[5G RRC] The meaning and calculation process of RSRP, RSRQ and SINR are introduced in detail

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I work for an internationally renowned terminal manufacturer and am responsible for the research and development of modem chips.
In the early days of 5G, he was responsible for the development of the terminal data service layer and the core network. Currently, he is leading the research on technical standards for 6G computing power networks.


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       computing power network explanation (cloud computing, edge computing, end computing)
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The meaning and calculation process of RSRP, RSRQ and SINR are introduced in detail

1. NR SS-RSRP

       UE measures SS-RSRP and uses it for cell selection, cell reselection, power control, mobility and beam management procedures . L1 (Phy) and L3 (RRC) will generate and report RSRP measurement values. For example, UE can measure SS-RSRP at L1 when sending CSI to gNB, and provide measurement results to L3 when sending a measurement report.

       When generating SS-RSRP results, the UE is allowed to use PBCH-DMRS measurement results. DMRS and SS-Signal are transmitted at the same power, so the results can be averaged directly. When the UE reports the measured SS-RSRP to L1, the UE can be configured to use the CSI-RS measurement as an additional input. Compared with SS-Signal and PBCH DMRS, CSI-RS may have different transmission power. The gNB will provide offset information to the UE to assist the measurement process.

1.1 Features of SS-RSRP

• SS-RSRP is the average power received from a single RE (Resource Element) allocated to SS-Signal;
• Average values ​​are calculated in linear units of milliwatts (mWatts) rather than dBm;
• Power is calculated by measuring the energy received in the useful part of the symbol, excluding the cyclic prefix part;
• For FR1, measurements are performed at the UE antenna connector, assuming that the UE has a single antenna element per receive path, rather than an antenna array;
• For FR2, assuming that the UE has an antenna array for each receive path, the measurement is based on the combined signal strength of all antenna elements belonging to a single receive path;
• The measured values ​​are filtered at L1 and L3;
• SS-RSRP L1 measurements are useful for beam management procedures, as this requires UEs to quickly switch between beams;
• 3GPP specification 38.133 stipulates the mapping relationship between the reported value and the measured value of L1 and L3 RSRP;
• According to the 3GPP specification, the minimum RSRP defined by LTE is -140 dBm, but in order to meet the coverage performance of eMTC applications, this value is reduced to -156 dBm. In order to consider the beam gain of the UE, the maximum RSRP of the LTE system -44dBm is increased to -31dbm;

1.2 L1 filtering of SS-RSRP

• L1 filtering is to eliminate the influence of noise;
• Compared with L3 RSRP, the reporting scope of L1 RSRP is smaller;
• If reportQuantity in CSI-ReportConfig is set to "ssb-Index-RSRP", configure UE to report SS-RSRP of L1;
• L1 measurement isbeam levelinstead ofCommunity level, which means that each SS-RSRP result is associated with a specific SS/PBCH Block;
• RSRP value used7 digitsThe payload is represented, and the mapping is shown in the following table:
  
• L1 SS-RSRP or CSI-RSRP can be expressed between 16 (-140dBm) and 113 (-44dbm);

1.3 L3 filtering of SS-RSRP

• L3 filtering is performed toEliminate fast fadingandReduce short-term variations in measurement results；
• SS-RSRP L3 measurements are useful for handover procedures;
• The defined maximum L3 RSRP is -31dBm and the minimum L3 RSRP is -156dBm;
• The full RSRP range has 128 entries (-31 dBm to -156 dBm) and can be7 digitsTo represent;
• L3 measurements can bebeam levelcan also beCommunity level, and can be reported to gNB in ​​the measurement report message;
• For L3 measurement, gNB provides UE with SS/PBCH Block measurement timing configuration (Measurement Timing Configuration);

2. NR SINR

       SINR (Singal to Interference Noise Ratio, signal-to-noise ratio) is an indicator to measure the quality of the signal. It can be defined as the ratio of the desired signal strength to the unwanted interference plus noise.

       A good SINR helps to achieve higher spectral efficiency because it is able to decode higher modulation coding schemes (MCS). Network operators always seek to maximize the SINR at all sites to provide the best user experience, either by increasing transmit power or reducing interference and noise. According to Shannon channel capacity (C), theoretical channel capacity is a function of bandwidth (B) and SINR.

Therefore, optimizing SINR can help improve cell capacity, support higher-order QAM modulation, thereby increasing peak data rate, reducing the number of dropped calls, and ultimately improving user experience .

