Summary on the theme of master's work

Content

Introduction

Needs of mobile users are growing so rapidly that existing networks, generation of 3G, which have been successfully rooted in the leaders of communication services can not keep up while modern broadband technologies can satisfy them.

LTE Technology is a broadband technology that supports flexible carrier bandwidth from 1.4 MHz to 20 MHz, works by using frequency – FDD (Frequency Division Duplex) and temporal – TDD (Time Division Duplex) duplexes. The aim is to create a mobile network with reliable radiocovery qualitatively new services, low latency and high bandwidth on existing networks via GSM.

1. Benefits of using LTE technology

LTE technology is a logical continuation and improvement of 3G networks. Technology can provide a dramatic surge in data transmission in modern mobile networks.

For example:

– GSM is a second generation communication network (2G). GSM routers can provide the transmission of information at the speed of 5,6–13 kbit/s. This standard is designed for the exchange of voice traffic. GPRS is a generation of 2,5 G (56–114 kbit/s), EDGE – generation(up to 473.6 kbit/s). 3G networks' opportunities allow the transmission of information at speeds up to 3.6 Mbit/s.

– When introducing LTE transmission rate can be ensured to 326.4 Mbit/s or higher than a base station for a user, in the reverse direction already is up to 172.8 Mbit/ s.

Opportunities which are provided by modern LTE equipment logically explain interest in them by the operators. The deployment of LTE– networks today is more profitable and expedient. The project is much more advantageous, for example, than the further deployment of third–generation networks, because LTE uses a frequency center better(has a lower signal delay and increased capacity).

Thanks to the introduction into the practice of innovative technology LTE, operators can significantly reduce operating and capital costs, reduce the total cost of network ownership, expanding the range of services that relate to the transmission of data via high–speed channels. This improvement is important also for the subscribers – in fact due to a significant increase in the speed of information transfer Can significantly improve the overall quality of services offered.
The possibility of using technology LTE:

– High–speed Internet access for laptops and netbooks.

– Possibilities of mobile TV and video calling for mobile phones.

– Users can participate in interactive games, quickly downloading satellite maps, view interactive video content with smartphones and communicators .

2. Technical details of the implementation

2.1 Frequency band

In contrast to other mobile standards LTE is not tied with a specific frequency band. Currently 3GPP developers allocated about 40 bands for which manufacturers produce standard LTE radioequipment. Here trapped both the frequencies currently used by other standards (e.g., 900, 1800 (GSM), 2100 (UMTS), 2500 (WiMAX), and "new", e.g. 700–800 MHz. Not all of the possible ranges will find wide distribution, especially as a large number of ranges is very difficult to implement in a subscriber's unit, and it is a problem for global roaming. Coverage area of one BS in LTE depends on the frequency range, and the lower it is, the greater is the distance signal can be transmitted.

Network deployment in low–frequency region of the spectrum is more attractive in terms of cost and better suited to cover areas with low population density(suburban and rural). In urban conditions cell radius can be from a few hundred meters to several kilometers. In densely populated areas, the use of high frequencies for LTE will require additional measures to improve indoor coverage. Thus, the most attractive are:

– 800 MHz – is allocated to LTE, – beneficial in terms of the cost of providing complete coverage; equipments produced by leading manufacturers;

– 2.5 GHz – is allocated to LTE, while ensuring profitable vessel in a hot spot; equipment is produced by all leading manufacturers.

– 1800 MHz – will be releasing by leasting reduce number of GSM–only phones and extend coverage 3G, good in terms of the balance between the network capacity and coverage [1].

Choosing the right range for the development of LTE is a rather difficult task. In the lower ranges, where everything is fine coated problem is to find a strip of sufficient width for LTE.V upper ranges usually are well frequency resourced, but the BS need to be putted every 400–500 meters, which is not economically viable.

2.2 Network architecture

LTE network architecture is designed to support packet–based traffic with a so–called "smooth" ("seamless", seamless) mobility minimum delay of packet delivery and high levels of quality service. Mobility as a function of the network is provided by two of her species: a discrete mobility (roaming ) and continuous mobility(handover). Since the LTE network should support roaming and handover procedures with all existing networks to LTE – subscribers (terminals) should be given widespread coverage of wireless broadband services. Packet transmission allows all services, including the transfer of the user voice traffic. Unlike most previous generations of networks, in which there is high enough diverse nature and hierarchy nodes(the so–called distributed network responsible), the architecture of LTE networks can be called "flat", as almost all networking occurs between two nodes: the base stationtion(BS), which is called in the technical specifications B-node (Node–B, eNB) and mobility control unit PCB Selling, usually involving W gateway (GW, Gateway), ie, there are combo boxes MME/GW.

BOOM works only with service information so–called signaling network so that IP-packets containing user information through it does not pass. The advantage of having such a separate alarm unit that bandwidth can grow independently for user traffic, and for service information. The main function is to control the PCB user terminals (PT), on hold, including the execution and redirect calls, authorization and authentication, roaming and handover, establishing service and custom channels, etc. Among all gateways separately allocated two : Serving Gateway OR (S–GW, Serving Gateway) and packet network gateway (P–GW, Packet Data Network Gateway), or, in short, batch gateway (PN). OR functions as a control unit of the local mobility, accepting and forwarding data packets belonging to the BS and served them to the PT. PN is the interface between the BS and the different set of external networks and also performs some of the functions of IP–networks such as address allocation, providing user–defined policies, routing, packet filtering, etc [2].

