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PDCCH Order – Network Initiated RACH in New 5G

Introduction

In 5G NR, PDCCH order is a mechanism using which gNB can force the UE to trigger the RACH procedure. There are  number of reason why UE can triggered the RACH and PDCCH Order is one of them. gNB take PDCCH Order decision when it detect the UE is out-of-sync in Downlink and Downlink data is available for the UE.

In out-of-sync scenario, the gNB triggers a PDCCH order by sending a DCI Format 1_0 on the SSB beam index UE is camped along with a PRACH preamble and RACH occasion. If the gNB find that there is DL Data to be sent to UE in its MAC Buffer and there is a UL synchronization issue due to the expiry of the Time Alignment timer at UE, then the gNB triggers a PDCCH order in order to re-synchronize with the UE.

Telco sought Key Pointers

PDDCH Order Call Flow Sequence

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