1. Oea000041 Lte Sae System Overview Issue 1.03

Contents1 Network Architecture1-21.1 Evolution of Cellular Networks1-31.1.1 Evolution of Cellular Networks1-31.1.2 3GPP Releases1-71.2 EPS Architecture1-131.2.1 User Equipment1-141.2.2 Evolved Node B1-161.2.3 Mobility Management Entity1-171.2.4 The Serving Gateway (S-GW)1-181.2.5 The PDN Gateway1-181.3 E-UTRAN Protocol Stack Structure1-181.3.1 Uu Interface1-191.3.2 S1 Interface1-211.3.3 X2 Interface1-222 LTE Air Interface Principles2-12.1 Principle of OFDM2-22.1.2 OFDM Symbol Mapping2-62.1.3 Advantage 1 of OFDM: High Spectral Efficiency2-72.1.4 Advantage 2 of OFDM: Effectively Withstand Multi-Path2-82.1.5 Advantage 3 of OFDM: Resistant to Frequency Selection Fading2-92.1.6 Disadvantage 1 of OFDM: Vulnerable to Frequency Offset2-102.1.7 Disadvantage 2 of OFDM: High PAPR2-112.1.8 OFDM Advantages and Disadvantages2-112.2 Multiple Access and Duplex Technologies2-122.3 Carrier Frequency and EARFCN2-222.3.1 LTE Release 8 Bands2-222.4 LTE Frame Structures2-242.4.1 LTE Frame Structure Type1-FDD2-252.4.2 LTE Frame Structure Type2-TDD2-252.4.3 Cyclic Prefix2-272.4.4 LTE Resource Block Conception2-282.5 LTE Channel Structures2-312.5.1 Logical Channels2-312.5.2 Transport Channels2-332.5.3 Physical Channels2-342.5.4 Radio Channels2-342.5.5 Mapping Relationship between Physical Channels and Other Channels2-352.5.6 Application of LTE Physical Channels2-362.5.7 Cell Specific Reference Signals2-372.5.8 LTE Physical Signals2-392.5.9 Downlink Reference Signals2-392.6 Physical Procedures2-402.6.1 LTE Cell Search Procedure2-402.6.2 Cell Search2-412.6.3 PLMN Selection2-452.6.4 Random Access Procedure Overview2-472.7 Multiple Input Multiple Output2-492.7.1 Background of Multi-antenna Technology2-492.7.2 The Classification of Multi-antenna Technology2-502.7.3 MIMO Overview2-512.7.4 The Advantage of MIMO2-553 eNB Product Overview3-13.1 The Huawei eNB Family3-23.1.1 BTS3900(A) LTE3-23.1.2 DBS3900 LTE3-43.2 Products and Application Scenarios3-53.2.1 BTS3900(A) LTE3-53.2.2 DBS3900 LTE3-63.3 Operation and Maintenance3-63.3.1 The Operations and Maintenance System3-63.3.2 Benefits3-74 Glossary4-9

FiguresFigure 1-1 Evolution of Cellular Networks1-3Figure 1-2 Second Generation Mobile Systems1-4Figure 1-3 Third Generation Mobile Systems1-6Figure 1-4 Fourth Generation Mobile Systems1-7Figure 1-5 3GPP Releases1-7Figure 1-6 HSDPA (Release 5)1-9Figure 1-7 HSUPA (Release 6)1-9Figure 1-8 HSPA+ (Release 7)1-10Figure 1-9 Release 8 HSPA+ and LTE1-11Figure 1-10 Release 9 and Beyond1-11Figure 1-11 LTE Reference Architecture1-13Figure 1-12 EPS Network Architecture-2G/3G Co-existence1-14Figure 1-13 User Equipment Functional Elements1-15Figure 1-14 Evolved Node B Functional Elements1-17Figure 1-15 E-UTRAN Interfaces1-19Figure 1-16 Uu Interface Protocols1-19Figure 1-17 S1 Interface Protocols1-21Figure 1-18 X2 Interface Protocols1-23Figure 2-1 Use of OFDM in LTE2-2Figure 2-2 Frequency Division Multiple2-3Figure 2-3 Time Division Multiple2-3Figure 2-4 Code Division Multiple2-3Figure 2-5 FDM Carriers2-4Figure 2-6 OFDM Subcarriers2-4Figure 2-7 Inverse Fast Fourier Transform2-5Figure 2-8 Fast Fourier Transform2-5Figure 2-9 OFDM Symbol Mapping2-6Figure 2-10 OFDM PAPR (Peak to Average Power Ratio)2-7Figure 2-11 Multicarrier modulation technology2-7Figure 2-12 Delay Spread2-8Figure 2-13 Cyclic Prefix2-9Figure 2-14 Resistant to Frequency Selection Fading2-9Figure 2-15 Vulnerable to Frequency Offset2-10Figure 2-16 Multi-carrier system signal process procedure2-11Figure 2-17 Radio Interface Techniques2-12Figure 2-18 Frequency Division Multiple Access2-12Figure 2-19 Time Division Multiple Access2-13Figure 2-20 Code Division Multiple Access2-13Figure 2-21 Orthogonal Frequency Division Multiple Access2-14Figure 2-22 The comparison between DM and DMA2-15Figure 2-23 From FDM/FDMA to OFDM/OFDMA2-16Figure 2-24 SC-FDMA Subcarrier Mapping Concept2-18Figure 2-25 SC-FDMA Signal Generation2-19Figure 2-26 SC-FDMA and the eNB2-19Figure 2-27 Frequency Division Duplex2-20Figure 2-28 Time Division Duplex2-21Figure 2-29 TDD: The uplink and downlink use different slots.2-21Figure 2-30 FDD: The uplink and downlink use different frequencies.2-22Figure 2-31 EARFCN Calculation2-24Figure 2-32 Example Downlink EARFCN Calculation2-24Figure 2-33 FDD Radio Frame2-25Figure 2-34 TDD Radio Frame2-26Figure 2-35 Special Subframe2-27Figure 2-36 Normal and Extended Cyclic Prefix2-27Figure 2-37 CP classification2-28Figure 2-38 LTE resource block2-28Figure 2-39 Resource Block and Resource Element2-30Figure 2-40 Relationship between Channel BW and RB2-31Figure 2-41 LTE Channels2-31Figure 2-42 Location of Channels2-31Figure 2-43 BCCH and PCH Logical Channels2-32Figure 2-44 CCCH and DCCH Signaling2-32Figure 2-45 Dedicated Traffic Channel2-33Figure 2-46 LTE Release 8 Transport Channels2-34Figure 2-47 Radio Channel2-35Figure 2-48 Mapping Relationship between Physical Channels and Other Channels2-35Figure 2-49 Application of LTE Physical Channels2-36Figure 2-50 Reference Signals - One Antenna Port2-37Figure 2-51 Reference Signal Physical Cell ID Offset2-38Figure 2-52 Reference Signals - Two Antenna Ports (Normal CP)2-38Figure 2-53 Reference Signals - Four Antenna Ports (Normal CP)2-38Figure 2-54 Downlink Cell ID2-39Figure 2-55 Initial Procedures2-40Figure 2-56 PSS and SSS for Cell Search (FDD Mode)2-41Figure 2-57 PSS and SSS Location for FDD2-42Figure 2-58 PSS and SSS Location for TDD2-42Figure 2-59 Downlink Cell ID2-43Figure 2-60 Physical Cell Identities2-43Figure 2-61 System information scheduling2-44Figure 2-62 Contents of System Information2-44Figure 2-63 PLMN Selection2-45Figure 2-64 LTE Cell Selection2-47Figure 2-65 Overall Random Access Procedure2-48Figure 2-66 Random Access RRC Signaling Procedure2-48Figure 2-67 Uplink synchronization2-49Figure 2-68 The relationship between spectrum efficiency of channel and signal power & signal bandwidth2-50Figure 2-69 Tx diversity mode2-50Figure 2-70 Spatial multiplexing mode2-51Figure 2-71 Beamforming mode2-51Figure 2-72 MIMO2-52Figure 2-73 SISO2-52Figure 2-74 MISO2-52Figure 2-75 SIMO2-53Figure 2-76 MIMO2-53Figure 2-77 SU-MIMO, MU-MIMO and Co-MIMO2-54Figure 2-78 The advantage of MIMO2-55Figure 3-1 BTS3900(A) LTE Architecture3-3Figure 3-2 BBU39003-3Figure 3-3 LRFU3-4Figure 3-4 DBS3900 LTE Architecture3-4Figure 3-5 RRU3-5Figure 3-6 O&M System3-7

ContentsLTE/SAE System OverviewTraining Manual

LTE/SAE System OverviewTraining ManualContents

iiHuawei Proprietary and Confidential Copyright Huawei Technologies Co., LtdIssue 01 (2010-05-01)

Issue 01 (2010-05-01)Huawei Proprietary and Confidential Copyright Huawei Technologies Co., Ltdi

TablesTable 1-1 2G, 2.5G and 2.75G GSM/GPRS Systems1-4Table 1-2 IMT Advanced Features1-5Table 1-3 UE Categories1-14Table 2-1 LTE Channel and FFT Sizes2-6Table 2-2 SC-FDMA verses OFDMA2-20Table 2-3 LTE Release 8 Frequency Bands2-22Table 2-4 DL/UL Subframe Allocation Item2-26Table 2-5 Special Subframe Allocation Item2-27Table 2-6 Channel bandwidth and RB2-30Table 2-7 LTE DL/UL MIMO mode2-54

Network ArchitectureObjectivesOn completion of this section the participants will be able to:1.1 Describe the evolution of cellular networks.1.2 Summarize the evolution of 3GPP releases, from Release 99 to Release 9 and beyond.1.3 Explain the logical architecture of the E-UTRAN.1.4 Describe the interfaces and associated protocols within the E-UTRAN.1.5 Explain the logical architecture of the EPS.

