LTE Advanced

LTE Advanced is a mobile communication standard, formally submitted as a candidate 4G system to ITU-T in late 2009, was approved into ITU, International Telecommunications Union, IMT-Advanced and was finalized by 3GPP in March 2011. It is standardized by the 3rd Generation Partnership Project (3GPP) as a major enhancement of the Long Term Evolution (LTE) standard. The technology received its first commercial implementation in October 2012 by Russian network Yota.

Background

The LTE format was first proposed by NTT DoCoMo of Japan and has been adopted as the international standard. LTE standardization has matured to a state where changes in the specification are limited to corrections and bug fixes. The first commercial services were launched in Sweden and Norway in December 2009 followed by the United States and Japan in 2010. More LTE networks were deployed globally during 2010 as a natural evolution of several 2G and 3G systems, including Global system for mobile communications (GSM) and Universal Mobile Telecommunications System (UMTS) (3GPP as well as 3GPP2).

The work by 3GPP to define a 4G candidate radio interface technology started in Release 9 with the study phase for LTE-Advanced. Being described as a 3.9G (beyond 3G but pre-4G), the first release of LTE did not meet the requirements for 4G (also called IMT Advanced as defined by the International Telecommunication Union) such as peak data rates up to 1 Gb/s. The ITU has invited the submission of candidate Radio Interface Technologies (RITs) following their requirements in a circular letter, 3GPP Technical Report (TR) 36.913, "Requirements for Further Advancements for E-UTRA (LTE-Advanced)." These are based on ITU's requirements for 4G and on operators’ own requirements for advanced LTE. Major technical considerations include the following:

• Continual improvement to the LTE radio technology and architecture
• Scenarios and performance requirements for working with legacy radio technologies
• Backward compatibility of LTE-Advanced with LTE. An LTE terminal should be able to work in an LTE-Advanced network and vice versa. Any exceptions will be considered by 3GPP.
• Consideration of recent World Radiocommunication Conference (WRC-07) decisions regarding frequency bands to ensure that LTE-Advanced accommodates the geographically available spectrum for channels above 20 MHz. Also, specifications must recognize those parts of the world in which wideband channels are not available.

Likewise, 'WiMAX 2', 802.16m, has been approved by ITU as the IMT Advanced family. WiMAX 2 is designed to be backward compatible with WiMAX 1 devices. Most vendors now support conversion of 'pre-4G', pre-advanced versions and some support software upgrades of base station equipment from 3G.

The mobile communication industry and standards organizations have therefore started work on 4G access technologies, such as LTE Advanced. At a workshop in April 2008 in China, 3GPP agreed the plans for work on Long Term Evolution (LTE). A first set of specifications were approved in June 2008. Besides the peak data rate 1 Gb/s as defined by the ITU-R, it also targets faster switching between power states and improved performance at the cell edge. Detailed proposals are being studied within the working groups.

Proposals

The target of 3GPP LTE Advanced is to reach and surpass the ITU requirements. LTE Advanced should be compatible with first release LTE equipment, and should share frequency bands with first release LTE. In the feasibility study for LTE Advanced, 3GPP determined that LTE Advanced would meet the ITU-R requirements for 4G. The results of the study are published in 3GPP Technical Report (TR) 36.912.

One of the important LTE Advanced benefits is the ability to take advantage of advanced topology networks; optimized heterogeneous networks with a mix of macrocells with low power nodes such as picocells, femtocells and new relay nodes. The next significant performance leap in wireless networks will come from making the most of topology, and brings the network closer to the user by adding many of these low power nodes — LTE Advanced further improves the capacity and coverage, and ensures user fairness. LTE Advanced also introduces multicarrier to be able to use ultra wide bandwidth, up to 100 MHz of spectrum supporting very high data rates.

