LTE-Essentials-Award-Solutions.pdf

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All rights reserved. This course book and the material and information contained in it ("course material") are owned by Award Solutions, Inc. ("Award"). The course material shall not be modified, reproduced,

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This course book is designed to be distributed as a student guide with the courses taught by Award’s authorized employees and contractors. It is not designed to be a standalone text book. Award makes no representations or warranties and disclaims all implied warranties with respect to the information contained herein or products derived from use of such information and undertakes no obligation to update or otherwise modify the information or to notify the purchaser or user of any update or obsolescence. Award’s total liability in connection with the course material is the amount actually received by Award from the purchaser/user for the purchase of the course material.

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The 3GPP and LTE logos are the property of Third Generation Partnership Project (3GPP). The 3GPP2 logo is property of Third Generation Partnership Project (3GPP2) and its organization partners. The content of this document is based on 3GPP/LTE and 3GPP2 specifications which are available at www.3gpp.org, and www.3gpp2.org.

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Award Solutions, Inc.

provides exceptional training and consulting in advanced wireless and Internet technologies. Our proven experience enables us to offer a complete suite of services: Cutting edge technology training, customized training solutions, and advanced technology consulting. Our products and services provide our clients with innovative, flexible, and cost-effective solutions that help rapidly boost workforce productivity and competence to more quickly meet market demands. Our areas of expertise include: • Technology for Business • WiMAX • Emerging Trends • 1x & 1xEV-DO • LTE • GSM & GPRS/EDGE • IP Convergence & IMS • Wireless Fundamentals • UMTS/HSPA/HSPA+

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1x & 1xEV-DO

1x and 1xEV-DO Fundamentals ...2 days

Technology for Business

Cloud Computing for Google Apps ... 1 day The M2M Ecosystem... 1 day Unified Communications and IMS ... 1 day IP Convergence for Sales and Marketing ... 1 day LTE Services for Enterprise Customers (EVDO) ... 1 day LTE Services for Enterprise Customers (UMTS) ... 1 day

Emerging Trends

OFDM and MIMO Fundamentals ... 1 day

* New Course

*

LTE

The Road to LTE ... 1 day LTE Essentials... 1 day Mastering LTE ...2 days Exploring IPv6 for LTE Networks ...2 days Voice and IMS in LTE-EPC Networks ...3 days Exploring TD-LTE ...2 days Mastering LTE Air Interface ...2 days Mastering TD-LTE Air Interface ...2 days LTE Protocols and Signaling ...3 days LTE and 1x/1xEV-DO (eHRPD) Interworking ...2 days LTE and GSM/UMTS Interworking ...2 days LTE-EPC Networks and Signaling ...3 days LTE-Advanced (R10) Technical Overview ...2 days LTE RF Planning and Design Certification Workshop ...5 days TD-LTE RF Planning and Design Certification Workshop 5 days LTE-EPC Planning and Design Certification Workshop ...4 days

WiMAX

Exploring WiMAX...2 days

IP Convergence & IMS

IP Convergence Essentials ... 1 day Ethernet Backhaul Essentials ... 1 day IP Convergence for Sales and Marketing ...3 days Exploring IPv6 ... 1 day Exploring MPLS ...2 days Exploring IMS (R8) ...3 days Exploring SIP, VoIP and IP Convergence ...4 days Exploring Ethernet Backhaul ...2 days Voice and Video over IP Protocols and Technologies ...2 days Exploring IP Routing and Ethernet Bridging ...2 days Ethernet Backhaul Planning ...3 days SIP Signaling ...2 days IPv6 Networking Workshop for LTE Networks ...3 days IP Networking Workshop for 1xEV-DO/LTE ...4 days IP Networking Workshop for HSPA/LTE ...4 days

GSM and GPRS/EDGE

GSM Performance Workshop ...3 days GPRS and EDGE Performance Workshop...3 days

Wireless Fundamentals

Wireless and 3G Basics ... 1 day Exploring GSM/EGPRS/UMTS/HSPA/HSPA+ ...5 days 3G Comparative Overview ... 1 day

Exploring Wireless Landscape and IP Convergence ...2 days

Exploring Wireless Technologies and Networks ...5 days Fundamentals of RF Engineering ...2 days

UMTS (WCDMA)/HSPA/HSPA+

Exploring UMTS (WCDMA) ...2 days Exploring HSPA+ (R7, R8 & R9) ...2 days Mastering UMTS Core Networks (R99 to R7) ...3 days Mastering UMTS Radio Protocols and Signaling ...4 days Mastering HSPA Protocols and Signaling ...3 days HSPA+ Protocols and Signaling ...2 days Multi-Carrier HSPA+ (R8 & R9) ... 1 day IMS in UMTS (R8) Networks ...3 days 3GPP Packet Core Networks (R99 to R8) ...3 days 3GPP Packet Switched Core Networks and Backhaul ....4 days UMTS/HSPA/HSPA+ Air Interface ...3 days UMTS Transport Network Planning ...4 days UMTS/HSPA (WCDMA) RF Design Mentoring ...5 days UMTS (WCDMA) RF Optimization Mentoring ... 10 days UMTS/HSPA+ RF Optimization Workshop ...4 days

*

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Emerging Trends

Overview of OFDM (e) ...2 hours Multiple Antenna Techniques (e) ...3 hours

(e) eLearning Course

*

LTE

Welcome to LTE (e) ...1 hour LTE Overview (e) ...3 hours LTE SAE Evolved Packet Core (EPC) Overview (e) ...3 hours LTE Air Interface Signaling Overview (e) ...3 hours Overview of IPv6 for LTE Networks ...3 hours VoLTE Overview ...3 hours

WiMAX

Overview of WiMAX (e) ...3 hours

*

IP Convergence & IMS

Welcome to IP Networking (e) ...3 hours IP Convergence Overview (e) ...4 hours Overview of MPLS (e) ... 3.5 hours Overview of IMS (e) ... 2.5 hours Voice and Video over IP (VoIP) Overview (e) ...3 hours IP Quality of Service (QoS) (e) ...3 hours Session Initiation Protocol (SIP) (e) ...2 hours Ethernet Backhaul Overview (e) ...3 hours IP Basics (e) ...1 hour IP Routing (e) ...1 hour QoS in IP Networks (e) ...1 hour TCP and Transport Layer Protocols (e) ...1 hour Ethernet Basics (e) ...1 hour Ethernet VLANs (e) ...1 hour Ethernet Bridging (e) ...1 hour Interconnecting IP Networks (e) ...1 hour Welcome to IPv6 (e) ...1 hour

