5G : Handling of measurement gaps

3GPP specifications has outlined certain DO’s and Dont’s for the UE when it is in measurement gap period. The procedure outlined in the 3GPP specification deals with the handling of measurement gaps, which are periods during which the UE (User Equipment) is not actively communicating with the network but is instead performing measurements. Here’s a detailed explanation of the steps involved in handling measurement gaps:

MAC Entity Behavior:

  • During a measurement gap, the MAC (Medium Access Control) entity adjusts its behavior on the Serving Cell(s) in the corresponding frequency range of the configured measurement gap.
  • Several actions are taken to minimize interference and optimize resource usage during this period.

Transmission Restrictions:

    • Certain transmissions are halted during measurement gaps to prioritize measurement tasks.
    • The MAC entity refrains from transmitting:
      • HARQ (Hybrid Automatic Repeat Request) feedback, which is used for error correction in data transmissions.
      • Scheduling Requests (SR), which are requests sent by the UE to the network to request resources.
      • Channel State Information (CSI) reports, which provide feedback on the quality of the radio channel.
      • SRS (Sounding Reference Signal), which is used for channel estimation by the network.
    • The UE only transmits on the uplink Shared Channel (UL-SCH) for specific purposes, such as Msg3 or the MSGA payload as specified in the standard.

    PDCCH Monitoring:

      • If certain timers related to contention resolution or message reception are active (ra-ResponseWindow, ra-ContentionResolutionTimer, or msgB-ResponseWindow), the UE continues to monitor the Physical Downlink Control Channel (PDCCH) during the measurement gap.
      • This monitoring allows the UE to remain synchronized with the network and respond promptly to scheduling requests or contention resolution procedures if necessary.

      Reception Restrictions:

        • If no timers requiring PDCCH monitoring are active, the UE suspends PDCCH monitoring to conserve power and resources.
        • Additionally, the UE does not receive data on the Downlink Shared Channel (DL-SCH) during measurement gaps, as it is primarily focused on measurement tasks rather than data transmission.

        Overall, this procedure ensures efficient utilization of resources and maintains communication reliability during measurement gaps. By adjusting its transmission and reception behavior according to the configured measurement gap parameters, the UE can effectively perform measurements without disrupting network operations or sacrificing performance.

        Reference :

        TS 38.321 NR; Medium Access Control (MAC) protocol specification

        Further reading