In the research phase many proposals have been studied as candidates for LTE Advance technologies. The proposals could roughly be categorized into:

• Support for relay node base stations
• Coordinated multipoint (CoMP) transmission and reception
• UE Dual TX antenna solutions for SU-MIMO and diversity MIMO
• Scalable system bandwidth exceeding 20 MHz, up to 100 MHz
• Carrier aggregation of contiguous and non-contiguous spectrum allocations
• Local area optimization of air interface
• Nomadic / Local Area network and mobility solutions
• Flexible spectrum usage
• Cognitive radio
• Automatic and autonomous network configuration and operation
• Support of autonomous network and device test, measurement tied to network management and optimization
• Enhanced precoding and forward error correction
• Interference management and suppression
• Asymmetric bandwidth assignment for FDD
• Hybrid OFDMA and SC-FDMA in uplink
• UL/DL inter eNB coordinated MIMO
• SONs, Self Organizing Networks methodologies
• Multiple carrier spectrum access.

Within the range of system development, LTE-Advanced and WiMAX 2, can use up to 8x8 MIMO and 128 QAM. Example performance: 100 MHz aggregated bandwidth, LTE-Advanced provides almost 3.3 Gbit peak download rates per sector of the base station under ideal conditions. Advanced network architectures combined with distributed and collaborative smart antenna technologies provide several years road map of commercial enhancements.

A summary of a study carried out in 3GPP can be found in TR36.912.

Timeframe

Standardization work was done in 3GPP Release 10, which was frozen in April 2011. Trials have taken place based on pre-release equipment. Major vendors support software upgrades to final versions and ongoing improvements.

Technology demonstrations

• In February 2007, NTT DoCoMo announced the completion of a 4G trial where it achieved a maximum packet transmission rate of approximately 5 Gbit/s in the downlink using 12 transmit and 12 receive antennas and 100 MHz frequency bandwidth to a mobile station moving at 10 km/h.
• In February 2011 at Mobile World Congress, Agilent Technologies demonstrated the industry's first test solutions for LTE-Advanced with both signal generation and signal analysis solutions.
• On 9 October, 2012, Russian carrier Yota launched the first-ever commercial implementation of the technology, at 11 of its base-stations around Moscow. However compatible handsets won't be available until the first-half of 2013.

References

• Qualcomm
• Harri Holma, Antti Toskala, LTE for UMTS - OFDMA and SC-FDMA Based Radio Access, John Wiley & Sons 2009, ISBN 978-0-470-99401-6 Chapter 2.6: LTE Advanced for IMT-advanced, page 19-21.
• Moray Rumney (editor), LTE and the Evolution to 4G Wireless: Design and Measurement Challenges, Agilent Technologies Publication 2009, ISBN 978-0-470-68261-6, Chapter 8.7: Proving LTE Advanced, page 425
• Christina Gessner (editor), Long Term Evolution: A concise introduction to LTE and its measurement requirements, Rohde & Schwarz Publication 2011, ISBN 978-3-939837-11-4,
• Preben E. Mogensen, Tommi Koivisto, Klaus I. Pedersen 1, et al.; Nokia Siemens Networks;LTE Advanced: The Path towards Gigabit/s in Wireless Mobile Communications, Wireless VITAE'09.

External links

• LTE Advanced page on Qualcomm site
• 3GPP Official 3GPP Standardisation Page on LTE Advanced
• LTE Advanced overview
• Future use of LTE A femtocells
• LTE Portal – 3GPP LTE / LTE Advanced Technology, dedicated portal created for information sharing, collaboration, and networking

Resources (white papers, technical papers, application notes)

• LTE Blog – LTE Blog
• ITU-R Confers IMT-Advanced (4G) Status to 3GPP LTE – LTE Advanced is officially 4G
• The LTE / LTE Advanced Guide – a semi-annual publication on LTE / LTE Advanced, May and November 2010 publications are now available
• LTE-Advanced Technology Introduction - This white paper summarizes necessary improvements, which are known as LTE-Advanced
• Introducing LTE-Advanced - Application Note
• LTE Bitstream Verification - Application Note about verification of baseband data of LTE/LTE-A-ready products.
• LTE Transmission Modes and Beamforming - This white paper discusses the basics of beamforming and explains the eight MIMO transmission modes in LTE Release 9.