Evolution of Cellular NetworksEvolution of Cellular NetworksCellular mobile networks have been evolving for many years. The initial systems, which are referred to as First Generation, now had been replaced with Second Generation and Third Generation solutions. However today, 4G or Fourth Generation systems are now being deployed.Evolution of Cellular Networks

First Generation Mobile SystemsThe 1G (First Generation) mobile systems were not digital, i.e. they utilized analogue modulation techniques. The main systems included: AMPS (Advanced Mobile Telephone System) - This first appeared in 1976 in the United States and was mainly implemented in the Americas, Russia and Asia. Various issues including weak security features made the system prone to hacking and handset cloning.TACS (Total Access Communications System) - This was the European version of AMPS but with slight modifications including the operation on different frequency bands. It was mainly used in the United Kingdom, as well as parts of Asia.ETACS ((Extended Total Access Communication System) - This provided an improved version of TACS. It enabled a greater number of channels and therefore facilitated more users.These analogue systems were all proprietary based FM (Frequency Modulation) systems and therefore they all lacked security, any meaningful data service and international roaming capability. Second Generation Mobile Systems2G (Second Generation) systems utilize digital multiple access technology, such as TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access). Figure 1-2 illustrates some of the different 2G mobile systems including:GSM (Global System for Mobile communications) - this is the most successful of all 2G technologies. It was initially developed by ETSI (European Telecommunications Standards Institute) for Europe and designed to operate on the 900MHz and 1800MHz frequency bands. It now has world-wide support and is available for deployment on many other frequency bands, such as 850MHz and 1900MHz. A mobile described as tri band or quad band indicates support for multiple frequency bands on the same device. GSM utilizes TDMA and as such, it employs 8 timeslots on a 200kHz radio carrier.cdmaOne - this is a CDMA (Code Division Multiple Access) system based on the IS-95 (Interim Standard 95). It uses a spread spectrum technique which incorporates a mixture of codes and timing to identify cells and channels. The system bandwidth is 1.25MHz.D-AMPS (Digital - Advanced Mobile Phone System) - this is based on the IS-136 (Interim Standard 136) and is effectively an enhancement to AMPS. Supporting a TDMA access technique, D-AMPS is primarily used on the North American continent, as well as in New Zealand and parts of the Asia-Pacific region. Second Generation Mobile Systems

In addition to being digital, with the associated improvements in capacity and security, these 2G digital systems also offer enhanced services such as SMS (Short Message Service) and circuit switched data.2.5G SystemsMost 2G systems have now been evolved. For example, GSM was extended with GPRS (General Packet Radio System) to support efficient packet data services, as well as increasing the data rates. As this feature does not meet 3G requirements, GPRS is therefore often referred to as 2.5G. A comparison been 2G and 2.5G systems is illustrated in Table 1-1.2.75G SystemsGSM/GPRS systems also added EDGE (Enhanced Data Rates for Global Evolution). This nearly quadruples the throughput of GPRS. The theoretical data rate of 473.6kbit/s enables service providers to efficiently offer multimedia services. Like that of GPRS, EDGE is usually categorized as 2.75G as it does not fulfill all the requirements of a 3G system.2G, 2.5G and 2.75G GSM/GPRS SystemsSystemServiceTheoretical Data RateTypical Data Rate

2G GSM Circuit Switched9.6kbit/s or 14.4kbit/s9.6kbit/s or 14.4kbit/s

2.5G GPRS Packet Switched171.2kbit/s4kbit/s to 50kbit/s

2.75G EDGE Packet Switched473.6kbit/s120kbit/s

Third Generation Mobile Systems3G (Third Generation) systems, which are defined by IMT2000 (International Mobile Telecommunications - 2000), state that they should be capable of providing higher transmission rates, for example: 2Mbit/s for stationary or nomadic use and 348kbit/s in a moving vehicle. The main 3G technologies are illustrated in Figure 1-3.These include:W-CDMA (Wideband CDMA) - This was developed by the 3GPP (Third Generation Partnership Project). There are numerous variations on this standard, including TD-CDMA and TD-SCDMA. W-CDMA is the main evolutionary path from GSM/GPRS networks. It is a FDD (Frequency Division Duplex) based system and occupies a 5MHz carrier. Current deployments are mainly at 2.1GHz, however deployments at lower frequencies are also being seen, e.g. UMTS1900, UMTS900, UMTS850 etc. W-CDMA supports voice and multimedia services with an initial theoretical rate of 2Mbit/s however, most service providers were initially offering 384kbit/s per user. This technology is continuing to evolve and later 3GPP releases have increased the rates to in excess of 40Mbit/s. TD-CDMA (Time Division CDMA) - This is typically referred to as UMTS TDD (Time Division Duplex) and is part of the UMTS specifications, however it has only limited support. The system utilizes a combination of CDMA and TDMA to enable efficient allocation of resources. TD-SCDMA (Time Division Synchronous CDMA) - This was jointly developed by Siemens and the CATT (China Academy of Telecommunications Technology). TD-SCDMA has links to the UMTS specifications and is often identified as UMTS-TDD LCR (Low Chip Rate). Like TD-CDMA, it is also best suited to low mobility scenarios in micro or pico cells.CDMA2000 - This is a multi-carrier technology standard which uses CDMA. CDMA2000 is actually a set of standards including CDMA2000 EV-DO (Evolution-Data Optimized) which has various revisions. It is worth noting that CDMA2000 is backward compatible with cdmaOne. Third Generation Mobile Systems

WiMAX (Worldwide Interoperability for Microwave Access) - This is another wireless technology which satisfies IMT2000 3G requirements. The air interface is part of the IEEE (Institute of Electrical and Electronics Engineers) 802.16 standard which originally defined PTP (Point-To-Point) and PTM (Point-To-Multipoint) systems. This was later enhanced to provide mobility and greater flexibility. The success of WiMAX is mainly down to the WiMAX Forum, an organization formed to promote conformity and interoperability between vendors.Fourth Generation Mobile Systems4G (Fourth Generation) cellular wireless systems need to meet the requirements set out by the ITU (International Telecommunication Union) as part of IMT Advanced (International Mobile Telecommunications Advanced). Illustrated in Table 1-2, these features enable IMT Advanced to address evolving user needs. IMT Advanced FeaturesKey IMT Advanced Features

A high degree of common functionality worldwide while retaining the flexibility to support a wide range of services and applications in a cost efficient manner.

Compatibility of services within IMT and with fixed networks.

Capability of interworking with other radio access systems.

High quality mobile services.

User equipment suitable for worldwide use.

User-friendly applications, services and equipment.

Worldwide roaming capability.

Enhanced peak data rates to support advanced services and applications (100Mbit/s for high and 1Gbit/s for low mobility were identified as targets).

The three main 4G systems include:LTE Advanced - LTE (Long Term Evolution) is part of 3GPP family of specifications, however it does not meet all IMT Advanced features, as such it is sometimes referred to as 3.99G. In contrast, LTE Advanced is part of a later 3GPP Release and this has been designed specifically to meet 4G requirements.WiMAX 802.16m - The IEEE and the WiMAX Forum have identified 802.16m as their offering for a 4G system. UMB (Ultra Mobile Broadband) - This is identified as EV-DO Rev C. It is part of 3GPP2 however most vendors and service providers have decided to promote LTE instead.Fourth Generation Mobile Systems

3GPP ReleasesThe development of GSM, GPRS, EDGE, UMTS, HSPA and LTE is in stages known as 3GPP Releases. Hardware vendors and software developers use these releases as part of their development roadmap. Figure 1-5 illustrates the main 3GPP Releases that included key enhancements of the radio interface.3GPP Releases

3GPP Releases enhance various aspects of the network and not just the radio interface. For example, Release 5 started the introduction of the IMS (IP Multimedia Subsystem) in the core network.Pre-Release 99Pre-Release 99 saw the introduction of GSM, as well as the addition of GPRS. The main GSM Phases and 3GPP Releases include: GSM Phase 1.GSM Phase 2.GSM Phase 2+ (Release 96).GSM Phase 2+ (Release 97).GSM Phase 2+ (Release 98).Release 993GPP Release 99 saw the introduction of UMTS, as well as the EDGE enhancement to GPRS. UMTS contains all the features needed to meet the IMT-2000 requirements as those defined by the ITU. It is able to support CS (Circuit Switched) voice and video services, as well as PS (Packet Switched) data services over common and dedicated bearers. Initial data rates for UMTS were 64kbit/s, 128kbit/s and 384kbit/s. Note that the theoretical maximum was 2Mbit/s.Release 4Release 4 included enhancements to the core network and in particular the notion of it being bearer independent. Thus the concept of All IP Networks was included and service providers were able to deploy Soft Switch based networks, i.e. the MSC (Mobile Switching Centre) was replaced by the MSC Server and MGW (Media Gateways). This improved network utilization in addition to consolidating engineering knowledge and increasing vendor competition.Release 5Release 5 introduces the first major addition to the UMTS air interface by specifying HSDPA (High Speed Downlink Packet Access) in order to improve both capacity and spectral efficiency. Figure 1-6 illustrates some of the main features associated with Release 5 and these include:Adaptive Modulation - In addition to the original UMTS modulation scheme of QPSK (Quadrature Phase Shift Keying), HSDPA also includes support for 16 QAM (Quadrature Amplitude Modulation).Flexible Coding - Based on fast feedback from the mobile in the form of a CQI (Channel Quality Indicator), the UMTS base station, i.e. the Node B, is able to modify the effective coding rate and thus increase system efficiency.Fast Scheduling - HSDPA includes a 2ms TTI (Time Transmission Interval) which enables the Node B scheduler to quickly and efficiently allocate resources to mobiles.HARQ (Hybrid Automatic Repeat Request) - In the event a packet does not get through to the UE (User Equipment) successfully, the system employs HARQ. This improves the retransmission timing, thus requiring less reliance on the RNC (Radio Network Controller).HSDPA (Release 5)

Release 6Release 6 adds various features, with HSUPA (High Speed Uplink Packet Data) being of most interest to RAN development. Even though the term HSUPA is widespread, this 3GPP enhancement also goes under the term Enhanced Uplink. It is also worth noting that HSDPA and HSUPA work in tandem and thus the term HSPA (High Speed Packet Access) is now in common use. HSUPA, like HSDPA adds functionality to improve packet data. Figure 1-7 illustrates the three main enhancements which include:Flexible Coding - HSUPA has the ability to dynamically change the coding and therefore improve the efficiency of the system.Fast Power Scheduling - A key fact of HSUPA is that it provides a method to schedule the power from different mobiles. This scheduling can use either a 2ms or 10ms TTI.HARQ - Like HSDPA, HSUPA also utilizes HARQ. The main difference is the timing relationship for retransmissions.HSUPA (Release 6)

Enhancements introduced in Release 6 are not limited to HSUPA. For example, GAN (Generic Access Network) technologies are also included which enables alternative radio access technologies such as Wi-Fi (Wireless Fidelity) to be used yet still support true interworking.

