Introducing LTE-Advanced

Introducing LTE-Advanced

Application Note

LTE-Advanced (LTE-A) is the project name of the evolved version of LTE that is

being developed by 3GPP. LTE-A will meet or exceed the requirements of the

International Telecommunication Union (ITU) for the fourth generation (4G) radio

communication standard known as IMT-Advanced. LTE-Advanced is being speci-

fied initially as part of Release 10 of the 3GPP specifications, with a functional

freeze targeted for March 2011. The LTE specifications will continue to be

developed in subsequent 3GPP releases.

In October 2009, the 3GPP Partners formally submitted LTE-Advanced to the

ITU Radiocommunication sector (ITU-R) as a candidate for 4G IMT-Advanced [1].

Publication by the ITU of the specification for IMT-Advanced is expected by

March 2011. As more and more wireless operators announce plans to deploy

LTE in their next-generation networks, interest in LTE-Advanced is growing.

This application note covers the following topics:

• Summary of the ITU requirements for 4G

• Summary of 3GPP requirements for LTE-Advanced, including the expected

timeline

• Key solution proposals for LTE-Advanced

• Release 10 and beyond: Technologies under consideration

• Anticipated design and test challenges

The application note also introduces Agilent’s LTE-Advanced design and test

solutions that are ready for use by early adopters. These solutions will be con-

tinuously enhanced as the LTE-Advanced specifications are released.

 

 

 

LTE Advanced (LTE+)

With the standards definitions now available for LTE, the Long Term Evolution of the 3G services, eyes are now turning towards the next development, that of the truly 4G technology named IMT Advanced. The new technology being developed under the auspices of 3GPP to meet these requirements is often termed LTE Advanced.
In order that the cellular telecommunications technology is able to keep pace with technologies that may compete, it is necessary to ensure that new cellular technologies are being formulated and developed. This is the reasoning behind starting the development of the new LTE Advanced systems, proving the technology and developing the LTE Advanced standards.

In order that the correct solution is adopted for the 4G system, the ITU-R (International Telecommunications Union - Radiocommunications sector) has started its evaluation process to develop the recommendations for the terrestrial components of the IMT Advanced radio interface. One of the main competitors for this is the LTE Advanced solution.
One of the key milestones is October 2010 when the ITU-R decides the framework and key characteristics for the IMT Advanced standard. Before this, the ITU-R will undertake the evaluation of the various proposed radio interface technologies of which LTE Advanced is a major contender.

Key milestones for ITU-R IMT Advanced evaluation

The ITU-R has set a number of milestones to ensure that the evaluation of IMT Advanced technologies occurs in a timely fashion. A summary of the main milestones is given below and this defines many of the overall timescales for the development of IMT Advanced and in this case LTE Advanced as one of the main technologies to be evaluated.

Key Milestones on the Development of 4G LTE-Advanced
Milestone	Date
Issue invitation to propose Radio Interface Technologies.	March 2008
ITU date for cut-off for submission of proposed Radio Interface Technologies.	October 2009
Cutoff date for evaluation report to ITU.	June 2010
Decision on framework of key characteristics of IMT Advanced Radio Interface Technologies.	October 2010
Completion of development of radio interface specification recommendations.	February 2011

LTE Advanced development history

With 3G technology established, it was obvious that the rate of development of cellular technology should not slow. As a result initial ideas for the development of a new 4G system started to be investigated. In one early investigation which took place on 25 December 2006 with information released to the press on 9 February 2007, NTT DoCoMo detailed information about trials in which they were able to send data at speeds up to approximately 5 Gbit/s in the downlink within a 100MHz bandwidth to a mobile station moving at 10km/h. The scheme used several technologies to achieve this including variable spreading factor spread orthogonal frequency division multiplex, MIMO, multiple input multiple output, and maximum likelihood detection. Details of these new 4G trials were passed to 3GPP for their consideration
In 2008 3GPP held two workshops on IMT Advanced, where the "Requirements for Further Advancements for E-UTRA" were gathered. The resulting Technical Report 36.913 was then published in June 2008 and submitted to the ITU-R defining the LTE-Advanced system as their proposal for IMT-Advanced.
The development of LTE Advanced / IMT Advanced can be seen to follow and evolution from the 3G services that were developed using UMTS / W-CDMA technology.

