Preamble Only (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 channel estimation sequences in the preamble of the 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. burst are used for equalization. L-LTF Non-HT Long Training field is used to equalize the SIG symbols (L-SIG Non-HT SIGNAL field, HT-SIG High-Throughput SIGNAL field, or VHT very high throughput (VHT) physical (PHY) layer protocol data unit (PPDU):A PPDU transmitted using the TXVECTOR FORMAT parameter equal to VHT.-SIG). HT high throughput-LTF Long Training field (VHT-LTF for 802.11ac) is used to compute the equalizer coefficients for the Data symbols (and these equalizer coefficients are shown in the Ch Frequency Response trace).
The advantage of this method of equalization is that it models what a typical OFDM receiver would do when receiving transmissions from a base station. Thus 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. measured using this method will more accurately reflect the signal quality seen by a typical OFDM receiver.
The disadvantage of this method of equalization is that the measured EVM value may be higher for signals whose impairments change during the burst than it would be if the equalizer were trained over the entire burst.
See Also
