Lecture Notes: LTE Network Architecture Overview

Importance of Network Architecture in LTE

• Essential for understanding LTE Advanced and LTE Advanced Pro features

Overview of LTE Network Architecture

• Composed of two main parts: E-UTRAN (Radio Access Network) and EPC (Evolved Packet Core)
• Bi-directional communication between the two
• Radio Access Network (RAN) interacts directly with User Equipment (UE)
  • Manages traffic, passes it to EPC for external application access

Detailed Breakdown of LTE Architecture

• E-UTRAN (Radio Access Network) and EPC (Evolved Packet Core)
  • Multiple eNodeBs in E-UTRAN
  • eNodeBs communicate via X2 interface (handles signaling, control plane messages, user plane data traffic)
  • UU interface: communication between eNodeB and UE
  • S1C interface: eNodeB to MME (Mobility Management Entity)
  • S1AP protocol: used on S1C interface
  • MME communicates with HSS over S6a (using Diameter protocol)
  • MME to Serving Gateway (S11 interface)
  • Serving Gateway to Packet Gateway via S5 interface
  • eNodeB to Serving Gateway (S1U interface)
  • Packet Gateway to external network (SGi interface)
  • Solid arrows: user plane interfaces, Broken arrows: control plane signaling (exception: X2 interface handles both)

Functions of eNodeB in E-UTRAN

• Radio Resource Management
  • Scheduler manages spectrum resources, handles synchronization, interference control
• MME Selection
  • From a pool of MMEs or a specific MME
• Routing User Plane Traffic
  • To/from Serving Gateway via solid arrows
• Encryption and Integrity Protection
  • Ensures data security (encryption, integrity protection)
• IP Header Compression
  • Increases network capacity, link budget

Communication Techniques in RAN

• Downlink: OFDMA (Orthogonal Frequency Division Multiple Access) Technique
  • Spectral efficiency, robust to multipath, supports MIMO, flexible time-frequency allocation
• Uplink: SC-FDMA (Single-Carrier FDMA) Technique
  • Addresses high Peak-to-Average Power Ratio in OFDM
  • Sequential transmission, better cell-edge performance

Multiple Access Techniques in Wireless Communications

• TDMA
  • Divides channels in time slots
• FDMA
  • Divides frequency into chunks allocated per user
• OFDMA
  • Allocates frequency chunks across different times
• CDMA
  • Uses coding (spread spectrum technique)
• OFDMA in LTE
  • Uses subcarriers (orthogonal), divides bandwidth, supports 1.4 to 20 MHz schemes
  • Transmission every 1 ms (Transmit Time Interval)
• Resource Block Concept
  • Minimum allocation for users: 1 resource block pair (12 subcarriers across 1 ms)

EPC (Evolved Packet Core) Architecture

• Components
  • MME: Handles NAS signaling, security, tracking area list management, gateway selection, roaming, authentication, bearer management
  • S1 Bearer: Between eNodeB and Serving Gateway
  • S5S8 Bearer: Between Serving Gateway and Packet Gateway

Concept of Bearers in LTE

• End-to-end service bearer (spans UTRAN, EPC to external)
• Types of Bearers
  • Default Bearer: Non-GBR (Guaranteed Bit Rate)
  • Dedicated Bearer: GBR or Non-GBR
• Quality of Service Class Indicators (QCI)
  • Defines attributes (packet delay, packet loss, priority) e.g., QCI1 for VoIP/VoLTE

Conclusion

• Architecture in LTE is crucial for advanced features (LTE Advanced/Pro)
• Next section will focus on LTE Advanced features