LTE stands for Long Term Evolution and it was started as a project in 2004 by telecommunication body known as the Third Generation Partnership Project (3GPP). LTE uses both Time Division Duplex (TDD) and Frequency Division Duplex (FDD) mode. All interfaces between network nodes in LTE are now IP based, including the backhaul connection to the radio base stations. LTE provides downlink peak rates of at least 150Mbit/s and 50 Mbit/s in the uplink.

 

Advantages of LTE

  • High Bandwidth: Compared to 3G LTE has higher bandwidth.

  • High Throughput: High data rates can be achieved in both downlink as well as uplink.

  • FDD and TDD in same platform: Frequency Division Duplex (FDD) and Time Division Duplex (FDD) can be used on same platform.

  • Seamless Connection: LTE will also support seamless connection to existing networks such as GSM, CDMA and WCDMA.

  • Low latency: Time required to connect to the network is in range of a few hundred milliseconds and power saving states can now be entered and exited very quickly.

  • Security and QOS: LTE provides higher security and Quality of Service when compared to 2G/3G

 

LTE Architecture

Below is a brief description of each of the components from LTE architecture,

 

LTE Mobile communicates with just one base station and one cell at a time and there are following two main functions supported by eNodeB(eNB):

  • The eNodeB sends and receives radio transmissions to all the mobiles using the analogue and digital signal processing functions of the LTE air interface.

  • The eNodeB controls the low-level operation of all its mobiles, by sending them signalling messages such as handover commands.

 

The E-UTRAN handles the radio communications between the mobile and the evolved packet core and just has one component, the evolved base stations, called eNodeB. Each eNB is a base station that controls the mobiles in one or more cells. The base station that is communicating with a mobile is known as its serving eNB.

Each eNodeB connects with the EPC by means of the S1 interface and it can also be connected to nearby base stations (eNodeB) by the X2 interface, which is mainly used for signalling and packet forwarding during handover.

The LTE core network is called as Evolved Packet Core (EPC).

  • The Home Subscriber Server (HSS) component is a central database that contains information about all the network operator's subscribers. It also holds information about the PDNs to which the user can connect. This could be in the form of an access point name (APN) or a PDN address.

  • The Packet Data Network (PDN) Gateway (P-GW) communicates with the outside world using SGi interface. The PDN Gateway is responsible for IP address allocation for the UE, as well as QoS enforcement and PDN connectivity. Each packet data network is identified by an access point name (APN). The PDN gateway has the same role as the GPRS support node (GGSN) and the serving GPRS support node (SGSN) with UMTS and GSM.

  • The Serving Gateway (S-GW) acts as a router, and forwards data IP packets between the base station and the PDN gateway. It also retains the information about the bearers when the UE is in the idle state.

  • The Mobility Management Entity (MME) is the control node that processes the signaling between the UE and the CN. It also controls the high-level operation of the mobile by means of signalling messages and Home Subscriber Server (HSS).

  • The Policy Control and Charging Rules Function (PCRF) is a component is responsible for policy control decision-making, as well as for controlling the flow-based charging functionalities in the Policy Control Enforcement Function (PCEF), which resides in the P-GW.

 

The interface between the serving and PDN gateways is known as S5/S8. This has two slightly different implementations, namely S5 if the two devices are in the same network, and S8 if they are in different networks.