Comparison of LTE-A with other Cellular Technologies
	WCDMA (UMTS)	HSPA HSDPA / HSUPA	HSPA+	LTE	LTE Advanced (IMT Advanced)
Max downlink speed bps	384 k	14 M	28 M	100M	1G
Max uplink speed bps	128 k	5.7 M	11 M	50 M	500 M
Latency round trip time approx	150 ms	100 ms	50ms (max)	~10 ms	less than 5 ms
3GPP releases	Rel 99/4	Rel 5 / 6	Rel 7	Rel 8	Rel 10
Approx years of initial roll out	2003 / 4	2005 / 6 HSDPA 2007 / 8 HSUPA	2008 / 9	2009 / 10	2014 / 15
Access methodology	CDMA	CDMA	CDMA	OFDMA / SC-FDMA	OFDMA / SC-FDMA

LTE Advanced is not the only candidate technology. WiMAX is also there, offering very high data rates and high levels of mobility. However it now seems less likely that WiMAX will be adopted as the 4G technology, with LTE Advanced appearing to be better positioned.

LTE Advanced key features

With work starting on LTE Advanced, a number of key requirements and key features are coming to light. Although not fixed yet in the specifications, there are many high level aims for the new LTE Advanced specification. These will need to be verified and much work remains to be undertaken in the specifications before these are all fixed. Currently some of the main headline aims for LTE Advanced can be seen below:

1. Peak data rates: downlink - 1 Gbps; uplink - 500 Mbps.
2. Spectrum efficiency: 3 times greater than LTE.
3. Peak spectrum efficiency: downlink - 30 bps/Hz; uplink - 15 bps/Hz.
4. Spectrum use: the ability to support scalable bandwidth use and spectrum aggregation where non-contiguous spectrum needs to be used.
5. Latency: from Idle to Connected in less than 50 ms and then shorter than 5 ms one way for individual packet transmission.
6. Cell edge user throughput to be twice that of LTE.
7. Average user throughput to be 3 times that of LTE.
8. Mobility: Same as that in LTE
9. Compatibility: LTE Advanced shall be capable of interworking with LTE and 3GPP legacy systems.

These are many of the development aims for LTE Advanced. Their actual figures and the actual implementation of them will need to be worked out during the specification stage of the system.

LTE Advanced technologies

There are a number of key technologies that will enable LTE Advanced to achieve the high data throughput rates that are required. MIMO and OFDM are two of the base technologies that will be enablers. Along with these there are a number of other techniques and technologies that will be employed.

• Orthogonal Frequency Division Multiplex, OFDM   OFDM forms the basis of the radio bearer. Along with it there is OFDMA (Orthogonal Frequency Division Multiple Access) along with SC-FDMA (Single Channel Orthogonal Frequency Division Multiple Access). These will be used in a hybrid format. However the basis for all of these access schemes is OFDM.
  
  

  Note on OFDM:

  Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is split across all the carriers to give resilience against selective fading from multi-path effects..
  Click on the link for an OFDM tutorial
  
  
  
• Multiple Input Multiple Output, MIMO:   One of the other key enablers for LTE Advanced that is common to LTE is MIMO. This scheme is also used by many other technologies including WiMAX and Wi-Fi - 802.11n. MIMO - Multiple Input Multiple Output enables the data rates achieved to be increased beyond what the basic radio bearer would normally allow.
  
  

  Note on MIMO:

  Two major limitations in communications channels can be multipath interference, and the data throughput limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist between a transmitter and receiver to significantly improve the data throughput available on a given channel with its defined bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital signal processing, MIMO technology enables the system to set up multiple data streams on the same channel, thereby increasing the data capacity of a channel.
  Click on the link for a MIMO tutorial
  
  
  
  For LTE Advanced, the use of MIMO is likely to involve further and more advanced techniques including the use of additional antennas in the matrix to enable additional paths to be used, although as the number of antennas increases, the overhead increases and the return per additional path is less.
  