UMTS (WCDMA)/HSPA/HSPA+

Welcome to UMTS (e)... 1.5 hours Overview of UMTS (e) ...2 hours UMTS/WCDMA Air Interface Fundamentals (e) ...3 hours UMTS Signaling (e) ...1 hours UMTS Mobility (e) ...1 hours HSDPA (R5) (e) ...3 hours HSUPA (R6) (e) ... 2.5 hours HSPA+ Overview (R7) (e) ...4 hours

GSM and GPRS/EDGE

Welcome to GSM/GPRS (e) ... 1.5 hours

Wireless Fundamentals

Wi-Fi Overview (e) ...3 hours Welcome to Wireless Networks (e) ...1 hour Overview of 3G Wireless Networks (e) ... 1.5 hours

1x & 1xEV-DO

1xEV-DO Networks (Rev 0) (e) ...3 hours 1xEV-DO Networks (Rev A) (e) ...3 hours

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Chapter 1 LTE Overview ... 1

Trends in the Wireless Industry ... 3

4G Wireless Systems ... 8

LTE

- Long Term Evolution ... 14

Chapter 2 LTE-EPC Networks ... 19

LTE System Architecture ... 21

E-UTRAN Architecture ... 24

EPC Architecture ... 29

Chapter 3 LTE Air Interface ... 39

Principles of OFDM ... 41

Air Interface Features ... 48

OFDMA in LTE ... 50

Multiple-Antenna Techniques in LTE ... 55

Chapter 4 LTE Services ... 63

Drivers of 4G Services ... 65

Services in LTE ... 68

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Chapter 5 Life of an LTE Mobile ... 77

LTE Call Setup ... 79

Traffic Operations ... 87

Handovers ... 90

Chapter 6 LTE Deployment ... 97

Device Capabilities ... 99

Planning for LTE ... 101

Appendix A

Additional Topics ... 109

LTE and WiMAX: Similarities and Differences ... 111

Interworking with 3GPP ... 117

Interworking with 1x/1xEV-DO ... 119

LTE Performance... 121

Acronyms ... 125

References ... 129

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Award Solutions Confidential and Proprietary

Chapter 1:

LTE Overview

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Objectives

After completing this module, you will be able

to:

• Describe the trends in the wireless industry

• Identify the limitations of 3G technologies

• List the goals and requirements of 4G networks

• List the high-level characteristics of LTE networks

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Trends in the Wireless

Industry

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The wireless business is undergoing a major shift from voice-centric to data-centric applications. Studies indicate that data revenue has grown by more than 30 percent per year, whereas the voice revenue grew by just more than 4 percent.

The original wireless communications systems (now called 1G or first generation systems) initially focused solely on voice services. The arrival of the Internet led to the addition of data services; however, the primary demand was still focused on voice services. Second-generation (2G) cellular systems provided both voice and low-speed circuit-switched data services, including Global System for Mobile communications (GSM), IS-136 (TDMA) and IS-95 (CDMA).

To reduce the cost per data bit, 3G cellular systems started using packet technology in their core networks, and provided much higher data rates than 2G cellular systems. Examples of 3G systems include UMTS and CDMA2000.

The next generation of networks (so-called 4G) is now being defined to meet the requirements arising from this fundamental shift from circuit voice to packet data. The key 4G candidate technologies for mobile wireless network include the Mobile Worldwide Interoperability for Microwave Access (WiMAX) based on IEEE 802.16e, and the 3GPP Long Term Evolution (LTE) program.

Shifts in the Wireless Business

% Gr

ow

th

Time

Data

Voice

1G Circuit-switched voice 2G Higher voice capacity, Low-speed data 3G Voice and high-speed data,

value-added services 4G High-speed packet data, Voice over IP

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Although GSM remains the most widely deployed cellular technology in the world, 3G systems have been growing rapidly. Today, there are two separate but comparable technology streams for 3G networks.

• CDMA2000 provides an evolution path for 2G CDMA systems (IS-95). CDMA2000 (also called 1x, since each call uses a single 1.25 MHz radio channel) supports data rates up to about 150 kbps, while its enhanced standard, 1x Evolution - Data Optimized (1xEV-DO) provides data rates up to 3 Mbps or more. • UMTS provides an evolution path for GSM/GPRS/

EDGE systems. There are two options defined for UMTS networks: Wideband CDMA (WCDMA) uses Frequency Division Duplexing (FDD) to allow the mobile device and the network to talk simultaneously, while Time Division CDMA (TD-CDMA) uses Time Division Duplexing (TDD) to reduce the amount of radio spectrum required by the network.

Recent enhancements to the 3GPP standards introduced High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access

(HSUPA), which dramatically increase the data rates available over the radio interface, as high as 14 Mbps in a 5 MHz radio channel.

3G Wireless Technologies

3G

CDMA2000 (1x)

1xEV-DO

(Rev 0/A/B)

UMTS

WCDMA TD-CDMA

HSDPA/HSUPA

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Despite the success and performance of these 3G networks, the demands of the marketplace continue to evolve, and wireless technology must continue to evolve with it.

New value-added services (particularly video) require data rates far beyond what 3G networks can provide. Rates greater than 100 Mbps are now expected, more than an order of magnitude greater than what 3G can deliver. In addition, there is a desire to migrate the circuit voice services onto the packet data infrastructure in order to reduce the costs associated with maintaining two very different core networks. This means that the wireless networks must be able to handle Voice over IP (VoIP) services efficiently, with minimal delay and latency. 3G radio technologies were not designed with these requirements in mind.

Finally, the migration of services into call servers and IP-based interfaces will allow applications to be integrated and provide a richer experience for the end user.

This consolidation into a single packet-based infrastructure requires the networks to be optimized for IP and multimedia services, rather than circuit-oriented services.

3G Challenges

Data rates are too low for

high-bandwidth services like video

Delays and latencies are too high for

real-time services like voice

3G networks are not optimized for

IP-based multimedia services

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In order to overcome the limitations of current 3G technologies, a number of new approaches have been defined to create the next generation of wireless solutions. • New radio technologies, such as Orthogonal Frequency Division Multiplexing (OFDM) and multiple-antenna techniques, enable more information to be transmitted over the air to more users than ever before.

