4th GENERATION OF WIRELESS NETWORKS (LTE)

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4G(also known as Beyond 3G), an abbreviation for Fourth-Generation, is a term
used to describe the next complete evolution in wireless communications.
A 4G system will be able to provide a comprehensive IP solution where voice, data and
streamed multimedia can be given to users on an "Anytime, Anywhere" basis, and
at higher data rates than previous generations.

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4th GENERATION OF WIRELESS NETWORKS (LTE)

  1. 1. Table of Contents Abbreviation…………………………………………………………………………………….ii List of figures……………………………………………………………………………………v List of Tables…………………………………………………………………………………….vi I. GENERAL INTRODUCTION... ..................................................................................................... 1 II. Chapter 01: Wireless Evolution towards 4th G .................................................................................. 2 INTRODUCTION…………………………………………………………………………………2 WIRELESS EVOLUTION………………………………………………………………...............3 1. 2. III. Chapter 02: 4th Generation "LTE"……………………………………………………………………17 1. 2. 3. Introduction………………………………………………………………………………….17 Features and capabilities………………………………………………………………….….20 4G (LTE) the Technologies and Techniques………………………………………..……….21 3.A.LTE: The Downlink: ......................................................................................................... 21 1.OFDMA ............................................................................................................................ 21 2.OFDMA Parameterization ................................................................................................. 23 3.Downlink data transmission ............................................................................................... 27 4.Downlink reference signal structure and cell search ........................................................... 28 5.Downlink Hybrid ARQ (Automatic Repeat Request) ......................................................... 31 3.B. LTE: The Uplink: ............................................................................................................. 32 1.SC-FDMA ........................................................................................................................ 32 2.SC-FDMA parameterization ............................................................................................. 33 3.Uplink Data transmission .................................................................................................. 35 4.Uplink reference signal structure....................................................................................... 38 5.Uplink Hybrid ARQ (Automatic Repeat Request) ............................................................. 39 3.C. LTE: MIMO Concepts .................................................................................................... 40 3.D. LTE Protocol Architecture……………………………………………………………..…45 3.E. Evolution Of Applications And Services………………………………………………….47 4. Conclusion…………………………………………………………………………………51 IV. GENERAL CONCLUSION .......................................................................................................... 52 V. REFERENCES……………………………………………………………………………………….53 i
  2. 2. ABBREVIATION 4G ACK ARQ BCCH BCH CAPEX CCCH CCDF CCO CDD CP C-plane CQI CRC C-RNTI CS DCCH DCI DFT DL DL-SCH DRS DRX DTCH DTX DVB DwPTS eNB EDGE EPC E-UTRA E-UTRAN FDD FFT GERAN GP GSM HARQ HRPD HSDPA HSPA HSUPA IFFT IP LCID LTE MAC 4th Generation Acknowledgement Automatic Repeat Request Broadcast Control Channel Broadcast Channel Capital Expenditures Common Control Channel Complementary Cumulative Density Function Cell Change Order Cyclic Delay Diversity Cyclic Prefix Control Plane Channel Quality Indicator Cyclic Redundancy Check Cell Radio Network Temporary Identifier Circuit Switched Dedicated Control Channel Downlink Control Information Discrete Fourier Transform Downlink Downlink Shared Channel Demodulation Reference Signal Discontinuous Reception Dedicated Traffic Channel Discontinuous Transmission Digital Video Broadcast Downlink Pilot Timeslot E-UTRAN NodeB Enhanced Data Rates for GSM Evolution Evolved Packet Core Evolved UMTS Terrestrial Radio Access Evolved UMTS Terrestrial Radio Access Network Frequency Division Duplex Fast Fourier Transform GSM EDGE Radio Access Network Guard Period Global System for Mobile communication Hybrid Automatic Repeat Request High Rate Packet Data High Speed Downlink Packet Access High Speed Packet Access High Speed Uplink Packet Access Inverse Fast Fourier Transformation Internet Protocol Logical channel identifier Long Term Evolution Medium Access Control Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila ii
  3. 3. MBMS MIMO MME MU-MIMO NACK NAS OFDM OFDMA OPEX PAPR PBCH PCCH PCFICH PCH PDCCH PDCP PDN PDSCH PDU PHICH P-GW PHY PMI PRACH PS PUCCH PUSCH QAM QoS QPSK RACH RAN RA-RNTI RAT RB RF RI RIV RLC ROHC RRC RRM RTT S1 SAE SC-FDMA SDMA SDU SFBC Multimedia Broadcast Multicast Service Multiple Input Multiple Output Mobility Management Entity Multi User MIMO Negative Acknowledgement Non Access Stratum Orthogonal Frequency Division Multiplexing Orthogonal Frequency Division Multiple Access Operational Expenditures Peak-to-Average Power Ratio Physical Broadcast Channel Paging Control Channel Physical Control Format Indicator Channel Paging Channel Physical Downlink Control Channel Packet Data Convergence Protocol Packet Data Network Physical Downlink Shared Channel Protocol Data Unit Physical Hybrid ARQ Indicator Channel PDN Gateway Physical Layer Precoding Matrix Indicator Physical Random Access Channel Packet Switched Physical Uplink Control Channel Physical Uplink Shared Channel Quadrature Amplitude Modulation Quality of Service Quadrature Phase Shift Keying Random Access Channel Radio Access Network Random Access Radio Network Temporary Identifier Radio Access Technology Radio Bearer Radio Frequency Rank Indicator Resource Indication Value Radio Link Control Robust Header Compression Radio Resource Control Radio Resource Management Radio Transmission Technology Interface between eNB and EPC System Architecture Evolution Single Carrier – Frequency Division Multiple Access Spatial Division Multiple Access Service Data Unit Space Frequency Block Coding Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila iii
  4. 4. SISO S-GW SR SRS SU-MIMO TDD TD-SCDMA TPC TS TTI UCI UE UL UL-SCH UMTS U-plane UpPTS UTRA UTRAN VoIP WCDMA W LAN X2 Single Input Single Output Serving Gateway Scheduling Request Sounding Reference Signal Single User MIMO Time Division Duplex Time Division-Synchronous Code Division Multiple Access Transmit Power Control Technical Specification Transmission Time Interval Uplink Control Information User Equipment Uplink Uplink Shared Channel Universal Mobile Telecommunications System User plane Uplink Pilot Timeslot UMTS Terrestrial Radio Access UMTS Terrestrial Radio Access Network Voice over IP Wideband Code Division Multiple Access Wireless Local Area Network Interface between eNBs Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila iv
  5. 5. List of Figures Figure 1 : IMTS brief case phone from the 1970‟s ............................................................. 3 Figure 2 : 2G Wireless Infrastructures ................................................................................ 5 Figure 3 : Mobile network architecture .............................................................................. 6 Figure 4 : 2.5 G Wireless Infrastructures ............................................................................ 7 Figure 5 : Path to 3G Wireless infrastructure ..................................................................... 8 Figure 6 : 3G Architecture ................................................................................................ 10 Figure 7 : Speed of 3G Networks ..................................................................................... 11 Figure 8 : Evolution in Data Transmission Rate ............................................................... 12 Figure 9 : Requirements for 4G system ............................................................................ 13 Figure 10 : 4G system ....................................................................................................... 14 Figure 11 : Frequency-time representation of an OFDM Signal ...................................... 22 Figure 12 : OFDM useful symbol generation using an IFFT ........................................... 22 Figure 13 : OFDM Signal Generation Chain .................................................................... 23 Figure 14 : Frame structure type 1 .................................................................................... 23 Figure 15 : Frame structure type 2 (for 5ms switch-point periodicity) ............................. 24 Figure 16: Downlink Resource grid .................................................................................. 26 Figure 17 : OFDM A time-frequency multiplexing (example for normal cyclic prefix) . 28 Figure 18 : Downlink reference signal structure (normal cyclic prefix) .......................... 29 Figure 19 : Primary/secondary synchronization signal and PBCH structure (frame structure type 1/FDD, normal cyclic prefix) ..................................................................... 30 Figure 20 : Primary/secondary synchronization signal and PBCH structure (frame structure type2/TDD, normal cyclic prefix)...................................................................... 30 Figure 21: ACK/NACK bundling in TD-LTE .................................................................. 31 Figure 22 : Block diagram of DFT-s-OFDM (localized transmission) ............................ 33 Figure 23 : Uplink resource grid ....................................................................................... 34 Figure 24 : Intra-subframe hopping, Type 1 ..................................................................... 37 Figure 25 : Intra-subframe hopping, Type 1 (blue, UE1) and Type 2 (green, UE3) ........ 38 Figure 26 : PHICH principle ............................................................................................. 40 Figure 27 : Spatial multiplexing (simplified).................................................................... 41 Figure 28: Transmit diversity (SFBC) principle ............................................................... 44 Figure 29 : Architecture of LTE radio access (E-UTRAN) and core network (EPC) ...... 45 Figure 30 : Link layer structure for the downlink ............................................................. 47 Figure 31 : Mobile applications with technical requirements and growth drivers ........... 48 Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila v
  6. 6. List of Tables Table 1: Data rate and spectrum efficiency requirements defined for LTE ..................... 20 Table 2: Uplink-Downlink configurations for LTE TDD ................................................. 24 Table 3 : Special Sub frame configurations in TD-LTE ................................................... 25 Table 4: Number of resource blocks for different LTE bandwidths (FDD and TDD) ..... 26 Table 5 : Downlink frame structure parameterization (FDD and TDD) .......................... 27 Table 6: Number of HARQ processes in TD-LTE (Downlink) ....................................... 31 Table 7: Uplink frame structure parameterization (FDD and TDD) ................................ 34 Table 8 : Possible RB allocation for uplink transmission ................................................. 35 Table 9 : Contents of DCI format 0 carried on PDCCH ................................................... 36 Table 10 : Transmission Modes in LTE as of 3GPP Release 8 ........................................ 42 Table 11 : Precoding codebook for 2 transmit antenna case ............................................ 43 Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila vi
