In LTE networks, cell selection parameters play a crucial role in determining whether a User Equipment (UE) can camp on a specific cell. Here are the key parameters used for this purpose, along with simplified explanations:
Cell Selection Parameters of LTE.
QRxLevMin:
- Definition: Minimum required received signal level in dBm for a cell to be considered suitable.
- Range: -128 to -110 dBm.
- Function: Setting QRxLevMin to a lower value (e.g., closer to -128 dBm) makes it harder for the UE to camp on the cell, effectively discouraging camping on cells with weaker signals.
- Offset (QRxLevMinOffset): This can be adjusted from 0 to 2 to further discourage camping on cells with marginal signal strength.
Qqualmin:
- Definition: Minimum required signal quality level, typically measured in terms of Reference Signal Received Quality (RSRQ).
- Range: -22 to -18 dB.
- Function: Setting Qqualmin to a higher value (e.g., closer to -18 dB) discourages the UE from camping on cells with poor signal quality.
Pcompensation:
Compensation factor that adjusts the cell selection criteria based on the UE’s maximum transmit power capabilities. the formula is given below
Components:
- PEMAX: Maximum transmit power allowed by the network.
- PPowerClass: Maximum transmit power class of the UE.
- Function: Ensures that UEs with lower transmit power have stricter criteria for camping, making it harder for them to camp on cells where they might struggle to maintain a good connection.
PMaxServingCell:
Maximum transmit power for the serving cell.
- Range: 1000 (indicative value for maximum transmit power).
- Function: Sets an upper limit on the power that the UE can use to connect to the serving cell, ensuring that UEs with lower power capabilities find it harder to camp on cells where higher power is required.
Camping Criteria for Low Power UEs
For UEs with lower power capabilities, the criteria for camping on a cell are more stringent. Here’s how these parameters work together to enforce these criteria:
- Signal Level and Quality: QRxLevMin and Qqualmin are set to values that ensure only cells with sufficient signal strength and quality are considered. For example, setting QRxLevMin closer to -110 dBm and Qqualmin closer to -18 dB discourages camping on cells with marginal signal conditions.
- Power Compensation: Pcompensation adjusts the camping criteria based on the UE’s power class. For lower power UEs, this means stricter criteria, as they may struggle to maintain a connection with cells that require higher transmit power.
- Maximum Transmit Power: PMaxServingCell ensures that the UE does not exceed its power capabilities when trying to connect to the serving cell. This protects both the UE and the network from potential issues related to power limitations.
Example Scenario
- QRxLevMin: -120 dBm (discouraging camping on weaker signals).
- QRxLevMinOffset: 1 (further discouraging marginal signals).
- Qqualmin: -20 dB (ensuring good signal quality).
- Pcompensation: Calculated based on the UE’s power class and network settings, ensuring that lower power UEs have stricter camping criteria.
- PMaxServingCell: 1000 (maximum transmit power limit).
In this scenario, a low power UE will have to find a cell that meets these stringent criteria, ensuring that it only camps on cells where it can maintain a reliable connection. This helps in managing the overall network performance and user experience.