• The transition from circuit-oriented networks to packet-oriented systems based on IP allow operators to deploy cost-effective networks that support seamless mobility across access technologies. Voice can now be packetized (VoIP), providing high-quality voice conversations over the same infrastructure as data services.

• New integrated, multimedia services are now possible, combining voice, video, email, gaming and other applications in ways never before imagined.

4G Solutions

All-IP core networks for seamless

mobility and VoIP

Advanced services and mobile

broadband wireless

Advanced radio technologies (OFDM,

multiple antenna techniques)

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Fourth generation (4G) systems do not yet have a formal definition. Nonetheless, industry players have agreed on a number of requirements and goals to guide their efforts. • Higher Data Rates: 4G systems are expected to

provide at least an order of magnitude improvement in peak data rates, greater than 100 Mbps on the downlink and 50 Mbps on the uplink. In contrast, UMTS HSPA networks have peak rates of 14 Mbps and 5.76 Mbps, respectively.

• Shorter Delay (Latency): Latency is also a concern, especially with the move toward packetized voice (VoIP). The design of 4G networks is expected to introduce delays of no more than 10 ms across the radio access and 50 ms across the entire network.

• Better Efficiency: Radio spectrum is costly, so 4G systems must be able to deliver more bits of data over a given amount of spectrum. At the same time, network expenses must come down, both in terms of equipment costs (CAPEX) and ongoing operational costs (OPEX). In addition, in order to make the transition to 4G easier for existing 3G operators, 4G systems must provide solutions to interwork 3G and 4G networks.

A. Peak data rates

1. > 100 Mbps (downlink) 2. > 50 Mbps (uplink)

B. Latency

1. < 10 ms (radio network) 2. < 50 ms (end-to-end)

C. General goals

1. Better spectral efficiency 2. Lower costs

3. Interworking with 3G and other 4G systems

Wish List for 4G Networks



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Not surprisingly, the radio interface technology has a significant impact on the capabilities of the network, since it is the weakest link in the chain.

The original mobile wireless technologies used Frequency Division Multiple Access (FDMA) to support multiple users. These systems were very similar to commercial FM radio stations and supported only analog voice calls.

Toward the end of the 1980s and into the early 1990s, digital air interfaces were introduced as part of second generation of networks. These digital air interfaces were generally based on Time Division Multiple Access (TDMA), where the available narrowband frequencies were further divided into time slots, each of which could support one voice call and low-rate packet data services. TDMA-based technologies included IS-136, GSM, GPRS and EDGE. The 2G era also saw the introduction of the first Code Division Multiple Access (CDMA) system, IS-95.

All 3G systems are based on CDMA technology, which provides superior voice performance in a mobile environment. The two major 3G systems are CDMA2000 and UMTS. 3G networks offer voice services and

higher-speed packet data (greater than 2 Mbps), as well as broadcast/multicast capabilities. Additional enhancements to these air interfaces provided further improvements to the data rates, to 3 Mbps for 1xEV-DO and 14 Mbps for HSPA.

All 4G systems currently underway use Orthogonal Frequency Division Multiple Access (OFDMA), a variation of the original FDMA technique that allows for significantly greater spectral efficiency and data rates. OFDMA systems lend themselves to advanced multiple-antenna techniques that can boost data rates even higher and are inherently packet-oriented, leading to the use of VoIP to deliver voice services.

Radio Technology Evolution

FDMA • Analog radio • Voice services

1G

TDMA, some CDMA • Digital radio • Low speed packet

data

2G

CDMA • High speed packet

data • Broadcast/

multicast

3G

OFDMA • Very high speed

packet data • Multiple antennas • VoIP

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The capabilities of the radio interface dictate the design of the access and core networks. 1G and 2G networks were circuit-oriented to handle voice services, using centralized controllers within the Radio Access Networks (RANs) to manage the radio resources and switches in the core network to provide services and connectivity to the outside world.

With the introduction of packet data to some 2G systems (sometimes called 2.5G), a parallel packet-oriented network was added to manage data services and Internet access; 3G networks also used this architecture. This second network increased the cost and complexity of the operator’s network.

In 4G, the goal is to simplify. Radio control has been decentralized and moved into the base stations (sometimes called evolved base stations, or eBSs), while the circuit core network has been eliminated entirely. All services are now provided through the packet core network.

Network Architecture Evolution

Internet PSTN Circuit Core RAN Packet Core 2. 5G /3G PSTN Circuit Core RAN 1G /2G Internet 4G Evolved BS Packet Core PSTN RAN

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The 4G evolution programs, then, focus on three key areas: the air interface, the radio access network and the core network.

On the air interface, the use of Orthogonal Frequency Division Multiplexing (OFDM) and multiple-antenna techniques significantly increase the spectral efficiency. OFDM is a scalable solution, which allows operators to deploy the same technology in any available bandwidth from 1.4 MHz up to 20 MHz. The greater the bandwidth, the faster the data rates and the higher the capacity of the system.

In the access network, elimination of the centralized Radio Network Controller (RNC) allows decisions to be made locally at the base station. Thus reducing the overall latency of the network. The use of IP technology throughout simplifies network design and engineering, this allows the network to easily scale with traffic growth and reduces the costs of the network components and links.

Similarly, the transition to an all-IP packet core network enables the deployment and delivery of packet-oriented multimedia services, through the use of IP Multimedia Subsystem (IMS) servers. This results in lower costs for network operators.

4G Networks

Air Interface Access Network Core Network Service Network Spectrally efficient air interface • OFDM • Multiple antenna techniques Distributed, IP-based access network • Scalable • Reduced latency IP-oriented, IMS-based core network • Scalable • Low cost • Rapid service deployment

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The expected evolutionary paths for each of the current high-speed wireless data solutions are illustrated here. Every operator will make their own decision as to the correct option for their network, based on the capabilities of the technologies and the associated costs, timing and other factors.

UMTS operators will most likely proceed to Long Term Evolution (LTE) as their 4G solution, since the technology is explicitly designed to provide an easy transition for them.

1x and 1xEV-DO operators were expected to move to Ultra Mobile Broadband (UMB), another OFDM-based technology. However, most operators appear to be moving to LTE as their preferred solution.