Although no longer the correct terminology, UMA (Unlicensed Mobile Access) is still in common use to describe the 3GPPs GAN technology.Release 7The main RAN based feature of Release 7 is HSPA+. This, like HSDPA and HSUPA, provides various enhancements to improve packet switched data delivery. Figure 1-8 illustrates the main features which include:64 QAM - This is available in the DL (Downlink) and enables HSPA+ to operate at a theoretical rate of 21.6Mbit/s.16 QAM - This is available in the UL (Uplink) and enables the uplink to theoretically achieve 11.76Mbit/s.MIMO (Multiple Input Multiple Output) Operation - this is added to HSPA+ Release 7 and offers various benefits including the ability to offer a theoretical 28.8Mbits/s in the downlink.HSPA+ (Release 7)

Power Enhancements -Various enhancements such as CPC (Continuous Packet Connectivity) have been included. This includes DTX (Discontinuous Transmission), DRX (Discontinuous Reception) and HS-SCCH (High Speed - Shared Control Channel) Less Operation etc. Collectively these improve the mobiles battery consumption.Less Overhead - The downlink includes an enhancement to the MAC (Medium Access Control) layer which effectively means that fewer headers are required. This in turn reduces overhead and thus improves the system efficiency.Release 8There are many additions to the RAN functionality in Release 8, such as an enhancement to HSPA+. However the main aspect is the inclusion of LTE (Long Term Evolution). Figure 1-9 illustrates some of the main features for Release 8 HSPA+ and LTE.Release 8 HSPA+ enables various key enhancements, these include:64 QAM and MIMO - Release 8 enables the combination of 64 QAM and MIMO, thus quoting a theoretical rate of 42Mbit/s, i.e. 2 x 21.6Mbit/s.Dual Cell Operation - DC-HSDPA (Dual Cell - HSDPA) is a Release 8 feature which is further enhanced in Release 9 and Release 10. It enables a mobile to effectively utilize two 5MHz UMTS carriers. Assuming both are using 64 QAM (21.6Mbit/s), the theoretical maximum is 42Mbps. Note that in Release 8, a mobile is not able to combine MIMO and DC-HSDPA. Less Uplink Overhead - In a similar way to Release 7 in the downlink, the Release 8 uplink has also been enhanced to reduce overhead. Release 8 HSPA+ and LTE

LTE provides a new radio access technique, as well as enhancements in the E-UTRAN (Evolved - Universal Terrestrial Radio Access Network). These enhancements are further discussed as part of this course. Release 9 and BeyondEven though LTE is a Release 8 system, it is yet further enhanced in Release 9. There are a huge number of features in Release 9. One of the most important is the support of additional frequency bands. Release 9 and Beyond

Release 10 includes the standardization of LTE Advanced, i.e. the 3GPPs 4G offering. As such, it includes the modification of the LTE system to facilitate 4G services.3GPP Evolution: From LTE to LTE-A/B/C

Heterogeneous or HetNet for short stands for the different types of base stations (macro, micro, pico, relay) that are operating on different technologies (GSM, WCDMA and LTE)that are used together in the same network to build the good coverage and high capacity that end-users demand from their operator (contrary to homogeneous networks that are mainly built with one type of base station, often macro).FusionNet Huawei in Barcelona at the Mobile World Congress (MWC 2013) demonstrated the next generation LTE-B (R12/R13) network architecture FusionNet. It combines multi-system, multi-band, multi-layer heterogeneous networks, improved 500% cell edge user throughput, which really create borderless networks. The core of FusionNet is bases on LTE-B techniques (such as multi-flow aggregation, interference coordination, service adaptation, spectrum efficiency optimization, etc.), and with the existing LTE, LTE-A (such as multi-point coordinate, carrier aggregation), which realizes multi-system, multi-band, multi-layer network of deep integration, help operators significantly reduce CAPEX and OPEX, allowing users to enjoy ultra-broadband, zero-waiting and ubiquitous connectivity.LTE Technical Obiectives

EPS ArchitectureIn contrast to the 2G and 3G networks defined by the 3GPP, LTE can be simply divided into a flat IP based bearer network and a service enabling network. The former can be further subdivided into the E-UTRAN (Evolved - Universal Terrestrial Radio Access Network) and the EPC (Evolved Packet Core) where as support for service delivery lies in the IMS (IP Multimedia Subsystem). This reference architecture can be seen in Figure 1-11.LTE Reference Architecture

Whilst UMTS is based upon W-CDMA technology, the 3GPP developed new specifications for the LTE air interface based upon OFDMA (Orthogonal Frequency Division Multiple Access) in the downlink and SC-FDMA (Single Carrier - Frequency Division Multiple Access) in the uplink. This new air interface is termed the E-UTRA (Evolved - Universal Terrestrial Radio Access).EPS Network Architecture-2G/3G Co-existence

In the evolution of core network, packet domain of core network also evolves forward to SAE(System Architecture Evolution, also usually called EPC(Evolved Packet Core). SAE is based on packet domain, and does not support circuit domain any longer.

0. User EquipmentLike that of UMTS, the mobile device in LTE is termed the UE (User Equipment) and is comprised of two distinct elements; the USIM (Universal Subscriber Identity Module) and the ME (Mobile Equipment).The ME supports a number of functional entities including:RR (Radio Resource) - this supports both the Control Plane and User Plane and in so doing, is responsible for all low level protocols including RRC (Radio Resource Control), PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control) and the Phy (Physical) Layer.EMM (EPS Mobility Management) - is a Control Plane entity which manages the mobility management states the UE can exist in; LTE Idle, LTE Active and LTE Detached. Transactions within these states include procedures such as TAU (Tracking Area Update) and handovers.ESM (EPS Session Management) - is a Control Plane activity which manages the activation, modification and deactivation of EPS bearer contexts. These can either be default EPS bearer contexts or dedicated EPS bearer contexts.User Equipment Functional Elements

In terms of the Phy layer, the capabilities of the UE may be defined in terms of the frequencies and data rates supported. Devices may also be capable of supporting adaptive modulation including QPSK (Quadrature Phase Shift Keying), 16QAM (16 Quadrature Amplitude Modulation) and 64QAM (Quadrature Amplitude Modulation).In terms of the radio spectrum, the UE is able to support several scalable channels including; 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz and 20MHz whilst operating in FDD (Frequency Division Duplex) and/or TDD (Time Division Duplex). Furthermore, the UE may also support advanced antenna features such as MIMO (Multiple Input Multiple Output) which is discussed in at 2.7 .

UE Categories

UE IdentitiesAn LTE capable UE will be allocated / utilize a number of identities during operation within the network. These include:IMSI (International Mobile Subscriber Identity) - this complies with the standard 3GPP format and is comprised of the MCC (Mobile Country Code), MNC (Mobile Network Code) and the MSIN (Mobile Subscriber Identity Number). This uniquely identifies a subscriber from within the family of 3GPP technologies - GSM, GPRS, UMTS etc.IMEI (International Mobile Equipment Identity) - is used to uniquely identify the ME. It can be further subdivided into a TAC (Type Approval Code), FAC (Final Assembly Code) and SNR (Serial Number).GUTI (Globally Unique Temporary Identity) - is allocated to the UE by the MME (Mobility Management Entity) and identifies a device to a specific MME. The identity is comprised of a GUMMEI (Globally Unique MME Identity) and an M-TMSI (MME - Temporary Mobile Subscriber Identity).S-TMSI (Serving - Temporary Mobile Subscriber Identity) - is used to protect a subscribers IMSI during NAS (Non Access Stratum) signaling between the UE and MME as well as identifying the MME from within a MME pool. The S-TMSI is comprised of the MMEC (MME Code) and the M-TMSI.IP Address - the UE requires a routable IP address from the PDN (Packet Data Network) from which it is receiving higher layer services. This may either be an IPv4 or IPv6 address.Evolved Node BIn addition to the new air interface, a new base station has also be specified by the 3GPP and is referred to as an eNB (Evolved Node B). These, along with their associated interfaces form the E-UTRAN and in so doing, are responsible for:Functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);IP header compression and encryption of user data stream;Selection of an MME at UE attachment when no routing to an MME can be determined from the information provided by the UE;Routing of User Plane data towards Serving Gateway;Scheduling and transmission of paging messages (originated from the MME);Scheduling and transmission of broadcast information (originated from the MME or O&M);Measurement and measurement reporting configuration for mobility and scheduling;Scheduling and transmission of PWS (which includes ETWS and CMAS) messages (originated from the MME);CSG handlingEvolved Node B Functional Elements

Security in LTE is not solely limited to encryption and integrity protection of information passing across the air interface but instead, NAS encryption and integrity protection between the UE and MME also takes place. In addition, IPSec may also be used to protect user data within both the E-UTRAN and EPC.eNB IdentitiesIn addition to the UE identities already discussed, there are a number of specific identities associated with the eNB. These include:TAI (Tracking Area Identity) - is a logical group of neighboring cells defined by the service provider in which an LTE idle UE is able to move within without needing to update the network. As such, it is similar to a RAI (Routing Area Identity) used in 2G and 3G packet switched networks.ECGI (Evolved Cell Global Identity) - is comprised of the MCC, MNC and ECI (Evolved Cell Identity), the later being coded by each service provider.

