LTE: Background and Challenges

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The Long Term Evolution (LTE) technology, providing higher data rate to meet subscriber requirements, is the best option in the mobile broadband era. In the LTE era, how to inherit and improve traditional voice services and short message service (SMS) becomes carriers top concern.

Challenges

The third generation mobile telecommunication technologies, and the increasing popularity of smartphones have greatly driven user demand for mobile broadband services. Explosive growth of data traffic and the challenge of increasing network capacity force mobile carriers to upgrade their networks and increase the network transmission rate. The LTE technology is the best option for those carriers.

In the LTE era, the time has come for mobile carriers to move to voice over LTE (VoLTE). Globally, voice is still the major revenue source for the telecommunications industry, and will probably still be when LTE goes mainstream. However, basic voice may not be enough to remain relevant in an LTE environment, because subscriber communication is shifting from plain voice to rich voice. This document describes a solution with which carriers can provide voice and short message service (SMS) on an LTE network. This enhancement helps carriers move to multimedia voice services and improve their competitiveness against over-the-top (OTT) carriers.

LTE Overview

The LTE technology is mandatory for evolution from 3G to 4G and is the final version of current 3G mobile telecommunication technology before 4G is applied. The LTE technology is also the most advanced one evolved from the GSM. Figure 1 shows the LTE evolution.

Figure 1 LTE Evolution

Simplified LTE networks provide high-speed mobile packet data services. The optimization is as follows:

LTE base stations (eNodeBs) are connected to the evolved packet core (EPC) core network. The function of an independent base station controller (BSC) or radio network controller (RNC) is integrated in the eNodeB.
Functions of the packet switched (PS) domain are adjusted as follows:
- The signaling plane and forwarding plane of the serving GPRS support node (SGSN) are separated. The mobility management entity (MME) implements signaling plane processing of the SGSN, and the serving gateway (S-GW) implements forwarding plane processing of the SGSN.
- The PDN gateway (P-GW) provides the function of the gateway GPRS support node (GGSN).
- The EPC tolerates networks not complying with 3GPP, such as CDMA2000 high rate packet data (HRPD). Therefore, multiple radio access networks can connect to the EPC.

Key characteristics of LTE networks are as follows:

High data rate: The peak rate can reach 100 Mbit/s in the downlink and 50 Mbit/s in the uplink.
High spectral efficiency: The spectral efficiency is 5 (bit/s)/Hz in the downlink.
Packet transmission: IP-based LTE networks have the PS domain but not the CS domain. The PS domain cooperates with the IMS network to provide voice services.
QoS guarantee: LTE system design and QoS mechanism guarantee quality of real-time services, such as VoIP.
Flexible deployment: LTE networks support bandwidth ranging from 1.25 MHz to 20 MHz, ensuring flexible deployment.
Shorter delay: Subframe lengths of 0.5 ms and 0.675 ms ensure that downward compatibility is available and network delay is reduced.
Higher cell-edge rate: Cell-edge rates increase when eNodeB location remains unchanged.
Multi-access: LTE networks can interwork with networks that comply with or do not comply with 3GPP specifications. Subscribers can roam and switch among these networks.

Figure 2 shows LTE network development stages, including hot spot coverage, consecutive coverage, and full coverage. Before full coverage of LTE network is implemented, the VoLTE solution implements the roaming, handover, and service continuity between 2G/3G and LTE networks for LTE subscribers.

Figure 2 LTE network development stages

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