EMI Suppression Filters (EMC and Noise Suppression)Noise Suppression Measures for Wi-Fi 6 (1)

Contents

1Introduction of Wi-Fi 6

The new standard IEEE 802.11ax was established for “Wi-Fi 6”.
Its use is expected for public Wi-Fi in extremely crowded locations, such as stations and airports. Wi-Fi 6 is accessible even in crowded environments due to its enhanced maximum transmission speed through modulation (1024QAM) and orthogonal frequency-division multiple access (OFDMA), a technology that effectively assigns packets to multiple users.
However, modulation (1024QAM) is weak against noise and the importance of noise suppression measures may rise compared to conventional standards.

Changing of Wi-Fi Standards

Changing of Wi-Fi Standards

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Wi-Fi standard name Maximum communication speed Frequency New common name Year
IEEE 802.11a 54Mbps 5GHz band - 1999
IEEE 802.11b 11Mbps 2.4GHz band - 1999
IEEE 802.11g 54Mbps 2.4GHz band - 2005
IEEE 802.11n 600Mbps 2.4GHz band
5GHz band
Wi-Fi 4 2010
IEEE 802.11ac 6.9Gbps 5GHz band Wi-Fi 5 2015
IEEE 802.11ax 9.6Gbps 2.4GHz band
5GHz band
Wi-Fi 6 2020

2Checking the EVM Allowable Value

Noise issues for Wi-Fi 6 may be due to the deterioration of transmission and reception characteristics.
EVM is a parameter which indicates transmission characteristics. It is designed so the EVM stays below -35 dB in terms of standard and it is believed the ambient noise can cause deterioration in EVM value. We perform measurements as shown in the following diagram using a Wi-Fi 6 module to check how much EVM deterioration is acceptable in a 1024QAM communication.

Checking the EVM Allowable Value

■Measuring Conditions

Output
-20dBm(At SG Port)
Frequency
5210MHz
Bandwidth
80MHz
Data Rate
11ax MCS7/9/11
S/N Ratio
50~18dB

3Check Results of the EVM Allowable Value

The following diagram is the measurement result of “PER vs EVM.”
We found that the EVM had to be under -29 dBm if 1024QAM when the standard that meets the communication quality is under 10% PER (packet error rate).

Check Results of the EVM Allowable Value PER vs EVM

The relationship of S/N ratio between EVM and transmission waveform at this time is indicated in the diagram below.
We have found that communication becomes difficult if the S/N ratio deteriorates by 5 dB for 1024QAM even if the design satisfies EVM -35 dBm, a value that conforms to the standard.
The necessity to implement noise suppression measures increases since the condition is harsher compared to when the required margin was 12 dB in 64QAM.

Check Results of the EVM Allowable Value Tx S/N ratio vs EVM

The noise to consider may include Bluetooth® module signals, high speed I/F signals, and DC-DC converter noise.