How is the 6 ms length of measurement gap enough for identification of an UMTS cell?

Edited by Zahid Ghadialy

Last Updated: 11/10/2009

QUESTION: Let me ask for some clarification. I can see that the measurement gap in RRC_CONNECTED state of LTE is always 6 ms long and it is repeated at 40 ms or 80 ms intervals. The UE should be able to identify a new UMTS cell for which PSC is not provided. But, I thought, in Step 2 of Step 1/2/3 search, the UE needed to read the whole Secondary Synchronization Code of S-SCH from all 15 slots in 10 ms radio frame for code group identification. Can anyone help me understand how the gap length of 6 ms is enough?

ANSWER: Of course, in real network, you don't have any guarantee to decode in 6ms the PSCH/SSCH/ detect Scrambling codes/ CPICH of 3G cells in provided UARFCN. The idea is to use multiple gaps to for cell search ( save and restore the context at each IRAT gap). Also, In step 2, the UE after reading 3 or 4 SSC will be able to decode the SC Group and have the Frame Synchronization due to the SC group ID characteristics (sequence of 15 from 16 SSC)



SOURCE: Linkedin





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