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LTE Technology Overview

Long-Term Evolution (LTE) is the project name of a new, high performance air interface for mobile communication systems. Developed by the Third Generation Partnership Project (3GPP), LTE is the evolution of the Universal Mobile Telecommunication System (UMTS) towards an all-IP broadband network. LTE's evolved radio access technology—the E-UTRA— provides a framework for increasing data rates and overall system capacity, reducing latency, and improving spectral efficiency and cell-edge performance. It is documented in the 3GPP Release 8 and Release 9 specifications. This LTE overview gives some of the highlights.

OFDMA-based: Unlike UMTS, which is based on wideband code division multiple access (W-CDMA) technology, LTE is based on orthogonal frequency-division multiple access (OFDMA). In the downlink, an OFDMA-based transmission scheme—together with multiple-access techniques—provides high data-rate capacity and high spectral efficiency. In this regard, LTE is similar in concept to Mobile WiMAX™, another emerging technology for wireless broadband access, although the systems operate with different frame structures, sub-carrier spacing and channel bandwidths.

A new, OFDMA-based scheme called single carrier frequency division multiple access (SC-FDMA) was developed for the LTE uplink. SC-FDMA enables a lower peak-to-average ratio (PAR) to conserve battery life in mobile devices.

Flexible modulation schemes: The downlink supports QPSK, 16QAM, and 64QAM data modulation formats, and the uplink supports BPSK, QPSK, 8PSK, and 16QAM.

MIMO: At present, LTE offers a 100-Mbps download rate and 50-Mbps upload rate for every 20 MHz of spectrum. Support is intended for even higher rates (up to a maximum of 326.4 Mbps in the downlink) using multiple antenna configurations. LTE supports single-user multiple input/multiple output (SU-MIMO) and multiple-user multiple input/multiple output (MU-MIMO) antenna configurations of up to 4 x 4 MIMO. These should enable up to 10 times as many users per cell as 3GPP's original W-CDMA technology. See Keysight's application note, LTE Operation and Measurement--Excerpts on MIMO Test.

Spectral efficiency: LTE also features a scalable bandwidth from 1.4 to 20 MHz in both the downlink and the uplink, with subcarrier spacing of 15 kHz and 7.5 kHz possible in the case of multimedia broadcast multicast service (MBMS). Targets for spectral efficiency over 3GPP Release 7 high-speed packet access (HSPA) are three to four times in the downlink and two to three times in the uplink. Sub 5-ms latency will be provided for small IP packets.

FDD and TDD modes: To support as many frequency band allocations as possible, both paired and unpaired spectrum operation is supported using frequency division duplex (FDD) and time division duplex (TDD) techniques, respectively. Paired spectrum operation is known as FD-LTE and unpaired spectrum as TD-LTE.

Co-existence with legacy systems: LTE is designed to support voice as well as data in the packet domain. However, as LTE evolves toward an all-IP network, it will co-exist with legacy systems including 3GPP HSPA, W-CDMA UMTS, and GSM/GPRS/EDGE. In conjunction with the 3GPP Evolved Packet Core (EPC) network, LTE will support inter-domain handovers between packet-switched and circuit-switched systems. Specifications for the EPC network are being developed in a concurrent project known as System Architecture Evolution (SAE).

For more LTE overview, download Keysight's free LTE application note, 3GPP Long Term Evolution: System Overview, Product Development, and Test Challenges.

LTE Overview: Development and Deployment of LTE Technology

 

Work on LTE began in 2004. The first completed Release 8 specification was published in March 2009, and the specification is now considered sufficiently stable for commercial development. LTE standards development continues with 3GPP Release 9, with completion of the specification by December 2009. Trials are underway, and initial deployment of LTE is expected in 2010 and 2011.

LTE is expected to fulfill the wireless industry's needs for a decade or more. However, to meet the International Telecommunication Union (ITU)'s IMT-Advanced requirements for a true 4G technology, 3GPP is developing LTE-Advanced, defined in Release 10 and beyond. In October 2009, LTE-Advanced was submitted to the ITU as an IMT-Advanced candidate.

LTE Technology Overview: Global Standard

 

Today LTE is well on its way to becoming the first single global standard for cellular communications. It is being adopted by both GSM and CDMA operators alike. As the first technology to successfully meet its requirements it was selected by the Next Generation Mobile Networks Alliance (NGNM). 

LTE has been endorsed by organizations such as

The LTE/SAE Trial Initiative (LSTI), a global collaboration of leading telecommunication vendors and operators, is focused on accelerating the availability of commercial and interoperable LTE networks and devices. In September 2009, the group announced the successful completion of its phase-one Proof of Concept tests for both FD-LTE and TD-LTE, clearing the way for additional trials including interoperability development testing (IODT), interoperability testing (IOT), and friendly customer trials. Visit http://www.lstiforum.org 

LTE Technology Overview: Testing LTE

 

Successful deployment of LTE depends on the compatibility and effective interworking of the system's different elements. Conformance testing ensures that these elements meet a minimum level of performance as defined in the 3GPP specifications. The LTE conformance tests cover base station, user equipment, and radio resource management performance. They are a major focus of vendors today who are developing LTE network and user equipment.

The complex and flexible LTE air interface supports many options for modulation format, frequency bands, resource allocations, and mobility. As a result, the number of RF configuration permutations that can be tested is enormous. In selecting RF configurations for the LTE conformance tests, 3GPP identified combinations of parameters representing the most difficult operating conditions, so when a product passes the tests, it can be assumed the device will perform satisfactorily in many other, less-challenging scenarios.

Although the lists of conformance tests may seem large, other kinds of tests are still needed. For example, closer investigation of performance margins is important since conformance testing gives only a pass/fail result with no indication of how close the product is to a particular limit. LTE conformance tests are designed primarily to ensure that the network's underlying transport mechanisms can carry end-user services, so higher level applications still need to be tested. Operator acceptance testing is yet another step in the process and includes more user-centric tests. Thus the conformance tests represent an essential step toward LTE deployment, but they are neither the beginning nor the end of the test process. An LTE overview on conformance tests is found in Keysight's LTE overview application note, 3GPP Long Term Evolution: System Overview, Product Development, and Test Challenges.

Need More than an LTE Overview? Further suggested reading:

 

LTE Overview: Keysight Test Solutions

 

As a world leader in test and measurement solutions, Keysight Technologies is at the forefront of LTE, offering design and test solutions for the entire lifecycle, from early RF and digital design through product conformance testing, network deployment, and service assurance. For an overview of LTE test solutions, visit our LTE Test Equipment website.