Mobility Management Entity The MME hosts the following functions (see 3GPP TS 23.401 [17]):NAS signalling; NAS signalling security; AS Security control;Inter CN node signalling for mobility between 3GPP access networks;Idle mode UE Reachability (including control and execution of paging retransmission);Tracking Area list management (for UE in idle and active mode);PDN GW and Serving GW selection;MME selection for handovers with MME change;SGSN selection for handovers to 2G or 3G 3GPP access networks;Roaming;Authentication;Bearer management functions including dedicated bearer establishment;Support for PWS (which includes ETWS and CMAS) message transmission;Optionally performing paging optimisation.NOTE 1: For macro eNBs, the MME should not filter the PAGING message based on the CSG IDs.The Serving Gateway (S-GW)The Serving Gateway (S-GW) hosts the following functions (see 3GPP TS 23.401 [17]):The local Mobility Anchor point for inter-eNB handover;Mobility anchoring for inter-3GPP mobility;E-UTRAN idle mode downlink packet buffering and initiation of network triggered service request procedure;Lawful Interception;Packet routeing and forwarding;Transport level packet marking in the uplink and the downlink;Accounting on user and QCI granularity for inter-operator charging;UL and DL charging per UE, PDN, and QCI.The PDN GatewayThe PDN Gateway (P-GW) hosts the following functions (see 3GPP TS 23.401 [17]):Per-user based packet filtering (by e.g. deep packet inspection);Lawful Interception;UE IP address allocation;Transport level packet marking in the downlink;UL and DL service level charging, gating and rate enforcement;DL rate enforcement based on APN-AMBR;NOTE 2: it is assumed that no other logicalE-UTRAN node than the eNB is needed for RRM purposes. Moreover, due to the different usage of inter-cell RRM functionalities, each inter-cell RRM functionality should be considered separately in order to assess whether it should be handled in a centralised manner or in a distributed manner.E-UTRAN Protocol Stack StructureAs with all 3GPP technologies, it is the actual interfaces which are defined in terms of the protocols they support and the associated signaling messages and user traffic that traverse them.E-UTRAN Interfaces

0. Uu InterfaceThe Uu Interface supports both a Control Plane and a User plane and spans the link between the UE and the eNB / HeNB. The principle Control Plane protocol is RRC while the User Plane is designed to carry IP datagrams. However, both Control and User Planes utilize the services of PDCP, RLC and MAC.Uu Interface Protocols

Radio Resource ControlRRC deals with all the signaling between the UE and the E-UTRAN in addition to transporting NAS signaling between the UE and the MME. It also provides the main configuration and parameters to the lower layer protocols. For example, the Phy Layer will receive information from RRC on how to configure certain of its aspects. A UE A UE has 2 RRC states. There are RRC_IDLE and RRC_CONNECTED.RRC_IDLE: A UE is in RRC_IDLE state when the UE does not have an RRC connection.DRX can be used for the UE to save the UE power.The UE monitors the paging channel.The UE measures the neighboring cell and reselects a cell.The UE gets system information.The UE updates TAU periodically.

RRC_CONNECTED: A UE is in RRC_CONNECTED state when at least one RRC connection is established for the UE.The UE transmits downlink and uplink data.The UE manages the mobility.The UE provides channel quality and feedback information.The UE supports DRX configuration to save the UE power.Packet Data Convergence ProtocolPDCP operates on both the Control Plane and User Plane. In addition to IP header compression and sequencing / duplicate packet detection, PDCP is also responsible for security on the air interface. As such, its key responsibilities include:Encryption - Control Plane and User Plane.Integrity Checking - Control Plane.IP Header Compression - User Plane.Sequencing and Duplicate Detection - User Plane.Radio Link ControlAs the name would suggest, RLC provides radio link control in the UE and eNB and in so doing, it provides three delivery services to the higher layers. These are:TM (Transparent Mode) - this provides a connectionless service and is utilized for some of the air interface channels e.g. broadcast and paging.UM (Unacknowledged Mode) - like that of TM, this also provides a connectionless service but with additional functionality incorporating sequencing, segmentation and concatenation.AM (Acknowledged Mode) - this supports ARQ (Automatic Repeat Request) thereby operating in a connection orientated mode.Medium Access ControlMAC provides the interface between the E-UTRA protocols and the Phy Layer and supports the following services:Mapping - this is the mapping of information between the logical and transport channels.Multiplexing - in order to increase system efficiency, information from different Radio Bearers is multiplexed into the same TB (Transport Block).HARQ (Hybrid Automatic Repeat Request) - provides error correction services over the air interface. This requires close interworking with the Physical Layer.Radio Resource Allocation - this is the scheduling of traffic and signaling to users based upon QoS.PhysicalThe Physical Layer incorporates a number of functions. These include:Error Detection.FEC (Forward Error Correction) Encoding / Decoding.Rate Matching.Physical Channel Mapping.Power Weighting.RF (Radio Frequency) Modulation and Demodulation.Frequency and Time Synchronization.Radio Measurements.MIMO Processing.Transmit Diversity.Beamforming.RF Processing.S1 InterfaceThe S1 Interface can be subdivided into the S1-MME interface supporting Control Plane signaling between the eNB and the MME and the S1-U Interface supporting User Plane traffic between the eNB and the S-GW.S1 Interface Protocols

S1AP: The S1 Application Protocol is the application layer protocol between eNodeB and MME. SCTP: The Stream Control Transmission Protocol ensures the delivery of signaling messages on the S1 interface between the MME and the eNodeB. For details about SCTP, see RFC2960. GTP-U: The GPRS Tunneling ProtocolUser plane is used for user data transmission between the eNdoeB and S-GW. UDP: User Datagram Protocol is used for the user data transmission. For details about UDP, see RFC 768. The data link layer can use layer 2 technologies, such as PPP and Ethernet.S1 Application ProtocolThe S1AP spans the S1-MME interface and in so doing, supports the following functions:E-RAB (Evolved - Radio Access Bearer) Management - this incorporates the setting up, modifying and releasing of the E-RABs by the MME.Initial Context Transfer - is used to establish an S1UE context in the eNB, setup the default IP connectivity and transfer NAS related signaling.UE Capability Information Indication - is used to inform the MME of the UE Capability Information.Mobility - this incorporates mobility features to support a change in eNB or change in RAT.Paging.S1 Interface Management - this incorporates a number of sub functions dealing with resets, load balancing and system setup etc.NAS Signaling Transport - the transport of NAS related signaling over the S1-MME Interface.UE Context Modification and Release - this allows for the modification and release of the established UE Context in the eNB and MME respectively.Location Reporting - this enables the MME to be made aware of the UEs current location within the network.

X2 InterfaceThe X2 Interface interconnects two eNBs and in so doing supports both a Control Plane and User Plane. It also extends the S1 Interface when two or more eNBs lie between the UE and the EPC. The X2AP (X2 Application Protocol) Control Plane protocol resides on SCTP (Stream Control Transmission Protocol) where as the IP is transferred over the User Plane using the services of GTP-U (GPRS Tunneling Protocol - User) and UDP (User Datagram Protocol).The X2 interface is divided into the user plane (X2-U) and control plane (X2-C). The X2-U interface is required to be the same as the S1-U, and the X2-C is required to be the same as S1-C.The X2 interface data link layer can use layer 2 technologies, such as PPP and Ethernet.X2 Application ProtocolThe X2AP is responsible for the following functions:Mobility Management - this enables the serving eNB to move the responsibility of a specified UE to a target eNB. This includes Forwarding the User Plane, Status Transfer and UE Context Release functions.Load Management - this function enables eNBs to communicate with each other in order to report resource status, overload indications and current traffic loading.Error Reporting - this allows for the reporting of general error situations for which specific error reporting mechanism have not been defined.Setting / Resetting X2 - this provides a means by which the X2 interface can be setup / reset by exchanging the necessary information between the eNBs.Configuration Update - this allows the updating of application level data which is needed for two eNBs to interoperate over the X2 interface.X2 Interface Protocols

Stream Control Transmission ProtocolDefined by the IETF (Internet Engineering Task Force) rather than the 3GPP, SCTP was developed to overcome the shortfalls in TCP (Transmission Control Protocol) and UDP when transferring signaling information over an IP bearer. Functions provided by SCTP include:Reliable Delivery of Higher Layer Payloads.Sequential Delivery of Higher Layer Payloads.Improved resilience through Multihoming.Flow Control.Improved Security.

SCTP is also found on the S1-MME Interface which links the eNB to the MME.GPRS Tunneling Protocol - UserGTP-U tunnels are used to carry encapsulated PDU (Protocol Data Unit) and signaling messages between endpoints or in the case of the X2 interface. Numerous GTP-U tunnels may exist in order to differentiate between EPS bearer contexts and these are identified through a TEID (Tunnel Endpoint Identifier).

GTP-U is also found on the S1-U Interface which links the eNB to the S-GW and may also be used on the S5 Interface linking the S-GW to the PDN-GW.

4 GlossaryLTE/SAE System OverviewTraining Manual

LTE/SAE System OverviewTraining Manual4 Glossary

4-12Huawei Proprietary and Confidential Copyright Huawei Technologies Co., LtdIssue 01 (2010-05-01)

Issue 01 (2010-05-01)Huawei Proprietary and Confidential Copyright Huawei Technologies Co., Ltd4-11

LTE Air Interface PrinciplesObjectivesOn completion of this section the participants will be able to:2.1 Describe the principles of OFDM.2.2 Describe the multiple access and duplex technology.2.3 Describe the carrier frequency and EARFCN2.4 Describe the LTE frame structure2.5 Describe the LTE channel structure2.6 Have a good understanding of the OFDMA and SC-FDMA.2.7 Describe cell selection procedure and random access procedure.2.8 Describe MIMO.Principle of OFDMPrinciples of OFDMThe LTE air interface utilizes two different multiple access techniques, both of which are based on OFDM (Orthogonal Frequency Division Multiplexing). These are:OFDMA (Orthogonal Frequency Division Multiple Access) - used on the downlink.SC-FDMA (Single Carrier - Frequency Division Multiple Access) - used on the uplink.Use of OFDM in LTE

The concept of OFDM is not new and is currently being used on various systems such as Wi-Fi (Wireless Fidelity) and WiMAX (Worldwide Interoperability for Microwave Access). Furthermore, it was even considered for UMTS back in 1998. One of the main reasons why it was not chosen at the time however was the handsets limited processer power and the poor battery capabilities. LTE was able to choose an OFDM based access due to the fact mobile handset processing capabilities and battery performance have both significantly improved over the intervening years. In addition, there is continual pressure to produce ever more spectrally efficient systems.Division Multiplexing OverviewMultiplexed data streams can be used for one or multiple UEs.FDM (Frequency Division Multiplexing): Available spectrum divides into multi-sub-bands or channels. Each sub-bands or channel transmits one signal (data streams).TDM (Time Division Multiplexing): The entire transmission channel time is divided into several time slots, and these time slots are assigned to each signal source, each of the signal sources in their own exclusive channel time slot for data transmission.CDM (Code Division Multiplexing): All sub-channels can use the entire channel for data transmission at the same time, different codes are used to distinguish various original signals.Frequency Division Multiple