Some operators may choose to deploy 802.16e, Mobile WiMAX. Mobile WiMAX is an OFDM-based Broadband Wireless Access (BWA) solution that is similar in many respects to LTE, despite its very different origins.

Wireless LAN providers are beginning to deploy 802.11n solutions, which can offer 100+ Mbps in a wireless hot

Wireless Network Evolution

3 G

PP

_UMTS HSDPA/ HSUPA

LTE

3 G

PP

2

1x _{Rev 0/A/B}1xEV-DO

UMB

WiMAX

802.16 Fixed

802.16e

Mobile

WLA

N

802.11 802.11 b/g

802.11n

X

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LTE – Long Term

Evolution

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For LTE, the evolutionary process has been a while in the making, and is not likely to end anytime soon. Each 3GPP standards release since the original UMTS specification has continued to add to and expand the capabilities of the network:

• Release 99 (R99) defined the original UMTS system, supporting circuit voice services as well as theoretical peak data rates of up to 2 Mbps. Commercial systems delivered packet data services of up to 384 kbps.

• R4 defined a bearer-independent circuit-switched architecture, separating switches into gateways and controllers, and laying the groundwork for the IP Multimedia Subsystem (IMS).

• R5 defined High Speed Downlink Packet Access (HSDPA), which boosted packet data rates to 14 Mbps on the downlink. R5 also completed the design of the IMS.

• R6 increased data rates to more than 5 Mbps on the uplink with High Speed Uplink Packet Access

broadcast/multicast services (MBMS).

• R7 provided further enhancements to HSDPA and HSUPA, called HSPA+. Support for higher-order modulation and Multiple-Input/Multiple-Output (MIMO) antenna systems offered a significant increase in data rates, potentially up to 42 Mbps. • R8 defined the Long Term Evolution (LTE) system,

starting the transition to 4G technology.

Even as vendors and operators are working to roll out the first R8-based LTE systems, work is underway on defining additional improvements to LTE. R9 is looking at further LTE enhancements, including support for MBMS and the definition of Home eNBs for improved residential and in-building coverage. R10 includes the definition of LTE Advanced, offering support for 8x8 MIMO, channel aggregation up to 100 MHz, and relay repeaters. It has been a long road, but the journey has just begun.

R8

3GPP Roadmap

R99 R4 R5 R6 R7 R9 R10 Circuit voice, 2 Mbps packet data Bearer-independent circuit-switched architecture HSDPA, IMS HSUPA, MBMS HSPA+, Higher-order modulation, MIMO LTE LTE Enhancements LTE Advanced

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Summary

• The wireless industry is rapidly evolving toward an

IP-centric, data-oriented architecture.

– Voice is still the primary application, but packet data is

driving significant growth.

– “All-IP,” packet-based networks offer more advanced,

integrated services.

• Current 3G technologies do not provide the

capacity, quality and throughput needed to support

future applications.

– New radio technologies and network architectures are

needed.

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Review Questions

1. What types of services and applications are

driving the transition to 4G?

2. What are the key characteristics of a 4G system?

3. What are the advantages of an “all-IP” network?

4. Which of the following components and networks

will be unchanged in the transition to LTE?

–

The mobile device.

–

The radio interface.

–

The access network.

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Chapter 2:

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References:

[1] 3GPP TS 23.402; Architecture Enhancements for non-3GPP accesses

[2] 3GPP TS 23.401; GPRS enhancements for LTE access

[3] 3GPP TS 36.300; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial

Radio Access Network (E-UTRAN) [4] 3GPP TR 23.882; 3GPP System Architecture

Evolution

Objectives

After completing this module, you will be able

to:

• Explain the architectural goals of LTE

• Describe the E-UTRAN, its components and its

interfaces

• Describe the Evolved Packet Core (EPC), its

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LTE System

Architecture

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The 3GPP Long Term Evolution (LTE) program has its own set of goals and requirements, beyond the basic targets of 4G.

• High Data Rates: The desired peak data rate for LTE in a 20 MHz radio channel is 100 Mbps on the downlink and 50 Mbps on the uplink.

• Low Latency: Latency for signaling messages must be less than 100 ms, while data should be delivered over the air within 5 ms.

• Low Cost: The network architecture will be IP-based end-to-end, and must be capable of supporting high data rates for a large number of users.

• Flexible Roll-out: The system must have the flexibility to be deployed in a wide variety of radio bands, taking advantage of whatever bandwidth is available and using whichever duplexing scheme is most appropriate.

• Enhanced Services: The network must support VoIP and other real-time services with the appropriate Quality of Service (QoS) characteristics. Also, new

IP-based services should be able to be developed and deployed quickly and cost-effectively.

• Reduced Complexity: The E-UTRAN is expected to be significantly less complex, reducing the number of different nodes and interfaces, and streamlining the air interface channels.

• Enhanced Network: The LTE network must be capable of interworking seamlessly with other 3GPP (GSM or UMTS) and non-3GPP (1x and 1xEV-DO and WiMAX) networks. The design of the network must permit traffic to be distributed across many different nodes, with sufficient redundancy to ensure no single point of failure in the network.

LTE Architecture Goals

High Data Rates • 100 Mbps (DL) • 50 Mbps (UL) Low Cost • High capacity • All-IP architecture Flexible Rollout

• Spectrum, bandwidth and duplexing flexibility

Enhanced Services • Support for VoIP and

real-time applications

• Service differentiation and rapid service deployment

Low Latency • < 100 ms (signaling) • < 5 ms (data) Reduced Complexity • Streamlined network architecture Enhanced Network • Interworking with 3GPP and

non-3GPP systems (seamless mobility) • Load sharing and

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The LTE system is an all-IP system that can reap the benefits of IP, such as scalability and low cost.

In order to meet the required goals, the 3G Partnership Project (3GPP) is responsible for defining the appropriate LTE standards. 3GPP focuses on three key areas:

• Evolved Universal Terrestrial Radio Access (E-UTRA): This air interface is based on an OFDM physical layer and uses MIMO techniques to further increase data rates. LTE supports more than 300 Mbps in the downlink to the User Equipment (UE) and more than 75 Mbps in the uplink, using a scalable channel bandwidth of up to 20 MHz.

