In this tutorial, we will discuss on the LTE Architecture Overview.
What is LTE?
- LTE stands for Long Term Evolution
- Next Generation mobile broadband technology-By 3GPP
- Promises data transfer rates of 100Mbps
- Based on UMTS 3G technology
- Optimized for All-IP traffic
Motivation for LTE ?
- LTE can be used to get the higher data rate and and spectral efficiency.
- Need for Packet Switched optimized system
- Need for high quality of services
- Need for ALL IP low cost infrastructure (Simple architecture/reduce number of NEs)
LTE characteristics
Performance:
- LTE uses 100 Mbps (DL) with OFDMA and 50 Mbps (UL) with SC-FDMA.
- C-plane Latency < 100ms and U-plane < 5ms
- Higher Bandwidth
Efficiency:
- Uses MIMO multiple antenna technology
- SC-FDMA: Reduces Inter cell Interference
- 200 users per cell in active state
Compatibility:
- Can be in parallel with existing RAT
- Support of VoIP
Flexibility:
- New and existing bands
- Scalable channel bandwidths of 1,4, 3, 5, 10, 15 and 20
- Simpler E-UTRAN architecture. RNC and CS domain are not used
- Duplex Flexibility – FDD and TDD
LTE Architecture
- The E-UTRAN consists of eNBs, providing the E-UTRA U-plane (PDCP/RLC/MAC/PHY) and C-plane (RRC) protocol terminations towards the UE.
- Each eNBs are interconnected with each other through X2 interface.
- Each eNBs are connected with EPC core network through S1 interface.
S1-MME with MME
S1-U with SGW
Functionalities:
EnodeB : (E-UTRAN Node B)
- Scheduling and dynamic allocation of resources to UE in both uplink and downlink direction.
- Controlling mobility of UE in connected mode
- Triggers state transition from IDLE to connected mode and vice versa
- Admission control and congestion control
- Buffering of the data during handover
MME: (Mobility Management Entity)
- Handles mobility management in idle mode.
- Maintains UE context during RRC idle state.
- Responsible for NAS signalling and NAS signalling security
- Does bearer management for the UE.
- Tracking Area list management
SGW: (Serving Gateway)
- Acts as mobility anchor for the data bearers.
- Buffers the downlink data when UE is in IDLE mode
- Packet routing and forwarding.
- Synonymous to SGSN of pre release 8 networks
PGW: (PDN Gateway)
- Allocation of IP address to the mobile
- Filters downlink user IP packets into different QoS based bearers.
- Contacts PCRF to determine the QoS for bearers
- Packet filtering, charging and Policy Enforcement features.
PCRF (Policy and Charging Rules Function)
- Takes charging enforcement decisions.
Now we have understood the LTE Architecture Overview. Let’s discuss LTE EPC Overview in next tutorial.