As in most third–generation networks, based on the principles of building the LTE network is necessary separation of the two aspects: the physical realization of individual network units and the formation of functional connections between them. In this task the physical implementation are solved on the basis of the concept of area (domain), and functional relationships are discussed in the framework of the layer (stratum). The primary division of the physical layer network architecture is the separation of the region of the user equipment (UED, User Equipment Domain) and the area of network infrastructure (ID, Infrastructure Domain). UE – a set of PT with different levels of functionality used by the network subscribers to access the LTE-services. At the same time as the user terminal may appear as real subscribers, using, for example, voice traffic services and impersonal apparatus for transmitting/receiving a specific network or user applications [3].

LTE has been allocated for dozens of different frequency bands, as well as two different systems designed duplex, ie, the simultaneous transmission of data in both forward and reverse channels.

More common (90% of total) network FDD (Frequency Division Duplex) – is the frequency separation at which the forward and reverse channel uses different frequency bands: that is, the transfer takes place at a single frequency, and reception – on the other. The advantage of this technology lies in the symmetry of the link: the data transmission rate of both the subscriber and the subscriber can be equally high. However, it is also a disadvantage: the majority of the subscribers to download data from the main network, and the network is not so great speed in the reverse channel it is not needed. At the same time to build a network need to find FDD paired frequencies, and much of the scarce frequency resources will be used inefficiently, ie, idle.

Network TDD (Time Division Duplex) using time division and reception and transmission are performed at the same frequencies, but alternately transfer session is divided into timeslots, and some of them are used for transmission and the other for receiving. Time slot duration is measured in milliseconds, so from the viewpoint of the subscriber data transmission appears simultaneously. The main advantage of TDD is that the operator can control the ratio of timeslots allocated for reception and transmission, and thus make full use of the frequency resource. At the same time for comparable data rates requires twice less bandwidth, and does not need to search for paired frequencies.

In order to expand the network from the number of resource blocks 25 LTE (5 MHz) at the operator 5 MHz FDD need for Uplink, and 5 MHz for Downlink (total 10 MHz), whereas when it is only necessary TDD 5 MHz. This allows the operator to save the frequency resource (and consequently money for a permit).
FDD performance is slightly better, but not always possible to have two pairs of the channel. Therefore, in the case of unpaired frequency LTE TDD is the most suitable radio access technology. Today, most operators have launched LTE network in the standard FDD, TDD but interest is growing. Of 213 commercially launched LTE networks in the world 21 – it's LTE TDD, and 10 networks applied jointly use FDD and TDD.

Currently, you can note the growing interest in LTE TDD technology in the world – producers are ready to provide ready–made solutions and the largest operators or tested or are already deploying commercial networks. Technology has a number of significant differences in comparison with LTE FDD, associated with the use of the spectrum and can be used both independently and as a complementary technology to LTE FDD. Manufacturers say the potential market that is oriented technology – it is quite high, and the growing needs of customers in the high–speed data require the use of new frequency resources. The general frequency resource, under standardized LTE TDD, is significant and is 849 MHz against 2h427 MHz for LTE FDD.

Equipment radiopodsistem two identical technologies by 90% and only 10% at the level of different protocols to ensure the radio part of, the support network is the same for both unified standards. In the LTE TDD technology available the same functionality as in LTE FDD, and also supports full interoperability with networks 2G/3G – roaming, handover, load balancing and other functions. All this suggests the LTE TDD industry maturity and its merchantability also prove it implemented projects for commercial operators such as Japan's Softbank, STC and Mobili in Saudi Arabia, Aero2 in Poland and elsewhere.

Solutions based on LTE TDD can be used in several ways. First, just as mobile broadband technology to provide data services. Secondly, for the organization of the transport network (Mobile Backhaul) [4].

3. LTE protocols

In its structure, the radio access network RAN – Radio Access Network – looks like the network UTRAN UMTS, or eUTRAN, but it has one addition: two-way radio antenna base stations interconnected by a specific protocol X2, which unites them in a cellular network – Mesh Network – and enables base stations communicate with each other directly without using this controller RNC – Radio Network Controller. In addition, the relationship of base stations with mobile device management system MME – Mobility Management Entity – and service gateways S-GW – Serving Gateway – is carried out by "many to many", which allows you to get a great rate due to slight delays.

Network Topology LTE

Figure 1 – Network Topology LTE.

