What is RSRP (Reference Signal Received Power) in LTE

In modern cellular systems like LTE and 5G NR, RSRP (Reference Signal Received Power) is one of the most important metrics used for evaluating signal strength and making mobility-related decisions. RSRP is measured at the UE and plays a pivotal role in cell selection, reselection, handovers, and overall radio link management.

What is RSRP?

In simple terms, RSRP is the average received power of the resource elements (REs) that carry the Reference Signals (RS) in a cell. These reference signals are always transmitted on specific OFDM symbols and subcarriers — regardless of whether data is being transmitted.

Definition (3GPP TS 36.214):

RSRP is the linear average of the received power of the resource elements (REs) carrying cell-specific reference signals (CRS) within the considered measurement bandwidth.

Key Characteristics:

• Unit: dBm
• Range: -140 dBm to -44 dBm
• Bandwidth Independent: Depends only on the power of RS REs
• Reported as: Integer values from 0 to 97 in RRC signalling
• Reference Point: UE antenna connector

Reference -3gpp spec 36.133

How is RSRP Calculated?

RSRP is computed by the UE in the following way:

• Identify all resource elements that carry the Cell-Specific Reference Signals (CRS).
• Measure the power of each of those REs.
• Calculate the linear average of the measured power values.
• Convert the result into logarithmic scale (dBm).

Where:

• Pi is the power of the i-th reference signal resource element
• N is the total number of RS REs in the measurement window

Note:

• The measurement excludes the cyclic prefix energy
• Power measurement is based only on the useful part of the OFDM symbol

RSRP and SINR vs Distance

Role of RSRP in LTE

1. Cell Selection
   UE uses RSRP to choose the best serving cell during initial registration.
   Ensures the UE connects to the cell with the strongest signal.
2. Cell Reselection (Idle Mode Mobility)
   When idle, UE continuously monitors neighbour cells.
   RSRP is used to decide when to reselect a better cell for improved coverage or signal strength.
3. Handover Decision (Connected Mode Mobility)
   In connected mode, UE measures RSRP of neighbouring cells.
   Triggers mobility events like A3, A5, etc., based on RSRP thresholds and offsets.
4. Radio Link Monitoring (RLM)
   RSRP is used to detect degradation of the serving cell signal.
   Helps UE decide when to initiate a radio link failure (RLF) recovery procedure.
5. Coverage Estimation
   Network uses RSRP reports from UEs to visualize and map coverage.
   Assists in identifying coverage holes and planning small cell deployments.
6. Uplink Power Control Support
   UE can estimate downlink path loss using RSRP.
   Supports open-loop uplink power control calculations.
7. Inter-Frequency & Inter-RAT Measurements
   RSRP is used to evaluate signal strength of cells on other LTE carriers or different RATs (e.g., UMTS).
   Enables efficient inter-frequency handovers and reselections.
8. Network Optimization and Drive Testing
   Field engineers use RSRP logs to assess signal propagation.
   Helps fine-tune antenna tilt, transmit power, and neighbor relations.
9. Carrier Aggregation Cell Management
   Secondary cells are added/removed based on their RSRP values.
   Improves throughput and reliability in CA deployments.
10. QoE and Performance Analysis
    RSRP trends are analysed alongside RSRQ/SINR to understand real-world user experience.
    Supports service assurance and troubleshooting.

Common Misunderstandings

• RSRP is not the same as RSSI:
  RSRP measures only the power of reference signals, while RSSI includes all power in the measurement bandwidth — including interference and noise.
• RSRP is not the same as SINR or RSRQ:
  RSRP measures signal strength, whereas SINR and RSRQ reflect signal quality.

References

• 3GPP TS 36.214 – LTE Physical Layer Measurements
• 3GPP TS 36.133 – LTE UE Radio Requirements
• MathWorks LTE Toolbox
• CableFree Wireless LTE Resources
• TechTrained LTE Measurement Tutorials