• Evolved Universal Terrestrial Radio Access Network (UTRAN): Unlike the UMTS access network, the E-UTRAN has only one node - the evolved Node B, or eNodeB (eNB). The eNB is responsible for the physical layer operations of OFDM and MIMO, as well as the scheduling of downlink and uplink resources, handovers and Radio Resource Management (RRM).

• Evolved Packet Core (EPC): In LTE, the network is a greatly simplified IP-based network, replacing 3G network components with Mobility Management Entities (MMEs) and Serving Gateways (S-GWs) and Packet Data Network Gateways (P-GWs). The EPC is connected to both the E-UTRAN and the Internet, and any IP services network. The UE has a logical link with the Evolved Packet Core network (EPC) that provides IP connectivity to the UE. The EPC represents a migration from the traditional hierarchical system architecture to a flattened architecture.

LTE System Architecture

EPC

E-UTRAN

UE E-UTRA • Downlink: 300 Mbps • Uplink: 75 Mbps • OFDM and MIMO

E-UTRAN • Simplified architecture • Evolved Node B

EPC

(Evolved Packet Core) • Simplified architecture • IP-based services MME PDN-GW S-GW eNB eNB eNB

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Let’s take a look inside the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). The primary difference between the E-UTRAN and any other 3G radio network is the absence of a Radio Network Controller (RNC). The E-UTRAN eNodeB is the only node in the E-E-UTRAN. The traditional functionality of the RNC has been moved into the eNBs.

The E-UTRAN is a pure IP-based network where all kinds of information exchange is done using IP packets for transport. The eNBs are connected to the EPC via the S1 interface. The IP network is used to provide a distributed fully meshed connectivity between eNBs and multiple gateways within the EPC. This allows for load sharing and redundancy. The eNBs are interconnected by the X2 interface, to coordinate handovers and data transfers. The primary difference between a UTRAN and an E-UTRAN is the absence of an RNC. The functionality of the RNC has now been moved into the eNBs. The eNBs are connected to the MME and S-GWs via the S1 interface.

An eNB is able to communicate with multiple gateways, in order to enable load sharing and redundancy. eNBs are interconnected by the X2 interface, to coordinate handovers and data transfers.

LTE Radio Network (E-UTRAN)

UE eNB eNB MME S-GW X2 S1-MME E-UTRAN • No centralized controller (RNC) • eNBs communicate directly via X2 interface

E-UTRAN

Uu

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The traditional functionalities of the RNCs have been moved to the eNB. An eNB performs the following functions:

• Radio Resource Management (RRM) functionalities like radio bearer control and radio admission control; • IP header compression and encryption of the user

data stream;

• Uplink/downlink radio resource allocation in both the uplink and downlink;

• Transfer of paging messages over the air; • Transfer of broadcast information over the air; • Selection of the MME when a UE attaches to the

network; and

• Handover management.

The eNBs communicate over the X2 interface. The eNBs are connected to the MME and the S-GW by the S1 interface. The eNBs and the MME/S-GW have a many-to-many relationship to support load sharing and redundancy among the MME/S-GW.

eNodeB

Functions

• Radio resource management • Header Compression • Encryption • BCCH information transfer • Paging transfer

• Mobility in Active State • MME selection S- GW MME eNB S1 X2 X2 X2 eNB eNB

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The X2 interface is the interface between the eNBs. X2 functionalities are split into control-plane and user-plane functionalities.

The X2 Control Plane:

• Intra-LTE access-system mobility support for the UE. • Context transfer from the source eNB to the target

eNB.

• Control of user plane tunnels between the source eNB and the target eNB.

• Handover cancellation. • Uplink load management.

• SCTP as the transport layer protocol. The X2 User Plane:

• Tunnels end-user packets between the eNBs. • Identifies packets with tunnels and packet-loss

management.

• GTP-U over UDP/IP as the transport layer protocol.

• S1-UP and X2-UP use the same U-plane protocol to minimize protocol processing for the eNB at the time of data forwarding.

X2 Interface

eNB eNB eNB

X2 Interface Functions

• Multi-cell RRM

• Handover functions

• Load management

• Tunneling of user packets

X2 Interfaces (All-IP)

Supports Intra-LTE Mobility

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The S1 interface is the interface between the E-UTRAN and evolved packet core. S1 functionalities are split into C-plane and U-plane functionalities.

The S1 Control Plane:

• Delivering a signaling protocol between the eNB and the MME.

• Consists of SCTP over IP, and provides guaranteed data delivery.

• The application signaling protocol is an S1-AP (Application Protocol).

• EPS bearer set up and release procedures. • Handover signaling procedure.

• Paging procedure. • NAS transport procedure. The S1 User Plane:

• Responsible for delivering user data between the eNB and the S-GW.

• Consists of GTP-U over UDP/IP and provides

non-guaranteed data delivery.

• One GTP tunnel per radio bearer carries user traffic. • IP Differentiated Service Code Point (DSCP) marking

is supported for QoS per radio bearer. Award Solutions Confidential and Proprietary

(All-IP)

S1 Interfaces

S1 Interface

eNB S-GW eNB eNB MME Supports Many-to-Many Relationships

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Let’s take a look inside the Evolved Packet Core (EPC). The entities in the EPC include the Mobility Management Entity (MME), the Serving Gateway (S-GW), the Packet Data Network (PDN) Gateway (P-GW) and the Evolved Packet Data Gateway (ePDG). A primary difference between other 3G core networks and the EPC is that the EPC is only for packet data services, and there is no dedicated core network for voice services. Voice is treated as another service running on a packet data connection. The EPC is a pure, IP-based network where all kinds of information exchange is done using IP packets for transport. The MME/S-GW are nodes/functions that provide connectivity to the E-UTRAN via the S1 interface.

Inside the EPC

EPC

UE GERAN SGSN UTRAN UE UE S-GW MME _Wi-Fi P-GW E-UTRAN 1xEV-DO HSS AAA/AuC ePDG UE UE Non-Trusted Non-3GPP Network Trusted Non-3GPP Network PSTN Operator IP Services (IMS) Internet

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The functions of the MME are listed below: • Managing and storing UE contexts,

• Generating temporary identifiers for the Ues, • Idle-state mobility control,

• Distributing paging messages to eNBs, • Security control,

• Roaming,

• Authentication, and • Bearer control.

