Question: In UL-TDOA (Uplink Time Difference of Arrival) positioning, what triggers the transmission of SRS (Sounding Reference Signal) signals from the UE for uplink positioning measurements?
Option 1: Direct request from TRPs (Transmission Reception Points) to the UE
Option 2: Periodic network scanning by the UE initiating SRS transmission
Option 3: Autonomous decision by the serving gNB (next-generation Node Base) without external trigger
Option 4: Indication from the LMF (Location Management Function) to the serving gNB, which then directs the UE
Explanation: In UL-TDOA positioning, the process of obtaining uplink measurements requires knowledge of the SRS signal characteristics. The LMF initiates this process by indicating to the serving gNB the need for uplink positioning, leading to the gNB directing the UE to transmit SRS signals with specified configurations, which are then communicated back to the LMF for forwarding to TRPs. This coordinated approach ensures that all parties have the necessary information for accurate positioning.