  In additional to the numbers of antennas increasing, it is likely that techniques such as beamforming may be used to enable the antenna coverage to be focused where it is needed.
• Carrier Aggregation, CA:   As many operators do not have sufficient contiguous spectrum to provide the required bandwidths for the very high data rates, a scheme known as carrier aggregation has been developed. Using this technology operators are able to utilise multiple channels either in the same bands or different areas of the spectrum to provide the required bandwidth. Read more about Carrier Aggregation, CA
• Coordinated Multipoint :   One of the key issues with many cellular systems is that of poor performance at the cell edges. Interference from adjacent cells along with poor signal quality lead to a reduction in data rates. For LTE-Advanced a scheme known as coordinated multipoint has been introduced. Read more about Coordinated Multipoint, CoMP
• LTE Relaying:   LTE relaying is a scheme that enables signals to be forwarded by remote stations from a main base station to improve coverage. Read more about LTE Relaying
• Device to Device, D2D:   LTE D2D is a facility that has been requested by a number of users, in particular the emergency services. It enables fast swift access via direct communication - a facility that is essential for the emergency services when they may be on the scene of an incident. Read more about Device to Device communications

LTE Technology Leyers

LTE video tutorial

Rohde & Schwarz's 14-part presentations provide an excellent introduction to LTE. The presentations start with a background on LTE. This is followed by lectures that cover LTE frequency bands, OFDM, OFDMA, SC-FDMA and LTE signaling. The lectures also cover channel mapping and UE categories.

---

LTE physical layer

An excellent overview of the LTE physical layer. Get an overview of OFDM and SC-FDMA transmit and receive chains. LTE channels and reference signals are described in detail. Highly recommended.

---

LTE link layer design

This article describes the LTE link-layer protocols, which abstract the physical layer and adapt its characteristics to match the requirements of higher layer protocols.The LTE link-layer protocols are optimized for low delay and low overhead and are simpler than their counterparts in UTRAN. The state -of-the-art LTE protocol design is the result of a careful crosslayer approach where the protocols interact with each other efficiently. This article provides a thorough overview of this protocol stack, including the sub-layers and corresponding interactions in between them, in a manner that is more intuitive than in the respective 3GPP specifications.

---

Introduction to LTE architecture

This article provides an overview of the LTE radio interface, together with a more in-depth description of its features such as spectrum flexibility, multi-antenna transmission, and inter-cell interference control. The performance of LTE and some of its key features is illustrated with simulation results.
This article provides a high-level overview of LTE and some of its key components: spectrum flexibility, multi-antenna transmission, and ICIC. Numerical simulations are used to show the performance of the first release of LTE, as well as assess the benefit of the key features. Indeed these contribute strongly to LTE meeting its performance targets. An outlook of the evolution of LTE toward LTE-Advanced and full IMT-Advanced capabilities complete the article. Clearly, LTE offers highly competitive performance and provides a good foundation for further evolution.

---

LTE network architecture

This paper provides a short, but comprehensive, overview of the LTE network architecture and interfaces. The paper introduces control plane and user plane architecture. LTE procedures on S1 and X2 interfaces are described in detail. The paper also briefly touches the bearer establishment procedure.

---

EPS architecture overview

This excellent video by Russell DeLong covers the EPS in detail. The topics covered here are:
Terminology clarifications for "4G LTE" and the EPS.
Overview of each component of EPS. Russell walks you through the role of the MME, the S-GW and the P-GW.
Overview of each logical connection between each component on the EPS.

---

LTE channels and protocol layers

This paper provides an overview of the MAC for 3GPP™ Long Term Evolution (LTE) also referred to as E-UTRAN, with a focus on the handset or User Equipment (UE). The protocol stack functions consist of the Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP), and Radio Resource Control (RRC).
LTE uses all the time on the downlink for conveying data; the downlink PHY is fully scheduled so there are no gaps due to arbitration or contention except for the initial access on the random access procedure. The downlink carries multiple logical channels over one link, so a lot of information is multiplexed together in one transport block, as opposed to other networks where any given packet is only carrying one type of information at a given time, such as in a control plane or a user plane..

---

LTE physical layer presentation

The presentation covers LTE architecture, frame structure, channels, MIMO and scheduling. OFDM and SC-FDMA are also covered.

---

---

LTE ( 4G ) Optimisation and R&d: LTE INTRODUCTION

LTE ( 4G ) Optimisation and R&d: LTE INTRODUCTION: INTRODUCTION TO LTE....... LTE stands for Long Term Evolution and it was started as a project in 2004 by telecommunication body kno...