  7. 7. I. GENERAL INTRODUCTION The objective of the current communication systems is the distribution and transfer of the everyday augmented massive volumes of data presented in many forms and types of Multimedia applications such as web browsing, video and audio streaming and data transfer wirelessly at high Broadband speed. Ensuring the availability and the proper functioning of these services requires the transmission of signals on the mobileradio channel, and regardless of the position and mobility of the user. Crossing the channel, these signals will be exposed to the phenomena of multipath and frequency shift by the Doppler Effect and many other unpredicted phenomenons altering and changing the information totally and beyond recognition. They provide distortion and induce degradation of the quality of communication and therefore limited and low Broadband speed and this issue led to many handicaps in the world of communication rendering it the most invested and based on research domain by many R&D companies and facilities in the present time and the future. Transmission techniques were created and developed by many pioneers in the field of telecommunications and were designed primarily to address these issues and problems. And one of the current time techniques and methods lead to the wireless revolutionary telecommunication system LTE based on the 4th generation of mobile and wireless communication and known also as beyond 3G. Our goal in this project is to introduce this revolutionary technology, and it‟s current impacts and future one‟s on human kind, and to do so many chapters were set and put on action to give you a proper introduction in a fairly presented dissertation. The dissertation is structured as follows.in the first chapter a brief introduction to the world of telecommunication in the mobile and wireless communication systems. Next, we introduce the previous technologies to the 4th generation (LTE), from the most primitive way of telecommunication till evolved Second Generation, next to Third Generation. Thereafter the evolution towards Fourth Generation is described in the second chapter with the Release 8 (LTE). The most important features of this release are explained in the corresponding subsections as well as the improvements in the throughput, the specifications and the modifications regarding previous releases. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 1
  8. 8. th Chapter 01: Wireless Evolution towards 4 1. G INTRODUCTION This paper discusses the challenge of evolving the core network of today‟s 2G and 3G networks to enable the unprecedented growth in voice and data expected with the migration to 4G wireless networks. The introduction of packet core infrastructure into digital wireless networks offers both challenges and opportunities for wireless service providers and its users. Despite the economic situation and recent world events, the basic drivers of growth in mobile computing are as strong as ever. In fact, telecommuting and decentralized workforces are options many companies are looking at increasingly as they reevaluate their physical security vulnerabilities and develop risk management plans. Mobile devices have become significantly more powerful, and in many cases smaller and lighter versions are available for handheld. Storage and processor speeds have advanced as expected. While 3G haven‟t quite been implemented totally, designers are already thinking about the deployment of 4G technologies across the Globe. The hope once envisioned for 3G as a true broadband service has all but dwindled away. It is apparent that 3G systems, while maintaining the possible 2-Mbps data rate in the standard, will realistically achieve 384-kbps rates. To achieve the goals of true broadband cellular service, the systems have to make the leap to a fourth-generation (4G) network. This is not merely a numbers game. 4G is intended to provide high speed, high capacity, low cost per bit, IP based services. The goal is to have data rates up to 20 Mbps, even when used in such scenarios as a vehicle traveling 200 kilometers per hour. New design techniques, however, are needed to make this happen, in terms of achieving 4G performance at a desired target of onetenth the cost of 3G. That‟s the goal of 4G. In short, Fourth Generation (4G) mobile devices and services will transform wireless communications into on-line, real-time connectivity. 4G wireless technologies will allow an individual to have immediate access to location-specific services that offer information on demand at an amazingly high speed and low cost. Welcome to the world of amazing realities of an amazingly high-speed data communication and mobile technology at a very low cost. That‟s The 4th G. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 2
  9. 9. th Chapter 01: Wireless Evolution towards 4 2. G WIRELESS EVOLUTION A. First generation In the MTS/IMTS world, if a user travelled outside the coverage area of a base station, any ongoing call dropped and would have to be re-established when the user reentered system coverage area. In the cellular world, users had smooth and relatively seamless mobility over multiple cells. A major underlying success factor for cellular and its seamless mobility control technique was the availability of the microprocessor, which provided sophisticated, intelligent control at both the mobile and network. In 1983, the first commercial cellular system, the Advanced Mobile Phone Service (AMPS) was deployed in the Chicago area. AMPS is typically referred to as 1st Generation Cellular. In addition to aggressive spatial frequency reuse and instantaneous mobility management techniques, regulators in the United States provided AMPS with a substantial quantity of radio spectrum. Instead of 8 or 16 channels per metropolitan area, AMPS now had 666 channels available which provided a capacity increase of over a million times in large metropolitan areas. AMPS was still FM in the beginning, but now many more phone numbers were available and adoption was rapid throughout the 1980‟s and early 1990‟s. Similar technologies were developed and deployed around the globe, e.g. the Nordic Mobile Telephone Service (NMT) in 1981, Total Access Communication System (TACS) and Extended TACS (ETACS) in Europe. Figure 1 : IMTS brief case phone from the 1970‟s During the years 1983 through about 1986, cellular mobile equipment was still expensive. A typical automotive installation brought a fixed cost of $2,000 to $4000 US Dollars plus the monthly subscription fees to the mobile operator. Incremental costs of making and receiving calls was on top of the cost of equipment and service. Therefore, Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 3
  10. 10. th Chapter 01: Wireless Evolution towards 4 G even after the introduction of the AMPS cellular system, the primary market segment for mobile telephony was still largely commercial users. But with the availability of equipment and phone numbers, there was an element of high-end personal users entering the cellular user community as well. Throughout the 1980‟s and 1990‟s, the learning curve brought down the cost of manufacturing equipment (Freeman, 1997). With lower costs came lower prices, and with lower prices came greater demand. By the early 1990‟s, most middle class adults owned mobile telephone equipment of some kind. B. Second Generation (2G) The second generation of digital mobile phones appeared about ten years later to First Generation mobile phones, along with the first digital mobile networks. During the second generation, the mobile telecommunications industry experienced exponential growth both in terms of subscribers as well as new types of value -added services. Mobile phones are rapidly becoming the preferred means of personal communication, creating the world's largest consumer electronics industry. This way the telecommunication industry experienced for the first time the growth and profits of mobile telecommunication with advancement of technology. This prompted them to build more powerful communication means. The second generation (2G) of the wireless mobile network was based on lowband digital data signaling. The most popular 2G wireless technology is known as Global Systems for Mobile Communications (GSM). GSM systems, first implemented in 1991, are now operating in about 140 countries and territories around the world. An estimated 248 plus million users now operate over GSM systems. GSM technology is a combination of Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA). The first GSM systems used a 25MHz frequency spectrum in the 900MHz band. FDMA is used to divide the available 25MHz of bandwidth into 124 carrier frequencies of 200 kHz each. Each frequency is then divided using a TDMA scheme into eight timeslots. The use of separate timeslots for transmission and reception simplifies the electronics in the mobile units. Today, GSM systems operate in the 900MHz and 1.8 GHz bands throughout the world with the exception of the Americas where they operate in the 1.9 GHz band. In addition to GSM, a similar technology, called Personal Digital Communications (PDC), using TDMA -based technology, emerged in Japan. Since then, several other TDMA-based systems have been deployed worldwide and serve an estimated 89 million people worldwide. While GSM technology was developed in Europe, Code Division Multiple Access (CDMA) technology was developed in North America. CDMA uses spread spectrum technology to break up speech into small, digitized segments and encodes them to identify each call. CDMA systems have been Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 4
  11. 11. th Chapter 01: Wireless Evolution towards 4 G implemented worldwide in about 30 countries and serve an estimated 44 million subscribers. Figure 2 : 2G Wireless Infrastructures While GSM and other TDMA-based systems have become the dominant 2G wireless technologies, CDMA technology is recognized as providing clearer voice quality with less background noise, fewer dropped calls, enhanced security, greater reliability and greater network capacity. The Second Generation (2G) wireless networks mentioned above are also mostly based on circuit-switched technology. 2G wireless networks are digital and expand the range of applications to more advanced voice services, such as Called Line Identification. 2G wireless technology can handle some data capabilities such as fax and short message service at the data rate of up to 9.6 kbps, but it is not suitable for web browsing and multimedia applications. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 5
  12. 12. th Chapter 01: Wireless Evolution towards 4 G Figure 3 : Mobile network architecture What improvements were needed? Fundamentally, wireless users wanted even more from their mobile sets:       Email and fast internet access Synchronization of mobile personal management tools with popular personal management software such as Microsoft Outlook, Lotus Organizer or Symantec ACT! Location-based services such as navigation and mobile yellow pages Robust "buddy" features such as messaging Video Global roaming, etc. To meet these demands, network operators and wireless equipment manufacturers alike were turning toward a third generation (3G) of wireless systems that deliver higher data rates based on packet transmission and new modulation formats. But the path toward 3G, though evolving, was far from clear. In fact, there are many parallel paths, and at least one, probably two, generations of transitional technologies. A first step in realizing the benefits associated with a packet core is to understand that voice gateways can play a crucial role. Packet media gateways are part of a new generation of switching technology that enables the integration of wireless (2G/2.5G/3G), fixed IP, PSTN and IN-based services. There are three key elements to this next-generation switching architecture: core IP/ATM switches/routers, media gateways in which wireless is just another access method, and call servers and application platforms. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 6
