March 4, 2016 | by Wayne Smith

Long Term Evolution

This article examines the 4th Generation (4G) technology known as LTE. It identifies the author of the 4G specifications and its motivation and briefly describes the system’s architecture, components and specifications.

Who Developed the LTE Specifications?

LTE requirements were developed by the 3rd Generation Partnership Project (3GPP) and originally released in 2008. The3GPP is a collaboration of telecommunications associations with the objective of advancing the evolution of 3rd Generation systems. Note there have been several updates and releases since 2008. The 3GPP was motivated by a need to achieve continuity with 3G systems, higher data rates, better quality of service, an optimized Internet Protocol (IP) based packet-switched system, simplified architecture, and to avoid the fragmentation of frequency band operations and technologies.

What is LTE?

LTE, also called the Evolved Universal Terrestrial Access Network (E-UTRAN) is the access part of the Evolved Packet System (EPS). For reference, the other part of the EPS is the Evolved Packet Core (EPC). LTE is essentially the long term evolutionary path of the Universal Mobile Telecommunications System (UMTS). It is a significant development that replaces the old 3G GSM/UMTS and CDMA2000 hybrid circuit-voice and data networks with an IP based data-only network. It is fair to say that LTE is a revolutionary step forward for wireless broadband networks and high-speed mobile devices.

EPS Components

For convenience, we will divide the EPS into three components. The first is access or the E-UTRAN, the second is the EPC and finally external IP networks.

E-UTRAN

The basic access requirements of LTE are high spectral efficiency, high peak data rates, low latencies and flexible use of frequencies and bandwidths. The access network consists of a flat architecture with distributed intelligence among a network of eNodeB base stations. The distribution of intelligence is critical in reducing connection and hand-over times. The access technology is based on Orthogonal Frequency Division Multiple Access (OFDMA). OFDMA supports higher modulation, bandwidths up to 20 MHz, downlink spatial multiplexing up to 4X4 (4 transmitting antennas and 4 receiving antennas). OFDMA is a multicarrier technology that subdivides bandwidth into many sub-carrier channels, each sharing multiple users. Channel bandwidths are flexible and can range between 1.4 MHz and 20 MHz. OFDMA can operate on frequency bands between 700 MHz and 2.7 GHz. It supports both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) although FDD is the preferred choice for most networks. The access system also supports Multimedia Broadcast Multicast Service (MBMS) and Home eNodeB (HeNodeB). MBMS can broadcast information to all users like streaming TV. HeNodeB will support very small cells that are typically in-building services owned by private parties and connected to the EPC. As for performance, this access system has high peak transfer rates of 300 Mbit/s for downlinks and 75 Mbit/s for the uplink and it can handle up to 200 simultaneous clients for each 5 MHz of bandwidth.

EPC

The EPC is also a flat architecture that separates the control plane and the user plane. This separation makes the network highly scalable. The control plane is composed of the Home Subscriber Server (HSS) and the Mobility Management Entity (MME). The HSS is the database that manages user information and supports MME with user authentication, session set-up, handovers and other access information. MME handles signaling, mobility management and security.

The user plane consists of a Serving Gateway (SGW) and the Packet Data Network Gateway (PDN-GW) which handles user data. The combination of the SGW and PDN-GW transport IP data between user equipment and external networks. The SGW acts as a router between the radio network (eNodeB) and the PDN-GW and is connected to other network elements like the MME. The PDN-GW is the connection to external IP networks.

External IP Networks

The EPC supports multiple access technologies other than E-UTRAN. These technologies include GSM/GPRS, WCDMA, HSPA, WiMAX, CDMA2000 and other fixed networks. In addition, the system supports several self organizing network (SON) and Heterogeneous Network (Het-Net) functions as well as the IP Multimedia System (IMS).

When comparing LTE to the original ITU-R specifications, it clearly meets all of the 4G requirements except the peak data rate criterion. You may want to compare the LTE specifications against the 4G requirements as defined by the International Telecommunications Union- Radio (ITU-R). You can find these at the bottom of a previous article entitled, “The Wireless Generations – Part I.”