LTE (Long Term Evolution) is the technology which is used in 4G wireless networks. It was standardized in 3GPP Release 8 in 2009. LTE is capable of delivering peak rates of up to 300 Mbit/s in the downlink direction and up to 75 Mbit/s in the uplink direction. Some of its other characteristics include low latency of up to 5 ms in the radio access network and support for fast-moving mobile devices.
LTE supports both FDD (frequency division duplexing) and TDD (time-division duplexing). FDD uses separate frequencies for the downlink and the uplink, while TDD uses the same frequencies for both directions, with changes through time.
LTE is the first wireless technology which supports a unified IP network for all services, as defined in the IMS (IP Multimedia Subsystem) architecture. It includes VoLTE (Voice over LTE) as a new way for delivering voice calls over an IP-based network, unlike previous generations of wireless networks, which used a separate circuit-switched core network for voice.
LTE-Advanced, which was standardized in 3GPP Release 10 in 2011, adds various capabilities to LTE. One of its main enhancements is Carrier Aggregation, in which the traffic from multiple wireless channels – commonly called component carriers – is aggregated, thus adding up the throughput of each of these carriers. LTE-Advanced is capable of delivering peak rates of up to 3 Gbit/s in the downlink and up to 1.5 Gbit/s in the uplink.
MIMO (Multi Input Multi Output) is another technique which is used to increase the overall throughput rate. It uses transmission of two or more different data streams on two or more different antennas, to be received by two or more antennas. One of the additional major enhancements in LTE-Advanced is the introduction of 8x8 MIMO in the downlink and 4x4 in the uplink.
The LTE and LTE-Advanced technologies were adopted warmly and quickly by mobile operators, and by the end of 2017 more than 550 operators worldwide had commercial LTE and LTE-Advanced deployments.
The term LTE-Advanced Pro, also known as 4.5G, refers to 3GPP Releases 13 and 14. It is a natural evolution of LTE, which incorporates a number of new technologies that are planned to be used in the 5G standard to progressively evolve existing networks into 5G.