What is LTE?
Requirements for LTE
SAE Technology
E-UTRAN Architecture
Physical Interface
OFDMA
Physical Channel Structure
Transport Channel
Layer 2 Structure
Logical Channels
RRC Protocol
LTE eNodeB
What is the LTE eNB?
LTE eNB Functions
LTE eNB Architecture
LTE-Advanced Background
LTE Breaks Through to Real 4G
DL/UL Acceleration
DL/UL Acceleration Technologies
Carrier Aggegation
New MIMO Techniques
CoMP Techniques
Deployment Possibilities
LTE-A Pro
Centralized Radio Access Network
LTE (Long Term Evolution) is the project name given to development of a high performance air interface for cellular mobile communication systems. It is the last step toward the 4th generation (4G) of radio technologies designed to increase the capacity and speed of mobile telephone networks. While the former generation of mobile telecommunication networks are collectively known as 2G or 3G, LTE is marketed as 4G.
According to 3GPP, a set of advanced requirements was identified:
Reduced cost per bit
Increased service provisioning – more services at lower cost with better user experience
Flexibility of use of existing and new frequency bands
Simplified architecture, Open interfaces
Allow for reasonable terminal power consumption
Figure 1 : Roadmap to 4G
Although there are major changes between LTE and its 3G predecessors, it is nevertheless looked upon as an evolution of the UMTS / 3GPP 3G standards. LTE uses a different form of radio interface (OFDMA / SC-FDMA instead of CDMA), but there are many similarities with the earlier forms of 3G architecture and opportunities for re-use of some elements of 3G network architecture. LTE can be seen as providing an evolution of functionality, increased speeds and general improved performance compared to 3G.
LTE and 3G/3.5G Specification
(from NTT docomo Press Release)
3G WCDMA (R99)
3.5G HSPA
Frequency Common frequency assigned for 3G
Bandwidth 5MHz 1.4/3/5/10/20 MHz
Radio Access DS-CDMA DL: OFDMA
UL: SC-FDMA
Uplink Peak Rate 384kbps 5.7Mbps >50Mbps
Downlink Peak Rate 384kbps 14Mbps >100Mbps
Frequency Common frequency assigned for 3G Common frequency assigned for 3G Common frequency assigned for 3G
Radio Access DS-CDMA DS-CDMA DL: OFDMA
Radio Access DS-CDMA DS-CDMA UL: SC-FDMA
LTE has introduced a number of new technologies when compared to previous cellular systems. They enable LTE to operate more efficiently with respect to the use of spectrum, and also provide the much higher data rates that are now required.
OFDM (Orthogonal Frequency Division Multiplex)
OFDM technology has been incorporated into LTE because it enables high data bandwidths to be transmitted efficiently while still providing a high degree of resilience to reflections and interference.
MIMO (Multiple Input Multiple Output)
One of the main problems that previous telecommunications systems have encountered is that of multiple signals arising from the many reflections that are encountered in antenna deployments. By using MIMO, these additional signal paths can be used to advantage and are able to be used to increase the throughput.
SAE (System Architecture Evolution)
With the very high data rate and low latency requirements for 3G LTE, the system architecture must evolve to achieve the performance improvement benchmarks. One change is that a number of the functions previously handled by the core network have been transferred out to the periphery. Essentially this provides a much "flatter" form of network architecture. In this way latency times can be reduced and data can be routed more directly to its destination.