5G DL Spectral Efficiency
Spectral Efficiency (SE) is the user downlink throughput per unit of used radio bandwidth, expressed in bits/s/Hz.
With ROMES Export Measurement Files (s), it is possible to export data to calculate the theoretical Spectral Efficiency using:
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MCS/Layer (gNB perspective)
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CQI/RI (UE perspective)
Picture 1 illustrates the ROMES Exporting Measurement Files.
The export result is save under .asc which is required to be converted with "Text to Columns"
in Excel.
The example of exported values is shown below. It is important to include parameters under "5G NR UE" for PCell (i.e. in EN-DC mode, SCG-PSCell) :
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Net PDSCH Thp
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Avg. PDSCH MCS
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Avg. PDSCH Layers
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Avg. CQI WB
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Avg. Rank
Other parameters e.g. PCI, SS-RSRP, PDSCH BLER and so on would be optional for individual interests or other purpose of evaluations.
Remark:
Although ROMES supports exporting the "5G NR UE/ PDSCH MCS Table", the values should be treated with caution. The logfile measured with ROMES older than version 25.3 [Build 4759- Dated: Sep 30 2025], numerous entries contain "?", denoting that the corresponding information was not available.
Once the data is successfully converted, there are 2 tasks need to be processed before the spectral efficiency can be calculated.
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VLOOKUP Table for MCS Values
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VLOOKUP Table for CQI Values
VLOOKUP Table for MCS
The exported PDSCH MCS data (Column G) must be converted to the corresponding Spectral Efficiency using Excel VLOOKUP function. See example in Picture 3.
The Avg PDSCH MCS in Column G, example G28, MCS = 19 --> its Spectral Efficiency = 5.1152 when the MCS Table is 256QAM.
Note:
The below example logfile was measured using ROMES Version 24.02 which does not contains the PDSCH MCS Table value in the exported file, hence, it is required an extra look-up into the ROMES L3 View.
How to find out what is the configured 5G MCS table ?
In 5G NR, the L3 message "RRC Reconfiguration" contains parameter "mcs-Table" in PDSCH-Config.
The "mcs-Table" tells UE which MCS table to be used.
In DL (PDSCH), there are 3 MCS table:
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table 1 (64QAM)
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table 2 (256QAM)
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table 3 (64QAM with Low Spectral Efficiency)
RRC Reconfiguration message shows that the PDSCH is configured with 256QAM table.
Hence, the VLOOKUP table must provide Column A for MCS Index and Column B for Spectral Efficiency for 256QAM table.
VLOOKUP Table for CQI
The exported Avg. CQI WB data (Column M) must be also converted to the corresponding Spectral Efficiency using Excel VLOOKUP function. See example in the picture below.
The Avg. CQI WB in Column M, example M28, Wideband CQI = --> its Spectral Efficiency = 5.5547 when the MCS Table is 256QAM.
Spectral Efficiency Calculation
The last step is to calculate Spectral Efficiency using:
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MCS * PDSCH Layer i.e. Column H * Column I
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CQI * Rank i.e. Column N * Column O
Spectral Efficiency Calculation
The last step is to calculate Spectral Efficiency using:
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MCS * PDSCH Layer i.e. Column H * Column I
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CQI * Rank i.e. Column N * Column O
Spectral Efficiency Comparison between different HTTP DL Sessions
The figure below is a CDF (cumulative distribution function) comparison of spectral efficiency for different HTTP downlink sessions under 5G EN-DC (NSA) conditions.
The X-axis shows Spectral Efficiency (0 - 30 bps/Hz)
The Y-axis show CDF (0-1)
Each color represents a different number of parallel HTTP DL sessions:
NSA_1T, 2T, 3T, 4T, 5T
For each scenario, two estimation methods are plotted:
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Solid lines: Spectral Efficiency derived from MCS * PDSCH Layer
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Dotted lines: Spectral Efficiency derived from CQI * RI
Key Observation
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Servers plays roles in the above measurement files, as we can see NSA_4T and NSA_4T_DifferentServer shows significant gap in spectral efficiency.
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With default server, increasing number of parallel HTTP DL sessions does not guarantee higher spectral efficiency. In the measurement, NSA_3T case shows the lowest spectral efficiency distribution, while NSA_1T and NSA_2T provide better spectral efficiency.