Preamble, Pilots & Data (802.11n/ac/ax/be)
is one of two possible selections for Equalizer Training for 802.11n/ac/ax/be demodulation measurements. When is selected, the Data symbols are also used to equalize the signal. This type of training generally gives a more accurate estimate of the true response of the transmission channel than Preamble Only.
This is a two-pass equalization. The signal is first equalized using as described in Preamble Only and demodulated. Then the equalizer coefficients calculated from HT high throughput-LTF Long Training field (VHT very high throughput (VHT) physical (PHY) layer protocol data unit (PPDU):A PPDU transmitted using the TXVECTOR FORMAT parameter equal to VHT.-LTF for 802.11ac) are updated by using the demodulated Data symbols. Finally, the signal is demodulated again using the updated equalizer coefficients. These updated coefficients are shown in the Ch Frequency Response trace.
Advantages of this method of equalization include the following:
- The equalizer coefficients typically reflect the linear channel impairment with greater accuracy than , as the data set used to train the equalizer is larger and is less affected by turn-on transient effects in the burst.
- The EVM is typically lower than 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. using because the equalizer is less impacted by noise and other forms of distortion. EVM represents the error due to noise, non-linear distortion, spurious and residual linear distortion.
The disadvantage of this method is that it is less likely to accurately reflect the performance of a typical OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. receiver. This type of equalizer computation is less likely to be used in practical receivers because it is more complicated and therefore more expensive to implement.
See Also