LTE Glossary

Term	Description
3GPP	3rd Generation Partnership Project
3GPP2	3rd Generation Partnership Project 2
ARIB	Association of Radio Industries and Businesses
ATIS	Alliance for Telecommunication Industry Solutions
AWS	Advanced Wireless Services
CAPEX	Capital Expenditure
CCSA	China Communications Standards Association
CDMA	Code Division Multiple Access
CDMA2000	Code Division Multiple Access 2000
DAB	Digital Audio Broadcast
DSL	Digital Subscriber Line
DVB	Digital Video Broadcast
eHSPA	evolved High Speed Packet Access
ETSI	European Telecommunications Standards Institute
FDD	Frequency Division Duplex
FWT	Fixed Wireless Terminal
GSM	Global System for Mobile communication
HSPA	High Speed Packet Access
HSS	Home Subscriber Server
IEEE	Institute of Electrical and Electronics Engineers
IPTV	Internet Protocol Television
LTE	Long Term Evolution
MBMS	Multimedia Broadcast Multicast Service
MIMO	Multiple Input Multiple Output
MME	Mobility Management Entity
NGMN	Next Generation Mobile Networks
OFDM	Orthogonal Frequency Division Multiplexing
OPEX	Operational Expenditure
PAPR	Peak to Average Power Ratio
PCI	Peripheral Component Interconnect
PCRF	Policing and Charging Rules Function
PDSN	Packet Data Serving Node
PS	Packet Switched
QoS	Quality of Service
RAN	Radio Access Network
SAE	System Architecture Evolution
SC-FDMA	Single Carrier Frequency Division Multiple Access
SGSN	Serving GPRS Support Node
TDD	Time Division Duplex
TTA	Telecommunications Technology Association
TTC	Telecommunication Technology Committee
TTI	Transmission Time Interval
UTRA	Universal Terrestrial Radio Access
UTRAN	Universal Terrestrial Radio Access Network
WCDMA	Wideband Code Division Multiple Access
WLAN	Wireless Local Area Network

 

LTE OFDM Technology

To overcome the effect of multi path fading problem available in UMTS, LTE uses Orthogonal Frequency Division Multiplexing (OFDM) for the downlink - that is, from the base station to the terminal to transmit the data over many narrow band careers of 180 KHz each instead of spreading one signal over the complete 5MHz career bandwidth ie. OFDM uses a large number of narrow sub-carriers for multi-carrier transmission to carry data.
Orthogonal frequency-division multiplexing (OFDM), is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method.
OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates. The basic LTE downlink physical resource can be seen as a time-frequency grid, as illustrated in Figure below:
The OFDM symbols are grouped into resource blocks. The resource blocks have a total size of 180kHz in the frequency domain and 0.5ms in the time domain. Each 1ms Transmission Time Interval (TTI) consists of two slots (Tslot).
Each user is allocated a number of so-called resource blocks in the time.frequency grid. The more resource blocks a user gets, and the higher the modulation used in the resource elements, the higher the bit-rate. Which resource blocks and how many the user gets at a given point in time depend on advanced scheduling mechanisms in the frequency and time dimensions.
The scheduling mechanisms in LTE are similar to those used in HSPA, and enable optimal performance for different services in different radio environments.

Advantages of OFDM

• The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions (for example, attenuation of high frequencies in a long copper wire, narrowband interference and frequency-selective fading due to multipath) without complex equalization filters.
• Channel equalization is simplified because OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal.
• The low symbol rate makes the use of a guard interval between symbols affordable, making it possible to eliminate inter symbol interference (ISI).
• This mechanism also facilitates the design of single frequency networks (SFNs), where several adjacent transmitters send the same signal simultaneously at the same frequency, as the signals from multiple distant transmitters may be combined constructively, rather than interfering as would typically occur in a traditional single-carrier system.

Drawbacks of OFDM

• High peak-to-average ratio
• Sensitive to frequency offset, hence to Doppler-shift as well

SC-FDMA Technology

LTE uses a pre-coded version of OFDM called Single Carrier Frequency Division Multiple Access (SC-FDMA) in the uplink. This is to compensate for a drawback with normal OFDM, which has a very high Peak to Average Power Ratio (PAPR).
High PAPR requires expensive and inefficient power amplifiers with high requirements on linearity, which increases the cost of the terminal and drains the battery faster.
SC-FDMA solves this problem by grouping together the resource blocks in such a way that reduces the need for linearity, and so power consumption, in the power amplifier. A low PAPR also improves coverage and the cell-edge performance.

