One of WiFi test tips: the usage of Full packet

When testing WiFi signals, I often encounter the confusion of "Do I need to turn on Full Packet".

In wireless transmission, in order to obtain better signal analysis performance, channel estimation algorithms are generally used to compensate the channel. There are two methods for channel estimation: Raw Long Symbols and Full packet.

The difference between the two methods is whether to track or estimate the channel changes caused by the changes in the surrounding environment and the incomplete stability of the device.

Raw Long Symbols refers to channel estimation using the frame header training sequence of the WLAN signal to analyze EVM, but this method does not follow-up estimation of channel parameters. Full Packet uses the frame header training sequence and the data packets after the frame header to estimate, and iteratively optimizes the calculation of each parameter value. Tracking the channel changes, the estimated parameters will be more accurate and stable.

Compared with Raw Long Symbols, Full packet can usually increase the EVM index by 2~3dB, and sometimes it can reach 4~6dB.

Whether to choose Raw Long Symbols or Full packet in the test is actually related to the chip scheme used in the product. Different chip schemes have different choices.

At present, the usual practice in the Wi-Fi testing industry is to turn off Full packet when testing 11a/g/n and select Raw Long Symbols; when testing 11ac, turn on Full packet.

How to open Full packet? For the WT series instruments launched by iTest, when developing and debugging, open WLAN Meter→device setting→analysis setting→OFDM setting area channel estimation, as shown in the figure below: