Пояснительная записка Корнет Н.А (1208183), страница 2
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The following frequencies arepermissible: 1.4, 3, 5, 10, 15 and 20 MHz. LTE uses OFDMA (Orthogonal Frequency-Division Multiple Access) in downlink and multiple access technique with onesubcarrier SC-FDMA(single carrier FDMA) in uplink as a multiple access system.Despite the fact that the SC-FDMA complicates the design of the transmitting andreceiving unit (by adding the main generator FDMA, such as Fourier transformation),3GPP standard (was decided to use) uses it in order to reduce the average transmission power (PAPR- Peak to Average Ratio), thereby saving mobile energy.
It plays aprimary role in the choice of access technologies.The entire spectrum is partitioned into subcarriers that are orthogonal to each other, using the OFDMA technology. The number of subcarriers may be 72, 180, 300,600, 900 or 1200, depending on the width of each subcarrier channel. For each subcarrier different modulation types is available , for example: QPSK, 16QAM,64QAM.The organization of multiple access is possible if one part of subcarriers inthe frame is determined to one user, the second part - a second user, etc.10The main advantage of OFDMA technology is that it reduces the signal receivedat the negative effects caused by multipath propagation.
However, this technology also has some inherent disadvantages. This technology is sensitive to the frequency ofsynchronization. In addition, the OFDMA signal obtained is characterized by highaverage power transmitting PAPR (Peak to Average Ratio).LTE standard uses MIMO transmission technology (Multiple Input MultipleOutput), which increases the peak data rate and spectral efficiency value.Previously, the main way to improve the performance was the development ofsignal-code constructions and error-correcting coding techniques.
MIMO does notchange the frequency band, power of signals, and only by spatial increasing thenumber of antennas complexity of a signal processing method , is able to increasethe capacity and robustness of communication systems in times.The data transfer rate is not increased when the antennas transmit the same data.When antennas transmit different data streams, there is an increase data rate.
Maximum downlink is supported by the scheme 4x4 (4 receiving and transmitting antennas 4). In this case, the data rate can be increased up to 4 times (in fact slightly lessdue to the increased number of pilot signals).Algorithms adopting MIMO solutions are quite difficult, but they are built on acomprehensive knowledge of the transfer function on the receiving side. But how toimplement it, if at a certain frequency we transmit information, and it is a randomvariable? An effective solution is to add in the signal structure other signals , the parameters of which are known and they help produce a signal estimate.When the spectral width of the channel is 20 MHz maximum data transfer rate is300 Mbit / s in the downlink and 170 Mbit / s upstream.The requirements for LTE spectral efficiency values given as 5 bits / s / Hz forthe downlink channel and 2.5 bits / s / Hz for the uplink (this is equivalent to a capacity of 100 Mbit / s and 50 Mbit / s).111.2 LTE-Advanced .General informationThe International Telecommunication Union has recognized LTE-Advanced andWiMAX as a standard for the fourth-generation communication in 2012 at the Geneva Conference.LTE-Advanced provides the use of a wide range of frequencies, Carrier Aggregation (CA) spectrum is possible complication (?) that means that antenna MIMOtransmission technology supports LTE Signal relay function, as well as the deployment of heterogeneous networks (HetNet).Yota was the First in the world, who launched LTE-Advanced mobile communication technology in a commercial network.
The launch was attended by 11 BS.Megafon launched network within the LTE-Advanced Moscow's Garden Ringwith a maximum speed (downlink 300 Mbit / s, 50 Mbit / s uplink) in 2014.1.3 Main characteristics of the LTE Advanced standard (Rel.10)Network type is called E-UTRAN - Evolved Universal Terrestrial Radio AccessNetwork (developing universal terrestrial radio access network). The main parameters of LTE Advanced (Rel.10) standard are shown below.Multiple access technology:Direct channel (Downlink - DL) - OFDMA;The return channel (Uplink - UL) - SC-FDMA;Operating frequency: 450 MHz; 700 MHz; 800 MHz; 1800 MHz; 2.1 GHz; 2.4 2.5 GHz; 2.6 - 2.7 GHz. In addition to these frequency bands the following bands areadded :450-470 MHz;698-862 MHz;790-862 MHz;2.3-2.4 GHz;3.4-4.2 GHz;4.44.99 GHz .Bit rate:Direct channel (DL) MIMO 4TX × 4RX: 1 Gbit / s;Reverse channel (UL): 500 Mbit / s.The width of the radio channel bandwidth up to 100 MHz.Cell radius of 5 - 30 km.12The capacity of the cell (number of subscribers):More than 200 users in a bandwidth of 5 MHz;More than 400 users at more than 5 MHz band.In LTE-Advanced MIMO can support:Direct channel (DL): 8TX × 8RX;The return channel (UL): 4TX × 4RX.The value of the delay (latency): 10ms.For the downlink channel spectral efficiency is 3.7 bits / s / Hz / sector (with 4x4configuration), and uplink - 2.0 bits / s / Hz / sector (with 1x4 configuration).Modulation Types:Direct channel (DL) :, QPSK, 16 QAM, 64 QAM.Reverse channel (UL): QPSK, 16 QAM.Duplex channel separation: FDD (Frequency Division Duplex) and TDD (TimeDivision Duplex).1.4.Stuctural scheme of the LTE Advanced network (Rel.10)As part of the LTE Advanced technology, the new network infrastructure calledSAE (System Architecture Evolution) has been proposed for the organization of LTEnetworks.SAE core network is fully built on IP protocol.
