском крае полосу частот 2570-2595 МГц [5].По нашей оценке, порядка 40% потенциальных пользователей будут пользоваться в микрорайоне «Строитель» услугой доступа к Интернету, предоставляемой компанией «Мегафон» (всего около 8 тысяч).