 

LTE Communication Channels

The information flows between the different protocols are known as channels and signals. LTE uses several different types of logical, transport and physical channel, which are distinguished by the kind of information they carry and by the way in which the information is processed.

• Logical Channels : Define whattype of information is transmitted over the air, e.g. traffic channels, control channels, system broadcast, etc. Data and signalling messages are carried on logical channels between the RLC and MAC protocols.
• Transport Channels : Define howis something transmitted over the air, e.g. what are encoding, interleaving options used to transmit data. Data and signalling messages are carried on transport channels between the MAC and the physical layer.
• Physical Channels : Define whereis something transmitted over the air, e.g. first N symbols in the DL frame. Data and signalling messages are carried on physical channels between the different levels of the physical layer.

Logical Channels

Logical channels define what type of data is transferred. These channels define the data-transfer services offered by the MAC layer. Data and signalling messages are carried on logical channels between the RLC and MAC protocols.
Logical channels can be divided into control channels and traffic channels. Control Channel can be either common channel or dedicated channel. A common channel means common to all users in a cell (Point to multipoint) while dedicated channels means channels can be used only by one user (Point to Point).
Logical channels are distinguished by the information they carry and can be classified in two ways. Firstly, logical traffic channels carry data in the user plane, while logical control channels carry signalling messages in the control plane. Following table lists the logical channels that are used by LTE:

Channel Name	Acronym	Control channel	Traffic channel
Broadcast Control Channel	BCCH	X
Paging Control Channel	PCCH	X
Common Control Channel	CCCH	X
Dedicated Control Channel	DCCH	X
Multicast Control Channel	MCCH	X
Dedicated Traffic Channel	DTCH		X
Multicast Traffic Channel	MTCH		X

Transport Channels

Transport channels define how and with what type of characteristics the data is transferred by the physical layer. Data and signalling messages are carried on transport channels between the MAC and the physical layer.
Transport Channels are distinguished by the ways in which the transport channel processor manipulates them. Following table lists the transport channels that are used by LTE:

Channel Name	Acronym	Downlink	Uplink
Broadcast Channel	BCH	X
Downlink Shared Channel	DL-SCH	X
Paging Channel	PCH	X
Multicast Channel	MCH	X
Uplink Shared Channel	UL-SCH		X
Random Access Channel	RACH		X

Physical Channels

Data and signalling messages are carried on physical channels between the different levels of the physical layer and accordingly they are divided into two parts:

• Physical Data Channels
• Physical Control Channels

Physical data channels

Physical data channels are distinguished by the ways in which the physical channel processor manipulates them, and by the ways in which they are mapped onto the symbols and sub-carriers used by Orthogonal frequency-division multiplexing (OFDMA). Following table lists the physical data channels that are used by LTE:

Channel Name	Acronym	Downlink	Uplink
Physical downlink shared channel	PDSCH	X
Physical broadcast channel	PBCH	X
Physical multicast channel	PMCH	X
Physical uplink shared channel	PUSCH		X
Physical random access channel	PRACH		X

The transport channel processor composes several types of control information, to support the low-level operation of the physical layer. These are listed in the below table:

Field Name	Acronym	Downlink	Uplink
Downlink control information	DCI	X
Control format indicator	CFI	X
Hybrid ARQ indicator	HI	X
Uplink control information	UCI		X

Physical Control Channels

The transport channel processor also creates control information that supports the low-level operation of the physical layer and sends this information to the physical channel processor in the form of physical control channels.
The information travels as far as the transport channel processor in the receiver, but is completely invisible to higher layers. Similarly, the physical channel processor creates physical signals, which support the lowest-level aspects of the system.
Physical Control Channels are listed in the below table:

Channel Name	Acronym	Downlink	Uplink
Physical control format indicator channel	PCFICH	X
Physical hybrid ARQ indicator channel	PHICH	X
Physical downlink control channel	PDCCH	X
Relay physical downlink control channel	R-PDCCH	X
Physical uplink control channel	PUCCH		X

The base station also transmits two other physical signals, which help the mobile acquire the base station after it first switches on. These are known as the primary synchronization signal (PSS) and the secondary synchronization signal (SSS).