Symbol Time Adjustment (802.11n/ac/ax/be)

Symbol Time Adjustment adjusts the "useful symbol time period" (TFFT Fast Fourier Transform: A mathematical operation performed on a time-domain signal to yield the individual spectral components that constitute the signal. See Spectrum.) within 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. extended symbol time period" (TS). Symbol Time Adjustment shifts the start of the TFFT period earlier in the TS time period. The amount of TFFT shift is specified as a percentage of the TFFT length.

Mode - Selects between automatic and manual symbol time adjustment.

Auto: The VSA will find the symbol timing adjustment to best optimize 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..

Manual: (default) Manually enter a symbol time adjustment in the Adjustment field.

Adjustment - When Manual is selected, enter the symbol time adjustment value.

Default = -3.125%

Minimum = -(guard interval)/100

Maximum = 0

The extended OFDM symbol time period (TS) consists of a guard interval (TGI Guard interval) plus a "useful symbol time period" (TFFT). Within the TS, the VSA performs the demodulation and data analysis on only one TFFT time period. The Symbol Time Adjustment parameter moves the TFFT within the TS.

Typically, the TGI time period is ignored and only the TFFT time period is used. The Symbol Time Adjustment parameter causes the demodulation start time to begin earlier within each extended symbol time.

Moving the TFFT period away from the ending transition time (TTR) into the Guard Interval (TGI) may help avoid intersymbol interference. Make sure that the TFFT period is not shifted so much that it includes corrupt data from the transition time at the beginning of the symbol-time.