  13. 13. th Chapter 01: Wireless Evolution towards 4 G C. Second Generation (2G+/2.5) Wireless Networks As stated in a previous section, the virtual explosion of Internet usage has had a tremendous impact on the demand for advanced wireless data communication services. However, the effective data rate of 2G circuit -switched wireless systems is relatively slow -- too slow for today's Internet. As a result, GSM, PDC and other TDMA based mobile system providers and carriers developed 2G+ technology which was packet-based and increases the data communication speeds to as high as 384kbps. These 2G+ systems are based on the following technologies: High Speed CircuitSwitched Data (HSCSD), General Packet Radio Service (GPRS) and Enhanced Data Rates for Global Evolution (EDGE) technologies. HSCSD is one step towards 3G wideband mobile data networks. This circuit-switched technology improves the data rates up to 57.6kbps by introducing 14.4 kbps data coding and by aggregating 4 radio channels timeslots of 14.4 kbps. To meet the needs of today‟s subscribers, wireless service providers are in the process of upgrading their 2G networks to 2.5 G networks. These 2.5G networks continue to use the 2G architecture to deliver voice and circuit-switched data applications while adding a packet data overlay to support additional packet data services. Upgrading a 2G wireless infrastructure to support 2.5G enables subscribers on this network to attain data rates up to 170 kbps, a substantial increase over 2G data rates. Choosing a multi-service core network solution that efficiently handles multiple traffic types (e.g., packet data, voice, etc.) not only gives the operator the capability of providing new services with increased data rates, but also saves on TDM voice expenditures as previously outlined. . Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila Figure 4 : 2.5 G Wireless Infrastructures 7
  14. 14. th Chapter 01: Wireless Evolution towards 4 G D. Moving Towards 3G The "path to 3G" (see Figure 5) begins with several parallel 2G paths depicting the currently deployed technologies. It has become increasingly apparent that subscribers will not wait until the final 3G technologies have been deployed. For this reason, many of the 2.5G standards were been developed for deployment in the interim. Surprisingly, many of these, notably GPRS, EDGE, and IS136B/HS, may offer sufficient capabilities to satisfy end user customers for years to come. It seems likely that, short term, significantly more rather than fewer standards will emerge and be used concurrently, often running on adjacent or common carrier frequencies. The 2.5G transition period promises to be even more complex than today's 2G market. As we look at the "road map" (Figure 5) of the transition from 2G to 3G, it's important to note that the journey begins with several parallel 2G paths (GSM, CDMA, etc.), which split into even more paths before converging, ideally, on a single 3G standard. HSCSD (High-speed Circuit-Switched Data) and GPRS (General Packet Radio Service) will share the market with emerging variants of IS-136 and IS-95. The 2.5G transition period promises to be even more complex than today's 2G market. Figure 5 : Path to 3G Wireless infrastructure As Figure 5 implies, equipment manufacturers and network operators will continue to need test solutions for multiple standards during the 2.5G period, even more so than they have in the past. Given that many different standards will exist, equipment manufacturers must be able to adopt flexible design and manufacturing processes to meet Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 8
  15. 15. th Chapter 01: Wireless Evolution towards 4 G changing demands. For many equipment manufacturers it may be necessary to design and manufacture GSM, TDMA, CDMA One, HSCSD, GPRS, EDGE, EGPRS, IS-136B/HS, and IS-95B phones and network elements concurrently, often building them on the same manufacturing lines. E. Third Generation (3G) Wireless Networks 3G wireless technology represents the convergence of various 2G wireless telecommunications systems into a single global system that includes both terrestrial and satellite components. One of the most important aspects of 3G wireless technologies is its ability to unify existing cellular standards, such as CDMA, GSM, and TDMA, under one umbrella. The following three air interface modes accomplish this result: wideband CDMA, CDMA2000 and the Universal Wireless Communication (UWC -136) interfaces. Wideband CDMA (W-CDMA) is compatible with the current 2G GSM networks prevalent in Europe and parts of Asia. W-CDMA will require bandwidth of between 5 MHz and 10 MHz, making it a suitable platform for higher capacity applications. It can be overlaid onto existing GSM, TDMA (IS-36) and IS95 networks. Subscribers are likely to access 3G wireless services initially via dual band terminal devices. W-CDMA networks will be used for high-capacity applications and 2G digital wireless systems will be used for voice calls. The second radio interface is CDMA 2000, which is backward compatible with the second generation CDMA IS-95 standard predominantly used in US. The third radio interface, Universal Wireless Communications – UWC-136, also called IS-136HS, was proposed by the TIA and designed to comply with ANSI-136, the North American TDMA standard. 3G wireless networks consist of a Radio Access Network (RAN) and a core network. The core network consists of a packet-switched domain, which includes 3G SGSNs and GGSNs, which provide the same functionality that they provide in a GPRS system, and a circuit -switched domain, which includes 3G MSC for switching of voice calls. Charging for services and access is done through the Charging Gateway Function (CGF), which is also part of the core network. RAN functionality is independent from the core network functionality. The access network provides a core network technology independent access for mobile terminals to different types of core networks and network services. Either core network domain can access any appropriate RAN service; e.g. it should be possible to access a “speech” radio access bearer from the packet-switched domain. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 9
  16. 16. th Chapter 01: Wireless Evolution towards 4 G Figure 6 : 3G Architecture 3G: what's new? Is 3G is designed to deliver      A wide range of market-focused applications Long-term market-driven creativity, an innovative value chain and real user benefits, driving genuine market demand Advanced, lightweight, easy-to-use terminals with intuitive interfaces· Instant, real-time multimedia communications Global mobility and roaming A wide range of vendors and operators, offering choice, competition and affordability High-speed e-mail and Internet access Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 10
  17. 17. th Chapter 01: Wireless Evolution towards 4 1. G The Speed Figure 7 : Speed of 3G Networks 3G enabled users to transmit voice, data, and even moving images. In order to realize these services, 3G improves the data transmission speed up to 144Kbps in a highspeed moving environment, 384Kbps in a low-speed moving environment, and 2Mbps in a stationary environment. 3G provides services like Internet connection, transmission of large-scale data and moving contents photographed by digital cameras and videos, and software downloading. At present, maximum data transmission speed is 64Kbps offered in 3G services, and it was expected that by toward early 2001, 384Kbps would be possible. At the early stage of 3G services, a 144Kbps-transmission speed is expected. By around 2005 when 3G is in general use; a maximum speed of 2Mbps will be possible. 2. What are the standards saying? It is important to understand what people mean when they talk about an all-IP network. For instance, does it play at the transport, service or application level? Clearly the ultimate goal and one of the prime reasons for adopting IP as a unifying protocol is convergence on a single protocol at the application layer. For example, the architectural principles for the all -IP UMTS network clearly state that the UMTS core network shall be independent of the underlying trans-port mechanism. More specifically, for the IP transport layer, Layer 2 options are ATM, PPP or MPLS. Therefore, wireless operators have several options with regard to implementing the initial packet core infrastructure, as long as the core can be evolved to support the high bandwidth requirements of the future. Streams of traffic on each physical facility (between the end user and the network or between network switches) Virtual circuits can be statically configured as permanent virtual circuits (PVC) or dynamically controlled via signaling. While 3G haven‟t quite arrived, designers are already thinking about 4G technology. With it comes challenging RF and base band design headaches. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 11
  18. 18. th Chapter 01: Wireless Evolution towards 4 G Figure 8 : Evolution in Data Transmission Rate Cellular service providers are slowly beginning to deploy third-generation (3G) cellular services. As access technology increases, voice, video, multimedia, and broadband data services are becoming integrated into the same network. The hope once envisioned for 3G as a true broadband service has all but dwindled away. It is apparent that 3G systems, while maintaining the possible 2-Mbps data rate in the standard, will realistically achieve 384-kbps rates. To achieve the goals of true broadband cellular service, the systems have to make the leap to a fourth-generation (4G) network. This is not merely a numbers game. 4G is intended to provide high speed, high capacity, low cost per bit, IP based services. The goal is to have data rates up to 20 Mbps, even when used in such scenarios as a vehicle traveling 200 kilometers per hour. New design techniques, however, are needed to make this happen, in terms of achieving 4G performance at a desired target of onetenth the cost of 3G. The move to 4G is complicated by attempts to standardize on a single 3G protocol. Without a single standard on which to build, designers face significant additional challenges. F. Multi carrier modulation To achieve a 4G standard, a new approach is needed to avoid the divisiveness we've seen in the 3G realms. One promising underlying technology to accomplish this is multi carrier modulation (MCM), a derivative of frequency-division multiplexing. MCM is not a new technology; forms of multi carrier systems are currently used in DSL modems, and digital audio/video broadcast (DAB/DVB). MCM is a base band process that uses parallel equal bandwidth sub-channels to transmit information. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 12
  19. 19. th Chapter 01: Wireless Evolution towards 4 G Normally implemented with Fast Fourier transform (FFT) techniques, MCM's advantages include better performance in the inter symbol interference (ISI) environment, and avoidance of single -frequency interferers. However, MCM increases the peak-toaverage ratio (PAVR) of the signal, and to overcome ISI a cyclic extension or guard band must be added to the data. G. Fourth Generation Wireless Systems(All-IP) Reasons to Have 4G  Support interactive multimedia services: teleconferencing, wireless Internet, etc.  Wider bandwidths, higher bit rates.  Global mobility and service portability.  Low cost.  Scalability of mobile networks. Figure 9 : Requirements for 4G system What's New in 4G? Entirely packet-switched networks  All network elements are digital.  Higher bandwidths to provide multimedia services at lower cost (up to 100Mbps).  Tight network security. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 13
  20. 20. th Chapter 01: Wireless Evolution towards 4 G What is 4G? 4G takes on a number of equally true definitions, depending on whom you are talking to. In simplest terms, 4G is the next generation of wireless networks that will replace 3G networks sometimes in future. In another context, 4G is simply an initiative by academic R&D labs to move beyond the limitations and problems of 3G which is having trouble getting deployed and meeting its promised performance and throughput. In reality, as of first half of 2002, 4G is a conceptual framework for or a discussion point to address future needs of a universal high speed wireless network that will interface with wire line backbone network seamlessly. 4G is also represents the hope and ideas of a group of researchers in Motorola, Qualcomm, Nokia, Ericsson, Sun, HP, NTT DoCoMo and other infrastructure vendors who must respond to the needs of MMS, multimedia and video applications if 3G never materializes in its full glory. Figure 10 : 4G system Motivation for 4G Research Before 3G Has Not Been Deployed?    3G performance may not be sufficient to meet needs of future highperformance applications like multi-media, full motion video, wireless teleconferencing. We need a network technology that extends 3G capacities by an order of magnitude. There are multiple standards for 3G making it difficult to roam and interoperate across networks. We need global mobility and service portability 3G is based on primarily a wide-area concept. We need hybrid networks that utilize both wireless LAN (hot spot) concept and cell or base-station wide area network design. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 14