Time Division Multiple

Code Division Multiple

OFDM OverviewOFDM is based on FDM (Frequency Division Multiplexing) and is a method whereby multiple frequencies are used to simultaneously transmit information. Figure 2-5 illustrates an example of FDM with four subcarriers. These can be used to carry different information and to ensure that each subcarrier does not interfere with the adjacent subcarrier, a guard band is utilized. In addition, each subcarrier has slightly different radio characteristics and this may be used to provide diversity.FDM Carriers

FDM systems are not that spectrally efficiency (when compared to other systems) since multiple guard bands are required.OFDM follows the same concept as FDM but it drastically increases spectral efficiency by reducing the spacing between the subcarriers. Figure 2-6 illustrates how the subcarriers can overlap due to their orthogonally with the other subcarriers, i.e. the subcarriers are mathematically perpendicular to each other. As such, when a subcarrier is at its maximum, the two adjacent subcarriers are passing through zero. Furthermore, OFDM systems still employ guard bands. These are however located at the upper and lower parts of the channel in order to reduce adjacent channel interference.OFDM Subcarriers

The centre subcarrier, known as the DC (Direct Current) subcarrier, is not typically used in OFDM systems due to its lack of orthogonality. Fast Fourier TransformsOFDM subcarriers are generated and decoded using mathematical functions called FFT (Fast Fourier Transform) and IFFT (Inverse Fast Fourier Transform). The IFFT is used in the transmitter to generate the waveform. Figure 2-7 illustrates how the coded data is first mapped to parallel streams before being modulated and processed by the IFFT. Inverse Fast Fourier Transform

Modulation procedure of OFDM is realized by IFFT (Inverse Fast Fourier Transform), N is the sampling period of symbol.For example: Sampling rate fs =1/Ts =N*fFor bandwidth 20MHz, N=2048, f15kHzsampling rate30.72MHz At the receiver side, this signal is passed to the FFT which analyses the complex/combined waveform to generate the original streams. Figure 2-8 illustrates the FFT process. Fast Fourier Transform

Similar to modulation procedure of OFDM FFT process is used in the demodulation procedure of OFDM.LTE FFT SizesFast Fourier Transforms and Inverse Fast Fourier Transforms both have a defining size. For example, an FFT size of 512 indicates that there are 512 subcarriers. In reality, not all 512 subcarriers can be utilized for data transfer due to the channel guard bands and the fact that a DC (Direct Current) subcarrier is also required.Table 2-1 illustrates the channel bandwidth options available to LTE, as well as the FFT size and associated sampling rate. Using the sampling rate and the FFT size, the subcarrier spacing can be calculated, e.g. 7.68MHz/512 = 15kHz.LTE Channel and FFT SizesChannel BandwidthFFT SizeSubcarrier BandwidthSampling Rate

1.4MHz12815kHz1.92MHz

3MHz2563.84MHz

5MHz5127.68MHz

10MHz102415.36MHz

15MHz153623.04MHz

20MHz204830.72MHz

The subcarrier spacing of 15kHz is also used to identify the OFDM symbol duration.OFDM Symbol MappingThe mapping of OFDM symbols to subcarriers is dependent on the system design. The first 12 modulated OFDM symbols are mapped to 12 subcarriers, i.e. they are transmitted at the same time but using different subcarriers. The next 12 subcarriers are then mapped to the next OFDM symbol period. In addition, a CP (Cyclic Prefix) is added between the symbols. OFDM Symbol Mapping

LTE allocates resources in groups of 12 subcarriers. This is referred to as a PRB (Physical Resource Block).In the previous example, 12 different modulated OFDM symbols were transmitted simultaneously. Figure 2-10 illustrates how the combined energy from this will result in either constructive peak (when the symbols are the same) or destructive nulls (when the symbols are different). OFDM PAPR (Peak to Average Power Ratio)

Advantage 1 of OFDM: High Spectral Efficiency Subcarriers in the OFDM system are overlapping and orthogonal, which greatly improves the spectral efficiency. How does OFDM work? IFFT on the OFDM transmitter side and FFT on the OFDM receiver side reduce system complexity, enabling OFDM to be widely used. Why does OFDM not become a practical reality until the latest two decades? The development of DSP chips turns OFDM to a practical reality.Figure 2-11 illustrate the traditional FDM multicarrier modulation technology and OFDM multicarrier modulation technology.Multicarrier modulation technology

In traditional FDMA transmission, a channel is divided into multiple independent sub-channels to transmit data streams in parallel, and the sub-channels are separated by a group of filters on the receiver. This method is simple and direct while the spectral efficiency is low because guard-bands are required between sub-channels, which are difficult to achieve by filters. However, subcarriers in the OFDM system are overlapping and orthogonal, which greatly improves the spectral efficiency compared with common FDA systems, as shown in the preceding figure. The orthogonal modulation and demodulation in each sub-channel can be performed using IDFT and DFT. For systems with large N value, FFT can be used. IFFT and FFT are easy to perform with the development of large-scale integrated circuit and DSP technologies, as shown in the preceding figure.Advantage 2 of OFDM: Effectively Withstand Multi-Path The OFDM signal provides some protection in the frequency domain due to the orthogonality of the subcarriers. The main issue to overcome however is delay spread, i.e. multipath interference. Figure 2-12 illustrates two of the main multipath effects, namely delay and attenuation. Without the protection interval between symbols, multi path will produce ISI and ICI. ISI: Inter-symbol Interference, time domain ICI: Inter-Carrier Interference, frequency domain

AltitudeDelay Spread

Receiver, which synchronously receives the multi-delay- signaling of previous symbol (dash line) and the normal signaling of the next symbol (real line), which affect the normal receiving, is affected by ISI in time domain and ICI in frequency domain. TimeISI is typically combated with equalizers. However for the equalizer to be effective, a known bit pattern or training sequence is required. This reduces the system capacity, as well as impacting on the processing required within the device. Instead, OFDM systems employ a CP (Cyclic Prefix).In OFDM system, the loss of orthogonality among subcarriers causes ICI. ICI is often modeled as Gaussian noise and affects both channel estimation and detection of the OFDM symbols.Cyclic PrefixA Cyclic Prefix is utilized in most OFDM systems to combat multipath delays. It effectively provides a guard period for each OFDM symbol. Figure 2-13 illustrates the Cyclic Prefix and identifies its location in the OFDM Symbol. Notice that the Cyclic Prefix is effectively a copy from the back of the original symbol which is then placed in front to make the OFDM symbol (Ts). Cyclic Prefix

LTE has two defined Cyclic Prefix sizes, normal and extended. The extended Cyclic Prefix is designed for larger cells. The size of the Cyclic Prefix relates to the maximum delay spread the system can tolerate. As such, systems designed for macro coverage, i.e. large cell radius, should have a large CP. This does however impact on system capacity as the number of symbols per second is will be reduced. Advantage 3 of OFDM: Resistant to Frequency Selection Fading If deep fading occurs in a frequency, modulate the UE to another subcarrier. Deep fading does not occur simultaneously in all subcarriers due to the frequency selectivity. Therefore, dynamic bit or subcarrier allocation technology can be used to utilize the sub-channels with high SNR and improve the system performance. In a multi-user system, a subcarrier that is in poor performance for a user probably is in good performance for another user. Therefore, a sub-channel is not disabled unless it is in poor performance for all users, which occurs at a low probability. The single-carrier system performs adaptive modulation and coding (AMC) based on the average SINR in the entire system, while the multi-carrier system performs AMC based on the average SINR in different frequency bands. Resistant to Frequency Selection Fading

Disadvantage 1 of OFDM: Vulnerable to Frequency OffsetOrthogonality is required because spectrums of sub-channels overlap each other. Frequency offset of radio signals, such as Doppler Shift, can be caused by radio channel change with time. In addition, the difference between transmitter carrier frequency and receiver oscillator frequency can also cause frequency offset, destroying the orthogonality of subcarriers in the OFDM system. As a result, inter-carrier interference (ICI) among sub-channels is generated, deteriorating the BER of the system. The vulnerability to the frequency offset is the primary disadvantage of the OFDM system. Vulnerable to Frequency Offset

We can use frequency synchronization to solve the frequency offset.Disadvantage 2 of OFDM: High PAPR OFDM systems can suffer from high PAPR (Peak to Average Power Ratio), resulting from the great number of subcarriers in the same phase overlapping in time domain, thus increasing the requirement to power amplifier.Multi-carrier system signal process procedure

Different from single-carrier systems, multi-carrier system outputs combined signals of multiple sub-channels. If these signals are in the same phase, the power of combined signals must be higher than the average power of signals, resulting in a high PAR. To reduce the high PAR, high linearity of the PA in the transmitter is required. If the dynamic range of the PA cannot adjust to the signal change, signals are deformed, changing the spectrum of the combined signals. As a result, the orthogonality of signals in multiple sub-channels is destroyed, leading to interference and deteriorated system performance. We can use high-performance PA in the downlink and SC-FDMA in the uplink to solve these problems.OFDM Advantages and DisadvantagesOFDM AdvantagesOFDM systems typically have a number of advantages:OFDM is almost completely resistant to multi-path interference due to its very long symbol duration.Higher spectral efficiency for wideband channels - 5MHz and above.Flexible spectrum utilization.Relatively simple implementation using FFT and IFFT.OFDM DisadvantagesOFDM also has some disadvantages:Frequency errors and phase noise can cause issues.Doppler shift impacts subcarrier orthogonality.Some OFDM systems can suffer from high PAPR (Peak to Average Power Ratio). Accurate frequency and time synchronization.Multiple Access and Duplex TechnologiesIn wireless cellular systems, mobiles have to share a common medium for transmission. There are several categories of assignment but the main four are: FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access), CDMA (Code Division Multiple Access) and OFDMA (Orthogonal Frequency Division Multiple Access).Radio Interface Techniques

Frequency Division Multiple AccessIn order to accommodate various devices on the same wireless network, FDMA divides the available spectrum into subbands or channels. The concept of FDMA is illustrated in Figure 2-18. Using this technique a dedicated channel can be allocated to a user, whilst other users occupy other channels, i.e. frequencies. In a cellular system, mobiles typically occupy two channels, one for the downlink and one for the uplink. This does however make FDMA less efficient since most data applications are downlink biased. Frequency Division Multiple Access

