5G NR EVM Measurements with the USRP N320/N321 - Revision history

Ettus at 19:36, 17 April 2019

2019-04-17T19:36:52Z

Ettus at 19:36, 17 April 2019

2019-04-17T19:36:36Z

Ettus: Created page with "== Application Note Number == '''AN-452''' == Revision History == {| class="wikitable" !Date !Author !Details |- |style="text-align:center;"| 2019-04-17 |style="text-align:..."

2019-04-17T19:35:23Z

Created page with "== Application Note Number == '''AN-452''' == Revision History == {| class="wikitable" !Date !Author !Details |- |style="text-align:center;"| 2019-04-17 |style="text-align:..."

New page

== Application Note Number ==
'''AN-452'''

== Revision History ==
{| class="wikitable"
!Date
!Author
!Details
|-
|style="text-align:center;"| 2019-04-17
|style="text-align:center;"| Drew Fischer
|style="text-align:center;"| Initial creation
|}

5G NR EVM Measurements with the USRP N320/N321

== Abstract ==
Example EVM measurements are shown using the USRP N320/N321 receiver and the 5G New Radio (5G NR) modulation standard. The use of I/Q image calibration and spur-dodging are demonstrated as methods to improve EVM performance.

== Measurement Description ==
The NI-RFmx NR software [ http://sine.ni.com/nips/cds/view/p/lang/en/nid/217188 ] and the PXIe-5840 Vector Signal Transceiver [ http://www.ni.com/en-us/support/model.pxie-5840.html ] were used to continuously generate a waveform using the 5G NR modulation standard. The waveform was configured for 100-MHz bandwidth, 256 QAM, and DFTS OFDM. The modulated signal generated by the Vector Signal Transceiver was connected to the RX2 input of the USRP N320/N321. Additional test code was written to acquire and post-process the received waveform in order to calculate EVM.

== Raw Performance ==
The gain index of the USRP N320/N321 receiver was fixed at 30 dB and the carrier frequency was swept from 500 MHz to 6 GHz. The modulated waveform was acquired and analyzed to compute the EVM. The corresponding results are shown in the following plot:

[[File:evm_fig_1.png|400px|center]]

== I/Q Image Calibration ==
One key contributor to EVM performance is the image level. Images are generated by the I/Q demodulator in the signal chain and are an artifact of this receiver architecture. The image level can be measured and accounted for using the I/Q image calibration utility available in UHD, as shown in the example below.

From directory:
~/src/uhddev/host/build/utils

For CH0, run:

sudo ./uhd_cal_rx_iq_balance --subdev A:0 --freq_start 0.5e9 --freq_stop 6e9 --freq_step 0.1e9 --verbose

For CH1, run:

sudo ./uhd_cal_rx_iq_balance --subdev B:0 --freq_start 0.5e9 --freq_stop 6e9 --freq_step 0.1e9 --verbose

The image level was measured using external equipment before and after calibration to show the improvement, as shown in the plot below:

[[File:evm_fig_2.png|400px|center]]

The EVM versus frequency was measured once again after applying the RX I/Q calibration. Significant improvements can be observed as demonstrated in the following comparison plot:

[[File:evm_fig_3.png|400px|center]]

== Spur-Dodging Mode ==
At some frequencies, synthesis spurs can be higher than desired and can result in EVM degradation. A spur-dodging algorithm was implemented for the USRP N320/N321 to improve the spurious performance when desired. By default, the spur-dodging algorithm is disabled, but can be enabled by adding the following device argument:

--args “spur_dodging=enabled”

During the original measurement above, a few frequencies exhibited spur levels high enough to degrade the EVM performance. These frequencies were remeasured after enabling the spur-dodging algorithm. The corresponding EVM performance improved at these frequencies as highlighted in the following plot:

[[File:evm_fig_4.png|400px|center]]

== Conclusions ==
The USRP N320/N321 receiver with the 5G NR modulation standard exhibits excellent EVM performance. This performance can be further improved by taking advantage of the RX I/Q calibration utility available in UHD as well as the spur-dodging algorithm unique to the USRP N320/N321.

Footnotes
The EVM performance presented here was measured on a single unit at room temperature during product development. The performance demonstrated here is for informational purposes only and is not covered by warranty.

@@ Line 12: / Line 12: @@
 |style="text-align:center;"| Initial creation
 |}
 == Abstract ==

@@ Line 24: / Line 24: @@
 The gain index of the USRP N320/N321 receiver was fixed at 30 dB and the carrier frequency was swept from 500 MHz to 6 GHz.  The modulated waveform was acquired and analyzed to compute the EVM.  The corresponding results are shown in the following plot:
-[[File:evm_fig_1.png|400px|center]]
+[[File:evm_fig_1.png|800px|center]]
 == I/Q Image Calibration ==
@@ Line 42: / Line 42: @@
 The image level was measured using external equipment before and after calibration to show the improvement, as shown in the plot below:
-[[File:evm_fig_2.png|400px|center]]
+[[File:evm_fig_2.png|800px|center]]
 The EVM versus frequency was measured once again after applying the RX I/Q calibration.  Significant improvements can be observed as demonstrated in the following comparison plot:
-[[File:evm_fig_3.png|400px|center]]
+[[File:evm_fig_3.png|800px|center]]
 == Spur-Dodging Mode ==
@@ Line 56: / Line 56: @@
 During the original measurement above, a few frequencies exhibited spur levels high enough to degrade the EVM performance.  These frequencies were remeasured after enabling the spur-dodging algorithm.  The corresponding EVM performance improved at these frequencies as highlighted in the following plot:
-[[File:evm_fig_4.png|400px|center]]
+[[File:evm_fig_4.png|800px|center]]
 == Conclusions ==