Mobility Management Entity (MME)

MME Functions

• Manage UE Contexts • Mobility Control • Security • Authentication

• Bearer Path Control S1

X2 X2 X2 MME eNB eNB eNB P-GW S-GW

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There are two gateways in the EPC, one facing toward the E-UTRAN (the S-GW) and one facing toward the external packet data network (the P-GW). A UE may connect to only one S-GW, but it may use multiple P-GWs. The functions of the S-GW are listed below:

• Anchoring the user plane for inter-eNB handover, • Anchoring the user plane for inter-3GPP mobility, • Similar to an SGSN in a pre-LTE 3GPP Network,

anchoring like a GGSN,

• Acting similar to a Foreign Agent (FA) in MIP in a pre-LTE 3GPP2 network, and

• Packet routing and forwarding.

Serving Gateway (S-GW)

S1 X2 X2 X2 S- GW eNB eNB eNB P-GW

S-GW Functions

• Anchor User Plane • Packet Routing and

Forwarding • Similar to SGSN • Similar to FA

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The PDN Gateway (P-GW) is similar to the GGSN in UMTS, or the HA in MIP. It hosts the following functions:

• Provide connectivity to the PDN and packet routing for the UE;

• Allocates IP addresses to the UE;

• Accounting and QoS, such as per-user-based packet filtering, transport-level packet marking based on QoS parameters, rate enforcement, and charging; and • Anchoring the user plane for mobility during

inter-MME/S-GW handovers, LTE and Prel-8 3GPP handovers, and 3GPP and non-3GPP handovers.

Packet Data Network Gateway

Functions

• Similar to GGSN and HA • Provide PDN Connectivity • Packet Routing

• IP Address Assignment • Accounting and QoS • Anchor the User Plane

During Inter-MME/S-GW Handover and During 3GPP-to-Non-3GPP Handovers S1 X2 X2 X2 S-GW MME eNB eNB eNB PDN-GW

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HSS (Home Subscriber Server): The HSS is a user database that stores subscription-related information to support other call-control and session-management entities. It is a storehouse for user identification, numbering and service profiles. It is mainly involved in user authentication and authorization. During registration, the MME talks to the HSS via the S6a interface for user authentication and ciphering. The HSS generates security information for mutual authentication and integrity check, ciphering, and can also provide information about the user's physical location. We can have one or more than one HSS in a home network, depending on the number of mobile subscribers and the equipment capacity.

Home Subscriber Server (HSS)

Serving Gateway (S-GW)

Evolved Packet

Core (EPC)

Operator’s IP Services (e.g., IMS) PDN Gateway (PDN-GW) • Master Database:

• Stores user subscription information,

identification, service profile, and location

• Generates security-related information

S6a

Authentication

HSS

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This architecture gives a feel for the IP Multimedia Subsystem (IMS). It is the IP-based core/services network of 3GPP. The IMS allows mobiles operating in packet mode to establish voice calls using SIP to communicate the request to the Call Session Control Function (CSCF). In this case, the voice data is transmitted as packets throughout the LTE network. The HSS in this case is simply an IP-based Home Location Register (HLR).

IP Multimedia Subsystem (IMS)

E-UTRAN

UE

EPC

IMS

ISUP HSS MME/S-GW P-GW MGCF MGW SGW AS CSCF (SIP Server) PSTN IP Network

(44)

Summary

• The LTE network architecture is designed to:

– Simplify the network,

– Enable enhanced services, and – Provide seamless mobility.

• The E-UTRAN contains only one node, the eNodeB

– Radio Network Controller (RNC) functions have been distributed to the eNodeBs.

– eNodeBs communicate and collaborate over the X2 interface.

• The Evolved Packet Core (EPC) is an all-IP network.

– The Mobility Management Entity (MME) provides signaling and control functions, while the Serving Gateway (S-GW) handles user traffic.

– The PDN Gateway (P-GW) provides an interface to services and external networks.

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Review Questions

1. How do a user’s packets flow through the

E-UTRAN and EPC?

2. Why is the X2 interface needed?

3. Which node is responsible for:

–

Tracking the mobile’s location?

–

Assigning IP addresses?

–

Allocating radio resources?

4. What is the advantage of allowing an eNodeB to

connect to multiple MMEs?

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Chapter 3:

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References:

[1] 3GPP TS 36.300; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN)

Objectives

After completing this module, you will be able

to:

• Identify and describe the basic concepts of

Orthogonal Frequency Division Multiplexing

(OFDM)

• Identify the key features of the LTE air interface

• Illustrate how Orthogonal Frequency Division

Multiple Access (OFDMA) is defined in LTE

• List the multiple-antenna techniques (MIMO)

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OFDM has many attractive characteristics.

• Scalable Design: Scalability allows the radio technology to utilize a variable bandwidth (up to 20 MHz) using the same radio access technology. In effect, scalability creates more channels as the spectrum grows, without requiring modifications in the device capability. So, in areas where a lot of capacity is needed, the operator can allocate more bandwidth and use less bandwidth in areas where the spectrum is not available or the capacity not needed. • Time and Frequency Scheduling: Radio resources can

be allocated across multiple channels (supporting bursts of high data rates), or across multiple transmission symbols (efficiently supporting longer sessions for VoIP or other real-time services), or both, depending on the capabilities of the device and the requirements of the application.

• Reduced Interference: By design, OFDM channels do not interfere with one another within a cell; therefore, a user using one set of channels cannot interfere with another user using a different set.

• Higher Data Rates: The more channels a user is assigned, the more data bits can be sent in a given amount of time. OFDM has hundreds of channels available for transmission due to the narrowband nature of each channel. When assigned in large numbers, and in parallel, these channels can achieve very high data rates.

• Support for Smart Antennas: OFDM systems lend themselves to the use of multiple-antenna techniques (“smart antennas”) to further improve performance, capacity and throughput. In certain situations, the energy from the radio beams can be focused toward the user, thus increasing performance. In other situations, the multiple antennas can be used to send more bits per second by transmitting differently from each antenna.

Why OFDM?

Support for Smart

Antennas

Time and

Frequency

Domain

Scheduling

Scalable Design – Up to 20 MHz

Higher Data

Rates

Reduced

Interference

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As data rates increase over a single radio channel, the symbol modulation rates eventually become too great to handle effectively. Synchronization becomes difficult, and inter-symbol interference (ISI) completely overwhelms the system. Sometimes, slower is better.