LTE and WiMAX standards are close enough to each other. They both use encryption technology and OFDM transmission system MIMO. And in fact, and in another standard applied FDD and TDD– duplekirovanie with bandwidth up to 20 MHz. And, both of the communication systems are used as its protocol IP. Accordingly, in reality, the two technologies are used equally well its frequency range and provide comparable data transmission speed internet access. But, of course, there are also some differences. One of these differences is a much simpler network infrastructure WiMAX, and therefore more reliable and technically.
This standard is ensured by its simplicity designed exclusively for data transmission. On the other hand, the "complexity"LTE needed to maintain compatibility with previous generation standards – GSM and 3G. And this we will work with you definitely need.
Scheduling radio resources in WiMAX technology produced Frequency Diversity Scheduling, according to which subcarriers provides subscribers are distributed throughout the spectrum channel. It is necessary to randomize the effect of averaging and frequency-selective fading wideband channel on.

In LTE networks used different technology to eliminate the frequency-selective fading . It is called frequency-selective scheduling resources – Frequency Selective Scheduling. Thus for each subscriber station for each frequency block and carrier are channel quality indicators CQI – Channel Quality Indicator [5].

Another very important issue related to planning networks use mass – reusability factor frequencies. His role – show efficient use of available radio frequency bands for each base station separately. The basic structure of reusability frequency band of WiMAX is 3 frequency channels. When using a three–sector configuration of sites(base stations specified frequency range), each of the sectors is implemented one of 3 channels of the frequency. The coefficient is equal to the frequency reusability 3rd. In other words, at each point of space there are only a third radio frequency band. Job network LTE (4G) is produced by a factor of reusability frequency equal to 1. That is, it turns out that all LTE base stations operate on a single carrier. Intersystem interference in such a system can be reduced to a minimum thanks to the frequency– selective scheduling, flexible frequency plan and coordinate the interference between the individual cells. Subscribers in the center of each cell can be given the resources of the entire band of free channels, and users at the edges of cells are available only from the frequency sub–bands. The above features of LTE and WiMAX have a big impact on one of their main characteristics – degree coverage . Based on this parameter is determined by the required number of base stations for quality cover a specific territory. Accordingly, it directly affects the final cost of the construction of networks of LTE [6].

According to calculations, the LTE network is able to provide better coverage for the same number of base stations, which is an advantage for all mobile operators.

4. Job prospects

In this work a model was created network format LTE, in the simulation environment NS2. Opting for NS2 was made due to the fact that the simulator is free and suited for modeling a wireless network at the system level, so that the proposed model is suitable for simulating a real network LTE/SAE, or any other network. Moreover, NS– 2 is one of the most popular in academic circles because of its open source, and many other advantages.

Wireless models are essentially composed of MobileNode, with support for additional features that allow you to simulate multi–hop ad hoc networks, wireless LANs, etc. Block diagram is presented in MobileNode figure 2.

Block diagram MobileNode.

Figure 2 – Block diagram MobileNode.

Next, consider the individual components:

Link Layer(data link layer) contains a module ARP, who decides to convert IP to MAC addresses. All outgoing packets are sent to LL from the agent routing (RTagent). Next LL transmits packets in the queue interface (ifq). For incoming packets, the MAC layer transmits them to the LL, which is further transmitted node_entry_ point. Class LL described in ~ ns/ll. {Cc, h} and ~ ns/tcl/ lan/ns–ll.tcl.

Address Resolution Protocol module receives requests from the link layer (LL). If ARP has the hardware address of the destination, it writes it to the MAC header of the packet. Otherwise, it sends an ARP request packet, and temporarily caches . For each unknown hardware (MAC) address of the recipient with a buffer for 1 pack. If you come to the new packages, they are sent to the ARP, and the old package in the buffer is lost. When the hardware address of the next hop'a package becomes known, the packet is transmitted to the queue. ARPTable class is described in ~ ns/arp. {Cc, h} and ~ ns/tcl/lib/ns–mobilenode.tcl.

Interface Queue (IFq). PriQueue class is implemented as a priority queue, which gives priority to routing protocol packets, inserting them into the head of the queue. It supports the filter for all packets in the queue and removes packets with the specified destination. See ~ ns/priqueue. {Cc, h}.

Network Interface – a hardware interface used for accessing mobilenod'om channel. This interface is in accordance with the collisions and radio propagation model receives packets that are transmitted by another node. See ~ ns/phy. {Cc.h} and ~ ns /wireless–phy. {Cc, h}.

Radio Propagation Model – uses 1/r2 attenuation at close distances and 1/r4 at large distances. See ~ ns/tworayground. {Cc, h}.

Was chosen for modeling the topology of a primitive that allows the possible scenarios display data from the base station to the user and vice versa. The network topology is shown in Figure 3.

Figure - 3 (GIF, repetition cycle 1, 10 shots, 320h205, 150 KB) Modeling network LTE.

Figure – 3 (GIF, repetition cycle 1, 10 shots, 320h205, 150 KB) Modeling network LTE.

Findings

Established model will perform a detailed analysis of the physical characteristics:

• definition of the minimum necessary, but meeting the needs of the transmission, processing and storage equipment;

• assessment of an adequate supply of equipment performance, providing a possible increase in production requirements;

• Multiple selection of equipment to fit your needs and prospects for development on the basis of the criterion value of the equipment;

• checking the network, composed of recommended equipment.

When writing this aftoreferata master's work is not yet complete. Final completion: December 2014. Complete text of the materials can be obtained from the author or his manager after that date.

List of sources

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