MUSIM Gaps in 5G NR
1. Introduction to MUSIM Gaps
Multi-User Subscriber Identity Module (MUSIM) gaps are specialized gap patterns introduced in 3GPP Release 17. If a User Equipment (UE) requires gap patterns for MUSIM purposes—such as cell identification, measurement, paging monitoring, SIB acquisition, or on-demand System Information (SI) requests of a target cell in a target network—the network may provide one or more per-UE MUSIM gap patterns via the MUSIM-GapConfig Information Element (IE).
Key Configuration Constraints
- Pattern Limit: The UE can be configured with a maximum of three periodic MUSIM gap patterns and/or one aperiodic MUSIM gap pattern.
- Scope: The UE is not required to perform MUSIM-related activities (e.g., paging monitoring) outside of the configured MUSIM gaps.
- Timing: The UE determines MUSIM gap timing based on the gap offset provided by the serving cell via higher-layer signaling.
2. Supported MUSIM Gap Configurations
The following table defines the supported MUSIM Gap patterns as specified in 3GPP documentation.
| Pattern ID | Gap Length (MGL, ms) | Repetition Period (MGRP, ms) |
|---|---|---|
| 0 | 6 | 40 |
| 1 | 6 | 80 |
| 2 | 3 | 40 |
| 3 | 3 | 80 |
| 4 | 6 | 20 |
| 5 | 6 | 160 |
| 6 | 4 | 20 |
| 7 | 4 | 40 |
| 8 | 4 | 80 |
| 9 | 4 | 160 |
| 10 | 3 | 20 |
| 11 | 3 | 160 |
| 12 | 10 | 80 |
| 13 | 20 | 160 |
| 14 | 6 | 320 |
| 15 | 6 | 640 |
| 16 | 6 | 1280 |
| 17 | 6 | 2560 |
| 18 | 10 | 320 |
| 19 | 10 | 640 |
| 20 | 10 | 1280 |
| 21 | 10 | 2560 |
| 22 | 20 | 320 |
| 23 | 20 | 640 |
| 24 | 20 | 1280 |
| 25 | 20 | 2560 |
| 26 | 20 | 5120 |
| 27 | 10 | N/A (Aperiodic) |
| 28 | 20 | N/A (Aperiodic) |
[!NOTE] Patterns #27 and #28 are aperiodic gap patterns and do not have a defined Repetition Period (MGRP).
3. Applicability and Deployment Scenarios
MUSIM gaps are primarily used in NR Standalone (SA) operation, including single carrier and Carrier Aggregation (CA) configurations.
| Configuration | Serving Cell | Purpose | Applicable IDs |
|---|---|---|---|
| Per-UE MUSIM Gap | FR1, FR2, or FR1+FR2 | Cell ID, Paging, SIB, On-demand SI | 0-28 |
4. Prioritization and Collision Handling
When multiple gaps are configured, the UE must resolve potential timing collisions based on a strict priority framework.
Priority Rules
- Aperiodic Gaps: An aperiodic MUSIM gap is unconditionally kept if it collides with any other gap occasions.
- Periodic Gaps: Collisions between periodic MUSIM gaps are resolved based on assigned priorities. The gap with the higher priority is maintained, while the lower-priority gap is dropped.
- Distance Threshold: Two gap occasions are considered to be in collision if they overlap or if the distance between them is equal to or smaller than 4 ms.
Collisions with Standard Measurement Gaps
If a MUSIM gap collides with a standard measurement gap (configured via GapConfig):
- Priority-Based: If priorities are assigned, the higher priority gap is kept.
- MGRP-Based: If no priorities are assigned, the gap with the longest repetition period (MGRP) is kept. In case of equal MGRP, the behavior is implementation-dependent.
5. Requirement for Non-Interruption
A critical aspect of MUSIM gaps is the interruption requirement. A slot is considered interrupted by a MUSIM gap if it overlaps with any occasion of a configured (and not dropped) MUSIM gap. The UE is not required to conduct reception or transmission from or to the network during these active gap windows.
Further Reading
WirelessBrew Team
Technical expert at WirelessBrew, specializing in 5G NR, LTE, and wireless system optimization. Committed to providing accurate, 3GPP-compliant engineering tools.
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