telecom • networking • design

an EventHelix.com blog


Leave a comment

LTE Random Access Procedure and Contention Resolution

LTE random access procedure is used by the UEs to initiate a data transfer. The UEs also obtain uplink timing information from the initial handshake.

This sequence diagram describes the tale of three UEs (UE-A, UE-B and UE-C) that are powered on at the same time:

  1. UEs synchronize with the downlink channel by decoding the PSS and SSS signal. The UEs are synchronized to the downlink frames after completing this procedure.
  2. The three UEs initiate the random access procedure at exactly the same time. Two of them (UE-A and UE-B) happen to pick the same preamble. This results in a resulting in a collision. UE-C picks a distinct preamble so it succeeds in the random access procedure.
  3. Contention between UE-A and UE-B is resolved in UE-A’S favor. UE-A proceeds with the RRC connection.
  4. UE-C times out and retries the random access procedure.

LTE random access procedure


Leave a comment

LTE Video Presentations

OFDM Time Frequency Multiplexing

Rohde & Schwarz‘s presentations provide an excellent introduction to LTE. The presentations are accompanied with an audio narration. The topics covered are covered:

  1. LTE Introduction
    • Motivations for LTE
    • LTE market and background
    • Requirements
    • Evolution path to LTE
  2. LTE Parameters and Downlink Modulation
    • LTE parameters and frequency bands
    • What is OFDMA?
    • OFDMA multiple access and downlink frame structure
    • OFDMA transmit and receive chains
  3. OFDMA and Downlink Frame Structure Details
    • Downlink OFDMA time-frequency multiplexing
    • LTE Spectrum Flexibility and Bandwidth
    • FDD downlink frame structure detailed
    • TDD frame structure
  4. SC-FDMA and LTE Uplink
    • Introduction to SC-FDMA and uplink frame structure
      • Marriage of single carrier transmission and FDMA
    • Uplink SC-FDMA tranmsit and receive chains
    • Peak to Average Power Ratio (PAPR) comparison with SC-FDMA and OFDMA
  5. Network and Protocol Architecture
    • LTE/SAE network architecture
    • EPC -Evolved Packet Core
    • Base Station control plane and user plane protocol stacks
    • EPC protocol stacks
  6. Channel Mapping and UE Categories
    • Logical and transport channel mapping in downlink and uplink
    • LTE UE Categories
  7. Initial Cell Search and Cell Selection
    • Downlink physical channels and signals
    • Cell Search and Selection in LTE
      • Primary synchronization signal
      • Secondary synchronization signal
      • Reference signals
  8. System Information
    • Downlink reference signal details
    • Master Information Block on PBCH
    • System Information on DL-SCH
  9. Random Access Procedures and EPS Bearer Setup
    • Random access preamble transmission to eNodeB
    • Random access response from eNodeB
    • Resource allocation and contention resolution
    • Signaling on PDCCH
    • Hybrid ARQ
    • RRC Connection Setup and EPS Bearer Setup
  10. Uplink Channels and Signals
    • Uplink physical channels and signals
    • PU-SCH: Physical Uplink Shared Channel
    • Uplink assignment signaling on PDCCH
    • Uplink frequency hopping
    • PUCCH
  11. LTE Mobility and MIMO Introduction
    • Intra MME Handover over the X2 interface
    • RRC States
    • MIMO Basics
      • Transmit diversity
      • Spatial multiplexing
      • Beamforming
  12. Downlink and Uplink MIMO in LTE
    • Downlink MIMO modes
      • Transmit diversity
      • Spatial multiplexing
      • Cyclic delay diversity
      • Beam forming
    • Spatial multiplexing downlink transmitter chain
      • Code book based precoding
    • Uplink MIMO
      • Uplink transmit antenna selection
      • Multi-user MIMO
  13. eNodeB and UE Performance Requirements
    • eNodeB modulation quality measurements
    • eNodeB performance requirements
    • UE performance requirements
  14. UE Certification and Field Trials
    • LTE terminal testing stages
    • LTE terminal certification
    • LTE field trial scenarios