2019年11月19日 星期二

LTE procedures overview

Source: https://www.sharetechnote.com/ > LTE

01. UE is Off
02. Power On UE
04. Timing Sync
     Time and Frame Synchronization : In this process, PSS and SSS will be decoded as well.
             PCI (Physical Cell ID) is derived (a.k.a PCI detection)
05. Cell Search : Normally a UE would find multiple cells in this process 
07. MIB decoding
      UE can figure out System Bandwidth and Transmission Mode in this process. 
      (As you see in Downlink Framestructure, MIB/PBCH is located at the 6 RBs around the 
      center frequency. So the success of MIB decoding does not guarantee that signal quality
      across the whole band is good)
      Detect CSR (Cell Specific Reference Signal) and perform Channel Estimation and 
      Equalization. In this process, UE will detect/measure reference signal across the whole
      system bandwidth. So RSRP/RSRQ measured at this step can be a good indicator for 
      overall signal quality.
      Decode PDCCH and extract DCI information for SIB. PDCCH is spread across the whole 
      bandwidth, so the signal quality across the whole bandwidth should be good enough 
      for this step.
08. SIB deconding (SIB1 should be decoded first and then SIB2 and then remaining SIBs)
      Cell Selection: UE tries camp on to HPLM cell with the highest priority.
10. Registration/Authentication/Attach
11. Default EPS Bearer Setup
      11.A Now UE is in IDLE Mode
      11.B (If the current cell become weak or UE moves to another cell regisn) Cell Reselection
12. (When Paging message comes or User make a call) RACH Process
13. Setup Dedicated EPS Bearer
      13.A Receive data
      13.B Transmit data
              (Full duplex is possible for FDD bands)
      13.C (If UE power is percieved too weak by the network)
              Network send TPC command to increase UE Tx Power
             (If UE power is percieved too strong by the network)
              Network send TPC command to decrease UE Tx Power
14. (If UE moves to another cell region) Network and UE perform Handover procedure
15. User stop call and UE gets into IDLE mode

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