Long Term Evolution (Advanced) - LTE(-A)
Introduction

The next evolution step of UMTS mobile networks is known as Long Term Evolution (LTE). The LTE is defined by 3GPP releases 8 and 9. Contrary to UMTS, LTE uses OFDMA and SC-FDMA (Single Carrier OFDMA) access for downlink and uplink respectively at physical layer instead of WCDMA used in UMTS. Therefore, the transmission features are quite different comparing to UMTS. Nevertheless, LTE is still considered as a part of 3G systems as it does not fulfil requirements defined by ITU for 4G networks. The first standard denoted as 4G is LTE-A (Long Term Evolution - Advanced) according to 3GPP Release 10, standardized in June 2011. It is evolution of former LTE Release 8 or Release 9 and it is based on the same principles as both LTE releases, but it is aligned with the set of requirements known as IMT-Advanced defined by ITU. LTE-A adds new features and capabilities on top of LTE. Comparing to LTE, LTE-A introduces carrier aggregation, inter-cell interference coordination, or enhances multiple antennas transmission (MIMO). All these improvements enable LTE-A to meet IMT-Advanced requirements for 4G mobile networks and offer peak data rates up to 1 Gbps. Besides LTE-A, also WiMAX (Worldwide Interoperability for Microwave Access) according to IEEE 802.16m, standardized by IEEE (The Institute of Electrical and Electronics Engineers) was approved as 4G technology for mobile networks. Nevertheless, WiMAX is not expected to be heavily deployed in Europe. Therefore, we focus only on LTE/LTE-A in the following chapters. First, let us give a short overview of the LTE/LTE-A evolution in terms of 3GPP releases with focus on major innovations with respect to the former releases.

## Release 8

This release adopted OFDMA modulation for user's access. In addition, the cell can utilize wider channel bandwidth, mostly only in downlink, by means of DC achieving downlink capacity up to 84 Mbps (64 QAM together with DC).

## Release 9

This release introduces femtocells, denoted as Home eNodeB (HeNB), to the networks architecture. It further enables support of MBMS (Multimedia Broadcast Multicast Services) and enhances LBS (Location Based Services).

## Release 10

This release is the first 3GPP 4G compliant standard. New techniques such as carrier aggregation, enhanced downlink MIMO, uplink MIMO, or support of relays are introduced. To enable dense deployment of femtocells, advanced techniques for interference coordination are defined.

## Release 11

This release is still under development. Contrary to the release 10, the new version should further enhance carrier aggregation, introduce Cooperative MultiPoint communication (CoMP), increase spectral efficiency, and ensure higher energy efficiency.