5G NR defines the following two types of SINR:

• SS-SINR : Can be used for switching process in connected mode. Both the desired signal power and the interference plus noise power are measured from the REs used by the SSS;
• CSI-SINR : Similar to SS-SINR, it can also be used for the handover process in connected mode. The signal power and interference plus noise power required here are measured by the REs used by the CSI reference signal;

2.1 Summary of 5G NR SINR key information

• SS-SINR is an optional UE function, and the UE must declare it separately for FR1 and FR2;
• The UE uses the ss-SINR-meas flag to notify its SS-SINR capability in the MeasAndMobParametersFRX-Diff parameter structure , and uses the CSI-SINR-meas flag to notify its CSI-SINR capability;
• The UE measures the PBCH demodulation reference signal (DMRS) when generating SS-SINR results;
• In the 5G network, the value of SINR is sent to gNB through the measurement report;
• 3GPP specification 38.133 specifies the mapping relationship between reported values ​​and measured values;
• The reporting range is 0 ~ 127, a total of 128 values, the reported value 0 is equal to SINR < -23 dB, and the reported value 127 means SINR > 40 dB;
• The 3GPP specification defines that the accuracy of the measurement report is 0.5 dB;

2.2 Mapping relationship between SINR and reported value

The following table shows the mapping relationship between reported and measured values ​​of SINR. This table applies to both SS-SINR and CSI-SINR.

2.3 Example of calculating SINR

According to the value reported by the UE in the measurement report, the SINR value in dB can be calculated:

• The index value of the SINR reported by the UE = 73;
• SINR (in dB) = 73/2 -23 = 36.5 – 23；
• SINR (in dB) = 13.5 dB；

3. NR RSRQ

       RSRQ (Reference Signal Recived Quality) is a measurement performed by the UE to know the quality of the received reference signal. In 5G NR, RSRQ can be SS-Reference Siganls and CSI-Reference Siganls. SS-RSRQ measurements can be used for cell selection, cell reselection and mobility , while CSI-RSRQ measurements can only be used for mobility .

3.1 Summary of 5G NR RSRQ Key Information

• It is a quantitative measure of the received SS (synchronization signal) or CSI (channel state information) reference signal;
• The measurement unit of RSRQ is dB, while the measurement unit of RSSI and RSRP is dBm;
• RSRQ measurement can be used for cell selection, reselection and handover process;
• There are two forms of RSRQ, namely SS-RSRQ and CSI-RSRQ;
• 5G RSRQ range is defined as -43dB to 20dB;
• 5G RSRQ can be positive or negative, while LTE RSRQ is always negative;
• The accuracy of the RSRQ defined by the specification is 0.5dB;
• The UE does not report RSRQ in dB, but reports an index value;
• 0.5 dB accuracy, in the full range RSRQ (-43dB ~ 20dB) can be mapped to 128 index values ​​(represented by 7 bits), where index 0 = -43dB RSRQ, index 127 = 20dB;
• The 3GPP specification TS 38.133 provides the mapping relationship between these index values ​​and absolute RSRQ values;
• The mapping relationship is common to both SS-RSRQ and CSI-RSRQ;
• 5G RSRQ measurements are filtered at L3 to remove the effects of fast fading and help reduce short-term variations in measurements;

3.2 Mapping relationship between RSRQ measurement value and index value

The following table shows the mapping between measured values ​​and indexed values:

3.3 RSRQ calculation process

SS-RSRQ can be defined as the ratio of SS-RSRP to RSSI multiplied by the RB number:

CSI-RSRQ can be defined as the ratio of CSI-RSRP to RSSI multiplied by the RB number:

we can use the above formula to calculate the theoretical value of RSRQ:

• The RSRP range of 5G NR is -156 dBm to -31 dBm;
• 5G NR has an RSSI range of -120 dBm to -13 dBm;
• The range of 5G resource blocks (N) is 24 ~ 275 RBs;

Since RSRP (dBm) and RSSI (dBm) are logarithmic, logarithmic conversion needs to be performed on the above RSRQ calculation formula. In logarithms, division (/) can be represented as subtraction (-) and multiplication can be represented as addition (+), for RBs we need to convert them to 10 log (RBs).

• Minimum value of RSRQ = -156 – (-120) + 10*log(24) = -22.19 dB
  • The corresponding index value is 42;
• Maximum value of RSRQ = -31 – (-13) + 10*log (275) = 6.39 dB
  • The corresponding index value is 99;

3.4 Example of RSRQ calculation process

According to the value reported by the UE in the measurement report, the RSRQ value in dB can be calculated:

• UE reports RSRQ index value = 45;
• RSRQ (in dB) = 45/2 -43 = 22.5 – 43
• RSRQ (in dB) = -20.5 dB

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参考：
3GPP TS 38.215 – 5G NR, Physical layer measurements
3GPP TS 38.133 – 5G NR, Requirements for support of radio resource management
3GPP TS 38.214 – 5G NR, Physical layer procedures for data

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