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 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.
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 Advanced (LTE-A) 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, commonly referred to as 2x2 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 or Carrier Aggregation (CA).
Within the range of system development, LTE-Advanced and WiMAX 2, can use up to 8x8 MIMO and 128 QAM in downlink direction. 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 and introduction of additional features
Original standardization work for LTE-Advanced was done as part of 3GPP Release 10, which was frozen in April 2011. Trials were based on pre-release equipment. Major vendors support software upgrades to later versions and ongoing improvements.
In order to improve the quality of service for users in hotspots and on cell edges, heterogenous networks (HetNet) are formed of a mixture of macro-, pico- and femto base stations serving corresponding-size areas. Frozen in December 2012, 3GPP Release 11 concentrates on better support of HetNet. Coordinated Multi-Point operation (CoMP) is a key feature of Release 11 in order to support such network structures. Whereas users located at a cell edge in homogenous networks suffer from decreasing signal strength compounded by neighbor cell interference, CoMP is designed to enable use of a neighboring cell to also transmit the same signal as the serving cell, enhancing quality of service on the perimeter of a serving cell. In-device Co-existence (IDC) is another topic addressed in Release 11. IDC features are designed to ameliorate disturbances within the user equipment caused between LTE/LTE-A and the various other radio subsystems such as WiFi, Bluetooth, and the GPS receiver. Further enhancements for MIMO such as 4x4 configuration for the uplink were standardized.
The higher number of cells in HetNet results in user equipment changing the serving cell more frequently when in motion. The ongoing work on LTE-Advanced  in Release 12, amongst other areas, concentrates on addressing issues that come about when users move through HetNet, such as frequent hand-overs between cells.
- 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 December 2009 TeliaSonera launched the first commercial LTE services in Sweden and Norway.
- 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 mobile implementation of the technology, at 11 of its base-stations around Moscow. However compatible handsets weren't available until the first-half of 2013.
- On June 25th, 2013, Korea's SK Telecom announced the launching of LTE-Advanced services in Korea. 
- On June 26th, 2013, Samsung Electronics released an LTE-Advanced version of the Galaxy S4. 
- On July 18th, 2013, Korea's LG U Plus unveiled an LTE-Advanced network.
- On August 18th, 2013, Philippines’ SMART Communications tests the LTE-Advanced network.
- On November 5th 2013, two major carriers in the United Kingdom (Vodafone and EE) announced they would be holding LTE - A trials in the London area.
- On November 15th 2013, Telefonica and Vodafone have announced that they are testing LTE-Advanced in the German cities of Munich and Dresden
- 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.
- Stefan Parkvall, Erik Dahlman, Anders Furuskär et al; Ericsson, Robert Syputa, Maravedis; ITU global standard for international mobile telecommunications ´IMT-Advanced´; LTE Advanced - Evolving LTE towards IMT-Advanced; Vehicular Technology Conference, 2008. VTC 2008-Fall. IEEE 68th 21-24 Sept. 2008 Page(s):1 - 5.
- Faster cell phone services planned
- "TeliaSonera launches world's first 4G mobile network". swedishwire. Retrieved 25 November 2013.
- "Requirements for further advancements for Evolved Universal Terrestrial Radio Access (E-UTRA) (LTE-Advanced)"
- Beyond 3G: “LTE Advanced” Workshop, Shenzhen, China
- 3GPP specification: Requirements for further advancements for E-UTRA (LTE Advanced)
- Agilent , Introducing LTE-Advanced, pg. 6 , March 8, 2011, accessed July 28, 2011.
- Nomor Research: White Paper on LTE Advanced
- 3GPP Technical Report: Feasibility study for Further Advancements for E-UTRA (LTE Advanced)
- Introduction to LTE-Advanced Rel.11
- 3GPP News & Events, Dec.12th, 2012 and Apr.8th, 2013 entries
- NTT DoCoMo Achieves World's First 5 Gbit/s Packet Transmission in 4G Field Experiment
- Agilent Technologies Introduces Industry's First LTE-Advanced Signal Generation, Analysis Solutions
- "Yota Networks has launched the world's first mobile communication technology LTE Advanced". YOTA. Retrieved 19 October 2012.
- "LTE-Advanced 4G network launches in South Korea". BBC News. 26 June 2013. Retrieved 18 July 2013.
- Chloe Albanesius (26 June 2013). "Samsung reveals LTE-Advanced version of Galaxy S4". PC Magazine. Retrieved 18 July 2013.
- Lance Whitney (18 July 2013). "South Korea launches its second LTE-Advanced networ.". CNET News. Retrieved 18 July 2013.
- J.M. Tuazon (21 August 2013). "200MBPS IN DAVAO - Smart tests LTE-Advanced system down south.". Interaksyon. Retrieved 21 August 2013.
- "Telefonica und Vodafone testen LTE-Advanced". heise online. 15 November 2013. Retrieved 15 November 2013.
- 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 improvements on LTE known as LTE-Advanced Rel.10
- Introducing LTE-Advanced - Application Note
- Introduction to LTE-Advanced Rel.11 - Summarization of improvements specified in LTE-Advanced Release 11.
- LTE Transmission Modes and Beamforming - this white paper discusses the basics of beamforming and explains the eight MIMO transmission modes for LTE Release 9 onwards.