Consider a high-speed data stream of 100 Mbps. If the data is split into 10 substreams, each substream runs at 1 Mbps, one-tenth of the original data rate. If each one of these slower data streams modulates its own radio carrier, the result is 10 narrowband signals instead of one wideband radio signal. This is called Multicarrier Modulation (MCM). Each of the narrowband channels is called a subcarrier.

The fast data stream is converted into a number of parallel, slower data streams. These slower data streams are then sent on different subcarriers. In general, guard bands are required between different subcarriers to reduce inter-carrier interference (ICI).

MCM is used in many broadband-cable and fiber-optic transmission schemes. It is a broadband transmission technique, and is similar to replacing a single high-speed

coaxial cable with a multi-conductor cable. However, since MCM is not a very efficient user of bandwidth, it is rarely used in radio.

Multicarrier Principle

1 0

0 1 1 1 0 0 1 1 1 0 1 0 1 1 1 1 0 1 0 0

Fast

_Data

1 1 1 1 0 1 0 1 1 0 1 1 1 0 0 0 Serial-to-Parallel Converter

Slow

Data

Subcarrier Guard Band

0 1

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OFDM employs a similar multicarrier technique, where data is sent over a large number of channels called subcarriers. However, OFDM also implements some tricks to completely remove the guard bands normally required in MCM. Without guard bands, less bandwidth is needed to support the same number of subcarriers.

Guard bands are used to ensure that subcarriers do not interfere with one another. OFDM eliminates the need for guard bands by exploiting a property called orthogonality. Signals are said to be orthogonal if they do not interfere with each other.

Signals can be orthogonal in several domains, including time, space and frequency. Signals are orthogonal in the time domain if they occur on the same frequency, but not at the same time. For example, high-frequency (3 to 30 MHz) short-wave broadcasters can maintain orthogonality if they adhere to a worldwide transmission schedule. Two signals can be sent on the same frequency at the same time, but remain orthogonal if they are transmitted from places far away from each other (for example, Los Angeles and New York).

OFDM allows guard bands to be omitted by (a) separating the subcarriers making up the OFDM signal by exactly the inverse of the modulation rate, (b) ensuring the modulation rate is the same on all subcarriers, or (c) ensuring there is exactly an integer number of radio carrier cycles during a modulation symbol time.

The OFDM Advantage

FD

M

OFD

M

_{Saved Bandwidth}

The same number of subcarriers require less

RF bandwidth No interference between

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Orthogonal Frequency Division Multiplexing (OFDM) can be explained using a shower-head analogy. A shower head receives a large amount of water through a relatively thick pipeline. It divides the water into numerous parallel streams. Each stream carries only a small amount of water, but all of the streams together together carry a large amount of water.

Similarly, in an OFDM system, a large amount of data is distributed among multiple narrowband channels, with each narrowband channel carrying only a small amount of data. For example, 10 Mbps of data can be delivered to a user over 100 narrowband channels, with each channel carrying just 100 kbps.

Simplified View of OFDM

1 00 kb ps 1 00 kb ps 1 00 kb ps 1 00 kb ps 1 00 kb ps

1

0 Mb

ps

OFDMA

Large flow of water Many small streams High-speed data flow Many low-speed data streams

(54)

Orthogonal Frequency Division Multiple Access (OFDMA) allows multiple users to communicate simultaneously over an OFDM radio channel. In this example, the eNB has 1000 subcarriers, each capable of carrying 10 kbps of data. The total peak rate of the eNB is therefore 1000 x 10 kbps = 10 Mbps. However, the eNB does not have to give that entire bandwidth to one user. Instead, subsets can be allocated, depending on the needs and capabilities of each user.

User 1 is using a VoIP application, which only requires a single subcarrier (10 kbps). User 2 is browsing a Web site, and is assigned 99 subcarriers (990 kbps). User 3 is viewing a streaming video application and receives the remaining 900 subcarriers (9 Mbps). All of the users send and receive data at the same time, without interfering with one another.

As users come and go, or as their data requirements change, the eNB can adjust their subcarrier allocations accordingly, making the maximum use of the available resources.

What is OFDMA?

User 2 User 3 User 1 f1 f2 f3 f100 f101 f102 f998 f999 f1000 900 subcarriers @ 10 kbps each = 9 Mbps 99 subcarriers @ 10 kbps each = 990 kbps 1000 10 kbps subcarriers = 10 Mbps total bandwidth available eNB 1 subcarrier = 10 kbps

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Scalable OFDMA ensures that the definition of a subcarrier (its frequency spacing, symbol time, etc.) remains the same regardless of how much radio spectrum is used by the system. All that changes is the number of subcarriers available, not the subcarriers themselves. Scalability simplifies the design of OFDMA systems, by choosing a particular set of OFDM parameters that applies to all networks using that system. In this way, the subcarriers will have the same sensitivity to time, frequency errors and multipath effects, whether they are used in a 1.4 MHz system or a 20 MHz system. The signal processing requirements are therefore identical, allowing the same chipsets to be used everywhere, which reduces costs and simplifies design and development.

Scalable OFDMA

10 MHz = 1024 subcarriers 5 MHz = 512 subcarriers Same subcarrier spacing regardless of bandwidth Same channel characteristics (symbol duration) Same sensitivity to time and frequency errors and multipath

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Although all 4G systems use OFDM/OFDMA as their basic RF technology, LTE’s implementation provides a number of unique capabilities.

• Flexibility: LTE is designed to be as flexible as possible, to allow operators around the world the ability to deploy the technology in whatever spectrum they have available.

• Radio Access Technology: Orthogonal Frequency Division Multiplexing (OFDM) can provide higher data rates and spectral efficiency over the air interface. LTE uses Orthogonal Frequency Division Multiple Access (OFDMA) in the downlink, but uses a variation of OFDMA, called Single Carrier Frequency Division Multiple Access (SC-FDMA) in the uplink to improve performance by reducing the Peak-to-Average Power Ratio (PAPR).

• Multiple-Antenna Technology: Multiple-antenna techniques have been around for a long time, but have not yet seen wide-scale deployment. LTE will include a wide variety of advanced antenna techniques, including diversity, Single-User MIMO (SU-MIMO), Multi-User MIMO (MU-(SU-MIMO), Spatial Division Multiple Access (SDMA) and beamforming.

