LTE - 3G LTE - 3GPP LTE - UMTS LTE (Long Term Evolution)

LTE, 3GPP LTE or 3G LTE (Long Term Evolution) is the new generation radio interface of 3GPP. It is the follow up and evolution of the 3GPP air interface UMTS (evolved UTRA) and its associated radio access network (evolved UTRAN). LTE offers even higher peak data rates with a reduced latency. LTE will be a completely packet-optimized radio-access technology. 3GPP LTE improves spectral efficiency, allowing for a large increase in system capacity and reduced cost per gigabyte. LTE is able to offer more services with better user experience. Initial deployment of LTE took place in 2009.

The technical objectives for LTE include:

• Significantly increased peak data rate
  instantaneous data rate of 100 Mbit/s on the downlink and 50 Mbit/s on the uplink in a 20 MHz channel;
• Improved user throughput
  the user throughput should be improved by a factor of 3 and 2 for the downlink and uplink respectively;
• Improved data rate at cell edge
  data rate at cell edge should be improved by a factor of 2 to make higher data rates available with wide-area coverage without the need for additional cell sites;
• Improved spectrum efficiency
  
• Scalable bandwidth
  1.25, 1.6 (TDD only), 2.5, 5, 10, 15 or 20 MHz channels, dependent on the data rate needed by the user;
• Optimised for low mobile speed but also supporting high mobile speed
  
• Compatibility with earlier releases and with other systems
  Adding mobility towards RLAN and other non 3GPP air interfaces.

LTE uses Orthogonal Frequency Division Multiplexing (OFDM) on the downlink to cope with multipath and to allow scalable bandwidths. OFDM uses a large number of individual sub-carriers with a spacing of 15 kHz. OFDM parameters can be adjusted in such a way that even very large cells with a radius exceeding 120 km can be used.

The uplink uses only a single carrier combined with FDMA (SC-FDMA). FDMA is chosen to allow for power-efficient transmission of the user terminal. The bandwidth can be varied to handle the data rate needed by the user. Users are separated by assigning the a unique time interval on an assigned frequency. The users are separated primarily by assigning them a unique time-interval. If the terminal has a limited transmission power or not enough data to transmit also frequency separation is used.

3G LTE can utilize existing 2G and 3G spectra as well as new spectra.