  21. 21. th Chapter 01: Wireless Evolution towards 4 G   1. 2. 3. 4. 5. We need wider bandwidth Researchers have come up with spectrally more efficient modulation schemes that cannot be retrofitted into 3G infrastructure  We need all digital packet networks that utilize IP in its fullest form with converged voice and data capability. Specification: o 4G can provide 10 times increase in data transfer over 3G. o This speed can be achieved through OFDM. o OFDM can not only transfer data at speed of more than 100mbps, but it can also eliminate interference that impairs high speed signals. Applications: o 4G will provide for a vast no. of presently nonexistent application for mobile devices. o 4G device will differ from present day mobile device in that there will be navigation menus. o 4G will provide a seamless network for users who travel & required uninterrupted voice/data communication. Need of 4G: o Firstly 3G‟s maximum data transfer rate of 384 kbps to 2 mbps is much slower than 20mbps to 100mbps of 4G. o With its use of existing technologies & communication standards, 4G present a comparably inexpensive standard. o 4G will utilize most of the existing wireless communication infrastructure. Issue in 4G: o Access o Handoff o Location co-ordination o Resource co-ordination to add new user o Support for quality of service. o Wireless securities & authentication. o Network failure & backup. o Pricing and billing. Technique used in 4G: o OFDM o UWB(Ultra Wide Band) o Millimeter wireless. o Smart Antennas Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 15
  22. 22. th Chapter 01: Wireless Evolution towards 4 G o Long term power prediction. o Scheduling among users. o Adaptive modulation and power control. 6. Advantages and Disadvantages of 4G : Advantages: o Support for interactive multimedia voice, streaming video, internet & other broadband services. o IP based mobile system. o High speed, high capacity & low cost per bit. o Global access, service portability & scalable mobile services. o Better scheduling and call admission control technique. o Ad-hoc & multi-hop network. o Better spectral efficiency. o Seamless network of multiple protocols & air interfaces. Disadvantages: o Expensive o Battery uses are more hard to implement o Need complicated hardware. 4G mobile phone technology promises faster communication Speeds (100 Mbps to 1 Gbps), capacity and diverse usage formats. These formats would provide richer content and support for other public networks such as optical fiber and wireless local area networks. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 16
  23. 23. C hapter 2: 4GLTE 1. Introduction Fourth generation wireless (4G) is an abbreviation for the fourth generation of cellular wireless standards and replaces the third generation of broadband mobile communications. The standards for 4G, set by the radio sector of the International Telecommunication Union (ITU-R), are denoted as International Mobile Telecommunications Advanced (IMT-Advanced). An IMT-Advanced cellular system is expected to securely provide mobile service users with bandwidth higher than 100 Mbps, enough to support high quality streaming multimedia content. Existing 3G technologies, often branded as Pre-4G (such as mobile WiMAX and 3G LTE), fall short of this bandwidth requirement. The majority of implementations branded as 4G do not comply with the full IMT-Advanced standard. The premise behind the 4G service offering is to deliver a comprehensive IP based solution where multimedia applications and services can be delivered to the user anytime and anywhere with a high data rate, premium quality of service and high security. Seamless mobility and interoperability with existing wireless standards is crucial to the functionality of 4G communications. Implementations will involve new technologies such as Femto cell and Pico cell, which will address the needs of mobile users wherever they are and will free up network resources for roaming users or those in more remote service areas. Two competing standards were submitted in September 2009 as technology candidates for ITU-R consideration:   LTE Advanced - as standardized by the 3GPP 802.16m - as standardized by IEEE These standards aim to be:      Spectrally efficient Able to dynamically allocate network resources in a cell Able to support smooth handover Able to offer high quality of service (QoS) Based on an all-IP packet-switched network WiMax is touted as the first 4G offering. It is an IP based, wireless broadband access technology, also known as IEEE 802.16. WiMax services offer residential and business customers with basic Internet connectivity. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 17
  24. 24. C hapter 2: 4GLTE Present implementations of WiMAX and LTE are largely considered a stopgap solution offering a considerable boost, while WiMAX 2 (based on the 802.16m specification) and LTE Advanced are finalized. Both technologies aim to reach the objectives traced by the ITU, but are still far from being implemented. Mobile networks have become an important means of Internet access recently, although these networks were primarily designed for voice transmission between two users. With the establishment of the third generation of mobile networks (e.g. UMTS – Universal Mobile Telecommunications System, CDMA2000 – Code Division Multiple Access 2000) and their upgrades (e.g. HSPA – High-Speed Downlink Packet Access, EVDO – Evolution-Data Optimized), data rates have been continuously increasing but still have not reached those of fixed networks. At the same time, the amount of user data transferred and the number of mobile Internet users have also increased. The increasing amount of transferred data and new applications such as mobile games and television, Web 2.0 and video streaming have motivated the 3GPP (Third Generation Partnership Project) organization to start the LTE project. The project‟s aim is to issue a series of recommendations (called Release 8) for new radio access that will support recent trends in mobile communications. Although often designated as a fourth-generation (4G) mobile technology, LTE actually does not yet meet the requirements to be a 4G mobile network [1], [2] so it is often designated as 3.9 G. Nevertheless, LTE will bring improvements in efficiency and quality of service, lower operator costs, better utilization of the frequency spectrum and integration with existing open standards. LTE will introduce characteristics to mobile networks similar to those in fixed networks. Most of the UMTS networks worldwide have been already upgraded to High Speed Packet Access (HSPA) in order to increase data rate and capacity for packet data. HSPA refers to the combination of High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA).While HSDPA was introduced as a 3GPP Release 5 feature, HSUPA is an important feature of 3GPP Release 6. However, even with the introduction of HSPA, evolution of UMTS has not reached its end. HSPA+ is a significant enhancement in 3GPP Release7, 8, 9 and even 10.Objective is to enhance performance of HSPA based radio networks in terms of spectrum efficiency, peak data rate and latency, and exploit the full potential of WCDMA based 5MHz operation. Important Release7 features of HSPA+ are downlink MIMO (Multiple Input Multiple Output), higher order modulation for uplink (16QAM) and downlink (64QAM), improvements of layer 2 protocols, and continuous packet Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 18
  25. 25. C hapter 2: 4GLTE connectivity. Generally spoken these features can be categorized in data-rate or capacity enhancement features versus web-browsing and power saving features. With higher Release 8, 9 and 10 capabilities like the combination of 64QAM and MIMO, up to four carrier operations for the downlink(w/o MIMO), and two carriers operation for the uplink are now possible. This increases downlink and uplink data rates up to theoretical peaks of 168 Mbps and 23 Mbps, respectively. In addition the support of circuit-switched Services over HSPA (CS over HSPA) has been a focus for the standardization body in Terms of improving HSPA+ functionality in Release 8 [3]. However to ensure the competitiveness of UMTS for the next decade and beyond, Concepts for UMTS Long Term Evolution (LTE) have been first time introduced in 3GPP Release 8. Objectives are higher data rates, lower latency on the user plane and control plane and a packet-optimized radio access technology. LTE is also referred to as E-UTRA (Evolved UMTS Terrestrial Radio Access) or E-UTRAN (Evolved UMTS Terrestrial Radio Access Network). Based on promising field trials, proving the concept of LTE as described in the following sections, real life LTE deployments significantly increased from the start of the first commercial network in end 2009.As LTE offers also a migration path for 3GPP2 standardized technologies (CDMA2000®1xRTT and 1xEVDO) it can be seen as the true mobile broadband technology. This application note focuses on LTE/E-UTRA technology. In the following, the terms LTE, E-UTRA or E-UTRAN are used interchangeably. LTE has ambitious requirements for data rate, capacity, spectrum efficiency, and latency. In order to fulfill these requirements, LTE is based on new technical principles. LTE uses new multiple access schemes on the air interface: OFDMA (Orthogonal Frequency Division Multiple Access) in downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) in uplink . Furthermore, MIMO antenna schemes form an essential part of LTE. In order to simplify protocol architecture, LTE brings some major changes to the Existing UMTS protocol concepts. Impact on the overall network architecture including the core network is referred to as 3GPP System Architecture Evolution (SAE). LTE includes an FDD (Frequency Division Duplex) mode of operation and a TDD (Time Division Duplex) mode of operation. LTE TDD which is also referred to as TD LTE provides the long term evolution path for TD-SCDMA based networks. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 19
  26. 26. C hapter 2: 4GLTE 2. Features and capabilities The LTE project targets the following features and capabilities of the evolved radio access network (E-UTRAN – Evolved Universal Terrestrial Radio Access Network) [4]: Peak data rates of 100 Mb/s on the downlink and 50 Mb/s on the uplink within a 20 MHz spectrum allocation. Control plane capable of carrying signalization for 200 simultaneously active users for spectrum allocations up to 5 MHz and for at least 400 users for higher spectrum allocations. Switch time between idle and active state shorter than 100 ms. Radio access network latency below 10ms. Spectral efficiency 5 bit/s/Hz on the downlink and 2.5 bit/s/Hz on the uplink. Table 1: Data rate and spectrum efficiency requirements defined for LTE Downlink (20 MHz) Unit Mbps bps/Hz Requirement 100 5 2x2 MIMO 172.8 8.6 4x4 MIMO 326.4 16.3 Uplink (20 MHz) Unit Mbps Bps/Hz Requirement 50 2.5 16QAM 57.6 2.9 64QAM 86.4 4.3 Radio access network optimized for mobile user speeds up to 15 km/h. The system should support high performance for speeds up to 120 km/h. Links should be maintained at speeds up to 350 km/h, or up to 500 km/h depending on the frequency band. The system should support the targeted performance within a 5 km range. A slight degradation in performance is tolerated within a 30 km range. Ranges up to 100 km or even more should not be precluded by the specifications. Enhanced broadcast and multicast transmissions compared to HSPA standards. Scalable bandwidth allocation of 1.25 MHz, 1.6 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz . Bandwidths narrower than 5 MHz enable a smooth transition to the spectrum of the previous generations of mobile systems. Deployment in frequency bands of the previous generations of mobile systems: 450 MHz, 700 MHz, 800 MHz, 900 MHz, 1600 MHz, 1700 MHz, 1900 MHz, 2100 MHz and other. Because a large set of frequency bands is available, global roaming will be possible. Support for paired and unpaired spectrum for FDD (Frequency Division Duplex), TDD (Time Division Duplex) and the combination of both. The advantage of combined TDD and FDD use are simplified terminals at the expense of higher data rates that could be achieved with the frequency duplex. Interoperability with existing mobile systems at the same location on adjacent channels. The time needed for handover between E-UTRAN and other radio Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 20