LTE Air Interface Features

Flexibility to support different

deployment scenarios • Spectrum

• Bandwidth • Duplexing

Multiple-Antenna Technologies to increase coverage, capacity and throughput

• Transmit Diversity for better coverage

• MIMO for higher throughput and capacity

• Beamforming for better coverage and capacity Radio Access Technologies to

support high-speed packet services • OFDMA in the DL for high data rate

and simpler mobile design • SC-FDMA in the UL for reduced

power consumption and lower PAPR

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Some key OFDMA/SC-FDMA transmission parameters are provided in this table. LTE is a scalable system, so the subcarrier spacing (15 kHz) is the same, regardless of the amount of spectrum. A 10 MHz system, for example, has a total of 1024 subcarriers, out of which 50 resource blocks (50*12 = 600 subcarriers) are for assignment to users.

LTE Transmission Parameters

Parameters Values Bandwidth (MHz) 1.4 3 5 10 15 20 Subcarrier spacing 15 kHz FFT size 128 256 512 1024 1536 2048 Usable Sub-carriers 72 180 300 600 900 1200 Resource Blocks 6 15 25 50 75 100

OFDM symbols per

slot 7 or 6

Modulation schemes

BPSK, QPSK (Signaling) QPSK, 16QAM, 64QAM (Data)

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The duration of one LTE radio frame is 10 ms. One frame is divided into 10 subframes of 1 ms each, and each subframe is divided into two slots of 0.5 ms each.

Generic Frame Structure

UE

Frame n Frame n+1 Frame n+2 Frame n-1

10 ms

Subframe 0 Subframe 1 Subframe 2 Subframe 9

slot 0 slot 1

1 ms

0.5 ms

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In LTE, radio resources are allocated in units of Physical Resource Blocks (PRBs). Normally, a PRB will contain 12 subcarriers over 7 symbols, for a total of 84 modulation symbols. If the system is configured to use the longer Cyclic Prefix in order to protect against excessive multipath, then the PRB will contain only six symbols.

Physical Resource Blocks

slot 0 slot 1 1 2 Subc ar rie rs PRB 7 Symbols

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LTE defines a number of channels and signals used to convey specific information in the uplink and downlink. • Broadcast Channel: Contains system configuration

and overhead information.

• Paging Channel: Carries paging indications to idle mobiles.

• Control Channel: Used by the eNB to assign resources to the UE, control uplink power, request channel quality reports, and so on.

• Traffic Channel: Carries the actual signaling messages and user data to the mobiles.

• Reference Signals: Provides known signals that can be easily detected for system access and synchronization, and measured for channel estimation.

• Random Access: Used for initial system access.

LTE Channels and Signals

UE

Broadcast Channel Paging Channel Control Channel Traffic Channel

Random Access Channel Control Channel

Traffic Channel Reference Signals

Reference Signals

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Multiple-Antenna

Techniques in LTE

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Multiple-antenna techniques make optimal use of the available spectrum, improving the quality of the signal received by the UE (on the downlink) and the eNB (on the uplink). This improved radio link results in higher throughput, lower interference, lower power levels and better coverage.

Multiple-Antenna Benefits

Better overall

signal quality

Reduced power

consumption

Lower

interference

Greater range or

improved coverage

Higher capacity or

throughput

Improved spectral

efficiency

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LTE is designed to support a number of different antenna techniques to improve quality, capacity, coverage and throughput.

• Diversity: Diversity techniques exploit variations in the signals sent and received from different antennas to improve the robustness and quality of the radio link. • Multiple Input Multiple Output (MIMO): Also known as

spatial multiplexing, MIMO techniques send different data streams over different antennas simultaneously. In SU-MIMO (Single-User MIMO), the streams are destined for the same user, increasing the net data rate. In MU-MIMO (Multi-User MIMO), the streams are intended for different users, which can be used to increase the overall capacity of the cell.

• Beamforming: Beamforming directs the energy of the radio signal at the specific user, improving the strength and range of the signal. Spatial Division Multiple Access (SDMA) is the most complex beamforming technique, and is the theoretical foundation of MU-MIMO. Simple beamforming can be implemented as a special case of SU-MIMO, where a single transmission layer is sent on each antenna. Award Solutions Confidential and Proprietary

Multiple-Antenna Techniques

Mult iple -A nt enna T ec hni ques Receive Diversity Transmit Diversity Single-User MIMO (SU-MIMO) Multi-User MIMO (MU-MIMO) Space Division Multiple

Access (SDMA) Simple Beamforming

(Single TX Layer SU-MIMO)

Diversity

MIMO/ Spatial Multiplexing

(66)

The two basic forms of diversity are receive diversity and transmit diversity. In receive diversity, the receiver uses multiple antennas to retrieve different copies of the same transmitted signal. These copies are combined together to produce a better signal than would be possible with a single antenna. The odds that all copies are faded or impaired at the same time is quite low. Although receive diversity requires additional antennas and processing in the handset, the performance improvement has proven to be worth the cost.

In transmit diversity, multiple copies of the same signal are sent from separate transmit antennas and are received at the other end. Again, the likelihood of all copies being poor is greatly reduced. The advantage of this approach, especially for mobile devices, is that the transmitter bears the burden of the cost of implementation.

Diversity

Transmit Diversity • Multiple transmit antennas • Use space and time to obtain

multiple copies of the signal

Receive Diversity • Multiple receive antennas • Combine multiple copies of the

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Single-User MIMO (SU-MIMO) antenna techniques use multiple transmit antennas to send separate streams of data in parallel to the mobile device; the same radio frequencies and slots are used for both streams. Significant coding and processing is needed on the receiving side to extract the different streams, but the result is a significantly higher net data rate. Two transmit antennas can send twice as much data as one.

Single User MIMO

abcdefgh

abcd efgh

abcdefgh

abcd efgh

Parallel data streams to a single user

Transmit diversity provides a robust radio path

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Multiple-User MIMO (MU-MIMO) systems (also known as Space Division Multiple Access, or SDMA) allow multiple users separated in space to use the same frequencies and slots simultaneously. Each user, in effect, has access to all of the cell’s resources independently of what the other users are doing, resulting in a significant increase in spectral efficiency and system capacity. However, MU-MIMO/SDMA systems are extremely complex and costly to implement, especially on mobile devices.