FDMA channels also suffer since they cannot be too close together as the energy from one channel affects the adjacent/neighboring channels. To combat this, additional guard bands between channels are required which reduces the systems spectral efficiency.Time Division Multiple AccessIn TDMA systems, the channel bandwidth is shared in the time domain. Figure 2-19 illustrates the concept of TDMA. This illustrates how each device is allocated a time on the channel, referred to as a timeslot. These are then grouped into a TDMA frame. The number of timeslots in a TDMA frame is dependent on the system; for example GSM utilizes eight timeslots.Time Division Multiple Access

Devices must be allocated a timeslot; therefore it is usual to have one or more timeslots reserved for common control and system access. TDMA systems are typically digital and therefore offer additional features such a ciphering and integrity protection. In addition, they can employ enhanced error detection and correction schemes such as FEC (Forward Error Correction). This enables the system to be more resilient to noise and interference and therefore, they tend to offer greater spectral efficiency when compared to FDMA systems.Code Division Multiple AccessThe concept of CDMA is slightly different to that of FDMA and TDMA. Instead of sharing resources in the time or frequency domain, CDMA devices operate on the same frequency band at the same time. This is possible due to the fact that each transmission is separated using a unique code.Code Division Multiple Access

There are two main types of CDMA, FHSS (Frequency Hopping Spread Spectrum) and DSSS (Direct Sequence Spread Spectrum) however all the current major cellular systems utilize DSSS.In DSSS, the narrowband signal is spread with a wideband code prior to transmission. The receivers are designed to extract the encoded signal (with the correct code) and reject everything else as noise.UMTS, cdmaOne and CDMA2000 all use CDMA. However the implementation of the codes and the bandwidths used is different. For example UMTS utilizes a 5MHz channel bandwidth, whereas cdmaOne uses only 1.25MHz.Orthogonal Frequency Division Multiple AccessOFDMA (Orthogonal Frequency Division Multiple Access) is the latest addition to cellular systems. It provides a multiple access technique based on OFDM (Orthogonal Frequency Division Multiplexing). Figure 2-5 illustrates the basic view of OFDMA. Here it can be seen that the bandwidth is broken down to smaller units known as subcarriers. These are grouped together and allocated as a resource to a device. It can also be seen that a device can be allocated different resources in both the time and frequency domain. Orthogonal Frequency Division Multiple Access

Comparison Between DM and DMADM: Emphasize how to reuse multiple data, but no matter whether these data are used by one or several users.DMA: Emphasize how to reuse data from multiple users.The comparison between DM and DMA

From FDM/FDMA to OFDM/OFDMATraditional FDM divides the system frequency band into multi-carriers with bandwidth isolation from each other, and the receiver need to use a filter and receive the data from subcarrier. To avoid mutual interference of different carriers through isolate different subcarriers by protection bandwidth, but at the expense of the frequency utilization efficient. In addition, the filter is very difficult to achieve when there are hundreds of subcarriers.OFDM is essentially a FDM, the maximal characteristic of OFDM is overcome the low frequency efficient compare with traditional FDM. The receiver doesnt need to use a filter to distinguish between subcarriers.

From FDM/FDMA to OFDM/OFDMA

LTE DL Multiple Access Technology OFDMAOFDMA defines the technology of orthogonal frequency division multiple access. OFDMA is essentially the combination of TDMA and FDMA.

Compared with CDMA, OFDMA has the following advantages: Effectively eliminating multipath interference in radio communications by using cyclic prefixes Achieving orthogonal frequency multiplexing between users with an ensured spectral efficiency Combining OFDM and MIMO Technology Supporting frequency link adaptation and multi-user scheduling OFDMA is a multiple-access modulation scheme based on resources in the time and frequency domains. The scheduling resource in the frequency domain is subcarriers and the smallest unit in the time domain is slot.LTE UL Multiple Access Technology SC-FDMATo reduce the limitation of the high PAPR on the PA, LTE uses single carrier frequency division multiple access (SC-FDMA) in the uplink.

Compared with OFDMA, SC_FDMA has the following advantages: Lower PAPR, facilitating the design of UE PAs Achieving orthogonal frequency multiplexing between users with an ensured spectral efficiency Achieving multiplexing by using DFT and orthogonal subcarrier mapping Supporting frequency link adaptation and multi-user schedulingSC-FDMA Subcarrier Mapping ConceptSC-FDMA Subcarrier Mapping Concept

The basic transmitter and receiver architecture is very similar (nearly identical) to OFDM, and it offers the same degree of multipath protection. Importantly, because the underlying waveform is essentially a single carrier, the PAPR is lower. It is quite difficult to visually represent SC-FDMA in the time and frequency domain however this section aims to illustrate the concept.In Figure 2-24, the SC-FDMA signal generation process starts by creating a time domain waveform of the data symbols to be transmitted. This is then converted into the frequency domain, using a DFT (Discrete Fourier Transform). DFT length and sampling rate are chosen so that the signal is fully represented, as well as being spaced 15kHz apart. Each subcarrier will have its own fixed amplitude and phase for the duration of the SC-FDMA symbol. Next the signal is shifted to the desired place in the channel bandwidth using the zero insertion concept, i.e. subcarrier mapping. The signal is then converted to a single carrier waveform using an IDFT (Inverse Discrete Fourier Transform) in addition to other functions. Finally a cyclic prefix can be added. Note that additional functions such as S-P (Serial to Parallel) and P-S (Parallel to Serial) converters are also required as part of a detailed functional description.Figure 2-25 illustrates the concept of the DFT, such that a group of N symbols map to N subcarriers. However depending on the combination of the N symbols into the DFT, the output will vary. As such, the actual amplitude and phase of the N subcarriers is more like a code word.SC-FDMA Signal Generation

At the eNB, the receiver takes the N subcarriers and reverses the process. This is achieved using an IDFT (Inverse Discrete Fourier Transform) which effectively reproduces the original N symbols. Figure 2-26 illustrates the basic view of how the subcarriers received at the eNB are converted back into the original signals.Note that the SC-FDMA symbols have a constant amplitude and phase and like ODFMA, a CP (Cyclic Prefix) is still required. SC-FDMA and the eNB

OFDMA Verses SC-FDMAThe main reason SC-FDMA was specified for the uplink was because of its PA (Power Amplifier) characteristics. Typically, the SC-FDMA signal will operate with a 2-3 dB lower PAPR. This makes the system more efficient, thus increasing the UEs battery life. SC-FDMA also performs better when in larger cells.It must be noted that OFDMA is better in a number of areas, such as Inter-symbol orthogonality and the ability to provide a more flexible frequency domain scheduling mechanism. This increases the system performance. In addition, OFDMA is more suitable for uplink MIMO (Multiple Input Multiple Output) operation and its associated high date rate services.Table 2-2 highlights three main features and indicates which technology is best suited.SC-FDMA verses OFDMAFeatureSC-FDMAOFDMA

Low PAPRYX

Performance XY

Uplink MIMOXY

Duplex TechnologiesCellular systems can be designed to operate in two main transmission modes, namely FDD (Frequency Division Duplex) and TDD (Time Division Duplex).Frequency Division DuplexThe concept of FDD is illustrated in Figure 2-27. A separate uplink and downlink channel are utilized enabling a device to transmit and receive data at the same time (assuming the device incorporates a duplexer). The spacing between the uplink and downlink channel is referred to as the duplex spacing. Frequency Division Duplex

Normally the uplink channel (mobile transmit) operates on the lower frequency. This is done because higher frequencies suffer greater attenuation than lower frequencies and therefore it enables the mobile to utilize lower transmit power levels.Some systems also offer half-duplex FDD mode, where two frequencies are utilized, however the mobile can only transmit or receive, i.e. not transmit and receive at the same time. This allows for reduced mobile complexity since no duplex filter is required.Time Division DuplexTDD mode enables full duplex operation using a single frequency band with time division multiplexing for the uplink and downlink signals. One advantage of TDD is its ability to provide asymmetric uplink and downlink allocations. Depending on the system, other advantages include dynamic allocation, increased spectral efficiency, and improved use of beamforming techniques. The later being due to the carrier has the same uplink and downlink frequency characteristics. Time Division Duplex

Duplex Technologies: Distinguishing UL/DL SignalsTDD: The uplink and downlink use different slots.

The characteristics of TDD are as follow:Advantages: TDD is used for scenarios where traffic is unbalanced. It allocates different amount of time slots to the uplink and downlink, improving the flexibility and spectral efficiency. Disadvantages: TDD is complicated and requires GPS synchronization and phase synchronization. The interference between the DL and UL is difficult to control.Applications: LTE TDD, TD-SCDMA, and WiMAX.FDD: The uplink and downlink use different frequencies.

The characteristics of FDD are as follow:Advantages: FDD is easy to accomplish. Disadvantages: Spectral efficiency is low.When the uplink and downlink traffic (primarily data services) is unbalanced. Applications: LTE FDD, WCDMA, CDMA2000.Carrier Frequency and EARFCNLTE Release 8 BandsThe LTE Radio interface, namely the E-UTRA (Evolved - Universal Terrestrial Radio Access), is able to operate in many different radio bands. Table 2-3 illustrates the Release 8 frequency bands as well as other parameters which are used to identify centre frequencies. FDD requires two centre frequencies, one for the downlink and one for the uplink. These carrier frequencies are each given an EARFCN (E-UTRA Absolute Radio Frequency Channel Number) which ranges from 0 to 65535. In contrast, TDD only has one EARFCN. The parameters required to calculate the EARFCN(s) include:FDL_low - This is the lower frequency of the downlink band.FDL_high - This is the higher frequency of the downlink band.NOffs-DL - This is a parameter used as part of the downlink EARFCN calculation.NDL - This is the actual downlink EARFCN number.FUL_low - This is the lower frequency of the uplink band.FUL_high - This is the higher frequency of the uplink band.NOffs-UL - This is a parameter used as part of the uplink EARFCN calculation.NUL - This is the actual uplink EARFCN number.LTE Release 8 Frequency BandsBandDuplexFDL_low(MHz)FDL_high(MHz)NOffs-DLNDLFUL_low(MHz)FUL_high(MHz)NOffs-ULNUL