  27. 27. C hapter 2: 4GLTE access networks must be shorter than 300 ms for real time services and 500 ms for other services. The architecture of E-UTRAN must be packet-based, but it must also support real-time services. Support for various types of services (e.g. VoIP – Voice over IP, data transfer). Reasonable system and terminal complexity, cost and power consumption. 3. 4G (LTE) The Technologies And Techniques LTE is based on existing technologies that were not widely used in mobile communications in the past. The reason was in their large processing requirements, which, due to technological progress, are no longer problematic. LTE introduces new models of multiplexing and multiple access techniques on a radio interface, such as OFDM (Orthogonal Frequency Division Multiplex) and OFDMA (Orthogonal Frequency Division Multiple Access) on the downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) on the uplink. Advanced antenna techniques, such as MIMO (Multiple-Input Multiple-Output), are also important in LTE. MIMO increases radio network throughput by transmitting multiple data streams simultaneously within the same frequency band. The signals propagate along different paths, which is a common phenomenon in mobile communications. The receiver separately receives the signals with different delays, creating parallel channels. A. LTE: The Downlink: 1. OFDMA As opposed to single-carrier systems, OFDM does not demand higher symbol rates to achieve higher data rates [5], [6]. The downlink transmission scheme for E-UTRA FDD and TDD modes is based on conventional OFDM. In an OFDM system, the available spectrum is divided into multiple carriers, called subcarriers. Each of these subcarriers is independently modulated by a low rate data stream. OFDM is used as well in WLAN, WiMAX and broadcast technologies like DVB. OFDM has several benefits including its robustness against multipath fading and its efficient receiver architecture. Figure 11 shows a representation of an OFDM signal. In this figure, a signal with 5MHz bandwidth is shown, but the principle is of course the same for the other E-UTRA bandwidths. Data symbols are independently modulated and transmitted over a high number of closely spaced orthogonal subcarriers [7]. In E-UTRA, downlink modulation Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 21
  28. 28. C hapter 2: 4GLTE schemes QPSK, 16QAM, and 64QAM are available. In the time domain, a guard interval is added to each symbol to combat Inter-Symbol Interference (ISI) due to channels delay spread. The delay spread is the time between the symbol arriving on the first multi-path signal and the last multi-path signal component, typically several µs dependent on the environment (i.e. indoor, rural, suburban, city center). The guard interval has to be selected in that way, that it is greater than the maximum expected delay spread. In E-UTRA, the guard interval is a cyclic prefix which is inserted prior to each OFDM symbol. Figure 11 : Frequency-time representation of an OFDM Signal In practice, the OFDM signal can be generated using IFFT (Inverse Fast Fourier Transform) digital signal processing. The IFFT converts a number N of complex data Symbols used as frequency domain bins in to the time domain signal. Such an N-point IFFT is illustrated in Figure 12 where a (mN+n) refers to the nth subcarrier modulated data symbol, during the time period mTu < t ≤ (m+1) Tu. Figure 12 : OFDM useful symbol generation using an IFFT The vector sm is defined as the useful OFDM symbol. It is the time superposition of the N narrowband modulated subcarriers. Therefore, from a parallel stream of N sources of data, each one independently modulated, a waveform composed of N orthogonal Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 22
  29. 29. C hapter 2: 4GLTE Subcarriers is obtained, with each subcarrier having the shape of a frequency sinc function (see Figure 11). Figure 13 illustrates the mapping from a serial stream of QAM symbols to N parallel streams, used as frequency domain bins for the IFFT. The N-point time domain blocks obtained from the IFFT are then serialized to create a time domain signal. Figure 13 : OFDM Signal Generation Chain In contrast to an OFDM transmission scheme, OFDMA allows the access of multiple Users on the available bandwidth. Each user is assigned a specific time-frequency resource. As a fundamental principle of E-UTRA, the data channels are shared channels, i.e. for each Transmission Time Interval (TTI) of 1ms, a new scheduling decision is taken regarding which users are assigned to which time/frequency resources during this TTI. 2. OFDMA Parameterization Two frame structure types are defined for E-UTRA:  Frame structure type 1 for FDD mode,  And frame structure type 2 for TDD mode. For the frame structure type 1, the 10ms radio frame is divided into 20 equally sized slots of 0.5ms. A sub frame consists of two consecutives lots, so one Radio frame contains ten sub frames .This is illustrated in Figure 14. Figure 14 : Frame structure type 1 Ts (sampling time) is expressing the basic time unit for LTE, corresponding to a Sampling frequency of 30.72MHz. This sampling frequency is given due to the defined subcarrier spacing for LTE with f =15 KHz and the maximum FFT size to generate the OFDM symbols of 2048. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 23
  30. 30. C hapter 2: 4GLTE Selecting these parameters ensures also simplified Implementation of multi standard devices, as this sampling frequency is a multiple of the chip rate defined for WCDMA (30.72MHz/ 8=3.84Mcps) and CDMA2000®1xRTT (30.72MHz/ 25=1.2288Mcps). For the frame structure type 2, the 10ms radio frame consists of two half-frames of Length 5ms each. Each half-frame is divided into five sub frames of each 1ms, as Shown in Figure 15 below. All sub frames which are not special sub frames are defined as two slots of length 0.5ms in each sub frame. The special sub frames consist of the three fields DwPTS (Downlink Pilot Time Slot), GP (Guard Period), and UpPTS (Uplink Pilot Time Slot). These fields are already known from TD-SCDMA and are maintained in LTE TDD. DwPTS, GP and UpPTS have configurable individual lengths and a total Length of 1ms. Figure 15 : Frame structure type 2 (for 5ms switch-point periodicity) Seven uplink-downlink configurations with either 5ms or 10ms downlink-to-uplink switch-point periodicity are supported. In case of 5ms switch-point periodicity, the special sub frame exists in both half-frames. In case of 10ms switch-point periodicity The special sub frame exists in the first half frame only. Sub frames 0 and 5 and DwPTS Are always reserved for downlink transmission. UpPTS and the sub frame immediately Following the special sub frame are always reserved for uplink transmission. Table 2 Shows the supported uplink-downlink configurations, where ”D” denotes a sub frame reserved for downlink transmission, “U” denotes a sub frame reserved for uplink transmission, and “S” denotes the special sub frame. Table 2: Uplink-Downlink configurations for LTE TDD Uplink-Downlink Configuration 0 1 2 3 4 5 6 Downlink to Uplink Switch point periodicity 5 ms 5 ms 5 ms 10 ms 10 ms 10 ms 5 ms 0 D D D D D D D 1 S S S S S S S Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 2 U U U U U U U Subframe number 3 4 5 6 7 U U D S U U D D S U D D D S U U U D D D U D D D D D D D D D U U D S U 8 U U D D D D U 9 U D D D D D D 24
  31. 31. C hapter 2: 4GLTE There is always a special sub frame when switching from DL to UL, which provides a Guard period. Reason being is that all transmission in the UL from all the different UEs must arrive at the same time at the base station receiver. When switching from UL to DL only the base station is transmitting so there is no guard period needed. Beside UL DL configuration there is also 9 special sub frame configurations. And the length of the DwPTS, Guard Period (GP) and UpPTS is given in numbers of OFDM symbols. As it can be seen there are Different lengths for GP, which is necessary to support different cell size, up to 100km. Table 3 : Special Sub frame configurations in TD-LTE Normal cyclic prefix in downlink Extended cyclic prefix downlink Special UpPTS UpPTS Subframe Guard Normal Extended Guard Normal Extended Config. DwPTS Period Cyclic Cyclic DwPTS Period Cyclic Cyclic prefix prefix Prefix Prefix In uplink In uplink 0 3 10 3 8 1 9 4 8 3 1 1 1 1 2 10 3 9 2 3 11 2 10 1 4 12 1 3 7 2 2 5 3 9 8 2 6 9 3 9 1 2 2 7 10 2 8 11 1 It can be also extracted that downlink and uplink in TD-LTE can utilize different cyclic prefixes, which is different from LTE FDD. Figure 16 shows the structure of the downlink Resource grid for both FDD and TDD. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 25
  32. 32. C hapter 2: 4GLTE Figure 16: Downlink Resource grid In the frequency domain, 12 subcarriers form one Resource Block (RB). With a subcarrier spacing of 15 kHz a RB occupies a bandwidth of 180 kHz. The number of resource blocks, corresponding to the available transmission bandwidth, is listed for the six different LTE bandwidths in Table 4. Table 4: Number of resource blocks for different LTE bandwidths (FDD and TDD) Channel Bandwidth [MHz] 1.4 3 5 10 15 20 Number of resource blocks 6 15 25 50 75 100 To each OFDM symbol, a cyclic prefix (CP) is appended as guard time, compare Figure11. One downlink slot consists of 6 or 7 OFDM symbols, depending on whether Extended or normal cyclic prefix is configured, respectively. The extended cyclic prefix Is able to cover larger cell sizes with higher delay spread of the radio channel, but reduces the number of available symbols. The cyclic prefix lengths in samples and µs are summarized in Table 5. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 26
  33. 33. C hapter 2: 4GLTE Table 5 : Downlink frame structure parameterization (FDD and TDD) Resource Block size Number Of Symbols 12 12 7 6 Configuration Normal cyclic prefix Ext cyclic prefix Cyclic prefix Length in samples Cyclic prefix length in µs 160 for first symbol 144 for other symbols 512 5.2 µs for first symbols 4.7 µs for other symbols 16.7 µs With a sampling frequency of 30.72 MHz 307200 samples are available per radio Frame (10ms) and thus 15360 per time slot (0.5ms). Due to the maximum FFT size Each OFDM symbol consists of 2048 samples. With usage of normal cyclic prefix Seven OFDM symbols are available or 7*2048=14336 samples per time slot. The remaining 1024 samples are the basis for cyclic prefix. It has been decided that the first OFDM symbol uses a cyclic prefix length of 160 samples, where the remaining six OFDM symbols using a cyclic prefix length of 144samples. Multiplying the samples With the sampling time TS, results in the cyclic prefix length in µs. Please note that for E-MBMS another cyclic prefix of 33.3µs is defined for a different Subcarrier spacing off =7.5 kHz in order to have a much larger cell size. 3. Downlink data transmission Data is allocated to a device (User Equipment, UE) in terms of resource blocks, i.e. one UE can be allocated integer multiples of one resource block in the frequency domain. These resource blocks do not have to be adjacent to each other. In the time domain, the scheduling decision can be modified every transmission time interval of 1ms. All scheduling decisions for downlink and uplink are done in the base station (enhanced NodeB, eNodeB or eNB).The scheduling algorithm has to take in to account the radio link quality situation of different users, the overall interference situation, Quality of Service requirements, service priorities, etc. and is a vendor-specific implementation. Figure 17 shows an example for allocating downlink user data to different users (UE1-6). The user data is carried on the Physical Downlink Shared Channel (PDSCH). The PDSCH(s) is the only channel that can be QPSK, 16 QAM or 64 QAM modulated. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 27