Access to it can be done via thesecond radio access network and third-generation (UTRAN / GERAN), through not3GPP network(WiMAX, Wi-Fi), as well as through a wired network (ADSL +,FTTH).SAE describes the distribution of the necessary functions to logical nodes and therequired interfaces between the ties. According to figure 1, the architecture of the system is divided into two parts: the first radio access network (Radio access network RAN) The second one is core network.13Below (see.
Figure 1) a simplified diagram of SAE architecture within the LTEnetwork is shown.Figure 1.1— The simplified diagram of SAEFigure 1.2 - Architecture SAE within the LTE networkThe gateway can perform the functions of packet data network (PDN) and servinggateway (SWG), it is able to work on one or both networks. Functional mobilitymanagement node (MME) is separated from the gateway in order to facilitate the deployment of the network, to become an independent technology and for the mostflexible scalability.14PDN- provides IP-stable switching point for all users regardless of mobility.MME - Mobility Management Module (Mobility Management Entity) providesstorage of service subscriber information and manage this information. This is themain control element in LTE network.
It carries only control functions, and does notwork with user data. It has a direct link with the UE (user equipment area).PCRF (Node billing customers accounts - Policy and Charging Rules Function):Policy Function (policy management) can also be divided into two functions: a gateway control (gating control) and quality control.Gating control is error free detection of events such as start of the work, changesettings, the completion of services, etc.Quality management involves continuous monitoring and maintenance of specified subscriber quality of performance parameters of Service (QoS).HLR / HSS (Home Subscriber Server - server network subscriber data) is a largedata base used for the storing subscriber data.HLR / HSS is used to store the following information:- User IDs, numbers and address information;- Safety subscribers data: information for control the network access, authentication and authorization;- Information about the location of the subscriber at the gateway level, i.e even ifthe user leaves the current LTE network operator, information about the network willbe saved in HSS .
The subscribe used this network in order to receive incoming call;- Information about the subscriber's profile.- It generates data for the purpose of encryption procedures, authentication, etc.Therefore, LTE is a network in which the base station (eNodeB) are connected directly to the enhanced packet core (EPC). From the user's side the connection is established with the serving gateway (SGW), from the control side - with mobility support system (MME).15In 3GPP Relase 10 appears relay function that allows mobile terminals to communicate with the network through a relay node which is connected wirelessly to thedonor node eNodeB, using the radio access technology LTE and LTE spectrum asshown in Figure 1.3.
From the viewpoint of the terminal relay node appears "conventional" base station, this means that the previous equipment may be used as repeaters. The extension LTE network becomes possible.Area of radio access network is divided into two levels: the level of the radionetwork (RNL, Radio Network Layer) and the level of the transport network (TNL,Transport Network Layer). Interaction incoming to the radio access network is basedon X2-interface (see. Figure 1.3). Furthermore, there is a backhaul between base stations and a core network via a mobility management unit (MMU: S1 - MM-interface)or the service node (SN).
S1-interface supports multiple relationships between a setof BS and MMU.Fig.1.3. Transport Network Layer with the Radio Network layerThere are various interfaces through which the connection between the networkelements is carried out.16X2-communication interface BS.S1-coupling interface E-UTRAN and MME. This interface transmits control data.S1-U - coupling interface between E-UTRAN and the SAE. The user’s data aretransmitted via S1-US2 - interface for managing the connection between the PDN-Gateway and theaccess networks are not designed 3GPP.S3 - interface that provides a direct connection to the SGSN and MME. It servesto control data transfer for mobility between LTE and 2G / 3G networks.S4 - the interface that connects SAE and SGSN.
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