1FDD2110217000-599192019801800018000-18599

2FDD19301990600600-1199185019101860018600-19199

3FDD1805188012001200-1949171017851920019200-19949

4FDD2110215519501950-2399171017551995019950-20399

5FDD86989424002400-26498248492040020400-20649

6FDD87588526502650-27498308402065020650-20749

7FDD2620269027502750-3449250025702075020750-21449

8FDD92596034503450-37998809152145021450-21799

9FDD1844.91879.938003800-41491749.91784.92180021800-22149

10FDD2110217041504150-4749171017702215022150-22749

11FDD1475.91500.947504750-49991427.91452.92275022750-22999

12FDD72874650005000-51796987162300023000-23179

13FDD74675651805180-52797777872318023180-23279

14FDD75876852805280-53797887982328023280-23379

17FDD73474657305730-58497047162373023730-23849

33TDD190019203600036000-36199 190019203600036000-36199

34TDD201020253620036200-36349201020253620036200-36349

35TDD185019103635036350-36949185019103635036350-36949

36TDD193019903695036950-37549193019903695036950-37549

37TDD191019303755037550-37749191019303755037550-37749

38TDD257026203775037750-38249257026203775037750-38249

39TDD188019203825038250-38649188019203825038250-38649

40TDD230024003865038650-39649230024003865038650-39649

Carrier Frequency EARFCN CalculationThe EARFCN is calculated using a combination of the equations in Figure 2-31 and the values in Table 2-3.The channel raster for LTE is 100kHz for all bands, i.e. the carrier centre frequency must be an integer multiple of 100kHz. This is represented in the equation by the 0.1 value.EARFCN Calculation

The channel numbers that designate carrier frequencies close to the edges of the operating band are not used. This implies that the first 7, 15, 25, 50, 75 and 100 channel numbers at the lower operating band edge and the last 6, 14, 24, 49, 74 and 99 channel numbers at the upper operating band edge are not used for channel bandwidths of 1.4, 3, 5, 10, 15 and 20 MHz respectively.ExampleIt is possible to utilize the previous equations to calculate the frequency for a given EARFCN. In addition, it is possible to calculate the EARFCN for a given frequency. Figure 2-32 illustrates an example with a defined uplink and downlink frequency. The calculation shown in the figure translates a downlink frequency of 2127.4MHz to an EARFCN equal to 174. Example Downlink EARFCN Calculation

LTE Frame StructuresIn LTE, devices are allocated blocks of subcarriers for a period of time. These are referred to as a PRB (Physical Resource Block). The resource blocks are contained within the LTE generic frame structure. Two types are defined, namely type 1 and type 2 radio frames.LTE Frame Structure Type1-FDDThe type 1 radio frame structure is used for FDD and is 10ms in duration. It consists of 20 slots, each lasting 0.5ms. Two adjacent slots form one subframe of length 1ms. For FDD operation 10 subframes are available for downlink transmission and 10 subframes are available for uplink transmission, with each transmission separated in the frequency domain.Figure 2-33 illustrates the FDD frame structure, as well as highlighting the slots and subframe concept. In addition, it illustrates how the slots are numbered 0 to 19.FDD Radio Frame

LTE Time UnitThe LTE time unit is identified as Ts and is calculated as 1/(15000x2048), which equates to approximately 32.552083ns. Various aspects of LTE utilize this parameter, or multiple of it, to identify timing and configuration.LTE Frame Structure Type2-TDDThe type 2 radio frame structure is used for TDD. One key addition to the TDD frame structure is the concept of special subframes. This includes a DwPTS (Downlink Pilot Time Slot), GP (Guard Period) and UpPTS (Uplink Pilot Time Slot). These have configurable individual lengths and a combined total length of 1ms. For TDD operation the 10 subframes are shared between the uplink and the downlink. A 5ms and 10ms switch-point periodicity is supported however subframes 0 and 5 must be allocated to the downlink as these contain the PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal), as well as the broadcast information in subframe 0. The PSS and SSS are discussed in Section 2.6.1 TDD Radio Frame

There are various frame configuration options supported for TDD. Table 2-4 illustrates the different options. Configuration options 0, 1, 2 and 6 have a 5ms switching point and therefore require 2 special subframes, whereas the rest are based on a 10ms switching point. In the table, the letter D is reserved for downlink transmissions, U denotes subframes reserved for uplink transmissions and S denotes a special subframe with the three fields DwPTS, GP and UpPTS.Type 2 Radio Frame Switching Points & Special SubframeDL/UL Subframe Allocation Item

Subframe 1 in all configurations and subframe 6 in configuration with 5ms switch-point periodicity consist of DwPTS, GP and UpPTS. Subframe 6 in configuration with 10ms switch-point periodicity consists of DwPTS only. All other subframes consist of two equally sized slots.Subframes 0 and 5 and DwPTS are always reserved for DL transmission.Special Subframe Allocation Item

Special Subframe

Cyclic Prefix The concept of a CP (Cyclic Prefix) within OFDM systems has already been discussed. In LTE, two different cyclic prefix sizes, namely Normal and Extended were selected. In order to facilitate these, two different slot formats are required. Figure 2-36 illustrates the seven and six ODFM symbol options. Obviously, to facilitate a larger cyclic prefix, one of the symbols is sacrificed, thus the symbol rate is reduced. Normal and Extended Cyclic Prefix

The use of the extended cyclic prefix is intended for scenarios where the range of the cell needs to be extended, e.g. for coverage planning purposes or when multicast services are being employed in the cell.CP Classification and Scenario The following table shows the number of symbols in 1 slot. It is related to the CP (Cyclic Prefix) length and is configured by the cell.CP classification

f=7.5kHz is available for MBSFNMBMS over Single Frequency Networkwhich defined in 3GPP Protocol 8 but applied until 3GPP Protocol9. Attention: 7.5kHz is only adapted for downlink. LTE Resource Block ConceptionThe E-UTRA downlink is based on OFDMA. As such, it enables multiple devices to receive information at the same time but on different parts of the radio channel. In most OFDMA systems this is referred to as a Subchannel, i.e. a collection of subcarriers. However, in E-UTRA, the term subchannel is replaced with the term PRB (Physical Resource Block).Figure 2-38 illustrates the concept of OFDMA, whereby different users are allocated one or more resource blocks in the time and frequency domain, thus enabling efficient scheduling of the available resources.LTE resource block

RE (Resource Element)Minimum unit in physical resource Time domain: 1 OFDM Symbol, frequency domain: 1 Subcarrier RBResource BlockMinimum unit for resource allocation used for data transmission in physical layer Time domain: 1 Slot, frequency domain: 12 continuous subcarriersCCE(Control Channel Element)Resource unit for control channel 1 CCE = 36 REs1 CCE = 9 REGs (1 REG = 4 REs)TTI (Transmission Time Interval)Basic unit in time domain when scheduling data in physical layer1 TTI = 1 subframe = 2 slots1 TTI = 14 OFDM symbols(Normal CP)1 TTI = 12 OFDM symbols (Extended CP) Resource Grid StructureA PRB (Physical Resource Block) consists of 12 consecutive subcarriers and lasts for one slot, i.e. 0.5ms.Figure 2-39 illustrates the size of a PRB. The NRBDL parameter is used to define the number of RB (Resource Block) used in the DL (Downlink). This is dependent on the channel bandwidth. In contrast, NRBUL is used to identify the number of resource blocks in the UL (Uplink). Each Resource Block consists of NSCRB subcarriers, which for standard operation is set to 12. In addition, another configuration is available when using MBSFN (Multimedia Broadcast Multicast Service Single Frequency Network) and a 7.5kHz subcarrier spacing.The term RE (Resource Element) is used to describe one subcarrier lasting one symbol. This can then be assigned to carry modulated information, reference information or nothing.Resource Block and Resource Element

Relationship between Channel BW and RBFor details, please refer to protocol 36.101. Channel bandwidth and RB

Relationship between Channel BW and RB

LTE Channel Structures The concept of channels is not new. Both GSM and UMTS defined various channel categories, however LTE terminology is closer to UMTS. Broadly there are four categories of channel. LTE Channels

0. Logical ChannelsIn order to describe Logical Channels it is best to first identify where logical channels are located in relationship to the LTE protocols and the other channel types. Figure 2-42 illustrates the Logical Channels located between the RLC (Radio Link Control) and the MAC (Medium Access Control) layers.Location of Channels

Logical Channels are classified as either Control Logical Channels, which carry control data such as RRC (Radio Resource Control) signaling, or Traffic Logical Channels which carry User Plane data.Control Logical ChannelsThe various forms of these Control Logical Channels include the:BCCH (Broadcast Control Channel) - this is a downlink channel used to send of SI (System Information) messages from the eNB (Evolved Node B). These are defined by RRC.PCCH (Paging Control Channel) - this is a downlink channel used by the eNB to broadcast paging information.BCCH and PCH Logical Channels

CCCH (Common Control Channel) - this is used to establish an RRC Connection or specifically a SRB (Signaling Radio Bearer). It is also used for re-establishment procedures. Note, SRB 0 maps to the CCCH.DCCH (Dedicated Control Channel) - this provides a bi-directional channel for signaling. Logically there are two DCCH activated:SRB 1 - is used for RRC messages, as well as RRC messages which carry high priority NAS signaling.SRB 2 - is used for RRC carrying low priority NAS signaling. Prior to its establishment, low priority signaling is sent on SRB1.CCCH and DCCH Signaling

Traffic Logical Channels3GPP Release 8 LTE has one type of Logical Channel carrying traffic, namely the DTCH (Dedicated Traffic Channel). This is used to carry DRB (Dedicated Radio Bearer) information, i.e. IP datagram.Dedicated Traffic Channel

The DTCH is a bi-directional channel that can operate in either RLC AM (Acknowledged Mode) or UM (Unacknowledged Mode). This is configured by RRC and is based on the QoS (Quality of Service) applied to the E-RAB (EPS Radio Access Bearer).Transport ChannelsHistorically, transport channels were split between common and dedicated channels. However, LTE has moved away from dedicated channels in favor of the common/shared channels approach due to the associated efficiencies this provides. The main 3GPP Release 8 Transport Channels include the:BCH (Broadcast Channel) - this is a fixed format channel which occurs once per frame and it is used to carry the MIB (Master Information Block). Note that the majority of system information messages are carried on the DL-SCH (Downlink - Shared Channel).PCH (Paging Channel) - which is used to carry the PCCH, i.e. paging messages. It also utilizes DRX (Discontinuous Reception) to improve UE battery life.DL-SCH (Downlink - Shared Channel) - is the main downlink channel for data and signaling. It supports dynamic scheduling, as well as dynamic link adaptation. In addition, it utilizes HARQ (Hybrid Automatic Repeat Request) operation to improve performance. As previously indicated, it also facilitates the sending of system information messages.RACH (Random Access Channel) - carries limited information and is used in conjunction with Physical Channels and preambles to provide contention resolution procedures.UL-SCH (Uplink Shared Channel) - similar to the DL-SCH, this channel supports dynamic scheduling (eNB controlled) and dynamic link adaptation by varying the modulation and coding. In addition, it too supports HARQ (Hybrid Automatic Repeat Request) operation to improve system performance.LTE Release 8 Transport Channels