  34. 34. C hapter 2: 4GLTE Figure 17 : OFDM A time-frequency multiplexing (example for normal cyclic prefix) 4. Downlink reference signal structure and cell search The downlink reference signal structure is important for initial acquisition and cell search, coherent detection and demodulation at the UE and further basis for channel estimation and radio link quality measurements. Downlink reference signal provide further help to the device to distinguish between the different transmit antenna used at the eNodeB. Figure18 shows the mapping principle of the downlink reference signal structure for up to four transmit antennas. Specific pre-defined resource elements in the timefrequency domain are carrying the cell-specific reference signal sequence. In the frequency domain every six subcarrier carries a portion of the reference signal pattern, which repeats every fourth OFDM symbol. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 28
  35. 35. C hapter 2: 4GLTE Figure 18 : Downlink reference signal structure (normal cyclic prefix) The reference signal sequence is derived from a pseudo-random sequence and results in a QPSK type constellation. Frequency shifts are applied when mapping the reference signal sequence to the subcarriers, means the mapping is cell-specific and distinguish the different cells. During cell search, different types of information need to be identified by the UE: symbol and radio frame timing, frequency, cell identification, overall transmission bandwidth, antenna configuration, and cyclic prefix length. The first step of cell search in LTE is based on specific synchronization signals. LTE uses a hierarchical cell search scheme similar to WCDMA. Thus, a primary synchronization signal and a secondary synchronization signal are defined. The synchronization signals are transmitted twice per 10 ms on predefined slots; see Figure 19 for FDD and Figure 20 for TDD. In the frequency domain, they are transmitted on 62 subcarriers within 72 reserved subcarriers around the unused DC subcarrier. The 504 available physical layer cell identities are Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 29
  36. 36. C hapter 2: 4GLTE grouped into 168 physical layer cell identity groups, each group containing 3 unique identities (0, 1, or2). The secondary synchronization signal carries the physical layer cell identity group, and the primary synchronization signal carries the physical layer identity 0, 1, or 2. Figure 19 : Primary/secondary synchronization signal and PBCH structure (frame structure type 1/FDD, normal cyclic prefix) Figure 20 : Primary/secondary synchronization signal and PBCH structure (frame structure type2/TDD, normal cyclic prefix) As additional help during cell search, a Physical Broadcast Channel (PBCH) is available which carries the Master Information Block (MIB). The MIB provides basic physical layer information, e.g. system bandwidth, PHICH configuration, and system frame number. The number of used transmit antennas is provided in directly using a specific CRC mask. The PBCH is transmitted on the first 4 OFDM in the second time slot of the first sub frame on the 72 subcarriers centered around DC subcarrier. PBCH has 40ms transmission time interval, means a device need to read four radio frames to get the whole content. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 30
  37. 37. C 5. hapter 2: 4GLTE Downlink Hybrid ARQ (Automatic Repeat Request) Downlink Hybrid ARQ is also known from HSDPA. It is a retransmission protocol. The UE can request retransmissions of data packets that were incorrectly received on PDSCH. ACK/NACK information is transmitted in uplink, either on Physical Uplink Control Channel (PUCCH) or multiplexed with in uplink data transmission on Physical Uplink Shared Channel (PUSCH). In LTE FDD there are up to 8 HARQ processes in parallel. The ACK/NACK transmission in FDD mode refers to the downlink packet that was received four sub frames before. In TDD mode, the uplink ACK/NACK timing depends on the uplink/downlink configuration. Table 6: Number of HARQ processes in TD-LTE (Downlink) TDD UL/DL Configuration 0 1 2 3 4 5 6 Number of HARQ processes for normal HARQ operation 7 4 2 3 2 1 6 Number of HARQ processes for subframe bundling operation 3 2 N/A N/A N/A N/A 3 Two modes are supported by TD-LTE acknowledging or non-acknowledging data Packets received in the downlink: ACK/NACK bundling and multiplexing. Which mode is used, is configured by higher layers. ACK/NACK bundling means, that ACK/NACK information for data packets received in different sub frames is combined with logical AND operation. Figure 21: ACK/NACK bundling in TD-LTE Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 31
  38. 38. C B. hapter 2: 4GLTE LTE: The Uplink: 1. SC-FDMA During the study item phase of LTE, alternatives for the optimum uplink transmission scheme were investigated. While OFDMA is seen optimum to fulfill the LTE requirements in downlink, OFDMA properties are less favorable for the uplink. This is mainly due to weaker peak-to-average power ratio (PAPR) properties of an OFDMA signal, resulting in worse uplink coverage and challenges in power amplifier design for battery operated handset, as it requires very linear power amplifiers. Thus, the LTE uplink transmission scheme for FDD and TDD mode is based on SCFDMA [5], [8] (Single Carrier Frequency Division Multiple Access) with cyclic prefix. SCFDMA signals have better PAPR properties compared to an OFDMA signal. This was one of the main reasons for selecting SC-FDMA as LTE uplink access scheme. The PAPR characteristics are important for cost-effective design of UE power amplifiers. Still, SC-FDMA signal processing has some similarities with OFDMA signal processing, so parameterization of downlink and uplink can be harmonized. There are different possibilities how to generate an SC-FDMA signal. DFT spread OFDM (DFT-s-OFDM) has been selected for E-UTRA. The principle is illustrated in Figure22. For DFT-s-OFDM, a size-MDFT is first applied to a block of M modulation symbols. QPSK, 16QAM and 64QAM are used as uplink E-UTRA modulation schemes, the latter being optional for the UE. The DFT transforms the modulation symbols in to the frequency domain. The result is mapped on to the available number of subcarriers. For LTE Release8 uplink, only localized transmission on consecutive subcarriers is allowed. An N-point IFFT where N > M is then performed as in OFDM, followed by addition of the cyclic prefix and parallel to serial conversion. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 32
  39. 39. C hapter 2: 4GLTE Figure 22 : Block diagram of DFT-s-OFDM (localized transmission) The DFT processing is therefore the fundamental difference between SC-FDMA and OFDMA signal generation. This is indicated by the term “DFT-spread-OFDM”. In an SC-FDMA signal, each subcarrier used for transmission contains information of all Transmitted modulation symbols, since the input data stream has been spread by the DFT transform over the available subcarriers. In contrast to this, each subcarrier of an OFDMA signal only carries in formation related to specific modulation symbols. This Spreading lowers the PAPR compared to OFDMA as used in the downlink. It depends now on the used modulation scheme (QPSK, 16QAM, later on also 64QAM) and the Applied filtering, which is not standardized as in WCDMA for example. 2. SC-FDMA parameterization The LTE uplink structure is similar to the downlink. In frame structure type 1, an uplink radio frame consists of 20 slots of 0.5 ms each, and one subframe consists of two slots. The slot structure is shown in Figure 23 Frame structure type 2 consists also of ten subframes, but one or two of them are special subframes. They include DwPTS, GP and UpPTS fields, see Figure 14. Each slot carries 7 SC-FDMA symbols in case of normal cyclic prefix configuration and 6 SC-FDMA symbols in case of extended cyclic prefix configuration. SC-FDMA symbol number 3 (i.e. the 4th symbol in a slot) carries the demodulation reference signal (DMRS), being used for coherent demodulation at the eNodeB receiver as well as channel estimation. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 33
  40. 40. C hapter 2: 4GLTE Figure 23 : Uplink resource grid Table7 shows the configuration parameters. Table 7: Uplink frame structure parameterization (FDD and TDD) Configuration Number of symbols Cyclic prefix length in samples Cyclic prefix length in µs Normal cyclic prefix 7 Ext. cyclic prefix 6 160 for 1st symbol 144 for other symbols 512 5.2 µs for 1st symbol 4.7 µs for other symbols 16.7 µs Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 34
  41. 41. C 3. hapter 2: 4GLTE Uplink Data transmission Scheduling of uplink resources is done by eNodeB. The eNodeB assigns certain time/frequency resources to the UEs and informs UEs about transmission formats to use. The scheduling decisions may be based on QoS parameters, UE buffer status uplink channel quality measurements, UE capabilities, UE measurement gaps, etc. In uplink, data is allocated in multiples of one resource block. Uplink resource block size in the frequency domain is 12 subcarriers, i.e. the same as in downlink. However, not all integer multiples are allowed in order to simplify the DFT design in uplink signal processing. Only factors 2, 3, and 5 are allowed. Table 8 shows the possible number of RB that can be allocated to a device for uplink transmission. Table 8 : Possible RB allocation for uplink transmission 1 15 40 81 2 16 45 90 3 18 48 96 4 5 6 8 9 10 12 20 24 25 27 30 32 36 50 54 60 64 72 75 80 100 In LTE Release 8 only contiguous allocation is possible in the downlink transmissions with resource allocation type 2. The number of allocated RBs is signaled to the UE as RIV. The uplink transmission time interval is 1 ms (same as downlink). User data is carried on the Physical Uplink Shared Channel (PUSCH). DCI (Downlink Control Information) format 0 is used on PDCCH to convey the uplink scheduling grant. The content of DCI format 0 is listed in Table 9. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 35
  42. 42. C hapter 2: 4GLTE Table 9 : Contents of DCI format 0 carried on PDCCH Information type Flag for format 0/ format1A Differentiation Hopping flag Number of bits on PDCCH 1 1 Resource block assignment and hopping resource allocation Depending on resource block allocation type Modulation and coding scheme and redundancy version 5 New date indicator 1 TPC command for scheduled PUSCH 2 Cyclic shift for demodulation reference signal Uplink index (TDD only) 3 CQI request 1 2 Purpose Indicates DCI format to UE Indicates whether uplink frequency hopping is used or not Indicates whether to use type 1 or type 2 frequency hopping and index of starting resource block of uplink resource allocation as well as number of contiguously allocated resource blocks Indicates modulation scheme and, together with the number of allocated physical resource blocks, the transport block size indicates redundancy version to use Indicates whether a new transmission shall be sent Transmit power control (TPC) for adapting the transmit power on the Physical Uplink Shared Channel (PUSCH) Indicates the cyclic shift to use for deriving the uplink demodulation reference signal from the base sequence Indicates the uplink subframe where the scheduling grant has to be applied Requests the UE to send a channel quality indication (CQI)aperiodic CQI reporting Frequency hopping can be applied in the uplink. The uplink scheduling grant in DCI format 0 contains a 1 bit flag for switching hopping ON or OFF. By use of frequency hopping on PUSCH, frequency diversity effects can be exploited and interference can be averaged. The UE derives the uplink resource allocation as well as frequency hopping information from the uplink scheduling grant that was received four subframes before. LTE supports both intra- and inter-subframe frequency hopping. It is configured per cell by higher layers whether either both intra- and inter-subframe hopping or only inter-subframe hopping is supported. In intra-subframe hopping (inter slot hopping), the UE hops to another frequency allocation from one slot to another within one subframe. In inter-subframe hopping, the frequency resource allocation changes from one subframe to another, depending on a pre-defined method. Also, the UE is being told whether to use type 1 or type 2 frequency hopping. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 36
