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5G NR EVM Measurement | EVM test and measurement in 5G NR

This page describes 5G NR EVM Measurement as defined in 3GPP. The EVM test and measurement procedure and EVM formula/equations used in 5G NR system are also explained. It mentions 5G NR BS (Base Station) EVM requirements or limits for different BS classes/types.

Introduction:
• EVM or Error vector magnitude provides insight into quality of the modulated signal/symbol.
• This modulated signal originates when bits are mapped to symbols in a complex modulation systems such as QPSK, 16-QAM, 64-QAM etc.
• It is also referred as RCE (Relative Constellation Error).
• It can be expressed in units of "dB" or "rms".
Refer Error Vector Magnitude basics >> and EVM unit converter >> for more information.

 Error Vector Magnitude
EVM Equation

The figure-1 depicts concept of EVM measurement. The basic EVM equation is also mentioned.

5G NR EVM Measurement

EVM measurement 5G NR

As shown in the module level diagram for part of the 5G NR physical layer receiver, EVM is measured after FFT and after channel equalization (i.e. after zero forcing equalizer). EVM is measured after all the transmitter impairments and channel impairments are compensated at the baseband receiver.

As shown in the formula-1, EVM is measured over one subframe duration (i.e. 1 ms) and (NBW)RB subcarriers (i.e. 180 KHz) in frequency domain.

EVM formula 5G NR

Where,
T = Set of symbols with selected modulation type within subframe
F(t) = Set of carriers within (NBW)RB subcarriers with selected modulation type within symbol 't'
I(t,f) = Ideal reconstructed signal by equipment in accordance with relevant Tx models.
Z'(t,f) = Modified signal under test as per following equation-2.

5G NR modified signal

Where,
z(v) = Time domain samples of signal under test
Δt = Sample time difference between ideal and FFT processed samples
Δf = RF Frequency Offset
Φ(f) = Phase Response of Tx Chain
a (f) = Amplitude Response of Tx Chain

Average EVM

Average EVM 5G NR

The equation-3 used to calculate average EVM. EVM is averaged over all allocated DL (downlink) RBs (Resource Blocks) with selected modulation type in frequency domain. Minimum of 10 downlink subframes are used.
Where,
Ni = Number of RBs with selected modulation in subframe "i" and Ndl is number of allocated DL subframes in one frame.

5G NR EVM compliance limit

➤FR1 (i.e. sub-6 GHz) frequency range: Residual EVM measurement should be less than 0.5% (-46.0 dB)
➤FR2 (i.e. mmwave) frequency range: Residual EVM measurement should be less than 0.75% (-42.5 dB)
➤Following equation can be used to convert EVM (dB) to EVM (rms) and vice versa.


EVM,Error Vector Magnitude calculator

Following table-1 mentions EVM requirements or limits for BS classes 1-C and 1-H. PDSCH channel with required modulation scheme should be used during testing.

Modulation type used for PDSCH Required EVM (%)
QPSK 17.5%
16QAM 12.5%
64QAM 8%
256QAM 3.5%

Table-1: EVM requirements for BS Type-1C and BS Type 1-H

Following table-2 mentions EVM requirements or limits for BS class 2-O. PDSCH channel with required modulation scheme should be used during testing.

Modulation type used for PDSCH Required EVM (%)
QPSK 17.5%
16QAM 12.5%
64QAM 8%

Table-2: EVM requirements for BS Type 2-O

References:
• TS 38.104 Base Station (BS) radio transmission and reception



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This 5G tutorial also covers following sub topics on the 5G technology:
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5G Frequency Bands
5G millimeter wave tutorial
5G mm wave frame
5G millimeter wave channel sounding
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5G testing and test equipments
5G network architecture
5G NR Physical layer
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5G NR PDCP layer

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