Physical ChannelsThe Phy (Physical) Layer facilitates transportation of MAC Transport Channels, as well as providing scheduling, formatting and control indicators.Downlink Physical ChannelsPhysical Channels on the downlink include the:PBCH (Physical Broadcast Channel) - used to carry the BCH.PCFICH (Physical Control Format Indicator Channel) - is used to indicate the number of OFDM symbols used for the PDCCH.PDCCH (Physical Downlink Control Channel) - used for resource allocation.PHICH (Physical Hybrid ARQ Indicator Channel) - used as part of the HARQ process.PDSCH (Physical Downlink Shared Channel) - used to carry the DL-SCH.Uplink Physical ChannelsThere are a number of Uplink Physical Channels in LTE. These include the:PRACH (Physical Random Access Channel) - this channel carries the Random Access Preamble. The location of the PRACH is defined by higher layer signaling, i.e. RRC.PUCCH (Physical Uplink Control Channel) - this carries uplink control and feedback. It can also carry scheduling requests to the eNB.PUSCH (Physical Uplink Shared Channel) - which is the main uplink channel and is used to carry the UL-SCH. It carries both signaling and user data, in addition to uplink control. It is worth noting that the UE is not allowed to transmit the PUCCH and PUSCH at the same time.Radio ChannelsThe term Radio Channel is typically used to describe the overall channel, i.e. the downlink and uplink carriers for FDD operation and the carrier for TDD operation.Radio Channel

Mapping Relationship between Physical Channels and Other ChannelsThere are various options for multiplexing multiple bearers together such that Logical Channels may be mapped to one or more Transport Channels. These in turn are mapped into Physical Channels. Mapping Relationship between Physical Channels and Other Channels

In order to facilitate the multiplexing of Logical Channels to Transport Channels, the MAC Layer typically adds a LCID (Logical Channel Identifier).

Application of LTE Physical ChannelsApplication of LTE Physical Channels

As an example, the applications of the channels in a complete network access procedure are as follows:The UE obtains the PCI and gets synchronized with the eNodeB in the downlink on the P-SCH and S-SCH. The downlink synchronization includes frame synchronization and symbol synchronization.The UE gets system information (SIB1) on the PDSCH. MIB and SIB1 are always scheduled on the PBCH and other SIBs are dynamically scheduled on PDSCHs. Periods and listening windows of other SIBs are broadcast in SIB1. After the UE receives SIB1, it knows the other SIBs to be received later.The UE initiates the random access on the PRACH and gets synchronized with the eNodeB in the uplink.After random access, the UE requests uplink scheduling on the PUCCH.If there is uplink or downlink data to be transmitted, the UE needs to listen to the PDCCH to get information about the PUSCH and PDSCH. Then, the UE sends data on the PUSCH and receives data on the PDSCH.Reference signalReference signal is a special data sequence which is located at specific location (resource elements) in DL/UL frame which is supposed to be decoded by UE/eNodeB and taken as a signal for RSRP, RSRQ.

Cell Specific Reference SignalsIn LTE, the cell specific reference signals are arranged in a two dimensional lattice of time and frequency. This has been done so that they are equidistant and therefore provides a minimum mean squared error estimate for the channel. In addition, the spacing in time between the Reference Symbols is an important factor for channel estimation and relates to the maximum Doppler spread supported, i.e. speed. In LTE, this works out at 2 Reference symbols per slot. The spacing in the frequency domain is also an important factor, as this relates to the expected coherent bandwidth and delay spread of the channel. In LTE there is a 6 subcarrier separation of reference signals, however these are staggered in time such that they appear every 3 subcarriers. The downlink reference signals consist of known reference symbols inserted in the first and third last OFDM symbol of each slot. There is one reference signal transmitted per downlink antenna port. The number of downlink antenna ports equals 1, 2, or 4.One Antenna Port ConfigurationThe location of the RSs is dependent on the number of antennas and use of a Normal CP or Extended CP. Figure 2-50 illustrates the two options.Reference Signals - One Antenna Port

This is used for a single TX (Transmit) antenna. The reference signals are transmitted during the first and fifth OFDM symbols of each slot when the normal CP is used and during the first and fourth OFDM symbols when the extended CP is used.Cell ID OffsetIt is worth noting that the position of the reference signals is dependent on the value of the Physical Cell ID. As such, the system performs a calculation (Physical Cell ID mod 6) to determine the correct offset. Figure 2-50 illustrates two cells, each producing a different offset.Reference Signal Physical Cell ID Offset

Two Antenna Port ConfigurationLTE is designed to operate with multiple transmit antennas for MIMO, or Transmit Diversity. The concept of reference signals is used to define different patterns for multiple antenna ports. Figure 2-52 illustrates the concept for two antennas. The RS pattern corresponding to a given antenna port enables the device to derive channel estimation. Reference Signals - Two Antenna Ports (Normal CP)

Whilst Reference Symbols are transmitted on one antenna, the other antennas resource element is null. In addition, like the single antenna port configuration the location of the reference signals is offset based on the Physical Cell ID.Four Antenna Port ConfigurationLTE supports up to four cell-specific antenna ports (0 to 3). As such, the device is required to derive up to four separate channel estimates. Figure 2-53 illustrates the configuration for four antenna ports.Reference Signals - Four Antenna Ports (Normal CP)

Antenna port 2 and antenna port 3 both have a reduced number of reference symbols. This is to reduce the reference signal overhead. It does also have a negative impact on the system since the lack of reference signals will mean that in high mobility, i.e. fast channel variations, the channel estimation will not be as accurate. This however can be offset by the fact that spatial multiplexing MIMO with 4 antennas will mostly be performed in low mobility scenarios. In addition, like the single antenna port configuration the location of the reference signals is offset based on the Physical Cell ID.LTE Physical SignalsIn order for the UE to be able to access the network, the eNB must broadcast various downlink signals. As the downlink is scalable from 1.4MHz to 20MHz and the device may not be aware of the eNB configuration, the method of finding the system needs to be consistent. Consequently synchronization and cell identity information must appear on the downlink in a fixed location irrespective of the radio spectrum configuration. Figure 2-54 illustrates the structure of the NIDcell (Cell Identity).Downlink Cell ID

In LTE, there are two synchronization sequences. These are referred to as the PSS (Primary Synchronization Signal) and the SSS (Secondary Synchronization Signal). The location of these is dependent on the transmission mode, i.e. FDD or TDD, as well as the use of the normal or extended cyclic prefix. Primary Synchronization SignalThe PSS provides downlink synchronization information for the UE. The signal sent is one of three ZC (Zadoff-Chu) sequences. This provides a pseudo noise pattern which devices can correlate, whilst at the same time enabling adjacent cells/sectors on the eNB to utilize different synchronization signals. The NID (0,1 or 2) is mapped to a Zadoff-Chu root index which is used in the sequence generation processSecondary Synchronization SignalThe SSS is generated from the interleaved concatenation of two 31 bit binary sequences which are cyclic shifted based on the value of NID.Downlink Reference SignalsUnlike other systems, the LTE air interface does not employ a frame preamble. Instead it utilizes various RS (Reference Signal) to facilitate coherent demodulation, channel estimation, channel quality measurements and timing synchronization etc. Fundamentally there are three types of downlink reference signals:Cell Specific (non-MBSFN).MBSFN (Multimedia Broadcast Multicast Service Single Frequency Network).UE Specific.Cell Specific Reference SignalsIn LTE, the cell-specific reference signals are arranged in a two dimensional lattice of time and frequency. This has been done so that they are equidistant and therefore provides a minimum mean squared error estimate for the channel. In addition, the timing between the reference symbols is an important factor for channel estimation and relates to the maximum doppler spread supported, i.e. speed. In LTE, this works out at two reference symbols per slot. The spacing in frequency domain is also an important factor, as this relates to the expected coherence bandwidth and delay spread of the channel. In LTE there is a six subcarrier separation of reference signals, however these are staggered in time such that they appear every three subcarriers. MBSFN Reference SignalsThe LTE system also defines a set of reference signals for MBSFN. These are only present when the PMCH (Physical Multicast Channel) is present and uses the extended cyclic prefix.UE Specific Reference SignalsUE Specific Reference Signals are supported for single antenna port transmission on the PDSCH and are transmitted on antenna port 5. It is typically used for beamforming when non-codebook based pre-coding is applied.Physical Procedures0. LTE Cell Search ProcedureThe LTE device needs to perform an LTE Attach procedure, i.e. transition from the LTE Detached to LTE Active State, to connect to the EPC (Evolved Packet Core) and ultimately services.Initial Procedures

In order to access a cell the device must find and synchronize to the cell. It is then able to decode the System Information messages and perform PLMN (Public Land Mobile Network) and Cell Selection. Once this has been completed, the device is in a position to access the cell and establish a RRC connection, i.e. a SRB (Signaling Radio Bearer).0. Cell SearchThe downlink in LTE is based on scalable OFDMA with channels ranging from 1.4MHz to 20MHz (Note that not all bandwidths are available at the different frequency bands). Initially the UE is unaware of the downlink configuration of the cell, unless it has stored information from when it was previously attached. Assuming no information, the synchronization process must be quick and concise. Figure 2-56 illustrates the location of the PSS and SSS.PSS and SSS for Cell Search (FDD Mode)

Synchronization Channel: Cell Search and Downlink Synchronization In LTE there are two synchronization sequences, known as the PSS (Primary Synchronization Signal) and the SSS (Secondary Synchronization Signal). The location of these is dependent on the transmission mode, i.e. FDD or TDD, as well as the use of the normal or extended cycli