  43. 43. C hapter 2: 4GLTE The available bandwidth i.e. 50 RB is divided into a number of sub-bands, 1 up to 4. This information is provided by higher layers. The hopping offset, which comes as well from higher layers, determines how many RB are available in a sub-band. The number of contiguous RB that can be allocated for transmission is therefore limited. Further the number of hopping bits is bandwidth depended, 1 hopping bit for bandwidths with less than 50 RB, 2 hopping bits for bandwidth equals and higher 50 RB. The UE will first determine the allocated resource blocks after applying all the frequency hopping rules. Then, the data is being mapped onto these resources, first in subcarrier order, then in symbol order. Type 1 hopping refers to the use of an explicit offset in the 2nd slot resource allocation. Figure 24 shows an example, of a complete radio frame for a 10 MHz signal applying a defined PUSCH hopping offset of 5 RB and configuring 4 sub-bands. Figure 24 : Intra-subframe hopping, Type 1 Type 2 hopping refers to the use of a pre-defined hopping pattern. The hopping is performed between sub-bands (from one slot or subframe to another, depending on whether intra- or inter-subframe are configured, respectively). In the example (Figure 25) the initial assignment is 10 RB with an offset of 24 RB. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 37
  44. 44. C hapter 2: 4GLTE Figure 25 : Intra-subframe hopping, Type 1 (blue, UE1) and Type 2 (green, UE3) 4. Uplink reference signal structure There are two types of uplink reference signals: The demodulation reference signal (DMRS) is used for channel estimation in the eNodeB receiver in order to demodulate control and data channels. It is located on the 4 th symbol in each slot (for normal cyclic prefix) and spans the same bandwidth as the allocated uplink data. The sounding reference signal (SRS) provides uplink channel quality information as a basis for scheduling decisions in the base station. The UE sends a sounding reference signal in different parts of the bandwidths where no uplink data transmission is available. The sounding reference signal is transmitted in the last symbol of the subframe. The configuration of the sounding signal, e.g. bandwidth, duration and periodicity, are given by higher layers. Both uplink reference signals are derived from so-called Zadoff-Chu sequence types. This sequence type has the property that cyclic shifted versions of the same sequence are orthogonal to each other. Reference signals for different UEs are derived by different cyclic shifts from the same base sequence. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 38
  45. 45. C hapter 2: 4GLTE The available base sequences are divided into groups identified by a sequence group number u. within a group, the available sequences are numbered with index v. The sequence group number u and the number within the group v may vary in time. This is called group hopping, and sequence hopping, respectively. Group hopping is switched on or off by higher layers. The sequence group number u to use in a certain timeslot is controlled by a pre-defined pattern. Sequence hopping only applies for uplink resource allocations of more than five resource blocks. In case it is enabled (by higher layers), the base sequence number v within the group u is updated every slot. 5. Uplink Hybrid ARQ (Automatic Repeat Request) Hybrid ARQ retransmission protocol is also used in LTE uplink. The eNodeB has the capability to request retransmissions of incorrectly received data packets. ACK/NACK information in downlink is sent on Physical Hybrid ARQ Indicator Channel (PHICH). After a PUSCH transmission the UE will therefore monitor the corresponding PHICH resource four subframes later (for FDD). For TDD the PHICH subframe to monitor is derived from the uplink/downlink configuration and from PUSCH subframe number. The PHICH resource is determined from lowest index physical resource block of the uplink resource allocation and the uplink demodulation reference symbol cyclic shift associated with the PUSCH transmission, both indicated in the PDCCH with DCI format 0 granting the PUSCH transmission. A PHICH group consists of multiple PHICHs that are mapped to the same set of resource elements, and that are separated through different orthogonal sequences. The UE derives the PHICH group number and the PHICH to use inside that group from the information on the lowest resource block number in the PUSCH allocation, and the cyclic shift of the demodulation reference signal. The UE can derive the redundancy version to use on PUSCH from the uplink scheduling grant in DCI format 0, see Table 9. 8 HARQ processes are supported in the uplink for FDD, while for TDD the number of HARQ processes depends on the uplink-downlink configuration. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 39
  46. 46. C hapter 2: 4GLTE Figure 26 : PHICH principle C. LTE: MIMO Concepts Multiple Input Multiple Output (MIMO) systems form an essential part of LTE in order to achieve the ambitious requirements for throughput and spectral efficiency. MIMO refers to the use of multiple antennas at transmitter and receiver side. For the LTE downlink, a 2x2 configuration for MIMO is assumed as baseline configuration, i.e. two transmit antennas at the base station and two receive antennas at the terminal side. Configurations with four transmit or receive antennas are also foreseen and reflected in specifications. Different gains can be achieved depending on the MIMO mode that is used. In the following, a general description of spatial multiplexing and transmit diversity is provided. Afterwards, LTE-specific MIMO features are highlighted. Spatial multiplexing Spatial multiplexing allows transmitting different streams of data simultaneously on the same resource block(s) by exploiting the spatial dimension of the radio channel. These data streams can belong to one single user (single user MIMO / SUMIMO) or to different users (multi user MIMO / MU-MIMO). While SU-MIMO increases the data rate of one user, MU-MIMO allows increasing the overall capacity. Spatial multiplexing is only possible if the mobile radio channel allows it. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 40
  47. 47. C hapter 2: 4GLTE Figure 27 : Spatial multiplexing (simplified) Figure 27 shows a simplified illustration of spatial multiplexing. In this example, each transmit antenna transmits a different data stream. This is the basic case for spatial multiplexing. Each receive antenna may receive the data streams from all transmit antennas. The channel (for a specific delay) can thus be described by the following channel matrix H: [ ] In this general description, Nt is the number of transmit antennas, Nr is the number of receive antennas, resulting in a 2x2 matrix for the baseline LTE scenario. The coefficients hij of this matrix are called channel coefficients from transmit antenna j to receive antenna i, thus describing all possible paths between transmitter and receiver side. The number of data streams that can be transmitted in parallel over the MIMO channel is given by min {N , N } and is limited by the rank of the matrix H. The transmission quality degrades significantly in case the singular values of matrix H are not sufficiently strong. This can happen in case the two antennas are not sufficiently decorrelated, for example in an environment with little scattering or when antennas are too closely spaced. The rank of the channel matrix H is therefore an important criterion to determine whether spatial multiplexing can be done with good performance. Note that Figure 27 only shows an example. In practical MIMO implementations, the data streams are often weighted and added, so that each antenna actually transmits a combination of the streams; see below for more details regarding LTE. Transmit Diversity Instead of increasing data rate or capacity, MIMO can be used to exploit diversity and increase the robustness of data transmission. Transmit diversity schemes are already known from WCDMA Release 99 and will also be part of LTE. Each transmit antenna transmits essentially the same stream of data, so the receiver gets replicas of the same signal. This increases the signal to noise ratio at the receiver side and thus the robustness Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 41
  48. 48. C hapter 2: 4GLTE of data transmission especially in fading scenarios. Typically an additional antennaspecific coding is applied to the signals before transmission to increase the diversity effect. Often, space-time coding is used according to Alamouti [9]. Switching between the two MIMO modes (transmit diversity and spatial multiplexing) is possible depending on channel conditions. 1. Downlink MIMO modes in LTE as of Release 8 Different downlink MIMO modes are envisaged in LTE which can be adjusted according to channel condition, traffic requirements, and UE capability. The following transmission modes are possible in LTE: Table 10 : Transmission Modes in LTE as of 3GPP Release 8 Transmission Mode TM1 TM2 TM3 TM4 TM5 TM6 TM7 Description Single Antenna transmission (SISO) Transmit Diversity Open-loop spatial multiplexing, no UE feedback (PMI) on MIMO transmission provided Closed-loop spatial multiplexing, UE provides feedback on MIMO transmission Multi-user MIMO(more than one UE is assigned to the same resource block) Closed-loop precoding for rank=1(i.e. no spatial multiplexing, but precoding is used) Single-layer beam forming (mandatory TD-LTE, optional LTE FDD) In LTE spatial multiplexing, up to two code words can be mapped onto different spatial layers. One code word represents an output from the channel coder. The number of spatial layers available for transmission is equal to the rank of the matrix H. Precoding on transmitter side is used to support spatial multiplexing. This is achieved by multiplying the signal with a precoding matrix W before transmission. The optimum precoding matrix W is selected from a predefined “codebook” which is known at eNodeB and UE side. The codebook for the 2 transmit antenna case in LTE is shown in Table 11. The optimum pre-coding matrix is the one which offers maximum capacity. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 42
  49. 49. C hapter 2: 4GLTE Table 11 : Precoding codebook for 2 transmit antenna case Codebook index Number of layers v 1 0 1 2 [ ] [ [ ] 2 [ ] 3 [ ] ] [ ] [ ] - The codebook defines entries for the case of one or two spatial layers. In case of only one spatial layer, obviously spatial multiplexing is not possible, but there are still gains from precoding. For closed-loop spatial multiplexing and v=2, the codebook index 0 is not used. The UE estimates the radio channel and selects the optimum precoding matrix. This feedback is provided to the eNodeB. Depending on the available bandwidth, this information is made available per resource block or group of resource blocks, since the optimum precoding matrix may vary between resource blocks. The network may configure a subset of the codebook that the UE is able to select from. In case of UEs with high velocity, the quality of the feedback may deteriorate. Thus, an open loop spatial multiplexing mode is also supported which is based on predefined settings for spatial multiplexing and precoding. In case of four antenna ports, different precoders are assigned cyclically to the resource elements. The eNodeB will select the optimum MIMO mode and precoding configuration. The information is conveyed to the UE as part of the downlink control information (DCI) on PDCCH. DCI format 2 provides a downlink assignment of two code words including precoding information. DCI format 2a is used in case of open loop spatial multiplexing. DCI format 1b provides a downlink assignment of 1 code word including precoding information. DCI format 1d is used for multi-user spatial multiplexing with precoding and power offset information. In case of transmit diversity mode, only one code word can be transmitted. Antenna transmits the same information stream, but with different coding. LTE employs Space Frequency Block Coding (SFBC) which is derived from [9] as transmit diversity scheme. A special precoding matrix is applied at transmitter side. At a certain point in Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 43
