LTE standards are in matured state now with release 8 frozen. While LTE Advanced is still under works. Often the LTE standard is seen as 4G standard which is not true. 3.9G is more acceptable for LTE. So why it is not 4G? Answer is quite simple - LTE does not fulfill all requirements of ITU 4G definition.

Brief History of LTE Advanced: The ITU has introduced the term IMT Advanced to identify mobile systems whose capabilities go beyond those of IMT 2000. The IMT Advanced systems shall provide best-in-class performance attributes such as peak and sustained data rates and corresponding spectral efficiencies, capacity, latency, overall network complexity and quality-of-service management. The new capabilities of these IMT-Advanced systems are envisaged to handle a wide range of supported data rates with target peak data rates of up to approximately 100 Mbit/s for high mobility and up to approximately 1 Gbit/s for low mobility.

LTE-Advanced Requirements

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 is now published.

General requirements for Advanced E-UTRA and Advanced E-UTRAN states that Advanced E-UTRA and Advanced E-UTRAN shall be an evolution of Release 8 E-UTRA and E-UTRAN. Further, Advanced E-UTRA and Advanced E-UTRAN shall meet or exceed IMT-Advanced requirements.

As per requirements Advanced E-UTRA should support significantly increased instantaneous peak data rates. At a minimum, Advanced E-UTRA should support the key feature of IMT-Advanced which is stated in the Circular Letter from the ITU-R as "enhanced peak data rates to support advanced services and applications (100 Mbit/s for high and 1 Gbit/s for low mobility were established as targets for research)". The system should target a downlink peak data rate of 1 Gbps and an uplink peak data rate of 500 Mbps.

The overall C-Plane/U-Plane latency shall be significantly decreased compared to EPS Rel-8.
Over all 36.913 specifies a number of more requirments in the areas of System performance, Deployment, E-UTRAN architecture and migration

Below are the requirements for LTE-Advanced which were part of the 3GPP RAN Chairmans’ presentation to the ITU-R WP 5D Third Workshop on IMT-Advanced.
General Requirements
LTE-Advanced is an evolution of LTE
LTE-Advanced shall meet or exceed IMT-Advanced requirements within the ITU-R time plan
Extended LTE-Advanced targets are adoptedSystem

System Performance Requirements
Peak data rate
 - 1 Gbpsdata rate will be achieved by 4-by-4 MIMO and transmission bandwidth wider than approximately 70 MHz
Peak spectrum efficiency
 - DL: Rel. 8 LTE satisfies IMT-Advanced requirement
 - UL: Need to double from Release 8 to satisfy IMT-Advanced requirement
Capacity and cell-edge user throughput
 - Target for LTE-Advanced was set considering gain of 1.4 to 1.6 from Release 8 LTE performance

Other Important Requirements
Spectrum flexibility
 - Actual available spectra are different according to each region or country
 - In 3GPP, various deployment scenarios for spectrum allocation are being taken into consideration in feasibility study
 - Support for flexible deployment scenarios including downlink/uplink asymmetric bandwidth allocation for FDD and non‐contiguous spectrum allocationTotal

LTE-Advanced will be deployed as an evolution of LTE Release 8 and on new bands.
LTE-Advanced shall be backwards compatible with LTE Release 8 in the sense that
 - a LTE Release 8 terminal can work in an LTE-Advanced NW,
 - an LTE-Advanced terminal can work in an LTE Release 8 NW
Increased deployment of indoor eNBand HNB in LTE-Advanced.