LTE - Long Term Evolution

Why LTE? The first question came into mind is why LTE? we are having 2G and 3G well established in market, then what is the requirement of LTE or so called 4G.

But before proceeding let me clear LTE is not considered as 4G but the 3.9G due to some limitation.

To answer the question, the subscribers and business users are discovered the power of wireless broadband through the advanced phones. Today internet are used for video streaming, live video, You Tube,  Maps, Social Sites and web search.
Because of so much to do on internet, consumers wants the high speed in data transfer on the go and the solution is LTE. The standards of LTE developed by 3GPP.

LTE Provides following features and application for users and business:

• Improve QoS by decreasing the latency time.
• provide the connectivity for non-traditional device like cars
• provide the communication, entertainments, personal assistance.
• Improving the services
• Reducing the transport network cost.
• All IP Network (AIPN).

2G/3G vs LTE:

- 2G and 3G supports voice traffic on CS (Circuit Switched) Network and Data service on packet netwok

-  LTE provides voice and data over IP (packet network); single channel End to End and all-IP. however current release of LTE (3GPP Release 8) does not support voice over LTE.

LTE Architecture:

Entity Summery:

MME (Mobile Management Entity): MME provides mobility and session control management.

SGW (Serving Gateway): Routes and forwards the user data packets.

PGW (PDN Gateway): Provides UE session connectivity to external packet data network (PDN).

PCRF : Supports service data flow detection, policy enforcement, and flow based charging.

eNodeB: Receive and sends radio signals to and from the antennas. Schedules uplink and downlink data      to/from the UE. Provides Ethernet links to the EPC elements and other eNodeB.

LTE eUTRAN architecture elements:

MIMO (Multiple-Input and Multiple-Output): Input output refers to the channels. It requires multiple antennas at transmitter and receivers. It increase throughput.

LTE Modulation Techniques:  

•  OFDMA (Orthogonal Frequency Division Multiple access): OFDMA on the downlink, Minimal interference. easily adapts to frequency and phase distortions. It provides higher throughput in same bandwidth by the overlapping frequencies. It requires more power at transmission.

• SC-FDMA (Single-Carrier Frequency Division Multiple Access): SC-FDMA on the uplink, low  sensitivity to carrier frequency offset. Chosen over OFDMA for uplink because OFDMA uses a lot of power. Lower throughput than OFDMA because no overlap and it require less power. It is used UL to convey UE battery.

MME Functionality: 

• Communicates with the HSS for the user authentication and subscriber profile downloads. 
• Communicates with the eNodeB and SGW for the session control and bearer setup.

MME Interfaces:

• S10: To other MMEs
• S1-MME: MME to eNodeB 
• S6a: MME to HSS
• S11: MME to HSS
• S13: MME to EIR
• X1_1 and X2: to IRI for Lawful interception

SGW Functionality:

• Serves as local mobility anchor for the UE - terminates the packet data network interface towards the eUTRAN.
• Support user-plan mobility - performs IP routing and forwarding functions and maintains data paths between the eNodeBs and the PGW.

SGW Interfaces:

• S5 from the PGW (User and Control traffic)
• S8 from visiting SGW to Home PGW 
• S11 to the MME (For Control Traffic)
• S1-U to the eNodeB (User Traffic)

PGW Functionality:

• Provide the UE with the IP address.
• Connect user to PDN.
• Facilitates flow-based charging (Provides records to external billing systems)
• Serves as the cross-technology mobility anchor (Support mobility between 3GPP/non-3GPP access to Non-3GPP/3GPP access.
• Per-User based packet filtering.

PGW interfaces:

• S5 from the SGW ( for the user and control traffic)
• S8 from the visiting SGW to Home PGW (Roaming, user and control traffic)
• SGi to the packet data network (User traffic).
• Gx to the PCRF (for the policy control)

PCRF Functionality:

• Policy management entity that provides dynamic control of QoS and charging policies for the service data flows (SDFs)
• Decide how the SDFs will be treated by the PGW
• On the UE attachments, the PCRF:

1. Receive the request for the policies for the default bearers.
2. Retrieve the user profiles from SPR and executes the rule-sets for the decision for the policy and charging.
3. Responds the PGW with the PCC rule.

PCRF Interfaces:

• Gx to the PCRF (policy contol)
• Sp to the SPR (For the subscriber repository).