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Mobility & RAN

5G & LTE Idle Mode Reselection Calculator | 3GPP Mobility Analysis

Verify RAN mobility parameters and R-criteria logic. Convert IE values to dBm thresholds for TS 38.304 (5G NR) and TS 36.304 (LTE) compliant network planning.

SIB Configuration

Minimum RX Level (QrxLevMin IE)-128 dBm

Intra-Frequency Search (S_IntraSearch IE)-66 dBm Trigger

Reselection Hysteresis (Qhyst dB)

Frequency Offset (Qoffset dB)

Reselection Timer (Treselection s)

Measurements

Serving Cell RSRP (dBm)

Neighbor Cell RSRP (dBm)

Reselection Result

Pass

Measurements ActiveReselection Triggered

Neighbor Rank (-95 dBm) > Serving Rank (-101 dBm). Reselection PASS.

Treselection Counter

Pro Engineering Insights: Cell Reselection Strategy

Ping-Pong Mitigation

In high-density deployments, set Qhyst between 2-4dB and Treselection to at least 1s. This ensures UEs don't oscillate between cells, preserving battery life and reducing signaling overhead on the core network.

"A high S_IntraSearch value (e.g., 31) allows for maximum neighbor discovery but may lead to higher UE power consumption due to constant background measurements."

Priority Tiering (5G vs LTE)

NR Dominance
Set 5G NR bands with higher cellReselectionPriority (e.g., 7) than LTE (e.g., 5) to offload traffic quickly.
Coverage Stability
Ensure QrxLevMin is set realistically based on the edge-of-cell RSRP to prevent UEs from camping on weak signals.
Threshold Tuning
Use ThreshXHigh to control the exact point a UE jumps to a higher capacity layer.

3GPP Technical Specifications Archive

TS 38.304 (5G NR)

Defines User Equipment (UE) procedures in idle mode and RRC Inactive state, including the 5G NR S-Criteria and R-Criteria for cell selection and reselection.

TS 36.304 (LTE)

The definitive standard for LTE idle mode procedures. Covers intra-frequency, inter-frequency, and inter-RAT reselection logic.

Reselection Engineering FAQ

Q: What is Qhyst in LTE and 5G NR?

A: Qhyst (Hysteresis) is a parameter used in the R-criteria for cell reselection. It adds a buffer to the serving cell's signal strength to prevent rapid and unnecessary switching (ping-ponging) between cells of similar quality.

Q: How does Treselection work?

A: Treselection is a timer that ensures the reselection criteria are met for a specific duration (e.g., 1s or 2s) before a UE triggers a cell change. This filters out transient signal fluctuations and ensures connection stability.

Q: What are S_IntraSearch and S_NonIntraSearch?

A: S_IntraSearch triggers measurements of same-frequency neighbors when the serving cell drops below a threshold. S_NonIntraSearch does the same for different-frequency or inter-RAT neighbors to prioritize discovery of higher priority bands.

Q: Which 3GPP specifications define idle mode reselection?

A: 5G NR reselection is defined in 3GPP TS 38.304, while LTE reselection is defined in TS 36.304. Both specifications detail the S-criteria and R-criteria logic.

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