Address Phase Compensation Challenge in 5GNR Signal Generation

Address Phase Compensation Challenge in 5GNR Signal Generation

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Introduction

RF test engineers may have the experience that at LTE time, a single waveform can be transmitted at different frequencies on a signal generator for specific test purposes, and this procedure could be further automated to achieve good test efficacity. However, this will not be the case in 5G NR signal generation due to phase compensation. Phase compensation is a new concept introduced into 5G NR baseband signal generation in TS38.211 as below, to address a typical 5G scenario that Tx and Rx frequencies may not be the same. In that case, without properly compensating the phase, the receiver would not be able to correctly demodulate the received signal.

From the 3GPP specification equation above, it can be observed that phase compensation is performed for a specific transmission frequency f0. So that means, even if the same signal configuration needs to be transmitted at multiple frequencies, we’ll have to generate a different waveform for each frequency point. As a result, the number of test waveforms will increase significantly along with the frequency number. This would be a big challenge for test engineers, considering the complexity of 5G NR signal configurations - they have to maintain a large waveform library and identify each waveform carefully with its ‘frequency tag’.

Going back to the same approach as LTE test, an ideal solution would be playing the same 5G NR waveform while performing phase compensation along with transmission frequency change automatically. Now, this capability, so-called real-time phase compensation has been supported by Keysight N5172B EXG and N5182B MXG signal generators with its latest B.01.80 firmware and N7631C Signal Studio for 5G NR v4.0.0.0 software. Here real-time means, phase compensation is done by FPGA over the playing waveform in a real-time manner, instead of pre-compensating it into each waveform file. Users can access real-time phase compensation features either through software GUI operation or SCPI commands for test automation.  

Table of Content

  • Run with N7631C Signal Studio
  • Run with SCPI Commands
  • Typical Configuration for 5G NR Signal Generation with  Real-time Phase Compensation