Common Pilot Error (CPE) represents the following imperfections that affect demodulation:

  • Amplitude jitter across time
  • Residual Carrier Frequency Offset (CFO) caused due to close-in phase noise of the system

OFDM signals for WLAN transmit the pilot subcarriers with a known data sequence. This information is used to determine the error, in amplitude and phase, between an ideal signal and the received signal. This error data, known as CPE, is used to correct imperfections on both the pilot subcarriers and the data subcarriers. This correction results in more accurate demodulation.

Estimation and correction of the phase error component in CPE is mandatory in the Transmitter Modulation Accuracy (Error Vector Magnitude) Test as defined in sections 17.3.9.8, 19.3.18.7.4, and 21.3.17.4.4 of IEEE Standard 802.11-2016, section 27.3.18.4.4 of IEEE Standard P802.11ax/D8.0, section 36.3.20.4.4 of IEEE Standard P802.11be/D7.0 and section 38.3.25.4.3 of IEEE Standard P802.11bn/D0.3.

Note Estimation and correction of Amplitude Error component of CPE is optional.

The following figure describes the procedure to compute CPE.

You can obtain the CPE for the received pilot subcarrier by correlating the received pilot subcarrier with its ideal value.

The CPE for symbol l is as follows.

Where the values are the following.

  • Amp(.) represents the amplitude component of a complex signal.
  • Ph(.) represents the phase component of a complex signal.
  • k is the pilot subcarrier index.
  • M is the number of pilot subcarriers.
  • X(k) is the received pilot subcarrier at index k.
  • XI(k) is the ideal pilot subcarrier at index k.

If CPE tracking is enabled (Amplitude Tracking Enabled and Phase Tracking Enabled properties), all subcarriers are reduced by the amplitude error δl and de-rotated by the phase error ∅l, for each symbol. The corrected subcarrier for symbol l is given by

where

  • Xr(k) is the received subcarrier at index k
Note CPE result is the RMS value of the phase error component of CPE across all symbols.