EVM Minimization (NB-IoT)

Default: 3GPP, all types of corrections selected

Range: Off, 3GPP, Tracking
Types: Amplitude, Timing, Frequency/Phase

EVM Minimization uses the NRS reference signal to correct the signal. There are three types of corrections that can be applied to the signal to minimize the EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format.. They are Amplitude, Timing and Frequency/Phase.

In addition, there are two types of EVM minimization, 3GPP and Tracking.

When 3GPP EVM minimization is selected, the demodulator calculates timing and frequency/phase corrections using the reference signal and NPDSCH data subcarriers.

The demodulator applies the corrections on a subframe-by-subframe basis for downlink, as defined by the NB-IoT standard.

When Tracking is selected, the demodulator applies corrections on a symbol-by-symbol basis and the Equalizer Training parameter determines whether data subcarriers are included in calculating corrections. When Equalizer Training is set to RS+Data, EVM Minimization Tracking is performed using the reference signal and the NPDSCH data subcarriers. When Equalizer Training is set to RS or Off, EVM Minimization Tracking is performed using only the reference signal.

When Off is selected, EVM minimization corrections are not applied to the signal.

Reference signal subcarriers are transmitted periodically in time and frequency. The demodulator compares the reference signals with the expected data sequence and computes an error, or correction value, that can be used to track phase, amplitude, and timing at the symbol level when Tracking is selected, and at the slot or subframe level when 3GPP is selected. For subcarriers that do not have a corresponding reference subcarrier to compare to, the correction value is calculated by linearly interpolating between RS (and data subcarriers, when Equalizer Training is set to RS+Data) subcarrier corrections.

When corrections are averaged and applied to a slot or subframe, the same correction is applied to each symbol in the slot or subframe.

These are the three types of EVM Minimization corrections available. Click on the name of a correction type for more information.

Amplitude - When selected, the average reference signal amplitude error will be used to correct the amplitudes of the subcarriers.
Frequency/Phase - When selected, the average reference signal phase difference will be used to adjust subcarrier phase.
Timing - When selected, the average slope (average rate of change) of the reference signal's phase in the frequency domain is used to correct the timing.

For downlink, equalization occurs over the entire Measurement Interval and 3GPP EVM Minimization occurs on a subframe-by-subframe basis.