  50. 50. C hapter 2: 4GLTE time, the antenna ports transmit the same data symbols, but with different coding and on different subcarriers. Figure 28 shows an example for the 2 transmit antenna case, where the transmit diversity specific precoding is applied to an entity of two data symbols d (0) and d (1). Figure 28: Transmit diversity (SFBC) principle Cyclic Delay Diversity (CDD) Cyclic delay diversity is an additional type of diversity which can be used in conjunction with spatial multiplexing in LTE. An antenna-specific delay is applied to the signals transmitted from each antenna port. This effectively introduces artificial multipath to the Signal as seen by the receiver. By doing so, the frequency diversity of the radio channel is increased. As a special method of delay diversity, cyclic delay diversity applies a cyclic shift to the signals transmitted from each antenna port. 2. Uplink MIMO Uplink MIMO schemes for LTE will differ from downlink schemes to take into account terminal complexity issues. For the uplink, MU- can be used. Multiple user terminals may transmit simultaneously on the same resource block. This is also referred to as spatial division multiple access (SDMA). The scheme requires only one transmit antenna as well as transmitter chain at UE side which is a big advantage. The UEs sharing the same resource block have to apply mutually orthogonal pilot patterns. To exploit the benefit of two or more transmit antennas but still keep the UE cost low, transmit antenna selection can be used. In this case, the UE has two transmit antennas but only one transmitter chain and power amplifier. A switch will then choose the antenna that provides the best channel to the eNodeB. This decision is made according to feedback provided by the eNodeB. The CRC parity bits of the DCI format 0 are scrambled with an antenna selection mask indicating UE antenna port 0 or 1. The support of transmit antenna selection is an UE capability. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 44
  51. 51. C hapter 2: 4GLTE D. LTE Protocol Architecture 1. System Architecture Evolution (SAE) SAE (System Architecture Evolution) is a core network architecture that supports the characteristics of LTE. SAE introduces a packet switched mobile core network EPC (Evolved Packet Core) with the following elements:  S-GW (Serving Gateway) and PDN (Packed Data Network) gateway on the user plane and  MME (Mobility Management Entity) on the control plane. The elements of EPC can be incorporated into one or more physical nodes, linked with standardized interfaces, which enable the use of hardware of various manufacturers. Fig. 29 shows a simplified SAE network architecture. SAE separates the user and the control plane. The latter is managed especially by the MME. Because there are no radio network controllers, as individual network elements in SAE, the base station (eNB, eNodeB) connects directly with the MME or S-GW for the exchange of user and control information (Fig. 29). Besides routing data towards the EPC, the eNodeB also schedules and transmits paging messages, selects an MME during network attachment, etc. The eNodeB communicates with mobile terminals over link layer protocols and the RRC, and also implements the functionality of the physical layer presented in the next sections. Figure 29 : Architecture of LTE radio access (E-UTRAN) and core network (EPC) Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 45
  52. 52. C hapter 2: 4GLTE MME is the key control node in the network. It performs the signalization and controls the entities in various layers of the protocol stack. The Serving Gateway supports mobility anchoring during inter-eNodeB handover and inter-3GPP network mobility. It also supports charging and performs routing, forwarding, buffering, marking and interception of data packets. The PDN Gateway ensures the connectivity of the mobile terminal with other packet data networks. The functions of the PDN Gateway include filtering, intercepting and marking of data packets, DHCP (Dynamic Host Configuration Protocol), support for charging and traffic shaping. 2. The Upper Layers Of The LTE Protocol Stack Fig. 30 presents the structure of the link layer for the downlink [10]. The scheme for the uplink is similar. The SAPs (Service Access Points) of the physical layer are known as the transport channels, while those of the MAC (Media Access Control) sublayer are known as logical channels and the SAPs of the link layer are radio bearers. Transport channels correspond to services provided by the physical layer. These services are defined by how and with what characteristics data are transported over the radio interface. Logical channels correspond to the data transfer services that are offered by the MAC sublayer and are defined by the type of information they carry. Logical channels are divided on the control channels that carry data on the control plane and traffic channels that carry the user plane data. Radio bearers correspond to the type of information and quality of service at transmission on the radio interface, e.g. to VoIP, video streaming, file transfer and control plane communications. The MAC sublayer [11] controls access to the physical medium. It performs the mapping among logical and transport channels, and the multiplexing/demultiplexing of these channels. It also performs radio resource allocation, priority handling and HARQbased error corrections. The RLC (Radio Link Control) [12] controls links on the radio interface, performs traffic control, segmentation and reassembly of data packets and error correction based on ARQ (Automatic Repeat reQuest). It provides different modes of operation suitable for different radio bearers. The PDCP (Packet Data Convergence Protocol) [13] converts the PDUs of the higher layers into a format suitable for transfer over the radio interface. It provides insequence delivery of PDUs and security mechanisms, and performs header compression of network-layer PDUs. The RRC (Radio Resource Protocol) [14] is a network layer protocol of the control plane that handles signalization. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 46
  53. 53. C hapter 2: 4GLTE It supports the transmission of broadcast system information and dedicated control information, establishes and maintains services, and controls the QoS. Figure 30 : Link layer structure for the downlink E. Evolution Of Applications And Services The success of the evolution in mobile communications and the improvement of user experience will mostly depend on:  sufficient network capabilities to provide high data rates and low latencies;  sufficient radio signal quality and coverage to ensure availability of services over entire cell area;  efficient means for creating and maintaining connections and quality of services;  independence of services from different access networks;  Competitive prices with various flat-rate fees and unified cost control dependent on the service and not on the access network. While voice transmissions will remain the primary application for the majority of users, new services in LTE will be mainly focused on data and multimedia communications (Fig. 31). The following trends are expected [15], [16]:  Converged services independent of means of Internet access will replace separate fixed and mobile services. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 47
  54. 54. C hapter 2: 4GLTE  Mobile Web 2.0 applications will enable user participation in various communities. Mobile users will be able to create multimedia content and interact in virtual worlds.  Increasing popularity of streaming services, such as video on demand and mobile television.  Real-time and interactive games will become important also in mobile world. The game industry already has a turnover of tens of millions of dollars per year.  The quadruple play (voice, mobile television, Internet, mobile services) will blur the fixed-mobile divide.  Mobile offices with smart phones, portable computers, mobile broadband access and advanced security solutions will free business users from their desks. Figure 31 : Mobile applications with technical requirements and growth drivers 1. New Primary Internet Connection When data rates reach and exceed those of fixed networks, user experience will be the same in fixed and in mobile networks. Users will be able to browse the Web, send and receive e-mails with large attachments, share files on the same servers and play network games anywhere and anytime. Mobile broadband connection could become a Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 48
  55. 55. C hapter 2: 4GLTE primary network connection in portable computers, providing an alternative to DSL (Digital Subscriber Line) technologies. 2. Various Degrees of Services The support for quality of service in LTE enables operators to offer various mobile broadband services for different prices and needs. While service bundles with high data rates and low latencies will suit the needs of companies, those for more affordable prices will increase penetration of mobile broadband services among population. 3. Audio and Video on Demand Higher data rates could also enable service providers to offer high quality audio and video on demand. Users will be able to access rich multimedia content more quickly. For example, it would take only a few minutes to download a movie in VGA quality. 4. Mobile Web 2.0 With the increasing popularity of Web 2.0 applications, such as blogging and social networking, more and more users share their own photos, music and videos. Fast uplink connection will enable faster transfer of such multimedia content. 5. Consumer Electronics LTE will also enable service providers to better support consumer electronic devices, such as portable multimedia players, video game consoles and digital cameras. Currently, the majority of portable multimedia players uses a cable connection to a desktop computer to download desired multimedia content. Although there are some devices with wireless network interfaces on the market, the coverage of wireless networks is limited. With mobile broadband connection game players could play multiplayer tournaments anywhere and anytime. Multiplayer games usually require realtime interaction among participants that could be easily achieved with LTE. An important field is also consumer electronics in cars. Navigation and mapping systems could be updated anywhere and anytime as also car computer software. The car will become an Internet terminal with interfaces that will provide passengers with access to applications and data. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 49
  56. 56. C 6. hapter 2: 4GLTE Business Applications The LTE„s capabilities will allow operators to offer services dedicated to business users. An example of such a service is a videoconference in which the employees could participate regardless of their location; they could be in their office or in the field. 7. Instantaneous Synchronization Instantaneous synchronization of data in different devices distributed around the globe will also be possible. For example, documents or multimedia that will be created or modified with a device supporting LTE will be automatically synchronized with the user's home computer and accessible with the cell phone. Master²: Systèmes de télécommunication Numérique (STN) Univ.Msila 50

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